Increasing bandwidth of orthogonally polarised omnidirectional antenna composed of halo and sleeve antennas

Abstract In this study, we developed and investigated a small‐diameter, low‐profile, wideband orthogonal‐polarisation multiple‐input multiple‐output (MIMO) antenna. A polarisation MIMO antenna is a combination of a modified sleeve antenna for vertical polarisation and a halo antenna with four parasitic elements for horizontal polarisation. Four parasitic elements vertically were loaded above and below the halo antenna, and a sleeve antenna with an upper sleeve structure was inserted inside the halo antenna to achieve a low profile, wideband antenna with a small diameter. Simulation and measurement results showed that the proposed antenna achieved a relative bandwidth of 10.1% (|S11| and |S22| ≤ −10 dB). For the lower frequency wavelength (λmin) in the required bandwidth, the diameter and height of the proposed antenna are 0.14λmin and 0.57λmin respectively. Additionally, it is capable of orthogonal‐polarisation isolation of approximately 20 dB within the operating frequency bandwidth.