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This paper discusses and demonstrates the most popular sub-harmonic Gilbert mixers in 2-[micro]m GaInP/GaAs HBT technology. High two local oscillators (2LO)-to-RF isolation is important to alleviate the self-mixing problem of the sub-harmonic mixer. The demonstrated GaInP/GaAs HBT stacked-local oscillator (LO) mixer topology has achieved the best 2LO-to-RF isolation when compared with the previous literature. On the other hand, the leveled-LO sub-harmonic mixers have advantages in terms of the high speed and low dc supply voltage at the cost of much larger LO pumping power. Among all the structures, the bottom-LO sub-harmonic mixer has the lowest current consumption and the simplest circuit structure at the expense of the 2LO-to-RF isolation. Index Terms--DC offset, GaInP/GaAs HBT, Gilbert mixer, self-mixing, sub-harmonic mixer, two local oscillators (2LO)-to-RF isolation. Digital Object Identifier 10.1109/TMTT.2007.895169

A single-ended wideband downconversion Gilbert micromixer is demonstrated in this paper using 0.35-[micro]m SiGe BiCMOS technology. A transimpedance amplifier with resistive feedback is utilized in the IF stage while a broadband Marchand balun is employed to generate wideband differential local oscillator signals. The planar Marchand balun topology employed in this paper can generate truly balanced signals even in the presence of the lossy low-resistivity (~10 [OMEGA] * cm) silicon substrate. A systematic approach to measure the frequency response of each individual stage in a Gilbert mixer is developed in this paper. This single-ended wideband mixer has the conversion gain of 15 dB, I[P.sub.1dB] of -19 dBm, II[P.sub.3] of -7 dBm, and the noise figure of 13 dB. The mixer works from 3.5 to 14.5 GHz. Index Terms--Downconverter, Marchand balun, micromixer, SiGe BiCMOS, silicon substrate, transimpedance amplifier (TIA), wideband.

The use of mixin-inheritenace to perform meta class composition to define and compose reusable class property by introducing mixins at meta class level is explored. It uses mixin-based inheritance to assign specific property to classes while still ensuring compatibility.

The analysis of direct conversion CMOS active mixers tailored to ReFlex standard is presented. To minimize 1 / f noise, the switching stage pMOS devices have large area, low biasing current. pMOS and nMOS transconductors shunt together form the input stage. A 0.35-[micro]m prototype performs at 900 MHz as follows: 18 dB SSB NF averaged in the 100 Hz-3 kHz band, 18 dB gain, --4-dBm IIP3, 30-dBm IIP2 with 6 mA from 2.7-V supply. Index Terms--Active mixers, analog integrated circuits, CMOS mixers, direct conversion, flicker noise, frequency conversion, Gilbert cell, mixer noise, mixers.

Research describing phonon cooled ultra-thin film superconducting NbN bolometer mixers is presented. Measurements of sensitivity and gain bandwidth are investigated.

Research describing microwave measurements of hot electron bolometer mixers is presented. The dependence of conversion efficiency and mixer noise on bias voltage for aluminum devices is investigated.

Research is presented describing the study of voltage differentiation when applied to diffusion-cooled thermal time constant electron-hot superconducting mixers.

Research is presented describing the study of superconductor-normal-metal-superconductor junction to determine the negative resistance of mow-voltage mixers.

Research is presented describing the study of circuit fabrication mixer substrates to measure the receiver noise temperature and intermediate frequency levels.

A study of the noise levels of waveguide superconductor-insulator-superconductor (SIS) mixers with NbTiN/SiO2/Al tuning circuits is presented. These mixers are examined for their performance and sensitivity between 0.7 and 1.1 THz.

A study of superconducting hot-electron bolometer (HEB) mixers with aluminum is presented with emphasis on their characteristics. The performance of these HEBs at submillimeter wavelengths is examined and their application to astrophysics described.

A study of a superconducting Nb hot-electron bolometer mixer with quasi-optical coupling is presented with emphasis on its response at 2.5 terahertz. A new coupling circuit with microstrip lines is incorporated in this mixer.

Results demonstrate that performance of hot-electron bolometer in the heterodyne region is severely affected by an ineffective thermalization. Data suggest that local oscillator power increase, a lower noise temperature, and intermediate frequency bandwidth increase optimizes the mixer operation.

A study fabricated high-quality Nb/Al-oxide/Al/Nb edge junctions using a Nb/SiO2 bilayer film as the base electrode for use as traveling wave mixers. The Nb/Al-oxide/Al/Nb material system was selected as it potentially provides low leakage currents and specific capacitance. The mixer was tested in a liquid helium cooled cryostat from 240 GHz-300 GHz. A receiver noise temperature as low as 60 K was measured at 260 GHz. Other experimental findings are presented.

Research was conducted to examine the conversion efficiency for some type of high-critical temperature superconducting junctions which have negative derivative on current-voltage characteristics. The Andreev reflections in superconductor/normal metal boundaries can explain the distinguishing features of current-voltage characteristics. An excess noise was defined as the difference between the measured experimental noise and the calculated thermal noise.

Theoretical and experimental investigations of negative-resistance mixers were conducted. The objective was to gain an insight into the nonequilibrium effects of mesoscopic superconductor-normal metal-superconductor (SNS) junctions at non-zero voltage state and mixer operation. Experimental results illustrate the rough profile of the density of states in N-regions of SNS weak-links.

A sub-millimeter wavelength oscillator based on high temperature superconducting step-edge Josephson junctions coupled on-chip with detector Josephson junction-mixer was fabricated and tested. A new type of 2D arrays of Josephson junctions, namely, a shorted 2D array biased in parallel, was considered. The best results such as the steep Shapiro steps up to the 4th order and significant depression of the critical current were obtained from 150 GHZ and 200 GH z.

Research was conducted to investigate the performance of a NbN based phonon-cooled Hot Electron Bolometric quasioptical mixer in the 0.65-3.12 THz frequency range. The mixer was built from a 3 nm thick NbN film on high resistivity Si and integrated with a planar spiral antenna on the same substrate. The receiver has shown low-noise performance, very broad radio frequency bandwidth and a large dynamic range.

Research was conducted to examine a waveguide receiver employing a phonon-cooled superconductive hot-electron bolometer mixer for operation near 80- GHz and to conduct astronomical observations with it. The receiver exhibited sufficient IF bandwidth, reasonable noise performance and is generally a very usable, practical system. It was successfully used to conduct test observations of a number of celestial sources in a number of astronomically important spectral lines.

A study was conducted to assess the non-thermal response of a diffusion-cooled hot-electron bolometer mixers in the heterodyne regime at tetrahertz frequencies. Experimental results show that the bolometer mixers have a few tens of GHz bandwidth and may exhibit quantum limited noise temperature. It was also noted that the mixers' superconducting energy gap exhibit increased sensitivity to the concentration of low energy quasiparticles.

A microbolometer treated as a distributed element was modeled as a refinement of the commonly used simple discrete-element model. The model seems to predict better than the lumped-parameter one most features of diffusion-cooled hot-electron bolometric mixer performance. A reasonable agreement is found between the present mixer performance calculations and experimental data. Results also illustrate that terahertz radiation is dissipated more effectively than dc electrical power which has implications on how mixer sensitivity is measured.

Noise temperature measurements were conducted on a phonon cooled NbN hot-electron bolometric (HEB) mixer at 5 frequencies from 0.693 to 2.5465 THz. The measurements were done with a pumped signal path and without window between the hot and cold loads and the mixer. Results illustrate that the combination of a hyperhemispherical lens with a phonon cooled HEB mixer integrated in a spiral antenna leads to a very wideband heterodyne receiver with a sensitivity comparable to diffusion cooled devices.

Research was conducted to illustrate that a potential distinction in ultimate performance of phonon-cooled and diffusion-cooled hot-electron bolometric (HEB) superconducting mixers is not caused by the cooling mechanisms but rather due to the different characteristics of available superconductors. Results show that developing HEB devices with lower critical temperature may permit the mixer to more readily reach quantum-limited noise performance at THz frequencies.

Research was conducted to examine NbN phonon-cooled hot electron bolometric (HEB) mixers above 1 THz. The HEB mixers have generated promising results in terms of DSB receiver noise temperature. An antenna-coupled device, which would require LO power of less than 1 microW and a noise temperature goal of tem times the quantum limit, was used. Results indicate that the NbN HEB mixer provides a strong alternative to the Nb diffusion cooled mixer for ultra low noise THz applications.

A tunerless cryogenic millimeter-wave ring filter has been designed for a space application. Detuning of the center frequency caused by thermal deformations has been compensated by a novel mechanism based on the use of two materials with different temperature expansion coefficients. An improvement of 1:8 in the detuning of the center frequency, compared to an uncompensated ring filter, is reported. By applying the new design, external tuning aids can be avoided even in applications where a wide operational temperature range is of interest. Thus, the new ring filter is especially advantageous in space-borne millimeter-wave receivers. Index Terms - Diplexer, ring filter, space application, temperature compensation.

A dual six-port-based measurement setup was developed to synthesize five source and load impedances simultaneously. The setup can perform nonlinear measurements with multifrequency excitation. Active source - pull/load-pull measurements obtained for an NE-9001 transistor operated in a C-band field-effect transistor (FET) resistive mixer mode allow one to optimize the linearity of the mixer while maintaining a typical conversion loss of approximately 7 dB. Two-tone verification at 3.9000 and 3.9005 GHz showed that the level of in-band third-order intermodulation products could be reduced to -50 dBc, with a well-chosen output intermediate frequency (IF) load impedance and sufficient local oscillator (LO) power. The measured performance of the realized mixer is in good agreement with that predicted at the transistor characterization step of the design. Index Terms - Characterization, intermodulating, load-pull, nonlinear, resistive mixer, six-port.

This paper presents a 50-GHz-band high-gain monolithic balanced gate mixer. IF impedance of the balanced gate mixer is approximated from a small-signal equivalent circuit, and conversion gain of the mixer is improved by using an external IF balun with high impedance-transforming ratio. The maximum conversion gain of 8.2 dB is achieved at LO power of 0 dBm. Effectiveness of the described mixer is confirmed experimentally. Index Terms - Baluns, impedance matching, millimeter-wave mixers, MMIC mixers.

With the aid of the van Cittert-Zernike theorem we develop an analytical expression for the ensemble-averaged heterodyne mixing efficiency in coherent lidar receivers that are looking at a diffuse target that is in the receiver's far field. Our extremely simple and straightforward analysis shows that the dependence of the mixing efficiency on the receive aperture size [d.sub.R] first follows a parabolic decrease and later approaches a [([d.sub.R]).sup.-2] function. As a consequence, the signal-to-noise ratio does not increase proportionally to the aperture area but saturates. For the system model chosen, the heterodyne mixing efficiency exhibits the same functional dependence on the lidar geometry as the reciprocal of the number of speckle cells within the receive aperture.

It is clear that NbN based low noise bolometric mixers are feasible, according to research into mixed performance of NbN transition edge microbolometers. This research involved investigating parallel arrays of three NbN microbridges. Mixing two oscillator sources made it possible to demonstrate the heterodyne process in NbN microbolometers at 806 GHz. It is not expected that the mixer performance of microbolometers will degrade in the THz frequency range.

To achieve low conversion-loss and high image-rejection performance in the wide band for up and down conversion, an SSB subharmonically pumped mixer using an inphase RF divider/combiner is proposed. The SSB mixer monolithic microwave integrated circuit (MMIC) is integrated in a small area of 1.8 x 1.3 [mm.sup.2] and shows good performance at 21.6 to 30.8 GHz. Index Terms - Image-rejection mixer, monolithic microwave integrated circuit (MMIC), quasi-lumped stub, subharmonically pumped mixer, wide-band mixer.

Subharmonic sampling is a discrete-time solution to the signal downconversion problem. It can be used either to replace a traditional continuous-time mixer in a superheterodyne receiver or can be combined with other discrete-time analog signal processing blocks in novel receiver architectures. We present a 2-GHz bandwidth integrated mixer based on subharmonic sampling operating at sampling frequencies from 40 MHz to 1.5 GHz. The conversion efficiency is optimized by appropriate choice of the clock duty cycle. The sampler uses a two-diode topology with a 3-V supply. The downconversion loss for the passive sampler is 1 dB and the total system gain 3 dB. The mixer achieves IIP3 of +16-dBm and -1-dB compression +7 dBm for a single-tone input. The circuit was implemented with a 0.6[[micro]meter] GaAs metal-semiconductor field effect transistor (MESFET) process. Index Terms - Frequency conversion, integrated circuits, MESFET circuits, MMIC mixers, mobile communication, sampled data circuits, subharmonic sampling.

A 125-180 GHz fixed-tuned superconductor-insulator-superconductor (SIS) mixer was proposed for radio astronomy applications. The ultra low noise mixer uses a novel coplanar tuning circuit for the SIS junction. The 2 micrometer2 Nb/Al oxide/Nb junctions exhibit a 4.2 KA/cm2 critical Josephson current density. A minimum DSB receiver noise of 19 K and a minimum DSB mixer noise of 11 K were observed.

A study was conducted on the conversion gain and noise in superconductor-insulator-superconductor mixers using Nb/MgO/NbN junctions at the submillimeter and millimeter wavelengths. The junctions exhibited a lowest receiver noise of 65 K with -6 dB conversion gain at 162 GHz. At 306 GHz, receiver noise was 230 K with -10 dB conversion gain. The junction has a 2 micrometer2 junction area and a 1.4 KA/cm2 Josephson critical current density.

A superconductor-insulator-superconductor transmission line's non-linear quasiparticle tunnel current was used to develop a novel distributed mixer. The mixer employs Nb/Al/AlOx/Nb junctions with lengths between 1 and 2 guided wavelengths and a width of 200 nm. The mixer uses simpler tuning circuity, lower critical currents densities and lower magnetic field as compared to traditional submillimeter lumped element quasiparticle mixers.

A study was conducted on diffusion-cooled hot-electron bolometer mixers' input and output noise. A noise bandwidth that is larger than the gain bandwidth was observed by simultaneously measuring the noise and gain as function of intermediate frequency for a 0.16 micrometer diffusion cooled Nb device. Results reveal a 340 K DSB mixer noise and a 55 K output noise. Results also demonstrate the THz receiver applications of diffusion cooled devices.

A quasioptical Nb hot-electron bolometer mixer was fabricated for a heterodyne receiver operating a 2.5 THz. The mixer was developed from a 12 nm thick Nb film and has an in-plane size of 0.30 micrometer x 0.15 micrometer. A twin-slot planar antenna on elliptical Si lens was utilized for radio frequency coupling. The receiver's double sideband noise temperature was experimentally measured at less than or equal to 3000 K.

A study was conducted on different quasi-optical superconductor-insulator-superconductor mixer designs operating at frequency ranges between 300-1200 GHz. The mixers employ a two-junction tuning circuit, twin-slot antenna and an antireflection-coated silicon hyperhemispherical lens. Fourier transform spectrometry was utilized in measuring the broad-band frequency response.

A study was conducted on the output noise of a YBa2Cu3O7-delta superconducting hot-electron bolometer operating at a large frequency range of 10 kHz to 8 GHz. The device can consist of either a 30 nm thick film on a MgO substrate or a structured 50 nm thick YBa2Cu3O7-delta film on LaAlO3. Results show that the major noise sources at higher frequencies are Josephson noise and a current dependent noise, and the major source at frequencies lower than 1 MHz is flicker noise.

High temperature superconducting hot-electron bolometers (HEB) are proposed for heterodyne mixing at frequencies over 1 terahertz. The frequencies of Nb HEB mixers are not restricted by superconducting energy gap and their performance are comparable to that of tunnel junctions. YBa2Cu3O7-delta HEB mixers may be used in low power heterodyne detectors for 90 K applications in closed-cycle refrigeration.

A study was conducted on the noise characteristics of a NbN phono-cooled hot-electron mixer operating at a frequency of 2.5 THz. A = 23 dB system conversion loss at intermediate frequencies of up to 1 GHz and a =14000 K double sideband mixer noise temperature were achieved for optimal operation. The mixer temperature noise was found to be dependent on local oscillator power, bias voltage and intermediate frequency.

A diffusion cooled superconducting hot electron bolometer is proposed for heterodyne mixing applications at terahertz frequencies. The processing approach utilized a 10 nm niobium thin film that was defined to dimensions of 80 nm by electron beam lithography as the bolometer element. Applications at 1.2 and 2.5 terahertz were made possible by embedding the microbridge in a normal antenna structure.

A quasioptically coupled diffusion-cooled hot-electron bolometric mixer was used to measure receiver noise temperatures at a local oscillator frequency of 1267 GHz and an intermediate frequency of 1.4 GHz. Results reveal a 1880K double-sideband receiver noise temperature with a 945K mixer noise and -19 dB conversion efficiency. Results prove that the mixer's sensitivity is not easily reduced by increasing frequency.

A study was conducted on a 2.5 THz NbN hot electron bolometer mixer integrated with a broken linearly tapered slot antenna fabricated on a SiO2 membrane. NbN films that are 4-7 nm thick and 1 micrometer wide deposited by direct current magnetron reactive sputtering on a SiO2 layer were used to develop the phonon-cooled type mixer. Anisotropic etching of the GaAs in mixture of H2O2 and HNO3 was also conducted.

A diffusion-cooled superconducting hot electron bolometer was used at intermediate frequencies from 1-2 GHz in heterodyne mixing experiments between 630-820 GHz. A two-step electron beam lithography technique was employed in fabricating the 0.3 micrometer x 0.15 micrometer niobium bolometer. The device has a film thickness of 30 nm with temperatures of 6.1 K and 0.7 K.

A study was conducted on a spiral antenna Nbn hot-electron bolometer quasioptical mixer operating at submillimeter frequencies. The device was fabricated from superconducting 3.5-5 nm thick NbN films with 10-12 K critical temperature and 10(super 7)A/cm2 critical current density at 4.2 K. A total conversion loss of Lt=16 dB in the frequency range 500-700 GHz, an optimal LO absorbed power of =4 microW, an IF bandwidth of 3-4 GHz and DSB receiver noise temperature below 1500 K were observed in the device.

High current density NbN/AlN/NbN tunnel junctions were developed for superconducting SIS mixers operating at submillimeter wave regions. Good Josephson tunneling, sensitive heterodyne mixing and excellent terahertz response properties were observed in junctions with current densities as high as 50 kA/cm2. the I-V curve with irradiation of up to 1.02 THz exhibited photon-assisted tunneling steps.