3.1 UWB CPW-fed LPDA for wireless applications

This section presents a LPDA for UWB applications [39]. The antenna consists of cascading four U-shaped elements of different line lengths with balun circuit to improve the antenna impedance matching. The proposed antenna area dimensions are 50 50 mm<sup>2</sup> built on FR4 substrate thickness 0.8 mm. Simulator HFSS is used for modeling the designed antenna. The pulse distortion is verified by measuring the proposed antenna performance with virtually steady group delay. The simulation and measurement results show that the designed antenna exhibits good impedance matching, stable radiation patterns throughout the whole operating frequency bands, acceptable gain and stable group delay over the entire operating band.

the number of trial steps is needed, the scale-factor τ, spacing factor δ, and the number of the dipole elements N should be determined. Second, the length of the longest arm, which responses to the lowest resonance frequency f1, should be

> Wi�<sup>1</sup> Wi

<sup>δ</sup> <sup>¼</sup> Lisep 4Wi

<sup>W</sup><sup>1</sup> <sup>¼</sup> <sup>λ</sup>1,eff

where λ1eff, Bo, N, and int i are the longest effective operating wavelength, the operating frequency, number of elements, and i is an integer that varies from 2 to 5, respectively. To improve the impedance, matching the balun circuit with suitable dimensions is used as shown in Figure 9. Table 2 introduces the dimensions of the

The designed antenna is fabricated by using photolithographic technique, as shown in Figure 10, and parameter performance is measured. The simulated and measured input reflection coefficient of the antennas is in good agreement, as shown in Figure 10(b). The designed dipole impedance bandwidth at �10 dB of antenna extended from 1.85 to 11 GHz to cover most of the wireless applications and FCC UWB regulation. The antenna gain data are compared between measured and simulated results as shown in Figure 11. The designed LPDA antenna achieves simulated average gain 5.5 dBi, and the peak realized gain around 6.5 dBi at 2.7 GHz as shown in Figure 11(a). The measured results show very good agreement with simulated results and about �3 dBi difference on average over the operating band. Wheeler cap method [44] can be used to calculate the antenna radiation efficiency. The average radiation efficiency is around 70% over the operating band as shown in

Then the radiation efficiency measured result is done by using horn antenna to

Lsub Lg Wsub Wg W1 W2 W3 SgW4 50 13.5 50 24 15.3 11.7 8.5 0.9 0.6 6 Lsep L4 Lfeed L3 L1 L2 Wf KP d 7.6 2.1 45 2.8 3.6 3 6 8.5 4.5 1000

Dimensions of the proposed antenna (dimensions in mm) [39].

complete the designed antenna radiation efficiency measurement as shown in Figure 11(b). In the designed antenna, the radiator and the ground plane are contributing to radiation. For UWB applications, omnidirectional radiation pattern is an important requirement. At lower frequency band of operation, the pattern resembles a conventional dipole antenna, but at higher end of the UWB spectrum,

¼ τ (1)

<sup>4</sup> (3)

N ¼ 1 � ð Þ lnBs=ln τ (4) Ba ¼ 1:1 þ 30:7 δ ð Þ 1 � τ (5)

Bs ¼ BaBo (6)

(2)

computed by following Eqs. (1)–(6) [39].

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

Passive Components for Ultra-Wide Band (UWB) Applications

proposed antenna [39].

3.1.2 Measured results

Figure 11(b).

Table 2.

109

LPDA is UWB with the multiple resonance property; its bandwidth can be enhanced by increasing the number of the dipole elements [40–42]. Balanced structure, CPW fed antennas are very good candidates since the feed lines and the slots are on the same side of the substrate. There are many researches done to design LPDA but most of the published papers are not compact and their length is near from wavelength. The compact antenna dimensions, as shown in Figure 9, are <sup>50</sup> <sup>50</sup> 0.8 mm3 . The proposed USLPDA antenna introduces USUWB with the multiple resonant property and compact size compared to earlier designs where UWB was realized using a rectangular slot [43], U-shaped dipole elements or stubs [38]. The bandwidth of this antenna at 10 dB reflection coefficient extends from 1.85 to 11 GHz which is wide enough to cover the FCC approved UWB in addition to wireless communications. The antenna exhibits good performance and can operate at wireless applications.
