Figure 6 shows the simulated and measured ?Sll? of the
antenna with linear polarization. The measured return loss is
less than -10 dB over the frequency range of 912 to 939 MHz.
The obtained bandwidth is 27 MHz. In this experiment, the
copper wire is used to short between the main radiation patch
and the comer to produce linear polarization. When the patch is
shorted at the comer, the current flows through the copper wire
to the comer. The two orthogonal linear components are in
time phase. Therefore, the antenna produces linear polarization
[4]. From the measured result, the antenna provide the linear
polarization with good impedance matching. So, this can be
assumed that the antenna can switch between linear and
circular polarization by shorting between the main radiation
patch and the comer by any conductor or semiconductor such a
PIN diode. The technique and the result of using PIN diode
have been described in [1]-[3]