Research On Down-conversion Technology In W Band

Low noise amplifier and mixer are often on the front stage of the whole receivingsystem, for processing received signal well and guaranteeing the performance of thesystem. W-band wave has such high frequencies that it’s hard to get a local oscillator(LO)with great power. Using the fourth harmonic mixer can reduce the frequency oflocal signal to1/4of the radio frequency(RF), and avoid the use of high power localoscillator in high frequency, thus reducing the cost. In this paper, a fourth harmonicdown converter of W band is studied, and made. Its performance is test.This paper first introduces the mixing principle of diodes and related technicalindexes of mixer. Referring to some commonly used mixer circuits, we design the mixerto meet the need. We select an anti-parallel diode pair called DMK2308, and make thefourth harmonic mixer in the Rogers substrate with thickness of0.127mm. The fin-linetransition structure helps the RF signal transform from the waveguide to the micro-stripline. The use of four open stubs is to recycle the main unwanted signals. Design of theband-pass filter and low-pass filter is to isolate the output and LO signal, and preventsthe leakage of them.In the design process, we use ADS and HFSS to simulate and optimize every partof the circuit, then we get the whole of it. We have it machined, then test it. The testresults show that, with the LO power of20.5dBm, the measured minimum conversionloss is about15dB. When the radio frequency is between90.5GHz and93.5GHz, theloss is less than20dB. The LO power tested data in intermediate frequency port displaythat the isolation of LO port and output port is about38dB. The tested results andsimulation results are different.We analyze the reason causing the differences At last,we put forward the plan that the low noise amplifier chip ALH504produced byNorthrop Grumman company, can be used to counterbalance the conversion loss andkeep the noise coefficient of the whole circuit lower than7dB.The experimental results don’t meet the requirements of the system. There are stillsome deficiencies, which makes us to study more and design better. The Mixer’sperformance should be further improved. There is some reference value in the present work.