Last October, a radar antenna wreaked havoc at Boston's Logan Airport. According to the Boston Globe, test results fingered antenna as the cause of erroneous blips on their air-traffic controllers' radar screens. Those blips or "false targets" set off collision alarms. Although a replacement radar antenna resolved the issue, the fix did not come until many flights were delayed over two days' time. In addition, the Deferal Bureau of Investigation (FBI) had to be called in to make sure it was not a terrorist-related problem. As this example shows, radar antennas remain an extremely vital part of the world's day-to-da operations. As far as technology and innovation are concerned, however, many newer antennas far outpace them.

Most radar antennas simply comprise a reflector and antenna feed capable of sending and receiving large pulses. The time of arrival (TOA), angle of arrival (AOA), and other characteristics of those pulses pinpoint where things are and how fast they are moving. Radar antennas are used in marine, defenense, aviation, and countless other applications. Because the demand for them remains steady, a plethora of companies supply them. Examples include Rhode & Schwarz, Garmin, and more. M/A-COM (Lowell, MA), for example, offers a 2 x 2 patch-array, radar-altimeter antenna that boasts a frequency of 4.2 to 4.3 GHZ and a peak gain of more than 7.0 dBil. The gain over ±22.5 deg. is more than 4.5 dBil. In contrast, a radar-altimeter antenna from Rozendal Associates, Inc. (Santee, CA) flaunts a 50-deg., 3-dB beamwidth with 10 dBi of gain. It operates from 4.2 to 4.4 GHz.

Such radar antennas perform their designated functions very well. compard to the antennas designed for mobile applications, however, they are physically much larger. In the area of embeddable chip antennas, for example, Antenna Factor (Grants Pass, OR) recently released two new models (Fig. 1). By using multilayer, low-temperature confired-ceramic (LTCC) technology, they were able to attain a size of 16 x 3 x 2 mm. The antennas offer a 50-Ω characteristic impedence, omnidirectional pattern, and greater than unity gain with a linear polarization. Their usuable bandwidth is 10 MHz (868 and 916 MHz) and 180 MHz (2.45 GHz). Among their numerous target applications are Bluetooth, IEEE 802.11, telemetry, data collection, industrial process monitoring, and external-antenna elimination.

In the cellular arena, a new broadband antenna is targeting the high and low ends of the frequency band to ensure consistent coverage for both the uplink and downlink sides of a call. EMS Technologies, Inc.'s (Atlanta, GA) Controllable Radiating Aperture (Cobra) line of vertical electrical downtitl antennas is designed to operate in the frequency spectrum 1710 to 2180 MHz. Aside from the traditional 1900-MHz spectrum, the QuadPol Cobra antenna can support the soon-to-be-released 1700-MHz and 2100-MHz frequencies. It can therefore continue to be deployed for 1900-MHz coverage while being used where new UMTS spectrum is utilized. The QuadPol Cobra offers two crosspol, 45-deg. antenna networks within a single 12-in. wide atenna package. It has a return loss of 17.5 dB across the entire board.

With a new tri-band, fiberglass omnidirectional antenna, Antenex, Inc. (Glendale Heights, IL) also is anticipating the demand for a GSM/UMTS frequency antenna (Fig. 2). The FGT880/21703 antenna targets multiple frequency ranges including GSM900 (870 to 960 MHz), GSM1800 (1710 to 1880 MHz), and UMTS (1900 to 2170 MHz). It boasts a UV-treated radome that resists sun damage and is rated to withstand 125- mph wind velocities.

Non-line-of-sight (NLOS) broadband wireless is spurning antenna development as well. Pacific Wireless (Bluffdale, UT) has come out with a 900-MHz, vertically polarized sector antenna with 120- deg. horizontal beamwidth and 13 dBi gain. The SA9-120-13 operates in the 860-to-960-MHz frequencies. These sector- antenna systems are constructed of a heavy-duty aluminum extrusion and covered with a UV-resistant ABS radome.

In February, Pacific Wireless announced a wideband Yagi antenna line for the 860- to-960-MHz frequency range. These antennas are available in 9, 11, and 13 dBi. This NLOS-series antenna system is constructed of stainless steel. The elements are each welded to the main beam for permanent attachment. By ensuring high conductivity across the antenna surface, these welded elements promise more consistent signal performance. The antennas boast high gain and good frontto- back performance to minimize external interference.

Although all of these products are noteworthy, recent years have seen even more cutting-edge antenna technologies. Specifically, “smart” antennas have garnered a lot of industry attention. A smart-antenna system merges different antenna elements with signal processing. As a result, it can optimize its radiation or reception pattern automatically according to the signal environment. ArrayComm (San Jose, CA) has been at the forefront of this technology. Its software currently runs in a plethora of base stations.