Bandwidth Enhancement of Double-Dipole Quasi-Yagi Antenna Using Stepped Slotline Structure

Abstract

In this letter, a method to enhance the bandwidth of a double-dipole quasi-Yagi antenna using a stepped slotline structure is presented. A stepped slotline with different widths is employed in the coplanar stripline connecting the two dipoles in order to improve impedance matching over a wide frequency band. In addition, two parasitic strip directors are appended to the antenna to enhance the gain in the high-frequency region. A detailed design procedure for the proposed antenna is explained, along with a performance comparison of the input impedance, voltage standing-wave ratio (VSWR), and realized gain. To demonstrate the effectiveness of the proposed design method, a prototype antenna operating in the 1.60–3.60 GHz frequency range with a gain $ > 6~\hbox{dBi}$ is designed and fabricated on an FR4 substrate. Experiment results show that the proposed antenna has the desired impedance characteristics with a frequency band of 1.59–3.64 GHz (78.4%) for a ${\rm VSWR} , and a stable gain of 6.4–7.4 dBi in the 1.60–3.60-GHz frequency range. Moreover, a measured front-to-back ratio $ > 10~\hbox{dB}$ is obtained.