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 +18 dBm. Moreover, the input 1-dB compression point is measured to be about +7 dBm at an LO power of +13 dBm.