MICROWAVES Introduction to Laboratory Classes

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1 MEEC, 1 st semester 2011/2012 DEEC MICROWAVES Introdution to Laboratory Classes Custódio Peixeiro

2 Laboratory Classes 4 Sessions T1 Contat with a mirowave benh T2 Mathing on an impedane load T4 Measurement of the S-parameters of a waveguide T - juntion T5 Measurement of dieletri properties of materials Classes onentrated in 4 weeks (separated 4 weeks) T September T Otober T November T Deember 2

3 Maximum duration: 3 hours 2 students per group (few exeptions with 3 students) 5 groups per lass (5 benhes) On-line registrations in Fénix (from 15h30 September 13 until 23h59 September 15) Support to students on the days of the laboratory lasses, 15h30-17h00, room North Tower (ext. 2167) Classes start next week (19 September) 3

4 Evaluation Marks Final Mark = 70% Written Exam Mark + 30% Laboratory Mark Laboratory Mark = 50% Oral Evaluation Mark + 50% Written Report Mark Witten Exam Mark individual (0 to 20) Oral Evaluation Mark individual (0 to 10) Written Report Mark group (0 to 10) 4

5 Mirowave Benh Students use a mirowave didati benh (X band: 8-12 GHz) with retangular metalli waveguide 5

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7 Reports Editor Use of the desktop omputer available in eah benh to write the session report Fixed template for eah session report The templates follow the laboratory guide (Portuguese version available in Seção de Folhas, AEIST) Report printing at the end of the lass Report marks given two weeks after the last lass of eah session 7

8 Important Notes It is absolutely neessary to prepare the laboratory sessions by reading the orresponding guide. If you don t do that usually you will not be able to finish the session. Always follow thoroughly the safety reommendations given in the first session Although low power is used (10 mw) mirowaves radiation hazards must be avoided Always follow the handling reommendation given in the first session to handle the omponents and equipment with are Very expensive and fragile equipment 8

9 Take a USB flash drive to eah lass to store the report Register in paper all the results obtained Download the evaluation reord sheet file from the Fénix web page, print it and take it (with name and photo of eah student) for the first session Take a alulator for every session The lasses start at the indiated time (08h00 or 17h00) and FINISH at the indiate time (11h00 or 20h00) 9

10 Transmission Line Basis As already indiated the mirowave benh uses metalli retangular waveguide omponents TE (transversal eletri) and TM (transversal magneti) modes are defined for the metalli retangular waveguide The fundamental mode of the metalli retangular waveguide (ab) is the TE 10 (a > b). The orresponding utoff frequeny is f TE10 2a λ z TE 10 1 λ λ 2a 2 10

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12 Eah waveguide mode an be represented by equivalent voltage and urrent (fititious) distributions Transmission line theory an be used to study the field distribution along the mirowave benh Z g I 1 I 2 V g V 1 Z 0 V 2 Z -l 0 z 12

13 V(z) I(z) Vi (z) Ii(z) Vr (z) Ir(z) 1 Z o Vi (Vi jk z jk z 2 e Vr2 e 2 e jk z Vr 2 e jk z ) Γ Vr Vi 2 jθ Γ e 2 Load (voltage) refletion oeffiient V(z) I(z) Vi Vi Z 2 (e (e jk z Γe Γe jk z 2 jk z jk z o Vi 2 V2 Z I2 Vi 2 (1 Γ) Z (1 Γ) Z ) ) o z Z Z o 1Γ 1Γ Γ z z 1 1 y 1 1 y Γ I Γ y y

14 Z 1 V(z l) I(z l) Z o e e jkl jk l Γe Γe jk l jk l Z o Z Z o jz jz o tan(kl) tan(kl) z 1 Z Z 1 o z 1 j tan( k l) j z tan( k l) Γ(z) Vr Vi Vr Vi jk z 2 e j2k z Γe jk z 2 e Voltage standing wave ratio (VSWR) Refletion oeffiient along the line VSWR V V max min 1 1 Γ Γ Γ VSWR VSWR 1 1 Γ 0,1 VSWR [1, [ In spae and time Download VSWR.EXE from Fénix web page V(z,t) Vi 2[os (ωt kz) Γ os (ωt kzθ)] 14

15 Smith Chart 15 jx r z 1 z 1 z e Γ Γ jθ b j g y 1 y 1 y e Γ Γ jθ I I I π θ θ Γ Γ I I Re ( or I ) Im ( or I ) 1 (r + j x) I (g + jb) or I

Example Z = 25 + j 50 Zo = 50 z = 0.5 + j 1 y= 0.4 j 0.

16 Example Z = 25 + j 50 Zo = 50 z = j 1 y= 0.4 j 0.8 Γ 0.62 e j 0.46 π VSWR = 4.27 Γ db 20 log (0.62) 4.15dB 16

17 Impedane Mathing with Stub d Z 0 Z y y y s lim lim lim z d (from right) z d (from left) z' l s y s (z') y (z) y (z) l s Z 0 0 z y ( g ( g s s g jb g s jb ) ( g ) j(b y s s b y jb ) ) Goal is y - = 1 + j 0 (perfet mathing) g bs s g b 1 0 b s g 1 b b s otan(kl s ) b 17

Example Z = 25 + j 50 Zo = 50 z = 0.5 + j 1 y= 0.4 j 0.8 Two solutions (a, b) da / = (0.115+0.

18 Example Z = 25 + j 50 Zo = 50 z = j 1 y= 0.4 j 0.8 Two solutions (a, b) da / = ( )=0.293 lsa / = ( ) = db / = ( )=0.437 lsb / = ( )=

19 Input Refletion Coeffiient [db] Solutions a and b are equivalent ( = 0 = - db, VSWR = 1) at entral frequeny (but) have different bandwidths (BW) For VSWR 2 ( db) Solution a BW = 16.2 % Solution b BW = 8.1 % ,7 0,8 0,9 1 1,1 1,2 1,3 Normalized Frequeny Solution a Solution b 19

20 VSWR Several other speifiations may be used VSWR db VSWR db 5 4,5 4 3,5 3 2,5 2 1,5 1 0,7 0,8 0,9 1 1,1 1,2 1,3 Normalized Frequeny Solution a Solution b 20

21 RF Virtual (Software Tool) Down load the software tool from the Fénix web page Basi setup (T1) Choose frequeny and type of load Inlude (or not) slide srew tuner Visualization of the VSWR meter measurement Can be very useful to prepare T1 and T2 21

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23 VSWR Meter It is a dediated equipment to measure diretly the VSWR in the slotted waveguide Tuned (1 khz) amplifier and voltmeter Calibration needed eah time the load onditions are hanged Pointer defletion (stronger voltage) lokwise Very important to learn you to use it 23

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26 VSWR Measurement Proedure 1. Move the probe arriage to the right limit of the slotted waveguide (losest to the load) 2. Move the probe arriage slowly to the left until you find a maximum 3. Adjust the gain (use the buttons for 10 db steps and the knob for ontinuous adjustment) until the meter indiates 1.0 on the upper sale 4. Move the probe arriage to a minimum Move to the right if in 2 you have passed a minimum and to the left otherwise Do not hange the gain 26

27 5. Read the VSWR diretly in the upper sale (1 - ) 6. If VSWR > 4 then inrease the gain 10 db and read the VSWR in the seond sale (3.2 10) 7. If VSWR > 10 then inrease the gain 10 db again, read the VSWR in the first sale and multiply by If VSWR > 40 then inrease the gain 10 db again, read the VSWR in the seond sale and multiply by You an ontinue this inrease of gain and hange of sale proedure if needed (VSWR > 100) 10. The third (red) sale is used to obtain more aurate measurements when VSWR 1.3. In that ase you need to press the (red) EXPAND button. 27

Transmission Lines: Coaxial Cables and Waveguides

Transmission Lines: Coaxial Cables and Waveguides Jason ClIItis 1 April 8, 00 1. Introdution This pap er investigates the wave veloities in oaxial ables and retangular waveguides. Coaxial ables and waveguides