mW Of Local Oscillator Power Research Articles

A High-Performance 330-GHz Subharmonic Mixer Using Schottky Diodes

This letter presents the design of a state-of-the-art 330-GHz subharmonic mixer (SHM) using planar Schottky diodes. Unlike conventional mixers, the embedded impedances of the diode chip are accurately extracted and then used for direct synthesis of the diode's peripheral circuit to efficiently design SHMs with good performance. Band-stop filters (BSFs) using symmetrical open stubs are adopted to recycle RF and local oscillator (LO) energy while simplifying the circuit. At room temperature, the mixer exhibits a single sideband (SSB) conversion loss (CL) of less than 10 dB from 292 to 356 GHz, with 3 mW of LO power at 164.5 GHz. A minimum SSB CL of 7.5 dB is achieved at 334 GHz. The measured return losses at RF and IF ports are typically better than 14 dB.

Design of low-cost 183 GHz subharmonic mixers for commercial applications

Techniques are presented for designing fixed-tuned millimetre-wave components with the least number of parts to minimise the cost and maximise the potential for volume manufacture. Design techniques for millimeter-wave mixer components targeted at potentially high volume applications, such as medical and security screening and nondestructive testing, require certain compromises in the use of CAD tools. The compromise techniques are demonstrated using commercially available foundry diodes in the design of a 183 GHz subharmonic mixer for earth observation applications. The resulting mixer exhibits 6.85 dB double sideband conversion loss and a mixer temperature of 988 K using 5 mW of local oscillator power at 92 GHz.

Improved 240-GHz subharmonically pumped planar Schottky diode mixers for space-borne applications

Low-noise broad intermediate frequency (IF) band 240-GHz subharmonically pumped planar Schottky diode mixers for space-borne radiometers have been developed and characterized. The planar GaAs Schottky diodes are fully integrated with the RF/IF filter circuitry via the quartz-substrate upside-down integrated device (QUID) process resulting in a robust and easily handled package. A best double-sideband-mixer noise temperature of 490 K was achieved with 3 mW of local-oscillator power at 2-GHz IF. Over an IF band of 1.5-10 GHz, the noise temperature is below 1000 K. This state-of-the-art performance is attributed to lower parasitic capacitance devices and a low-loss waveguide circuit. Device fabrication technology and the resulting RF mixer performance obtained in the 200-250-GHz frequency range will be described.

Fixed-tuned submillimeter wavelength waveguide mixers using planar Schottky-barrier diodes

The design, construction, and evaluation of fixed-tuned submillimeter wavelength waveguide mixers using planar Schottky diodes are presented in this paper. Electromagnetic fields within the planar diode package were analyzed using the finite-element method (FEM). Mixers using the University of Virginia SCIT5 planar diode were designed at both 585 and 690 GHz. A double sideband (DSB) system noise temperature of 2380 K was measured at 585 GHz using 1.16 mW of local oscillator (LO) power, and a system noise temperature of 2970 K DSB was measured at 690 GHz using 1.04 mW of LO power. In addition, the 585 GHz mixer was cooled to both 77 K and 4.2 K, with measured system noise temperatures of 1240 and 880-K DSB using LO powers of 0.47 and 0.14 mW, respectively. The modeling techniques were found to predict the measured conversion loss to within 1 dB. The performance of planar diode mixers is now within a factor of 1.5 of the best whisker-contacted Schottky diode mixers in this frequency range.

Coherent detection with a GaAs/AlGaAs multiple quantum well structure

A GaAs/AlGaAs multiple quantum well (MQW) structure has been investigated as a coherent detector using a CO2-laser local oscillator (LO). At an operating temperature of 77 K, an LO power of 10 mW, an LO wavelength of 10.2 μm, and a bias voltage of 2.0 V, a 150-μm-diam detector displayed an external quantum efficiency η0 of 11% and a 3-dB electrical bandwidth BIF of 1.5 GHz. Under the same conditions the noise-equivalent power density (NEPHET/Δf) at an intermediate frequency of 1.5 GHz was 5.5×10−19 W/Hz, which is within 50% of the photon-noise limit for this detector. A 75-μm-diam detector with a lower-capacitance bond wire was found to have a BIF of 8 GHz and an NEPHET/Δf of 4.1×10−19 W/Hz with only 2.5 mW of LO power. The photoelectron lifetime in the MQW structure at 77 K was estimated to be 2.5 ps corresponding to an intrinsic detector bandwidth of 64 GHz.

Low-barrier-height epitaxial Ge-GaAs mixer diodes

Using a thin Ge-GaAs structure, barrier height lowering of 0.2–0.3 eV has been attained. These X-band diodes have a noise figure of 6.0–6.5 dB at 0.75–1.0 mW of local-oscillator power. The diodes have superior power-handling capability with Pt-Ti-Mo-Au metallisation.

Beam-lead Schottky-barrier diodes for low-noise integrated microwave mixers

This paper describes the fabrication and performance of beam lead <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</tex> on <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n^{+}</tex> silicon-molybdenum, barrier dual Schottky diodes. The fabrication is by a process sequence which allows the use of a single molybdenum gold-metal deposition step for both the Schottky barrier and beam-lead interconnection system. Typical <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I-V</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/C^{2}-V</tex> plots indicate uniformity of barrier heigh and n factor. Values of n less than 1.1 were measured with the barrier height at 0.61 eV. Measurements of change in barrier height with temperature up to 500°C show less than ± 10 mV variation. Dc characteristics of these devices give forward current matching of ± 10 mV at 1 mA. The R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> is 10 ohms and the C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</inf> is less than 0.3 pF, giving an RC product less than 3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> seconds. Using these devices in a chrome-gold on alumina microstrip integrated mixer, overall single sideband noise figures of 6.5-7.0 dB were measured, with a 1.5 dB IF noise figure, at 9.4 GHz. Measured noise figure was essentially constant over a range of 1-10 mW of local oscillator power, and the diodes will with stand over 500 mW CW RF power. These values compare favorably with discrete packaged devices. Fabrication in series pairs, matched quads or other configurations can be accomplished with good uniformity.