A double-balanced mixer for 2 GHz

The design and construction of the mixer and of a microstrip-line filter are described. The mixer and filter are intended to upconvert a signal of 75 MHz, +10 dBm to an IF, signal at 1995 MHz. The mixer output signal will feed an earth station transmitter. In order to function with this high input level, the mixer was built with four pairs of Schottky diodes, each pair connected, in series to a star configuration. The coupling of the signals to the diodes is accomplished through a strip-line balanced line hybrid coupler. Strip-line baluns are used to connect the balanced line hybrid to the unbalanced 50 ohms ports. Using conventional glass-encapsulated diodes, the mixer exhibited a dB conversion loss, and the measured 1 dB compression point was +10 dBm.