A Novel Compact Microstrip Antenna for Ultra Narrowband Applications

There is an increasingly demand for ultra narrowband (UNB) technologies to support the physical layer communication link, particular the massive connectivity of low power wide area (LPWA) networks. A higher system capacity in a limited bandwidth (BW) is highly depend on the numbers of narrowband channels, which also brings easy mitigation of the interference impact. In this work, we demonstrate a novel microstrip ring antenna, aiming at the exploration of the very narrow fractional BW, leading to high frequency selectivity and increased quality factor (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$Q$</tex-math></inline-formula>) for UNB wireless applications. We demonstrate an S-band antenna, composed of a microstrip ring resonator as the radiating element and a microstrip dual-open loop bandpass filter for narrowing the BW, leading to high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$Q$</tex-math></inline-formula> for the planar circuit. The entire structure is designed on a single layer of substrate for easy integration and low-cost fabrication. Measurement results show that at 2.483 GHz, the fabricated antenna exhibits a very narrow fractional BW at 0.201%, with a realized gain of 3.63 dBi. The narrowest BW is measured at 4.9 MHz (0.193%) with a high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$Q$</tex-math></inline-formula> around 500 at 2.533 GHz, exhibiting a realized gain of 3.81 dBi. The proposed approach provides a simplified front-end design for antennas and feasibility of ultra high frequency selectivity in low-cost 2D planar antennas.