Antenna designers have long been faced with one of the more challenging tasks for any component in a high-frequency system: deliver reliable performance without physically calling attention to the component. Newer antennas may support multiple frequency bands, but they must do so with the smallest physical profile possible. As a result, antennas are being designed in more creative ways, such as body-worn components or as conformal arrays that fit the shapes of their target systems. Still, they are counted upon to transmit and receive reliably, and often under less-than-ideal environmental conditions.

As wireless services continue to extend outward in support of voice, data, and video for commercial sectors, antennas are being designed to handle multiple frequency bands [such as cellular and wireless-local-area-network (WLAN) bands] in a departure from traditional antenna designs for single-function use. The latter category includes radio antennas for amplitude-modulated (AM) and frequency-modulated (FM) radio bands, as well as television antennas for very-high-frequency (VHF) and ultra-high-frequency (UHF) broadband bands. An emerging application area in commercial and military antenna applications is for ultrawideband (UWB) communications, in which a large continuous segment of bandwidth must be covered.

Of course, the market for “textbook” UWB communications applications from 3.1 to 10.6 GHz may not emerge in the consumer world, with only variants to appear in military applications such as for communications with unmanned aerial vehicles (UAVs) and unmanned ground vehicles (UGVs). Current definitions for UWB frequencies vary from manufacturer to manufacturer, but the principle of the antennas is to provide adequate bandwidth to enable multiple communications functions.

For example, the Fractus Media+™ UWB Chip Antenna from Fractus is a monopole UWB chip antenna that measures just 10 x10 x 0.8 mm, making it well suited for adding short-range wireless capability to digital cameras and other consumer electronic devices. The tiny antenna operates with more than 60% radiation efficiency and more than 4 dBi gain from 3.1 to 5.0 GHz using linear polarization. It exhibits less than 2.0:1 VSWR and works across operating temperatures from -40 to +85°C.

Perhaps closer to the classic definition of UWB frequencies spanning 3.1 to 10.6 GHz, Pharad developed its octane® wearable UWB antenna (Fig. 1) for applications from 3 to 10 GHz. The UWB antenna can be integrated with military helmets and tactical vests, and includes a waterproof cover. Like the Fractus chip antenna, it works with vertical polarization and delivers 0-dBi gain at 3 GHz, 5-dBi gain at 6 GHz, and 3.5-dBi gain at 9 GHz. It can handle as much as 5 W power with less than 2.50:1 VSWR. The wearable UWB antenna measures just 2.25 x 2.00 in. with a 16-in. cable terminated in an SMA connector. The antenna offers a near omnidirectional pattern with less than 2 oz. radiator weight.

1. The octane® wearable antenna can handle UWB communications from 3 to 10 GHz. (Photo courtesy of Pharad.)

Another UWB design from OMRON Corp. is the model WXA-N2SL surface-mount polymeric antenna; this offering is taking aim at the WiMedia Alliance UWB BandGroup 1 (from 3.1 to 4.9 GHz). The antenna is optimized for this frequency range and can effectively suppress out-of-band noise to function in the manner of a wireless Universal Serial Bus (USB). Yet another UWB antenna design is the BroadSpec™ planar elliptical dipole antenna from Time Domain, designed for use with the firm’s PulseON 400 ultrawideband module. The antenna yields about 3 dBi gain from 3 to 6 GHz with an omnidirectional radiation pattern and about 90% nominal radiation efficiency.