Figure 5 shows the measured input characteristics for the planar antenna by adding the shortbars on the loop antenna one by one, i.e., adding the short-bar sb1 first, then sb2 and sb3.
It is shown that the loop antenna without the shortbars has only isolated resonances at around 500 and 800 MHz.
Adding sb1 and sb2 increases the bandwidth of the isolated resonances and adding sb3 improves the impedance matching in the whole range from 470 to 970 MHz with a voltage standing wave ratio (VSWR) less than 3.