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The design and development of a proximity fed dualband microstrip patch antenna based on David fractal geometry are presented. David fractal microstrip antenna offers good performance in the 1.754 - 1.816 GHz and 3.37 - 3.415 GHz bands and is suitable for GSM 1800, WiMAX applications. The use of David fractal geometry offers miniaturization of the antenna structure. The proposed first iteration fractal configuration is fabricated and measured results along with simulation results are presented. Good radiation patterns and moderate gain are also obtained.

Nowadays antennas with multi-band and smaller dimensions than conventional ones are preferred. Multiple resonances with good gain in a single patch are not directly attainable in simple microstrip antenna. Various techniques have been utilized in the antenna research to reduce size and to achieve multi-band characteristics in a single patch. A review of various techniques to minimize the antenna size is given in Ref. [

Recently fractal techniques have been widely applied to antenna design to reduce the antenna size and to achieve multi-band behavior. Fractal antennas can be physically small but have electrically long lengths in small packages. Fractal geometry composed of multiple iterations of a single elementary shape, can be continued infinitely thus forming a shape within a finite boundary but of infinite length or area. This compactness in property is highly desirable in mobile wireless applications. The advantages of fractal antenna compared with a standard microstrip antenna are centered on miniaturization and bandwidth. Various geometries have been utilized to develop fractal antennas in order to have multi-band characteristics and miniaturization. Much intensive researches have been done in recent years to develop fractal antennas: long periodic fractal Koch antenna [

Compared with the conventional square and circular patch antennas nowadays a lot of fractal antennas are developed with pentagon and hexagon shaped patches. A slotted grounded hexagonal microstrip antenna with a parasitic element is presented in [

The recent growth and rapid development of mobile communication systems and devices operating at multiple frequency bands have led to the requirement of antennas which support multi-band or wideband operation. Various wireless communication services have been available which may use frequency spectrum allocation like WiMAX/Wi-Fi etc. along with GSM communication system. This leads to development of multi-band antennas, where GSM mobile communication as well as WiMAX/Wi-Fi can be used simultaneously. Various research papers have reported about dual band antennas that are suitable for above mentioned application [

In this paper, a novel hexagonal fractal microstrip antenna is proposed for multi-band applications. David fractal [

The fractal design of antennas results from the blend of two discipline, electromagnetic theory and fractal geometry. The term fractal and fractal dimensions were coined by B. Mandelbrot [

The antenna is fabricated onan FR-4 substrate of thickness 1.6 mm with relative permittivity of 4.4 and loss tangent of 0.002. The zeroth iterated level antenna consists of a hexagonal patch, with each side of the patch having a length of 24.6 mm, resonating at 1.8 GHz called the initiator as shown in the

The measurements were carried out in an anechoic chamber using HP 8510C Network Analyzer. The chamber was arranged such that the source remains stationary as the antenna under test (AUT) rotates. A standard horn antenna is used as the reference antenna for the measurements. The antenna under test is placed in an antenna

Parameter | Value | Parameter | Value | Parameter | Value |
---|---|---|---|---|---|

L_{1} | 72 | W_{1 } | 84 | LS_{1} | 21.4 |

holder, which is set to rotate the antenna in small steps of 1˚ to obtain a 360˚ radiation pattern. The microwave materials that covers the wall, top and bottom surfaces absorbs electromagnetic energy so that the anechoic chamber to replicates a space equivalent.

^{st} level iterated David fractal hexagon patch antenna. It can be seen that the −10 dB bandwidth for the measured return loss is 62 MHz (1.754 - 1.816 GHz) and 45 MHz (3.37 - 3.415 GHz) respectively, which can cover GSM mobile communication system and WiMAX applications in the 4 G mobile phones.

The co-polar and cross polar radiation patterns have been measured at two different frequencies of 1.79 GHz and 3.385 GHz for both E and H plane. The radiation pattern data are normalized in order to plot the co-polar and cross polar patterns in one graph. The measured far field radiation patterns of the dual band David fractal first level iterated antenna in the E plane (y-z plane) and H plane (x-z plane) are plotted at the frequency of 1.79 GHz and 3.385 GHz is shown in

Parameter | Simulated | Measured |
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Resonance frequency f_{1} (GHz) | 1.8 | 1.79 |

Bandwidth_{1} (MHz) | 55 | 62 |

S_{11} (dB) | −18.7 | −13.54 |

Gain (dBi) | 6.93 | 6.5 |

Resonance frequency f_{2} (GHz) | 3.4 | 3.385 |

Bandwidth_{2} (MHz) | 31 | 45 |

S_{11} (dB) | −14.3 | −16.48 |

Gain (dBi) | 5.3 | 4.9 |

The measured gain of the antenna is 6.5 dBi at the lower resonant frequency and 4.9 dBi at the upper resonant frequency. The upper band characteristics will find useful in the non-line of sight applications including WiMAX. It is also observed that size reduction up to 18.3% in terms of overall size and 23.4 % in terms of the copper cladding is obtained in comparison with a hexagon patch microstrip antenna resonating in the first resonant frequency band.

The proposed hexagon shaped David fractal microstrip patch antenna has demonstrated its potential for multi-band operation. The antenna generates two resonating modes centered at the measured frequencies of 1.79 and 3.385 GHz; the first band finds application in GSM mobile phone communication and the second band finds application in WiMAX. The proposed multi-band antenna provides moderate gain and good radiation characteristics.

Authors would sincerely express the gratitude to Mr. Kuruvilla George, Verdant Telemetry and Antenna Systems (P) Ltd. for providing the measurement facilities.