Broadband, low-profile antenna for portable data terminal

The planar inverted F antenna (PIFA) and the closely-related quarter-wave microstrip antenna are well-known, low-profile antenna designs which offer broad bandwidth and high radiation efficiency. These antennas offer reduced size over traditional microstrip patch antennas because they operate at quarter-wave rather than half-wave resonance. The PIFA offers much improved bandwidth over the wire inverted F antenna from which it was derived. Nevertheless, only moderate impedance bandwidths have been achieved even with the use of external matching elements. Several approaches have been used to improve the bandwidth of PIFAs. One particularly good approach has been the use of an edge-coupled, parasitic quarter-wave resonator in what was termed a "radiation coupled inverted L" configuration. Here, two designs based on an arrangement of stacked, broadside-coupled resonators are presented. The lowest resonator is essentially a wide, flat PIFA while the upper resonator(s) is a dielectric loaded microstrip patch antenna. In contrast to stacked microstrip patch designs, the top resonator is directly fed, while the actual PIFA is capacitively coupled to the patch resonator. As will be shown here, this new design gives broad bandwidth (15 percent) in a package which protrudes only 1/40th of a wavelength (at center frequency) from the handheld unit to which it is mounted. This broad bandwidth design can thus serve as a low-profile multi-function antenna thereby reducing the number of antennas required for some handheld data terminals.