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A novel S-shaped periodic defected ground structure (PDGS) is proposed to reduce mutual coupling between antenna elements. Coplanar placed antenna elements work at the same frequency band with centre frequency 2.57 GHz. Centre-to-centre distance between the antenna elements is 50 mm which is ∼0.43λ. The PDGS is three S-shaped defected ground structure units placed between microstrip antenna elements. By using the proposed PDGS, more than 40 dB mutual coupling reduction between microstrip antenna elements is achieved.

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A dual-band dual-sense circularly polarised (CP) square slot antenna is presented. The proposed antenna consists of a L-shape patch and two rectangular strips around two opposite corners on the lower ground. By adjusting the size of them, a broadband dual-band dual-sense CP antenna can be obtained. It can radiate right-hand circular polarisation at 3.0 GHz and left-hand circular polarisation at 5.5 GHz at +z direction. The measured results of impedance bandwidths for S 11 < −10 dB are 38.8% (2.51-3.72 GHz) and 27.5% (4.83-6.37 GHz). The 3 dB axial ratio bandwidths are 37.4% (2.50-3.65 GHz) and 16.3% (5.02-5.91 GHz). Introduction: In recent years, printed slot antenna has been paid more attraction for light weight, low cost and wider bandwidth in modern communication systems, such as radio-frequency identification, wireless local area network and global positioning system. Many printed slot antennas are presented to obtain broadband circularly polarised (CP) operation in [1]. Some antennas [2-4] are proposed to achieve a single band CP radiation. A series microstrip-line-feed configuration is used to couple two orthogonal sides of the square-ring slot to excite a CP wave in [2]. The axial ratio bandwidth (ARBW) is more than 6%. A T-shaped metallic strip, which is protruded from the ground plane, is employed to achieve CP radiation in [3]. The ARBW can reach to 18%. Two inverted-L strips around two opposite corners are designed to produce CP radiation in [4]. A wideband ARBW larger than 38.2% can be attained. Several antennas are proposed to achieve dual-band dual-sense CP radiation in [5-8]. Two printed oppositely directed spiral slots can excite dual-band dual-sense CP radiation in [5]. The impedance bandwidth (IBW) is >18% for both bands. The ARBWs are 4.5 and 3.5% for the right-hand circular polarisation (RHCP) and left-hand circular polarisation (LHCP) bands, respectively. A modified annular-slot antenna, which is fed by a single-layer microstrip, can obtain dual band and dual sense by four unequal linear slots in [6]. The IBWs for the lower (RHCP) and higher (LHCP) bands are 26.7 and 11.3%, respectively. The ARBWs are 6.1 and 6.0%. Similar to [6], an annular slot and cross slot are proposed to produce two different frequency bands in [7]. Asymmetry structure on both annular slot and cross slot is introduced to obtain CP radiation at the two frequency bands. The ARBWs are 8.3 and 5.1%. A slot antenna with a C-shaped grounded strip, which is fed by coplanar waveguide, is proposed for dual-band and dual-sense CP radiation in [8]. The IBW is >106.9% (1.01-3.33 GHz). The ARBWs can be up to 32.35% (1.41-1.96 GHz) and 5.6% (2.45-2.59 GHz). In this Letter, a microstrip-line-feed with a L-shape radiation patch slot antenna is proposed for dual-band dual-sense CP radiation. It radiates RHCP at 3.0 GHz and LHCP at 5.5 GHz. The measured ARBWs can reach up to 37.4% (2.50-3.65 GHz) and 16.3% (5.02-5.91 GHz). The bandwidths of the proposed antenna and previous designs [5-8] are summarised in Table 1. The comparison results ...

A dual-band ten-element MIMO array based on dual-mode inverted-F antennas (IFAs) for 5G terminal applications is presented in this paper. The proposed dual-mode IFA is composed of two radiators, which are etched on the outer and inner surfaces of the side-edge frame. The outer part of the antenna generates the low-order mode at 3.5 GHz, while the inner part radiates another one-quarterwavelength mode at 4.9 GHz. In this way, the IFA can achieve dual-band operation within a compact size of 10.6 × 5.3 × 0.8 mm 3 . Based on the proposed antenna, a dual-band ten-element multiple-input and multipleoutput (MIMO) array is developed for 5G terminal applications. By combining neutralization line structures with decoupling branches, the isolations between the elements are improved. To validate the design concept, a prototype of the ten-element MIMO array is designed, fabricated, and measured. The experimental results show that the proposed antenna can cover the 3.3-3.6 GHz and 4.8-5.0 GHz bands with good isolation and high efficiency. Furthermore, the envelope correlation coefficient (ECC), and channel capacity are also calculated to verify the MIMO performances for 5G sub-6GHz applications.INDEX TERMS Dual-band antenna, dual-mode IFA, fifth generation (5G) communication, MIMO antenna.