A new SPDT switch based on PIN diode for transceiver applications in microwave band

SPDT switches are used as duplexer in wireless systems, as WIMAX, to switch between transmit and receive states. Microwave SPDT switches may be designed using FET’s or PIN diodes. However, PIN diode is suitable for duplexer applications due to its high power handling capability. I general, in frequencies higher than 3 GHz, isolation better than 30 dB is a challenge. This is due to the parasitic inductance of PIN diode.In this paper, we propose a new structure for SDPT PIN diode switch to overcome this challenge. In the proposed structure a micro-strip line is adopted parallel to the diode. This line, in conjunction with another micro-strip line that is in series with the diode, eliminates the diode inductance in on-state and the diode capacitance in off-state, and hence improves both of isolation and insertion loss. The proposed structure has been analyzed mathematically and analytic equations have been derived to design the proposed switch. Finally, simulation results have been used to validate the performance of the switch. Simulations are performed using SMP1340 PIN diode and the model presented by the diode manufacturer. The simulations are in ADS and EM and EM_Cosim simulators are used to simulate the switch layout and include the layout effects accurately. Simulation results show more than 50dB isolation and less than 0.2dB insertion loss.