Singly Balanced Mixer Using Substrate Integrated Waveguide Magic-T Structure

This paper presents, for the first time, a singly balanced mixer on the basis of a substrate integrated waveguide (SIW) magic-T structure. This scheme has a number of attractive inherent features such as a high isolation between input ports and also a stable phase relation between output ports. The mixer is designed and fabricated by means of a standard printed circuit board (PCB) process and measurements agree well with simulations. The measured conversion gain is higher than -9.5 dB in the case of applying -20 dBm RF signal for both high and low LO power configurations at 10.6 GHz over the entire RF frequency band of 10-10.55 GHz. Furthermore, the conversion gain attains a constant maximum of -6.5 +/- 0.7 dB when the injected LO power is increased from +5 dBm to +18dBm. Moreover, the input 1-dB compression point is measured to be about +7 dBm at an LO power of +13 dBm.