3.2.2 Design and EM models with parametric study

The main design parameter for UWB antenna is the lower frequency edge (fL) rather than the resonance frequency (fr) as in Eq. (7). The lower band edge frequency of the designed antenna is calculated approximately by equating their surface area with that of an equivalent cylindrical monopole antenna of the same height as given by [45]. If R1 is the height of the planar monopole antenna in cm, which is taken the same as that of an equivalent cylindrical monopole, and r in cm is the effective radius of the equivalent cylindrical monopole antenna, which is determined by equating area of the planar and cylindrical monopole antennas, then the lower band edge frequency is given as [45]:

$$f\_L = \frac{7.2}{L\_f + R\_1 + r} \text{GHz} \tag{7}$$

The design started with first semi arc 1800 with radius 25 mm and with 5 mm width modified ground plane Lg = 19 mm as shown in Figure 13(a), and related |S11| is shown in Figure 14. To improve the bandwidth, second semi sector with radius 17 mm and width 3.5 mm as shown in Figure 13(b) with the same previous dimensions is added to add second resonant as shown in Figure 14. Third sector with radius 7.5 mm and width 2.5 mm is added, and keeping previous dimensions the same as shown in Figure 13(c), a third resonance is achieved as shown in Figure 14. Another extension of the bandwidth is done by adding circular disk with radius 4 mm as shown in Figure 13(d), and related reflection coefficient is shown in Figure 14. Modified ground plane is used to improve the bandwidth with ellipse with major radius 25 mm and minor radius 15 mm, as shown in Figure 13(e), is suggested, and the related reflection is shown in Figure 14. The evolution of designing the proposed configuration is demonstrated in Figure 13(f), and their corresponding optimized dimensions are tabulated in Table 3. The antenna gain and radiation efficiency are also studied as shown in Figure 15. The proposed antenna with SRR achieves an average gain of 7.5 dBi, and the peak realized gain around 22.5 dBi at 7.5 GHz as shown in Figure 15(a). The designed antenna gain without SRR achieves an average gain around 5.5 dBi, while peak gain realized is 15 dBi at 8.5 and 10 GHz. The gain of the designed antenna is also measured, and there is good agreement between results especially at high frequency. The antenna radiation efficiency was simulated for both monopole antennas with and without SRR by using wheeler cap method [44]. The average radiation efficiency is around 70% over the operating bands for PMPA with SRR and around 65% without SRR as

Passive Components for Ultra-Wide Band (UWB) Applications

DOI: http://dx.doi.org/10.5772/intechopen.88444

shown in Figure 15(b).

Figure 14.

Table 3.

113

Design procedures of the proposed antenna [45].

Dimensions of the proposed antenna (all dimensions in mm) [45].

Lsub Wsub W1 W2 W3 R1 R2 50 50 5 3.5 2.5 25 17 R3 Rs S1 S2 Wf Lf Rg 7.5 4 5 2.4 3 20 20

where Lf is the length of the 50 Ω feed line in cm.

Figure 13.

Evolution of the design steps of the proposed printed monopole. (a) First step, (b) second step, (c) third step, (d) fourth step, (e) fifth step, and (f) sixth step [45].
