Millimeter-Wave Planar Varactor Frequency Doublers

A pair of millimeter-wave frequency multipliers, a 40/80 GHz balanced doubler and an 80/160 GHz balanced doubler, were designed using advanced three dimensional electromagnetic simulation tools. The doublers comprise a mechanically rugged planar GaAs Schottky varactor chip mounted on a quartz circuit housed in a split waveguide block. The doublers are designed for wide-band, fixed-tuned operation. Methodologies for designing the planar varactor chips and circuits were developed. The 40/80 GHz doubler exhibits record fixed-tuned bandwidth, output power and efficiency. Moreover, there exists a high level of agreement between the simulated and measured results, validating the design methodology and the simulation tools.

The 40/80 GHz doubler exhibits a measured 3 dB bandwidth of 17% at an input power of 200 mW. At 41/82 GHz, the measured efficiency is 51% at an input power of 150 mW. The efficiency drops to 48% at an input power of 200 mW. The measured and simulated bandwidths are nearly identical and the measured peak output power is within 1.8 dB of the simulated result. The 40/80 GHz doubler is also evaluated at cryogenic temperatures in a calibrated dewar. The measured efficiency is 61% at an input power of 150 mW and a block temperature of 14 K. The efficiency drops to 48% at an input power of 365 mW and output power of 175 mW.

Simulations for the 80/160 GHz doubler show efficiency and bandwidth similar to the 40/80 GHz design. Measured results indicate a peak efficiency of 21%, peak output power of 16 mW, and fixed-tuned bandwidth of 15%.