Wideband quasi-log-periodic microstrip antenna

Abstract

The paper describes a new design method for a wideband array of log-periodically scaled microstrip resonator antennas. The radiating elements are series-fed by a simple coplanar microstrip network. This network consists of an open-circuited feed line with a branch line connected to each radiating element. Both a network and a radiating model for the complete structure are explained. These models predict with good accuracy the input impedance and the radiation pattern as a function of frequency. The results for a 5-element S-band antenna are presented as an illustrative example. This antenna combines a good impedance match (VSWR ≤ 2.6) with a reasonable power gain in broadside direction (> 5.5 dB) over a 22% bandwidth. This means a tenfold increase in the bandwidth in comparison with a single microstrip resonator antenna.