In this paper a low profile circularly polarized annular ring slot antenna (CPARSA) with high gain is presented. An inverted U-shaped meandered slot is cut at the inner patch of annular ring to obtain the circularly polarized (CP) radiation. This annular slot loaded ground plane on a substrate thickness of 0.5 mm results in a very low profile (0.009λ۰) antenna in term of free space wavelength at its center operating frequency. The largest side lengths of octagonal shaped antenna are 0.89λ۰×۰٫۸۹λ۰ according to its center frequency. Measured impedance bandwidth of 23.54% from 5.4 GHz – ۷٫۰ GHz (for |S11| ≤ −۱۰ dB) and AR bandwidth (AR<3dB) of 5.15% from 5.67 GHz – ۵٫۹۷ GHz are achieved by the antenna. Meanwhile, stable radiation pattern is observed throughout the entire bandwidth with peak gain of 7.6dBi at the center frequency of 5.8 GHz. A defected ground plane is employed in the design which results in reduction of surface waves leading towards higher gain of antenna. The proposed antenna operating at 5.8 GHz band is fabricated on low cost substrate with standard printed circuit board (PCB) process. The proposed design provides favorable characteristics for various lightweight applications including miniaturized drones and airborne applications. To validate the prototype, measured results are compared with simulation outcomes and good agreement is obtained.

Introduction

Circularly polarized (CP) and high gain antennas with their favorable characteristics such as low profile, less massy and planner structure that offer ease in integration with monolithic IC’s are demanded recently. CP antennas are also favorable in situations where polarization mismatch may degrade the performance of communication system [1], [2]. Advantages of circular polarization over linear polarization are generally because of high efficiency in mobility, alleviate in multi-path distortion and polarization mismatch losses [3]–[۵]. Moreover, CP antennas have influence to overcome multipath fading and mitigate Farady rotation effects [6] that can help to reduce the loss. These characteristics make them favorable candidate for wireless power transfer applications. Circular polarization requires generation of two equal but orthogonal radiating modes. This can be achieved either by employing multiple feeds or a single feed. Several CPARSA designs producing circular polarization have been reported in literature [5]–[۱۳]. A circularly polarized antenna based on fractal geometry architect was reported for UHF RFID applications. The measured gain of the antenna is 1.35 dBi [5]. Another design based on metallic ground reflector was presented in [6] for dedicated short range communication (DSRC) applications. Although the antenna retains peak gain at 4.95 dBic but its 6.926 mm dense profile limits the use of antenna for various lightweight applications.