S.R. Davies

Fabrication and characterization of micromachined rectangular waveguide components for use at millimeter-wave and terahertz frequencies

The fabrication and characterization of micromachined reduced-height air-filled rectangular waveguide components suitable for integration is reported in this paper. The lithographic technique used permits structures with heights of up to 100 /spl mu/m to be successfully constructed in a repeatable manner. Waveguide S-parameter measurements at frequencies between 75-110 GHz using a vector network analyzer demonstrate low loss propagation in the TE/sub 10/ mode reaching 0.2 dB per wavelength. Scanning electron microscope photographs of conventional and micromachined waveguides show that the fabrication technique can provide a superior surface finish than possible with commercially available components. In order to circumvent problems in efficiently coupling free-space propagating beams to the reduced-height G-band waveguides, as well as to characterize them using quasi-optical techniques, a novel integrated micromachined slotted horn antenna has been designed and fabricated, E-, H-, and D-plane far-field antenna pattern measurements at different frequencies using a quasi-optical setup show that the fabricated structures are optimized for 180-GHz operation with an E-plane half-power beamwidth of 32/spl deg/ elevated 35/spl deg/ above the substrate, a symmetrical H-plane pattern with a half-power beamwidth of 23/spl deg/ and a maximum D-plane cross-polar level of -33 dB. Far-field pattern simulations using HFSS show good agreement with experimental results.

A new micro-machined millimeter-wave and terahertz snap-together rectangular waveguide technology

A novel technique for micro-machining millimeter and submillimeter-wave rectangular waveguide components is reported. These are fabricated in two halves which simply snap together, utilizing locating pins and holes, and are physically robust, and cheap, and easy to manufacture. In addition, S-parameter measurements on these structures are reported for the first time and display lower loss than previously reported micro-machined rectangular waveguides.

A Single-Waveguide In-Phase Power-Combined Frequency Doubler at 190 GHz

This work represents the first demonstration of in-phase power-combined frequency multipliers above 100 GHz based on a dual-chip single-waveguide topology, which consists of two integrated circuits symmetrically placed along the E-plane of a single transmission waveguide. This strategy increases by a factor of 2 the maximum sustainable input power with regard to traditional waveguide multipliers. A biasless 190 GHz Schottky doubler based on this novel concept has been designed and tested with a 6-10% conversion efficiency measured across a 177-202 GHz band when driven with a 50-100 mW input power at 300 K.

Active micromachined integrated terahertz circuits

Schottky barrier diodes have been integrated into on-chip rectangular waveguides. Two novel techniques have been developed to fabricate diodes with posts suitable for integration into waveguides. One technique produces diodes with anode diameters of the order of microns with post heights from 90 to 125 microns and the second technique produces sub-micron anodes with post heights around 20 microns. A method has been developed to incorporate these structures into a rectangular waveguide and provide a top contact onto the anode which could be used as an I.F. output in a mixer circuit. Devices have been fabricated and D.C. characterized.

Use of novel photoresists in the production of submillimeter-wave integrated circuits

A new technique is reported for micro-machining millimeter and submillimeter-wave rectangular waveguide components using an advanced thick film UV photoresist known as EPONTM SU-8. The recent introduction of this resist has been of great interest to the millimeter-wave and terahertz micro-machining communities, as it is capable of producing features up to 1 mm in height with very high aspect ratios in only a single UV exposure. It therefore represents a possible low-cost alternative to the LIGA process. S-parameter measurements on the new rectangular waveguides show that they achieve lower loss than those produced using other on-chip fabrication techniques, they have highly accurate dimensions, are physically robust, and cheap and easy to manufacture.

A membrane planar diode for 200 GHz mixing applications

The design and fabrication of a monolithically integrated subharmonic mixer for 200 GHz is described. The 1.5 /spl mu/m diameter Schottky diodes are formed on a 5 micron thick GaAs membrane suspended across the RF waveguide. Predicted mixer performance shows improved conversion loss compared with that of conventional flip-chip diodes.

The TIRGO project: A compact 800-900 GHz heterodyne receiver for submillimetre astronomical spectroscopy

We describe a new Nb SIS junction heterodyne waveguide receiver working in the frequency range between 800–810 GHz. The receiver is light and compact and is designed to fit most infrared and optical telescopes with the minimum of reconfiguration. We present a description of the receiver and its associated RF performance.

Micromachined submillimeter-wave frequency multipliers

The work described here uses microfabrication methods to integrate semiconductor devices with micromachined waveguide cavities to form submillimetre-wave frequency multipliers. Processing schemes involve both planar and three-dimensional lithography, using conventional photoresist and epoxy based SU8. Two approaches have been used. In the first, micromachining methods were employed to fabricate an integrated 270-810GHz frequency tripler. This includes a varactor diode contacted via an electroplated whisker, which is integrated with a stripline filter and waveguide probe. In the second approach, a specially designed Schottky diode chip incorporating the stripline filter/bias circuit is mounted in a micromachined, waveguide circuit block to form a 135-270GHz frequency doubler.

Microwave power generation by magnetic superlattices

We report on microwave power emission by ballistic electrons as they cross a region of spatially inhomogeneous magnetic field. Magnetic finger gates were fabricated at the surface of high mobility GaAs/AlGaAs Hall bars embedded in a coplanar waveguide. By modulating the current injected through the Hall bar and measuring the second harmonic of the signal rectified by a Schottky detector, we obtain the microwave power emitted by the superlattice. This power (∼6 W m−2) is compared to the fluorescence of electron spins that undergo spin resonance as they cross domains of opposite magnetic field.

A low-noise 810 GHz heterodyne receiver for molecular-line astronomy

A low-noise 810 GHz heterodyne receiver for astronomy is described. The mixer consists of a NbTiN SIS junction, mounted in a half-height rectangular waveguide mixer block. The receiver has been successfully tested on the UK Infrared Telescope, Hawaii, with a DSB system noise temperature of 280 K at 808 GHz. Observations of several astronomical sources have verified the sensitivity of the instrument.