While remaining vital for traditional applications like radar, new types of antennas with higher gain and different forms are being developed to support standards like UWB, WiMAX, and UMTS.
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.
Most recently, ArrayComm announced a collaboration with Texas Instruments (Dallas, TX). ArrayComm's Network MIMO software has been ported to TI's 1-GHz TMS320TCI6482 digital signal processor (DSP). This optimized DSP promises to perform at nearly twice the clock speed of other available solutions while consuming just 3 W of power. Thanks to the DSP's software-programmable nature, users will be able to upgrade their solutions to meet the needs of evolving standards. For operators, the combined technologies are expected to result in a fourfold improvement in wireless system coverage, data rates that are more than doubled, and up to a 10X increase in capacity.
The first element of this collaboration is a reference design for WiMAX infrastructure applications. By incorporating ArrayComm's Network MIMO software, it supports multiple-input/ multipleoutput (MIMO), adaptive-antenna-system (AAS), and combined MIMO/AAS modes. The software implements all of the WiMAX-profile antenna-processing aspects that have been approved by the WiMAX Forum Mobile Task Group (MTG) for IEEE 802.16e.
Another company also is vowing to boost network capacity through antenna technologies. Dubbed DiversityPlus, this family of RF chip-set products is designed around Magnolia Broadband's (Bedminster, NJ) algorithms for CDMA, UMTS, and WiMAX mobile terminals. By combining transmit RF signals from two antennas in a unique manner, wireless operators can increase their network capacity while improving coverage and data rates to the individual subscriber. The DiversityPlus algorithms reside in the ARM processor of the baseband IC. In April, Magnolia Broadband announced that it has conducted final field testing of DiversityPlus with a US-based CDMA carrier. The testing demonstrated that the technology is able to boost the CDMA wireless network's voice capacity by an average of 42 percent.
Of course, antennas also play a critical role in testing applications. An example is the new double-ridged broadband horn antenna from Schaffner EMC, Inc. (Edison, NJ). It offers a frequency range of 1 to 18 GHz. The BHA 9118 includes a precision N connector that provides good power-handling capability and an average voltage standing wave ratio (VSWR) of 1.5:1. The antenna offers field strength of 250 V/m at 1 m. Its typical gain is 5.5 to 15 dBi.
Because the antenna space is so diverse and new innovations are constantly emerging, the industry must improve its ways of evaluating antennas. Many companies are working on such test and measurement capabilities. Diamond Engineering (Diamond Springs, CA), for instance, has released version 5 of its DAMS 6000 Antenna Measurement System. This system provides a representation of a measured antenna with two-axis precision movement and advanced 3D measurement software. The platform features a frequency range of DC to 18 GHz. It offers 360-deg. horizontal rotation and 45-deg. elevation movement. The software provides up to 801 frequencies, a real-time measurement display, data import/export functions, and high-resolution 3D plots.
Such measurement systems should help the industry embrace newer antenna technologies. Traditionally, the form and functionality of antennas have been derived from older, more basic applications like radar. The value of such antennas and their applications clearly remains critical. With the rise of telecommunications, however, antennas began to evolve at a more rapid pace. The form and function of today's antennas are constantly changing to meet the demands of cellular standards, Ultra Wideband, WiMAX, and more. Whether those antennas incorporate software or the newest frequencyselective materials, this market will continue to occupy both the past and the present for the foreseeable future.