Approaches for improving LO-RF isolation of MMIC 90°-hybrid-IRM

Image reject mixer (IRM) is one of common devices used in microwave receivers. A classical structure is IQ output single balanced Schottky diode mixer using 90deg hybrid. It´s widely used in many engineering areas. The advantages of this structure are high-dynamic range capability, good VSWRs and suppression of noises. But the disadvantage caused by this structure is poor LO-RF isolation. This paper gives some methods to improve the LO-RF isolation of MMIC IQ output single balanced Schottky diode mixer and analyses the influence on the other performances. It also gives a simulative and experimental result of MMIC Ka-band mixer design using these methods.