X-band 용 Zero IF 구조의 저항성 주파수 혼합기 설계 및 구현

Abstract

A mixer is a key component in the wireless communication systems. In this paper, we design a mixer which is used in a frequency modulated continuous wave(FMCW) radar system. The frequency sweep range of the radar is from 10 GHz to 11 GHz. The transmitted and received signals of the radar are applied to LO and RF ports of the mixer, but the frequency difference between the two signals, which is called beat frequency, is under a few KHz and depending on the distance to target. Thus the isolation between the LO and RF ports is very important factor to design this mixer.

In this paper we propose a single balanced resistive mixer using GaAs MESFET for this application. We first design a single-ended type resistive mixer using a simulation tool, and next design a balanced type to increase the LO-to-RF isolation of the mixer. We fabricated the mixer using GaAs MESFET on substrate of dielectric constant 10 and thickness 0.635 mm. The measured results show that the isolation and conversion loss of the mixer over the frequency band is 20dB and 10.5dB, respectively. The LO input power for operating the proposed mixer is +3dBm, which is lower than a general conventional mixer's LO power. The 1 dB compression point is 6dBm.