1. Design Regular Fractal Slot-antennas for Ultra-wideband Applications
Majed O. Dwairi, Mohamed S. Soliman, Ahmad A. Alahmadi,
Iman I. M. Abu Sulayman, and Sami H. A. Almalki

2. Abstract: This paper presents design of fractal regular slots patch antennas for Ultra-wideband (UWB) systems. The reference antenna has a rectangular radiator mounted on a dielectric substrate and fed by a microstrip feed line of 50 Ω characteristic impedance. Different fractal slots with regular configurations have been inserted randomly to the patch to modify the antenna characteristics and decrease the patch area. Four proposed antennas iterations are the investigation was in terms of the antennas different parameters including impedance band-width, radiation patterns, gain, and group delay evaluation. The simulation results prove that the fractal slot configurations and positions create a filtering behavior in form of the mismatch band and band reject characteristics.

3. Outlines Introduction Antenna structure and design
Results and discussion
Conclusions

4. 1. Introduction
Since February 2002, the Federal Communications Commission’s (FCC) in United States accredit the radio frequency band from 3.1 GHz to 10.6 GHz for commercial civil services of Ultra-wideband (UWB)communication system
Planner compact configuration with high performance characteristics is a main challenge and an essential target for antenna designers and researchers
Many comprehensive studies in the fractal antenna issue have been developed
This projet proposes design of fractal regular slots patch antennas for UWB applications. The reference antenna is a monopole patch antenna. Different fractal slots with regular configurations have been inserted randomly to the patch to modify the antenna characteristics and decrease the patch area. Four antennas iterations are investigated in terms of the antennas different parameters including impedance band-width, radiation patterns, surface current distribution, gain, and group delay evaluation

5. 2. Antenna Structure and Design
The reference ultra-wide band antenna is a mono-pole type which was reported in [16] figure.1. It has a copper patch mounted on FR4-epoxy substrate with a relative permittivity of 4.4, and a dielectric tangent loss of The other side of the antenna has a partially coppered ground sheet as shown in figure 1. The overall dimensions of the reference antenna are listed in Table 1
Fig.1.
Table1: The dimensions of the reference ultra–wideband antenna.
Antenna Element
Dimension Parameter
Patch
Wp=13 mm, Lp=14 mm,tp=0.07 mm
Feed line
Wf=2 mm, Lf=20 mm, Xf=8.5 mm
Substrate
Ls=36 mm, Ws=24 mm, ts=1.52 mm
Ground Plane
Lg=18 mm, tg=0.07mm

6. The proposed fractal regular slots patch configurations In this study, regular fractal deterministic slots have been inserted randomly in the radiator of the reference to modify the antenna characteristics. Four different iterations have been designed and modeled as shown in figure 2. The area of the proposed fractal slots for each iteration and the total area reduction is listed in table 2
Fig.2

7. Table 2The areas of the proposed different fractal slots

8. 3. Results and Discussion
3.1 Impedance Band-width Characteristics The simulated return loss characteristics have been carried by Ansoft High-Frequency Structure Simulator (HFSS) [17] for the reference antenna and all the proposed four fractal patch iterations as illustrated in figure 3.
Fig.3

9. It is clear that, there is no bandwidth enhancement for all antennas
It is clear that, there is no bandwidth enhancement for all antennas. The band notched or reject band characteristics can be found in all antennas except itr_2, itr_3, Most of antennas have one mismatched band except itr_3 provided two mismatched bands, as summarized in table 3.
Table 3: Reject bands and mismatch bands for the proposed four different fractal antennas
Antenna Number
Reject bands
(S11>-7dB)
in GHz
Mismatch bands
(-10dB<S11<-7dB)
Itr_1
Itr_2 -
Itr_3 ,
Itr_4

10. The variation of the simulated VSWR for the selected four iterations and the reference antenna is less than 2 for the most UWB spectrum as shown in figure 4. There is slight change in the VSWR to be more than 2 in the frequency range from 8.4 GHz to 10 GHz, where the maximum value of the VSWR occurred at 9.1GHz for itr_1, itr_2, itr_4 is 2.69,2.45and 2.59 respectively, while for itr_3 is 2.26 at 9.3GHz
Fig.4

11. 3.2 Radiation Patterns Figures 5(a){(e) shows the simulated 3Dradiationpattern characteristics for the proposed antennas (reference, itr 1, itr 2, itr 3, itr 4) at 4.3 GHz, 6.3 GHz, 7.5 GHz, and 10.4 GHz. It can be observed bthat as the solution frequency changes form 4.3 GHz to 10 GHz, the radiation shape is alternating gradually from a stable directive-monopole pattern to slightly near to omnidirectional characteristic.

12. Figure 5: The simulated 3D radiation pattern at frequencies 4.3 GHz, 6.3 GHz, 7.5 GHz, and 10.4 GHz forthe
propose antennas. (a) Reference. (b) Itr 1. (c) Itr 2. (d) Itr 3. (e) Itr 4.

13. 3.3. Gain Characteristics Figure 6 shows the total gain characteristics where the maximum gain for the reference antenna, itr 1, itr 2, itr 3, and itr 4 is 5.97 dB at 11.7 GHz, 6.04 dB at 11.5 GHz, 6.13 dB at 11.5 GHz, 4.97 dB at 11.6 GHz, 5.78 dB at 11.4 GHz respectively. Moreover, the estimated gain variation in the UWB frequency range for the reference antenna, itr 1, itr 2, itr 3, and itr 4 is dB{5.241 dB, dB{5.254 dB, dB{5.279 dB, dB{4.385 dB, and dB{5.213 dB respectively.

14. Figure 6: The simulated gain characteristics for the reference antenna, itr 1, itr 2, itr 3, and itr 4.

15. 3.4. Group Delay Evaluation Figure 7 shows the simulated variation in the group delay characteristics for the reference antenna, itr 1, itr 2, itr 3, and itr 4. The delay characteristics is almost constant over all the UWB frequency range, except for itr 1 and itr 3 where the maximum value of variation in the group delay occurred at 5.8 GHz of 1.64 ns and 1.59 ns respectively. Fig.7

16. 4. CONCLUSIONS
This paper presented design of fractal regular slots patch antennas for Ultra-wideband (UWB) systems. The reference antenna is a monopole type patch antenna of a rectangular radiator mounted on a dielectric substrate and fed by a 50­ feed line. Four different fractal slots with regular conjurations have been inserted randomly to the reference patch antenna. These four proposed antennas iterations are investigated in terms of the antennas different parameters including impedance band- width, radiation patterns, gain, and group delay evaluation. The band reject and mismatch band are less than 0.65 GHz and 1.90 GHz respectively. Good radiation pattern has been observed which alternating gradually from a stable directive-monopole pattern to slightly near to omnidirectional characteristic. The maximum gain is more than 4.97 dB. The group delay mainly constant with a small variation less than 1.65 ns over entire UWB spectrum ensure good antenna performance. The average radiation effciency is about 85% for all proposed cases. Additionally, the reduction in the patch area is greater than 30% in some cases for same or good antenna performance. This add a new feature for the proposed antennas to be good candidates for the UWB portable applications.

17. Thank you for your attention