We present the design and measurement of a radio telescope receiver front end cooled to 100 K physical temperature, and working over 400 MHz to 3 GHz frequency band. The system uses a frequency independent feed developed for operation as a feed for parabola using sinuous elements and integrated with an ultra-wideband low noise amplifier. The ambient temperature system is tested on the 43 m radio telescope in Green Bank, WV and the system verification results on the sky are presented. The cryogenic receiver is developed using a Stirling cycle, one stage cryocooler. The measured far field patterns and the system noise less than 80 K over a 5:1 bandwidth are presented.

The conventional approach to generating local oscillator (LO) power for millimeterand submillimeter-wave heterodyne mixers is to generate power at a lower frequency using a suitable phase-locked source, and to convert this power to the desired commensurate frequency using a nonlinear diode such as a varactor in a frequency multiplier circuit. Although useful for single-dish telescope receiver systems, the conventional approach, using current state-of-the-art components, is highly impractical for large array-type radio telescopes for which manageable cost and high reliability are important factors.

This white paper offers cautionary observations about the planning and development of new, large radio astronomy instruments. Complexity is a strong cost driver so every effort should be made to assign differing science requirements to different instruments and probably different sites. The appeal of shared resources is generally not realized in practice and can often be counterproductive. Instrument optimization is much more difficult with longer lists of requirements, and the development process is longer and less efficient. More complex instruments are necessarily further behind the technology state of the art because of longer development times. Including technology R&D in the construction phase of projects is a growing trend that leads to higher risks, cost overruns, schedule delays, and project de-scoping. There are no technology breakthroughs just over the horizon that will suddenly bring down the cost of collecting area. Advances come largely through careful attention to detail in the adoption of new technology provided by industry and the commercial market. Radio astronomy instrumentation has a very bright future, but a vigorous long-term R&D program not tied directly to specific projects needs to be restored, fostered, and preserved.

Distance measuring equipment (DME) signals transmitted by aircraft in flight present a strong source of interference in radio astronomy bands around 1 GHz. In this paper, we present a method for greatly suppressing this interference without significant loss of radio astronomy data. The method exploits the known structure of the DME waveform to perform a time/frequency domain blanking on the aggregate signal. Results are presented that illustrate the effectiveness of the procedure. Efficient implementation of the blanking algorithm is also considered.

The neutral hydrogen 21 cm spectral line (1420.4 MHz) and the four 18 cm lines of the hydroxyl molecule (1612–1720 MHz) are observable at redshifts that put their measured line frequencies well below their protected frequency bands. Part of the redshift ranges (z = 0.171–0.477 for H I and z = 0.37–0.73 for OH) fall in the 960 to 1215 MHz band that is allocated to aircraft navigation. Most of the signals in this band are pulsed emissions of low duty cycle so much of the time between pulses is interference-free. This paper outlines the structure and measured properties of signals in this band and demonstrates a signal processing strategy that is effective at removing the pulsed signals from spectra at sensitivities produced by several hours of integration.

We consider the use of spatial filtering algorithms for radio frequency interference (RFI) mitigation in conjunction with a focal plane feed array of electrically small elements. Numerical simulations are used to study the performance of 7 and 19 element hexagonal dipole arrays with a 25 m reflector at an operating frequency of 1612 MHz. Using the maximum SNR algorithm to generate array weights, an interfering signal was attenuated by 40 dB or more. The effective sensitivity of the system, including interferer power in the system noise temperature, was comparable to the sensitivity attained in the absence of RFI. Moving the interferer through the reflector pattern sidelobes caused fluctuations in the gain and system sensitivity. This effect was exacerbated by a reflector model with random surface distortions. These results indicate that array feeds are a promising approach for RFI mitigation, but achieving stable radiation patterns in the presence of an interferer may require a trade‐off between pattern control and maximum attainable sensitivity.

Only a small fraction of the radio spectrum can be reserved exclusively for passive scientific measurements, so radio astronomers must expect to observe some natural radiation at frequencies allocated to an increasing number of active users of the spectrum. This paper presents a scheme for removing pulsed transmissions of air surveillance radar from astronomical data based on the temporal and amplitude characteristics of the radar signals. Two filter schemes for maximizing the separation of the radar signals from normally distributed noise are compared on the same real data. The goal is to remove as little of the useful data as possible. Removal of both strong- and weak-signal interference to the level of detectability in a 5 s integration and a scheme for compensating for the frequency dependence of the excision algorithm are demonstrated.

These measurements represent the first test of a local-oscillator (LO) driver based on a multiplied YIGtuned oscillator (YTO) locked to a variable frequency photonic mm-wave reference. The reference is provided as a beatnote between two optical signals and is carried from a remote location by 10 meters of optical fiber to a photomixer at the LO driver site. Phase noise measurements were performed at about 80 GHz. A pre-prototype of the Central Reference Generator (CRG) developed in Socorro was also used in the tests as the fundamental reference from which all other sources were synchronized.

In this memo, we present measurements of the noise of YIG-tuned oscillators (YTOs) at their fundamental frequency and multiplied to millimeter-wave frequencies. Based on these measurements, we verify that the phase noise goals for this component can be met with a 300-kHz bandwidth phase lock loop (PLL) as long as the fundamental YTO frequency is not above 27 GHz. We also present measurements of phase noise added by multipliers and power amplifiers, with the conclusion that their contribution is insignificant. Preliminary W-band amplitude noise measurements using a SIS mixer are also presented, indicating that specifications can be met with this architecture. Phase and amplitude noise measurements are compared to a millimeter-wave Gunn oscillator.

GaAs Schottky barrier diodes remain a workhorse technology for submillimeter-wave applications including radio astronomy, chemical spectroscopy, atmospheric studies, plasma diagnostics and compact range radar. This is because of the inherent speed of these devices and their ability to operate at room temperature. Although planar (flip-chip and beam-lead) diodes are replacing whisker contacted diodes throughout this frequency range, the handling and placement of such small GaAs chips limits performance and greatly increases component costs. Through the use of a novel wafer bonding process we have fabricated and tested submillimeter-wave components where the GaAs diode is integrated on a quartz substrate along with other circuit elements such as filters, probes and bias lines. This not only eliminates the cost of handling microscopically small chips, but also improves circuit performance. This is because the parasitic capacitance is reduced by the elimination of the GaAs substrate and the electrical embedding impedance seen by the diodes is more precisely controlled. Our wafer bonding process has been demonstrated through the fabrication and testing of a fundamental mixer at 585 GHz (T mix < 1200K) and a 380 GHz subharmonically pumped mixer (T mix < 1000K). This paper reviews the wafer bonding process and discusses how it can be used to greatly improve the performance and manufacturability of submillimeter-wave components.

We report on the design and evaluation of a 40-80-GHz (40/80-GHz) high-power wide-band fixed-tuned balanced doubler. The active device is a single GaAs chip comprising a linear array of six planar Schottky varactors. The varactors and a quartz microstrip circuit are embedded in a split waveguide block. We have achieved a measured 3-dB fixed-tuned bandwidth of 17% and measured flange-to-flange peak efficiency of 48% at an input-power level of 200 mW. The doubler operates at near-peak efficiency (45%) at an input power of 250 mW. We have cooled the block to 14 K and achieved an efficiency of 61% at an input-power level of 175 mW and an efficiency of 48% at an input-power level of 365 mW. Emphasis has been placed on making the design easy to fabricate and scalable to higher frequencies.

Every year, an increasing amount of radio-frequency (RF) spectrum in the VHF, UHF, and microwave bands is being utilized to support new commercial and military ventures, and all have the potential to interfere with radio astronomy observations. Such services already cause problems for radio astronomy even in very remote observing sites, and the potential for this form of light pollution to grow is alarming. Preventive measures to eliminate interference through FCC legislation and ITU agreements can be effective; however, many times this approach is inadequate and interference excision at the receiver is necessary. Conventional techniques such as RF filters, RF shielding, and postprocessing of data have been only somewhat successful, but none has been sufficient. Adaptive interference cancellation is a realtime approach to interference excision that has not been used before in radio astronomy. We describe here, for the first time, adaptive interference cancellation in the context of radio astronomy instrumentation, and we present initial results for our prototype receiver.In the 1960s, analog adaptive interference cancelers were developed that obtain a high degree of cancellation in problems of radio communications and radar. However, analog systems lack the dynamic range, noised performance, and versatility required by radio astronomy. The concept of digital adaptive interference cancellation was introduced in the mid-1960s as a way to reduce unwanted noise in low-frequency (audio) systems. Examples of such systems include the canceling of maternal ECG in fetal electrocardiography and the reduction of engine noise in the passenger compartments of automobiles. These audio-frequency applications require bandwidths of only a few tens of kilohertz. Only recently has highspeed digital filter technology made high dynamic range adaptive canceling possible in a bandwidth as large as a few megahertz, finally opening the door to application in radio astronomy.We have built a prototype adaptive canceler that consists of two receivers: the primary channel (input from the main beam of the telescope) and a separate reference channel. The primary channel receives the desired astronomical signal corrupted by RFI (radio-frequency interference) coming in the sidelobes of the main beam. A separate reference antenna is designed to receive only the RFI. The reference channel input is processed using a digital adaptive filter and then subtracted from the primary channel input, producing the system output. The weighting coefficients of the digital filter are adjusted by way of an algorithm that minimizes, in a least-squares sense, the power output of the system. Through an adaptive-iterative process, the canceler locks onto the RFI, and the filter adjusts itself to minimize the effect of the RFI at the system output. We have designed the adaptive canceler with an intermediate frequency (IF) of 40 MHz. This prototype system will ultimately be functional with a variety of radio astronomy receivers in the microwave band. We have also built a prototype receiver centered at 100 MHz (in the FM broadcast band) to test the adaptive canceler with actual interferers, which are well characterized. The initial laboratory tests of the adaptive canceler are encouraging, with attenuation of strong frequency-modulated (FM) interference to 72 dB (a factor of more than 10 million), which is at the performance limit of our measurements. We also consider requirements of the system and the RFI environment for effective adaptive canceling.

We report on the development of a high-power, broadband, fixed-tuned 80/160 GHz frequency doubler. The design is based on a similar 40/80 GHz doubler which exhibited a measured 3 dB bandwidth of 17% and peak efficiency of 48% at an output power of 100 mW. Simulations for the new 80/160 GHz doubler indicate similar bandwidth and efficiency. The focus of this paper is the design and simulation of the 80/160 GHz doubler. Test results will be presented at the conference.

State-of-the art frequency multipliers, particularly those that operate in the submillimeter wave band, suffer from several limiting factors that make them impractical for modern array applications. In this paper we review the unique requirements placed upon frequency multipliers by array systems, report on the progress of our multiplier development effort, and outline our future development goals toward a suite of multipliers for the NRAO Millimeter Array.

In the title compound, C8H5NO4, the heterocycle is planar within 0.02 Angstrom, and the nitro group plane makes an angle of 10.0(1)degrees to it. Dipolar interactions and possible weak C-H ... O hydrogen bonding feature in the crystal packing. In a series of phthalides, bond lengths in the lactone ring can be related to substituent effects; in the title compound, the nitro group exerts less influence than it does in the homologous 3-nitromethylenephthalide.

The authors present a diode-grid frequency tripler based on an array of bowtie antennas. The array permits DC biasing of the varactors and is scalable to millimeter and submillimeter wave frequencies. The tripler produced an output power of approximately 40 mW at 15 GHz with an efficiency of 14%. In addition, the circuit models for the linear components in the tripler were verified with quasi-optical S-parameter measurements. Simulations with the multiplier circuit model show that the efficiency of the tripler can be improved with external dielectric tuning slabs and input optics to focus the incident power. This multiplier grid has served as a proof-of-concept demonstration and is the initial step in the design of a fully monolithic 160 GHz tripler array.

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.

This paper reports on progress towards state-of-the-art submillimeter wavelength waveguide mixers using planar Schottky barrier diodes. A double-sideband system noise temperature of 2380 K was measured at 585 GHz with 1.2 mW of local oscillator power using a fixed tuned mixer in which the diode is mounted in a microstrip channel. A system noise temperature of 2550 K was measured with 1.1 mW of LO power using a mixer in which the diode was mounted in a waveguide in front of a tunable backshort. These represent the best planar diode mixer results in this frequency range. Simulations indicate an IF bandwidth in excess of 100% and an RF bandwidth of 40% are achievable using the fixed tuned mixer block design.