Wideband phase keyers

A wideband 0 to P1 phase keyer has been developed on the basis of a hybrid ring bridge formed by a half-wavelength symmetric slot line, with an incoming straight symmetric slot line and an outgoing asymmetric strip line connected at diametrally opposite points. The advantages of this device over a conventional one on the basis of a magic tee with an open loop formed by a quarter-wavelength asymmetric strip line are that diodes can be connected directly without matching devices and that a frequency-independent 180 deg phase shift occurs within the input tee. An experimental prototype of this new phase keyer was built on a 1-mm thick Polikor substrate with GaAs Schottky-barrier diodes. It was subsequently tested with a modulating 10 MHz meander signal. The results were a carrier attenuation of at least 30 dB over the entire 1.6 to 2.8 GHz range, with the loss of parasitic frequency conversion less than 7 dB per sideband and loss on the parasitic amplitude modulation not more than 0.3 dB, holding the nonuniformity of the amplitude-frequency characteristic below 2 dB.