Dual‐curl antennas for broadband circular polarisation

Abstract

A novel dual‐wire antenna to obtain wideband circular polarisation is proposed. The antenna consists of curl elements with a balanced feed above a ground plane. Using the moment method, an antenna with balanced feedlines having two sources is analysed first. Analysis reveals that the antenna shows a 3 dB axial‐ratio bandwidth of 36%. Next, an antenna with quasi‐balanced feedlines having one source to simplify the feed system is investigated. It is found both numerically and experimentally that the axial‐ratio bandwidth remains unchanged, and a VSWR of less than two is obtained.

A dual‐curl antenna with coplanar feedline for sequential rotation

“…The curl parameters ( C , d , L s ) and feedline length L f are selected for CP radiation. The other configuration parameters are the same as those in [1]: ( h , ρ) = (λ 0 /4, λ 0 /200), where λ 0 is the free‐space wavelength at a test frequency of f 0 .…”

“…Figures 6a,b show the quasi‐balanced feed using vertical parallel feedlines $$F_{\rm n}-F_{\rm n}'$$ ( n = 1 and 2). The feedlines of the radius ρ have a distance δ (= λ 0 /40 [1]) and length h . The top ends F n are connected to the dual curl, and the bottom ends $$F_{\rm n}'$$ are excited with one or two sources for quasi‐balanced or balanced feeds, as shown in Figure 6b,c.…”

“…This letter is a sequel to the previous one [1] and aims to expand the axial‐ratio bandwidth of a dual‐wire antenna. For this, we use a non‐resonant curl element [1], a simplified version of a single wire spiral [6], and newly adopt a coplanar feedline for sequential rotation (SR) [2]. The antennas with and without SR are analysed using the method of moments [7].…”

“…It is seen that the present study with a non‐resonant element employs a coplanar feedline for SR for the first time, leading to the maximum CP wave bandwidth. It should be emphasized that this bandwidth expansion is a significant advance in dual‐wire antennas since the maximum bandwidth so far has been 36% [1]. Furthermore, the coplanar‐feedline length is found to be a critical parameter for the bandwidth expansion, which is entirely different from the case for a resonant element [2, 8].…”

“…Introduction: A dual-wire antenna backed by the ground plane radiates a circularly polarised (CP) wave [1][2][3][4][5]. A single balanced feed characterises the simple two-element array configuration.…”