CSRR based patch antenna for Wi-Fi and WiMAX Applications

In this paper, a novel compact microstrip patch antenna is proposed for WiFi and WiMAX bands. To achieve miniaturization the dimensions of the square radiating patch are chosen with reference to the high frequency band (3.3 GHz). The dual band is achieved by loading a Complementary Split Ring Resonator (CSRR) into the radiating patch. The left handed nature of the CSRR is the cause for low frequency band (2.4 GHz). To improve the return loss bandwidth and axial ratio bandwidth at upper band the fractal concept is introduced along the edges of the square patch. Thus a low volume dual band antenna is simulated using HFSS. A comparison with measured data is also presented. The fabricated antenna is found to be occupying 25% less volume (with reference to 2.4 GHz) than existing antennas which is mainly due to the blending of the two recent concepts ‘metamaterials and fractals’.


Introduction
The modern wireless hand held gadget need to operate at multiple bands to be able to provide communication as well as GPS types of other services [1].Instead of using multiple antennas for multiple operating frequencies, a single Microstrip Patch Antenna (MPA) which serves at all operating frequencies like WLAN, Wi-Fi and WiMAX applications with less size and wider bandwidth at each operating frequency is the most wanted candidate for today's wireless hand held devices.In conventional dual band or multiband MPAs the dimensions of the radiating patch are taken with reference to lowest frequency band which requires more size, however in the case of dual band antennas based on metamaterials the dimensions of the radiating patch are taken with reference to high frequency band which requires less size because of left handed nature.The novelty of this antenna is to embed metamaterials and fractal curves into the conventional MPA to realize at Wi-Fi and WiMAX applications.
Metamaterials are classified into Epsilon Negative materials (ENG), Permeability Negative materials (MNG), and Double Negative materials (DNG) [2,3].These materials can be realized by using metallic , Split Ring Resonators (SRRs) and the combination of both Vias and SRRs respectively.The characteristics of SRRs and CSRRs have been studied and analyzed by several groups [4][5][6][7][8][9][10][11][12][13][14][15][16][17].By applying the concept of duality to the negative permeability nature of SRR, the negative permittivity nature of CSRR can be obtained.The CSRR unit cell has strong potential applications in designing CP antennas and dual band antennas because of its special property of zero mode resonance.In [5][6][7][8], dual band antennas are presented by inserting CSRR in the radiating patch.In [9][10][11][12][13], single band and dual band antennas are designed by etching CSRR from the ground plane.In [14][15][16], dual band and single band antennas are designed by using MNG materials.In [17], the combination of both DNG and Double Positive materials is used to get dual band antenna.The antennas mentioned above occupy a large volume in terms of surface area or thickness for Wi-Fi and WiMAX applications and also provide low bandwidth.However, with thin sized hand held devices becoming popular, there is a need for designing an ultra thin antenna to operate at 3.4 GHz and 2.4 GHz with wide bandwidth at each frequency.To obtain CP with a single feed arrangement at patch mode (High frequency) the fractal concept is introduced into the symmetrical radiating patch [18,19].
In this paper, with a single layer patch antenna is proposed using both poly fractal concept as well as CSRR for the first time.The probe feed mechanism is adopted for its ease of use.Ansoft HFSS (High Frequency Structure Simulator) software tool is used to simulate the proposed antenna.The measurement with the fabricated antenna is compared with the simulated data.

Geometry of the proposed antenna
The geometry of the proposed antenna is shown in the Fig. 1.Rogers RT/Duroid 5880 substrate with dielectric constant 2.2 and thickness 3.175 mm is used.CSRR is etched from the patch to get dual band operation.The dimensions of the proposed antenna are listed in Table 1.3.5

CSRR and fractal curves
The two topologies of Split Ring Resonator (SRR) and CSRR are shown in the Fig. 2. According to Babinet's principle CSRR is the dual structure of the SRR in which the roles of metal and air are interchanged, and also the role of electric and magnetic field components.The SRR can act as magnetic dipole that can be excited by an external magnetic flux where the CSRR can act as electric dipole that can be excited by external electric field.The equivalent circuit diagram of SRR and CSRR are shown in the Fig. 3, where the C0 is the total capacitance between the rings, L0 is the total inductance, Ls is the series inductance of the SRR, Lc is the shunt inductance, Cc is the shunt capacitance and Cs is the series capacitance of the lower and upper halves of the SRR.The resonant frequency of the SRR is given by Based on duality concept of SRR and CSRR the resonant frequency of CSRR is same as the resonant frequency of SRR.

Simulation Results
The evolution of the proposed design can be understood by considering an evolution of patch antenna design shown in Fig. 5.The simulated return loss characteristics of all proposed antennas are shown in the Fig. 6.By loading CSRR in the radiating patch, the dual band dual polarization operation is obtained.The circular polarization bandwidth at patch mode can be achieved by inserting poly fractal curves along the edges of the patch.The 10-dB return loss bandwidth of all resonating frequencies is listed in Table 2.     3 gives the comparison between the results of the proposed antenna and the antennas which already exist in the literature.The proposed antenna is more compact and producing wide bandwidth compared to remaining antennas listed in Table 3. 16.8x20.840x50x0.494.9, --5.3, -

Conclusion
A novel miniaturized single probe feed poly fractal boundary patch antenna loaded with CSRR for dual band operation has been presented.The Simulated 10-dB return loss bandwidth of proposed antenna is <1% (resonating at 2.4GHz only) at the lower resonating frequency and is 8.72% (3.07-3.35GHz) at the upper resonating frequency.The 3-dB axial ratio bandwidth of the antenna at upper frequency band is around 2.49% (3.17-3.25 GHz).Proposed antenna can be conveniently used in portable devices because of its compactness for Wi-Fi and WiMAX applications.

Figure 1 :
Figure 1: Geometry of the proposed antenna

Figure 5 :
Figure 5: Evolution of the proposed antenna Initially, the square patch Ant1 is chosen as a reference which is resonating at 3.4 GHz with linear polarization.Poly fractal curves are introduced along edges of the square patch Ant1 to get Ant2 which results in CP.Ant3 can be obtained by introducing CSRR in the patch which results in double band operation with Linear Polarization.Ant4 represents the dual band dual polarization version achieved by introducing poly fractal curves to the edges of Ant3.Finally, Ant4 is the proposed antenna with dual band dual polarization.The simulated return loss characteristics of all proposed antennas are shown in the Fig.6.By loading CSRR in the radiating patch, the dual band dual polarization operation is obtained.The circular polarization bandwidth at patch mode can be achieved by inserting poly fractal curves along the edges of the patch.The 10-dB return loss bandwidth of all resonating frequencies is listed in Table2.

Figure 6 :Figure 7 :
Figure 6: Return loss characteristics of the proposed

Figure 8 :Figure 8 :
Figure 8: Radiation efficiency of the proposed antenna4.Measured ResultsThe proposed antenna (Ant4) fabricated on Rogers RT/Duroid substrate with dimensions 37x37x3.175mm3 is shown in Fig.8.The return loss characteristics are measured using Agilent 8719A microwave network analyzer.Radiation pattern measurements are taken in an anechoic chamber having the physical dimensions of 22.5 x 12.5 x 11.5 m3 and with the operating frequency range of 400 MHz to 18 GHz.

Figure 9 :
Figure 9: Return loss characteristics of the fabricated antenna The 10-dB return loss bandwidth is 8.22% (3.01-3.27GHz) at upper resonating frequency band due to current at patch edges and <1% (resonance at 2.4 GHz only) at

Figure 10 :Figure 11 :Figure 12 :Figure 13 :
Figure 10: Axial Ratio characteristics of the proposed antenna The radiation patterns of the proposed antenna at the lower and upper resonating bands (2.4 GHz and 3.2 GHZ) are shown in the Fig. 11& 12 respectively.The gain of the proposed antenna is given in Fig. 13.

Table 1 :
This is an example of a table.

Table 3 :
Comparison with existing literature.