When the digital logic level at the control input is low, the PIN diode is forward-biased by the CMOS gates. The two 1-KO bias resistors limit this current to the PIN diode`s safe forward current limit. In this state, the switch is on. When the control input is high, the diode is reverse-biased and the switch is ~ott. This switch is well-suited for electronically steered antenna arrays, multiple path switching, and other applications requiring small, low-cost rf switches.
This particular design was used in a four-pole rotary switch for a Doppler-shift radio direction-finder operating at 144 MHz.