Peter Sobis

A Low VSWR 2SB Schottky Receiver

A novel high performance waveguide integrated sideband separating (2SB) Schottky receiver operating in the 320-360 GHz band is presented. The unique receiver design is based on a core of two subharmonic Schottky diode mixers with embedded LNAs with a minimum noise figure of 1.8 dB, fed by LO and RF quadrature hybrids. At room temperature, a typical receiver SSB noise temperature of 3000 K is measured over most of the band reaching a minimum of 2700 K, with only 4 mW of LO power. The sideband ratio (SBR) is typically below 15 dB over the whole band and the measured LO input return loss is typically below 15 dB broadband. High performance sideband separating Schottky receivers can now for the first time be considered for submillimeter wave systems enabling new types of instrument concepts.

Development of a 557 GHz GaAs monolithic membrane-diode mixer

We present the development of a monolithically integrated 557 GHz membrane Schottky diode mixer. RF test shows state-of-the-art performance with an optimum receiver noise temperature below 1300 K DSB and an estimated mixer DSB conversion loss of 9 dB and a mixer DSB noise temperature of 1100 K including all losses.

A Broadband, Low Noise, Integrated 340 GHz Schottky Diode Receiver

A 340 GHz subharmonic Schottky diode mixer and a multioctave (3-16 GHz) custom low noise amplifier (LNA) have been integrated to form a compact receiver front-end module, exhibiting ultra low noise with an exceptional flat response and broadband instantaneous frequency coverage. At room temperature, a receiver noise temperature of 870 K is measured at an LO drive of 1.2 mW at 170 GHz. The total dc power consumption of the LNA is below 120 mW. Measurements are in good agreement with simulations taking the mixer and LNA mismatch interaction into account.

A 170 GHz 45

We present a 135deg/45deg phase shifter hybrid intended to be used in subharmonic sideband separation mixer schemes at submillimeter-wave frequencies. The design consists of an increased height 90deg 6-arm branch guide coupler with a three stub loaded differential line 45deg phase shifter at the output. The device has been implemented at G-band in an E-plane WR-05 splitblock design with a center frequency of 170 GHz and 15 % bandwidth. Measured S-parameter are in good agreement with simulations showing an isolation and return loss better than 20 dB and an amplitude and phase imbalance within 0.4 dB and 2deg, respectively.

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We demonstrate S-parameter characterization of membrane circuits in the WR-03 frequency band (220-325 GHz) utilizing thru-reflect-line (TRL) -calibration technique. The TRL calibration kit design features 3 μm thick GaAs membrane circuits packaged in E-plane split waveguide blocks with the reference planes inside the membrane circuit structure. A 300 GHz membrane ring resonator filter circuit has been characterized by applying the proposed calibration kit, showing good agreement with simulations.

Hybrid for Submillimeter Wave Sideband Separating Subharmonic Mixers

This paper investigates the impact of the waveguide width tolerance in TE10 mode waveguide TRL/LRL calibration kits. This is important for vector network analyzer measurements in the THZ range where waveguide tolerances become large compared the wavelength and to cross sectional dimensions. Besides causing reflections in the waveguide interface, the waveguide width tolerance also causes a change in the propagation constant that can shift the reference planes and cause problems in estimating the propagation constant of the Line standard. We conclude that the tolerances may cause a significant uncertainty contribution and may limit the useful band of the calibration kit.

Submillimeter Wave

3-D models have been developed to study the series resistance (Rs) at DC and the extrinsic parasitic elements (capacitance and inductance) at high frequencies for a Schottky diode chip. For the Rs study, a comparison with the experimental result has been carried out. High frequency properties and the corresponding S-parameters of the Schottky diode chip are simulated using a 3-D finite element electromagnetic solver. The parasitic elements are then extracted and studied as a function of the diode geometry. The outcome of the studies shows the existence of a significant pad-to-pad capacitance through the semi-insulating substrate which could be improved by implementing tapered shape pads.

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We present the progress of the technological development of a full e-beam based monolithically integrated Schottky diode process applicable for sub-millimetre wave multipliers and mixers. Evaluation of the process has been done in a number of demonstrators showing state-of-the-art performance, including various multiplier circuits up to 200 GHz with a measured flange efficiency of above 35%, as well as heterodyne receiver front-end modules operating at 340 GHz and 557 GHz with a measured receiver DSB noise temperature of below 700 K and 1300 K respectively.

-Parameter Characterization of Integrated Membrane Circuits

We present a sensitivity analysis on TRL calibrated S-parameter measurements of membrane circuits in the WR-03 waveguide band (220-325 GHz). The impact of waveguide and membrane circuit misalignment, as well as waveguide dimension mismatch is investigated. The analysis is performed for the thru-reflect-line (TRL) calibration applied to E-plane split waveguide blocks carrying membrane circuits. The analysis shows a large influence of the waveguide width tolerance on transmission and reflection phase after the TRL calibration. For a 20 mm long rectangular waveguide with a ± 5 μm width tolerance a phase uncertainty as large as ± 45° for reflection and ± 30° for transmission measurements is observed.

Influence of waveguide width errors on TRL and LRL calibrations

We report on a heterodyne terahertz spectrometer based on a fully integrated 557-GHz receiver and a digital fast Fourier transform spectrometer. The receiver consists of a chain of multipliers and power amplifiers, followed by a heterostructure barrier varactor tripler that subharmonically pumps a membrane GaAs Schottky diode mixer. All sub-components are newly developed and optimized with regard to the overall receiver performance such as noise temperature, power consumption, weight and physical size. The receiver works at room temperature, has a double sideband noise temperature as low as 2000 K at a maximum power consumption of 4.5 W with an Allan time of 10 s and a sideband gain ratio of 0.52. The performance of the spectrometer is demonstrated by absorption spectroscopy of H2O and CH3OH with an instantaneous bandwidth of 1.5 GHz and a resolution of 183 kHz. Several pressure broadening parameters of methanol absorption lines were determined, that agree with other published data. Using the experimentally determined molecular parameters the CH3OH absorption spectrum could be modeled with very high precision.