Abstract
We investigate a circularly polarized (CP) transmission-line antenna composed of loop radiation elements, called a loop-line antenna. To enhance the CP wave bandwidth, an isolated loop radiation element is first analyzed using the method of moments. It is found that a CP wave bandwidth for a 3 dB axial-ratio criterion has a maximum value of 8%. On the basis of the analysis results, we design the loop-line antenna. It is found that the antenna shows a CP wave bandwidth of 6%, which is twice as wide as that of a conventional loop-line antenna. The analysis results are verified with experimental ones. In addition, a condition for wideband CP radiation is discussed and found to be a composite radiation element consisting of two CP loops.
Highlights
A transmission-line antenna is in a class with a series-fed linear array and can radiate a circularly polarized (CP) wave [1, 2]. e antenna is characterized by a simple feed system in comparison with that of a conventional array, since the feed line itself contributes to CP wave radiation
Is paper is an extended version of the preliminary conference one [7] written by the present authors. e study of the isolated loop element is newly focused on the reason why the wideband CP radiation is obtained
It is found that each modified antenna does not show wideband CP radiation in comparison with the present antenna, as shown in Figure 2. is fact means that wideband CP radiation is obtained for a composite antenna consisting of the two CP-modified loops, since both the modified loops are created from the present antenna, as mentioned in Figure 5
Summary
A transmission-line antenna (line antenna) is in a class with a series-fed linear array and can radiate a circularly polarized (CP) wave [1, 2]. e antenna is characterized by a simple feed system in comparison with that of a conventional array, since the feed line itself contributes to CP wave radiation. The line antennas have been designed using several kinds of radiation elements above a ground plane, such as rampart [3], crank [4], and loop elements [5, 6]. A recent study using a loop element has shown that the CP wave bandwidth of a line antenna can be increased [7]. E loop height above the ground plane has been selected for wideband CP radiation. E study of the isolated loop element is newly focused on the reason why the wideband CP radiation is obtained. Note that there have been only simulated results in [7], since the input impedance that satisfies a VSWR of less than 2 has yet to be researched
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