Cavity Backed Cross Dipole Antenna With Wide Axial Ratio Beamwidth and High Efficiency

This paper presents the design and realization of broadband and wide-beam right hand circularly polarized (RHCP) cross dipole antenna. The crossed dipole is backed by a conical shaped cavity to achieve improved axial ratio beam-width over a wide frequency band with enhanced gain. The design incorporates a conventional feeding technique using a coaxial probe. A sleeve is designed which is soldered with the cable to ensure strength for the cable. The fabricated prototype of the proposed antenna has an overall size of $0.87 \lambda \mathrm{X} 0.87 \lambda \mathrm{X} 0.38\lambda$ ($\lambda$ is the free-space wavelength at the lowest CP operating frequency). The obtained impedance bandwidth (RL >15dB) is 18% (2-2.4GHz) and axial ratio bandwidth (AR <3dB) is 9%. The axial ratio (AR <3dB) beam-width achieved overall phi planes is 120° for 5.5% bandwidth. Efficiency achieved is above 90% for complete bandwidth.

I. Introduction

Circularly polarized (CP) antennas are currently widely used for satellite communication systems. They provide various advantages over linearly polarized (LP) antennas such as multi-path effects, impact due to Faraday rotation, and flexible orientation of transmitting and receiving antennas. A plethora of literature is available on various circularly polarized antennas. Conventionally, patch antennas with slight perturbations fed at a single point such as corner truncated, nearly square antennas [1]–[3] are used for wireless communications due to their compactness and simplicity. Another conventional approach is to generate two orthogonal modes by dual feeding and providing 90° phase shift by using either hybrid or Wilkinson power divider with line is the wavelength at the operating frequency) to generate the additional 90° phase difference on one of its arm. Multi-feeding mechanisms are also reported in the literature. However, these antennas exhibit narrow Axial-Ratio (AR) bandwidth. Although currently widely used for satellite communication systems multi resonators and complex feeding structure [4]. Also, the sequential arrangement of circularly polarized and linearly polarized antennas is used to improve CP radiation for wider bandwidth at the cost of a larger form factor [5]. Quadrifilar helix antennas generate a wide-beam CP pattern and have a larger profile as compared to the planar antennas [6].