Adaptive duplexer implemented using feedforward technique with a BST phase shifter

As the complexity of modern modulation schemes increases, the noise levels inserted in the receive band by the transmitter are also increased. In this paper a technique to enhance the isolation of a duplexer is introduced, which reduces the noise levels in the receive band of the system. Feedforward techniques are used to create an adaptive null in the receive band, which can be targeted at any channel across the band. This null has been shown to give an improved isolation of 20 dB for the duplexer over a 2 MHz bandwidth. This feedforward system is implemented using a BST phase shifter to enable tenability of the enhancement null.