Fig. 2 Chronological developenent of the proposed antenna with
first four iterative processes.
In section one preliminary design of the UWB notch antenna is presented
with four iterative processes. The chronological developenent of the
proposed antenna with first four iterative processes is shown in
figure2. Figure 3 shows the simulated reflection coefficient
(|S11|) of all the first four
iterations of the preliminary design of the UWB notch antenna. In first
iteration shown in top and bottom view of figure2 (a), a simple circular
radiating patch is created which is fed by the microstrip feed line with
a partial ground plane as shown. With these configurations a poor
impedance matching is obtained as the impedance bandwidth obtained as
6.6 GHz (bandwidth from 3.1 GHz to 9.7 GHz). In the second iteration
shown in figure 2 (b), an open-ended rectangular slot is created at the
middle of the ground plane just below the microstrip feed line. The
open-ended rectangular slot in the middle of the ground plane enhances
the bandwidth from 3.1 GHz to 11 GHz with impedance bandwidth 7.9 GHz.
The enhancement of bandwidth due to the creation of an open-ended slot
in the ground plane helps in proper impedance matching between the
microstrip feed line and the circular radiating patch. In the third
iteration a square slot is created for more enhanced impedance matching
purpose which is shown in the figure 2 (c). After the simulation of the
third iteration the bandwidth extended from the 4 GHz to 12 GHz with the
impedance bandwidth 8 GHz. Though the impedance bandwidth increases from
7.9 GHz (second iteration) to 8 GHz (third iteration) but the lower
frequency is increased to 4 GHz which is not acceptable for UWB
operation point of view. To address this problem and for the creation of
notch at fn =5.5 GHz to mitigate out the WLAN
operation in the UWB band, a thick rectangular stub is erected which is
protruding down from the top middle edge of the square slot towards the
center of the square slot created in the circular patch which is the
fourth iteration as shown in the figure 2 (d). Due to this rectangular
thick stub the bandwidth is extended from the 2.8 GHz to 12.4 GHz which
has the impedance bandwidth 9.6 GHz which is 1.6 GHz more than the
impedance bandwidth obtained in third iteration. But at the same time
the protruding rectangular stub creates a notch centered atfns1 =4.7 GHz which is having the notch band
extended from 4.1 GHz to 5.3 GHz. The theoretical notch frequency
(fnt1 ) can also be expressed in terms of the
effective physical electrical current path length
(Leff1 ) around the protruding rectangular stub
and is given by
\(f_{nt1}=\frac{c}{2L_{eff1}\sqrt{\varepsilon_{\text{eff}}}}\)———————————–(1)
where is the effective permittivity of the substrate whose expression is
given by
\(\varepsilon_{\text{eff}}=\frac{\varepsilon_{r}+1}{2}+\frac{\varepsilon_{r}-1}{2}\frac{1}{\sqrt{1+12\frac{h}{W_{f}}}}\)———————————–(2)
εr =4.4 is the permittivity of the substrate andc is the speed of light in vacuum. Putting all the numerical
above in the above expression, the effective dielectric constantεeff was found to be εeff=3.324. The effective physical electrical current path length
(Leff1 ) around the protruding rectangular stub is
found to be 18 mm. Hence applying the equation (1) the theoretical notch
frequency is found to be 4.6 GHz, which is very close to the simulated
value of the center of notch frequency fns1 =4.7
GHz. The difference between the theoretical fnt1and simulational fns1 is due to the different
simulation environment adopted for simulation. Though with the
introduction of protruding rectangular stub enhances the band but
creates a notch with the center notch frequency offns1 =4.7 GHz which is not the required notch
center frequency for WLAN which is fn =5.5 GHz.
From figure 3, the sufficient enhancement of the impedance bandwidth is
depicted with a notch characteristic at aroundfns1 =4.7 GHz. Hence to obtain the required notch
frequency at fn =5.5 GHz and also extended
impedance bandwidth, an open-ended slit ring and a SRR is embedded in
the proposed antenna structure which is described in section two.