Hal Schrank

Low sidelobe reflector antennas

A front feed reflector antenna with a dish reflector has a reflector focal length to reflector diameter ratio of less than 0.25. A wave guide is coupled to a proximal end of the dish reflector, projecting into the dish reflector along a longitudinal axis. A dielectric block is coupled to a distal end of the waveguide and a sub-reflector is coupled to a distal end of the dielectric block. A shield is coupled to the periphery of the dish reflector. The sub-reflector diameter is dimensioned to be 2.5 wavelengths or more of a desired operating frequency.

Approximations to the radiation resistance and directivity of circular-loop antennas

The purpose of this article is to derive approximate formulas for the radiation resistance (R), and the directivity (D) of circular loop antennas. It is shown that simple approximations to the Bessel functions can be employed, to accurately model the oscillatory behavior of the Bessel function integral for both small and intermediate-sized loop antennas. Furthermore, when these approximations are combined with the usual asymptotic contributions to the integral in the case of a large input parameter ka (a=loop radius, a=2/spl pi///spl lambda/) accurate and relatively simple results for R and D can be secured for all loop sizes. Numerical results can, if necessary, be obtained using a simple pocket calculator.<<ETX>>

Antenna Designer's Notebook-design curves for reducing the number of phase shifters in-phased arrays by subarraying

A major obstacle in the realization of large-aperture phased array antennas is the associated large number of phase shifters. The number of phase shifters can be reduced by assigning several radiating elements to one phase shifter. Each such group is called a subarray. As the subarray size increases, the FOV (field of view, or beam-steering range) generally decreases. A set of design curves that can be used to optimize the tradeoff between field of view and subarray area is presented.<<ETX>>

The shaped-beam polyrod antenna

The polyrod antenna (or the dielectric-rod antenna) has been known for some time. It is used primarily for its simplicity and unique pattern characteristics. The most interesting characteristic of this antenna is that the radiation pattern can be controlled not only by the cross section, dielectric properties, and length, but also by shaping its axis. By shaping the rod axis, various patterns can be obtained, some of them very useful. The antenna described paper has a typical polyrod pattern in the azimuth plane (H-plane), and a quasi-cosec/sup 2/ pattern in the elevation plane (E-plane).<<ETX>>

A Trilogy of Antenna Observations

Three observations are presented on (1) sidelobes of rectangular antennas; (2) maximum off-boresight antenna gain; and (3) antenna near-field as a function of direction.

Beam squint in parabolic reflector antennas with circularly polarized feeds [Antenna Designer's Notebook]

The beam squint phenomenon is an important design issue for modern reflector antennas, because it can affect the antenna pointing performance. For long-distance communications, like satellite or deep-space communications, this effect must be care- fully taken into account in order to avoid any degradation. In some design considerations, one may use the squint phenomenon to ones advantage in separating two RHC- and LHC-polarized beams. Squint was previously observed in offset parabolic reflectors with an on-focus circularly polarized feed [l], such as that shown in Figure 1. It must be emphasized that this squint only occurs for antennas with circularly polarized feed, but not for those for which the feed is linearly polarized.

Space Attenuation Chart [Antenna designer's notebook]

This graph provides a new convenient display of attenuation between antennas as a function of freouency and antenna separation in meters, feet, or miles (Friis transmission equation). Distances covered are 10 feet to more than 1000 miles in the frequency range of 10MHz to above 100GHz.

A Centennial of electromagnetics

A third of a century! When you say it that way, it sounds like a long time. To some of you here, it represents your entire 1 ife so far, and yet some o f us senior citizens have been in the antenna business even longer than that. But what is really remarkable to me is the fact that our field of interest antennas, o r to put it more generically, the business of electromagnetic radiation and reception is just about one century old!