How can I share a 900 MHz antenna between two radios?
This switch is based on a design from an article I wrote about diodes.
The 50 Ohm resistor makes the switch absorptive for the transceiver, so that it doesn't short the output. The receiver can be shorted with a reflective switch. This will improve the isolation, which will help keep power from the transmitter from overloading the receiver too much.

PIN diodes make good RF switches. They have low on-resistance and low off-capacitance, and are usually lower cost than IC RF switches. The inductors need to be high-impedance at the signal frequencies. They need to be high-impedance at the frequencies of interest. The 2.2uH chokes in this schematic are not optimized for your application. If you can tolerate a little bit of loss, a 1K or 2K resistor is a lower-cost and easier-to-design substitute for the choke.

More details are in The PIN Diode Circuit Designer's Handbook from Microsemi.