A loop antenna with quasi‐two sources for circular polarisation

Abstract

A novel method of exciting a circularly polarised (CP) loop antenna is proposed using the moment method. A horizontal square loop above the ground plane has two corners connected to a vertical, branched feedline with one source. First, the authors show the radiation characteristics of a reference antenna whose corners are excited with two sources having the same amplitudes and a phase difference of 90°. Next, we excite the loop corners with one source using the branched feedline. It is found that when the branch location along the feedline is selected, the antenna radiates a CP wave. The frequency responses of the antenna show that the 3 dB axial‐ratio bandwidth is 12%, where the gain is more than 7.3 dBi. The simulated results are verified with experimental ones.

Impedance matching for curl and truncated spiral antennas above the ground plane

“…We further reveal that in the parallel feedlines’ adaption, the antenna circumference is a critical parameter for mitigating an abrupt gain drop versus frequency (see Figure 8a), which has not been observed in case [5]. The present study also demonstrates that we can still apply a crank feedline to impedance matching in a broader CP wave bandwidth (30%) than that (12%) in [7]. In summary, our contributions are as follows: (1) Adopting a crank feedline to a curl antenna can lead to a VSWR< 2 bandwidth of 30%.…”

“…The ground plane is assumed to be of an infinite extent, and the image theory is applied to the analysis. The wire radius is fixed to be ρ = λ 0 /200 [5,7] throughout this paper, where λ 0 is the free-space wavelength at a test frequency of f 0 . The other configuration parameters are varied, subject to the objectives of the analysis.…”

“…Subsequently, input impedance matching a coaxial line is investigated at an antenna height of 0.25 wavelengths, which has not been studied previously [6]. For this, crank [7] and parallel feedlines [5] are adopted for the curl and spiral antennas, respectively, as shown in Figure 2. The radiation characteristics are evaluated using the current distribution determined by the moment method [8].…”

Dual‐loop antennas with an expanded axial ratio bandwidth

“…It is emphasised that the maximum value is 41%, three times as wide as that (12%) of an isolated loop antenna without the array environment [5]. Note that the isolated loop antenna is not the reference antenna shown in Figure 1d but the antenna discussed in [5].…”

“…The purpose of this paper is to propose a novel antenna with an expanded 3‐dB axial ratio bandwidth. For this, we newly use a loop element with quasi two‐sources for CP radiation [5] (see Figure 1) and reveal the effects of the element distance on the axial ratio bandwidth using the method of moments (MoM) [6].…”