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This paper introduces an effective solution for improving isolation in linear antenna array. The array is composed of three-element E-plane single feed patch antennas (the overall size is 0.59 λ 0 × 1.02 λ 0), which are closely placed with approximately 0.037 λ 0 , where λ 0 is the free-space wavelength at 4 GHz. The decoupling structure consists of T-shaped and rectangular ring shaped defect ground structure (DGS) with six metal-vias. The decoupling mechanism is illustrated by investigating the current vector on the ground plane. The current distribution indicates that the decoupling structure along the outer edge of the radiation patch sever as coupling current converter to produce reverse current opposite to the direction of the ground coupling current, which transmits along the outer edge of the radiation edge. The measured results show that the enhancement in the isolation at 4 GHz is 10.8 dB for |S21|, 17.5 dB for |S23| and 16.6 dB for |S31|. After applying the decoupling structure, the 10-dB impedance bandwidth (3.95-4.04 GHz) of antenna 1 remains unchanged. Meanwhile, the 10-dB impedance bandwidth of the antenna, which is located in the middle of the three-element antenna array, increases by 86 MHz (from 114 MHz to 200 MHz). When the decoupling structure is loaded, the maximum gain only decreases by 0.12 dB (from 3.94 to 3.82 dB). The decoupling structure has the advantages of simple structure, easy processing, and independent design of the array, so it can be applied to multielement patch array, such as massive multiple-input multiple-output (M-MIMO) system. INDEX TERMS Linear antenna array, defect ground structure (DGS), mutual coupling, isolation.

In this paper, a novel decoupling technique for closely spaced E-plane patch antennas using defect ground structure (DGS) is proposed. The electric field coupling between the antennas is suppressed by etching DGS which consists of a pair of rectangular slots and four stubs on the ground plane. Moreover, unlike the other methods, the DGS is not etched in the middle of the antennas but loaded along the outer edge of the radiated patch. Thus, through the adopted technology the distance between the antenna elements is reduced and the isolation is increased. To validate the improvements by adopting the proposed technology, the array with DGS loading has been fabricated and then measured. The measurement results show that designed antennas have 95 MHz 10-dB impedance bandwidth, which is 25 MHz higher than that of the antenna without DGS. More importantly, isolation improvements have been increased from 8.5 to 31.3 dB by using the decoupling technique when the antennas are placed with a 0.032 λ0 edge-to-edge distance, where λ0 is the free-space wavelength. Therefore, this technique can be widely applied to improve isolation in a compact and low profile antenna system.

A hybrid composite right/left handed (CRLH) structure based leaky-wave antenna with continuous wide beam scanning is proposed in this article. Six series-wound periodic units, combining spoof surface plasmon polariton (SSPP) with CRLH, form the radiating portion of proposed antenna. The unit is connected to the ground with metal hole, which provides the equivalent parallel inductance, and the unit is separated from its adjacent unit at prescheduled intervals, which provides the equivalent series capacitance. Additionally, the unit operates at balanced state and the open stopband is obviously suppressed. Dispersion diagram is also used to analyze this continuous scanning. A prototype of proposed antenna is fabricated and measured. The main beam of the antenna scans continuously from −70 to +40 in the range from 5.2 to 8.8 GHz. The antenna radiation efficiency reaches a maximum of 92% in the working band. Measurement results agree quite well with the simulation, which indicate this leaky wave antenna can find potential applications in communication systems and radars. K E Y W O R D SCRLH, high efficiency, leaky-wave, SSPP, wide-angle scanning

This article presents the Gui-shaped Chinese character array antenna (GCCAA), which is loaded with the L-shaped defect ground structure (LDGS) to improve isolation between the antennas. The GCCAA is obtained by arranging two Tu-shaped antennas up and down. By etching a pair of LDGS on the ground, the direction of the coupling current is changed on the ground. Most importantly, the LDGS is not etched in the middle of the antenna elements, but loaded along the outer edge of the GCCAA, which not to destroy the appearance of the GCCAA and maintain the compact nature of the Chinese character. The measured results show that LDGS improves isolation from 15.4 to 37.4 dB when the antennas are placed with a 0.065 λ 0 edge-to-edge distance. Meanwhile, it has little influence on reflection coefficient and radiation patterns. The decoupling technique is simple and straightforward which can be easy applied in Chinese character array antenna. K E Y W O R D SChinese character array antenna, defect ground structure, isolation enhancement, mutual coupling

A novel array-antenna decoupling surface (ADS) for mutual coupling reduction in microstrip patch antenna is proposed in this paper. The proposed ADS is composed of a group of primary reflector patches and a pair of rectangular and T-shaped secondary reflector patches. Through generating the reflected waves with equal magnitude but out of phase of the coupling waves, the isolation of the antenna elements could be significantly improved by the novel proposed ADS. Then, for verification, a two-element microstrip antenna array covered by the proposed ADS with an edge-to-edge separation of 0.11λ 0 (λ 0 is the wavelength of the operating frequency in free space) was designed and fabricated. As expected, the experimental results have demonstrated that an additional 40.4 dB isolation enhancement at the resonant frequency was achieved by the proposed ADS. Moreover, a much wider bandwidth of the isolation was also obtained than that of return loss of 10 dB. In addition, a gain improvement of 0.95 dB was achieved at 2.45 GHz by utilizing the novel ADS. Thus, the decoupling structure can be applied to multiple-input multiple-output (MIMO) systems for its simple structure and high isolation providing.

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