Design of Wideband and High-Gain Slotline Antenna Using Multi-Mode Radiator

In this paper, a novel wideband slotline antenna with high gain characteristic is presented by using a multi-mode radiator under the circumstance of the optimized ground plane. The proposed antenna is analyzed from a traditional slot antenna with one full-wavelength radiation mode. Subsequently, two pairs of slot stubs are symmetrically loaded along the arms of the initial antenna near the nulls of the magnetic current of the full-wavelength radiation mode. By suitably choosing the lengths of the loaded stubs, extra two radiation modes can be introduced and merged with the full-wavelength one, resulting in a wide impedance bandwidth with three resonances. Finally, the size of the ground plane and locations of stubs are investigated to suppress the sidelobes and ensure high gain within the impedance bandwidth. For validation, a prototype antenna is fabricated and its electrical performances are measured. The experimental results show that the operating fractional bandwidth (FBW) of the proposed antenna can be effectively increased to 40.8% while keeping the inherent narrow slot structure. Besides, the measured average peak gain and its corresponding ripple within the impedance bandwidth are 6.2 dBi and 1.1 dB, respectively, and the radiation patterns are maintained constant. Compared with the reported works, the proposed design can allow a slotline antenna to achieve high gain and constant radiation patterns in a wide bandwidth simultaneously.