Analysis and Development of Triangular Gasket Diagonal Slot Embedded Fractal Patch Antenna for Multiband Wireless Applications

This paper presents novel reduced size diagonal slot embedded Triangular Gasket fractal patch antenna for multiband wireless applications. The diagonal slot geometry is embedded in triangular patch antenna for initial size reduction of the basic cell and further miniaturization is achieved by fractalization of the cell upto third order. Three frequency resonances of 2.4, 6.5 and 9.23 GHz are optimized for WiFi, WiMAX and WLAN (Wireless Local Area Network) applications in the S, C and X frequency bands. Size reduction upto 55.32 and 80.74% is achieved in terms of whole antenna area and copper cladding remaining respectively in comparison to triangular patch antenna. Antenna 3D (Three-Dimensional) modeling, simulation and optimization for the desired BW (Bandwidth) and gain requirements are done in HFSS (High Frequency Structure Simulator) and CST (Computer Simulation Technology). Effects of embedding diagonal slot in the basic triangular cell is analyzed in terms of the diagonal slot length and width with corresponding frequency response variations. Microstrip feed line dimensions and ground plane separation from the radiating top layer is optimized for achieving acceptable BWs less than -10 dB for the desired multiple resonances. E-field, H-field, current density and surface current plots are presented to verify the radiations for multiband wireless applications. Proposed slot embedded fractal radiator is fabricated and measured frequency responses and gain patterns are demonstrated in comparison with simulated results for verification of the concept.

. Overall array size and inter element mutual coupling is reduced by using fractal based EBG (Electromagnetic Band Gap) decoupling rows placed between the array elements [2], with insertion loss improvement of 13 dB is attained by compact structure as well as embedding of slots at the ground plane. Hexagonal shaped fractal antenna is used for providing wideband by combining the patch radiating element with Sierpinski square shapes [3], where stable omnidirectional radiation patterns are attained over the wide range of BW.
Sierpinski triangles can also be used to provide radiation for WLAN and WiMAX applications by providing multiport antenna structure with different auxiliary and main ports [4], and enabling time reversal propagation for obtaining enhanced received signal strength in comparison to the transmitted signal strength. Hilbert fractal antennas are used for detecting various partial discharge types in oil insulated system applications [5], where different antenna structures are selected with noisy conditions based on the level of detected signal to noise ratios. Koch Island fractal configuration is numerically and experimentally analyzed and employed in microstrip patch antennas for miniaturization purposes achieving directive patterns having localized current distributions due to higher order modes [6]. Sierpinski fractal antenna with triangular configuration can be used for thermal transfer applications by using diode circuits for switching between ISM (Industrial Scientific and Medical) and UHF (Ultra High Frequency) frequency bands [7]. Dual band operation using two parasitic patches for BW enhancement is presented in [8]. RLC (Resistor Inductor Capacitor) resonators electrical circuit model is presented.
Antenna is optimized using method of moment commercial code for achieving 4.7 and 6.8% BW for the two resonant bands. The radiation in first and second resonance bands is demonstrated using current distribution plots for the top and bottom layer patches respectively. Different ratios of the Sierpinski fractal radiator are analyzed for providing improved input impedance in [9]. Use of pentagonal fractal geometry with embedded first order Koch geometry for miniaturization and multiband radiations is shown in [10].
Sierpinski fractals can also be used along with the dielectric resonator configured antenna for providing dual band radiation characteristics for WiMAX and WLAN applications [11].
Sierpinski fractal carpet antennas can be used for providing improved radiations pattern due to unwanted surface wave cancellation techniques by embedding EBG structures at the ground plane and analyzing the characteristics by using combination of segmentation and modified contour integral methods [12]. Here the impedance BW of the fractal radiator is improved upto 9% in comparison to traditional fractal antennas with impedance BW of 2%. Circular polarization is achieved in microstrip patch antenna by combining layer wise Peano and square structures [13], with multiband characteristics and some degree of miniaturization also achieved, where the microstrip antenna is fed through electromagnetic coupling. Generalized Sierpinski antenna is presented with log periodic characteristics implemented through Pascal triangle [14]. Various fractal element radiator antennas are designed for USB (Universal Serial Bus) dongle, mobile and energy harvesting applications [15][16][17][18][19].     Table 1.
where  is the dilectric constant of the material used for propagation of electromagnetic fields and  is the angular frequency representing the operational frequency of the wave propagation and K is the propagation constant.

MEASURED AND SIMULATED RESULTS
The Triangular Gasket radiator 3D modeling, structure Measured impedance BW for two frequency points in C Band are centered at 5.577 and 6.33 GHz with BW of S 11 less than -10 dB from 5.50-5.65 and 6.28-6.37 GHz respectively. Simulated X band frequency response is centered on 9.208 GHz at -10.41 dB with the impedance BW of S 11  -10dB of 9.14-9.27 GHz, while the measured impedance BW for the X band frequency response is  Fig. 13. The current flow is along y-axis where the Efields for 2.41 GHz is illustrated in Fig. 13(a), signifying the resonance due to the maximum length of the radiator.
The E-fields at 6.5 GHz in C band is shown in Fig. 13