Evolution of the large Deep Space Network antennas

The evolution of the largest antenna of the US NASA Deep Space Network (DSN) is described. The design, performance analysis, and measurement techniques, beginning with its initial 64-m operation at S-band (2295 MHz) in 1966 and continuing through the present Ka-band (32-GHz) operation at 70 m, is described. Although their diameters and mountings differ, these parabolic antennas all employ a Cassegrainian feed system, and each antenna dish surface is constructed of precision-shaped perforated-aluminum panels that are secured to an open steel framework     

Compound-taper feed horn for NASA 70-m antennas

A compound taper feed horn structure is described that was used to move the phase center of a corrugated feed horn without any significant degradation in its other major characteristics. Based on this technique, an X-band feed horn has been designed for use in the National Aeronautics and Space Administration's (NASA) 70-m antennas. The compound taper structure consists of a conventional corrugated flared section (a standard 22-dB feed horn) and a corrugated straight section. This feed horn is designed to move the phase center of the standard feed horn to a desired location without the addition of significant loss to the system. The feed horn was checked extensively by a computer program. Excellent agreement between theoretical and measured results was established, and the feed horn was shown to perform as well as the standard feed horn for all practical purposes     

An experimental radome panel evaluation

Modern antenna radomes are made of materials that tend to shed water to minimize their RF attenuation when wet. The microwave performance of these materials has been studied experimentally. Radome attenuation was measured as a function of frequency, rain rate, rain incidence angle, RF incidence angle, and polarization. The tests were performed on (1) new, clean radome panels, (2) used, dirty radome panels, (3) cleaned, used radome panels, and (4) panels treated with hydrophobic paint. The results show weak loss dependence on frequency over the 13-20 GHz frequency range of interest, which increases slowly with rain rate from 2.5 to 29 mm/h except for surfaces that are wettable, where the dependence on rate is much stronger. Loss is nearly independent of rain incidence angle, but it is strongly a function of surface condition. Hydrophobic paint is shown to be very effective. The test setup used, limitations imposed by the real world, and a simplified model of radome loss derived from the test results are described     

Effects of solar transit in Ku-band VSAT systems

Behavior of networks of very small aperture satellite terminals (VSATs) operating at Ku band during the solar transit period, is compared to more traditional C or Ku-band satellite networks. Based on analyses and experiments, it is explained why solar transit outages are rarer in Ku-band VSAT systems than conventional satellite communications systems. In many cases, Ku-band VSAT systems will operate through periods of Sun transits without any significant increase in transmission error rates or incidences of link outages     

Combating sun outage in satellite television distribution systems

Two methods of sun outage avoidance in satellite television transmission are discussed. Each method requires two satellites and dual-beam antennas. The two C-band satellites transmit identical programs at the time when the sun outage period occurs. The separation of the spacecraft is dependent on the dual-feed earth station antenna size. For large television receive-only antennas, the separation must be small; for small antennas, or antennas with large beamwidths, the satellite separation can be large. If the separation is larger than 8° on the geosynchronous arc, only one transmit station is required to transmit program information. Scaling this system for Ku-band use is then considered. It is concluded that in a Ku-band direct-broadcasting system with earth station antenna diameters of 1-m and below, the rise in noise temperature due to sun outage is not significant and can be overcome by a modest amount of system margin, equivalent to that normally provided against rain fades     

A new method for obtaining antenna gain from backscattermeasurements

A method is presented for determining the gain of an antenna from analysis of backscatter data of the antenna. This approach is different from those which have been presented in the past because it accounts for the presence of resonances which can occur in the antenna during a backscatter measurement. In particular, this type of resonance appears in the backscatter measurement of symmetric reflector antennas. This technique is applied to determine the gain of a Ka-band Cassegrain antenna and an X-band prime focus-fed antenna     

Microstrip linear slot array antenna for X-band

The X-band microstrip slot antenna array is described as an attempt to achieve moderate bandwidth and overcome the problems of radiation from microstrip feed lines and surface waves in the dielectric. The discussion covers development of a mathematical simulation that computes the radiation pattern of a single microstrip slot and the feeding microstripline; construction of a uniform broadband microstrip slot antenna array; development of a mathematical simulation that computes the radiation pattern in the H- and E-planes; and investigation of the mutual coupling between the slots. A comparison is made between computed and measured results at X-band frequencies     

On the Characteristics of Radome Enclosed Archimedean Spiral Antennas

The effects of the superspheroidal radomes on the characteristics of Archimedean spiral antennas are investigated in detail, which may provide some useful insights in the design of the radome-antenna system in practical engineering. All interactions between the radome and antennas are rigorously included in the coupled surface integral equation (CSIE) model, which leads to more accurate results than those of the existing methods based on the high-frequency algorithm or the decoupled radome-antenna analysis procedure especially when the antennas are placed in the close proximity of the radome. Numerical results show that the performance of the spiral antenna is significantly changed due to the presence of the radome.      

Deformation of the horizontal radiation pattern of TV transmittingantennas due to a thin dielectric radome

Two methods are presented to study the effect of a thin dielectric radome on the horizontal radiation pattern of TV transmitting antennas. Examples are given for two antenna systems, each consisting of four columns of horizontal dipoles supported by a perfectly conducting carrier post of either circular or square cross section. The radome is a thin circular cylindrical dielectric shell enclosing the antenna system. The problem is modeled by a two-dimensional system and two different surface formulations are used to determine the effect of the radome on the radiation pattern. The procedure developed is general; the post and the radome may be of arbitrary cross sections. The noncircularity of the radiation pattern is computed for transmitting antennas in TV bands IV and V (f=470-790 MHz). It is observed that the presence of a radome does not always imply degradation in the circularity of its pattern; it may even enhance the pattern circularity at some frequencies     

Waveguide-fed parallel plate slot array antenna

A novel planar antenna in which radiating slots are arrayed on one side of a square parallel plate waveguide and coupling slots occupy the other side is proposed. The antenna is excited via the coupling slots by a rectangular waveguide. In order to suppress unwanted reflections and to assure the purity of the transverse electromagnetic traveling-wave mode in the parallel plate waveguide, all the slots are arrayed in pairs. An X-band model antenna was fabricated, and uniform aperture illumination was demonstrated with 48% antenna efficiency. These results demonstrate the feasibility of antennas of this type     

Interference effects on Space Station Freedom and Space Shuttleorbiter Ku-band downlinks

The Space Shuttle orbiter (SSO) Ku-band single access return (KSAR) link and the Space Station Freedom (SSF) KSAR link via the tracking and data relay satellite system (TDRSS) use the same carrier frequency. The interference between spacecraft is minimized by opposite antenna polarizations and by TDRSS antenna beam pointing, but if the SSF and SSO are in close proximity, it is expected that mutual interference will be significant. It is shown that a simplified analytical approach will yield adequate accuracy for the expected range of operating conditions. Relative degradation in bit-energy-to-thermal-noise power spectral density ratio to achieve a 10^-5 coded bit-error probability is determined to be 4 dB for the Ku-band SSO-to-TDRS I-channel return link with a 4.5-dB effective signal-to-interference total power ratio (S/I) when the Ku-band SSF-to-TDRS return link interferes. For the Ku -band SSF-to-TDRS return link, both analysis and simulation results yield a relative signal degradation of 0.4 dB at the effective S/I=21.6 dB     

Absolute radiometric calibration of the CCRS SAR

Determining the radar scattering coefficients from SAR (synthetic aperture radar) image data requires absolute radiometric calibration of the SAR system. The authors describe an internal calibration methodology for the airborne Canada Centre for Remote Sensing (CCRS) SAR system, based on radar theory, a detailed model of the radar system, and measurements of system parameters. The methodology is verified by analyzing external calibration data acquired over a six-month period in 1988 by the C-band radar using HH polarization. The results indicate that the overall error is ±0.8 dB (1σ) for incidence angles ±20° from antenna boresight. The dominant error contributions are due to the antenna radome and uncertainties in the elevation angle relative to the antenna boresight     

S/Ka双频段馈源新型喇叭罩设计

论述了一般喇叭罩的设计原则和思路,提出了采用B夹层结构的聚四氟乙烯S/Ka双频段馈源喇叭罩的设计思想,及喇叭罩的具体设计方法.实验证明,该喇叭罩性能优良,已成功应用到某大型S/Ka双频段工程中.     

A Radiometric Method for Measuring the Insertion Loss of Radome Materials

Though radomes have been used for years as a means of protecting antennas from the elements, little appears in the Iiterature to aid the engineer in his choice of the radome material to use in a particular installation. This may be due to the fact that many radome materials are adequate when used with a receiving system having a mixer (i.e., relatively hot) front end. However, an improper choice of radome material can seriously degrade a receiving system that employs a maser or other low-noise front end. A radiometric technique for the measurement of insertion loss is described, and a sample calculation, including error analysis, is presented.     

Calibrated imaging radar polarimetry: technique, examples, andapplications

The authors developed a calibration procedure for imaging radar polarimeters and applied it to a set of images acquired by the NASA DC-8 multifrequency radar system. The technique requires the use of ground reflectors of known cross-section for absolute calibration, that is, solution for σ⁰; however, the image data themselves can usually provide all information necessary for phase calibration and for antenna crosstalk correction. The accuracy of the approach, as measured by calculating the cross-section residuals of known targets in each calibrated scene, is on the order of ±1-2 dB at the P- and C-band, but improves to ±0.5 dB at the L-band. The authors present the results of applying this technique to radar scenes of lava flows of varying roughness, temperate and tropical rain forests, and ocean water surfaces. They also present several example applications which are feasible with calibrated data but which would be difficult to implement with uncalibrated data     

An integrated mobile satellite broadcast, paging, communicationsand navigation system

The design of an integrated mobile satellite broadcast, paging, communications, and navigation system is described. Ku-band RadioSat ground stations will broadcast digital audio signals and data packets (including alphanumeric pages and group cells) to mobiles through a satellite to be launched in 1993. Each mobile radio will simultaneously receive L-band digital audio and data broadcasts from the satellite and L-band navigation broadcasts from the Global Positioning Systems (GPS) through a common omnidirectional mobile antenna and receiver front end. RadioSat mobile radios will use GPS broadcasts and differential corrections sent through the satellite to navigate with 2-m accuracy. With optional transmitters, RadioSat mobile radios can support two-way voice and data communications     

Transient response of a receiving dipole array: bounds andmaximization

The optimum solution for a receiving array of dipole antennas connected to a load through a feed network is obtained. It is given in terms of the incident electric field waveform that maximizes, at a specific time t₀, the received voltage across a specified load impedance. This result is used to set an upper limit on the peak voltage that the antenna can deliver to a load, thus providing guidelines for the design of pulse-protection circuits. The analysis uses the method of moments to approximate the currents induced in the wires by the incident field and S-parameter techniques to describe the feed incident electromagnetic plane waves. The Lagrange multiplier technique is then used to maximize the receive load voltage. The solutions presented are based on an idealized model for the feed network; however, the analysis can be extended easily to account for loss and asymmetry of physically realizable feed networks     

Performance degradation of dielectric radome covered antennas

Performance is evaluated by a method based on the reciprocity theorem. The asymptotic expression for the radome Green's function that allows the characterization of the radome by itself, independently of any specific antenna, is identified. The concept of the modified aperture distribution, which radiating in free space produces the same pattern as the radome-covered antenna, is introduced. It can be used for the design of the radome stratification and for the optimization of the antenna location. On the basis of the formulation of a computer code has been developed that analyzes the degradation induced by radomes with surfaces and dielectric stratifications that can be defined numerically. Theoretical predictions and experimental results are compared     

An E-field integral equation solution for the radiationfrom reflector antennas with struts

The E-field integral equation is applied to rotationally symmetric reflector antennas with struts. Current is allowed to flow on all the reflector surfaces and continuity is enforced at the conductor junctions. Radiation patterns are presented for a small paraboloid antenna, and the effects of the struts are clearly defined. These include the strut cone radiation, pattern asymmetries introduced by the struts, and gain loss and sidelobe level changes