Fig. 10Simulated and measured gain (dBi) of the proposed antenna
The stability of radiation pattern, gain, polarization, reflection
coefficient etc, when radiated at different frequencies, the phase
difference is not taken into account. At the same time all the frequency
components of the UWB system are radiated. In order to reconstruct the
phase on reception for different components, the stability must take
into account the phase difference. The group delay is considered as the
figure of merit. In the UWB communication system, UWB pulse distortion
by an antenna is an important issue as the UWB system helps in pulse
transmission. A constant group delay (linear phase response) is needed
in the UWB system in true sense. The simulated and measured group delay
of the proposed UWB notch antenna is shown in figure 11. The simulated
group delay for the UWB notch antenna is around 2 ns at the notch
frequency of 5.5 GHz. This disturbance of phase response as group delay
occurs due to notch characteristics of the proposed UWB notch antenna at
5.5 GHz. At this frequency of 5.5 GHz, linear phase response of the UWB
notch antenna is disturbed. On the other hand, the measured group delay
of the proposed antenna is in accordance with the simulated one. The
measured group delay of the proposed antenna is around 2.8 ns. Apart
from this notch band the phase response of the proposed antenna in the
UWB frequency range for simulation and measurement are consistent and
are at the approximate average value of 0.2 ns from 3.097GHz to 13.326
GHz. Hence from figure 10 it is clear that the proposed antenna exhibits
excellent linear response in the UWB range of 3.097GHz to 13.326 GHz
except at the notch band centered at 5.5 GHz.