Modified Sierpinski Fractal Based Miniaturized Dual Band Patch Antenna

Abstract

최근들어무선통신시장에안테나의소형화, 경량화, 저가격화의필요성이증가하고있으며, 소형안테나는낮은가격으로큰안테나와동일한성능을이룰수있을뿐만아니라다른시스템과의접목이용이하다.따라서안테나크기의축소는설계의중요한요소가되고있다.또한듀얼밴드마이크로스트립안테나는일반적인단일밴드안테나에비해송수신시많은장점을갖는다. 그러므로, 소형및다중밴드기능을가진안테나는급속도로성장하고있는무선통신시스템에매우적합하다. 그러므로, 본논문에서는소형화된듀얼밴드안테나설계에중점을두었다. 마이크로스트립패치안테나는인쇄기판으로제작하기때문에제작이쉽고, 대량생산에적합하며경제적인특징으로인해현대무선통신시스템의안테나로많이활용되고있다. 기존의패치안테나는소형의다중밴드안테나를위하여다양한방식으로기본적인구조만을변형시켜왔다. 논문에서는마이크로스트립패치안테나의기본적인구조에Sierpinski carpet 프랙탈구조를활용하여기본구조, 1차반복구조, 2차반복구조, 3차반복구조안테나를설계하였다. 그리고, 제작의용이성과안테나성능, 크기축소율등을고려하여최종적으로는 2차반복구조를변형하여고조파를제거한듀얼밴드마이크로스트립패치안테나를제작하였다. 제안한안테나는 3차원초고주파해석시뮬레이션프로그램인Ansoft사의HFSS(ver. 10)를이용하였으며, 반사손실, 임피던스매칭, 방사패턴, VSWR을시뮬레이션하였다. 실제 FR4 기판에제작한변형된 2차반복구조안테나는 ISM 대역인2.45 GHz 및 5.8 GHz에서공진을확인할수있었으며, 기본구조에비해약 25%의크기를축소할수있었다. 따라서소형다중밴드안테나를위하여매우복잡한구조의안테나가아닌프랙탈구조를활용함으로써가능하다고판단된다.|The necessity for compact size, light weight, and low cost antennas has increased in recent years with the widespread deployment of wireless communications. Compact antennas can achieve the same performance as large antennas do with low price and ease with integrated technology. Hence, reduction of antenna size is becoming an important design parameter. Also, dual-frequency microstrip antennas have the advantage of doubling the system capacity for transmission and reception. Thus, the antenna with miniaturization and multi band functionality are beneficial to cope with the rapid growth of wireless systems. The proposed work in this thesis is focused on designing a multiband antenna with significant size reduction. Microstrip patch antennas with several advantages such as conformal nature, low profile, and economical to manufacture have made them suitable candidate to design an effective antenna for modern wireless system. Conventional patch antennas are modified in various ways to obtain a miniaturized multiband antenna. In presented work, the basic geometry of microstrip patch antenna is modified by incorporating fractal structure. The fractal’s space filling capability can be utilized to reduce the antenna size and their property of being self-similarity enables antenna to have a large number of resonant frequencies. The proposed work initiated with the design of simple fractal, Sierpinski carpet on the edge-fed rectangular patch antenna. The fractal iteration of 2nd order was chosen for further modification because of its significant size reduction along with fabrication ease. Through the process of analysis and simulation, it was seen that inset fed Sierpinski fractal antenna with perturbation and the stub can resonate at two frequencies with fine impedance matching. The antennas are designed using finite element method based High Frequency Structure Simulator (HFSS) and their performances are demonstrated in terms of return loss, impedance matching, radiation pattern and VSWR. The size reduction of 25.98% was obtained with a resonant frequency at 2.45 GHz and 5.8 GHz (ISM band frequencies). The designed dual band antenna is fabricated on FR4 substrate and the slight deviation observed from simulated result is due to environmental effect and fabrication inaccuracies. This verifies that high degree of complexity in the structure of the antenna is not required to obtain a compact multiband patch antenna using fractal geometry.