On-frame dual-loop antenna with narrow ground clearance for the 2.4/5.2/5.8-GHz WLAN operation in the smartphone

Abstract

A dual-loop antenna with a 1-mm ground clearance on the main circuit board and an on-frame metal patch for the 2.4/5.2/5.8-GHz multiband WLAN operation in the smartphone was presented. The metal patch was printed on the inner surface of the side-edge frame of the smartphone and has a simple rectangular shape of size 6 × 12.7 mm2. Multiband operation of the antenna was obtained by short-circuiting the metal patch at two positions, respectively, through a capacitive shorting strip and a simple shorting strip, to the system ground plane on the main circuit board. In this case, two loop paths of different resonant lengths with acceptable isolation were obtained for the antenna to generate two wide operating bands. The larger (outer) and smaller (inner) loops thereof could generate their fundamental loop modes with corresponding resonant lengths much less than 0.25 wavelength (only about 0.12 wavelength at 2.45 GHz for the outer loop and about 0.17 wavelength at 5.5 GHz for the inner loop). The greatly decreased resonant lengths were owing to the aid of a simple matching circuit (a series capacitor and a series inductor) disposed on the main circuit board. The generated loop modes could cover the 2.4-GHz (2400–2484 MHz) and 5.2/5.8-GHz (5150–5350/5725–5875 MHz) WLAN bands. With narrow ground clearance and small on-frame metal patch, the dual-loop antenna was especially suitable to fit in the narrow region between the display panel and the side edge of the smartphone casing. Details of the proposed antenna and its working principle were presented. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1480–1485, 2016