Microwave Wireless Communication System

Transcription

1 Technical repor, IDE068, January 006 Microwave Wireless Communicaion Sysem Maser s Thesis in Elecrical Engineering Carl Dagne, Johan Bengsson, Ingemar Lindgren School of Informaion Science, Compuer and Elecrical Engineering Halmsad Universiy

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3 Microwave Wireless Communicaion Sysem Maser s hesis in Elecrical Engineering School of Informaion Science, Compuer and Elecrical Engineering Halmsad Universiy Box 83, S Halmsad, Sweden January 006

4 Descripion of cover page picure: A microwave anenna for he GHz band.

5 Preface This projec was performed during he auumn 005 wih Emil Nilsson and Arne Sikö as supervisors. We would like o sincerely hank boh supervisors for heir help wih boh heoreical and pracical maers. Their knowledge and ineres in he area has been a big aid o us in compleing our work. We would also like o hank our opponen Ola Johnsson a FMTS, for his houghs and commens. Carl Dagne, Johan Bengsson & Ingemar Lindgren Halmsad Universiy, January 006 i

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7 Absrac The purpose of he projec was o develop he hardware o a microwave wireless sysem working a he frequency.45 GHz. The funcionaliy of he sysem should also be easy o undersand since he sysem is o be used in an educaional purpose. Much ime has been spen impedance maching componens, a ask ha proved o be harder han we expeced. Oher work ha has been is layou of all pars, filer consrucion and he wriing of an easy o undersand hesis. Afer he pars had been compleed, hey were esed in a nework analyzer and/or specrum analyzer. Successful full sysem es has been done up o 400 meers, he lengh he sysem is o be used for. iii

8 Conens PREFACE...I ABSTRACT...III CONTENTS...IV 1 INTRODUCTION BACKGROUND ASSIGNMENT METHOD Presudy Design and Simulaion Measuremens and Tess READING INSTRUCTIONS... THEORETICAL BACKGROUND MICROSTRIPS IMPEDANCE MATCHING The Smih Char Scaering Parameers Impedance Maching wih Lumped Elemens (L-neworks) Impedance Maching wih Microsrips FILTERS Bandpass IF Filer Microsrip Filers Lowpass Microsrip Filer Bandpass Microsrip Filer MODULATION TECHNIQUE Phase Modulaion Modulaor De-Modulaor Phase Locked Loop OSCILLATORS LOW-NOISE AMPLIFIERS (LNAS) Impedance Maching of RF LNA The IF LNA MIXERS Diodes Single-Ended Mixers Balanced Mixers Double Balanced Mixers Impedance Maching of Downconverer Impedance Maching of Upconverer ANTENNAS CIRCULATORS POWER AMPLIFIER RESULTS MIXERS Downconverer Upconverer iv

9 3. FILTERS Lowpass IF Filer Lowpass Microsrip Filer Bandpass Microsrip Filer LOW-NOISE AMPLIFIER Microwave Low-Noise Amplifier IF Low-Noise Amplifier POWER AMPLIFIER OSCILLATOR MODULATOR DEMODULATOR SYSTEM TESTS Receiver Transmier Transmier Receiver Tes CONCLUSIONS REFERENCES PERMISSION... 6 v

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11 Inroducion 1 Inroducion 1.1 Background Today wireless echnology is used in many applicaions well inegraed ino our everyday life. One of he challenges for designing a microwave sysem is ha he funcionaliy of he elecronic componens changes when dealing wih he upper frequencies of he UHF band. This means for example he filer design will differ much from convenional design mehods, and ransmission lines have o be shor o make sure hey do no work as anennas and hereby disurb he sysem. 1. Assignmen The main purpose of his hesis is o consruc a microwave link beween Halmsad Universiy and he Agellis laboraory. The sysem has o be fas enough o suppor a video link, which means a bandwidh of a leas 4 MHz. The microwave link consruced will send signals a.45 GHz. This frequency was used since i belongs o he.4 GHz o.5 GHz band, which is one of he ISM frequency bands and is free o use. This hesis focuses on he RF par while he sofware inerface used o run he complee sysem will be designed by anoher hesis group. The complee sysem will also be used in laboraory exercises in a microwave communicaion course a Halmsad Universiy. The difference beween his projec and oher similar available producs is ha his projec will no ry o make a compac sysem soluion, bu a sysem where all componens are visible and he funcionaliy is easy o undersand. 1.3 Mehod The main goal of his hesis can be divided ino he following hree sub-goals: presudy, design and simulaion and measuremens and es Presudy An exhausive sudy on exising maerial abou microwave sysems and he pars included in such a sysem was he firs hing done. The sudied maerial consised of books, aricles and web sies Design and Simulaion Afer he presudy, circuis were designed and simulaed using PSpice and Orcad, produced by Cadence, and ADS 004A, by Agilen Measuremens and Tess Laboraory measuremens and esing of he designed circuis were done coninuously during he projec using specrum analyzer, signal generaor and nework analyzer o conrol he simulaed resuls. Finally, a es of he whole sysem was carried ou. 1

12 Microwave Wireless Communicaion Link 1.4 Reading Insrucions This hesis is inended o be read by persons sudying, or wih degree in, Elecrical or Compuer Engineering. Basic knowledge of radio communicaion sysems and filers is needed.

13 Theoreical Background Theoreical Background A wireless communicaion sysem consiss of several pars. Below is a block scheme of a ransceiver. This chaper will explain he funcionaliy of he pars in such a sysem and some basic heory needed for undersanding hese pars. Figure -1 Componens of a ransceiver sysem..1 Microsrips Microsrips are one ype of ransmission lines which are devices used o ransfer energy from one poin o anoher efficienly [4]. There are a number of differen ransmission lines, bu he mos imporan ype for his projec is microsrips. The microsrip consiss of a ground plane and a srip conducor, separaed by a dielecric subsrae, as seen in figure -. Figure - Microsrip ransmission line [3]. 3

14 Microwave Wireless Communicaion Link Microsrips are used a microwave frequencies where hey are more efficien han convenional wiring. A major advanage when using microsrips is ha i is easy o connec surface mouned componens. As wih all oher wires conducing a curren, he microsrip also has an elecric field, which ravels from he srip conducor o he ground plane. Bu since he elecric field is no sricly confined o he area under he srip conducor, he field will also ravel from he edge of he srip conducor o a place on he ground plane ha is no siuaed direcly under he conducor. This phenomenon is called fringing effec which will make he conducor seem elecrically longer han i really is. This means ha if a microsrip a quarer wavelengh is waned, he conducor has o be slighly shorer because of he fringing effecs. Anoher hing ha affecs he lengh is he dielecric subsrae ha has a relaive dielecric consan. Bu since he srip conducor has a dielecric subsrae on one side and air on he oher, an effecive dielecric consan has o be calculaed o compensae for he difference. A higher effecive dielecric consan will hen make he microsrip shorer because he speed of ligh is slower in a dens maerial, which in urn will make he wavelengh shorer since λc/f. This projec makes use of coaxial cables ha have a conducor in he middle and a ground plane around he conducor wih a dielecric subsrae in-beween. Like he microsrip, he elecric field for he coaxial cable will ravel from conducor o ground. When a coaxial cable and a microsrip ransfer signals from one o he oher, he elecric field has o change form and i is herefore imporan o add an exra microsrip o make his change possible. This exra microsrip should also have he characerisic impedance which in his case is 50Ω, a number ha can be alered by changing he widh of he srip conducor. The relaion is ha he smaller he impedance, he larger he widh [4], [].. Impedance Maching The reason for doing impedance maching is o deliver maximum power o a load. The only requiremen for a maching nework o be found is ha he load impedance, Z L, has a real par. When dealing wih impedance maching, here are wo differen caegories usually menioned. The firs one is maching of ransmission lines, where i comes down o erminaing he line wih Z 0, which is he characerisic impedance of he line. The oher is maching a source or a load by deriving is complex conjugae [3]...1 The Smih Char The impedance maching can be simplified by using a Smih char which is an easy-o-use ool ha can give an approximae soluion when deriving an impedance maching nework. I is represened by circles and lines as can be seen in figure -3. 4

15 Theoreical Background Figure -3 The Smih char The real axis passes horizonally hrough he middle of he char, while he ben lines from he righ hand side of he char o he ouer circle sand for complex values. The complex lines above he real line are posiive while he lines below are negaive. The cenre of he char represens he real value 1. I is also possible o find admiance values by urning he impedance char 180 degrees. When using he Smih char, he maching is made by moving from he complex conjugae of he impedance o he cenre of he char by adding reacive elemens ha do no consume acive power... Scaering Parameers A ype of parameer ha ofen is used when alking abou impedance maching of a sysem or device is he scaering parameer, also called S parameers. An S parameer can be calculaed using he following equaion. S ij V i - /V j + The above equaion says ha S ij can be deermined by sending an inciden wave of volage V j + ino por j and measure he refleced volage ampliude and phase V i -, coming ou of por i. If considering a simple wo-por device, S 11 will give a value of how well he inpu is mached and 5

16 Microwave Wireless Communicaion Link S will ell us how well he oupu por is mached. For a perfec mach S 11 and S should be zero, meaning ha nohing of he signal will be refleced...3 Impedance Maching wih Lumped Elemens (L-neworks) The simples way of impedance maching is by using he L secion. This kind of nework uses wo reacive elemens o mach load impedance. There are wo possible configuraions as shown in figure -4 below. Figure -4 Differen configuraions for L-secion maching neworks. When deciding which nework o use, he Smih char is used. Firs, he normalized load impedance is derived, z L Z L /Z 0. If his number lies inside he 1±jx circle on he Smih char, he nework in figure 1a should be used and if i is ouside he circle, he nework in figure 1b should be used. The reacive pars in he figure above may be eiher inducors or capaciors. If he frequency is below ca 1 GHz, lumped elemens can be used in he implemenaion. When dealing wih frequencies above 1 GHz, he lumped elemens should be convered ino microsrips. This because of parasiic capaciances and inducances ha becomes larger wih increasing frequency [3]. Anoher way o see which nework configuraion o use when calculaing he values of he componens in he nework is o find ou which nework works for which region. The allowed and he forbidden regions for he differen kind of nework configuraions are shown in figure -5, where an impedance should be conneced o he righ of he neworks. The deerminaion of values for he reacive componens can easily be approximaed using he Smih char. There are, however, some basic rules o be considered when dealing wih he Smih char in his way. A shun componen always moves on he admiance char while a series componen moves on he impedance char. By hemselves, an inducor always moves on he posiive side of he smih char while capaciors move on he negaive side []. 6

17 Theoreical Background Figure -5 Allowed and forbidden regions for differen nework configuraions [17]. Example Design an L secion maching nework o mach he impedance Z100-j50Ω, if Z 0 50Ω a he frequency of 500 MHz. Soluion Afer normalizing he impedance o z-j1ω, i is ploed on he Smih char of figure -6. 7

18 Microwave Wireless Communicaion Link Figure -6 Impedance an admiance char wih Z and is complex conjugae ploed. To achieve a mach, he complex conjugae, Z *, of he impedance has o be known. I is easily found by changing he sign on he complex par of he impedance. As seen in figure 3, here are wo possible nework soluions o he problem. When using he nework wih he shun inducor, he way o he cenre of he char is found by following he black lines b and c. b sreches from 0. o 0.5 on he admiance char, i.e. i is 0.3 long, while c can be read o be 1.. The values of he capacior and he inducor can now be found. 8

19 Theoreical Background Z 0 L a nh π fb C a π fz c pf 0 When calculaing he values of he wo reacances wih he oher maching nework where here is a shun capacior, he formulas will differ slighly. x C b 4.39 pf π fz 0 yz L 0 b 19.1nH π f where x is he lengh of he line from Z * o he circle wih he real value 1, bu on he opposie side of he real axis. This gives x he number of y is he same lengh as c bu is measured on he opposie side of he real axis of he char. The resuls of hese calculaions are shown in figure -7. Figure -7 The wo resuling maching neworks. The firs wo values should be applied o a and he second wo values o b...4 Impedance Maching wih Microsrips When dealing wih frequencies above ca 1 GHz, he normal performance of capaciors and inducors no longer applies. These lumped elemens have o be subsiued by microsrips o make a maching nework. The mos basic form of maching nework is using single-sub maching. The aim of using single-sub maching is o make he lengh of he sub and he ransmission line in such a way ha a mach is found for he admiance, Y. There are wo ways of doing his when using a single-sub mach. These are shown in figure -8. 9

20 Microwave Wireless Communicaion Link Figure -8 Single-sub maching nework wih a) open circui sub and b) shor-circui sub. The sub will ac differenly depending on he lengh of he line. The open circui sub will be capaciive when is lengh is from 0 o λ/4 and inducive when from λ/4 o λ/. The shor-circui sub will ac in he opposie way compared o he open circui sub. In microsrips, shor-circui subs are difficul o realize which means ha he open circui sub ofen is used [18]. Example Find he maching nework for he admiance load, Y L 0.3+j0.3, using microsrips. 10 Figure -9 Smih char for he maching nework.

21 Theoreical Background Saring a he load, he lengh of he microsrip is found by moving oward from poin A o poin B while keeping a consan disance from he cenre of he char. This disance is found o be λ. The lengh of he open sub can hen be found o be 0.15 λ by moving from poin B o he cenre of he char and measuring he lengh of he sub on he ouermos scale of he Smih char..3 Filers Several filers are needed in a microwave sysem like he one in his projec where heir main purpose is o shape he signal specrum. As can be seen in figure -1, various filers are needed. These filers are bandpass IF filer and bandpass RF filer, bu a RF lowpass filer will also be needed o filer ou he harmonics from he local oscillaor..3.1 Bandpass IF Filer The IF bandpass filer made wih he Cauer echnique, has a cenre frequency of 70MHz and a bandwidh of 10MHz. The lower sopband exends from zero o 60 MHz and he oher sopband reaches from 80 MHz o infiniy. 6 π * 65*10 C1 C S1 S π * 75*10 π *60 *10 π *80*10 If muliplying he wo passband frequencies and he wo sopband frequencies and comparing hese wo producs, i is easily seen ha hey differ from each oher. One frequency hen has o be changed o make hem equal. The firs sopband frequency is he chosen o be changed and will be given he new frequency MHz. The nex sep is o use frequency ransformaions o conver o lowpass filer Ω S Ω C rad/s 6 C C1 π *10 * 10 6 S S1 π * * 10 rad/s The order of he filer can hen be found o be N4 using MaLab. For he nework configuraion, a π-nework was chosen and he normalized values were found o be C , C 0.191, C , L 1.063, L , R 1 1, R 1, where R 1 and R are he normalized values o he 50Ω impedances. 11

22 Microwave Wireless Communicaion Link Figure -10 The normalized lowpass filer. Frequency ransformaion was made o ge he nework of he bandpass filer. The values were calculaed o be C 1 96pF, C 69.74pF, C pF, C 4 519pF, C pF, L nH, L 74.5nH, L 3 846nH, L 4 10nH, L 5 661nH, R 1 50Ω, R 50Ω. Figure -11 The bandpass filer. Since mos of he values of he lumped elemens are no available as sandard componens, he values had o be changed. The new values were found using ADS. C 1 330pF, C 8pF, C 3 8.pF, C 4 470pF, C 5 8.pF, L 1 15nH, L 68nH, L 3 680nH, L 4 10nH, L 5 680nH, R 1 50Ω, R 50Ω. Changing he values of hese elemens will of course change he characerisics of he filer. These changes will however be accepable according o ADS. However, i is very imporan o es he filer in a nework analyzer o confirm ha i works. This is no cerain since he componens have 5% olerance which means ha he characerisic of he filer sill can change..3. Microsrip Filers When dealing wih frequencies above ca 1 GHz, i is beer o use filers consruced wih microsrip ransmission lines insead of lumped elemens. There are lumped elemens ha can be used for high frequencies bu since hese have sandard values anoher advanage using microsrips is ha any lengh and widh of he ransmission line can be made. There are a number of differen configuraions o use when designing microsrip filers. When i comes o bandpass filers, wo frequenly used ypes are coupled line and capaciively coupled line filers [11]. 1

23 Theoreical Background Figure -1 shows hese wo ypes, where boh ypes can have differen lenghs, widh and spacing beween he lines. Figure -1 a) Capaciively coupled line filer and b) coupled line filer. Open sub filers are anoher ype of filer ha are used in microwave sysems, bu are used o creae lowpass filers. Figure -13 A hird order open sub filer wih 50 ohm ransmission lines. Designing open sub filers is done wih he use of Richard s ransformaion and Kuroda s ideniies. Richard s ransformaion is used o conver from lumped elemens o ransmission line secions. 13

24 Microwave Wireless Communicaion Link Figure -14 Richard s ransformaion for an inducor and a capacior [3]. The lengh λ in -15 is for he cenre wavelengh 0. Kuroda s ideniies are used because i is difficul o implemen series subs in microsrip filers. This is done by separaing filer elemens by using ransmission line secions [3]. 14

25 Theoreical Background Figure -15 The four Kuroda s ideniies used o conver from open-circuied subs o shor-circuied subs and vice versa, where n 1+Z /Z 1 [3]..3.3 Lowpass Microsrip Filer The reason o make a lowpass filer is mainly o eliminae he harmonics from he local oscillaor (LO). Since he LO is oscillaing a.38 GHz, he harmonics will be a N*.38GHz, where N is an ineger greaer or equal o. Using MaLab, he lowpass was calculaed o be a fifh order filer wih he passband frequency f c.5 GHz. The normalized values for he filers can also be found using MaLab. g

26 Microwave Wireless Communicaion Link g 1.3 g g g A T-nework was chosen for his filer. Richard s ransformaion is used o ransform he T- nework from lumped elemens o open- and shor-circuied subs, figure -16 a. Uni elemens are added o make he use of Kuroda s ideniies easy. Figure -16 Transformaion from shor-circuied subs o open subs using Kuroda s ideniies [3]. 16

27 Theoreical Background Denormalizaion wih he characerisic impedance 50Ω and he frequency.5 GHz gives he impedances of he final filer. The widh of he ransmission lines were hen calculaed using TXline. Afer hese calculaions were done, he filer was implemened in ADS and he parameers were uned o achieve bes possible resul..3.4 Bandpass Microsrip Filer Coupled line filer echnique was used and he cenre frequency should be f 0.45 GHz, wih a bandwidh from.4 GHz o.5 GHz. Where 17

28 Microwave Wireless Communicaion Link kn-1, Z 0e 1 means he firs even mode characerisic impedance and Z 0o 1 means he firs odd mode characerisic impedance. Using he characerisic impedance Z 0 50Ω gives he following impedances on he coupled lines. Z 1 0e 6.09 Z 1 0o Z 0e Z 0o Z 3 0e Z 3 0o Z 4 0e 6.09 Z 4 0o The lengh, widh and spacing beween he lines can hen be poorly esimaed wih TX-line and opimazaion and/or uning wih ADS or some oher compuerized ool is a mus o make his a working filer. The final filer can be found in figure -17. Figure -17 The complee bandpass filer. The filer is consruced of 4 regions, where he firs and he fourh are he same, jus as he second and he hird are he same. The firs and he las elemen are 50Ω impedances, he firs and fourh region consiss of lines wih widh W mils, lengh L mils and he spacing S 1 7 mils. The second and he hird region are consruced wih W 39 mils, L 838 mils and S 75 mils. Mils is one housandh of an inch and is a very common measure..4 Modulaion Technique The funcion of he modulaor and de-modulaor is of course o modulae and demodulae he signal. There are hree major ways o modulae a signal. The firs way is ampliude modulaion (AM). AM work in such a way ha he informaion signal causes he carrier signal o increase and decrease in ampliude, where high ampliude corresponds o a 1 and low ampliude corresponds o a 0. This form of modulaion is very sensiive o noise and is mosly used for sending daa a a low bi rae. The nex way o modulae a signal is by frequency modulaion (FM). The informaion signal makes he carrier signal o increase or decrease in frequency and wo differen frequencies correspond o 1 and 0. The las way of modulaing a signal is by phase modulaion. 18

29 Theoreical Background.4.1 Phase Modulaion Phase modulaion, or phase shif keying (PSK), is oday one of he mos used way of modulaing daa. There are also differen ways of doing PSK, wo examples are binary phase shif keying (BPSK) and quadraure phase shif keying (QPSK). BPSK uses differen phase o represen binary 1 and 0. The ype of modulaion used in his projec is QPSK. QPSK uses four differen phases o represen 00, 01, 10 and 11 and uses herefore he bandwidh more efficienly since every phase shif represens wo bis insead of one bi, as in BPSK. Figure -18 Phase diagram [1] The modulaion of he signal is done by dividing i ino signals, I and Q, muliplying he I wih a sinusoidal signal a 70 MHz and muliplying he Q wih a cosinusoidal signal a 70 MHz in a mixer. The resuls from he mixers are hen added o each oher o ge he quadraure phase signal. In our case, he binary bis 0 and 1 will be represened by he logical levels -1 and +1. The heory of how o ge he quadraure phase signal can be proven by he use of Euler s relaions. e sin( ) j e j j e cos( ) j + e j If I and Q equals 1, hen 19

30 Microwave Wireless Communicaion Link 0 4) / sin( ) ( 1 ) 1 ( ) 1 ( ) 1 1 ( ) 1 1 ( ) cos( ) sin( 4) / ( 4) / ( 4 / 4 / π π π π π j e e e e e e j j j e j j e j e j e e e j e e j j j j j j j j j j j j j j The resul if doing similar calculaions wih he differen kinds of inpu signal will be as shown in able -1. Binary inpu I (afer mixer) Q (afer mixer) Sum 00 -sin() -cos() sin(-135 ) 01 -sin() cos() sin(+135 ) 10 sin() -cos() sin(-45 ) 11 sin() cos() sin(+45 ) Table -1 Corresponding phase shif in he oupu signal for differen binary inpu signals [1]. When he phase quadraure signal received on he oher side of he sysem i has o be demodulaed. Figure -19 A simplified demodulaor. To make he demodulaor demodulae he received signal correcly, i has o know when a signal sars. I is herefore imporan o use a synchronizer circui which in his case will conain a

31 Theoreical Background phase locked loop (PLL), discussed laer on, and an elemen ha divides he frequency from he PLL by four. The basic funcion of he PLL is o muliply he IF signal frequency by four and by doing so eliminaing he differences in phase shif as can be seen in he equaions below [1]. One problem ha could arise is ha he local oscillaor possibly could have a consan phase error because of he differen pah lenghs beween he signal going hrough he synchronizer and he one going hrough he divider. ) sin(4 4 * 4) / 3 * 4 sin( ) ( ) sin(4 4 * 4) / 3 * 4 sin( ) ( ) sin(4 4* 4) / * 4 sin( ) ( ) sin(4 4 * 4) / * 4 sin( ) ( π π π π π π π π A A s A A s A A s A A s Afer he signal has gone hrough he PLL, i is divided by four so ha he original frequency is regained, wihou modulaed phase shif. This means ha he local oscillaor in he demodulaor is running a he correc frequency. The demodulaion of he received signal is hen be done by muliplying i in a mixer circui. This can be mahemaically proved by using Euler s relaions. ) cos( ) cos( ) cos( ) cos( 4 ) cos( 4 ) sin( ) sin( ) ( ) ( ) ( ) ( ) ( ) ( ϕ ϕ ϕ ϕ ϕ ϕ ϕ ϕ ϕ ϕ ϕ ϕ ϕ ϕ e e e e e e j e e j e e j j j j j j j j j j The only problem wih his mehod is ha i canno disinguish beween he phase shifs wih a + or a sign. Therefore, o decode all four quadrans, he inpu signal has o be muliplied by boh a sinusoidal and a cosinusoidal waveform. The higher frequency also has o be filered ou, which is done by using a lowpass filer. If muliplying he received signal wih a cosinusoidal waveform a he same frequency, his will afer a few seps give he following resul [1]. ) sin( ) sin( ) sin( ) cos( ϕ ϕ ϕ

32 Microwave Wireless Communicaion Link.4. Modulaor The modulaor, MAX45, an inegraed circui (IC) was chosen from Maxim ha filled he requiremens needed for his projec. Figure -0 A block diagram of he modulaor inegraed circui [7]. I and Q represen he wo bis sen a every phase shif. These signals will have a frequency of 600 khz. The I signal is hen mixed wih a sinusoidal signal and he Q wih a cosinusoidal signal, boh a 70 MHz, and added o each oher o ge he final quadraure phase signal. The local oscillaor is run by a TANK-circui ha conrols he operaing frequency, which in our case will be oscillaing a 140 MHz [1]..4.3 De-Modulaor The demodulaor used is he MAX 451 includes many of he pars ha can be found in he modulaor.

33 Theoreical Background Figure -1 Block diagram of he demodulaor inegraed circui [6]. The inpu signal o he demodulaor is he IF signal ha is oscillaing a 70.6 MHz. I is divided ino wo signals where one of hese signals is mixed wih a sinusoidal signal a 70 MHz and he oher is mixed wih a cosinusoidal signal a 70 MHz. The sinusoidal and he cosinusoidal signal are provided by he local oscillaor. The difference beween he modulaor and he demodulaor is ha he frequency of he local oscillaor in he demodulaor is no decided by a TANK-circui. Insead, a phase locked loop (PLL) is used. By using a PLL he demodulaor will be synchronized wih he modulaor sending he daa [1]..4.4 Phase Locked Loop Phase locked loops are analogue circuis ha are commonly used in many analogue and digial sysems. PLLs can be used for clock recovery in communicaion sysems, frequency synhesizers in TVs and wireless communicaion sysems o selec differen channels and much more. This is done by adjusing he PLL oscillaing frequency o ge i o mach he desired frequency. PLLs are non-linear sysems, bu when in lock, heir behaviour can be esimaed wih linear equaions. A PLL usually consiss of a phase deecor, a loop filer, a volage conrolled oscillaor (VCO) and a frequency divider as shown in he figure below. 3

34 Microwave Wireless Communicaion Link Figure - Basic srucure of a PLL []. The phase deecor compares he inpu signal o he signal received from he volage conrolled oscillaor (VCO). The bigger he phase difference, he bigger he oupu volage from he phase deecor. The loop filer makes he resul from he phase deecor smooher and passes i on o he VCO. The VCO hen changes is oscillaing frequency depending on he volage a he inpu. If he PLL is sable and he sysem reaches a poin where he wo inpus o he phase deecor are in phase, he signals will also have he same frequency since angular frequency is he derivaive of he phase wih respec o he ime. When changing he number N in he frequency divider, he synhesizer oupu signal will change accordingly. The phase deecor can be buil in differen ways. One way is o use a double balanced mixer o muliply he inpu signals, bu a much beer way is o use a phase frequency deecor (PFD). I conains wo D flip-flops and an AND gae as shown in figure -3. If f r or f v goes high, he Up por or he Dwn por will go high respecively. When hey boh have he logic value 1, he AND gae will cause he flip-flops o rese. This means ha he wo oupu pors only are 1 he amoun of ime i akes he AND gae o rese he flip-flops. The waveforms for he pors o he PFD can be found in figure -4. When f r and f v are he same, he oupu pors Up and Dwn will also be he same. This means ha when calculaing Up-Dwn, he resul should be zero for he wo inpu signals o be equal. If for example f r oscillaes a a higher frequency han f v, FF 1 will be se o one more ofen han FF. The wo flip-flops will however be rese o zero an equal number of imes. The resul of his will be ha he Up por will have a higher average value han he Dwn por. Making he calculaion Up-Dwn will hen give a posiive value which means ha he VCO in he PLL will be fed wih a higher volage, making i oscillae faser []. 4

35 Theoreical Background Figure -3 A PLL wih wo flip-flops and an and-gae []. Figure -4 Waveform of he PLL shown in he figure above []. The PLL used in his projec has he disadvanage ha i has no memory o remember for example he number in he frequency divider. The PLL herefore has o be reprogrammed every ime he device is urned on. The reprogramming of he PLL will be done using a program called Codeloader via a parallel cable. 5

36 Microwave Wireless Communicaion Link.5 Oscillaors Oscillaors are complicaed nonlinear circuis o design. A simplified and linearized version of an oscillaor can look like he one in figure -5. The wo por oscillaor consiss of an amplifier and a linear filer H(s), as a feedback componen. Figure -5 Basic srucure of an oscillaor. The inpu o he oscillaor can be hermal noise or a sep response ha is removed once he oscillaor reaches seady sae bu is necessary o sar he device. Since he neworks is supposed o oscillae, i has o have a pair of complex conjugae poles in righ-half complex plane of he uni circle. The oscillaor loop gain should be exacly one o preven he circui from aenuaing or increase unconrollably. This projec will be using a volage conrolled oscillaor (VCO) MAX753 o conver he signals o IF and RF. A VCO can be achieved by using a varacor in he filer and by doing his, he oscillaion frequency is changed. The oupu signal produced by he MAX753 will be made o oscillae a.38 GHz. This means ha here will be harmonics a n*.38 GHz, where n is an ineger. 6 Figure -6 Harmonics for he MAX753 [7].

37 Theoreical Background The harmonics of he oscillaor can be seen in figure -6. The firs harmonic is suppressed 30dBc (dbm compared o carrier) and he second harmonic 7dBc. The inducor and he varacor of he ank circui conrolling he frequency are inegraed on he circui which simplifies making of he exernal circuiry..6 Low-Noise Amplifiers (LNAs) The smalles signal ha can be received by a sysem defines he receiver sensiiviy and is se by he noise. The larges signal ha can be handled by he receiver wihou affecing he qualiy of he daa, gives an upper power limi. The Low-noise amplifier (LNA) plays a very imporan role in he receiver design. Is main purpose is o amplify exremely low signals wihou decreasing he signal o noise raio (SNR). When designing a LNA here are many parameers o consider and i is impossible o design a LNA wihou rade offs. Some of he parameers ha give a descripion of how well a LNA performs are gain, noise figure, sabiliy, lineariy, low power consumpion and inpu and oupu mach. Parameers ha inerfere wih each oher are for example low noise figure and good inpu mach, sabiliy and gain, IP3 and curren consumpion. The firs and mos imporan sep in a LNA design is he selecion of ransisor. There are hree design parameers ha firs should be aken ino consideraion which are noise, gain, IP3 and decide wha V CE and I C will give he bes performance, informaion ha can be found in he daashee for he device. LNA lineariy is also an imporan parameer and a measure of i is he 3 rd order inercep poin (IP3) which indicaes how well he LNA performs in presence of srong nearby signals and how well i deals wih harmonics. For bipolar juncion ransisors, he oupu-ip3 can be esimaed using he following formula: OIP 10*log( V CE * I *5) [dbm] [5] 3 C where V CE is in vols and I C is in ma. The Inpu-IP3 can also be esimaed aking he OIP3 subraced by he gain. Afer having chosen a suiable ransisor, he nex sep is o choose DC bias circuiry. I should give sable hermal performance, be cos effecive and simple soluion ha occupies smalles possible area. One of he simples forms of DC biasing ha fulfils he major requiremens is shown in figure -7. 7

38 Microwave Wireless Communicaion Link Figure -7 Simple form of DC biasing [5]. This DC bias is good since a sable biasing poin is waned. If I C decreases, V C will increase which will resul in a higher I b. Higher I b will in urn increase I C. If he emperaure increases, I C will increase. This will lower V C causing I B o decrease which finally will cause I C o decrease. For R b o have lile influence on he source maching, which is imporan for he noise figure, he feedback nework should be decoupled wih an inducor. Anoher possibiliy bias feedback can be realized wih an emier resisor and a capacior, shown in grey in figure -7. C e should presen a shor a he operaing frequency o make is influence on gain and noise performance as small as possible. Sabiliy is he nex hing o consider. The LNA should be uncondiionally sable, which means ha he device will no sar o oscillae no maer wha load is presened on he inpu or oupu por. Sabiliy can be conrolled using he s-parameers and by using hem in he following equaions. S S 11S S1S1 K 1 S 11 S S S S If he inermediae value S is less han 1 and he facor K (called Rolle Sabiliy Facor K) is larger han 1, he circui will be uncondiionally sable. There are some mehods o make he LNA sable. One of hem is o use R-L-C feedback beween collecor and base in order o lower he gain a lower frequencies and hereby improving he sabiliy. Anoher mehod is o use a maching filer, usually pu a he oupu of he ransisor o make he gain decrease for specific 8

39 Theoreical Background narrow bandwidh a high frequency. Ye anoher mehod is o use an emier feedback inducor in order o make he LNA more sable a higher frequencies. The nex hing o do is o mach he noise and inpu reurn loss (IRL) of he source. A usual approach is o mach he inpu impedance of he ransisor wih Γ op which gives he bes noise mach. Normally, his means ha he inpu reurn loss of he LNA will be sacrificed since he opimal IRL only can be achieved wih a maching nework ha erminaes he complex conjugae of S 11. How his is done is shown in he calculaion par of his chaper..6.1 Impedance Maching of RF LNA The low-noise amplifier used in his projec will be he MAX644 from Maxim. When calculaing he maching nework, here are several parameers ha have o be known. These can be found in [0]. The scaering parameers are found o be S / S / S /68.36 S /5.00 As can be seen in he scaering parameers, S 1 and S 1 differ a lo. This means ha he device is acive and is amplifying he signal ravelling from por 1 o por. This also means ha any maching circuiry placed a por wo will affec he inpu reflecion coefficien very lile, compared o wha a maching circui a por 1 would affec he oupu reflecion coefficien. In mos passive devices, he wo parameers, S 1 and S 1, would be he same. If looking a he suggesed surrounding circuiry for he MAX644 in figure -8 from he daa shee of he low-noise amplifier, i can be seen ha here are already a shun inducor and a series capacior on he inpu, where he capacior is o ac as a DC block and he shun inducor is a maching circuiry. This capacior does no have o be aken ino consideraion when calculaing he maching nework since is value is very big (33pF) i.e. is reacance will be very small. Figure -8 The surrounding circuiry of he MAX644 low-noise amplifier [0]. 9

40 Microwave Wireless Communicaion Link The firs hing ha will be checked is if he amplifier is uncondiionally sable by calculaing he inermediae value S and he sabiliy coefficien K. S S S S 0.301/ S1 K 1 S 11 S S S S.901 Since he inermediae value is less han 1 and he sabiliy coefficien is larger han 1, he amplifier is sable. I is now possible o calculae he maximum available gain. S1 MAG 10log + 10 log( K K S 1 1) 17.4 db For a perfec mach, S 11 should be 0, which means ha nohing of he inciden wave is reurned o por 1. This is naurally done by a maching nework. Bu, since he maching nework should consider he noise figure he calculaions will differ from convenional maching. Also, i is imporan o ake he reflecion coefficiens ino consideraion since he maching nework added o he inpu will make a difference o he reflecion coefficien on he oupu and vice versa. The nex sep is o calculae wo inermediae quaniies C and B so he load reflecion coefficien can be found. Γ L B ± S1S C 1 K 1 Where and This gives B C * 11 S S S / S S S 11 Γ.3968/ L The nex sep is o find he source reflecion coefficien by doing similar calculaions. Γ S B1 ± S1S1 C 1 K 1 30

41 Theoreical Background Where and C * 1 11 S S S / B 1+ S S S This gives Γ / S Γ in and Γ ou can now be calculaed. S1S 1ΓL Γin S / S Γ 1 L S1S 1ΓS Γou S / S Γ 1 11 S Since i is imporan o hink abou he noise, a noise figure circle is drawn o calculae he bes mach for he noise. According o he daashee for he device he minimum noise figure of he ransisor is F min db, he reflecion coefficien for opimum noise figure is Γ op 0.408/70.63, he equivalen noise resisance of he ransisor is R N 1.94Ω and he noise figure is db a maximum gain. The firs hing o do is o calculae he radius and he cenre of he db noise figure circle. N F Fmin 1+ Γop 4R N / Z * 1.94 / 50 C F Γop N + 1 R F N( N + 1 Γ N + 1 op )

42 Microwave Wireless Communicaion Link Figure -9 Smih char wih noise figure circle and consan gain circle. The nex sep would be o draw a gain circle around S 11 * and hen mach he poin where he wo circles inersecs. However, his is no necessary since i can be seen ha he complex conjugae o Γ in lies wihin he noise figure circle. I is herefore only necessary o mach his complex conjugae. More abou how o mach wih lowes possible noise can be found in []. Since his device will be working in he microwave region, i is beer no o use lumped elemens. Insead, hese elemens will be subsiued by microsrips. These will be derived from he Smih char. 3

43 Theoreical Background Figure -30 The deriving of microsrip lenghs using he Smih char. The mach will be done as explained in he impedance maching chaper. Working backwards, he firs hing ha will be calculaed is he lengh of he line on he inpu. The lengh will be found by moving from 1 oward he load o. This lengh is read o be.69λ and wih a λ ha according o TX-line will equal mm a.45 GHz for he laminae chosen for his projec, his means ha he lengh of he line will be.7mm. The lengh of he open sub is hen found o by moving from 3 o 0 which gives 0.146* λ1.33mm. The lengh of he line and he sub for he oupu is found if doing he same way as wih he inpu. The line will be.38* λ7.70mm and he open sub.117* λ9.88mm. ADS was used o une hese parameers and he final lenghs (in mm) can be found in figure

44 Microwave Wireless Communicaion Link Figure -31 The final maching nework..6. The IF LNA A low-noise amplifier for he inermediae frequencies will also be needed in he sysem. The MAX611 was chosen o mee he requiremens. The s-parameers of he LNA are already very good, hus, no exernal maching are needed. According o he daashee he LNA will amplify he inpu signal 19 db wih a noise figure of 3.6 db..7 Mixers The purpose of using mixers is o conver a signal o a differen frequency. To do his, a nonlinear elemen is used ha muliplies he wo inpu signals. This elemen is mos commonly a diode, bu can also be a ransisor. Mixers are hree por circuis ha have o be impedance mached a all pors o achieve good sensiiviy and low noise. This can be complicaed since several frequencies and heir harmonics are involved. An imporan parameer for a mixer is is conversion loss, defined as L C 10log (available RF inpu power/if oupu power) db []. Normally, he conversion loss is beween 4 and 7 db. A facor ha affecs he conversion loss of he mixer is he power level of he local oscillaor signal. For minimum conversion loss, mos LO powers should be more han 0 dbm and less han 10 dbm []..7.1 Diodes A diode can basically be seen as a non-linear resisor. Is DC V-I characerisic can be expressed as I(V) I (e S αv 1) where αq/nkt, and q is he charge of an elecron, k is Bolzmann s consan, T is he emperaure, n is he idealiy facor and I S is he sauraion curren. If he diode volage is se o be 34

45 Theoreical Background V V 0 where V 0 is he DC bias volage and v is an AC signal volage. This will change he V-I characerisic for he diode and can by using Taylor series be expressed as I ( V ) I di + v 1 + v 0 + v + dv V dv 0 V0 where I 0 I (V 0 ) is he DC curren. The firs derivaive can be seen as d I... di αv I Se I I S G 1 0 α α( 0 + ) d dv R V0 j which defines he juncion resisance of he diode, R j, and he dynamic conducance of he diode, G d 1/R j. The second derivaive is hen expressed as d I dv V0 dg d αv0 α I Se α ( I 0 + I S ) αgd dv V0 G ' d The V-I characerisic of he diode can now be rewrien as I ( V ) v + G ' I 0 + i I 0 + vgd d + and is hus he hree-erm approximaion for he diode curren [] Single-Ended Mixers The single-ended mixer is he simples ype of mixers and is ofen used as a par in more complex mixers. If a RF signal is mixed in a downconverer wih a signal from a local oscillaor and he signals can be described as v RF ( ) v RF cos( RF ) v LO ( ) v LO cos( From he hree-erm approximaion for he diode curren i is possible o see ha he diode curren will consis of a DC curren, he RF and local oscillaor frequencies. The v erm will hen give rise o he following oupu curren. LO ) 35

46 Microwave Wireless Communicaion Link ' Gd i ( v ' Gd ( v ' Gd ( v 4 + v v RF RF RF LO RF cos( cos ( ) + v + v LO cos(( RF RF + v RF ) + v RF cos( LO LO cos( RF v LO RF ) ) + v LO )) cos( ) + v RF v LO LO RF )cos( cos( cos(( LO RF LO ) ) + v + LO LO ) )) cos ( )) The DC erms can be ignored since i only changes he volage level and he erms RF, LO and RF + LO will be filered ou. This means ha he erm of imporance, RF - LO, are lef []. LO.7.3 Balanced Mixers A balanced mixer is made of wo or more idenical single-ended mixers ogeher wih a 3 db hybrid juncion (90 or 180 ) o give beer inpu SWR or RF/LO isolaion. A hybrid juncion is a four-por device ha when sending a inciden wave ino por 1 will couple o por and 3 bu no o por 4. The angle 90 or 180 ells how much he oupu pors will differ in phase. If he local oscillaor por is in ani-phase (balanced) he mixer will rejec all producs where he RF signal has a harmonic wih even number. If he RF por is in ani-phase he mixer will rejec all producs where he LO signal has a harmonic wih an even number. Since he por ha is in ani-phase also is cancelled a he IF por, he LO is ofen chosen o use his por because he LO should be driven a a higher level han he RF signal []..7.4 Double Balanced Mixers In a double-balanced mixer, boh he LO and he RF are balanced. Anoher hing ha makes i differen from he single-balanced mixer is he fac ha i normally uses four diodes in a ring or sar configuraion. The advanages of using a double-balanced mixer is ha all pors are isolaed o each oher and ha i has increased lineariy which gives i improved suppression of harmonics. All even order producs are suppressed. By using more diodes he IP3 is also improved. On he negaive side, he LO has o be driven a a higher level and he mixer requires wo hybrid juncions..7.5 Impedance Maching of Downconverer MAX680 is a low noise downconverer from Maxim ha operaes a low volage. In his projec he RF inpu signal has been seleced o operae a.45 GHz and is mixed wih a LO signal operaing a.38 GHz using a double balanced mixer. This gives a down convered IF oupu signal operaing a 70 MHz [3]. In he daashee [3] i is possible o find he impedance loads for differen frequencies which will be mached wih a ransmission line Z 0 50 ohm. These impedance loads are found o be 36

47 Theoreical Background Z RF-por 33+j73 Z IF-por 803+j785 (for RF inpu por a.45 GHz) (for IF oupu por a 70 MHz) In his case i is no necessary o mach he LO inpu por because i has a VSWR beer han 1.5:1. This means ha he impedance load lies somewhere inside a circle wih a radius of 0.5 from he cenre of he Smih char (see figure -3). The LO-por is considered o be close enough o he cenre of he char, where i is known o be perfecly mached. I is more imporan o have a mached RF-por for he weak incoming RF-signal and a mached ougoing IF-por so he signal will be srong enough o be deeced by he demodulaor [3]. Figure -3 A VSWR beer han 1.5:1 [4]. To mach he RF inpu por and IF oupu por here are rules o follow. They can be found in he impedance maching chaper. In he fig -33 you can see z in and z ou which are he normalized complex conjugae o he impedance loads Z RF and Z IF respecively. 37

48 Microwave Wireless Communicaion Link Figure -33 Impedance maching wih Smih char. Figure -33 shows ha he z in lies ouside he 1±jx circle and will have he configured nework like figure -4b. I also shows ha z ou lies inside he 1±jx circle and will have he nework like figure -4a. To calculae he values of he capaciors and inducors for he maching nework he disance from he impedance loads o he cenre has o be analyzed. Saring a z in and following line a and moving in he negaive direcion indicaes ha i is a capacior. Since line a is moving on he impedance char his indicaes ha i is a serial capacior. Following line b o he cenre by moving on he admiance char means ha his is a parallel componen. Because of he movemen in posiive direcion indicaes ha i is an inducor. The same rule applies for z ou which give us a parallel inducor and a serial capacior. By measuring he lines, a, b, c and d, i is possible o calculae he inducors and he capaciors values. 38

49 C Z aπf 50 * ( ) * π * 450 *10 pf 0 0 Z 0 50 L µh 6 bπf 0.75* π * 450*10 0 Z 0 50 L µh 6 cπf 0 0.1* π *70* C pf 6 Z d πf 50 * 6 * π * 70 * Theoreical Background The calculaed values are an approximaion and had o be simulaed in ADS o ge more precise values, C pF, L µH, L 0.96µH, C 7.73pF. The final maching nework configuraion is o be seen in he Fig -34. Figure -34 Maching nework for he downconverer. Since Z RF has an incoming signal a.45 GHz i should be mached wih microsrip componen. I is no necessary o do his because here are lumped componen ha works a higher frequencies. Bu a good approach o ge a precise maching is using microsrips. Mehods for impedance maching wih microsrips can be found in he impedance maching chaper. The elemens ha will be subsiued by microsrips are C 1 and L 1. These will be derived from he Smih char in figure

50 Microwave Wireless Communicaion Link Figure -35 Deriving he lenghs of he microsrips using he Smih char. To calculae he lengh d you have o move from 1 owards he load o. This lengh is shown o be 0.403λ. The laminae chosen for his projec has a wavelengh ha equals λ mm a.45 GHz. This means ha he lengh of he line d 33.95mm. The lengh l of he open sub is hen found o by moving from 3 o 4 which gives 0.17* λ14.36mm. Since a dc-block has o be placed beween he microsrip and he RF inpu por, a capacior a 68 pf was added. This moved our impedance load on he Smih char so insead of recalculae he values, a simulaion was made in ADS. The new lenghs were found o be 40

51 Theoreical Background d mm l mm Figure -36 The microsrip maching nework for he RF inpu por..7.6 Impedance Maching of Upconverer MAX 671 is a low noise upconverer using a double balanced mixer operaing a low volage. The IF inpu signal has been seleced o operae a 70 MHz and is mixed wih a LO signal operaing a.38 GHz. This gives an upconvered RF-oupu signal a.45 GHz [8]. In Maxim s daashee [8] you find recommended values for inducors and capaciors ha will be used as a maching nework a he RF-por. If you analyze hese values he load will no be correcly mached o a 50Ω source. In his approach he recommended componens will be used o ge he correc bias curren o he RF por and a complemenary maching nework o hese componens will be done. The impedance loads were found o be Z RF-por 31-j95 Z IF-por 00-j300 (by RF oupu por a.45 GHz) (by IF inpu por a 70 MHz) The same approach o calculae he impedance maching nework were done like he downconverer, so he value will only be displayed. The final maching nework was simulaed by ADS and had he configuraion like Fig

52 Microwave Wireless Communicaion Link Figure -37 Impedance maching nework for he upconverer in ADS..8 Anennas There are many differen anennas o choose from when designing a wireless sysem. The challenge is o find an anenna ha fi a paricular sysem. The size of he anenna is relaed o he wavelengh. Since hese anennas are made in solid maerials, he wavelengh will be shorer. When designing anennas i is a big advanage if i is possible o make he anenna of such a lengh where i is resonan, which means ha is has no reacance. Anoher aspec o ake ino consideraion when choosing an anenna is he polarizaion i uses. A verically polarized anenna canno receive horizonally polarized radiaion, jus as a horizonally polarized anenna is no able o receive verically polarized radiaion. This can also be an advanage since less noise is received. Radio links can for example double is bi-rae by sending boh horizonally and verically polarized on he same frequency. One of he mos basic anennas is he dipole anenna. The dipole anenna is fed a is cenre and has normally he oal lengh of half a wavelengh. The dipole anenna can be good o use since i is easy o mach is radiaion resisance o a ransceiver. A loop anenna can be a good choice when making a hand-held ransmier sysem since i can be prined on a small circui board. The bigges disadvanage when using a loop anenna is ha i is very inefficien. The pach anenna is an anenna used exensively for he.4ghz band and higher. Like he loop anenna, he pach anenna is also prined on a circui board. The form of he anenna is normally circular or recangular, alhough oher shapes are also used. The radiaion is generally maximum perpendicular o he board. The reason ha he lengh L of he pach has o be a lile bi shorer han a forh of a wavelengh is because of he so called fringing effec. Fringing effec occurs because a fracion of he field generaed by he anenna lies ouside he physical pach dimensions W*L. 4

53 Theoreical Background Figure -38 Recangular microsrip anenna. When designing he anenna, here are a number of hings o consider. The lengh L of he pach, decides he resonance frequency, a criical parameer since he bandwidh of he pach is very small. The widh of he anenna does no affec he resonance frequency much bu is a major facor when calculaing he inpu resisance and he bandwidh. When using a large pach, his will increase he power oupu and herefore decrease he resonance resisance bu increase he bandwidh and he radiaion efficiency [13], [5]. The anennas used are wo pach anennas made by Svenska Anennspeciallisen AB wih a gain of 9 dbi. Using he Friis power ransmission equaion i is possible o calculae how srong he signal will be a he receiver. The formula reads P r P G G λ (4πR r ) where P r is he received power, P is he ransmied power, G is he ransmier gain, G r is he gain for he receiver and R is he lenghs beween he anennas..9 Circulaors RF circulaors are passive devices used o conrol he propagaion of an RF signal. A hree-por circulaor can look as he device in figure -39. The ineracion beween magnes and ferrie maerials give rise o a circular moion in he magneic field which can be srong and will cause a signal on a por o follow he magneic field around o anoher por and no being able o ravel in he opposie direcion. 43

54 Microwave Wireless Communicaion Link Figure -39 Overview of a hree-por circulaor. If a signal is sen from por 1 and he magneic field ravels in he clockwise direcion as in he figure above, he signal will firs come o por. If his por is mached, he signal will ener his por bu if i is mismached, he signal will be refleced a por and coninue o por 3 and ener i if his por is mached [4]. A circulaor will no be consruced in his projec, bu will insead be bough..10 Power Amplifier A Power Amplifier is placed before he filer a he end of a ransmier as near he anenna as possible o avoid aenuaion of he signal being ransmied. Is purpose is o give a high oupu power of he modulaed signal so i can be deeced and decoded by he receiver. For his projec a componen produced by Minicircui has been chosen. This componen (ERA-3SM) is a broadband amplifier designed o deliver an oupu power of minimum 9dBm in he frequency range DC o 3GHz. The ypical gain for a signal a GHz is 18,7dB wih a minimum of 16dB. For maching purpose, he scaering parameers were measured wih bias circuiry only. A maching nework was hen calculaed from hese parameers. 44

55 Resuls 3 Resuls All he finished circuis were esed in a nework analyzer, specrum analyzer and/or oscilloscope o verify heir funcionaliy. The resul of hese measuremens is presened in his chaper. 3.1 Mixers Downconverer The downconverer was esed in he nework analyzer and was mached a he IF side by uning a rimmer capacior and changing he inducor value o 0.7uH. The RF side also had o be adjused by using a small amoun of copper-ape. Afer being fairly mached a es using he specrum analyzer was done o see how he downconverer worked. Driving he LO inpu por wih a power of -5 dbm a a frequency of.38 GHz, he IF oupu power was measured. The power a he RF inpu por was changed from -4dBm o -50 dbm..45 GHz 70 MHz RF: -4 dbm IF: -1.3 dbm RF: -30 dbm IF: -7.3 dbm RF: -40 dbm IF: -37 dbm RF: -50 dbm IF: -47 dbm As we can see he RF oupu signal is amplified bu according o is daashee [3] an amplificaion a around 7dB should occur. One of he reasons for his could be ha he downconverer was fairly mached, bu no properly. Since he VCO, which should drive he LO por, hade an oupu power of -11 dbm and could no be improved, anoher es was done wih his power..45 GHz 70 MHz RF: -4 dbm IF: -4 dbm RF: -30 dbm IF: -30 dbm RF: -40 dbm IF: -40 dbm RF: -50 dbm IF: -50 dbm I could be seen from he IF oupu por was ha he amplificaion we had disappeared bu no aenuaion of he ougoing signal in proporion o he incoming signal was seen. The.38 GHz signal was also leaking hrough he IF oupu por. This signal was suppressed -0 dbm and had a power of -31dBm. The values were considered o be good enough for he receiver par. 45

56 Microwave Wireless Communicaion Link 3.1. Upconverer The es using he nework analyzer of he upconverer showed ha adjusmens of he maching had o be done a boh sides. The inducor and he capacior was changed o 0. uh and 17.5 pf a he IF side while he RF side was adjused wih copper ape. Afer being fairly mached a es on he specrum analyzer was done o see how he upconverer worked. By driving he LO inpu por wih a power of -11 dbm a a frequency of.38 GHz, he RF oupu power was measured. The power a he IF inpu por was -4dBm. The resul showed hree signals. Frequency Ampliude.31 GHz(f LO -f IF ) -40 dbm.38 GHz(LO) -1 dbm.45 GHz(RF) -40 dbm The firs signal wih a frequency of.31ghz is a mixed signal beween he LO and IF (f LO -f IF ). I could be seen of he wo oher signals is an amplified LO signal and a suppressed RF signal. The waned resul was a - dbm suppressed LO signal and a 9 db amplified RF signal according o he daashee [8]. The problem was solved by removing he inducor and changing he capacior o 0 pf. The es resuled in he following signals. Frequency Ampliude.4 GHz(f LO -*f IF ) -4 dbm.31 GHz(f LO -f IF ) -17 dbm.38 GHz(LO) -36 dbm.45 GHz(RF) -16 dbm.5 GHz(f LO +*f IF ) -4 dbm We go he expeced resul for he LO bu he RF signal was no amplified as much as saed in he daashee. Apar from his, wo new signals were found a.4 GHz and.5 GHz. These new signals were raher weak and will no be any problem bu he.31 GHz signal wih an ampliude of -17 dbm has o be filered. 3. Filers 3..1 Lowpass IF Filer The bandpass filer for he IF region was esed in he nework analyzer. When looking a he resul i was obvious ha his could no be used since he filer response was exremely bad. Insead a new filer was designed wih he help of ADS only. This ime, a simple lowpass filer configuraion was used. The filer response can be seen in figure Figure 3-1 The finished IF lowpass filer.

57 Resuls IF lowpass filer Ampliude (db) S11 (db) S1 (db) -90 Frequency (GHz) Figure 3- IF filer response. A 70 MHz S 11 is -0.7 db and S 1 is -1 db. 3.. Lowpass Microsrip Filer The heoreical resul of he filer given by ADS can be seen in figure

58 Microwave Wireless Communicaion Link Figure 3-3 Theoreical lowpass filer response. This can be compared o he filer response from he nework analyzer seen in figure 3-4. The consruced filer is close o he heoreical filer response bu here is a peak a approximaely 5.5 GHz ha need o be suppressed in order o make he filer work beer. To eliminae his peak, he filer was improved by connecing i o he nework analyzer and puing small paches of copper ape on i. The improved filer response can be seen in figure GHz lowpass filer Ampliude (db) Frequency (GHz) S11 (db) S1 (db) Figure 3-4 The characerisics of he lowpass filer. 48

59 Resuls Tuned.38 GHz lowpass filer Ampliude (db) Frequency (GHz) S11 (db) S1 (db) Figure 3-5 Improved lowpass filer response using copper ape. I is obvious ha he final filer is much beer han before he adjusing using copper ape. Since his filer is going o be used o filer ou he harmonics of he local oscillaor (LO), i is imporan ha S 1 is low for hese frequencies. There is a small peak a 1.5 GHz bu since his is very far away from he cenral frequency of he local oscillaor. Figure 3-6 The RF lowpass filer wih uning Bandpass Microsrip Filer This filer was also esed wih he nework analyzer and gave he graph in figure 3-7. Is heoreical response can also be seen in figure

60 Microwave Wireless Communicaion Link.45 GHz bandpass filer Ampliude (db) S11 (db) S1 (db) -90 Frequency (GHz) Figure 3-7 Characerisics for he bandpass filer. I is clear ha hese wo graphs differ because of irregulariies when he filer was fabricaed, bu i is sill a filer ha will work for he purpose i was made for. The firs peak on S 1 is a.45 GHz, wih he aenuaion 1.9 db. A his poin, he reurn loss is 7.4 db. Figure 3-8 RF bandpass filer. 50

61 Resuls Figure 3-9 Characerisics for he heoreical bandpass filer. 3.3 Low-Noise Amplifier Microwave Low-Noise Amplifier The firs ime he RF LNA was esed, i did no ampliy he signal a all. To make i work, he connecions o he ground plane had o be shorened o be as small as possible, he shorer hey where, he higher he gain. Afer making hem as small as possible, a gain a abou 15 db was achieved, bu no he 16 db as promised in he daashee for he device. The dip in S 11 ha was supposed o be a.45 GHz was a.8 GHz. The LNA impedance maching nework was herefore uned o ge a beer value. Figure 3-11 shows he scaering parameers for he uned LNA. Figure 3-10 RF Low noise amplifier. 51

62 Microwave Wireless Communicaion Link LNA scaering parameers 0 10 Ampliude (db) ,5 1 1,5,5 3 3,5 S11 (db) S1 (db) S (db) S1 (db) Frequency (GHz) Figure 3-11 Scaering parameers for he RF LNA. A.45 GHz S 1 is db, S db, S db and S db IF Low-Noise Amplifier The IF LNA was no mached in any way, bu simply pu ogeher wih is bias circuiry. Is scaering parameers can be seen in figure The gain of he LNA is approximaely 19.5 db and he refleced signal will be aenuaed 13 db. Figure 3-1 The IF low-noise amplifier. 5

63 Resuls IF LNA scaering parameers Ampliude (db) S11 (db) S (db) S1 (db) S1 (db) Frequency (GHz) Figure 3-13 S 11 and S 1 for he IF LNA. 3.4 Power Amplifier The resul from he power amplifier can be seen in figure The gain of he device can be read as ca 14 db and he refleced signal was aenuaed a bi more han 15 db. Figure 3-14 The power amplifier. 53

64 Microwave Wireless Communicaion Link Power amplifier 0 10 Ampliude (db) ,5 1 1,5,5 3 3,5 S11 (db) S1 (db) S (db) S1 (db) Frequency (GHz) Figure 3-15 Scaering parameers for he power amplifier. 3.5 Oscillaor Figure 3-16 Oscillaor. The oscillaor was fabricaed as saed in he daashee for he device. The conrol volage was chosen o be conrolled wih a poeniomeer. The oscillaor is also frequency dependan which means ha i has o be rese o.38 GHz every ime i is locaion wih differen emperaure. Looking a he oscillaor frequency specrum using he specrum analyzer i could be seen ha he frequency.38 GHz had an oupu power a -11 dbm. The firs harmonic was suppressed 13.5 dbc and he second 3 dbc. Boh hese figures are less han saed in he daashee bu since hey are far away from he carrier frequency, i will no be a problem o suppress hem. Anoher wo harmonics were found, he firs a 11.9 GHz and he second a 14.8 GHz, boh of hem suppressed 50 dbm. No signal was found a 9.5 GHz. 3.6 Modulaor The modulaor was esed wih an oscilloscope and was found o be working raher poorly. When he prescaler oupu from he circui was esed, a signal ha should have been a square wave a 17.5 MHz was found o be a riangular wave ha varied from 17 MHz o 18 MHz. The IF signal 54

65 Resuls was even worse and varied from 65 MHz o 75 MHz. Afer some improvemens he oupu signal varied 3 MHz which is no good enough. 3.7 Demodulaor The demodulaion of he signal is done wih hree circuis, phase locked loop, frequency divider and he demodulaor iself. The frequency divider divides he signal by wo, from 80 MHz o 140 MHz and is working fine. Bu because he PLL is no working, we have no been able o es he demodulaor. 3.8 Sysem ess Receiver Afer each par had been confirmed o work he receiver side was pu ogeher o conrol is funcionaliy. During hese ess, he demodulaor was no used since here was no signal o demodulae. An inpu signal was creaed using a signal generaor and sen o he firs par of he receiver sysem, he LNA, using a cable. This means ha here was no acual wireless ransmission, bu a simulaed weak inpu signal via a cable. During hese simulaions we found ha he local oscillaor leakage hrough he downconverer o he IF side was significan. Two oher signals a 4.83 GHz and 4.9 GHz could also be deeced even if hey where weak. To be sure o eliminae hese signals anoher lowpass filer was added o he IF side. The firs es wih anennas was done indoors in a 0 meer long corridor. The ransmied power was se o 0 dbm and could be seen a he specrum analyzer conneced o he receiver. The only problem was ha he received power varied some, somehing ha probably could be explained by he inerference of signals ravelling differen ways. To furher es he sysem, a signal was sen beween wo buildings of approximaely 35 meers. The received signal power was could be measured o dbm and dbm for a ransmied power of 0 dbm and -10 dbm respecively. A ransmission was also done using anennas only, which gave a resul of dbm and dbm for he same ransmied signal powers. These values can be conrolled using he Friis equaion which will give he resul dbm and dbm. The nex sep was o check if he receiver could deec a signal sen from 400 meers away, he lengh i is supposed o be working a. Sending a signal of 0 dbm gave a received signal power of -59 dbm wih a noise floor a -85 dbm. To ge a beer signal, anoher LNA was added o he RF side of he receiver, making he final value -48 dbm. I should be noed ha he ransmied signal power is adjused by he signal generaor and ha he anennas will cause an amplifying effec of he signal of 9 db. When calculaing he received power using he Friis equaion, a higher value will be found. This depends on ha he anennas are hard o align manually which means ha he anenna amplificaion will no be 9 db bu a value slighly less han ha Transmier Since we knew ha an oupu power of 0 dbm was sufficien for he receiver o deec, he ransmier side of he sysem only had o be esed by iself o make sure i fulfilled his crierion. Using only he power amplifier afer he upconverer and feeding he upconverer wih -7 dbm 55

66 Microwave Wireless Communicaion Link a 70 MHz from a signal generaor, gave a signal power of -1.5 dbm. Adding an exra LNA before he PA gave an oupu power of 10 dbm Transmier Receiver Tes Again, he 400 meer srech was used o ransmi our signals and wo LNAs were used a he receiver side. This ime, a -7 dbm, 70 MHz signal was used as inpu o he upconverer. The power a he receiver was measured o -36 dbm when using he PA afer he upconverer and -5 dbm when adding he LNA in beween hese wo circuis. A es was also done o see how he signal looked for he RF por of he downconverer. A he receiver side, he wo LNAs and a bandpass filer was used. Figure 3-17 RF inpu o he downconverer. As can be seen in figure 3-17 he.31 GHz signal, wih second larges ampliude, from he upconverer is no suppressed enough, as well as he LO signal, beween he.31 GHz signal and he.45 GHz signal, which is he one wih he highes ampliude. Since i is imporan o eliminae hese signals, especially he.31 GHz signal, a new bandpass filer wih smaller bandwidh was needed a he ransmier. The wo signals o he far lef are signals ransmied from elsewhere and no from our ransmier. Since we wan o suppress hese signals furher, a new bandpass filer wiher smaller bandwidh will be added o he receiver oo. The same es wih he new bandpass filers can be seen in figure Figure 3-18 RF inpu o downconverer using he new BP filers.