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Compact quadrifilar-helix antenna has exceptionally uniform and axially symmetric radiation pattern. It resists shock and vibration and gives excellent radiation characteristics which make it potentially useful for mobile citizenband radios and other terrestrial communications sytems.
Radiation patterns switched within microseconds. According to concept, digital beam-steering information destined for number of phased antenna elements transmitted in serial multiplex along optical fiber to optoelectronic integrated circuit (OEIC), demultiplexing information into parallel electronic channels to phase shifters associated with various elements. Because of small distances between elements of such arrays, compactness of optical fibers makes them attractive for distribution of beam-steering (phase-shifting) control signals. Also offers advantages of light weight, low attenuation, mechanical flexibility, large bandwidth, and immunity to both crosstalk and electromagnetic interference.
NASTRAN-GAP programs for analyzing antenna radiation patterns of reflectors distorted by gravity and thermal loads
Numerical double integral evaluation technique for antenna radiation patterns, discussing error data
Recording systems and other associated electronic equipment were engineered, calibrated, and used to measure antenna radiation patterns of aircraft structures. Antenna design, measured and computed results, and performance are discussed. Data show measured and computer data to be in agreement.
In making microwave radiometer calculations of sea surface temperature, it is necessary to consider the errors resulting from the antenna radiation pattern. This is especially true for antennas with high sidelobes that are scanned in viewing angle and for antennas with high cross-polarized components. It is concluded that the plane wave brightness temperature is not by itself sufficient to describe the true radiometer temperature of the sea surface. This discrepancy can be attributed to one or more of the following: failure to use the total radiation pattern, error in determining the sea surface dielectric constant, error in sky model profile, or radiation pattern spillover onto water surroundings.
Log-helix conical antennas were examined as a way to satisfy the requirement for circular polarization of antennas for spacecraft use. It was concluded that a multiple-helix antenna which allows the helix lead angle to be changed can be used when the radiation and directivity in the direction of the reception point must be changed during flight.
A simple procedure is described for determining the excitation coefficients of an array feed which compensates for the surface distortion of a reflector antenna to improve the radiation pattern in such a way as to approximate the performance of the undistorted antenna. A computer simulation for a practical feed array is presented as an example of compensation for the distortion of an actual antenna.
The reflector antenna may be thought of as an aperture antenna. The classical solution for the radiation pattern of such an antenna is found by the aperture integration (AI) method. Success with this method depends on how accurately the aperture currents are known beforehand. In the past, geometrical optics (GO) has been employed to find the aperture currents. This approximation is suitable for calculating the main beam and possibly the first few sidelobes. A better approximation is to use aperture currents calculated from the geometrical theory of diffraction (GTD). Integration of the GTD currents over and extended aperture yields more accurate results for the radiation pattern. This approach is useful when conventional AI and GTD solutions have no common region of validity. This problem arises in reflector antennas. Two dimensional models of parabolic reflectors are studied; however, the techniques discussed can be applied to any aperture antenna.
The Juno mission to Jupiter requires an antenna with a torus-shaped antenna pattern with approximately 6 dBic gain and circular polarization over the Deep Space Network (DSN) 7-GHz transmit frequency and the 8-GHz receive frequency. Given the large distances that accumulate en-route to Jupiter and the limited power afforded by the solar-powered vehicle, this toroidal low-gain antenna requires as much gain as possible while maintaining a beam width that could facilitate a +/-10deg edge of coverage. The natural antenna that produces a toroidal antenna pattern is the dipole, but the limited approx. = 2.2 dB peak gain would be insufficient. Here a shaped variation of the standard bicone antenna is proposed that could achieve the required gains and bandwidths while maintaining a size that was not excessive. The final geometry that was settled on consisted of a corrugated, shaped bicone, which is fed by a WR112 waveguide-to-coaxial- waveguide transition. This toroidal low-gain antenna (TLGA) geometry produced the requisite gain, moderate sidelobes, and the torus-shaped antenna pattern while maintaining a very good match over the entire required frequency range. Its "horn" geometry is also low-loss and capable of handling higher powers with large margins against multipactor breakdown. The final requirement for the antenna was to link with the DSN with circular polarization. A four-layer meander-line array polarizer was implemented; an approach that was fairly well suited to the TLGA geometry. The principal development of this work was to adapt the standard linear bicone such that its aperture could be increased in order to increase the available gain of the antenna. As one increases the aperture of a standard bicone, the phase variation across the aperture begins to increase, so the larger the aperture becomes, the greater the phase variation. In order to maximize the gain from any aperture antenna, the phase should be kept as uniform as possible. Thus, as the standard bicone fs aperture increases, the gain increase becomes less until one reaches a point of diminishing returns. In order to overcome this problem, a shaped aperture is used. Rather than the standard linear bicone, a parabolic bicone was found to reduce the amount of phase variation as the aperture increases. In fact, the phase variation is half of the standard linear bicone, which leads to higher gain with smaller aperture sizes. The antenna pattern radiated from this parabolic-shaped bicone antenna has fairly high side lobes. The Juno project requested that these sidelobes be minimized. This was accomplished by adding corrugations to the parabolic shape. This corrugated-shaped bicone antenna had reasonably low sidelobes, and the appropriate gain and beamwidth to meet project requirements.
The purpose of this paper is to analyze the interference to the Space Station Ultrahigh Frequency (UHF) Communication Subsystem (UCS) antenna radiation pattern due to its environment - Space Station. A hybrid Computational Electromagnetics (CEM) technique was applied in this study. The antenna was modeled using the Method of Moments (MOM) and the radiation patterns were computed using the Uniform Geometrical Theory of Diffraction (GTD) in which the effects of the reflected and diffracted fields from surfaces, edges, and vertices of the Space Station structures were included. In order to validate the CEM techniques, and to provide confidence in the computer-generated results, a comparison with experimental measurements was made for a 1/15 scale Space Station mockup. Based on the results accomplished, good agreement on experimental and computed results was obtained. The computed results using the CEM techniques for the Space Station UCS antenna pattern predictions have been validated.
The design verification of the LANDSAT-D antenna subsystem is addressed. In particular, the analysis of the antenna radiation patterns utilizing a full scale mockup of the LANDSAT-D satellite is discussed. Test antennas included two S-Band shaped beam antennas, two S-Band omni unit radiators (to operate in array), a GPS antenna, an X-Band shaped beam antenna, and one S-Band high-gain parabolic antenna.
Large aperture in-space antennas radiation pattern measurement from large launch vehicles and Apollo program
A horn antenna, combining two propagation modes at selected power ratios, reduces side lobes, and improves the radiation characteristics. Noise and unwanted signals are considerably suppressed.
Time-division multiple-access TDMA multichannels radio communication system implements scheme of temporal and spatial multiplexing of signals to approximate effect of spherical antenna radiation pattern. Signal to be transmitted sped up by factor of n and transmitted in n replicas via n antennas. During reception, incoming signal processed by use of maximum-signal-selection or diversity-reception demodulated-signal-combining technique.
A mathematical tool is developed for evaluation of antenna radiation pattern effects on the shuttle orbiter S band quad antennas. A ray optics approach is used which includes multiple internal reflections with special consideration to reflection from the metallic orbiter skin. Significant depolarization may occur as the angle from the normal increases. The effect of changing tile thickness on the beamwidth of the upper quads versus the lower quads results in a small increase in the lower quad beamwidth compared with the beamwidth in the upper quads. The optimization and evaluation of the S band quads and the computer tool developed may be used to evaluate other shuttle orbiter antennas.
A low gain, circularly polarized, L-band antenna; a low gain, linealy polarized, L-band antenna; and a low gain, circularly polarized, upper hemisphere, VHF satellite communications antenna intended for airborne applications are described. The text includes impedance and antenna radiation pattern data, along with physical description of the construction of the antennas.
The material in this Section will provide the novice Flight Test Engineer (FTE) with a brief overview of the radar cross section (RCS) concept. Brief details of radar range descriptions, operations, target calibrations, and data reduction are included. It is noted that these range operations concentrate on the "static" test range rather than the much more sophisticated "dynamic" test range. The dynamic test range is what the FTE will probably work with. Radar reflectivity measurement has developed over the last two decades from a relatively simple endeavor involving the measurement of target RCS amplitude statistics to involving wide band, coherent systems that can measure high resolution images of targets as well as, in many cases, the polarization and phasing properties. This rapid growth in RCS technology has occurred because of the increased use of radar in today's commercial and military systems. In general, the goal for commercial systems is to enhance radar reflectivity, whereas the military goal is to reduce radar reflectivity. Also, classification and identification are important for military purposes because in adverse weather radar may be the only system that may be capable of separating enemy targets from friendly ones. This Section will discuss the fundamentals of RCS. Since the flight test techniques associated with RCS measurements are very similar to those of antenna pattern measurements, both will be presented at the same time in Section 19B Antenna Radiation Pattern Measurements.