A single‐feed circularly polarized loop antenna using characteristic mode analysis

Abstract

A novel method for a single-feed circularly polarized (CP) loop antenna with both broad impedance bandwidth and axial ratio (AR) bandwidth is presented based on characteristic mode analysis (CMA). The circular polarization characteristics are generated by exciting two orthogonal degenerate modes (DMs) via single feeding simultaneously. The 90 phase difference is achieved by loading the lumped inductors or capacitors. The wide bandwidth characteristics are generated by splitting a pair of DMs. Consequently, the two overlapping resonance points are split. The positions of feeding and loadings are determined with the aid of CMA. Compared with conventional methods, the presented method can simplify the feeding structure and provided a compact antenna. Based on this method, a loop antenna with two inductors is demonstrated for circular polarization application. The measured results show an impedance bandwidth of 47% and 3 dB AR bandwidth of 8.3% at 2.4 GHz wireless local area network (WLAN) bands. Both the simulated and measured results agree well.

Circularly Polarized Antennas Using Characteristic Mode Analysis: A Review

“…In summary, this subsection has reviewed the CMA of optimal antenna designs without MTS for CP radiation and improvement in AR. The optimal designs discussed above [55][56][57] demonstrate that CMA provides important information for CP performance and ARBW enhancement from CM parameters and current or field distribution. On the other hand, the designs described above illustrate how to optimize the feed position to provide CP radiation and improvement in ARBW from the modal current distribution.…”

“…It has been observed that a square contour parallel dipole has shown a 90° phase difference for degenerating modes such as mode 2 and mode 3 by analyzing individual orthogonal current modes [52]. The designs discussed above have a low profile and can be fabricated easily [53][54][55][56][57][58][59]. However, some of those structures exhibit a narrow ARBW because the orthogonality and phase difference is achieved at a single frequency.…”

“…Using similar kinds of techniques, a CPW-fed rectangular slot antenna has been designed for wider ARBW [54][55][56][57]. The CP conditions are attained using an asymmetric slot [54] and asymmetric stubs [55] on the ground plane by altering the current distribution.…”

“…Recently, a CP loop antenna has been designed with a broad ARBW and impedance bandwidth with a single-feeding technique [57]. Here, a 90° phase difference is attained by loading the lumped inductors.…”

“…Thus, there is a degree of freedom in the feed network selection and feed location in the final antenna design. Therefore, the techniques for the selection of feed networks and their final optimization with the help of CMA are reviewed in the above section from the mentioned literature [50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65]. Fig.…”