Study On X-band Doppler Speed-measuring Radar Front-end

As the speed of space flying objects such as aircraft and satellite generally rangesfrom100m/s to8000m/s, it is necessary to replace the flying objects and their internalequipment with high-speed motion models to research the high-speed performance offlying objects. In the conventional photoelectric speed-measuring method,photo-electricity sensors are arranged along the movement patch of model, and thevelocity can be calculated by the time that the model reaches the sensors. Comparedwith photoelectric velocity measurement, the method of radar velocity measurement hasthe advantages of low-cost, easy to install, continuous measuring, etc. Based on thebackground of high-speed movement model, the paper represents a front-end ofspeed-measuring X-band Doppler radar, which works as a continuous speed-measuringdevice for the model and collects basic data for further study.The front-end adopts the coherent continuous wave radar technology, working atthe frequency of9GHz. This paper completes scheme design and quota distribution ofthe front-end which consists of three functional modules: signal source module,transmitting module and receiving module. The signal source module is made up of aphase-locked loop signal source, a microwave band-pass filter, a single-stagemicrowave amplifier, and a Wilkinson power divider. The transmitting module iscomposed of two-stage microwave power amplifier and transmitting antenna. Inaddition, a receiving antenna, a low-noise amplifier, a mixer, an IF low-pass filter andan amplifier make up the receiving module. In this paper, the principle and designmethod of each components are presented. The design, simulation and optimization ofmicrowave band-pass filter, power divider and other passive components andmicrowave amplifier are completed with software ADS and HFSS, while the circuitlayout and cavity are drawn with AutoCAD. With the use of spectrum analyzer andoscilloscope, this paper has completed the testing and commissioning of the hardwarecircuit to verify the correctness of each module’s design.In the font-end, transmitting and receiving antennas adopts coaxial line feedingmicrostrip patch antennas, with microwave band-pass filter adopting microstrip line parallel coupled structure, IF low-pass filter adopting LC structure, divider adoptingtwo-stage Wilkinson structure, mixer adopting integrated chip HMC553LC3B,microwave amplifier adopting FET TC2181, signal source adopting phase-locked loopfrequency synthesizer chip. The signal source module provides an output power of-18.5dBm, with an8dBm transmitting power of the transmitter module and a55.8dBconversion gain of receiver module. Whole test results shows that the velocitymeasurement error is less than0.6%. Finally, the analysis of the test results is done andimprovement method is proposed.