An RF activated antenna switch

The development of high power semiconductor technology has suggested that the mechanical antenna relay should be replaced by a highly reliable solid state system. Many approaches to this problem are possible using forward and reverse biasing with various types of switching diodes. However, the advantages of simplicity and convenience make the r-f activated system very attractive. The term "r-f activated" is used to mean a "block box" that has only three terminals; one each for the antenna, receiver, and transmitter. In its passive state the receiver is connected to the antenna and the transmitter is isolated. Application of r-f to the transmitter terminal connects the antenna to the transmitter and isolates the receiver. Two major problems must be overcome in order to make a useful r-f activated antenna switch. First, because of power loss in the unbiased switching diodes, considerable r-f power is lost during transmission requiring higher input power and large expensive power diodes. The second problem arises from the low threshold voltage of a simple P-N junction diode. Therefore, spurious antenna power can break down the switching diodes during the receiving mode. These problems have been solved by the unique application of known semiconductor phenomena.