High-Performance Air-Filled Multiband Antenna for Seamless Integration Into Smart Surfaces

A highly efficient air-filled multiband antenna is presented for unobtrusive integration into smart surfaces. By introducing a capacitive loading ridge in the cavity formed by two coupled eighth-mode resonators, the higher order modes are judiciously manipulated. A supplementary slot-mode resonance is provided by a resonant U-slot in the first resonator. These measures yield dual-band impedance matching, covering the SRD860 (863-870 MHz), 2.4 GHz ISM (2.4-2.4835 GHz), and LTE-7 (2.5-2.69 GHz) standards. The antenna, fully realized in low-cost FR-4 substrate layers, complies with standard printed circuit board manufacturing. Measurements on a prototype reveal an impedance bandwidth of 51.8 MHz (6.1%) and 428.6 MHz (17.0%) in the lower and upper frequency band, respectively. Furthermore, a total efficiency and peak gain of 86.1% and 3.8 dBi at 866 MHz, 75.2% and 9.0 dBi at 2.45 GHz, and 70.1% and 8.1 dBi at 2.6 GHz were obtained in standalone conditions. At 2.4 GHz, a measured total efficiency and gain of 73.9% and 8.9 dBi are reported for the antenna covered by a cork superstrate, and 73.6% and 6.6 dBi for the antenna inside a drywall construction.