Design of a directive and matched antenna with a planar EBG structure

Transcription

1 Design of a direcive and mached anenna wih a planar EBG srucure Halim Bouayeb, Kouroch Mahdjoubi, Anne-Claude Taro To cie his version: Halim Bouayeb, Kouroch Mahdjoubi, Anne-Claude Taro. Design of a direcive and mached anenna wih a planar EBG srucure. Sep 4, IEEE APS 4, pp , 4, <1.119/APS >. <hal-13374> HAL Id: hal hps://hal.archives-ouveres.fr/hal Submied on 7 Feb 7 HAL is a muli-disciplinary open access archive for he deposi and disseminaion of scienific research documens, wheher hey are published or no. The documens may come from eaching and research insiuions in France or abroad, or from public or privae research ceners. L archive ouvere pluridisciplinaire HAL, es desinée au dépô e à la diffusion de documens scienifiques de niveau recherche, publiés ou non, émanan des éablissemens d enseignemen e de recherche français ou érangers, des laboraoires publics ou privés.

2 DESIGN OF A DIRECTIVE AND MATCHED ANTENNA WITH A PLANAR EBG STRUCTURE H. BOUTAYEB 1, K. MAHDJOUBI and A.C. TAROT 1 INRS Telecommunicaions, Monreal Canada IETR, Universiy of Rennes 1, Rennes France Halim.Bouayeb@univ-rennes1.fr Absrac The purpose of his presenaion is o propose a mehod o design a direcive and mached anenna wih a planar Elecromagneic Band Gap (EBG) srucure. The EBG srucure of our example consis on meallic wires. This sudy use he FDTD mehod and analyical formulas. I Inroducion Several recen works concern periodic srucures associaed wih microwave anennas o enhance here direciviy [1][][3][4]. However, o our knowledge, he impedance aspec is no enough sudied. The objecive of his presenaion is o propose a mehod o mach an anenna pu inside a planar EBG srucure. Before insering a real anenna inside he EBG srucure, we presen a sudy of he angular filering characerisics of he EBG srucure and he inpu impedance wih an exciaion by a line source. II Plane waves and infinie long meallic wires : angular filering We firs ineres on he angular filering aspec due o he EBG srucure composed of wo layers of meallic wires on each side of he exciaion (Figure 1). Le us call T * he ransmission coefficien obained wih an exciaion by plane waves (Figure 1). T * is funcion of he frequency f and he angular incidence θ. We obain his coefficien (T * ) using (r, ), he complex reflecion and ransmission coefficiens of one surface of meallic wires. To simplify he sudy we don consider he angular dependency of (r, ). (r, ) are calculaed by he FDTD mehod. (r, ) Meallic wire of diameer mm Plane wave D=8mm θ D T * θ P =4mm Figure 1 Transmission coefficien of he srucure excied by plane waves F 1 T * a θ= F =f F Frequency (GHz) F 4 F 5 GP: Gap Band PB: Pass Band 1 s GB 1 s PB nd GB nd PB Figure T * versus frequency a normal incidence (θ= ). The coefficien T * (kd ) can be wrien in a simple closed form [4][5] :

3 wih T* ( kd' ) = 1 ( ) ( k) exp( jkd' ) kd' =, r ( kd' ) 1 r( k) exp( jkd' ) ( kd' ) exp( jkd' / ) r ( kd' ) exp( jkd' ) = r(k) 1+ 1 ( k) exp( jkd' ) r( k) exp( jkd' ) k is he free space wave number and D =Dcos(θ). Figure gives he ransmission coefficien T * versus he frequency a he normal incidence (θ= ). In his figure, is also represened he Gap Bands and he Pass Bands. We call f he frequency corresponding o he firs resonance. Figure 3 gives T * versus he incidence angle a he differen frequencies represened in Figure. These curves can be assimilaed as radiaion paerns. Unil he firs resonance f, he paerns have only one lobe a he normal, which is an objecive for a direcive anenna. A a frequency higher han f he paerns have muliple lobes one each sides of he normal. Figure 3 gives a carography form of T * versus f and θ. db T * θ ( ) F 1 F =f F 3 F 4 F 5 Figure 3 T * (θ) a he differen frequencies represened in Figure. T * Frequency (GHz) f Incidence angle ( ) Figure-4 T * versus incidence angle and frequency. More deails on he sudy of angular filering and direciviy of he srucure can be found in ref. [5], and will be presened during he presenaion.

4 III Line source and infinie long meallic wires : inpu impedance In his paragraph, we consider infinie long meallic wires and an infinie long line source as he exciaion (Figure 5a). In Figure 5b, we give he inpu impedance Z I for he source wih and wihou he EBG srucure. The inpu impedance is calculaed by he FDTD mehod. In he firs Gap Band, he EBG srucure gives a low real par which make difficul he maching of an anenna in his band. The maching is possible for frequencies higher han f. In he firs Pass Band, he EBG srucure add an imaginary par in he inpu impedance : as a resul, he real source mus be capaciive in his zone if we wan o obain a mached anenna. Meallic wire of diameer mm Wih EBG Re(Z I ) Im(Z I ) Source alone Re(Z I ) Im(Z I ) D=8mm P =4mm 6 4 Infinie line of curren source (a).5 1 f Frequency (GHz) Figure 5 (a) layers of meallic wires on each side of an infinie line source (b) Inpu impedances Z I for he source wih and wihou he EBG (FDTD). IV Monopole and finie long meallic wires Le us now consider finie long meallic wires and a monopole as he exciing source (Figure 6). The frequency resonance of he monopole is called f M. The maching curves for he monopole alone and for he complee srucure is given for a monopole resonaing before f (Figure 7a) and for a monopole resonaing afer f (Figure 7b). We know from paragraph II ha if we wan o obain a direcive anenna a he normal we should no go far away from f. The maching of he complee srucure is obained in he second case only : he mached band (6.7% for S 11 < 1dB) (Figure 7b) is beween f M and f, which correspond o he inersecion beween he possible maching zone and he capaciive zone of he monopole (f<f M ). (b) Meallic wire of diameer mm Monopole of lengh L M L R =14mm 7 wires L T =35mm P =4mm H D=8mm D Infinie ground plane Figure 6 Monopole inside he finie EBG srucure

5 Figure 8 shows he radiaion paern of he srucure in he H-plane (Figure 6) in he mached band (Figure 7b). S 11 (db) L M = 57.5mm S 11 (db) L M = 47.5mm Monopole alone - Monopole alone Monopole wih EBG srucure f =1.4 GHz (a) - f M Monopole wih EBG srucure GHz f =1.4 (b) Figure 7 Maching (a) Monopole resonaing before f (b) Monopole resonaing afer f (db) f =1.4 GHz 1.3 GHz GHz θ ( ) Figure 8 Radiaion paerns in he H-plane, in he mached band (Figure 7b)(FDTD). V Conclusion We have presened a mehod o design a direcive and mached anenna using a monopole as he exciing source. The mehod consis on using a monopole which resonaes a a frequency slighly higher han he firs resonance of he ransmission coefficien of he srucure (which is calculaed analyically). In a fuure paper we will ineres on srucures composed of a pach anenna as he exciing source. References [1] M. THEVENOT, C. CHEYPRE, A. REINEX and B. JECKO, Direcive Phoonic Band-Gap Anennas, IEEE Trans. On Microwave Theory and Techniques, vol. 47, no. 11, November [] R. BISWAS, E. OZBAY, B. TEMELKURAN, M. BAYDINDIR, M. SIGALAS e K.- M. HO, Excepionally direcional sources wih Phoonic Band-Gap crysals, Opical Sociey of America, v. 18, n. 11, November 1. [3] S. ENOCH, G. TAYEB, P. SABOUROUX, N. GUERIN and P. VINCENT, A Meamaarial for Direcive Emission, Phys. Rev. Le., volume 89, No. 1, November. [4] H. BOUTAYEB, K. MAHDJOUBI and A.C TAROT, EBG Anenna analysis/unificaion of frequency and angular dependencies, ESA 4. [5] H. BOUTAYEB, Eude des srucures périodiques planaires e conformes associées aux anennes. Applicaion aux communicaions mobiles, Thèse de l Universié de Rennes I, UFR Srucures e Propriéés de la Maière, PhD Thesis, December 3.