A low noise S-band image rejection mixer based on enhancement mode pHEMT

In this paper, a low noise S-band image rejection mixer (IRM) based on enhancement mode pseudomorphic HEMT (pHMET) is presented. The proposed IRM consists of a RF low-noise amplifier (LNA), pair of resistive FET mixer cores, an IF lumped quadrature hybrid and a quadrature LO splitter circuit with a drive amplifier. The resistive FET mixer cores utilize the conductance between the drain and source of the high linearity and low-noise pHEMT as a mixing element. It can offer low noise, good LO-to-RF isolation and high dynamic range with a moderate LO levels. The open-circuit stub loading is used to reduce the size of the LO quadrature hybrid. The proposed IRM was finally fabricated and measured. The measured results show that, when the RF frequency varies from 3.5 GHz to 4 GHz, the image rejection mixer achieves more than 20 dB of image rejection ratio (IRR), the noise figure (NF) is less than 1.8 dB, the conversion gain is 10 dB and the output power 1 dB compression point is -3 dBm. The output spurious rejection is better than 50 dBc in the frequency range from 10 MHz to 10 GHz. The proposed image rejection mixer is suitable for low IF system, low-noise transceivers for wireless communication or radio sensing and other RF and microwave systems.