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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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62 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

High-Aperture-Efficiency Horn Antenna

A horn antenna (see Figure 1) has been developed to satisfy requirements specific to its use as an essential component of a high-efficiency Ka-band amplifier: The combination of the horn antenna and an associated microstrip-patch antenna array is required to function as a spatial power divider that feeds 25 monolithic microwave integrated-circuit (MMIC) power amplifiers. The foregoing requirement translates to, among other things, a further requirement that the horn produce a uniform, vertically polarized electromagnetic field in its patches identically so that the MMICs can operate at maximum efficiency. The horn is fed from a square waveguide of 5.9436-mm-square cross section via a transition piece. The horn features cosine-tapered, dielectric-filled longitudinal corrugations in its vertical walls to create a hard boundary condition: This aspect of the horn design causes the field in the horn aperture to be substantially vertically polarized and to be nearly uniform in amplitude and phase. As used here, cosine-tapered signifies that the depth of the corrugations is a cosine function of distance along the horn. Preliminary results of finite-element simulations of performance have shown that by virtue of the cosine taper the impedance response of this horn can be expected to be better than has been achieved previously in a similar horn having linearly tapered dielectric- filled longitudinal corrugations. It is possible to create a hard boundary condition by use of a single dielectric-filled corrugation in each affected wall, but better results can be obtained with more corrugations. Simulations were performed for a one- and a three-corrugation cosine-taper design. For comparison, a simulation was also performed for a linear- taper design (see Figure 2). The three-corrugation design was chosen to minimize the cost of fabrication while still affording acceptably high performance. Future designs using more corrugations per wavelength are expected to provide better field responses and, hence, greater aperture efficiencies.

Pickens, Wesley↗
NASA NTRS1973

High performance S-band horn antennas for radiometer use

Horn antennas of four types: pyramidal corrugated, conical corrugated, pyramidal dual mode and conical dual mode, have been constructed and evaluated for use as S-band radiometer antennas. Each of the structures is described and radiation patterns and impedance and resistive loss measurements including a layer of foreign material on a thin radome, are presented. A precision method for determining reflection losses is described using a multiprobe reflectometer technique. The same technique is also applied to the measurement of resistive losses by closing the ends of the antennas with short circuit plates and determining the losses from an accurate measurement of the reflection coefficient. The radiation patterns were recorded with the aid of a real-time digital computer. The stored patterns were then processed to yield gain and beam efficiency. It was concluded that it is possible to design a highly efficient antenna for radiometer use and to measure its parameters precisely. However, it was found that it is necessary to modify the conventional definition of beamwidth somewhat if this term is to be meaningful for radiometer applications.

Caldecott, R.↗
NASA NTRS1981

The design of an ultra-low sidelobe offset-fed 1.22m antenna for use in the broadcasting satellite service

A feed design and reflector geometry were determined for an ultra low sidelobe offset fed 1.22 meter antenna suitable for use in the 12 GHz broadcasting satellite service. Arbitrary constraints used to evaluate the relative merits of the feed horns and range of f/D geometries are: minimum efficiency of 55 percent, -30 dB first sidelobe level (relative to on axis gain), a 0 dBi plateau beyond the near in sidelobe region, and a Chebyshev polynomial based envelope (borrowed from filter theory) for the region from the -3 dB beamwidth points to the 0 dBi plateau region. This envelope is extremely stringent but the results of this research effort indicate that two steps of corrugated feed and a cluster array of small 1 lambda horns do meet the constraints. A set of performance specifications and a mechanical design suitable for a consumer oriented market in the broadcasting satellite service was developed. Costs for production quantities of 10,000 units/yr. are estimated to be around $150.

Janky, J. M.↗
NASA NTRS1989

A multiflare horn with 1-megawatt power handling capability

The design and testing of the prototype horn for the proposed 1-megawatt radar are described. The unique features of this square horn include a multiflare design in which flare angle changes rather than corrugations are used to generate the required higher-order modes. A five-port combining section is used at the input. The design of this section and the multiflare section are described. Measured radiation patterns are in good agreement with theoretical patterns.

Hoppe, D. J.↗
NASA NTRS1986

A simple circular-polarized antenna: Circular waveguide horn coated with lossy magnetic material

A circular waveguide horn coated with a lossy material in its interior wall can be used as an alternative to a corrugated waveguide for radiating a circularly polarized (CP) field. To achieve good CP radiation, the diameter of the structure must be larger than the free-space wavelength, and the coating material must be sufficiently lossy and magnetic. This device is cheaper and lighter in weight than the corrugated one.

Lee, C. S.↗
NASA NTRS1988

A simple circular-polarized antenna: Circular waveguide horn coated with lossy magnetic material

It is shown that a circular waveguide horn coated with a lossy material in its interior wall can be used as an alternative to a corrugated waveguide for radiating a circularly polarized (CP) field. To achieve good CP radiation, the diameter of the structure must be larger than the free-space wavelength, and the coating material must be sufficiently lossy and magnetic. The device is cheaper and lighter in weight than the corrugated one.

Lee, Choon S.↗
NASA NTRS1988

Compound-taper feed horn for NASA 70-m antennas

A novel X-band feedhorn was designed for the Deep Space Network (DSN) 70-meter antennas. The feedhorn is a compound-taper structure consisting of a corrugated flared section and a corrugated straight section. This feedhorn is designed to closely imitate the characteristics of the standard feedhorn, while providing the proper phase center location, without adding any significant loss to the system. The use of the existing feedhorn and the ease of manufacturing the corrugated straight section have resulted in major overall cost savings.

Manshadi, Farzin↗
NASA NTRS2012

Low-Gain Circularly Polarized Antenna with Torus-Shaped Pattern

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.

Amaro, Luis R.↗