Design and implementation patch antenna with different fractal shape

This work presents the effect of fractal shapes on the patch antenna. It is a conventional rectangular patch antenna with dimension of 9.2 mm × 6.94 mm. It is implemented on FR-4 lossy substrate material with relative permittivity of εr = 4.3, thickness of 1.6 mm and loss tangent of 0.025. It is feed through a microstrip line with dimension of 6 mm × 3.11 mm. The overall dimension of the antenna is 35 mm × 30 mm × 1.6 mm. It operates over a frequency band from 8 GHz to 12 GHz with central frequency 10 GHz. Application of Pythagorean tree Sierpinski gasket, and Koch curve is to decrease the bandwidth and increase the gain of the designed antenna. The performance properties of the antenna such as resonant frequency, radiation pattern, and gain were examined by simulation. The design is implemented through CST microwave studio and measured through network analyser.


Introduction
Antenna makes possible communication between two or more stations by sending or receiving signals from stations in wireless communication. There are different types of antennas but patch antennas are chosen due to low profile and simple manufacturability. Patch antennas are low profile, conformable to planar and non-planar surfaces, simple and inexpensive to manufacture using modern printed-circuit technology, mechanically robust when mounted on rigid surfaces, compatible with Monolithic Microwave Integrated Circuits (MMIC) designs, and when the particular patch shape and mode are selected, they are adaptable regarding resonant frequency, polarization, pattern, and impedance. Furthermore, through adding loads between the patch and the ground plane, adaptive elements with varying resonant frequency, impedance, polarization, and pattern could be designed.
Main performance disadvantage of microstrip antennas are their low efficiency, low power, high Q (sometimes in excess of 100), poor polarization purity, poor scan performance, spurious feed radiation and very narrow frequency bandwidth. Although there are methods to increase the height of the substrate to increase the efficiency and the bandwidth, surface waves extract the power available [1][2][3][4]. In this paper, a microstrip feed patch antenna is designed at 10 GHz and 5GHz. The effect of fractal shapes is presented.

Microstrip Feeding
The most common methods of analysis are transmission line, cavity, and full wave. Transmission line model is used in which a conducting strip is connected directly to the edge of the microstrip patch. The conducting strip is slighter in width as compared to the patch. Transmission line method is simple, easy, and gives good insight, but not accurate and more difficult to model coupling.

Fractal Shapes
There are various types of fractal shapes but in this paper Pythagorean tree, Sierpinski gasket, and Koch curve are used. In Pythagorean tree, square patches only are used. In Sierpinski Gasket, triangular shape only used for cutting and filling patch with different various dimensions. In Koch curve, line segment keeps divided into four equal length line segments [5][6][7][8].   Moreover, another configuration is illustrated in figure 6 which represents the Koch curve on the conventional patch. The patch length equals to 5.65 mm and the patch cuts length equals to 1.2 mm.   The return loss of first Pythagorean iteration equals to -12 dB while the second Pythagorean iteration equals to -20.3 dB.
The bandwidth of iteration one equals to 336 MHz and iteration two equals to 331 MHz. The gain equals to 5dB and 3.02 dB respectively. Figure 9 shows the return loss of three Sierpinski iterations on the first Pythagorean iteration.
The return loss of second and third Sierpinski equals to -11.6 dB, while the first iteration's return loss equals to -13.85 dB. The gain values respectively are 4.8 dB, 4.7 dB, and 4.7 dB.

Conclusion
Patch antenna is presented showing its structure, features, manufacturing, applications and implementation using CST. It includes design of conventional patch antenna using FR4 substrate of relative permittivity 4.3, loss tangent 0.0025 and substrate thickness of 1.6 mm which conducted bandwidth of 0.675 GHz and gain of 3.45 dB at 10 GHz. Applying the Pythagorean first iteration to the conventional patch exhibits high gain of 5dB and lower bandwidth of 0.336 GHz which is fabricated and measured using network analyzer. The paper has 9 designs using fractals and simulated using CST. One notices an agreement between the simulated and the fabricated results. The Sierpinski gasket iterations added to the first Iteration Pythagorean tree exhibits lower bandwidth only. Furth more, Sierpinski gasket iterations are applied on the second iteration of the Pythagorean tree and resulted in lower gain, lower bandwidth, and lower beam width.