Millimeter-wave Harmonic Mixer

The performance of receiver is greatly affected by the mixer, which is always put ahead in the super-heterodyne receiver. The the sub-harmonic mixer is widely used in millimeter wave band, because the LO frequency of it can be reduced to 1/2, 1/4 or even much samller of the fundamental wave mixer, so the high performance LO source in microwave band can be used to avide the problem that the high performance LO source in millimeter wave band is hard to be got. Using anti-parallel diodes is a good structure in sub-harmonic mixers. In this paper, the fourth sub-harmonic mixers working in 8mm band and 3mm band are designed based on Anti-parallel diodes.While designing the 8mm fourth sub-harmonic mixer, the traditional diodes'circuit including four open/short stubs is used firstly. A 1G bandwidth is got according to the results by simulation. Although the results accords with the paper published earlier, the disadvantage of this mixer that the bandwidth is not large enough is obviously. So in the next way, the open stub used to reflect the RF is instead by a low pass filter. A better performance is got, the insert loss is less than -10 dB in the band from 33.3GHz to 36GHz, the bandwidth is enlarged into 2.7 G, and the minimum insert loss is -7.2dB at the center frequency. When RF is from 31.8 to 36.1GHz, the insort loss is between -10.2 dB to -12.5dB according to the experiment. After that, the design of the 3mm fourth sub-harmonic mixer is based on the improved structure of the 8mm fourth sub-harmonic mixer. The simulation result is that the insert loss is less than -17dB in the 4G bandwidth from 92.2GHz to 96.2 GHz, and the minimum is -14.2dB.Based on the frequency synthesis technique, the LO of the 8mm fourth sub-harmonic mixer is designed by the mix of two PLLs. the output frequency of the main PLL can be changed from 1.5GHz to 2.5GHz by a 10MHz step. And the output of the other PLL is 6.5GHz.The test datas that the output power bigger than 10dBm, the phase noise better than -89dBc/Hz@10k and the spurious suppression better than 41dBc meet the requirements.