The antenna structure is composed of one radiation part
which radiates circular polarization as shown in Fig.l. The
comer of the radiation patch has been separated from the main
patch by a slot. The radius of comer truncated are r], r2, r3 and
r4 respectively. The comer truncated r], r2, r3 and r4 are used to
improve the axial ratio of circular polarization. The slot (g) on
top left comer and bottom right comer are used to switch
between circular and linear polarization by shorting the comer
to the main radiation patch to make linear polarization. The
width of the slot (g) is 2 mm. The length and the width of the
radiation patch are 11 and WI respectively. The length and the
width of the FR4 substrate are 12 and W2 respectively.