An aperture-coupled small microstrip antenna with enhanced bandwidth

There has been considerable interest in the development of small microstrip antennas for personal communication. Common techniques for reducing the size of a microstrip antenna is to employ a substrate with high dielectric constant and/or to incorporate a shorting pin in a microstrip patch. It is well-known, however, that the bandwidth of the microstrip antenna becomes narrower as the size of the antenna becomes smaller. Consequently, it is difficult to achieve an impedance bandwidth of more than 3% for small microstrip antennas. It is also possible to enhance the bandwidth without enlarging the size of the antenna structure by designing a matching network in the feedline. We have applied this technique to the aperture-coupled small antenna-specifically, an open-circuited stub connected in shunt with the microstrip feedline. To further enhance the bandwidth of the antenna, an additional shunt stub and multiple shorting pins an incorporated. In this paper, the design of the aperture-coupled antenna with shunt stubs and shorting pins is described, and experimental data for the return loss and radiation pattern of the antenna are presented.