What is in this article?:
- Antennas Reach For More Bands
- Research-Based Requirements
Antennas continue to evolve into smaller configurations, sometimes adapting to fit the shapes of their systems.
Research applications typically drive exotic requirements for antennas. The US National Oceanic and Atmospheric Administration (NOAA) and its Environmental Technology Laboratory recently posted its need for performing wide-area mapping of soil moisture and salinity by means of an advanced antenna system and receiving electronics. The application calls for a large scanning antenna with aerodynamic form, narrow beamwidth, high efficiency, and dual polarization.
What poses a challenge for antenna designers is that the antenna system must operate at L-band frequencies from 1400 to 1427 MHz as well as at C-band frequencies from 6.0 to 6.5 GHz. It must deliver stable performance even with changes in environmental conditions. One of the proposed solutions for this antenna system, by FIRST RF Corp., involves the use of dual-polarized antennas to cover the two different frequency bands. The feeling is that a combined-frequency antenna would compromise the performance of either frequency and pose additional complexities in the antenna’s radome structure.
Satellite-communications (satcom) antennas are usually associated with fixed installations, but can also be called upon for mobile applications, such as onboard aircraft. Rantec Microwave Antennas, a leading supplier of space-qualified antennas, has long offered 11.5-in.-diameter airborne antennas for Ku-band transmit/receive satcom applications. The firm has also developed Ka-band airborne satcom antennas that can replace earlier Ku-band airborne antennas while achieving 48.6 dBW output power at 1-dB compression using dual circular polarization. The Ka-band antenna, with its 12-in. aperture, handles two frequency bands: band 1 with receive range of 19.5 to 20.2 GHz and transmit range of 29.0 to 30.0 GHz and band 2, with receive range of 20.2 to 21.2 GHz and transmit range of 30.0 to 31.0 GHz. The satcom antenna is designed for 11 A at +28 VDC and weighs 26 lbs. It is built for operating temperatures from -55 to +60°C.
Because the growing modern communications infrastructure relies so heavily on antennas, some companies such as CommScope have tried to simplify and improve the task of making microwave backhaul connections between cellular communications sites. The firm’s Sentinel line of antennas are designed to deliver European Telecommunications Standards Institute (ETSI) Class 4 performance in smaller, more compact units that enable efficient use of spectrum and easy installation and maintenance. The rugged antennas are built to survive wind speeds to 250 km/h (155 mph). They support higher-order modulation schemes for high capacity, and provide 10 dB or more off-axis interference discrimination.
A circuit technology that is receiving more attention among antenna designers, substrate integrated waveguide (SiW) technology, combines the traits of microstrip circuits and larger waveguide structures. It starts with a printed-circuit-board (PCB) substrate, with top and bottom metal layers forming effective waveguide walls. Parallel rows of viaholes are added to form the sidewalls of a waveguide structure on the PCB, including integrated antennas and filters. SiW technology, which can be manipulated with the aid of electromagnetic (EM) software simulation tools, can be used for form compact cavity-backed antenna structures. The EM software enables a designer to try possible layouts without fabricating them, closely projecting the performance levels from each approach.
2. This low-profile UHF antenna provides 3-dBi gain in a housing that is only 3.4 in. high. (Photo courtesy of Laird Technologies.)
Among traditional antenna designs, such as for UHF communications, Laird Technologies managed to create a low-profile UHF antenna that is only 3.4 in. high: it’s Phantom Elite® UHF antenna (Fig. 2). The antenna design, which has earned several US patents, is suitable for public safety, military mobile, and fixed-radio applications. The compact design is capable of power levels to 100 W across different segments of the frequency range from 410 to 512 MHz using vertical polarization. The antenna achieves an omnidirectional radiation pattern with 3-dBi gain and better than 2.0:1 VSWR.