Compact LTE frame antenna with a narrow metal clearance and a radiating feed network for the metal-casing smartphone

A compact LTE frame antenna with a 2-mm narrow metal clearance for the metal-casing smartphone is presented. The antenna requires only a radiating metal frame section of about a half of the short edge of the smartphone. The metal frame section is fed by a radiating feed network, which includes a feed network and two radiating branches. The feed network includes an inductive feed path (L-path), a capacitive feed path (C-path) and a matching circuit. By feeding the metal frame section through the L-path and C-path, a fundamental mode at low band and a dual-resonance mode at high band are generated. Radiating branches offer additional resonant modes to combine with the fundamental mode and the dual-resonance mode contributed by the radiating metal frame section to cover the LTE low band (824-960 MHz) and the LTE high band (1710-2690 MHz). The antenna structure, operation principle, and the experimental results of the proposed antenna are presented.