Tall microstrip transmission lines for dielectric resonator antenna applications

Dielectric resonator antennas (DRAs) excited by tall microstrip transmission lines (TMLs) are investigated. Two different TML-DRA structures are proposed and the impact of TML parameters on the antenna performance is studied when low-loss and lossy substrates are used. To validate the effectiveness of this approach, a set of prototype antennas was fabricated, measured and compared with simulation results. A good agreement is obtained. It is found that by adjusting TML parameters, excellent impedance matching and coupling to low-permittivity DRAs are achieved even on high-permittivity substrates. The impedance bandwidth of a single-mode simple-shape rectangular DRA with ε_rd = 9 can be as high as 25%. The radiation efficiency of the antenna on extremely lossy substrates is significantly improved and based on the measured results over 80% efficiency with a gain ranging from 4.2 to 5.5 dBi along the impedance bandwidth can be expected. Since TML is a low-loss transmission line, the DRA is a low-loss radiator and low-permittivity DRAs can be well matched by TML, the TML-DRA forms an excellent wideband antenna system with high radiation efficiency.