The widely used transversely corrugated surfaces and other alternative surfaces having the same anisotropic surface impedance deserve a common name. Here it is proposed to call them soft surfaces by analogy with the soft surfaces in acoustics. In the same way artificially hard surfaces are defined. Cylindrical hard waveguides of any cross-sectional shape can support TEM waves.

Definition of artificially soft and hard surfaces for electromagnetic waves

A dual-reflector microwave antenna comprises the combination of a paraboloidal main reflector having an axis; a waveguide and dual-mode feed horn extending along the axis of the main reflector, a subreflector for reflecting radiation from the feed horn onto the main reflector in the transmitting mode, and a shield extending from the outer edge of the main reflector and generally parallel to the axis of the main reflector, the inside surface of the shield being lined with absorptive material for absorbing undesired radiation. The subreflector is shaped to produce an aperture power distribution that is substantially confined to the region of the main reflector outside the shadow of the subreflector. The support for the subreflector is preferably a hollow dielectric cone having a resonant thickness to cause energy passing through said cone to be in phase with energy reflected off of said cone so as to achieve phase cancellation.

Dual reflector microwave antenna

A horn antenna for radiating or receiving a microwave is provided with a plurality of axially spaced radial fins fixedly mounted on the outer surface of the horn, which fins form a plurality of radial grooves and a front axial groove each having a depth of approximately equal to a quarter of a wavelength of the microwave. Those fins and grooves form a choke surface-wave structure which improves the radiation pattern and reduces undesired radiation and side lobe. A multimode horn arrangement for a higher frequency wave is employed for the horn so that two different frequency waves are efficiently radiated or received at a single horn antenna with a reduced side lobe and an excellent cross polarization characteristic.

Horn antenna with a choke surface-wave structure on the outer surface thereof

Channel Optimization in Half Duplex Communications Systems is provided herein. Methods may include obtaining at a first terminal, radio frequency (RF) spectral information local to the first terminal, analyzing at the first terminal, RF spectral information for a second terminal that is not co-located with the first terminal, transmitting data to the second terminal on a second terminal optimal frequency band, and receiving data from the second terminal on the first terminal optimal frequency band, where the first terminal optimal frequency being based upon the RF spectral information local to the first terminal.

Channel optimization in half duplex communications systems

An improved subreflector antenna with lower sidelobes than prior art subreflector antennas is disclosed herein A tapered, anisotropic, corrugated subreflector is attached to a waveguide and located at the focus of a near-parabolic deep dish main reflector The subreflector has corrugations of varying depth The varying depths of the corrugations result in varying reactance, or reactance taper, of the subreflector This taper is designed in such a manner to guide or steer the energy from the antenna feed to the main reflector in such a manner as to help assure sharply reduced sidelobes Further, the subreflector is physically shaped so as to further steer or guide the energy in the desired direction The deep geometry of the main reflector allows the reduced sized subreflector to be positioned within the rim of the main reflector such that the combination can be covered by a flat radome

Low sidelobe reflector antenna system employing a corrugated subreflector

A microwave antenna comprising the combination of a paraboloidal main reflector; a subreflector located such that the paraboloidal main reflector and the subreflector have a common focal point lying between the main reflector and the subreflector; a feed horn for transmitting microwave radiation (preferably symmetrically) to, and receiving microwave radiation from, said subreflector; and a shield connected to the peripheral portion of the subreflector and having an absorbing surface which reduces side lobe levels both by capturing the feed horn spillover energy and by reducing the diffraction of microwave radiation from the edge of the subreflector. The shield is preferably formed as a continuous axial projection extending from the periphery of the subreflector toward the main reflector substantially parallel to the axis of the feed horn. The reflective surface of the subreflector is suitably a section of an approximate ellipse.

Low side lobe gregorian antenna

The electromagnetic fields that can propagate through a parallel-plate waveguide having absorber walls are investigated, and it is shown that dominant TM/sup e//sub 10/ and TE/sup e//sub 10/ modes can propagate independently with both having a highly-tapered (cosine-type) transverse distribution, a phase velocity slightly exceeding the speed of light, and very low axial attenuation, especially for a wall-spacing large as compared to a free-space wavelength. In other words, such an absorber-guide acts life a corrugated waveguide having "lambda/4" teeth (balanced-hybrid mode) but it does so over virtually an unlimited bandwidth and with little sensitivity to the absorber's characteristics.

An Absorber-Wall Parallel-Plate Waveguide

A recently developed asymptotic technique is used to quickly determine the radiation fields and crosspolarisation discrimination (XPD) of the subject-type horns.

Y.B. Cheng

Papers

Low side lobe gregorian antenna

An Absorber-Wall Parallel-Plate Waveguide

Performance of corrugated and dielectric-loaded metallic-conical horns

Erratum: Performance of corrugated and dielectric-loaded metallic-conical horns