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Research describing the development of a low noise waveguide phonon-cooled hot-electron bolometer mixer receiver is presented. The bolometer elements are fabricated from thin film NbN on a quartz substrate.

Research describing the detection of electromagnetic radiation in millimeter and submillimeter ranges by means of Josephson junctions is presented. The dynamic range of a thin film quasioptical detector is investigated.

Research was conducted to examine unexpected geometrical anodization effect in the fabrication of Nb/Al-oxide/Nb junctions. The unexpected effect was attributable to the geometry of the mixer. It was observed that the electrical quality of anodically sealed junctions fabricated in the laboratory depends strongly on the geometry of the base electrode. The influence of Nb film stress, junction size and placement on the base electrode feature, wiring interconnection process and anodization conditions in the effect were investigated.

The heterodyne performance of lattice-cooled hot-electron bolometric mixers is determined at 200 GHz. Superconducting thin film niobium nitride strips with about 5 nm thickness are employed as waveguide mixer elements. A double-sideband receiver noise temperature of 750 K at 244 GHz is obtained at an intermediate frequency centered at 1.5 GHz with 500 MHz bandwidth and with 4.2 K device temperature. The instantaneous bandwidth for this mixer is 1.6 GHz. The local oscillator power needed is 0.5 microW. The mixer is linear to within 1 dB up to an input power level 6 dB below the local oscillator power.

A quasioptical mixer using only planar structures such as co-planar-waveguide and slotline is presented. The mixer, which can be scaled for millimeter-wave applications and placed on a substrate lens. uses orthogonal modes in a folded-slot antenna to achieve intrinsic RF/LO isolation without RF filtering or subharmonic pumping. The folded-slot balanced mixer was fabricated on RT/Duriod and obtained a minimum isotropic conversion loss of 1.2 dB at 11.6 GHz. Numerical integration of full two-dimensional antenna patterns yielded an antenna directivity of 7 dB, corresponding to a single side-band (SSB) mixer conversion loss of 8.2 dB. The mixer demonstrated -18 dB RF/IF isolation and -30 dB LO/IF isolation.

We have numerically solved the steady-state solutions of the initial value problem associated with a current-driven Josephson weak-link junction shunted by an Ohmic resistance. The nonlinear mixing action of the junction leads to Shapiro steps in the dc response with step height in units of the mixing frequency. Mixer gains have been calculated with a wide range of parameter values and intrinsic chaos are observed whenever Shapiro steps are prevalent.

A broadband quasi-optical superconducting tunnel junction (SIS) mixer with integrated tuning elements was designed and tested. We are able to achieve very low noise performance using commercially available niobium integrated circuit (IC) technology. The low critical current density (980 A/cm squared) and large are (12 micrometers squared) of the commercial SIS's is compensated by the ability to fabricate accurate integrated tuning structures in the mature niobium IC process available from Hypres, Inc. Noise measurements were made in the frequency range from 70 to 105 GHz. The best uncorrected double sideband receiver noise is 38 K at 77 GHz, with receiver noise temperatures less than 100 K from 75 to 102 GHz.

Hierarchical test approaches are a must for large designs due to the computational complexity and tight time-to-market requirements. In hierarchical test synthesis, test design is conducted at a subsystem level where the design complexity is manageable. For analog systems, tests are generally designed at the basic block level. This paper outlines a tool for translating basic block-level tests into system-level tests for large analog systems. Computational effectiveness is achieved by the use of high level models and by a pre-analysis of the system to identify feasible translation paths. A method to compute the fault and yield coverages of the resultant system-level tests is also provided in order to evaluate the translation. Experimental results show that test translation reduces design for testability overhead significantly while satisfying coverage requirements. Index Terms--Mixed-signal systems, parameter tolerances, probabilistic fault coverage, system-level test.

Ultra-broad-band star mixers using planar Mouw's hybrid junction [1] are presented in this paper. The planar Mouw's hybrid junction is realized by coplanar waveguide (CPW) to coplanar strip (CPS) or CPW to CPW T-junctions. A new explanation of Mouw's theory based on coupled transmission lines and including the transmission line losses is presented. The modified theory is more suitable for ultra-broad-band mixer design. Some prototype mixers with CPW to CPS or CPW to CPW T-junctions are fabricated with [Al.sub.2][O.sub.3] substrate. The prototype mixers show a bandwidth of greater than 20:1 if the even-mode resonance has been damped out. Method for damping out the even-mode resonance is also presented. All of the prototype circuits show much broader bandwidth than that of conventional star mixer. Index Terms--Doubly balanced mixer, hybrid junction, star mixer, ultra-broad-band mixer.

In this paper, we describe a superconductive hot-electron-bolometer mixer receiver designed to operate in the partially transmissive 350-[micro]m atmospheric window. The receiver employs an NbN thin-film microbridge as the mixer element, in which the main cooling mechanism of the hot electrons is through electron-phonon interaction. At a local-oscillator frequency of 808 GHz, the measured double-sideband receiver noise temperature is [T.sub.RX] = 970 K, across a 1-GHz intermediate-frequency bandwidth centered at 1.8 GHz. We have measured the linearity of the receiver and the amount of local-oscillator power incident on the mixer for optimal operation, which is [P.sub.LO] [approximately equals] 1[micro]W. This receiver was used in making observations as a facility instrument at the Heinrich Hertz Telescope, Mt. Graham, AZ, during the 1998-1999 winter observing season. Index Terms--Submillimeter-wave mixers, superconducting devices.

In this paper, a one-dimensional heat balance model for the hot-spot length of phonon-cooled hot-electron bolometer is set up and solved for the electron temperature profile along the bolometer bridge. A self-consistent theoretical method is presented to obtain the hot-spot length profile as a function of RF and bias heating power. This result is used to predict current-voltage characteristics. For a known hot-spot length profile, a small-signal model with different heating efficiencies for RF and bias heating is derived in the vicinity of an operating point. This small-signal model allows the conversion gain and fluctuation noise contribution to be calculated. Index Terms--Bolometers, millimeter-wave detectors, millimeter-wave mixers, mixer noise, submillimeter-wave mixers, superconducting device noise.

The OH radical is an important player in known ozone depletion cycles; however, due to its location in the atmosphere, it must be studied from either a balloon or spaceborne platform. For long-term mapping over large portions of the earth, a spaceborne platform is the most desirable. NASA's Earth Observing System Microwave Limb Sounder instrument is slated to house a 2.5-THz Schottky-diode receiver for such measurements. In this paper, we describe the design, fabrication, and testing of the receiver front end. Measured double-sideband (DSB) receiver noise temperatures of better than 9000 K are reproducibly achieved with all devices of our best design. Estimated mixer noise is 3500-K DSB for optimal bias conditions and at room temperature. Selected components will be used in the first terahertz heterodyne receiver to be flown in space. Index Terms--Antenna radiation patterns, atmospheric measurements, diplexers, heterodyning, horn antennas, membranes, micromachining, noise measurement, reliability, satellite applications, Schottky diode mixers, semiconductor device noise, space technology, submillimeter-wave receivers, terahertz.

In this paper, we describe the design and operation of a 350-GHz finline superconductor-insulator-superconductor mixer. The mixer is fed by a horn-reflector antenna, and the superconducting circuit is fabricated using planar-circuit technology and fully integrated tuning. An important feature of the mixer is that it employs an antipodal finline section, deposited on one side of a quartz substrate, which transforms the high impedance of the waveguide ([approximately equals] 300 [Omega]) to the low impedance of the microstrip ([approximately equals] 20 [Omega]). The Nb/Al-oxide/Nb tunnel junction is fabricated at the same time as the finline circuit. In this paper, we describe the design procedure in some detail. We pay particular attention to the synthesis of the finline taper and the electromagnetic design of the horn-reflector antenna. We have tested a finline mixer over the frequency range of 330-370 GHz and measured a receiver noise temperature of 90 K, which remained unchanged over the whole frequency range. Our investigation has demonstrated that it is possible to make superconducting finline mixers for frequencies as high as 350 GHz.

We describe an experimental investigation of two millimeter-wave oscillators one employing a single and the other using two InGaAs/InP heterojunction bipolar photo-transistors (photo-HBTs). The single HBT oscillator can be optically injection locked to improve its spectral purity. Alternatively, it can be modulated by analog or digital data carried by an optical signal. In the two photo-transistors case, one HBT oscillates and is optically injection locked while the second serves as a modulator. The two-transistor case proved to be superior in terms of carrier spectral purity, analog modulation efficiency and linearity as well as for digital modulation. Its advantages stem from the better isolation between the local oscillator and modulating signals and from the ability to separate the injection-locking and modulation functions. Index Terms--Heterojunction bipolar transistor, injection-locked oscillator, modulation, optoelectronic mixing, self-oscillator.

A time-varying theory of Volterra series is developed and applied in the sampled-data domain to solve for harmonic and intermodulation distortion of a MOS-based track-and-hold sampling mixer with a nonzero fall-time LO waveform. Distortion due to sampling error is also calculated. These results, when combined with the continuous-time solution, quantify harmonic and intermodulation distortion of a track-and-hold type mixer completely. Closed-form solutions are obtained. As a practical consequence, it is shown that for certain fall-time, the distortion of track-and-hold mixers can be better than what would be predicted by a simple application of time-invariant Volterra series theory. Index Terms - Harmonic distortion, intermodulation distortion, intermediate frequency (IF), radio frequency (RF), time-varying Volterra series, track-and-hold sampling mixer.

Experiments were conducted to test device performance as a function of device length under various operating conditions. Measurements of the spectrum of the output noise, mixer noise and conversion efficiency for phonon and diffusion cooled Nb devices of different thermal time constants are presented, and the measurement results are compared to theoretical predictions. Likewise, measurements of the device over a very broad band as well as thermometry measurements in the normal condition are presented. The results are discussed.