2-port cavity-backed slot antenna for reducing matching loss

A cavity-backed slot antenna which has two different impedance ports is proposed. Conventional antennas usually have a single port with a fixed port impedance. In a Wireless Body Area Network (WBAN) applications where low transmitting power is required, the optimum output impedance of the transmitter is generally much higher than the conventional antenna impedance (50 ohm) whereas the receiver needs a lower source impedance (50 ohm). In the case of using a conventional antenna impedance, the impedance matching circuit of transmitter causes overall efficiency degradation and narrow bandwidth because of the high impedance transform ratio and the finite Q of the LC element used in the matching circuit. In this paper, 2-port cavity-backed slot antenna which has different port impedances for the transmitter and receiver respectively is proposed. Each port has impedance which is equal to the optimum impedance of the transmitter and receiver. In demonstration, it is shown that the bandwidth and radiation patterns at each antenna port are almost identical. Using the proposed technique, the efficiency and bandwidth enhancement can be achieved by reducing the transform ratio of the matching circuit.