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In this letter, we present a systematic approach to design a compact dual-mode monopole-like patch antenna using characteristic mode analysis (CMA). The modal analysis of a slotted circular patch structure incorporating a new shorting pin loading technique is presented. To achieve a compact monopole-like antenna with the wideband operation, it is demonstrated that the first two significant modes with monopole-like patterns are the most suitable ones for dual-mode excitation. Based on the analysis of the modal currents and electric fields, four groups of shorting pins and four slots are introduced to individually tune the two modes, which facilitates the optimization. The effects of these slots and shorting pins on the resonant frequencies of the two modes are analyzed in detail. Finally, a CPW T-junction power divider is applied to simultaneously excite these two modes and suppress the undesired modes. Apart from a more compact form factor and higher gain than existing work, it also features a competitive gain-bandwidth per volume ratio.

This paper presents a broadside antenna with three ports operating at the same frequency. The TM030 and TM003 modes of a patch are excited by two coaxial cables to generate two orthogonal linear polarizations. The patch can be transformed into a slotted SIW cavity whose TE201 and TE102 modes are jointly excited by the third cable. A matching cavity and a matching patch are introduced to broaden the impedance bandwidth of the third port. The simulated results show that the isolations between these three ports are higher than 18 dB, even though the radiation patterns of the three ports are all broadside. The proposed three-port antenna can provide a solution to increase the number of the ports per unit area in outdoor massive MIMO antennas.