An Autonomously Adaptable Self-Structuring Patch Antenna
The patch antenna (PA) is widely used in communications and radar systems. Its primary benefits over other types of antennas are that it is conformal, and can thus be placed onto the surfaces of aircraft and land vehicles, that it is polarization diverse (can be configured for multiple polarizations), and that it is simple to construct. A typical PA is designed to work in a narrow band around a single frequency, with the resonant frequency determined by the dimensions of the patch. Many antenna applications require broader bandwidths or must be usable at two or more discrete frequencies. Designing a PA for broadband or simultaneous multi-frequency operation requires a great deal of effort.
Description of Technology
The Self-Structuring Patch Antenna (SSPA) is fabricated like a traditional PA with the patch etched onto a conductor-backed circuit board. The signal is fed with a coaxial cable attached to the conducting backplane. The center conductor of the cable extends through the dielectric layer of the circuit board to contact the patch. In the SSPA configuration several additional pins are introduced between the ground plane and the patch. These pins are either shorted to the ground plane or left open-circuited by the action of computer-controlled switches mounted beneath the ground plane. When a pin is shorted to the ground plane, it perturbs the field within the cavity, altering the behavior of the antenna. By having a multiplicity of pins, the field within the cavity, and thus the antenna radiation pattern, can be dramatically altered as the switches are opened and closed. Each combination of switch settings creates a different "state" for the antenna. Thus for an SSPA with N pins, there are 2^N possible antenna configurations available. A fast search algorithm is used to find the optimal configuration based on the feedback value of a selected parameter such as SWR, signal strength or signal-to-noise ratio.
- Simplified design: The SSPA requires minimal design. The pin state configuration is selected "on the fly" to assure that the antenna is always delivering the best performance.
- Improved flexibility: The SSPA may be configured through feedback to operate at any frequency within a broad range. It can also be configured to operate at several arbitrary frequencies simultaneously. Thus, a single SSPA can be used to support multiple, frequency diverse applications (GPS and satellite radio, for example).
- Wider bandwidth: The instantaneous bandwidth of the SSPA may be broadened by optimizing the patch to work at several adjacent frequencies.
- Enhanced adaptiveness: Unlike a conventional PA, which is designed for a specific environment and set of operating conditions, the SSPA can adapt as the environment changes. It can even be reconfigured if damaged, with the remaining portion of the patch compensating for the damaged portion.
Applications include GPS (SSPA can simultaneously operate at the required L1 and L2 frequencies), mobile devices (adaptively change operating frequencies) and military applications where survivability is paramount.
Edward Rothwell, Lynn Greetis
For Information, Contact:
Michigan State University