On the Matching of Microstrip-Fed Dielectric Resonator Antennas

As the permittivity of dielectric resonators decreases, it becomes difficult to feed the dielectric resonator antennas (DRAs) using direct microstrip lines. The variation of the resonant input resistance with the feed location becomes smaller, while the maximum achievable peak resistance dramatically drops to lower than 50 Ω in most cases. To satisfy the impedance matching, field matching, improve coupling to low-permittivity dielectric resonators, and further increase the antenna bandwidth associated with the dominant mode, without disturbing far-field properties, tapered microstrip line-fed DRAs are proposed, designed, fabricated and evaluated in this communication. Both measurements and simulation investigations are presented and the results are compared with other forms of microstrip feed lines. The impedance bandwidth can be 75% larger than the bandwidth achieved by the step-shape microstrip-fed DRA. Symmetrical radiation patterns with low cross-polarization levels (lower than -22 dB) and a gain ranging from 4.9 to 6.8 dBi, within the impedance bandwidth of the antenna, are observed in the measurements. It is also shown that the proximity coupled tapered microstrip line is an ideal feeding for high-permittivity DRAs in situations where the microstrip line cannot be positioned underneath the dielectric resonator. To verify, one such antenna is designed, simulated and experimentally investigated, obtaining satisfactory results.