Low-Profile Printed Octa-Band LTE/WWAN Mobile Phone Antenna Using Embedded Parallel Resonant Structure

A simple low-profile antenna for octa-band LTE/WWAN operation in the internal mobile phone application is proposed and studied in this article. Consisting of a feeding strip and a coupling strip mainly, the presented antenna can be easily printed on the no-ground area of the top of a FR4 substrate, yet it occupies only a size of 15 × 40 mm² and has a height of 3.5 mm. In this scheme, a chip inductor (L₁ = 20 nH) is loaded in the long inductive strip, which can form a parallel resonant structure together with the coupling strip section close to the feeding strip. With these presences, a double-resonance mode (λ/4 resonant mode) is successfully generated at about 720 and 900 MHz to cover the lower band of LTE700/GSM850/900 (704-960 MHz). While the desired upper band of DCS1800/PCS1900/UMTS2100/LTE2300/2500 (1710-2690 MHz) can be obtained with the help of second two resonant modes, including a high-order λ/2 resonant mode at 1800 MHz and a λ/4 resonant mode at 2550 MHz. That is to say that those two wide operating bandwidths are achieved to cover all the octa-band LTE/WWAN operation. Good radiation efficiency and antenna gain for frequencies over the desired operating bands is obtained. Detailed design considerations of the proposed antenna are described, and both experimental and simulation results are also presented and discussed.