Instead of a square MSA, a CMSA with multiple feeds could be used to yield CP.
A CMSA with two orthogonal feeds is shown in Figure 8.2(b).
A CMSA of radius a = 3.1 cm, e r = 1, and h = 0.4 cm fed with 1Ð0° and 1Ð90° at x = y = 1.3 cm, respectively, yields LHCP.
The VSWR BW is from 2.521 GHz to 2.661 GHz, and the AR remains below 1.9 dB within the VSWR BW.
As in the case of square MSA, when the CMSA is fed at four orthogonal feed points near the edges as shown in Figure 8.7, a wide VSWR BW of 481 MHz is obtained for a probe diameter of 0.12 cm with an AR less than 0.01 dB in the entire BW.
The BW further increases to 1.267 GHz when a probe diameter of 0.4 cm is used, which gives better impedance matching.