Design and Analysis of Compact Fractal Patch antenna with Enhanced Bandwidth and Harmonic Suppression for WiMAX Applications

A single-layer a compact fractal patch antenna with capabilities of both bandwidth enhancement and harmonic suppression is proposed. For this purpose, a pair of λ/4 microstripline resonators is introduced and coupled in proximity to a rectangular patch. First, the miniaturization is investigated by Koch slot to radiating edge of the reference antenna through its symmetry plan. The wideband property can be obtained by making partial ground and coupled radiating λ/4 resonators. Different from other reported dual-resonance patch antennas, the proposed antenna does not require the electrically thick substrate, so it has attractive lowprofile property. Thanks to the good features of λ/4 resonators and capacitive feeding scheme, harmonic radiating modes of the patch antenna can be significantly suppressed as highly demanded in modern highly integrated communication systems. The antenna has been designed on FR4 substrate with an overall dimension of 46mm *46mm *1.6mm. The substrate has dielectric constant of 4.4 and thickness of 1.6 mm. The simulated results show that the proposed antenna achieves good impedance matching an operating bandwidth of 2.52–4.27 GHz (52.91%). Thus it covers Wi-MAX 3.30-3.70GHz band, and LTE 2.50-2.69 GHz band. The working principle, and design procedure are extensively described. Finally, a prototype antenna operating at 3.5 GHz is designed and fabricated. The Simulated results show that its bandwidth 1750MHz is 17 times wider than that of the traditional insert-fed patch counterpart, and the harmful spurious radiation from other higher order radiating modes has been effectively suppressed. INTRODUCTION In Modern communication and radar systems, the antenna and the front-end are placed closely or even integrated together [1]. In these systems, the microstrip patch antenna is much popular since it can be easily integrated with many other active and passive circuits such as filters, amplifiers, oscillators, and mixers. Despite these attractive features, the microstrip antenna usually suffers from several inherent drawbacks. One is the narrow bandwidth because of its resonant property with a high Q; the other is the high level of harmonic radiation, which will decrease the efficiency of the system and even cause harmful interferences with other systems. To enhance the bandwidth of patch antennas, many efforts have been made by using the aperture coupling feed [2], proximity coupling feed [3], or stacked patch configurations [4] [6]. When compared with the probe-fed method, the microstrip fed approach is much useful in the implementation of an array antenna with a number of radiating elements. In this context, the microstrip feeding network and patch radiating elements can be fully integrated on a single-layer substrate and the entire array can be fabricated simultaneously by using the printing technology. However, the thickness of the dielectric substrate must be electrically small, so that it brings a challenging task in the design of a wideband microstrip fed patch antenna on a single-layer substrate. So far, a few techniques have been reported to solve this problem. In [6], additional non-radiating resonators are employed to construction impedance-matching network. In [7] and [8], a half wavelength (λ/2) resonator and a composite right/left-handed resonator is employed, respectively, to achieve the wideband performance. Since the sizes of the feeding networks are significantly enlarged, these approaches can hardly be applied in the design of an array. A size-miniaturization method is reported in [9], but the patch configuration is destroyed by an extra T-shaped resonator. Moreover, the harmonic radiation cannot be suppressed because this T-shaped resonator operates as a λ/2 resonator. In this paper, a microstrip-fed fractal patch antenna with enhanced bandwidth and good harmonic suppression performance is presented. As reported in [10], a patch could be capacitively fed by a coupling gap. In our method, a pair of λ/4 resonators is employed and placed in proximity to the radiating patch for wideband radiation under dual resonances. The advantages of this method are as follows. 1) Operating bandwidth of a single-layer patch antenna is enhanced even for an electrically thin substrate, and it can be further controlled to some extent by adjusting the gap width between the patch and the λ/4 resonators. 2) Harmonic radiation at high frequency is effectively suppressed thanks to the characteristics of capacitive feeding structure and λ/4 resonators. 3) The feeding-line section is small in size so as not to increase the overall size of the patch antenna in array applications. 6th International Conference on Recent Trends in Engineering & Technology (ICRTET 2018) 315 | ICRTET0061 www.ijream. org © 2018, IJREAM All Rights Reserved. GEOMETRY AND WORKING PRINCIPLE The dielectric chosen is FR4-epoxy substrate having relative permittivity of 4.4 and the thickness of 1.6mm. The resonant frequency of the rectangular patch antenna, of length L and width W can be calculated using the following formula. Geometry Calculation of Lambda (λ0)-