This paper presents a wide-angle scanning phased array antenna using high gain pattern reconfigurable antenna (PRA) elements. Using PRA elements is an attractive solution for wide-angle scanning phased array antennas because the scanning range can be divided into several subspaces. To achieve the desired scanning performance, some characteristics of the PRA element such as the number of switching modes, tilt angle, and maximum half-power beamwidth (HPBW) are required. We analyzed the required characteristics of the PRA element according to the target scanning range and element spacing, and presented a PRA element design guideline for phased array antennas. In accordance with the guideline, the scanning range was set as ±70° and a high gain PRA element with three reconfigurable patterns was used to compose an 8x1 array antenna with 0.9 λ0 spacing. After analyzing whether the active element patterns meet the guideline, the array antenna was fabricated and measured to demonstrate the scanning performance. The fabricated array can scan its beam from -70° to 70° by dividing the scanning range into three subspaces. It shows that even if the array antenna has large element spacing, the desired scanning performance can be obtained using the elements designed under the guideline.
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I. INTRODUCTIONIn multi-path environments, a high channel capacity is required in order to send more data in the desired direction. A multi-input multi-output (MIMO) antenna exploits multiple antenna elements to achieve a higher channel capacity that is proportionate to the number of antenna elements [1]. The conventional approach for MIMO applications is to arrange the antennas over more than half of the wavelength to avoid correlation [2]; thus, it extends the physical size of the antenna. Moreover, increasing the number of antenna elements in a mobile device affects MIMO performance due to mutual coupling between antennas.Several MIMO antenna designs have been proposed to minimize the mutual coupling between antenna elements and to simultaneously decrease the antenna size. The basic approach is to increase the space between antennas, but the space is limited, especially for mobile applications. Decoupling networks [3,4], the slit pattern [5], the parasitic element [6], and the electromagnetic band gap (EBG) [7,8] have been analyzed; however, these methods require additional space on an antenna. In this paper, we propose a compact low-profile planar MIMO antenna that unites eight inverted-F antennas with an isolationenhanced structure. We designed the proposed antenna to achieve high isolation between the antenna elements and we verified the antenna's function by identifying the surface current and radiation patterns.
II. DESIGN OF THE PROPOSED ANTENNAThe antenna shown in Fig. 1 An eight-element compact low-profile multi-input multi-output (MIMO) antenna is proposed for wireless local area network (WLAN) mobile applications. The proposed antenna consists of eight inverted-F antennas with an isolation-enhanced structure. By inserting the isolation-enhanced structure between the antenna elements, the slot and capacitor pair generates additional resonant frequency and decreases mutual coupling between the antenna elements. The overall size of the proposed antenna is only 33 mm× 33 mm, which is integrated into an area of just 0.5 λ× 0. Manuscript received May 28, 2016 ; Revised July 6, 2016 ; Accepted July 6, 2016. (ID No. 20160528-017J) This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. ⓒ
A highly efficient antenna array for unmanned aerial vehicle (UAV) mounted radar applications with a tilted-beam characteristic and a 360° beam coverage is proposed in this paper. The proposed array antenna is configured by four planar super J-pole antennas with 2-dimensional ground reflectors. Each super J-pole antenna element provides a high directivity where the peak gain is tilted about 45° facing toward the ground from the bottom of a UAV body. Thus, the air-to-ground communication difficulty due to the altitude difference between the UAV and ground targets can be effectively solved. Further, the four super J-pole elements with a switched operation can cover the whole 360° areas around the UAV while high antenna gain is maintained. To verify the performance, the proposed structure was implemented at 5.9 GHz with an overall volume of 0.88 × 0.88 × 0.83 λo3. The measured 10-dB impedance bandwidths for all four antenna elements were better than 27.2% and the isolation among the four antenna ports was also always better than 13 dB. The measured peak gain was better than 7.4 dBi and tilted at 45° in the elevation angle. Lastly, the measured half power beam widths in elevation and azimuth planes were more than 60° and 87°, respectively.
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