he Federal Communication Commission (FCC) allocated the frequency band spectrum from 3.1 to 10. 6 GHz for monetary communication applications in year 2002 [1]. This resulted in the development of several antennas which operate in the ultra wideband (UWB) range. It is also expected that in this range frequency satisfactory radiation properties are required. An UWB antenna which satisfies the more requirements like a small size, consistent group delay, omnidirectional radiation patterns, and gain beyond whole band [2,3]. There are several works reported in literature on these kinds of antennas [3][4][5][6][7][8][9][10][11][12][13][14][15]. By adding half wavelength V-shaped slot on radiating patch, UWB antenna achieves sharp band notched characteristics [3]. A lower pass band, 2.4 GHz Bluetooth band (2.4 -2.484 GHz), can be realized by adding a pair of U-shaped parasitic strips bilaterally beside the feed line which covers whole UWB band [4].

In [7], by inserting an U shaped slot on radiating patch which produces band notch characteristics. The main goal in UWB antenna design is achieving the wide impedance bandwidth with high radiation efficiency. Section 2 describes the basic geometry and its operation. Geometry oprtimization procedure is covered in Section 3. Experimental validation of the proposed antenna is presented in Section 4. Finally, Section 5 concludes the work carried out and guidelines the future scope.

Figure 1 shows basic geometry of the proposed antenna. The proposed antenna is having a low profile geometry with overall dimensions of 24 x 25mm x 1.6mm (LxWxh). The substrate used for design and fabrication is FR4 glass epoxy substrate with relative permittivity of 4.4, thickness of 1.6mm, and loss tangent equal to 0.02. The geometry is basically a CPW fed monopole antenna. An elliptical slot is etched in the ground with major axis radius of 11.55 mm and minor axis radius of 10 mm. Hexagonal stub is attached to the signal conductor of the CPW line to ensure the impedance matching. Also, a rectangular slot is made on the hexagonal stub to excite multiple bands and to enhance their bandwidths. The other dimensions are mentioned in Table 1 based on the optimization procedure discussed in Section 3.

Values (mm) 24 25 2.59 3.6 7.2 7.1 5.29 2.2 0.1 1 10 11.55 5.66

This section covers the geometry optimization by varying some parameters of the antenna geometry. The parameters utilized for optimization are gap ð??"ð??" 1 , The gap between signal conductor and ground (g 1) was varied from 0.1 to 0.2 in steps of 0.05 mm by keeping all other parameters constant. Effect of g 1 on S 11 characteristics is presented in Figure 2. From Figure 2 it may be noted that impeadance matching may be fine tuned with this parameter. From this study the gap value of ð??"ð??" 1 = 0.1mm was noted as an optimum.

In anoter effort, rectangular slot length (L s ) was varied from 5.7 mm to 7.2 mm in steps of 0.5mm with all other parameters kept constant. Effect of variation of rectangular slot's length on reflection coefficient characteristics are presented in Figure 4. In this observation, a slot value of L s = 7.2 mm offered the optimum impedance bandwidth. It may be noted that slot length beyond 7.2mm cuts the edges of the hexagonal signal conductor stub.

The prototype of antenna geometry shown in Figure 1 was fabricated and tested experimentally for its validation. The dimensions used for prototype development are as listed in Table 1. Substrte used for development is an FR4 glass epoxy material whose height is 1.6mm and having a relative permitivity of 4.4 with dielectric loss tangent of 0.02. The photograph of the fabricated design is as shown in Figure 6. Antenna's reflection coefficient parameters were measured using Agilent's network analyzer. Measured characteristics are compared with simulated values and presented in Figure 7. Although, a mismatch was observed due to fabrication inaccuracies, tri band operation was observed. Three resonances are obtained at 5.9GHz, 9.9GHz, and at 14.4GHz. V.

A planar patch antenna fed with CPW feed has been presented for tribands operation. Proposed antenna is basically a monopole antenna. A rectangular slot was loaded to excite three resonance bands. Slot and hexagonal dimensions are tuned for impedance matching of antenna. Three resonances obtained are at 5.9GHz, 9.9GHz, and at 14.4GHz. Stable radiation patterns have been obtained across the bands of operation. The proposed antenna is suitable for tribands applications. The future work includes the bandwidth optimization of the three frequency bands.