Compact Broadband Circularly Polarized CPW-Fed Antenna with Characteristic Mode Analysis

Wei Xu,Mingming Gao,Jingchang Nan,Trushit Upadhyaya

doi:10.1155/2022/9002700

Abstract

A compact circularly polarized (CP) antenna is proposed for low-profile and wideband operation based on characteristic mode analysis (CMA). A ring patch with a gap and two arc-shaped metallic stubs as the radiator is analyzed and optimized by CMA to figure out the orthogonal modes and operating frequency band for potential good axial ratio (AR) performance. The studies of these CP modes provide a physical insight into the property of broadband circular polarization. Such an in-depth understanding paves the way for the proposal of novel CP antenna with separation between the design of radiator and feeding network. A 50-Ω coplanar waveguide (CPW) is introduced and placed appropriately to excite the desired modes based on the information from CMA, which employs two asymmetric ground planes to improve the performance in terms of AR and impedance matching. The antenna with a compact size of 0.71λ0 × 0.76λ0 × 0.038λ0 (λ0 is the free-space wavelength at the center frequency of the 3-dB AR bandwidth) is fabricated and measured for validation. The realized gain varies from 1.6 to 3.1 dBic over the operating bandwidth characterized by the measured 10-dB impedance bandwidth of 83.8% (3.98–9.72 GHz) and 3-dB AR bandwidth of 70.3% (4.59–9.57 GHz), respectively.

Highlights

Polarized (CP) microstrip antennas with the characteristics of reducing the multipath effects, polarization mismatches, and Faraday’s rotation effects in the ionosphere [1, 2] are popular and attractive in modern wireless communication applications such as global positioning systems (GPS), synthetic aperture radar (SAR), radio frequency identification device (RFID) [3], etc
Circularly polarized (CP) radiation can be regarded as the superposition of two orthogonal linearly polarized (LP) radiations with equal amplitude and in-phase quadrature [4]
Massive investigations indicate that the most important issue associated with CP antenna design is how to optimize the patch shapes and recognize the two linear polarized modes to be combined for circular polarization

Summary

Introduction

Polarized (CP) microstrip antennas with the characteristics of reducing the multipath effects, polarization mismatches, and Faraday’s rotation effects in the ionosphere [1, 2] are popular and attractive in modern wireless communication applications such as global positioning systems (GPS), synthetic aperture radar (SAR), radio frequency identification device (RFID) [3], etc. By studying the current distribution and radiation pattern of the collection of CMs, the CPW-fed network consisting of a T-shaped strip, a tuning rectangle stub, and two asymmetric ground planes is designed and placed in the specified position according to the indication of CMA, which acts as a capacitive coupling element (CCE) to excite the desired modes. A mode wants to dominate an antenna radiation at specific frequencies; it has to be fed properly Another important parameter is characteristic angle (CA), which models the phase angle between a modal current and its associated characteristic field, defined as follows: CA 180∘ − tan−1 λn􏼁. The directivities of modal field at the same angle of interest can ensure a stable radiation pattern in far field

CP Antenna Design with CMA

Experimental Verification

GHz Y-Z Plane