Design and Development of 8kW Solid State Transmit …serialsjournals.com/serialjournalmanager/pdf/1505731318.pdfDesign and Development of 8kW Solid State Transmit Receive Module for

International Journal of Control Theory and Applications63

Design and Development of 8kW Solid State Transmit Receive Module for Gadanki Ionospheric Radar Interferometer

M. Durga Raoa, I. Srinivasa Raob, P. Kamarajc, R. Jagadeesh Kannand and A. Jayaramane

aCorresponding author, National Atmospheric Research Laboratory, Gadanki-517112. Email: [email protected] bVellore Institute of Technology, Vellore Campus, Tamilnadu. Email: [email protected] c,eNational Atmospheric Research Laboratory, Gadanki-517112 dVellore Institute of Technology, Chennai Campus, Tamilnadu

Abstract: Objectives: Design, development and realization of solid-state high power transmit-receive (TR) module for the ionospheric radar applications intended to generate the 8-kW pulsed output at 30-MHz frequency with better rise time and fall times.Methods/Statistical analysis: State-of-the-art technologies are incorporated such as digital phase shifter, digital attenuator, high power solid state amplifier and innovative design of passive transmit-receive switch in the realization of TR module. Highly reliable, robust designs are adopted in the realization, designs are carried out with Advanced Design Systems (ADS) software and the test results are well matching with those simulated results.Findings: The development of high power TR module for ionospheric radar applications is a unique design for the first time in India and tested with the radar system and providing round-the-clock observations with better reliability. High power requirements are achieved with better thermal designs. The TR module is providing very good rise and fall times with better droop. Future generation pulsed radars for atmospheric applications can adopt the methodologies such as low loss power combining with the Wilkinson based designs to generate the high power outputs mentioned in this paper.Application/Improvements: The developed TR module is being used in the Gadanki ionospheric radar interferometer working at 30-MHz frequency. Concepts mentioned in this paper are very useful to design TR module for all pulsed radar applications.Keywords: TR module, ionospheric radar, solid state, digital attenuator, power combiner.

InTRoDucTIon1. The requirement of accurate characterization of the ionospheric background parameters and their secular variations, strong fluctuations in electron density/electric field due to various instabilities and their local time

International Journal of Control Theory and Applications

ISSN : 0974-5572

„ International Science Press

Volume 9 • Number 51 • 2016

M. Durga Rao, I. Srinivasa Rao, P. Kamaraj, R. Jagadeesh Kannan and A. Jayaraman

International Journal of Control Theory and Applications 64

and seasonal dependence including the effects of magnetic storm become important for efficient and reliable use of the satellite based communication and navigation systems. Further, the forecasting capability became the requirement of the day for necessary correction and safety both for services and satellite based systems. Both experimental data and understanding the physical processes is required for developing a meaningful forecast. In this context, to characterize the low latitude ionospheric irregularities and their spatial and temporal variations with all time scales and develop an in-depth understanding on the governing physical processes, National Atmospheric Research Laboratory (NARL) has developed a new 30-MHz radar for strengthening the Ionosphere research activities. This radar employed state-of-the-art technologies such as solid-state transmit-receive (TR) modules, direct digital receiver, pulse compression etc. The detailed description of the TR module design is presented in section I, realization philosophies are presented in section II and sample results and conclusions are given in section III.

I. necessity of the TR Module in the Radar SystemThe figure of merit1 of any mono static pulsed Doppler radar system described by its power-aperture product (PA). The demands are always to have very high power aperture product, but due to the constraints for realizing very large apertures2, it is always beneficial to optimize the array configurations with the promising latest solid state technology in realizing high transmit power. The emerging concepts such as phased array approach3 in realizing very high peak power by space combining with better reliability, low electrical power requirements and less hazardous for user friendly operation attracts the new generation radars. State-of-the-art of solid state technology plays an important role in realizing the present generation high power compact TR modules.

Functionalities of TR module: The basic functionalities of TR module5 consist of amplifying incoming low power pulsed RF pulse from synthesizer to the rated high output power level and feed the antenna in transmit (Tx) path, providing low-noise amplification to the received weak echo signal collected by the antenna element in the receive (Rx) path. The advantages of these modules for pulsed radars such as less rise time and fall times, which mostly limited by the switching speed of the TR switches, less quiescent current requirements due to optimized selection of biasing and quick recovery time.

II. Description of TR ModuleBasic building blocks of the TR module are shown in Figure 1, consist of phase and gain control module (PGM), preamplifier module, driver amplifier module, power amplifier, TR directional coupler, front-end amplifier module, detector module and Timing and Control Signal Generation unit.

Phase and gain control module (PGM): Phase and Gain control module (PGM) responds to both transmit and receive paths. It comprises of 6-bit Digital Attenuator with 0.25 dB resolution. It is incorporated to set the overall gain of the TRM at desired level which in turn enables the user to use antenna synthesis techniques to achieve desired side lobe levels for the antenna array radiation pattern. Total range of 0-15 dB in steps of 0.25 dB is achieved with two numbers of HMC539LP3. For any phased array radar9, maintaining the phases of all the TR modules at desired levels is the key to steer the beam in a particular direction.

The required Phase shifts within 0-358.6o at 1.4o resolution are achieved based on propagation delay through 8-sections of pi-network using inductors and capacitors (LC) as shown in Figure 2. At the operating frequency ‘f ’which is 30 MHz in the present case, the values of L, the series arm element and C, the shunt arm element, in the p-section for a phase shift j are given by Zo sin j/2pf and sin j/2pf Zo respectively, where Zo is the system impedance which is equal to 50 ohm. The sample L and C values are simulated by using Advanced Design System (ADS) software as shown in Figure 3. Selection of a specific phase shift is accomplished by entering 8-bit digital



Figure 1: Functional block diagram of solid state TR module

word that in turn switches appropriate delay lines through fast switching CMOS dual absorptive type ADG936 SPDT switches. Constant attenuation levels are maintained at all phase-shifts with the help of attenuation pads. The phase and attenuation control signals are routed to phase-shifter and DAT through HCPL-2630 opto-couplers. Since these DAT and phase shifter network are common to both Tx and Rx, selection between Tx and Rx paths are achieved through TR switches based on Tx/Rx command. To have better isolation about 60 dB, three numbers of HMC349MS8G switches are incorporated. The typical rms error for amplitude is about 0.158dB, phase rms error is about 2.556o and total insertion loss for the PGM section is about 15dB.

Figure 2: Functional block diagram of 8-bit phase shifting network

Transmit section: Total peak power output from each TR module is 7.5-kW (68.75dBm) with +10 dBm as input from exciter. Since the input is further down by -15 dBm at PGM, the required gain from Tx amplifier section is about 63.75 dBm. This is achieved through a series of amplifier sections6 such as pre driver amplifier (PDR), driver amplifier (DR), power amplifier (PA) and TR directional coupler.

Pre driver amplifier: PDR section is used to provide a total gain of 38-40dB and a power level of 2W for the incoming RF siganal from PGM which is at -5dBm. As shown in Figure 3, it consist of power divider, SPDT switch, two lnear amplifiers and a gain module. Power divider (LRPS-2-1) divides the input power into two equal outputs, one output is connected to Over Drive circuit, is compared with a reference voltage set to the required level using a comparator (LM158) and generate Over Drive alarm (OD). Second out put of power divider is connected to a cascade of two linear amplifiers (SBB5089) via SPDT switch (HMC349) to achieve required gain. Gain of each amplifier is 16dB, operates with +5V. SPDT is used to control the PDR through PA ON command. Gain module (RFC1G21H4-24 DP-27) has a gain of 18dB, operates with +28V.



S -P AR AME T E R S

P 6P 5Term

TermC C

L

P 4P 3Term

TermC C

L

TermTerm

S _P aram

P 2P 1CC

L

Num=6Num=5Term6

Term5C 6 C 5

L 3

Num=4Num=3Term4

Term3C 4 C 3

L 2

Term2Term1

S P 1

Num=2Num=1C 2C 1

L 1

Z=50 OhmNum=6

Z=50 OhmNum=5

C =106.1 pF C =106.1 pF

R =L =265.2 nH

Z=50 OhmNum=4

Z=50 OhmNum=3

C =43.9 pF C =43.9 pF

R =L =187.5 nH

Z=50 OhmNum=2

Z=50 OhmNum=1

S tep=S top=32 MHzS tart=28 MHz

C =1.3 pFC =1.3 pF

R =L =6.5 nH

28.5 29.0 29.5 30.0 30.5 31.0 31.528.0 32.0

-1.45

-1.40

-1.35

-1.50

-1.30

freq, MHz

phas

e(S

(2,1

))

R eadout

m2

m2freq=phas e(S (2,1))=-1.404

30.00MHz

28.5 29.0 29.5 30.0 30.5 31.0 31.528.0 32.0

-48

-47

-46

-45

-44

-43

-42

-49

-41

freq, MHz

phas

e(S

(4,3

))

R eadout

m1

m1freq=phas e(S (4,3))=-44.973

30.00MHz

28.5 29.0 29.5 30.0 30.5 31.0 31.528.0 32.0

-96

-94

-92

-90

-88

-86

-84

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-82

freq, MHz

phas

e(S

(6,5

))

R eadout

m3

m3freq=phas e(S (6,5))=-90.001

30.00MHz

Figure 3: (a) Schematic of the phase shifting networks corresponding to 1.4o, 45o and 90o phase values. (b) ADS simulated outputs for the phase shifting networks corresponding to 1.4o, 45o and 90o phase values.

Driver amplifier: Driver amplifier amplifies the signal from PDR (2W) to the required level for power amplifier module (150W). The device used in driver amplifier is MOSFET (MRF 141G). Typical Gain offered by this stage is 14dB. The Amplifier is matched using broadband transformers7 at input and output for better impedance matching and to obtain wide band frequency response. The bias circuit consists of zener diode, potentiometer, resistors and thermistor and IDQ is limited to 400 mA by this circuit. Feedback network with resistors and capacitors provided from drain to gate for better stability.

Power module: The basic concept of high power RF generation is to develop a Basic Amplifier Module (BAM). Each BAM generates a peak power of +61dBm with two numbers of high power MOSFETs (MRF157) in parallel with typical Gain of 14dB. As shown in Figure4, it consists of 8-way Wilkinson power divider in the input section, four numbers of BAMs and 8-way power combiner to generate the required output power of 8-kW. Amplifier input and output impedances are matched using LC circuit at input and output sections for better impedance matching at narrow band frequency. Bias circuit consists of zener diode, potentiometer and resistors and the bias current is limited to 300 mA. Gate bias circuits with temperature compensation are used to achieve constant drain current. Combiner is designed for low insertion loss and high isolation over the band



and high power resistors are used for isolation. Quiescent drain current is provided to the MOSFETs 1µs before and after the Tx pulse by applying gated bias to avoid heat dissipation. The efficiency of the power amplifier is measured to be 55 %.

S -PAR AME T E R S

Term

Term

P 2

P 1

RRRR

RRR

R

C

C

L

C

C

L

C

C

L

C

C

L

C

C

L

C

C

L

C

C

L

C

C

L

S _P aram

Term2

Term1

N um=2

N um=1

R 19R 18R 17R 13

R 12R 11R 10

R 9

C 32

C 31

L16

C 30

C 29

L15

C 28

C 27

L14

C 26

C 25

L13

C 24

C 23

L12

C 22

C 21

L11

C 20

C 19

L10

C 18

C 17

L9

S P 1

Z =50 OhmN um=2

Z =50 OhmN um=1

R =50 OhmR =50 OhmR =50 OhmR =50 Ohm

R =50 OhmR =50 OhmR =50 Ohm

R =50 Ohm

C =37. 51 pF

C =37. 51 pF

R =L=750. 26 nH

C =37. 51 pF

C =37. 51 pF

R =L=750. 26 nH

C =37. 51 pF

C =37. 51 pF

R =L=750. 26 nH

C =37. 51 pF

C =37. 51 pF

R =L=750. 26 nH

C =37. 51 pF

C =37. 51 pF

R =L=750. 26 nH

C =37. 51 pF

C =37. 51 pF

R =L=750. 26 nH

C =37. 51 pF

C =37. 51 pF

R =L=750. 26 nH

C =37. 51 pF

C =37. 51 pF

R =L=750. 26 nH

S tep=S top=32. 0 MH zS tart=28. 0 MH z

Figure 4: (a) Schematic of the 8 way power combiner/divider used to generate the 8-kW power by using BPM. (b) ADS simulated outputs for 8way power combiner/divider circuit



8-way power divider/combiner: The main function of the power divider is to split the given input RF signal level into eight signals with equal amplitude. The output signals are in phase. The 8-way power splitter is reliased using inductor & capacitors. The schematic diagram of 8-way power divider/combiner simulate by using ADS software is shown in Figure 4. The advantage such approach is minimum insertion loss, perfect amplitude and phase balance between the output ports and better isolation.

TR directional coupler: TR directional coupler8 consist of Bi-Directional Coupler (BDC) and TR-Switch circuit, is to isolate the Tx and Rx Sinals. TR Switch transfers the high power Tx signal to Directional coupler through Tx port and the low power signals from the antenna (ANT) received by the Rx port. TR switch is made with BAV21 Diodes, inductors and capacitors with no bias voltage. The equivalent schematic diagrams during Tx ON and OFF conditions are simulated and the results are shown in Figure 5. Capacitors with high PIV are used to withstand high RF voltages. The main function of the Bi-Directional coupler is, it couples the signals in the forward and reverse direction.

S -PAR AME T E R S

P 6P 5

P 4

P 3P 2

P 1

R

R

R

Term Term Term

TermTerm

Term

S _P aram

CC

CC

L L

L L

L

N um=6N um=5

N um=4

N um=3N um=2

N um=1

R 1

R 2

R 3

Term1 Term2 Term3

Term4Term5

Term6

S P 1

C 1C 2

C 3C 4

L1 L2

L3 L4

L5 R =0. 5 Ohm

R =0. 5 Ohm

R =0. 5 Ohm

Z =50 OhmN um=1

Z =50 OhmN um=2

Z =50 OhmN um=3

Z =50 OhmN um=4

Z =50 OhmN um=5 Z =50 Ohm

N um=6

S tep=S top=32 MH zS tart=28 MH z

C =120 pFC =120 pF

C =120 pFC =120 pF

R =L=234 nH

R =L=234 nH

R =L=234 nH

R =L=234 nH

R =L=234 nH

28.5 29.0 29.5 30.0 30.5 31.0 31.528.0 32.0

-80

-60

-40

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0

freq, MHz

dB(S

(2,1

))

R eadout

m1m1freq=dB(S (2,1))=-55.854

30.00MHz

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(3,2

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R eadout

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m2freq=dB(S (3,2))=-0.065

30.00MHz

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dB(S

(3,1

))

R eadout

m3m3freq=dB(S (3,1))=-54.320

30.00MHz

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-0.24

-0.22

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-0.16

freq, MHz

dB(S

(5,4

))

R eadout

m4

m4freq=dB(S (5,4))=-0.213

30.02MHz

28.5 29.0 29.5 30.0 30.5 31.0 31.528.0 32.0

-41.0

-40.5

-40.0

-39.5

-39.0

-41.5

-38.5

freq, MHz

dB(S

(6,5

))

R eadout

m5

m5freq=dB(S (6,5))=-40.209

30.00MHz

28.5 29.0 29.5 30.0 30.5 31.0 31.528.0 32.0

-39.8

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-39.4

-39.2

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-40.0

-38.6

freq, MHz

dB(S

(6,4

))

R eadout

m6

m6freq=dB(S (6,4))=-39.225

30.02MHz

Figure 5: (a) equivalent schematics of the high power handling passive TR switch during Tx on and Tx oFF conditions. (b) ADS simulated outputs of passive TR switch during Tx on and Tx oFF conditions



Receive section: As shown in Figure 1, TR module receiver path consist of limiter, blanking switch and Low Noise Amplifiers (LNA). Limiter is used to protect the receiver from the transmitter leakage power; it restricts the signal level to a maximum level of 0dBm. BAT 85 are used as limiting diodes and it provides very low insertion loss to in-band small signals (the desired signals) in order to keep Receiver Noise Figure as low as possible. Blanking switch restricts the signals through receive path while transmission and passes only in receive interval. This SPDT (HMC349) provides high isolation and low insertion loss. LNA is a high performance SiGe Hetero junction bipolar transistor MMIC amplifier which offers low noise figure and high gain. Two numbers of SGA4586 are used to achieve the required gain of 45dB. The photographs of the TR module Tx section and Rx section are shown in Figure 6.

Figure 6: photograph of the TR module Tx section and Rx section

TR module protection: Protecting the TR module from various factors like output impedance mismatch, input over drive, excess duty ratio is impotant to have the better reliability and troublefree operation. To have these protection mechanisms, health of the sub-modules are monitored with module status (MS) card and the status of the same are updated to the control card. Detector is used to detect voltages of forward and reverse coupled signals of DDC to detect the forward and reverse voltages to protect the TR-Module from antenna mismatch. MS card also monitors other parametres like input RF over drive, high junction temperture, (VSWR )output load mismatch and update the control card.

Digital Timing and control Signal Generator: Digital Timing and Control Signal Generator (DTCSG) consist of CPLD(XC2C128) and Rabbit processor (R6000). It communicates with the radar controller through Ethernet. DTCSG uses the common clock generated by the Exciter unit and to initiate the operation, DTCSG receives trigger pulse at the rate of inter-pulse period (IPP) from MTCSG for synchronization. It generates a cover pulse in Transmit ON time for TR switch and a cover pulse for blanking switch based on pulse width, pre pulse, post pulse and delay with reference to IPP. Sets phase shift and DAT values to the phase shifter and digital attenuator during transmission and reception for proper beam formation. It counts the number of trigger pulses and repeats the same process till the completion of count.

Power supply unit: An integrated power supply unit is incorporated with the TR module to satisfy the requirements of low power linear RF circuits and non-liner RF high power devices which operates in pulsed mode. It consist of 12V linear supply, 28V and 60V Switched mode power supplies (SMPS). This unit provides



the required voltages for differenet sub-modules of the TR module.12V/2A uninterrupted linear power supply is used for receive front end section, PGM and DTCSG module, 28V/5A supply is used for DR and cooling fans for forced air cooling and 60V/45A is used for PA section.

Maximum peak power of the TR module is considered as 10-kW at 10% duty and efficiency as 50% for the power supply design, leads to an input DC power of 2000W. Additional tolerance of 70% is considered (2700W) keeping in view of the high power requirements, leads to the average current capability up to 45A at 60V for the power amplifier section. Similar considerations lead to a requirement of average current up to 5A at 28V for the driver amplifier and other needed circuitry. The DC current requirement for the linear circuitry is 2A at 12V. Un-interrupted power is provided for the linear power supply in order to provide continuous DC power to the DTCSG module and receive RF section, enables the user to continue the radar sequence of operation in receive mode even in case of power failure. Drain capacitor calculation plays a role in controlling the droop at the high power RF output for pulsed applications and use of optimum drain capcaitors will reduce the load on the DC supply for pulsed ouputs. Maximum droop of 0.5dB is considered for the drain capacitor estimations. Across the 28V supply capacitance estimated as 3mfd to cater the Driver amplifier peak ouput power of 150W and a drian capacitance 100mfd across 60V supply toa cater the 8-kW peak power for the maximum pulse width of 500us.

Thermal design of TR module: The efficiency of the power amplifier is found to be 45.45% and power dissipation is 73W per device, where as junction temperature is 82.4oC which is very well within in the range of the specification of the device MRF157 (200 oC). The power amplifier is designed for operating in class-AB mode and these modules are designed to place within airconditioned room, hence forced aircooling through fans (2Nos) is incorporated apart from adequate heat sink. Equation governing the junction temperature is given below

Junction Temperature of the Device is given by the following equation

Tj ={(qsa + qjc + qcs)Pd} + Ta

where, qsa is the thermal resistance of the heat sink

qjc is the thermal resistance of Device junction to case

qcs is the thermal resistance of case to heat sink

Pd is the power dissipation of device

Ta is the ambient temperature

TR module has four RF interfaces; (TR port) to/from RFDSU, antenna port (ANT), forward coupling (FC) and Reverse coupling (RC) ports for monitoring and calibration. Ethernet communication with the RC is provided through a circular connector. Three DC power supply interfaces are provided for +12V un-interrupted DC supply, +28V and +60V for DR and power amplifier sections. An exclusive ground connector and fuse are also provided. Gas discharge tubes (GDT) are placed in the RF receive path to protect TR module from lightning stokes. The overall specifications of the TR module is provide in Table 1.

ReSulTS2. The high power TR module designed for 30-MHz radar for dedicated probing of ionosphere4 has been developed and the obtained results in-line-with the specifications mentioned in Table-1. The performance of the TR module is described with the RF characterization tests such as peak power measurement, rise and fall time of the RF



pulsed output, bandwidth and harmonics and receive path gain. The tests has been carried out to measure the Tx peak power and Tx bandwidth and the corresponding pulse spectrum measured are shown in Figure 7. The obtained bandwidth is about 5MHz, which is essential for the minimum pulse width of 1micro second resolution. Rise time and fall time of the Tx pulse are very important in pulsed radar application, the present 8-kW TR module has about 200 micro sec as rise, fall times as shown in Figure 8. Similarly Tx pulse droop is measured to know the flatness of the output as shown in Figure 9. At the maximum pulse width of 500 micro sec it is measured as 0.4dB.

Table 1 overall specifications of the TR module

S.No. Parameter : Specifications1 Operating Frequency : 30 MHz2 Power Output : 8 kW 3 Duty ratio : 5%4 Pulse width : 1-500µs5 Pulse droop : <0.5dB6 Rise time/fall time : <250ns7 Harmonics : <-40dBc8 Spurious : <-50dBc9 Phase shifter type : 8 bit digital10 Phase resolution : 1.4deg11 Phase shifter difference attenuation : <0.5dB12 DAT type : 6-bit digital 13 DAT Attenuation resolution : 0.25dB14 DAT Attenuation range : 15.5dB15 T/R Switch Isolation : > 50 dB @ rated power16 T/R Switch Insertions loss : < 0.5 dB17 Bi-directional coupler Coupling : 30 dB18 Front end LNA Gain : 30 dB

Figure 7: (a) Pulse spectrum measurement of 8-kW TR module by using spectrum analyzer.

(b) Bandwidth measurement for the Tx section of TR module by using spectrum analyzer



Figure 8: Rise time and fall time measurements for the Tx path of TR module by using MSo

Figure 9: Tx pulse droop measurement by using Mixed Signal oscilloscope

concluSIon3. The high power state of the art solid-state TR module has been designed, developed and validated the performance. These modules are being used in the 30-MHz coherent back scatter radar for continuous and dedicated probing of the ionosphere. The outputs are very much stable and the unit is working satisfactorily.

AcknowledgmentThe First Author would like to express his gratitude to, VIT University, Vellore Campus, TamilNadu, India for giving constant guidance and support. The work has been done at National Atmospheric Research Laboratory, Gadanki. Authors also thank the local industries M/s Avantel Technologies Private Limited, Hyderabad for the production of TR module for 30-MHz radar. Authors very much appreciate Sri J. Raghavendra and Sri K.Jayaraj of NARL, for giving support in testing and integration of the system.



ReFeRenceSD.E. Barrick, “First-order theory and analysis of MF/HF/VHF scatter from the sea”, IEEE Trans. Antennas Propagat., Vol. [1] 20, pp. 2–10, 1972

Radar for meteorological and atmospheric observations, Shoichiro Fukao, Kyosuke Hamezu consulted by Richard J.Doviak, [2] ISBN 978-4-431-54334-3

Radar handbook, Merill I. Scholnik, Second edition, ISBN 0-07-057913-X.[3]

Davies, K.: Ionospheric Radio, IEE Electromagnetic Waves Series 31, Peter Peregrinus Ltd., London, 1990[4]

Nicholas J. Kolias and Michael T. Borkowski, “[5] The Development of T/R Modules for Radar Applications”, Proc. IEEE, Vol. 79, No. 3, pp. 308–34, 2012

Yin Liansheng, Gao Tie and Li jianxin, “[6] Integralization Design of T/R modules and Feeding networks for Solid-state Active Phased Arrays”, APMC, Vol. 1, pp. l-10, 1993

Mancuso Y., Gremillet P., and Lacomme P. “[7] T/R- modules technological and technical trends for phased array antennas,” in IEEE Microwave Theory and Techniques Symposium Digest, (San Francisco), pp. 614 - 617, June 2006.

Venkata Kishore Kothapudi, Vijay Kumar, Dangeti Anu Preetham, Mukundala Sai Rohit, “[8] Design and Fabrication of 430MHz unequal Amplitude Hybrid coupler for T-Radar Beam Forming unit”, Indian Journal of Science and Technology, 2016 Sep, 9(36), Doi no:10.17485/ijst/2016/v9i36/86223

Babu Saraswathi K. Lekshmi, I. Jacob Raglend, “[9] A Vivaldi Antenna for X-band Phased Array Radar”, Indian Journal of Science and Technology, 2015 Dec, 8(35), Doi no:10.17485/ijst/2015/v8i35/87395

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Design and Development of 8kW Solid State Transmit …serialsjournals.com/serialjournalmanager/pdf/1505731318.pdfDesign and Development of 8kW Solid State Transmit Receive Module for