It can be clearly seen from the return loss graph that the
antenna resonates at two frequencies that is at 2.41 GHz and
5.85 GHz, which are the operating bands for the RFID
applications. Effectively large impedance bandwidths have
been observed. Impedance bandwidth for -10 dB return loss in
the 2.41 GHz and 5.85 GHz center frequency are 0.71 GHz
(2.04 GHz to 2.75 GHz) and 2.27 GHz (4.58 GHz to 6.85
GHz) respectively and can fulfill the typical bandwidth
requirement for the RFID applications. The VSWR vs
frequency graph in the Fig. 3 demonstrates the resonance at
two frequencies that is at 2.41 GHz and 5.85 GHz for which
the VSWR graph attains the minimum VSWR value of 1.14
and 1.46 respectively. From the Fig. 4 the variation of the input
impedance of the C-shaped monopole antenna can be seen. At
the resonance frequencies of 2.56 GHz and 5.65 GHz, the
average value of the resistance (real part) is approximately 50Ohms
and the average value of the reactance (imaginary part)
is O-Ohms signifies the adequate impedance matching occur at
the two desired resonant frequencies . The Fig. 5 depicts the
variation of gain in dB of C-shaped monopole antenna with the
frequency. The gain (dBi) increases with the increase in
frequency and attains a maximum gain of 1.71 dBi at 6 GHz.
The gains at 2.4 GHz and 5.8 GHz are -2.70 dBi and 2.67 dBi