Design of a coupled line feed structure for the wideband characteristic of a mobile internal antenna

A method to design an adjustable wideband impedance matching structure based on the impedance transformer concept is proposed in order to enhance wideband impedance matching. The designed coupled line feed structure (CLFS) provides a wide impedance characteristic via an operating principle similar to that of an impedance transformer. The CLFS enables tuning capability for the impedance characteristic of an inverted-F antenna (IFA) through adjustments in the line width and gap between the two CLFS spirals. By adding the proposed CLFS to the antenna feed, the bandwidth of the original IFA can provide about 22% wider coverage when compared with an IFA alone, especially over the LTE band, without changing the original antenna design. For frequencies below 1100 MHz, the impedance bandwidth of an IFA is about 40% at a center frequency of 862 MHz. This covers the LTE 17 (704–746 MHz)/13 (746–787 MHz), GSM 850 (824–894 MHz)/900 (890–960 MHz)/1800 (1710–1880 MHz)/1900 (1850–1990 MHz), and WCDMA (1710–2170 MHz) bands. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:522–526, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27356