Fig. 1: A new microwave antenna design features a shorting bridge (right side) that changes the path along which current flows, improving performance for applications requiring a large frequency variation, or bandwidth. The colors represent current distribution, with blue representing areas of less current.
Reproduced from Ref. 1 © 2010 IEEE
The next generation of portable wireless devices will require antennas that work over a wide range (or band) of the microwave frequency spectrum while being small enough to fit into compact devices. The development of such ultrawide-bandwidth (UWB) antennas has been spurred by the recent release by the United States Federal Communication Commission of spectrum from 3.1 to 10.6 GHz.
Antennas defined on printed circuit boards can be very compact, but their performance for UWB frequency applications remains insufficient for some applications. Now, Zhi Ning Chen and co-workers at the Institute for Infocomm Research of A*STAR, Singapore, have designed a new printed antenna with superior performance across the entire 3.1–10.6 GHz spectrum.
The new antenna is 40 mm long, 18 mm wide and less than 1 mm thick. The design begins with a standard dipole antenna, which consists of a line that is split in its middle, an approach first conceived by Heinrich Hertz in 1886. To this, the researchers have added tapered edges and a ‘shorting bridge’, which connects the ends of the dipole (Fig. 1). The bridge makes the antenna a hybrid of the traditional dipole design, and the ‘loop’ design.
The shorting bridge increases the length along which current in the antenna can flow, leading to a corresponding decrease in the minimum frequency it can detect. This in turn increases the frequency bandwidth over which the antenna can operate, which is a key metric. In addition, by changing the path of current flow, the shorting bridge prevents large currents from flowing near to each other and in opposite directions, a phenomenon that tends to degrade antenna performance.
The net result is an improvement in the antenna efficiency, or gain. The researchers also found that it is better matched to the rest of the circuit in which it operates—a parameter known as ‘impedance matching’. Further, the observed reduction in variation of these various metrics with operating frequency, allows the antenna to better handle short-duration pulsed signals.
Commenting on the team’s next step, Terence See Shie Ping, a co-author of the paper, says: “the challenge is [to] further reduce antenna size while maintaining its impedance and radiation performance across the relevant spectrum.” The antenna is expected to be used in applications such as cellular phones and wireless networking products that take advantage of the newly released wireless spectrum.
The A*STAR-affiliated authors in this highlight are from the Institute for Infocomm Research.
