Abstract: A P-I-N type diode high frequency switch in a secondary radar interrogation device working with ISLS and RSLS and consisting of a transmitter, two receivers and two antennas. So as to reduce the high cost for P-I-N type diodes, including driver stages for the transmission and reception separation and to eliminate the necessity of an antenna switching unit, the terminals 19 and 20 of a pair of antennas are directly connected through single lines 23 and 24 to band pass filters 5 and 6 connected to respective receivers 7 and 8 with the band pass filters 5 and 6 blocking the transmission signal and allowing reception of received signals and wherein the electrical lengths of the line and the band pass filter is such that the input impedance corresponding to no-load operation occurs at the corresponding antenna terminal for the transmission frequency.

Abstract: A directional coupler formed as a strip line which consists of two transmission lines coupled to each other and formed on opposite surfaces of a dielectric carrier plate with one of the lines comprising a microstrip line. A directional coupler is formed which has very high sharpness of directivity and high coupling attenuation, and great electrical strength. The second transmission line is formed as a coplanar line which includes a strip line which is mounted on the grounded side of the microstrip line in an area which is free of the grounded line surface and which extends essentially parallel and has current which is opposite to the strip line of the microstrip line. The invention is particularly adaptable for use where a directional coupler having high coupling attenuation is required, as, for example, in VSWR monitoring in secondary radar devices.