Tom Y. Otoshi

Beam-waveguide antenna performance predictions with comparisons to experimental results

An overview of a NASA/JPL antenna project, with specific focus on the methodology used to predict the microwave performance of a 34-m-diameter beam-waveguide (BWG) reflector antenna, designated DSS 13, is given. Microwave performance predictions are given, as well as a summary of test results for the antenna, which has Cassegrain and centerline BWG operating models at X-band (8.450-GHz) and Ka-band (32-GHz) frequencies. Predictions were used to identify critical and poorly understood areas needing further study and diagnostic testing, and assisted in planning, scheduling, and evaluating the final results of a detailed test program. Predictions were assembled for all known losses that contribute to antenna performance degradation. It was found that predictions and experimental results agreed reasonably well for beam-peak gain and corresponding efficiency, and for several (but not all) noise temperatures. >

The electrical conductivities of steel and other candidate materials for shrouds in a beam-waveguide antenna system

This article presents the results of electrical conductivity measurements made at 8.420 GHz on samples of the structural steel material used to fabricate shrouds on a Deep Space Network (DSN) 34-m-diameter beam-waveguide (BWG) antenna. Test results show that the structural steel samples at this microwave frequency had effective conductivities that were about 50 times worse than published dc values and also 230 times worse than the measured conductivities of aluminum test samples. Conductivity data are also presented for other candidate materials that could be used to fabricate BWG shrouds. Of interest are the improvements or degradations that were observed after some of the metal test samples were surface treated, plated, or painted.

Efficiency measurement techniques for calibration of a prototype 34-meter-diameter beam-waveguide antenna at 8.45 and 32 GHz

Efficiency measurements at 8.45 and 32 GHz (X- and Ka-bands) have been carried out on a new 34-m-diameter beam-waveguide antenna now in use at the NASA/JPL Goldstone Deep Space Communications Complex. The use of portable test packages enabled measurements at both the Cassegrain and the beam-waveguide focal points. Radio sources (quasars and Venus) were used as calibrators, and updated determinations of flux and source size correction were made during the period of the measurements. Gain and efficiency determinations as a function of elevation angle are presented, and the effects of the beam-waveguide system and antenna structure are clearly seen. At the beam-waveguide focus, an 8.45-GHz peak efficiency of 72.38% was measured; at 32 GHz, 44.89% was measured. >

Maximum and minimum return losses from a passive two-port network terminated with a mismatched load

An analytical expression is derived for determining load-reflection coefficient phase-angle values that will lead to maximum and minimum return losses from a terminated two-port network. The expression is derived in terms of two-port network S-parameters and a load whose reflection-coefficient magnitude is a constant but can be any value greater than zero and less than or equal to unity. The equation is useful for cases where it is desirable to know how to position a load (1) to obtain maximum return loss for network-matching purposes or (2) to obtain minimum return loss for some types of reflector antenna applications. Two examples are given: One shows that for some types of reflector antennas with a mesh-type surface that is backed by another reflecting surface, a resonance phenomenon can occur and cause unexpectedly large dissipative losses (>30 dB) to occur. The other example shows that when a particular type of reflector antenna with a dielectric layer becomes wet from rain or condensation, large (>10 dB) signal losses can occur. For both examples, equations presented in this article were used to calculate the exact load-reflection coefficient phase values that led to worst-case return loss values. In practical situations, once the phenomenon is understood and predictable, steps can be taken to avoid these resonance regions. >

Precision Reflectivity Loss Measurements of Perforated-Plate Mesh Materials by a Waveguide Technique

A waveguide method is described for improving the precision and accuracy of reflectivity loss measurements of perforated-plate mesh materials. Overall accuracies of the order of ±0.005 dB can be achieved through the use of a dual-channel tuned reflectometer system and high-precision insertion loss test set.

Radiometric Evaluation of Antenna-Feed Component Losses

Low-noise antenna systems are frequently used in conjunction with measurements of atmospheric and cosmic background noise at microwave frequencies. The input transmission line losses of these receiving systems must be precisely calibrated to insure proper identification of the portion of operating noise temperature attributable to the external environment. Although most components in an antenna line can be calibrated by conventional insertion-loss measurements, many feed component losses must be evaluated by means of nonstandard techniques. This paper describes a radiometric method for calibrating the loss of multimode antenna-feed components in which the field is linearly or circularly polarized. The method consists of measuring operating noise temperature, first with the components under evaluation installed and again after substitution by a waveguide section of known loss. Calibration and error analysis equations are derived and discussed. Application of the radiometric method, for the calibration of a mode-generator and quarter-wave plate polarizing section, resulted in a loss measurement of (0.0069 ±0.0016 pe)/dB.

Portable microwave test packages for beam-waveguide antenna performance evaluations

Portable microwave test packages used to evaluate a new 34-m-diameter beam-waveguide (BWG) antenna are described. The experimental methodology involved transporting test packages to different focal points of the BWG system and making noise temperature, antenna efficiency, and holography measurements. Comparisons of data measured at the different focal points enabled determinations of performance degradations caused by various mirrors in the BWG system. It is shown that, due to remarkable stabilities and accuracies of radiometric data obtained through the use of the microwave test packages, degradations caused by the BWG system were successfully determined. >

Cosmic Background Noise Temperature Measurements at 13-cm Wavelength

Cosmic background noise temperature measurements which were made at 13.05-cm wavelength (2297 MHz) resulted in an experimental value of [266 ± 0.77 (3¿)] K. The two largest error sources were due to uncertainties in the calibration of the liquid helium cooled termination and the antenna transmission line. The 2.66 K value is in good agreement with the currently accepted value of 2.8 K. Measurements were made at 2297-MHz space communications frequency because cosmic background noise is an important consideration in the calculations of expected signal-to-noise ratios for spacecraft and ground receiving systems.

Development and evaluation of a set of group delay standards

Group delay standards of 15,30, and 60 ns have been developed at JPL. Calibration data provided by NBS and others are presented and compared. Calibrations were performed at microwave frequencies of 2113,2295, and 8415 MHz as well as at a baseband modulation frequency of 500 kHz. The uncertainties of the measurement and effects of dispersion and cable reflections are discussed.

Ground Instrumentation for Mariner IV Occultation Experiment

The Mariner IV occultation experiment imposed unique requirements upon the NASA/Jet Propulsion Laboratory Deep Space Instrumentation Facility. It was necessary to measure extremely small deviations in the frequency to a few parts in 109. The instrumentation used and the results obtained are described.