This paper investigates the effects of parasitic elements on the performance of MIMO patch antenna. Multiple square parasitic elements are added in close proximity to each of the rectangular patch elements. These parasitic elements affect the electromagnetic field distribution and consequently reduce the mutual coupling. In addition, wider bandwidth is also achieved. Two MIMO antennas coupled in H-plane and E-plane are designed and measured to demonstrate the proposed concept. The measured results show that both designs have a wide impedance bandwidth of 14% with isolation of more than 20 dB across the whole band (with a small antenna profile of 0.05λ ₀ ). For 40-dB isolation, the H-coupled and E-coupled design achieve a bandwidth of 2.7% and 1.5%, respectively. Compared to other methods, the proposed method has much simpler structure, wider bandwidth and comparable improvement in isolation, with the tradeoff in larger antenna element size.

This paper presents a compact and simple reconfigurable antenna with wide-band, dual-band, and single-band operating modes. Initially, a co-planar waveguide-fed triangular monopole antenna is obtained with a wide operational frequency band ranging from 4.0 GHz to 7.8 GHz. Then, two additional stubs are connected to the triangular monopole through two p-i-n diodes. By electrically switching these p-i-n diodes ON and OFF, different operating frequency bands can be attained. When turning ON only one diode, the antenna offers dual-band operations of 3.3–4.2 GHz and 5.8–7.2 GHz. Meanwhile, the antenna with single-band operation from 3.3 GHz to 4.2 GHz can be realized when both of the p-i-n diodes are switched to ON states. The proposed compact size antenna with dimensions of 0.27λ₀ × 0.16λ₀ × 0.017λ₀ at the lower operating frequency (3.3 GHz) can be used for several wireless applications such as worldwide interoperability for microwave access (WiMAX), wireless access in the vehicular environment (WAVE), and wireless local area network (WLAN). A comparative analysis with state-of-the-art works exhibits that the presented design possesses advantages of compact size and multiple operating modes.

A novel wideband dual-cavity-backed circularly polarized (CP) crossed dipole antenna is presented in this letter. The exciter of the antenna comprises two classical orthogonal straight dipoles for a simple design. Dual-cavity structure is employed to achieve unidirectional radiation and improve the broadside gain. In particular, the rim edges of the cavity act as secondary radiators, which contribute to significantly enhance the overall CP performance of the antenna. The final design with an overall size of 0.57λ_o × 0.57λ_o × 0.24λ_o where λ_o is the free-space wavelength at the lowest CP operating frequency of 2.0 GHzb yields a measured -10 dB impedance bandwidth (BW) of 79.4% and 3 dB axial-ratio BW of 66.7%. The proposed antenna exhibits right-handed circular polarization with a maximum broadside gain of about 9.7 dBic.

This paper investigates the isolation of a multipleinput multiple-output (MIMO) antenna system consisting of two circularly polarized (CP) antennas with opposite rotating senses. The challenge in achieving a high isolation for this type of antenna system is analyzed and discussed. Based on this, a low-profile wideband design is proposed and demonstrated, in which the role of the decoupling structure is also explained. As a validation, an antenna prototype is fabricated and measured. The operating bandwidth, in which |S11| and axial ratio (AR) are respectively less than 10 dB and 3 dB, is 8.3% (5.25.65 GHz). Within this band, the measured peak realized gain in broadside direction is 6.2 dBi and the isolation is better than 26 dB. In comparison with other related works, the proposed antenna has one of the smallest spacing while maintaining high isolation characteristics in a relatively wide bandwidth with a low-profile structure.

In this paper, a systematic design procedure of a compact and broadband circularly polarized (CP) antenna is proposed. The antenna is first designed with a C-shaped monopole and then a C-shaped slotted patch is utilized to produce CP radiation in the lower frequency band. Thus, the antenna’s overall CP bandwidth is significantly increased. Additionally, unlike the conventional method in which the operation is verified by the simulated surface current distribution, characteristic mode analysis (CMA) is carried out to give more insightful into the different modes on the antenna and generation of circular polarization. The CMA also helps to realize a structural optimization and identify an efficient feed location. The optimized antenna prototype with compact size of 0.29λo × 0.29λo × 0.01λo (λo is the minimum wavelength at the minimum operation frequency) achieves a usable .10-dB reflection coefficient and 3-dB axial ratio fractional bandwidth of 91% (2.1.5.6 GHz). The antenna realized broadside gain is varied from 1.5 to 3.2 dBic within this measured overlapped bandwidth.

A method of using a simple single parasitic element to significantly enhance a 3-dB axial-ratio (AR) bandwidth of a crossed dipole antenna is presented. This approach is verified by introducing one bowtie-shaped parasitic element between two arms of crossed bowtie dipoles to generate additional resonance and thereby significantly broadening AR bandwidth. The final design, with an overall size of 0.79 λ _o × 0.79 λ _o × 0.27 λ _o (λ _o is the free-space wavelength of circular polarized center frequency), resulted in very large measured -10-dB impedance and 3-dB AR bandwidths ranging from 1.9 to 3.9 GHz (~68.9%) and from 2.05 to 3.75 GHz (~58.6%), respectively. In addition, the antenna also yielded a right-hand circular polarization with stable far-field radiation patterns and an average broadside gain of approximately 8.2 dBic.