A Direct Down-conversion System Using Sub-harmonic Mixer with Microstrip Lines

摘要

The purpose of this paper is to design a direct down-conversion system using sub-harmonic mixer with microstrip lines, it is also called a zero intermediate frequency system. By utilizing the direct conversion configuration, it can not only avoid to use an additional voltage controlled oscillator and phase-locked loop which resulted from twice down conversions so as to simplify the configuration and reduce cost, but also suppress the mirror image frequency, and thus to diminish non-linear conversion distortion and to increase the receive dynamic range. The LO-RF and LO-IF isolations of sub-harmonic mixer with microstrip lines are greater than 60 dB, and the conversion loss is about 14 dB; the phase noise of VCO with spiral-shaped defected ground structure (DGS) is -96 dBc/Hz at 10 kHz. We have succeeded to develop a direct down-conversion system.