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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.

Abstract In this study, a simple technique is proposed to simultaneously achieve dual‐band characteristics and low mutual coupling between two planar inverted‐F antennas (PIFAs), which is one of the most popular antennas used in handset terminals such as mobile phones. The PIFAs initially operate only at a single band at 2.0 GHz (UTMS band). Although several solutions have been proposed to increase the operating frequency band as well as reduce the mutual coupling between multiple‐input multiple‐output antennas, most of them require adjustment of the original antenna size or configuration. This would be disadvantageous if these methods are applied under design conditions that hinder the adjustment of the original antenna. The proposed method uses a combination of linear parasitic elements (LPEs) and a bridge line (BL) and then loads them onto PIFAs. The loading of LPEs increases the operating frequency band at 2.4 GHz, which can help the PIFAs achieve dual‐band operation. Furthermore, the BL transmits opposite‐phase currents to cancel the coupling current between the two PIFAs. Consequently, the mutual coupling can be reduced to less than −10 dB in the dual band without having to adjust the original PIFAs.

Abstract A folded monopole antenna (FMA) with two different input impedances were investigated to develop an antenna that is robust to metal for applications in a space enclosed by metal objects. An antenna with a variable input impedance is required for improving its robustness to the metal. An FMA with a novel structure is proposed to control the input impedance using a simple configuration. The structure comprises six additional elements parallel to the FMA. However, the number is not limited to six. Some additional elements are electrically connected or disconnected depending on the requirement. Method of moment (MoM) and characteristics mode analysis (CMA) are used in the simulation. The MoM results demonstrate that the input impedance can be adjusted in a step‐wise manner based on the number of additional elements connected to the FMA. This result is similar to that of the input impedance of an FMA with different strip widths considering impedance step‐up ratios (SURs). Furthermore, the change in the antenna characteristics owing to the non‐connected additional elements is minimal. The CMA results reveal that the proposed antenna has the same operation mode as the FMA with different strip widths considering impedance SURs.

In this paper, a dual-band three-way power divider with unequally high power split ratio is proposed. The dual-band operation is achieved by using a two-section impedance transformer, and to reach a high split ratio, transmission lines with impractical high characteristic impedances are replaced with dual-band T-shaped structures. The design is conducted with a thorough analysis and systematic design procedure for facilitating the rapid development of the prototypes. To verify the effectiveness of the proposed design method, an example of a power divider with a power split ratio of 7:5:1 is investigated, fabricated, and measured on a Rogers RO4003C substrate. Good agreements between the simulation and measurement results are obtained. Compared with several three-way unequal dual-band power dividers in previous works of the others, our proposed power divider delivered high power split ratio while still retaining good performances of insertion loss, return loss, and isolation between output ports. [ABSTRACT FROM AUTHOR]