Search

Future radar transmitters will need to be able to quickly reconfigure their radio-frequency circuitry to change operating frequency and spectral output while maintaining high power-added efficiency (PAE). In this paper, fast tuning of a tunable-varactor matching network is demonstrated to optimize the PAE while meeting requirements on the adjacent-channel power ratio. The tunable varactor network, a first-level prototype of a tunable radar amplifier matching network, incurs nonlinear performance, providing possible challenges to measurement accuracy. To address the issue of nonlinearities while maintaining ability to quickly reconfigure, the tunable-varactor network is characterized at different input power levels to allow useful performance in its nonlinear regime. The power-dependent characterization is used in an algorithm for optimization of an amplifier's PAE, by looking up the matching network characterization performed at the power estimated to be output by the amplifier. Measurement results show that this characterization enhances the consistency of the optimized PAE. Using the tunable varactor network reduces the optimization time to one-fourth of the time required when using the algorithm with a traditional mechanical load-pull tuner.

Using a mutual coupling based calibration technique, a platform agnostic algorithm is developed to perform an initial alignment on phased array radar systems without the use of external equipment (far-field sources, near-field chambers and probes) or the need to implement additional internal calibration networks to already existing systems. By using coupling pairs from mutual coupling measurements, an overdetermined system of equations is created and solved. The solutions of the overdetermined system are the least-square error estimated complex gains of each element channel. A pre-phasing routine is implemented on the element channels to avoid possible phase ambiguity issues in the results since fully digital radar systems may contain phases from all possible angles (-π:π). Another improvement implemented to the algorithm is an iterative solution that can reduce the errors of the estimated results and also further aids in avoiding phased wrapped results. For diagnostic purposes, the algorithm can determine if an element has failed in either receive or transmit mode and then perform the initial alignment while ignoring the failing elements to avoid introducing errors from these failed elements. The algorithm is compatible with dual polarized systems.

In this study, a spectrum sharing technique is investigated for enhanced detection of moving targets. This approach, the spectrum sensing-multi-objective optimisation technique, passively monitors the electromagnetic environment for radio frequency (RF) emissions radiated by RF systems. This technique then identifies a continuous frequency sub-band that simultaneously maximises radar performance and reduces the radars spectral footprint. The goal of the investigation presented in this study is to quantify performance improvement of a notional radar model in the presence of RF emissions measured at 2.42 GHz (by a real-time spectrum analyser). In addition to an improved signal-to-interference plus noise ratio, the proposed radar model increases range resolution performance as the target approaches the radar.

A data collection system using software defined radios to perform multi-static radar measurements is presented. The basic architecture and operational capabilities of the selected software defined radios (SDRs) are described. Issues associated with device synchronization are discussed, and waveform implementation procedures are also outlined. Finally, results of preliminary experiments are presented, indicating the potential of SDRs for realizing a cost-effective radar system testbed. In particular, it is demonstrated that by rearranging the SDR configuration, it becomes possible to realize various receive array configurations for detection of moving targets.

Signal processing techniques employed by a software-defined radar are presented. First, the radar system is described in brief, illustrating how software-defined radios (SDRs) are leveraged to implement a baseline radar functionality. Next, multiple, required processing steps are presented, showing how target signatures can be extracted from raw radar measurements. All of these techniques are applied to the moving target indication (MTI) problem, and examples of multiple moving target signatures are displayed.

The rapid progress towards 5G wireless systems is accelerating the development of mm-wave semiconductor processes, broadband circuits, and system technologies. Similarly, next-generation radar is being expanded and redefined. Legacy radar systems are nearing the end of their life cycle and systems developers are aiming to upgrade their capability while reducing cost, size, and weight. Radar systems have requirements that result in technical circuit design challenges including high power, broadband, and low distortion. This paper focuses on MMIC design challenges specific to the design of next-generation radars that will operate in a crowded wireless environment, allow spectrum sharing, and dynamic frequency selection. Simulated and measured data are presented.

For future adaptive radio and radar transmission in a dynamic spectrum access environment, the radio-frequency circuitry will be need to be reconfigurable to allow adjustment of the operating frequency and the transmission spectrum in a congested environment. A prototype tunable amplifier matching network was implemented using varactors as the tunable elements. A method in which the control bias voltages of the varactors are directly tuned is compared with a previously demonstrated algorithm that tunes based on the reflection coefficient through a nonlinear characterization of the varactor matching network. The algorithms are both designed to optimize the power-added efficiency of the amplifier while keeping the adjacent-channel power ratio below a pre-specified constraint value. Lower average time per measurement is achieved for the voltage-based search, but the total search time is lower for the reflection-coefficient based search. This comparison of algorithms is useful in developing a reconfigurable transmitter amplifier that can adapt on the fly to meet changing spectral requirements.

Fast load impedance tuning of a varactor diode matching network to maximize amplifier gain in real-time reconfigurable circuitry is demonstrated. A published tunable varactor-diode matching topology is designed for operation at 1.3 GHz to provide significant Smith Chart coverage. A steepest-ascent algorithm is applied for fast optimization, and measurement results indicate excellent convergence from multiple starting points within the Smith Chart. Algorithm data compares well with traditional loadpull results measured with both a commercially available tuner and the tunable-varactor network, and searching with the varactor tuner search is much faster than a traditional mechanical tuner.

Today’s military radars are being challenged to satisfy multiple mission requirements and operate in complex, dynamic electromagnetic (EM) environments. They are simultaneously constrained by practical considerations like cost, size, weight and power (SWaP), and lifecycle requirements. Tomorrow’s radars need to be resilient to changing operating environments and capable of doing more with fewer resources. Radar research supports this shift toward more agile and efficient radar systems, and current trends include modular hardware and software development for multi-purpose, scalable radio frequency (RF) solutions. Software-defined radios (SDRs) and other commercial-off-the-shelf (COTS) technology are being used for flexible waveform generation, signal processing, and nontraditional radar applications. Adaptive RF technology, including apertures and other front-end components, are being developed for multi-purpose functionality and resiliency. Together, these research trends will result in a technology framework for more robust future systems that are capable of implementing cognitive processing techniques and adapting their behavior to meet the demands of a congested and contested EM environment.

We investigate how realistic architecture considerations affect the performance of wafer-scale electronically scanned millimeter-wave reflectarrays. Considering the application of a confocal Gregorian optics geometry with a small angular field of view, we examine how a reflectarray's discrete (digital) phase state quantization and electrical size impact scan angle accuracy and quantization lobe performance degradation. We quantify the impact of these effects on the camera's imaging performance and show that, for these reflectarrays, phase quantization of 2 bits is sufficient.

We present a study of the large signal frequency response of an HEB mixer over a wide frequency range. In our experiments, we have subjected the HEB mixer to incident electromagnetic radiation from 0.3 GHz to 1 THz. The mixer element is an NbN film deposited on crystalline quartz. The mixer chip is mounted in a waveguide cavity, coupled to free space with a diagonal horn. At microwave frequencies, electromagnetic radiation is applied through the coaxial bias port of the mixer block. At higher frequencies the input signal passes via the diagonal horn feed. At each frequency, the incident power is varied and a family of I-V curves is recorded. From the curves we identify 3 distinct regimes of operation of the mixer separated by the phonon relaxation frequency and the superconducting energy gap frequency observed at about 3 GHz and 660 GHz respectively. In this paper, we will present observed curves and discuss the results of our experiment.

The intermediate frequency (IF) bandwidth of a hot electron bolometer (HEB) mixer is an important parameter of the mixer, in that it helps to determine its suitability for a given application. With the availability of wideband low noise amplifiers, it is simple to measure the performance of an HEB mixer over a wide range of IF at a fixed LO frequency using the standard Y-factor method. This in-situ method allows us to measure both the gain and noise bandwidths simultaneously. We have also measured mixer output impedance with a vector network analyser. Intrinsic time constant has been extracted from the impedance data and compared to the mixer's bandwidths determined from receiver Y-factor measurement.

Recent observational evidence that magnetic fields are dynamically important in molecular clouds, compared to self-gravity and turbulence, is reviewed and illustrated with data from the NGC 2024 region. One piece of evidence, turbulence anisotropy, was found in the diffuse envelope of a cloud (A v ≈ 1; Heyer et al. 2008); our data further suggest turbulence anisotropy in the cloud (A v > 7) and even near the cloud core (A v ∼ 100). The data also show that magnetic fields can channel gravitational contraction even for a region with supercritical N(H 2 )/2B los ratio (the ratio between the observed column density and two times the line-of-sight observed field strength), a parameter which has been widely used by observers to estimate core mass-to-flux ratios. Although the mass-to-flux ratio is constant under the flux-freezing condition, we show that N(H 2 )/2B los grows with time if gravitational contraction is anisotropic due to magnetic fields.

It is a well known fact that SIS mixers exhibit gain compression when the output IF voltage swing becomes non-negligible compared to the width of the photon step. In this paper, we show that under certain circumstances, SIS mixers can also exhibit the inverse phenomenon-gain expansion. This non-linear behavior has been observed experimentally when the output power-voltage curve of an SIS mixer has a double peak feature over the photon step. In this case, if the device is biased at the valley position between the two peaks, the conversion gain of the mixer will increase with input signal power. Consequently, the noise temperature of the mixer deduced from a Y-factor measurement will be artificially reduced. Two different experimental methods have been used to characterize the linearity of SIS mixers. The accuracies of both methods are analysed.

We report on heterodyne measurements at submillimeter wavelengths using a receiver with a Superconductor-Insulator-Superconductor (SIS) mixer device and a Microwave Monolithic Integrated Circuit (MMIC) cryogenic low noise amplifier (LNA) module integrated into the same block. The mixer characterization presented in this work demonstrates the feasibility of operating a MMIC LNA in close proximity to the SIS device without penalty in mixer performance due to heating effects. Verification of this functionality is crucial for the ongoing development of SuperCam, a 64-pixel focal plane array receiver consisting of eight, 1 × 8 integrated mixer/LNA modules. The test setup included a mixer block modified to accept a MMIC amplifier. Our tests show that the LNA can be operated over a broad range of Vdrain voltages from 0.40–1.40 V, corresponding to dissipative powers of 2.6–29 mW. We observe no significant effect on the measured uncorrected receiver noise temperatures in the 345 GHz band.

Summary and analysis of 216 GHz polarimetric measurements of LQ situ rain Abigail S. Hedden 1 *, David A. Wikner 1 , Russell W. Bradley 1,2 1 U.S. Army Research Laboratory, 2800 Powder Mill Rd., Adelphi, MD 20783 2 Virginia Tech University, Blacksburg, VA 24061 ABSTRACT The Army Research Laboratory (ARL) has developed a polarimetric frequency-modulated continuous-wave (FMCW) instrumentation radar that has been used to study the polarization and backscatter properties of in-situ rain in the 220 GHz atmospheric window. A summary of the preliminary measurements is presented in this work including an analysis of the co -polarization backscatter and attenuation characteristics measured at 216 GHz . A marginal detection of the co-polarization backscatter signature of rain was made during a series of fast-moving, heavy downpour thunderstorm events . A detection limit of - 40 ±3 dB[m 2 /m 3 ] was found for the VV-polarization cross section per unit volume for rain rates up to 150 mm/hr. Co-polarization (VV- and HH-polarization) attenuation characteristics measured at high rain rates (> 20 mm/hr) were well described by a Joss thunderstorm drop distribution in the high frequency limit, where drop size is much greater than the observation wavelength. Observations at 216 GHz suggest attenuation levels of 8- 10 dB/km at rain rates above 20 mm/hr, strengthening previous evidence that attenuation through rain is independent of frequency under high rain rate conditions. Attenuation measurements at lower rain rates (< 20 mm/hr) were qualitatively consistent with both Laws and Parsons and Joss thunderstorm distributions. Keywords: millimeter wave propagation, backscatter, rain, millimeter wave radar, radar polarimetry

We have made continuum and spectral line observations of several outflow sources in the Mon OB1 dark cloud (NGC 2264) using the Heinrich Hertz Telescope (HHT) and ARO 12m millimeter-wave telescope. This study explores the kinematics and outflow energetics of the young stellar systems observed and assesses the impact star formation is having on the surrounding cloud environment. Our data set incorporates 12CO(3-2), 13CO(3-2), and 12CO(1-0) observations of outflows associated with the sources IRAS 06382+1017 and IRAS 06381+1039, known as IRAS 25 and 27, respectively, in the northern cloud complex. Complementary 870 micron continuum maps were made with the HHT 19 channel bolometer array. Our results indicate that there is a weak (approximately less than 0.5%) coupling between outflow kinetic energy and turbulent energy of the cloud. An analysis of the energy balance in the IRAS 25 and 27 cores suggests they are maintaining their dynamical integrity except where outflowing material directly interacts with the core, such as along the outflow axes., 28 pages including 6 figures, to be published in ApJ 01 July 2006, v645, 1 issue

We present preliminary results from the recent multi-epoch HI absorption measurements toward several pulsars using the Arecibo telescope. We do not find significant variations in optical depth profiles over periods of 4 months and 9 years. The upper limits on the optical depth variations in directions of B0823+26 and B1133+16 are similar on scales of 10--20, 350 and 500 AU. The large number of non detections of the tiny scale atomic structure suggests that the AU-sized structure is not ubiquitous in the interstellar medium., To appear in the proceedings of "Magnetic fields and star formation: theory versus observations", held in Madrid, April 21-25 2003. Uses Kluwer latex style file

The development of sensors that are capable of penetrating smoke, dust, fog, clouds, and rain is critical for maintaining situational awareness in degraded visual environments and for providing support to the Warfighter. Atmospheric penetration properties, the ability to form high-resolution imagery with modest apertures, and available source power make the extremely high-frequency (EHF) portion of the spectrum promising for the development of radio frequency (RF) sensors capable of penetrating visual obscurants. Comprehensive phenomenology studies including polarization and backscatter properties of relevant targets are lacking at these frequencies. The Army Research Laboratory (ARL) is developing a fully-polarimetric frequency-modulated continuous-wave (FMCW) instrumentation radar to explore polarization and backscatter properties of in-situ rain, scattering from natural and man-made surfaces, and the radar cross section and micro-Doppler signatures of humans at EHF frequencies, specifically, around the 220 GHz atmospheric window. This work presents an overview of the design and construction of the radar system, hardware performance, data acquisition software, and initial results including an analysis of human micro-Doppler signatures.

An atlas of a thorium-argon hollow cathode lamp in selected intervals of the 1-2.5 mm region is presented. Accurate wavelengths of the ∼500 lines recorded are given in a table. This material is intended for wavelength calibration of near-infrared spectra and is especially critical for high-resolution work.

Providing situational awareness to the warfighter requires radar, communications, and other electronic systems that operate in increasingly cluttered and dynamic electromagnetic environments. There is a growing need for cognitive RF systems that are capable of monitoring, adapting to, and learning from their environments in order to maintain their effectiveness and functionality. Additionally, radar systems are needed that are capable of adapting to an increased number of targets of interest. Cognitive nonlinear radar may offer critical solutions to these growing problems. This work focuses on ongoing efforts at the U.S. Army Research Laboratory (ARL) to develop a cognitive nonlinear radar test-bed. ARL is working toward developing a test-bed that uses spectrum sensing to monitor the RF environment and dynamically change the transmit waveforms to achieve detection of nonlinear targets with high confidence. This work presents the architecture of the test-bed system along with a discussion of its current capabilities and limitations. A brief outlook is presented for the project along with a discussion of a future cognitive nonlinear radar test-bed.

In this report, a unique cognitive nonlinear radar (CNR) is introduced. Research and development efforts for the CNR are currently funded by the U.S. Army Research Laboratory (ARL). The CNR adapts to (1) an increasingly cluttered electromagnetic (EM) environment, a growing problem for ground-based and airborne radar systems; (2) multiple targets; and (3) other radar, communication, and electronic systems that must operate without interfering with each other. The CNR uses a narrowband, nonlinear radar target detection methodology. This methodology has the advantage, as compared with other nonlinear radar systems that do not implement a cognitive scheme, to adapt to the radio frequency (RF) environment by intelligently selecting waveform parameters using adaptive algorithms. The adaptive algorithms optimize the waveform parameters based on (1) the EM interference, (2) target likelihood, and (3) permissible transmit frequencies as specified by regulations and allowable by other systems operations within the environment.

One puzzle in understanding how stars form in clusters is the source of mass -- is all of the mass in place before the first stars are born, or is there an extended period when the cluster accretes material which can continuously fuel the star formation process? We use a multi-line spectral survey of the southern filament associated with the Serpens South embedded cluster-forming region in order to determine if mass is accreting from the filament onto the cluster, and whether the accretion rate is significant. Our analysis suggests that material is flowing along the filament's long axis at a rate of ~30Msol/Myr (inferred from the N2H+ velocity gradient along the filament), and radially contracting onto the filament at ~130Msol/Myr (inferred from HNC self-absorption). These accretion rates are sufficient to supply mass to the central cluster at a similar rate to the current star formation rate in the cluster. Filamentary accretion flows may therefore be very important in the ongoing evolution of this cluster., Comment: 19 pages, 8 figures, 2 tables; accepted for publication in ApJ

This paper describes a free-space measurement method to determine the complex permittivity of dielectrics. A dielectric container comprising two plane-parallel slabs with known properties surrounds a central slab with unknown dielectric properties. The dielectric stack rotates in a free-space planewave measurement system, and we record the transmittance as a function of incidence angle. The best-fit of theoretical transmittance to measured transmittance yields the properties of the unknown dielectric. Experiments are performed at 218 GHz to validate the theory. An uncertainty analysis for the specific measurement geometry in this paper is described in detail, producing a combined uncertainty of 1 % in both the real and imaginary portions of the complex permittivity.

The goal of this project is to enable light-weight, durable, and portable systems capable of performing standoff detection of person-borne improvised explosive devices (PB-IEDs) through the development of millimeter-wave reflection-type phased arrays. Electronic beam steering eliminates the need for complex mechanical scanners that are commonly implemented with millimeter-wave imaging systems and would reduce overall system size and weight. We present a concept study of a 220 GHz reflection-type phased array for the purpose of performing beam scanning of a confocal reflector system. Requirements for effective imaging of the desired target region are established, including spatial resolution, total scan angle, and number of image pixels achievable. We examine the effects of array architecture on beam characteristics as it is scanned off broadside, including Gaussicity and encircled energy. Benchmark requirements are determined and compared with the capabilities of several potential phase shifter technologies, including MEMS-based variable capacitor phase shifters, switches, and varactor diode-based phase shifters.

This report explores the geometrical effects of a cylindrical chopper wheel on calculations of power coupling efficiency and noise equivalent temperature difference (NETD) of array elements. The overall efficiency of the cylindrical chopper wheel is found to be about 53% from geometrical arguments. In the limit that a detector beam fills the chopper aperture, if this efficiency is not accounted for, it can lead to detector NETD values that are a factor of 1.9 too high when calculated using standard double-modulation measurement techniques. For the particular geometry used with this setup, a power coupling efficiency of 78% was calculated for typical detector elements, resulting in values of detector NETD that were too large by a factor of 1.3 when the coupling efficiency was unaccounted for. This factor plays a role in accounting for some of the discrepancy between NETD values calculated based on diode sensitivity estimates and NETDs measured for individual array elements using double-modulation measurements.

We report on laboratory testing and telescope integration of SuperCam, a 64 pixel imaging spectrometer designed for operation in the astrophysically important 870 micron atmospheric window. SuperCam will be used to answer fundamental questions about the physics and chemistry of molecular clouds in the Galaxy and their direct relation to star and planet formation. The Supercam key project is a fully sampled Galactic plane survey covering over 500 square degrees of the Galaxy in ^(12)CO(3-2) and ^(13)CO(3-2) with 0.3 km/s velocity resolution. SuperCam will have several times more pixels than any existing spectroscopic imaging array at submillimeter wavelengths. The exceptional mapping speed that will result, combined with the efficiency and angular resolution provided by the HHT will make SuperCam a powerful instrument for probing the history of star formation in our Galaxy and nearby galaxies. SuperCam will be used to answer fundamental questions about the physics and chemistry of molecular clouds in the Galaxy and their direct relation to star and planet formation. Through Galactic surveys, particularly in CO and its isotopomers, the impact of Galactic environment on these phenomena will be realized. These studies will serve as “finder charts” for future focused research (e.g. with ALMA) and markedly improve the interpretation, and enhance the value of numerous contemporary surveys. In the past, all heterodyne focal plane arrays have been constructed using discrete mixers, arrayed in the focal plane. SuperCam reduces cryogenic and mechanical complexity by integrating multiple mixers and amplifiers into a single array module with a single set of DC and IF connectors. These modules are housed in a closed-cycle cryostat with a 1.5W capacity 4K cooler. The Supercam instrument is currently undergoing laboratory testing with four of the eight mixer array modules installed in the cryostat (32 pixels). Work is now underway to perform the necessary modifications at the 10m Heinrich Hertz Telescope to accept the Supercam system. Supercam will be installed in the cassegrain cabin of the HHT, including the optical system, IF processing, spectrometers and control electronics. Supercam will be integrated with the HHT during the 2009-2010 observing season with 32 pixels installed. The system will be upgraded to 64 pixels during the summer of 2010 after assembly of the four additional mixer modules is completed.

We have constructed an 810 GHz receiver system incorporating a HIFI Band-3 superconductor-insulator-superconductor (SIS) mixer developed for Herschel space observatory and a wide-band SiGe low noise amplifier (LNA) designed at Caltech. The instrument is currently installed at the RLT telescope (elevation 5500 m) in northern Chile. Hot/cold (280K/72K) load measurements performed at the telescope yield noise temperatures of 225 K (Y-factor = 1.7) including receiver optics. First-light observations indicate that the receiver is highly sensitive and functions stably. We present details of the receiver system, its performance at the telescope, and first-light observations with a Herschel mixer.

We report on the development of SuperCam, a 64 pixel imaging spectrometer designed for operation in the astrophysically important 870 micron atmospheric window. SuperCam will be used to answer fundamental questions about the physics and chemistry of molecular clouds in the Galaxy and their direct relation to star and planet formation. The Supercam key project is a fully sampled Galactic plane survey covering over 500 square degrees of the Galaxy in 12CO(3-2) and 13CO(3-2) with 0.3 km/s velocity resolution.

A spectral-line survey of IRC+10216 in the 345 GHz band has been undertaken with the Submillimeter Array. Although not yet completed, it has already yielded a fairly large sample of narrow molecular emission lines with line-widths indicating expansion velocities of ~4 km/s, less than 3 times the well-known value of the terminal expansion velocity (14.5 km/s) of the outer envelope. Five of these narrow lines have now been identified as rotational transitions in vibrationally excited states of previously detected molecules: the v=1, J=17--16 and J=19--18 lines of Si34S and 29SiS and the v=2, J=7--6 line of CS. Maps of these lines show that the emission is confined to a region within ~60 AU of the star, indicating that the narrow-line emission is probing the region of dust-formation where the stellar wind is still being accelerated., Comment: 5 pages, 5 figures, Accepted for publication in ApJ

We have used the Arecibo telescope to measure the HI absorption spectra of eight pulsars. We show how kinematic distance measurements depend upon the values of the galactic constants R_o and Theta_o, and we select our preferred current values from the literature. We then derive kinematic distances for the low-latitude pulsars in our sample and electron densities along their lines of sight. We combine these measurements with all others in the inner galactic plane visible from Arecibo to study the electron density in this region. The electron density in the interarm range 48 degrees < l < 70 degrees is [0.017 (-0.007,+0.012) (68% c.l.)] cm^(-3). This is 0.75 (-0.22,+0.49) (68% c.l.) of the value calculated by the Cordes & Lazio (2002) galactic electron density model. The model agrees more closely with electron density measurements toward Arecibo pulsars lying closer to the galactic center, at 30 degrees, Comment: Accepted by Astrophysical Journal September 2007

We report on the development of SuperCam, a 64 pixel, superheterodyne camera designed for operation in the astrophysically important 870 micron atmospheric window. SuperCam will be used to answer fundamental questions about the physics and chemistry of molecular clouds in the Galaxy and their direct relation to star and planet formation. The advent of such a system will provide an order of magnitude increase in mapping speed over what is now available and revolutionize how observational astronomy is performed in this important wavelength regime. Unlike the situation with bolometric detectors, heterodyne receiver systems are coherent, retaining information about both the amplitude and phase of the incident photon stream. From this information a high resolution spectrum of the incident light can be obtained without multiplexing. SuperCam will be constructed by stacking eight, 1x8 rows of fixed tuned, SIS mixers. The IF output of each mixer will be connected to a low-noise, broadband MMIC amplifier integrated into the mixer block. The instantaneous IF bandwidth of each pixel will be ~2 GHz, with a center frequency of 5 GHz. A spectrum of the central 500 MHz of each IF band will be provided by the array spectrometer. Local oscillator power is provided by a frequency multiplier whose output is divided between the pixels by using a matrix of waveguide power dividers. The mixer array will be cooled to 4K by a closed-cycle refrigeration system. SuperCam will reside at the Cassegrain focus of the 10m Heinrich Hertz telescope (HHT). A prototype single row of the array will be tested on the HHT in 2006, with the first engineering run of the full array in late 2007. The array is designed and constructed so that it may be readily scaled to higher frequencies., 12 pages, 14 figures, to be published in the Proceedings of SPIE Vol. 6275, "Astronomical Telescopes and Instrumentation, Millimeter and Submillimeter Detectors and Instrumentation for Astronomy III"

In November 2003 the heterodyne receivers WANDA (polarization diplexed 492/810 GHz) and PoleSTAR (2x2 810 GHz array) of AST/RO (Antarctic Submillimeter Telescope and Remote Observatory, located at the South Pole) were upgraded with new 810 GHz SIS (Superconductor-Insulator-Superconductor) waveguide mixers from KOSMA. Profiting from device development for the HIFI (Heterodyne Instrument for the Far-Infrared) Band 2 SIS mixers of the Herschel Space Observatory, a factor of approx. 2 improvement in receiver noise temperature (from 1100 K to 550 K DSB) was achieved with WANDA. The SIS mixer devices employ low-loss NbTiN-Al tuning circuits and are fabricated using electron beam lithographic junction area definition and CMP (Chemical Mechanical Polishing) of the tuning circuit dielectric. With the South Pole being one of the best possible sites for ground-based submillimeter astronomy, the 1.7 m telescope currently makes AST/RO well suited for sensitive, large scale spectral line mapping at 810 GHz. Low atmospheric opacity (tau < 1) and, consequently, very low system noise temperatures (< 3000 K) are regularly achieved at 810 GHz, making AST/RO an extremely sensitive observatory at these frequencies. "First light" astronomical measurements made with the upgraded 810 GHz channel of WANDA towards the galactic HII region NGC 3576 in CO J=7-6 (806.65 GHz) and the neutral carbon [CI] 3P2-3P1 (809.3 GHz) lines are presented.

We present the first astronomical results from DesertSTAR, a 7 pixel heterodyne array receiver designed for operation in the astrophysically rich 345 GHz atmospheric window. DesertSTAR was constructed for the 10m Heinrich Hertz Telescope located at 3150m elevation on Mt. Graham, Arizona. This receiver promises to increase mapping speed at the HHT by a factor of ~15 over the facility's existing single beam, dual polarization receiver. DesertSTAR uses tunerless, single-ended waveguide SIS mixers to achieve uncorrected receiver noise temperatures of ~60K. The instantaneous bandwidth is 2 GHz, with a 5 GHz Intermediate Frequency, offering 1600 km/s of velocity coverage. Cryogenic isolators are employed between the mixers and low noise amplifiers to assure a flat IF passband. The system uses a Joule-Thompson closed-cycle refrigerator with 180W capacity at 70K and 1.8W capacity at 4K. A novel reflective phase grating is used for Local Oscillator multiplexing, while a simple Mylar beamsplitter is used as an LO diplexer. Optics include only polyethelene mixer lenses and a single, cold, flat mirror, maximizing simplicity for high efficiency and easy optical alignment. The computer controlled bias system provides low noise bias for the SIS junctions, magnets and LNAs through a modular and hardware independent GUI interface, and allows remote operation and monitoring. We present measurements of receiver noise, beam quality, efficiency and stability in addition to astronomical observations obtained during engineering runs at the HHT.

We have proposed to develop a prototype 0.5-meter far-infrared telescope and heterodyne receiver/spectrometer system for fully-automated remote operation at the summit of Dome A, the highest point on the Antarctic plateau. The unparalleled stability, exceptional dryness, low wind and extreme cold make Dome A a ground-based site without equal for astronomy at infrared and submillimeter wavelengths. HEAT, the High Elevation Antarctic Terahertz Telescope, will operate in the atmospheric windows between 150 and 400 microns, in which the most crucial astrophysical spectral diagnostics of the formation of galaxies, stars, planets, and life are found. At these wavelengths, HEAT will have high aperture efficiency and excellent atmospheric transmission most of the year. The proposed superheterodyne receiver system will be comprised of 0.8, 1.4 and 1.9 THz channels which will observe the pivotal J=7-6 line of CO, the J=2-1 line of atomic carbon, and the far-infrared fine structure lines of N+ and C+, the brightest emission lines in the entire Milky Way Galaxy. When combined with the HEAT telescope, the receiver system represents a uniquely powerful instrument for reconstructing the history of star formation in our Galaxy, with application to the distant Universe. The receiver system itself serves as a valuable testbed for heterodyne Terahertz components, using leading-edge mixer, local oscillator, low-noise amplifier, cryogenic, and digital signal processing technologies that will play essential roles in future Terahertz observatories. The proposed study will pave the way for future astronomical investigations from Dome A.

We have searched for OH absorption against seven pulsars using the Arecibo telescope. In both OH mainlines (at 1665 and 1667 MHz), deep and narrow absorption features were detected toward PSR B1849+00. In addition, we have detected several absorption and emission features against B33.6+0.1, a nearby supernova remnant (SNR). The most interesting result of this study is that a pencil-sharp absorption sample against the PSR differs greatly from the large-angle absorption sample observed against the SNR. If both the PSR and the SNR probe the same molecular cloud then this finding has important implications for absorption studies of the molecular medium, as it shows that the statistics of absorbing OH depends on the size of the background source. We also show that the OH absorption against the PSR most likely originates from a small (10^5 cm^-3) molecular clump., 12 pages, 8 figures. Accepted for publication in ApJ

DesertSTAR is a 7 beam, 345 GHz heterodyne array receiver for the Heinrich Hertz Telescope (HHT) on Mt. Graham, AZ. The instrument uses fixed-backshort Superconductor-Insulator-Superconductor (SIS) mixers with a broadband waveguide probe. Instantaneous bandwidths greater than 2 GHz can be achieved over the entire 345 GHz atmospheric window. A cryostat with a Joule-Thompson (JT) mechanical refrigerator allows continuous operation and 1.8W of cooling capacity at 4K, and provides the needed temperature stability for low-noise operation. Local Oscillator (LO) distribution is accomplished with a novel phase grating that yields high efficiency and power uniformity in a hexagonally symmetric geometry. The computer controlled bias system is an evolution of a proven design that is simple and portable to any computer platform. The 2 GHz Intermediate Frequency (IF) bandwidth allows the future addition of a wideband backend optimized for extragalactic observations, with ~1700 km/s of velocity coverage. We present measurements of receiver performance and plans for integration on the HHT.

The advent of large format (~100 pixel) spectroscopic imaging cameras at submillimeter wavelengths would fundamentally change the way in which astronomy is performed in this important wavelength regime. While the possibility of such instruments has been discussed for more than two decades, only recently have advances in mixer technology, device fabrication, micromachining, digital signal processing, and telescope design made the construction of such an instrument possible and economical. In our paper, we will present the design concept for a 10×10 heterodyne camera.

Based on the excellent performance of NbN HEB mixer receivers at THz frequencies which we have established in the laboratory, we are building a Terahertz REceiver with NbN HEB Device (TREND) to be installed on the 1.7 meter diameter AST/RO submillimeter wave telescope at the Amundsen/Scott South Pole Station. TREND is scheduled for deployment during the austral summer season of 2002/2003. The frequency range of 1.25 THz to 1.5 THz was chosen in order to match the good windows for atmospheric transmission and interstellar spectral lines of special interest. The South Pole Station is the best available site for THz observations due to the very cold and dry atmosphere over this site. In this paper, we report on the design of this receiver. In particular, we report on HEB mixer device performance, the quasi-optical coupling design using an elliptical silicon lens and a twin-slot antenna, the laser local oscillator (LO), as well as the mixer block design and the plans for coupling the TREND receiver to the sky beam and to the laser LO at the AST/RO telescope site.

In this paper we present and discuss the great difference in OH absorption spectra against PSR B1849+00 and SNR G33.6+0.1 along the same line-of-sight. This finding is important as it clearly demonstrates that statistics of absorbing molecular gas depends on the size of the background source., Comment: To be published in the proceedings of "Magnetic fields and star formation: theory versus observations", held in Madrid, April 21-25 2003. Uses Kluwer style file

The authors analyze properties of a 220 GHz imaging system that uses a scanned reflectarray to perform electronic beam scanning of a confocal imager for applications including imaging meter-sized fields of view at 50 m standoff. Designs incorporating reflectarrays with confocal imagers have not been examined previously at these frequencies. We examine tradeoffs between array size, overall system size, and number of achievable image pixels resulting in a realistic architecture capable of meeting the needs of our application. Impacts to imaging performance are assessed through encircled energy calculations, beam pointing accuracy, and examining the number and intensity of quantization lobes that appear over the scan ranges of interest. Over the desired scan range, arrays with 1 and 2-bit phase quantization showed similar array main beam energy efficiencies. Two-bit phase quantization is advantageous in terms of pointing angle error, resulting in errors of at most 15% of the diffraction-limited beam size. However, both phase quantization cases considered resulted in spurious returns over the scan range of interest and other array layouts should be examined to eliminate potential imaging artifacts.

We present the first results from a project to map Giant Molecular Clouds (GMCs) in the 12CO J=2-1, 13CO J=2-1, and 12CO J=3-2 lines using the Heinrich Hertz Submillimeter Telescope (HHT) at the University of Arizona. We mapped nearly 2.5 sq. deg of W3 and 1.0 sq. deg of W51 in the J=2-1 lines. We have begun mapping in the J=3-2 line. We achieve angular resolutions of 33″ and 24″ in the J=2-1 and J=3-2 lines with 1.3 and 0.9 km s−1 resolution.