A PIN diode is a diode with a wide, undoped intrinsic semiconductor region between a p-type semiconductor and an n-type semiconductor region. At high frequencies, the diode behaves as a resistor. The high-frequency resistance is inversely proportional to the DC bias current through the diode. Therefore, if suitably biased, the PIN diode acts as a variable resistor. It has low reverse capacitance, that will attenuate RF signal, unless the diode is forward biased. These properties make it suitable for RF switches.
The device presented here can be used to switch two antennas. It can prove useful in a number of situations. You can have a VHF and a UHF antenna, or you can have two similar antennas that are pointed in opposite directions for different signals. This switch does not require an extra cable and does not cause significant signal losses. A low DC voltage is sent over the coaxial cable to forward bias one diode. If the polarity of this voltage is reversed, then the other diode will be biased.
