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A sampling of EW antennas.

Perhaps no phase of electromagnetics is as venerable as the antenna. May 1988 marked the 100th anniversary of Heinrich Hertz's paper "On Electromagnetic Waves in Air and Their Reflection," the seminal antenna treatise. Literally thousands of books and journal articles dealing with antennas and their properties have been published in the century since then.

The variety of antennas is almost limitless. Scientists at the National Institute of Standards and Technology (Boulder, CO) are developing microantennas that are 60 [micro]m in diameter. The tiny antennas, lithographed in gold, are used to collect and deliver infrared energy in the 5- to 30-[micro]m region to superconducting detectors.

At the other end of the size spectrum are the electronically scanned, HF, over-the-horizon backscatter radar antennas built by the General Electric Co. This system, operating in the 5- to 28-MHz frequency range, uses a 3,630-ft transmitting antenna located in Moscow, ME, and a 4,980-ft receiving antenna 110 miles southeast at Columbia Falls, ME.

THE PHASED ARRAY ANTENNA

In addition to magnitude-spanning size variations, modern EW antennas may assume guises that have no similarity to their wire and tubing ancestors.

An antenna installation is simplified when the positions of the transmitting and receiving antennas are fixed. Then the antennas can be aimed for maximum signal reception and bolted into place on their supports. But when the direction of propagation or reception is variable, and the maximum signal is wanted, something must move. Traditionally this was accomplished by physically rotating or wobbling the antenna. In many of today's electronic warfare applications, the rotating or wobbling motion has been replaced by electronic scanning.

Electronic scanning is accomplished using a phased array antenna (PAA). In this embodiment, the antenna beam moves, not the antenna. Examples of contemporary systems which rely upon the PAA abound. Raytheon's Patriot missile system antenna unit is an integral group of four antennas housed in a common structure (see "High Marks for Military Radar", JED, May 1991). The main phased array consists of more than 5,000 receiver/transmitter modules.

SARs AND ISARs

Even more bizzare than antennas which sit still and are able to move their beams are antennas which don't exist -- virtual antennas.

Accurate identification of ground targets and reference points using airborne radar requires fine resolution. To achieve the desired resolution, modern EW systems are employing a synthetic aperture radar (SAR). This technology is based upon the generation of a virtual, very long antenna -- a synthetic aperture.

To understand the workings of the SAR, we first consider a long linear array of physical radiating apertures. Phased array technology has shown us that by properly adjusting the arrival times, or phases, of the output from the various apertures, a single beam can be made which can electronically scan in space. The synthetic aperture radar is the converse of this linear array. Only a single radiating element is used in most cases. This element illuminates a target from a moving platform. A series of radar views of the target, in which both phase and amplitude data are preserved, is stored in the memory of a computer. As the platform moves, the stored signals strongly resemble the signals that would have been collected had a long linear array been used. Thus, when the stored signals are subjected to the same operations as used with an actual array, the results resemble those gathered by a very long antenna array.

Rounding out the synthetic aperture radar picture is an interesting variation termed the inverse SAR or ISAR. Here, the motion of the image, rather than the motion of the radar, is used to synthesize a long, virtual antenna. In the general case, both the target and the radar may be in motion. ISAR brings the added information of high-resolution in the cross-range dimension. Scatterers at different cross-range positions on the target will have different velocities, hence different Doppler shifts, relative to the radar. With appropriate processing, this information can be transformed into a cross-range profile of the target to assist in pattern recognition.

ON TO THE SAMPLING

The challenge in sampling the vast array of antennas was to devise an approach which would allow meaningful tabulation of the almost limitless variations of this technology. Toward this end, JED has borrowed heavily from the taxonomy developed by John D. Kraus, director of the Radio Observatory and professor (emeritus) at Ohio State University, which appeared in "EW Antennas: Our Electronic Eyes and Ears" published in the January 1989 issue of Microwave Journal. Professor Kraus based his classification on the materials of construction of the antennas: (1) wire and tubing, (2) conducting sheets, (3) nonconducting dielectrics and (4) arrays of the initial three categories. These classes were further divided using the emission patterns of antennas -- omnidirectional, sector and steerable. This classification scheme was devised by Murray Simpson, the founder of Sedco Systems (now part of Raytheon ESD), in his article "EW Antennas," which appeared in the 1987 issue of the EW Design Engineer's Handbook.

Without a doubt, antennas are ubiquitous and come in many shapes and forms. Their importance to the EW world can be gauged by the response generated by this sampling. More than 20 manufacturers supplied data covering almost 100 antenna models. This data is tabulated in the following tables.

ANTENNA SURVEY RESPONDENTS

AEL Defense Corp. 305 Richardson Rd. Lansdale, PA 19446 215-822-2929 Fax: 215-822-2611 Circle No. 230

AIL Systems, Inc. Commack Rd. Deer Park, NY 11729 516-595-6714 Fax: 516-595-6814 Circle No. 231

American Nucleonics Corp. (ANC) 696 Hampshire Rd. Westlake Village, CA 91359 805-496-2405 Fax: 805-379-2392 Circle No. 232

Anaren Microwave, Inc. 6635 Kirkville Rd. E. Syracuse, NY 13057 315-432-8909 Fax: 315-432-9121 Circle No. 233

Chelton (Electrostatics) Ltd. Fieldhouse Lane Marlow, Buckinghamshire SL7 1LR England 011-0628-472072 Fax: 011-0628-482255 Circle No. 234

Condor Systems, Inc. 2133 Samaritan Dr. San Jose, CA 95124 408-371-9580 Fax: 408-371-9589 Circle No. 235

Electro-Metrics, Inc. (E-M) 100 Church St. Amsterdam, NY 12010 518-843-2600 Fax: 518-843-2812 Circle No. 236

Flam & Russell, Inc. (F&R) P.O. Box 999 Horsham, PA 19044 215-674-5100 Fax: 215-674-5108 Circle No. 237

GTE Government Systems Corp. 100 Ferguson Dr. Mountain View, CA 94043 415-966-3551 Fax: 415-966-4460 Circle No. 238

Huber + Suhner, Inc. (H&S) One Allen Martin Dr. PO Box 400 Essex, VT 05451 802-878-0555 Fax: 802-878-9880 Circle No. 239

Loral Randtron Systems 130 Constitution Dr. Menlo Park, CA 94025 415-326-9500 Fax: 415-326-1033 Circle No. 240

Lucas Epsco Inc. 99 South St. Hopkinton, MA 01748 508-435-2400 Fax: 508-435-2022 Circle No. 241

Microwave Applications Group (MAG) 3030 Industrial Pkwy Santa Maria, CA 93455 805-928-5711 Fax: 805-925-5903 Circle No. 242

Microwave Printed Circuitry (MPC) 81 Old Ferry Rd. Lowell, MA 01854 508-452-9061 Fax: 508-441-0004 Circle No. 243

Nurad Technologies, Inc. 2165 Druid Park Dr. Baltimore, MD 21211 410-462-1700 Fax: 410-462-1742 Circle No. 244

Precision Specialties Inc. (PSI) 8740 Shirley Ave. Northridge, CA 91324 818-349-9774 Fax: 818-349-4367 Circle No. 245

Technology for Communications International 222 Caspian Dr. Sunnyvale, CA 94089 408-747-6100 Fax: 408-747-6101 Circle No. 246

Tecom Industries 9324 Topanga Canyon Blvd. Chatsworth, CA 91311 818-341-4010 Fax: 818-718-1402 Circle No. 247

Transco Products, Inc. 1001 Flynn Rd. Camarillo, CA 93012 805-987-8007 Fax: 805-484-0830 Circle No. 248

TRW Avionics & Surveillance Gp. Military Electronics & Avionics Div. One Rancho Carmel San Diego, CA 92128 619-592-3469 Fax: 619-592-3885 Circle No. 249

Watkins-Johnson Co. (W-J) 2525 N. First St. San Jose, CA 95131 408-435-1400 x3508 Fax: 408-435-2793 Circle No. 190

[TABULAR DATA OMITTED]
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Title Annotation:electronic warfare
Publication:Journal of Electronic Defense
Date:May 1, 1993
Words:1231
Previous Article:The Joint Electronic Warfare Center.
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