In this letter, a low-profile quad-band antenna array for multiple-input-multiple-output (MIMO) application has been presented. The proposed two-antenna array operates at GPS L1/Bluetooth/Wi-Fi/LTE2500/WiMAX/HIPERLAN1 frequency bands. Each antenna element has an area of 25×10 mm² over a small ground plane of the size 100×60 mm². To maintain the small size of the antenna element, folded patch is used. A rectangular slot is etched on the main radiator to utilize the higher-order mode. A quarter-wavelength resonator is integrated at the edge of folded patch to get an additional resonance for quad-band operation. An antenna prototype is fabricated, and measured results are in good agreement with simulated results. Radiation characteristics and diversity performance of the proposed structure are presented.

A metamaterial‐based novel compact microstrip antenna is presented for ultra‐wideband (UWB) applications. The antenna consists of two layers of metamaterials made by etching a π ‐shaped slot and crossed‐shaped slots, on the radiating patch and the ground plane, respectively. The series capacitance and shunt inductance developed due to the patterned radiating patch and ground plane lead to the left‐handed behaviour of the metamaterial. The proposed antenna has a compact size of 30.8 × 27.6 × 0.8 mm ³ and is fed by a 50 Ω microstrip line. The impedance bandwidth (−10 dB) is from 3 GHz to more than 14 GHz with maximum radiation in the horizontal plane and tends towards a directional pattern as the frequency increases.