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RECENT ADVANCEMENTS IN

RADAR TRANSMITTERS

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Improvements in Radar Transmitter Performance andReliability Using High-

Voltage Solid-State Modulators and Power Supplies

The operational life of high power radartransmitters that employ microwave VEDs

can be extended using high voltage, solid-state modulators and power supplies.

We present the Modern solid-state

modulator topologies along with theconventional topologies that they replace.

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INTRODUCTION

T. Weil wrote The Transmitter is typically one of the largest, heaviest, and most costly portions of a radar system.

As RF-tube selection has therefore become a vital

but hazardous occupation. The term "RF-tube"has been replaced with the term "vacuumelectron device" (VED).

A well-designed modulator maximizes radar

mission availability by increasing microwave-VEDlife, preventing damage, and delivering cost-efficiency over the life of the radar.

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MODULATORS

Two modulator technologies- Advanced Solid-State Modulators and Microwave-VEDs.

Modern Switch Modules, High-Voltage Power Supplies, and Opening Switches.

Solid-State, High-Voltage Modulator Switches

Switching High Voltage Power Supplies

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Conventional Vs Modern

Two power subsystems in a Radar transmitter1)High Voltage Power Supply (HVPS)2)Pulse Modulator

ConventionalModulator Switches

Increased size, weight,complexity

Higher operatingvoltages than requiredby VED

Low efficiency

Modern ModulatorSwitches

Better performance atreduced cost and size

Capable of providingvery accurate voltages

Good regulation withlow ripple

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DTI high-voltage, high-power,switching power supplies

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OVERVIEW OF CONVENTIONAL MODULATORS IN FIELDEDRADAR TRANSMITTERS

Cathode-Pulsed Modulatorso Cathode pulsars must control the full beam power

of the RF tube, either directly or through acoupling circuit.

C A T H O D E P U L S E

M O D U L A T O R S

DIRECTLYCOUPLED

TRANSFORMER

COUPLED

CONVENTIONAL-LINE TYPE

SCR-MAGNETIC

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Directly coupled

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Transformer-Coupledo Figure shows the arrangement with the switch tubecathode connected to ground, allowing the grid, screen,

and filament circuitry to also be ground-referenced.o However, the pulse transformer windings must be fully

insulated for the full DC HVPS voltage.o The original AN/SPG-60 klystron modulator used this

transformer-coupled arrangement.o Another example, at very-high average power, is the Land

Based Air Surveillance radar.o A high-power tetrode is used to provide klystron beam

pulse regulation. Transformer coupled systems oftenpresent difficulties because the pulse transformeradversely affects pulse shape .

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Transformer-Coupled

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Solid State Modulators

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Solid-state cathode-pulsed, prototype

modulator in SPS-49 transmitter

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Advantages of Solid State Modulators

Long, failure-free life Low transmitter voltage

Amplitude control of the transmittedwaveform by selectively switching modules orindividual devices on or off

Wide Bandwidth

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CONCLUSION "Appropriate technology" for radar transmitters combines

the best features of technically advanced switching HVPSsand solid-state high-voltage pulse modules to produce highperformance, highly reliable modulators that are ideal formicrowave-VEDs.

Many microwave-VED radar transmitters can now useswitching HVPS and solid-state modulator configurations.

For new designs, this configuration provides much higherlevels of performance and pulse flexibility thanconventional modulators.

For existing systems, the decision to upgrade is often drivenby reliability, parts availability, and operating cost issuesrather than performance improvements.

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REFERENCES

IEEE Paper written on Improvements of RadarTransmitters by Paul D. Brown.

T. Weil, "Transmitters", in M. Skolnik, ed,Radar Handbook.

R. S. Symons, "Modern Microwaves Tubes ForRadar," Tri-Service VED Workshopbook.