A slot-antenna bridge-frequency-multiplier design suitable for submillimeter wavelengths

We present a novel quasi-optical all-planar frequency doubler that could provide an alternative approach to conventional waveguide circuits for millimeter- and submillimeter-wave signal generation. By utilizing a quad-bridge-diode configuration, we are able to isolate the input and the output circuits without the use of complicated filter structures. Two pairs of polarization switched double-slot antennas are used for input and output coupling to free space and substitute for the hybrids commonly required in balanced circuits. Compact coplanar transmission line matching circuits, placed between the antennas and the diodes, an designed to achieve maximum conversion efficiency. The quad-bridge-diode/antenna circuit can then be mounted on a dielectric-filled parabola or substrate lens for coupling to quasi-optical propagation systems. Measurements on a low-frequency scale model show frequency conversion from 8.8 to 17.6 GHz with peak conversion loss of 16.1 dB and a bandwidth of 350 MHz. When external circuit losses are accounted for, an input to output loss of 8.6 dB is obtained with unoptimized diodes. This agrees closely with the value obtained from analysis using HP MDS.