Reconfigurable Active Circulator

Abstract

In today’s wireless communication, circulators are usually used as RF front-ends. They can take the place of duplexers to achieve both receiving and transmitting signals by using only one antenna. The mobile radio frequency band is from 800MHz to 2.2GHz. Conventional ferrite circulators are not practical because of the disadvantages like narrow bandwidth, big size and large weight. It is necessary to design a small size wide band circulator which can cover the frequency range. Active circulators are usually used. In this essay, a three port wideband active quasi circulator and a reconfigurable active circulator which based on distributed amplifier topology are discussed. Both of the circulators use phase equalization technique and are formed by three transistors. These two circulators can achieve high isolation between port 1 and port 3.