Millimeter Wave Generation Using a Uni-traveling-Carrier Photodiode

We have designed a new photomixer using a uni-traveling carrier photodiode (UTCPD) for generation of W-band radiation. The UTC-PD is integrated on a InP chip with DC and RF circuits and the chip is mounted upside down on a fused quartz substrate which is placed in a microstrip channel across a quarter-height W-band waveguide. A simple crossshaped microstrip-waveguide transition printed on the quartz substrate is used to couple power into the waveguide. From the simulation it is found that this microstrip-waveguide transition can give better than -15 dB return loss over 75-120 GHz. The UTC-PD is irradiated by combined two lasers from the back side of the InP chip. We have successfully produced difference-frequency radiation at 100 GHz with a power level of mW by the photomixer. Introduction Millimeterand submillimeter-wave heterodyne mixers based on the SuperconductorInsulator-Superconductor (SIS) junctions have used a local oscillator (1,0) source which is a combination of a Gunn diode and multipliers. Since the LO source with the combination of a Gunn diode and multipliers has a mechanical complexity and poor frequency coverage especially at submillimeter wavelength, a compact and mechanically-simple LO source with broad frequency coverage is highly required for submillimeter-wave SIS receivers in the radio telescopes. Photomixers, which generate a difference frequency of two diode lasers at millimeter and submillimeter wavelength by photoconductive mixing, have been alternatively developed.[1,2] Photomixers are so compact solid-state sources with broad frequency tunability that they meet the requirement for the LO source of the SIS receivers at millimeter and submillimeter wavelengths. The low-temperature-grown (LTG) GaAs films have been prevailingly used for a photornixer element. Although the LTG-GaAs photomixers can provide enough output power for a few applications such as molecular spectroscopy, improvement of the output power is