Simple Triple-Mode Dual-Polarized Dipole Antenna With Small Frequency Separation Ratio

A triple-mode dual-polarized dipole antenna topology with a very small frequency separation ratio is proposed. The antenna has a simple structure with a very low manufacturing cost while maintaining a good performance. A conventional dipole is fed by a feeding network also acting as a radiator to generate a second resonant mode. A shorted conductor loaded to the dipole is used to excite a third resonant mode. It is shown that the three modes can be tuned in order to cover different sets of applications. By fusing the two higher resonances, an antenna with a lower band and a very wide higher band can be obtained. Two orthogonal linear polarizations are achieved by integrating two of the aforementioned topologies. The conceptual structure is prototyped and measured. The realized antenna has a lower band of 2.38-2.54 GHz and a higher band of 3.11-4.15 GHz. Its electrical size is 0.8 × 0.8 λ
²
, with a profile of 0.27 λ (λ is the wavelength in free space at 2.4 GHz). The mutual coupling between the two ports is below -20 dB, which is quite beneficial for the diversity performance in multiple-input-multiple-output (MIMO) systems.