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Efficient and compact frequency converters are essential for frequency stabilization of terahertz sources. In this paper, we present a 3.5-THz, x6-harmonic, integrated Schottky diode mixer operating at room temperature. The designed frequency converter is based on a single-ended, planar Schottky diode with a sub-micron anode contact area defined on a suspended 2-$\mu$m ultra-thin GaAs substrate. The dc-grounded anode pad was combined with the radio frequency E-plane probe, which resulted in an electrically compact circuit. At 200 MHz intermediate frequency, a mixer conversion loss of about 59 dB is measured and resulting in a 40 dB signal-to-noise ratio for phase locking 3.5-THz quantum-cascade laser. Using a quasi-static diode model combined with electromagnetic simulations, good agreement with the measured results was obtained. Harmonic frequency converters without the need of cryogenic cooling will help in the realization of highly sensitive space and air-borne heterodyne receivers., Comment: Submitted to IEEE-TST

High frequency accuracy and stability are important requirements for local oscillators in terahertz heterodyne spectrometers. We report on a phase-locked loop for quantum-cascade lasers (QCLs) operating at 3.5 and 4.7 THz, two very important frequencies in atmospheric science and astronomy. The QCLs are locked to the multiplied output of a frequency synthesizer using a Schottky diode harmonic mixer.

In this paper, we report the development of single-ended, Schottky diode-based harmonic mixers operating at 3.5 THz and 4.7 THz, respectively. Both mixers utilize a sub-micron size Schottky diode fabricated with circuit elements on a suspended 2 µm-thick GaAs stripline circuit, and then assembled in a waveguide split-block. The diode is closely integrated with the RF-waveguide, resulting in an electrically small and compact circuit. For the 3.5-THz, ×6-harmonic mixer, a conversion loss of about 60 dB was measured at an intermediate frequency (IF) of 200 MHz. The predicted mixer performance versus dc bias agrees well with the measurements. Based on these results, the preliminary design and simulation results of a 4.7-THz, ×8-harmonic mixer, are presented.

Broadband Schottky diode mixers operating at room-temperature are crucial for terahertz heterodyne instrumentation in space-borne applications. In this paper, we present the design of a compact 3.5 THz fundamental single-ended Schottky diode mixer. The design is based on Schottky diodes with a sub-micron anode area, defined using nanolithography techniques, and integrated with suspended strip lines on an ultra-thin GaAs-membrane.

Efficient and reliable frequency converters, preferably operating at room temperature, are critical components for frequency-stabilizing terahertz sources. In this work, we present the analysis of optimum configurations for Schottky diode based x4, x6, and x8 harmonic mixers operating at 2.3 THz, 3.5 THz, and 4.7 THz respectively. Detailed large-signal analysis of the two basic single-ended Z- and Y-mixers was carried out using a standard Schottky diode model. For each case, the conversion loss was minimized by finding optimal embedding impedances at RF, LO, and IF frequencies. The analysis shows that the Y-mixer has less conversion loss at a low LO pump power. However, the Z-mixer provides reduced loss with increasing harmonic index and pump power due to the associated power dissipation in idler circuits. The results provide preliminary design guidelines for room-temperature frequency converters and their use in phase-locked loop applications.

Atmospheric science based on space-borne millimeter wave measurements require reliable and state-of-the-art receivers. In particular, the water vapor line at 183.3 GHz motivates the development of sensitive mixers at this frequency. Traditional assembly techniques employed in the production of Schottky diode receivers involve flip-chip mounting and soldering of discrete dies, which prohibit the implementation of reliable and repeatable production processes. In this work, we present a subharmonic 183 GHz mixer implementing a repeatable assembly method using beamlead Schottky diodes. The mixer was integrated with a InP HEMT MMIC low noise intermediate frequency amplifier resulting in a record-low receiver noise temperature of 450 K at 1 mW of local oscillator power measured at room-temperature. The measured Allan time was 10 s and the third order local oscillator spurious power was less than -60 dBm. The proposed assembly method is of particular importance for space-borne missions but also applicable to a wide range of terahertz applications.

We report on the development of two 874 GHz receiver channels with orthogonal polarizations for the international submillimetre airborne radiometer. A spline horn antenna and dielectric lens, a Schottky diode mixer circuit, and an intermediate frequency (IF) low noise amplifier circuit were integrated in the same metallic split block housing. This resulted in a receiver mean double sideband (DSB) noise temperature of 3300 K (minimum 2770 K, maximum 3400 K), achieved at an operation temperature of 40 C and across a 10 GHz wide IF band. A minimum DSB noise temperature of 2260 K at 20 C was measured without the lens. Three different dielectric lens materials were tested and compared with respect to the radiation pattern and noise temperature. All three lenses were compliant in terms of radiation pattern, but one of the materials leads to a reduction in a noise temperature of approximately 200 K compared to the others. The loss in this lens was estimated to be 0.42 dB. The local oscillator chains have a power consumption of 24W and consist of custom-designed Schottky diode quadruplers (5% power efficiency in operation, 8%-9% peak), commercial heterostructure barrier varactor (HBV) triplers, and power amplifiers that are pumped by using a common dielectric resonator oscillator at 36.43 GHz. Measurements of the radiation pattern showed a symmetric main beam lobe with full width half maximum

In this paper, we present WR05 (140–220 GHz) and WR03 (220–325 GHz) five-stage amplifier modules with novel membrane microstrip-to-waveguide transitions. The modules use a 250-nm InP double heterojunction bipolar transistor (DHBT) technology and multilayer thin-film microstrip transmission lines. The waveguide transitions use $E$ -plane probes on 3- $\mu$ m-thin GaAs membrane substrate. Beam lead connectors integrated on the transition eliminate the need of highly reactive bond wires. In addition, process steps such as backside metallization, backside vias, and nonrectangular dicing of the integrated circuits (ICs) are not required. The WR05 amplifier module demonstrates a peak gain of 24 dB at 245 GHz and more than 10-dB gain from 155 to 270 GHz. The WR-03 module has 19-dB gain from 230 to 254 GHz with input and output return loss better than 10 dB from 225 to 330 GHz. The two modules were also characterized in terms of noise. The minimum noise figures were measured to 9.7 dB at 195 GHz and 10.8 dB at 240 GHz for the WR05 and WR03 modules, respectively. To the authors' best knowledge, these are the first published results on an InP DHBT amplifier modules operating at these high frequencies. It is also the first time that membrane technology is used for IC packaging, regardless of IC technology.

We present a novel waveguide-to-suspended stripline loop-probe transition operating over the entire WR-1.0 waveguide band. The loop probe is designed for broadband response with simulated RL > 15 dB, and has an integrated DC return path, which can also be extended for biasing. The measured insertion loss for a back-to-back configuration is 1–2 dB in almost the entire frequency range of 750–1100 GHz.

This paper describes a single flange 2-port measurement setup for S-parameter characterization of waveguide integrated devices. The setup greatly reduces calibration and measurement uncertainty by eliminating vector network analyzer (VNA) extender cable movement and minimizing the effect of waveguide manufacturing tolerances. Change time of standards is also improved, reducing the influence of VNA drift on the uncertainty. A TRL calibration kit has been manufactured and measurements are demonstrated in WR-03 (220–325 GHz).

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.

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 LNA's 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.

We present an overview of research on integrated diode circuits for terahertz applications carried out at Chalmers University of Technology. This includes progress on heterogeneous integration of heterostructure barrier varactor multipliers on silicon substrates. The described technology uses silicon-on-insulator (SOI) substrates, for which accurate and well-defined substrate thickness for the microstrip circuitry is obtained.

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.

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.

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 H(2)O and CH(3)OH 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 CH(3)OH absorption spectrum could be modeled with very high precision.

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.

In this work the results of spectroscopic and performance measurements with a compact heterodyne receiver in the frequency range between 520 and 590 GHz are presented.

A single flange 2-port TRL calibration and measurement setup for accurate THz S-parameter characterization of integrated membrane circuit devices is proposed. The proposed setup facilitates shorter access waveguides, which greatly improves the calibration uncertainty.

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.

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.

This paper investigates the impact of the waveguide width tolerance in TE 10 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.

We present the development of integrated submillimeter wave receivers and transmitters based on Schottky- and HBV-diode technology at Chalmers University of technology.

A TRL-calibration kit enabling S-parameter characterization of membrane circuits has been developed for the WR-03 band. The TRL-design features 3 µm thick GaAs membrane circuits packaged in E-plane split waveguide blocks. Membrane filters have been characterized after the calibration.

Spreading resistance of a planar Schottky diode is studied as a function of the frequency and buffer layer thickness. The study shows an increase of effective high frequency resistance for a buffer layer thicker than skin depth, due to the parasitic capacitances induced current in buffer layer.

A fixed tuned subharmonic 340 GHz GaAs Schottky diode mixer design is presented. The mixer consists of a 3 mil quartz substrate that is suspended in a LO and RF reduced height waveguide splitblock, and uses a coaxial connector for the IF interface. It has been designed for the VDI SC1T2-D20 antiparallell diode chip that is flip-chip mounted on the circuit. The performance of three types of RF stop filter topologies have been evaluated and will be presented.

Two compact and simple to design differential phase shifter topologies, based on high/low-impedance transmission-line sections and open-ended coupled-line sections, are presented for the first time. The basic circuit theory for single section topologies is reviewed, leading to design equations and graphs for direct circuit synthesis. Balanced topologies and multiple section designs are also proposed improving the performance and feasibility of the phase shifters. Two planar microstrip single section differential phase shifter hybrids, at a centre frequency of 12 GHz and a 45 and 135° phase difference have been designed and manufactured. The designs have a simulated 0.5 dB amplitude and 1° phase imbalance over more than 25 and 40% bandwidth, respectively. Experimental results verify the circuit performance and feasibility of the proposed differential phase shifters.

3-D models have been developed to study the series resistance (R s ) at DC and the extrinsic parasitic elements (capacitance and inductance) at high frequencies for a Schottky diode chip. For the R s 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.

A low VSWR sideband separating receiver topology employing subharmonic Schottky diode mixers has been implemented at 340 GHz as an integrated module housing mixers, commercial LNA's and waveguide hybrids. Image rejection levels of around 20 dB and a receiver SSB noise of 9000 K are measured.