Design of Five Bit Digital Phase Shifter ))

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1 (( Design of Five Bit Digital Phase Shifter )) حسين ذاري خميس جامعة النھرين / كلية الھندسة / قسم ھندسة الليزر وااللكترونيات البصرية طالب زيدان تعبان الجامعة المستنصرية / كلية العلوم / قسم الفيزياء أ. د. محمد صالح مھدي الجامعة التكنلوجية / قسم ھندسة الليزر تقديم البحث : 2011/3/2 قبول نشر البحث : 2011/3/2 Abstract This research study the optimum design of a five-bit digital phase shifter, with special characteristics and specific technologies in order to applications in communication circuits. The digital phase shifters can be changed by only few predetermined discrete values such as 180,90,45,22.5 and11.25degree. The phase shifter has a phase advance of 32 discrete steps each step is The phase shifter has a characteristic frequency bandwidth of GHz. (C-X band), total gain of 64 db, the gain of the phase shifter is 4 db. An array antenna is used to search by varying the phase. In addition to discuss different types of digital phase shifters and also discuss the factors affecting in future of this design. الخالصة أن دراس ة ھ ذا البح ث م ن خ الل الت صميم األمث ل لمغي ر الط ور الرقم ي ذو المرتب ة الخام سة م ع دراس ة الخ واص الت صميمية لھ ذا المغي ر ويمك ن مالحظ ة ذال ك ف ي التطبيق ات االلكتروني ة م ن ض منھا دوائ ر االتصاالت وأن مغير الطور الرقمي سيعمل بتغيير موقع زاوية الطور وذلك بتغيير القيمة المجزاة بزيادة مقدارھا درجة الى 360 درجة بزيادة عددھا 32 مرة ان الطيف الترددي المستخدم مح صور ب ين ) كيك ا ھرت ز) ض من حزم ة( س ي اك س ( ل ذلك ت ستخدم م صفوفة للبح ث ع ن الط ور(الزاوي ة) ف ي أي مرتب ة وك ذلك نوق شت أن واع مختلف ة م ن مغي ر الط ور الت ي تعتم د عل ى ت أثير العوامل المھمة في التصميم للبحوث المستقبلية الرقمية. 169

2 1.Introduction The function of a phase shifter is to control the phase characteristics in the processing of a microwave signal. This device will shift a signal to a desired phase location via a digital or analog command and can be accomplished in a passive device. In order to achieve the maximum phase shift, the circuit parameters must be chosen carefully. A variable phase shifter can be characterized as a linear two-port device, which alters the phase of its output signal in response to an external electrical command. Mechanical phase shifters are not considered here. Expressing this mathematically, with the input µµذ signal sin (wt +(n)), the output will be A(n) sin ((wot+_(n)), where n is the programmed phase and A(n) is the insertion loss. The difference between the input phase and the output phase is the sum of the phase shift due to the propagation through the phase shifter plus the programmed phase shift. The relative simplicity of the idea that any reactance placed in series or shunt with a transmission line will produce a phase shift has given rise to many different circuits over the years for use as phase shifters at microwave frequencies.[1]. 2. Literature Survey There are many types of phase shifters to be used. The digital phase shifters are classified into ferrite phase shifters and semiconductor phase shifters as shown in Fig(1).The semiconductor phase shifters are divided into two parts; transmission type and reflection type. In reflection type phase shifters, the bias design unit is a non- port network, and it is the phase shift of the reflect signal that is changed by the control signal. These basic one-port phase shifters can be converted into useful two- port components either by using circulator or a hybrid because of the case of integration. The hybrid couple reflection type phase shifters are more common as far as the design of the basic one- port reflection phase shifter bit is concerned. One may use a switched length type or switched reactance type design. Other designs for semi conductor phase shifter may be called transmission type. Here there are three subgroups switched line type phase shifters loaded line phase shifters and switched net work type phase shifters. A M0SFETs in an active amplifier mode. This type of phase shifter is nonreciprocal and can not be designed by using pin diodes design 170

3 methods for the various types of phase shifters. The transmission type is subdivided into four types: switched line, loaded line, and switched network and amplifier type. The reflection type is also subdivided into two hybrid coupled. Each of the previous types: circulator coupled and two types is further divided into switched length and swisched reactance. Digital Phase Shifter Ferrite Semiconductor Reflection Type Transmission Type Circulat or Hybri d Switch ed Loade d Line Switche d Amplifi er Type Switche d Switche d Fig. (1) Various Types of Microwave Phase Shifters.[2] 3.The target of the study The aim of this study is to design a 5-Bit phase shifter with linearly changing phase until the phase shift reaches some multiples of The phase shifter has a phase advance of 32 discrete steps each step is The phase shifter has a 171

4 characteristic frequency bandwidth of GHz. (C-X band), total gain of 64 db, the gain of the phase shifter is 4 db and output power of 23 dbm minimum at 1 db. 4. Types of phase shifter. There are many types of phase shifters like diode phase shifters and semiconductor diode phase shifters work well as switching devices for radar phase shifters. They are capable of relatively high power and low loss, and they can be switched rapidly from one state to another (low impedance to high impedance, or vice versa). They are not significantly affected by normal changes in temperature; they can be switched with low control power; and they are compact in size. These kinds of digital phase shifters as shown. [3] a- Varactor Phase Shifter b- Pin Diode Phase Shifters c- Monolithic Microwave Integrated Circuit (MMIC) Phase Shifters a- Ferrite Phase Shifter b- Reggie Spencer Phase Shifter 5. Basic Theory The digital phase shifter will be discussed in details after explaining the variable functions, which affect the operation of the phase shifter and taken for selection. Perhaps suitable phase shifter will be designed as shown below. The equation below must be studied: [4] Φ = 2 π f 2 π fl 2 = = λ v π fl µε.(1) 172

5 Where f is the frequency in Hz, λ is the wavelength in meters, L is the length of the transmission line, v is the velocity of propagation in m/s, µ is the permeability in H/m and ε is the permittivity in F/m. From the above equation it is obvious that the variable phase is dependent on the above mentioned parameters. But with phase shift it can be different. Here we have assumed for simplicity that the velocity of propagation corresponds to that is in TEM mode. Transmission line such as coaxial cable and such guides is a bit more complicated, The Types of digital Phase Shifter a- Switched Digital Phase Shifter. b- Loaded Line Digital Phase Shifter. 6. The serrodyne as a frequency translator A microwave signal may be translated in frequency with law spurious frequency generation by the process of serrodyning. The function enabling the serrodyne frequency translation is a linear saw tooth phase modulation of the input microwave signal frequency. The outputs microwave frequency w o of a serrodyne system when the phase's rate dφ/dt modulates the input frequency w i is given by[5]. ws = wo + d Φ /dt.( 2) An ideal serrodyne with no phase rate discontinuity as nonlinearity translates the input frequency to output offset frequency according to the above equation with no spurious side band in the output when dφ/ dt is repetitive, saw tooth and Φ is 360. Then the saw tooth modulation frequency, ws is equal to the difference frequency of the output minus the input frequency (ws = wo - wί). A common implementation of the serrodyne technique is by the use of TWT, changing the voltage on the helix of the TWT changes the phase shift of the signal being amplified. 173

6 7. Velocity of Deception Using Digital Phase Shifter. The serrodyning action is provided by the digital phase shifter which consists of five sections of fixed phase shifters that can be switched in and out along the through path in the correct sequence. The 5-bit phase shifter section provides fixed shift steps of and a total of 32 steps from 0 to A waveform function generator provides the phase control. Fig (2) Typical phase shifter cell [6]. 8.Typical Cell Fig. 3 shows in details the block diagram of a typical phase shifter cell in RF section. The phase shifter consists of Schiff man type delay line, which consists of a pair of alternately switched lines, one of which is a dispersive line section containing a quarter wave coupled transmission line shorted on one end on the, the other is a non- dispersive transmission line with a linear phase shift slope with frequency as shown in fig 2. To achieve phase shift Φ (t) between non-dispersive sections in compared with specified bandwidth λ/4 coupled transmission line section, the phase shifter is given by the equation[7]. 174

7 Φ = cos 1 ρ ρ + tan tan 2 2 φ φ...(3) Where ρ = Z oe is the ratio of even/odd impedance? This results in a broad band phase shifter with very little phase error over the desired frequency band. 9. Phase Control Waveform Generator The Phase Control Waveform Generator is an integral part of velocity deception system. It is used to generate a linear ramp function and a second order curve. An integrating network is used to generate a constant amplitude (0-10 volt) ramp function so that shows in details the circuit analysis of a function generator. The linear ramp function is now passed through a noninverting variable gain amplifier. The liner is ramp function is now passed through a non- inverting variable gain amplifier. This amplifier allows the high end of the ramp to be changed (i.e. the 10v value adjustable) to provide stop frequency translation control like (15KHz-50KHz). The characteristics of amplifier. It has the characteristics from 2-30 MHz wide band linear amplifier that uses RCARF power transistor other than diode compensated 2n This amplifier uses an output of 5 watt PEP at this power level IMD product is more than 40 db below on a ton of two signal power gain is greater than 40 db in low power linear amplifier. The use of temperature compensating circuits. For SSB application with out temperature compensating is as follows[8]. Frequency = 30MHz,P (PEP) at 28v = 25w,Power gain min = 13 db, Collector efficiency = 40% min 175

8 10. The serrodyne as a frequency translator A microwave signal may be translated in frequency with law superious frequency generation by the process of serrodyning. The function enabling the serrodyne frequency translation is a linear sawtooth phase modulation of the input microwave signal frequency The outputs microwave frequency Wo of a serrodyne system when the phases rate dφ/dt modulates the input frequency Wi is given by[7]. Wo = Wi + dφ/dt (4 ) An ideal serrodyne with no phase rate discontinuity as nonlinearity translates the input frequency to output offset frequency according to the above equation with no spurious side band in the output when dφ/dt is repetitive, sawtooth and Φ is 360. Then the sawtooth modulation frequency, Ws is equal to the difference frequency of the output minus the input frequency (Ws = Wo - Wi ). A common implementation of the serrodyne technique is by the use of TWT, changing the voltage on the helix of the TWT changes the phase shift of the signal being amplified[8]. 11. Velocity of Deception Using Digital Phase Shifter 176

9 ECM applications utilize the serrodyning technique in order to deceive the detection tracking or other velocity related functions of A victim radar missile system that most commonly uses velocity deception technique is the velocity gate walk off (VGWO) [9].shows a typical GHz velocity deception system using the 5-bit serrodyne technique. The serrodyning action is provided by the digital phase shifter which consists of five sections of fixed phase shifters that can be switched in and out. A waveform function generator provides the phase control see the truth table number (1) witch is illustrated briefly about the degree of the phase shift. 177

10 Truth table (1) degree of the phase shift Discrete steps Number of bits ( Degree of the phase shift

11 12. Conclusion This design of the digital phase shifter, which consists of 5 sections of fixed phase shifter, which can be switched in and out along the true path in the correct sequence. The 5-bit phase shifter section provides fixed shift steps of o and total of 32 steps from 0 to º. The appropriate phase functions a provide 5-bit binary code to turn on the individual cell and off in phase shifter.the output translated frequency of the digital phase shifter section feeds a FET amplifier. References [1].Van Brunt Lcroy, B., Applied ECM Volume, EW Engineering Inc [ 2].Klein Gerald and Dubrowsky Leanard, The Digilater, Anew Broad 3.Band Microwave Frequency Translator, IEEE Trans. MTT Vol. 15 No. 2 pp Mar [ 3]. Schiffman, B.M, A New Class Of Broadband Microwave 90Degree Phase Shifters, IEEE Trans. MTT pp , Apr [4].Graner, R.V., Microwave Diode Control, Artech House, [5].Temme, D.H., Diode And Ferrite Phase Shifter Microwave Jor., State of Art Reference pp ,1989. [6].Hord, W.E., Microwave And Millimeter Ferrite Phase Shifter, Jor., [7].Whicker, L.R, (Ed), Ferrite Phase And Ferrite MIC Components, [8]. Schmidt, Kevin (W9CF), "Phase-Shift Network Analysis and Optimization," QEX, Apr 1994, pp [9]. Ro ber tl. Morris and John R.Miller by Designing with TTL integrated circuits 1978 pp