180-degree Substrate Integrated Waveguide Hybrid and Its Application to Broadband Millimeter-wave Single Balanced Mixer Design

This paper presents a broadband millimetre wave single balanced diode mixer that makes use of an innovative substrate integrated waveguide (SIW) based 180-degree hybrid, fabricated with conventional printed circuit board (PCB) technique. The proposed mixer has advantages over other previously reported millimetre-wave mixer structures judging from a series of aspects such as cost, ease of fabrication, planar construction and broadband performance. A K-band experimental prototype has been designed and fabricated to validate our proposed scheme. The mixer covers RF/LO operating frequency range from 20 to 26 GHz and IF port covers DC-4 GHz. Measured results show that the proposed mixer has low conversion loss of less than 10 dB and high port-to-port isolations over the frequency band of interest.