Transmitter and Receiver Isolation by Concentric Antenna Structure

A concentric antenna structure with transmitter (Tx) and receiver (Rx) isolation characteristic is proposed. For both cases that Tx and Rx use the same frequency or different frequencies, Tx leakage can be removed by the proposed antenna structure. The field couplings between antennas are mathematically presented and Tx leakage cancellation is theoretically examined. To theoretically verify the case that Tx and Rx use the same frequency, a set of 16 inverted-F antennas and a set of 4 inverted-F antennas are designed for Tx and Rx, respectively. For the case that Tx and Rx use different frequencies, a set of 4 monopole antennas is designed for Tx and Rx each. The measured result shows the Tx/Rx isolation characteristic of more than -50 dB.

I. Introduction

Isolation between transmitter (Tx) and receiver (Rx) is one of the most important issues in communication systems where Tx signal unintentionally flowing into Rx is called Tx leakage. Since Tx leakage may have higher values than received signal and makes active components saturated, it degrades the overall quality of the received signal. Tx leakage generated in the front-end of mobile communications is related to antenna and thus the method to remove Tx leakage varies according to the types of antennas used.