In this paper, a compact circularly polarized (CP) antenna with omnidirectional radiation is presented, which has a central symmetric configuration (CSC) and planar structure. It consists of three identical end-fire CP antenna units. Based on the combination of two parallel complementary current sources, each unit cell can be realized by a scalloped cavity and a couple of curved strip lines. Due to a single-layer circular structure with low profile, this configuration can be excited by a coaxial probe in the centre of the whole frame simultaneously. In addition, this prototype was miniaturized with a diameter of 32 mm (0.266
Since wireless communication systems have developed fast in recent years, the CP antenna has attracted strong attention due to its advantage of anti-multipath interference. Particularly, owing to 360 degree coverage and the same radiation strengths of the CP antenna, the omnidirectional CP antenna becomes very attractive. Therefore, a great deal of effort has been directed to design omnidirectional CP antennas [
Lots of classical types of antennas have been designed for omnidirectional CP antennas recently. In the approach in [
Certainly, several single-layer designs have also been put forward to realize the omnidirectional CP. One of the examples is given in [
There are also some new constructs with compact and low-profile feature of omnidirectional CP antenna. For example, in [
This paper presents a CSC and compact CP antenna with omnidirectional radiation motivated by aforementioned achievements. A planar circular array with the CSC composed of several end-fire CP antenna units is proposed. It has a compact single-layer structure with small size and a single feed and can be fabricated on a F4B easily (relative permittivity
In order to achieve an omnidirectional CP antenna with low profile and small size, we adopt a single-layer structure as much as possible. Certainly, the antenna must be designed to meet the antenna parameter requirements, such as VSWR, antenna gain, and AR. As for the omnidirectional antenna, it also needs to meet the requirements of out-of-roundness.
The geometry of the proposed CSC antenna based on a fan-shaped configuration that embraces three unit elements is presented in Figure
Geometry of the proposed omnidirectional CP antenna: (a) top layer; (b) bottom layer; (c) side view; (d) unit element.
The original prototype structure is shown in Figure
Sectorial cavity unit prototype structure (a), electric-field distribution E and surface electric current distribution J for the proposed antenna (b)
It is known from [
Inspired by the aforementioned CP mechanism, a CSC circular array comprising three identical end-fire CP elements is proposed in this paper. A shorted scalloped construct is formed by introducing a metallic aperture along the angular bisector. When several structures are placed with the CSC as in the proposed design, partial radiation will be cancelled out from their side apertures. Therefore, the effective radiation is only from the arc-shaped one. The electric current and magnetic current parallel to each other were converted into annular current source at the same time in the final design.
According to the classical electromagnetic field theory, the relationship between the radius of the circular patch and the resonant frequency can be determined by using the following equations:
For a CSC antenna array in the
To clarify the concept of proposed antenna more clearly, the design process is demonstrated in Figures
Evolution of the proposed antenna.
The conception of this configuration is inspired from [
The mechanism of the proposed antenna is similar to that in [
As can be seen from a quarter-wave shorted patch in [
Figures
Energy and surface current distribution (a, b); radiation pattern plot gain LHCP (c) and gain RHCP (d).
In order to better comprehend the mechanism of this proposed CSC antenna, we have investigated the effect of different related parameters on antenna performance. Several parameters, such as the coupling strips, the radius of the antenna, the position of the shorted aperture, and the length of the branches, were studied as described below.
It is the coupling strips that contribute to the miniaturization of this work to a large extent. The shorting pins act as several closed inductances, while the coupling strips can be considered as the closed capacitances. Hence, the closed inductances and capacitances can reduce the resonant frequency tremendously presented in Figure
Comparison of with and without coupling ring.
The size of each unit cavity is determined by
Effect of different
The shorted aperture plays a key role in antenna performance. It can be seen from Figure
Effect of different
Effect of different
The proposed antenna is constructed by printed circuit board (PCB) technology and shorting pins are achieved by metallized holes. The antenna measurement was done in an anechoic chamber with a vector network analyzer. Firstly, the test distance should meet the far-field condition (
S11 (a); AR curves of fr = 2.4918 GHz at
The gain curve of this antenna is shown in Figure
Similarly, the effect of the maximum gain and the lowest axial ratio can be obtained at the centre frequency shown in Figures
The proposed CP antenna bottom (a) and top (b).
The comparison between simulated and measured results of this antenna is shown in Figure
RHCP and LHCP patterns of fr = 2.49175 GHz; (a) normalized 2D pattern at
In this paper, an LHCP antenna is proposed. It can also be clearly seen from Figure
The proposed antenna has good AR characteristics in the whole azimuth plane as shown in Figure
Comparison of reference and the proposed antenna
Reference | Structure | Usable bandwidth (%) | Max gain (dBi) | Dimensions ( |
Height |
---|---|---|---|---|---|
[ |
Planar | 3.97 | 1.77 | 0.62 |
0.029 |
[ |
Planar | 4.3 | 3.3 | 1.74 |
0.039 |
[ |
Nonplanar | 0.9 | 1.01 | 0.16 |
0.03 |
[ |
Planar | 0.54 | −0.4 | 0.29 |
0.016 |
[ |
Nonplanar | 11.55 | 0.86 | 0.25 |
0.082 |
[ |
Planar | 0.78 | 0.82 | 0.29 |
0.02 |
[ |
Nonplanar | 7.3 | 2.04 | 0.32 |
0.27 |
This study | Planar | 1 | 1.15 | 0.27 |
0.012 |
As can be seen from Table
This paper presents a novel kind of CSC and omnidirectional CP antenna. It can easily be fabricated due to the simple construction. It is worth mentioning that the miniaturization technology of the proposed antenna is mainly realized by coupling arcs. Importantly, this work features the lowest profile and the smaller size relatively compared with the reference antennas. Moreover, it is omnidirectionally stable in the whole azimuth plane. The proposed antenna has an approximate 86% radiation efficiency, which has potential application in the field of the first generation of BeiDou Navigation System.
The data used to support the findings of this study are included within the article.
The authors declare that they have no conflicts of interest.
The authors wish to acknowledge the support from The National Science Foundation (61775175 and 61771378).
The data of different sheets are characterized by their own sheet names in the file of “graph-data.xlsx.” For example, the sheet of “without-with-ring” is the comparison of the S11 under the different conditions of with or without the coupling ring. The sheet of “S11-d” is the S11 variation with different sizes of parameter “d.” In addition, the value of several key parameters is given in the file of “size.docx.”