Wideband antenna using a multiple-mode slotline radiator: proposal and implementation

Abstract

A novel wideband antenna with a multiple-mode radiator on slotline is proposed. This slotline resonator is asymmetrically fed at a right angle by a short-ended microstrip line on the opposite side of the substrate. First, parametric studies are executed on frequency-dependent input impedance with respect to feeding positions and slot/strip widths, aiming at simultaneously exciting its first and second resonant modes for radiation. By properly choosing the port impedance, our initial predicted return loss exhibits the emergence of a wide operating band with a fractional bandwidth of 41.7% at 3.98 GHz, where two reflection zeros are created under dual resonant modes. Second, by introducing a quarter-wavelength impedance transformer, two 50-Ω microstrip-fed slotline antennas with short- or open-ended stubs in the feeding line are proposed and then designed for practical implementation of such a class of dual-mode slotline antennas. The measurements for these two antennas show that the impedance bandwidths are successfully achieved 40.0–41.0% as expected and the radiation patterns retain stable in the operating wideband with an antenna gain of about 4.0 dBi.