# A Fundamental Study on Circularly Polarized Double-Loop Antennas with Quasi-Two Sources
## 6 Discussion  
This section discusses our results compared to those of similar studies. The comparisons are summarized in Table 2. It is emphasized that the present axial ratio bandwidth is the widest among concentric double-loop antennas. Separate dual-loop antennas have wider bandwidths than the present antenna, which uses a larger configuration of side-by-side loops. It can also be seen that an annular single-loop antenna shows a comparable bandwidth of 38% using a complicated feeding system of two probes when compared to the present one. Table 2 incorporates the previous study [9] in the last row. A comparison between the previous and present studies reveals that (1) the previous study proposed a new method for CP radiation (quasi-two sources). In contrast, the present study with quasi-two sources increases the axial ratio bandwidth using a concentric double loop, characterized by a more straightforward design than a conventional one, as mentioned in the Introduction. (2) Since the present study is a sequel to the previous one, the operating frequency and antenna size are the same, but the axial ratio bandwidth is increased to 31% from 12%. It is necessary to explain the advantages of the present antenna over a reference one [13], which has a wider axial ratio bandwidth and a higher gain than the present one at the same operating frequency, as seen in Table 2. The advantages are as follows:  
* The present antenna size is 0.25 \(\times\) 0.25 \(\times\) 0.25\(\lambda_{0}\)\({}^{3}\), which is one-fifth as large as the reference one (0.5 \(\times\) 0.65 \(\times\) 0.25\(\lambda_{0}\)\({}^{3}\)); \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Study**} & \multirow{2}{*}{**Loop Type**} & \multicolumn{2}{c}{**Method for**} & \multicolumn{2}{c}{**3 dB Axial**} & \multirow{2}{*}{**ZinBW 1**} & \multirow{2}{*}{**Gain**} & \multirow{2}{*}{**Frequency**} & \multirow{2}{*}{**Antenna Size**} \\  & & **Circularly Polarized** & & & & & \\ \cline{5-7}  & & **Radiation** & & (\%) & & & \\ \hline \([11]\) & \multirow{2}{*}{annular single} & pins and slot & 19.1 & 8 \({}^{3}\) & - \({}^{2}\) & 2.4 & 0.13 \(\times\) 0.13 \(\times\) 0.01 \\ \cline{1-1} \cline{3-7}  & & two probes & 38 & 38 & 8 & 1.8 & 0.46 \(\times\) 0.46 \(\times\) 0.12 \\ \hline \([5]\) & \multirow{2}{*}{separate dual} & perturbation gap & 50 & 50 & 8 & 6 & 0.62 \(\times\) 0.62 \(\times\) 0.3 \\ \cline{1-1} \cline{3-7}  & & perturbation gap & 32 & 43 & 10 & 6 & 0.74 \(\times\) 0.74 \(\times\) 0.26 \\ \hline \([13]\) & \multirow{2}{*}{quasi-two sources} & 43 & - \({}^{2}\) & 9.1 & 3 & 0.5 \(\times\) 0.65 \(\times\) 0.25 \\ \cline{1-1} \cline{3-7}  & & perturbation gap & 25 & - \({}^{2}\) & 8 & 5.75 & 0.44 \(\times\) 0.44 \(\times\) 0.25 \\ \hline \([7]\) & \multirow{2}{*}{concentric double} & perturbation segment & 3.2 & 18 & 9 & 3 & 0.25 \(\times\) 0.25 \(\times\) 0.1 \\ \cline{1-1} \cline{3-7}  & & four apertures & 23 & 23 & 7.5 & 1.4 & 0.25 \(\times\) 0.25 \(\times\) 0.04 \\ \cline{1-1} \cline{3-7} present & & quasi-two sources & 31 & 45 & 7.1 & 3 & 0.25 \(\times\) 0.25 \(\times\) 0.25 \\ \hline previous [9] & wire single & quasi-two sources & 12 & \textgreater{}12 & 7.6 & 3 & 0.25 \(\times\) 0.25 \(\times\) 0.25 \\ \hline \hline \end{tabular}  
\({}^{1}\) Bandwidth of VSWR \(<\) 2, \({}^{2}\) Not described, \({}^{3}\) Return loss \(<\) \(-\)10 dB.  
\end{table} 
Table 2: Comparisons with similar studies. Figure 13: Photographs of a prototype for an inner parasitic loop with a crank feedline \(B\)–\(F_{2}\)\({}^{\prime}\). (**a**) Perspective view. (**b**) Side view. * The present antenna has an unbalanced feed and can be directly excited using a coaxial line. In contrast, the reference antenna has a balanced feed and requires a complicated balun circuit design for the excitation using a coaxial line. Before the conclusion, some questions will arise: (1) How do readers know which modes are responsible for the CP radiation? (2) Why is a decrease in the gain for the Inner-PL more appreciable than that for the Outer-PL (see Figure 8)?