A Ka Band Multi-Channel Integrated Receiver for Passive Millimeter Wave Imaging System

Passive millimeter wave imaging technology, with its harmless advantages to the human body, has been recognized as an important means to implement human security inspection. As the key component of the passive imager, the performance of the receiver directly determines the accuracy and stability of the whole system. Moreover, a passive imager usually use as an array radiometer, which requires a great quantity of receivers. So it is very important to study the high performance, low cost, miniaturized millimeter wave receiver. In this paper, a multichannel integrated receiver for Ka band is designed, machined and tested. That is, each receiver module contains 8 RF receiving channels working on 32 ~ 36 GHz, 8 independent LO operating at 9.875 GHz, and an IF output working from 3.5 to 7.5 GHz. The key parts of each receiving channel include: a)Waveguide-microstrip transition. Two kinds of structures are designed for the different polarization direction of the waveguide. One is the fin line form applied to a horizontally polarized waveguide and the other is a structure combining a ridge waveguide with a microstrip probe. b)Image reject filter implemented by microstrip circuit. c)Cascaded low noise amplifiers, mixer, multipliers active circuit. All of these circuit structures are realized on a complete Rodgers 5880 substrate (Er: 2.2, 254 μm thickness). After the final test, the module frequency conversion gain is 33 dB ± 7.5 dB adjustable. The Image rejection is greater than 26 dB. Noise figure is less than 4.5 dB. The most importance is that the receiver is more integrated and miniaturized, which is suitable for the array passive millimeter wave imaging system.