A 94-GHz transceiver with fiber optic feed

Edward C. Niehenke

doi:10.17918/00008806

The use of fiber optic links has the advantage of providing a low loss connection between microwave/millimeter wave elements eliminating heavy waveguide and coaxial connections with immunity from electromagnetic interference. For transmit/receive applications, the phase noise is an important system parameter and needs to be minimized. Millimeter waves have many applications such as signal distribution and radar. Working at 94 GHz has the advantage of operating in the atmospheric low-loss window with the potential for miniature equipment. Unfortunately, the hardware is generally bulky and expensive requiring novel techniques for miniaturization and cost reduction to make these systems practical. This dissertation addresses two of the key technology areas, namely, providing a low-cost, miniature 94-GHz transceiver, and innovating a fiber optic link architecture with low phase noise for this W-band frequency range. A unique, low-cost, planar transceiver has been conceived, developed, and tested that includes a two axis, monopulse fed, four element, switchable, right hand-left hand circularly polarized patch antenna. All circuits are microwave monolithic integrated circuits (MMICs) (amplifiers, mixer, and PIN diode switch) interconnected with low-loss Z-cut quartz microstrip. The miniature 1.1-inch diameter by 0.25-inch thick transceiver operated both in the transmit as well as the receive mode with 3-dB beamwidth of 58 degrees. When mounted as a feed for a 5-inch diameter parabolic dish, the assembly exhibited a 1.7 degree 3-dB beamwidth, 12-dB sidelobes, a gain of 26 dB, with a difference pattern null of 30 dB. A low phase noise optical link was innovated, fabricated, and evaluated. The link is at Ku band with an input power of 5 mW compatible with direct frequency coherent synthesizer, followed with a low-cost MMIC X6 multiplier/amplifier for W-band output of 70 mW and X3 multiplier/amplifier for the W-band X2 subharmonic mixer with an output of 33 mW. A diode pumped YAG laser at 1319 nm is modulated with a Mach-Zehnder modulator at Ku band and detected with a PIN diode photodetector. The measured Ku band phase noise floor of -145 dBc/Hz was obtained with a projected W-band phase noise of -129.4 dBc/Hz.

A 94-GHz transceiver with fiber optic feed

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A 94-GHz transceiver with fiber optic feed

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