Research On The Key Technology Of V-band Multi-channel Radiometer Front-end

The resonance absorption by oxygen and water vapor will lead to a large attenuation when the millimeterwave propagating in the aerosphere. As for oxygen, there are many resonance absorption lines distributing over 50 to 70 GHz. The high pressure of the lower atmosphere can cause the effect of pressure broadening, which will lead to a lot of overlap of resonance absorption lines with each other to form a consecutive absorption band. The temperature profiles of the aerosphere can be deduced by observing this strong absorption band with the V-band multi-channnel radiometer, which is an important method in the meso-micro scale realtime weather monitoring and forecasting. Therefor, this thesis makes some research on the following key technology for V-band multi-channel radiometer front-end.As for the need of building Hybrid Microwave Integrated Circuit(HMIC) module with coplanar transmission line I/O ports Microwave Monolithic Integrated Circuit(MMIC), research has been made on the transition from waveguide to coplanar transmission line. Considering the integral structure, E-plane and H-plane transitions have been designed respectively, which are integrated in a module by back-to-back structure. The measured results of the back-to-back structure(a 6.6mm long coplanar waveguide transmission line included) show that, in the whole V-band, the reflection coefficient is better than-13 dB, and the insertion loss is better than 1.1dB.The division of different channels of the radiometer front-end can be realized by using separate network. A magic-T with filters embedded in each output arms or a splitter can be employed in the separate network according to the band overlap exists or not between the two desired separate channels, respectively. For the desired 50 to 60 GHz frequency band, a broadband magic-T is simulated. The simulated results show that, in the 50 to 65 GHz frequency band, each port’s reflection coefficient is better than-20 dB, and the isolation between the two output arms is better than 28 dB. The splitter is realized in this structure, which is the combination of one H-plane T-junction and two waveguide iris filters. The simulated results show that, the reflection coefficient in both channels is nearly below-15 dB, and the isolation between the two center frequencies of the different channels is beyond 40 d B.A V-band Single-Pole Single-Throw(SPST) switch is designed for the noise-injection module which is for calibration. A simplified physical model of the PIN diode is created in HFSS. And by extracting the parameters again and again, the insertion loss of the designed SPST switch is below 1dB, and the isolation is beyond 16 dB in the 50 to 65 GHz frequency band.The detector changes high frequency signals into low ones which are convenient to deal with by the back-end. It is a key module in the radiometer front-end. Through building a simplified physical model of the detector diode and designing broadband DC-loop, Low-Pass-Filter(LPF) and matching circuit, the voltage sensitivity of the designed zero-biased detector is beyond 4800mV/mW in the 50 to 60 GHz frequency band.