A high-isolation low-insertion-loss filter-integrated PIN diode antenna switch

This paper presents a new technique for an antenna switch used in WiMAX applications. The switch is based on a PIN diode SPDT switch with a bandpass filter integrated in the receiving path. The filter is realised by using an inductor parallel to the PIN diode. When reverse biased, the diode behaves as a capacitor, which resonates with the inductor resulting in a bandpass response. In the experiment, the prototype has exhibited a good performance. At Tx ON state, it produces 38.5 dB of isolation and 1 dB of insertion loss. At Rx ON state, it produces 18.3 dB of isolation and 1.2 dB of insertion loss. The integrated bandpass filter has a 3-dB bandwidth of 650 MHz. It eliminates the need for a pre-selection filter prior to the LNA, hence improving the noise figure of the receiving system.