Mark S. Gatti

FFT applications to plane-polar near-field antenna measurements

The four-point bivariate Lagrange interpolation algorithm was applied to near-field antenna data measured in a plane-polar facility. The results were sufficiently accurate to permit the use of the FFT (fast Fourier transform) algorithm to calculate the far-field patterns of the antenna. Good agreement was obtained between the far-field patterns as calculated by the Jacobi-Bessel and the FFT algorithms. The significant advantage in using the FFT is in the calculation of the principal plane cuts, which may be made very quickly. Also, the application of the FFT algorithm directly to the near-field data was used to perform surface holographic diagnosis of a reflector antenna. The effects due to the focusing of the emergent beam from the reflector, as well as the effects of the information in the wide-angle regions, are shown. The use of the plane-polar near-field antenna test range has therefore been expanded to include these useful FFT applications. >

Proposed Array-Based Deep Space Network for NASA

The current assets of the deep space network (DSN) of the National Aeronautics and Space Administration (NASA), especially the 70-m antennas, are aging and becoming less reliable. Furthermore, they are expensive to operate and difficult to upgrade for operation at Ka-band (321 GHz is shorthand for the allocated 31.8-32.3 GHz. GHz). Replacing them with comparable monolithic large antennas would be expensive. On the other hand, implementation of similar high-sensitivity assets can be achieved economically using an array-based architecture, where sensitivity is measured by G/T, the ratio of antenna gain to system temperature. An array-based architecture would also provide flexibility in operations and allow for easy addition of more G/T whenever required. Therefore, an array-based plan of the next-generation DSN for NASA has been proposed. The DSN array would provide more flexible downlink capability compared to the current DSN for robust telemetry, tracking and command services to the space missions of NASA and its international partners in a cost-effective way. Instead of using the array as an element of the DSN and relying on the existing concept of operation, we explore a broader departure in establishing a more modern concept of operations to reduce the operations costs. This paper presents the array-based architecture for the next-generation DSN. It includes system block diagram, operations philosophy, users view of operations, operations management, and logistics like maintenance philosophy and anomaly analysis and reporting. To develop the various required technologies and understand the logistics of building the array-based low-cost system, a breadboard array of three antennas has been built. This paper briefly describes the breadboard array system and its performance.

Arraying performance of a 3-antenna demonstration array for Deep Space communications

NASA provides telecommunications services to its deep space scientific missions by way of its Deep Space Network (DSN) of large antennas Currently this DSN consists of monolithic antennas (34 m and 70 m diameter) located equidistant in longitude around the earth. The use of arraying has been proposed as a cost effective way to replace large antennas and/or add capability to the DSN in the future. A demonstration array was constructed at JPL as part of the study of arraying possibilities. This array consisted of three elements, two of which were 6 m-diameter antennas and one of which was a 12 m-diameter antenna. The array included a real-time FPGA based signal processing system capable of simultaneously operating as an interferometer and a signal combiner. The signal combiner was designed to sum the entire received spectrum from all elements of the array with the resulting signal compatible with the downlink tracking and telemetry system used by the DSN. The system was used to track various spacecraft at both frequencies of interest (X-band near 8.4 GHz and Ka-band near 32 GHz) as well as natural radio sources over broader bandwidths around the same frequencies. Signals from the combiner system were provided to a telemetry receiver where performance measurements could be compared to a single DSN antenna. Detailed results of these demonstrations with the Mars Reconnaissance Orbiter (MRO) and the Cassini Orbiter at Saturn are presented1 2.

A Phased Array Antenna for Deep Space Communications

This paper describes a phased array antenna that has been studied for use as the next generation deep space network (DSN) for NASA. The DSN currently consists of large reflector antennas located approximately equidistant around the earth and provides communications and navigation services to the NASA science missions to the solar system planets. These individual antennas range in size from 34-m to 70-m. In the future, there have been proposals to replace these antennas with a phased array, each element of which would consist of smaller reflector antennas than currently used. The total aperture could be increased as required by future missions, with total future aperture up to or more than 10 times that of the current DSN total aperture. One possible architecture for this phased array antenna is described. A breadboard phased array was constructed to demonstrate this concept. The performance of the individual antenna elements and their corresponding subsystems, and the performance of the phased array signal combiner developed for this breadboard phased array is described.

Deep Space Network Array - Update

JPL, in conjunction with the NASA HQ Science Mission Directorate, is evaluating a cost-effective method of obtaining large apertures for deep space communications, by arraying many small-diameter antennas. Drivers are the need to increase greatly the amount of information received from and transmitted to deep-space mission, both human and robotic, increase the precision of deep space navigation as NASA moves to the Kaband, and replace aging DSN assets. Plans and analysis were previously presented. This paper presents recent updates in the following areas: 1. Results on the cost-effectiveness and performance of small (6m-12m) antennas, at Xand Ka-band. We show performance data for two classes of low-cost antenna that nevertheless meet difficult performance requirements, including blind-pointing at Kaband and use of compact cryogenic front-ends. 2. Results on signal arraying. We show the flexible architecture and initial results of field tests in real-time combining broadband (500 MHz) signals from small antennas, to generate an effective large antenna 3. Methods to achieve a cost-effective uplink, in particular through arraying of uplink signals. We show that using an architecture that separates the uplink antennas from the downlink antennas, and through arraying of uplink antennas, we can achieve highly-efficient allocation of uplink capability to meet a wide range of mission needs in or nominal, emergency, and high-demand scenarios. 4. Selection process for antenna sites, through application of methodology for scoring and weighting of multiple criteria for all candidate sites. The methodology balances factors that tend to favors remote, desert sites that are superior for Ka-band operations, with factors that favor populated areas, e.g. the need to locate operations and maintenance staff near-by. The methodology can be adapted to other applications.

Operation's concept for array-based deep space network

The array-based deep space network (DSN-Array) will be a part of more than 103 times increase in the downlink/telemetry capability of the deep space network (DSN). The key function of the DSN-array is to provide cost-effective, robust telemetry, tracking and command (TT&C) services to the space missions of NASA and its international partners. It provides an expanded approach to the use of an array-based system. Instead of using the array as an element in the existing DSN, relying to a large extent on the DSN infrastructure, we explore a broader departure from the current DSN, using fewer elements of the existing DSN, and establishing a more modern concept of operations. This paper gives architecture and operations philosophy of DSN-array. It also describes customers view of operations, operations management and logistics, and maintenance philosophy, anomaly analysis and reporting

A radio telescope for the calibration of radio sources at 32 GHz

Knowledge of the flux of celestial sources is important to radio astronomers and telecommunications engineers who wish to accurately calibrate their large aperture antennas. At 32 GHz the flux of celestial objects is given by extrapolations using the spectral indices obtained from measurements at lower frequencies; there have been no direct calibrations. We have therefore developed a program whereby a 5-meter diameter radio telescope at the Owens Valley Radio Observatory (OVRO) operating at 32 GHz will observe a list of radio sources. By accurately calibrating the 5-meter antenna we will be able to have direct measures of celestial radio source fluxes. Accurate calibration of the 5-meter radio telescope must be done in-situ at OVRO; therefore, we have built a radio telescope intended to be a standard gain tool to be used to perform the accurate 5-meter calibration. This telescope uses a highly efficient 1.5-meter offset feed Cassegrainian optics configuration whose aperture efficiency is nearly 80%. The telescope uses a radiometer with a high electron mobility transistor (HEMT) low noise amplifier (LNA), and a pair of feeds to operate in a beam switching mode. When tracking a celestial source, one of the two beams is pointed to the source and the other is pointed to an empty part of the sky. Coherent detection of the difference signal of this rapidly switched signal provides a measure of the signal due to the source. The technical challenge for this standard gain telescope is that it must provide accurate tracking of the celestial source with minimum pointing errors; it must contribute a minimum noise temperature; each beam on the sky has to be nearly equal in performance; and a stable radiometer that can detect signals in millikelvins is required. Such a system is summarized.

A test-bed validation of electromagnetic surface wave propagation along a dielectric-coated metal pipe

This paper provides a summary of the results of an attempt at experimental verification of the propagation of electromagnetic surface waves at microwaves frequencies, in and along the uniform dielectric coating of a circular cylindrical metal pipe, based on the previously stablished theoretical investigation. These experimental results are of value for the diagnostic of anomalies on the surface of tar-coated pipes used in protecting the underground power transmission cables (feeder pipes). A test-bed was designed and implemented using an aluminum tubes (10” diameter) with an acrylic tube coating (0.25” thickness). Two identical wave launcher/receiver arrays, each of 32 elements around the tube for relatively uniform radiation/reception, were designed and fabricated at the frequency of interest (~6 GHz). This arrangement was put in a specially designed small anechoic chamber and attached to a network analyzer. A variety of tests were performed to stablish the launch efficiency, prove surface wave propagation along, and reflection from different types of anomalies on the coating. In the paper, a number of test results and supporting graphs will be provided and future work for improving the performance of the launch array and the testbed arrangement for better results will be outlined.

Calibration of Antennas During Construction or Expansion of Radio Arrays

The calibration of radio antenna performance is a well understood process, especially for single large-diameter antennas. However, the measurement of efficiency, optimal focus, pointing corrections, system temperature, and other parameters as functions of observing frequency, antenna elevation and azimuth, temperature, and wind velocity can be time-consuming. For any future arrays consisting of very large numbers of small antennas, it will be necessary to minimize the time spent calibrating each antenna. This paper considers ways to speed up the calibration of antennas being added to an existing array by taking advantage of interferometer measurements and script-based automation.

Challenging Implementation and Operations Traditions

The Deep Space Network (DSN) that provides for the communications link between the deep space missions and the science users currently consists of a small set of very large monolithic tracking antennas. This ground-based network includes a total of 12 antennas located in three roughly equidistant longitudes around the earth and utilizes a decentralized approach to it operations. Recently, however, studies have suggested that the number, complexity, and data throughput of the future set of space probes will be increasing dramatically. This demands more performance from the DSN than is currently available. In identifying the architecture for the future DSN required to support this mission set, one concept that proves promising is one that consists of a great many number of much smaller antennas configured in an array. This concept has been supported by the developments in antenna manufacturing technology and the consistent decrease in the cost of electronics required to receive, amplify, and combine signals from deep space probes. Furthermore, it is clear that past developments in the DSN have not benefited from the applications of economies of scale.