Article ID: 19.20220006
This letter presents a wideband slim monopole antenna operating on very-high-frequency (VHF) and ultra-high-frequency (UHF) bands. The monopole antenna is composed of a slim strip and a meander line loading. The monopole antenna is vertically mounted on the case of the radio station which is served as ground and modified with slots. The method of characteristic mode analysis (CMA) is used to design the proposed antenna. By loading the meander line, the resonant frequency of the characteristic mode 1 of the proposed antenna moves to the lower band and higher modes are effectively excited at the higher band, which leads to a wide impedance bandwidth. Moreover, by loading the slots on the case, the inverse currents of characteristic mode 3 on the case at higher band, having bad effects on radiation patterns, are canceled out. Hence, the gain at horizontal plane at higher band is improved. A prototype of the proposed antenna with a slim structure is fabricated and measured. The bandwidth (VSWR≤3:1) is 200-550 MHz (93.3%). The gain is greater than 0.5 dBi in the working band. The proposed antenna has omnidirectional radiation patterns and is suitable for backpacked radio station applications.
