Intenational Jounal of Electomagnetics and Applications 1, (): 6-1 DOI: 1.593/j.ijea.1. Numeical and Expeimental Analysis of Micostip Antennas Loaded with a Single DNG Resonato Fabio Ubani *, Luis D. Quinteo Depatment of Engineeing, The Univesity of Texas at Bownsville, Bownsville, 785, USA Abstact This pape deals with the numeical and expeimental analysis of the ects of non-conventional mateials on antenna pefomance. The pape is divided into two main sections: numeical simulations and expeimental chaacteization. Fist, a micostip antenna loaded with a Double-Negative (DNG) substate is numeically simulated to study its ect on size and pefomance. Then the same antenna using conventional substate is top loaded with a novel single-sided esonato (efeed as diamond dipole esonato o DDR) showing DNG behavio. The antenna is manufactued and measuements ae pefomed. The esults show that the use of the DDR poduces a damatic 73.9% etun loss impovement as well as a fequency shift. Issues about size eduction and negative efactive index ects ae futhe pesented and discussed. Keywods DNG: Double-Negative mateial, SRR: split ing esonato, FSS: Fequency Selective Sufaces, HFSS : High Fequency Stuctue Simulato, DDR: diamond dipole esonato 1. Intoduction Recent eseach on antennas based on non-conventional mateials has indicated many advantages ove those of taditional dielectic substates, which make them a new bodeline fo micowave design. Using non-conventional mateials is a potential and pomising solution to size eduction, inceased bandwidth and obtaining multiple esonances. The poposed pape intends to cay out numeical and expeimental investigation of metamateial-based micostip antennas. Recent developments in most consume electonic poducts ae towad miniatuization. The technology of integated cicuit is widely applied in the field of communication baseband modules and RF modules to make communication poducts smalle in size. Howeve, the technology of integated cicuits is difficult to use to design a compact antenna and antenna aays. Theefoe, the design of compact plana stuctues becomes a citical technique to educe the size of communication poducts. In ecent yeas, novel engineeed mateials with chaacteistics that may not be found in natue have been consideed in the design of micowave antennas and aays. The studies in the aea showed inceased diectivity and bandwidth, educed obsevability, and fequency shift that can be used to educe dimensions fo fixed woking fequencies[1] [6]. These encouaging esults ae the leading idea behind the pesent wok. Atificial mateial with novel electoma- gnetic * Coesponding autho: fabio.ubani@utb.edu (Fabio Ubani) Published online at http://jounal.sapub.og/ijea Copyight 1 Scientific & Academic Publishing. All Rights Reseved popeties ae often conceptualized and ealized as paticulate composite mateials. If the paticles ae electically small, the ective constitutive paametes and popeties can be estimated via vaious homogenization fomalisms. The synthesis and fabication of new mateials has to be matched by the development of new expeimental chaacteization techniques. The novel electomagnetic pefomance can be usefully employed to substantially educe the patch size with a coesponding impovement in tems of weight and space occupation[7]-[8]. Cuently, DNG mateials fo antenna applications ae used to eplace conventional substates. To this end, the substate is conceived as a peiodic epetition of a single unit called unit-cell. This appoach entails a consideable ot fom a simulation and manufactuing point of view. In ode to simplify both the simulation and manufactuing ots, this pape poposes to use one single-unit esonato to analyze its ect on the antenna pefomance and hence, confim the advantages mentioned above. The stuctue of the pape is as follows. In section micostip antenna design fomulas ae povided. The esults fom numeical simulations ae epoted in Section 3. Sections 4 and 5 explain the theoetical methodology behind the poposed appoach and the novel DNG geomety adopted. In Section 6 expeimental esults to show the capabilities and the ectiveness of the design technique developed in the pape ae epoted.. Antenna Design Within the micowave and millimete wave fequency bands, micostip antennas (MSA) have poved to be excellent adiatos fo many applications in the commecial and
Intenational Jounal of Electomagnetics and Applications 1, (): 6-1 7 specialized application fequency domains of micowaves and millimete waves. Aicaft and ship antennas, satellite communications, mobile adio, and biomedical ae just few of the application aeas of such devices. A MSA consists of a adiating patch on one side of a dielectic substate that has a gound plane on the opposite side. The adiating patch dimension width (W) and length (L) ae elated to the substate elative pemittivity and thickness though the tansmission line model as follows[9]: ΔL h W = c f L = f =.41 c ( +.3)( W h +.64) (.58)( W h +.8) + 1 ΔL Whee f is the antenna esonance fequency, c the fee-space speed of light, L epesent the ective length that accounts fo finge ects, and the ective dielectic constant static value given by: + 1 1 h + 1+ 1 W (1) = () Equations (1) seved as a stating point in the antenna design; dimensions ae then optimized though the simulation phase to achieve the desied antenna pefomance as descibed in the following section. 3. Numeical Simulation A mico stip fed patch antenna woking at 1 and loaded with conventional FR4 mateial was simulated. The esonant fequency is chosen in ode to match with the fequency whee the metamateial displayed double negative popeties. The antenna was then simulated on a dielectic slab modelled to have the same paametes as that of the metamateial. The DNG patch antenna was then shunk until it opeated at the same fequency as that of the patch antenna that used the conventional dielectic. The oiginal patch size, with the conventional dielectic, was 13 mm by 16 mm. By shinking the patch to 9.94 mm by 8.94 mm, while using the metamateial fo the dielectic, the antenna esonated at the same fequency as that of the antenna with the conventional dielectic. This povided a 57 pecent decease in the aea of the antenna s patch and a 6.9% of bandwidth impovement. A esult compaison is showed in Table 1[1]. Mateial Table 1. Results compaison Patch size (mm) Patch aea (mm ) Bandwidth (MHz) FR4 13 16 8. 39 DNG 8.94 9.94 88.87 145 4. Electomagnetic Paametes Retieval As stated in the intoduction, an impotant ule when designing a metamateial is to keep the size and peiodicity of the scatteing elements significantly smalle than the opeating wavelength (λ/1 o smalle) as this allows fo meaningful intepetation of the mateial's bulk popeties based on the behavio of the unit cell (ective medium). Nevetheless, this pape poposes a scatteing element with dimensions that esemble the wavelength in fee space. Given the unit-cell size, the poposed stuctue cannot be classified as bulk metamateial, which is conceived as discete media composed of a combination of unit cells of small electical size at the fequency of inteest[11]-[14]. Expeimental analysis will show that such a medium pesents DNG behavio and that the ective medium theoy can still be applied. In addition, the novel designed implant is single sided which impoves and simplifies the manufactuing pocess. The pemittivity and the pemeability μ fo a DNG medium must be simultaneously negative ove a cetain fequency ange. In ode to achieve this esult seveal numeical and expeimental models have been poposed in the liteatue[15]. The model poposed in this pape consists of diamond ing esonato and wie stips on a hosting isotopic dielectic medium (Fig. 1). Once the ective medium theoy can be applied, the engineeed medium can be chaacteized though macoscopic paametes such as dielectic pemittivity and magnetic pemeability. The chaacteization can be caied out by applying a paamete etieval pocedue based on the calculation o measuements of scatteing paametes followed by the deivation of macoscopic indicatos such as efactive index n and wave impedance z. The S-paamete etieval techniques that have been utilized ecently to chaacteize metamateials have been shown to be valid fo metamateials having symmetic unit cells, even when the optical path length (kd) is on the ode of the unit cell size. The efactive index and the wave impedance can be elated to the calculated scatteing paametes as follows: 1 1 1 S11 S 1 ( 1 + S11 ) + S1 n = cos z (3) k d S = 1 ( 1 S11 ) + S1 Once efactive index and wave impedance ae extacted fom the scatteing paametes, the coesponding and µ can be found using = n/z and µ = n z[16],[17]. n 1 8 6 4 - -4 Refactive Index Real Pat Imaginay Pat -6 9.5 1 1.5 11 Fequency [] Figue 1. Novel poposed single-sided Diamond Dipole Resonato (DDR)
8 Fabio Ubani et al.: Numeical and Expeimental Analysis of Micostip Antennas Loaded with a Single DNG Resonato 5. Diamond Dipole Resonato The DNG behavio of an atificial mateial can be obtained though the intoduction of conductive impuities in a host medium. The shape of the inclusions is chosen accoding to two main factos: a) it must povide the double-negative behavio to the hosting dielectic medium; and b) it must take into account manufactuing limitations. The fome guaantees that the shape contibutes to a simultaneous fomation of both electic and magnetic dipole moments while the latte assues that the shape can be manufactued accoding to the cuent technology. In this pape a novel single-sided metamateial, efeed as diamond dipole esonato (DDR), is poposed to impove antenna pefomance. The novel designed unit cell shows DNG behavio at about 1 (Fig. ), allowing the metallization to be located only on one side of the dielectic slab, thus simplifying the manufactuing pocess[18]. (RO435B) with a pemittivity/dielectic constant of 3.66. The patch measues 9.6x6.6 mm and is fed with a λ/4 tansmission line to match a 5 Ω chaacteistic impedance. The fabicated antenna shows excellent adiation popeties with a total gain as high as 5 dbi (Fig. 3). Figue 3. Conventional MSA adiation patten (vetical polaization). Retun Loss -5-1 Figue. DDR efactive index obtained fom the paamete etieval The negative efactive index shown in Fig. was achieved though scatteing paamete etieval pocedue. The DDR has been manufactued and tested. A peiodic thin-wie medium is esponsible fo the negative ective pemittivity, wheeas the peiodic diamond stuctue povides negative ective pemeability. DDR and wie pattens ae fabicated on the font sides of FR4 (.54 mm thick) pinted cicuit boads. The metal used fo deposition is one Oz coppe (1.4 mil =.355 mm) fo a total slab thickness of.895 mm. A single DDR cell size is X5mm, has a diamete of 18 mm, and the width of metallization is.1 mm. Retun Loss (db) -15 - -5-3 Conventional Antenna DDR-Loaded Antenna -35.95 1 1.5 1.1 1.15 x 1 1 Figue 4. Micostip antenna expeimental esults SWR.6.4. 1.8 1.6 Standing Wave Ratio Conventional Antenna DDR-Loaded Antenna 1.4 6 Expeimental Results DNG metamateial stuctues can be used to intoduce changes in antenna impedance and, consequently, to obtain impovement in antenna esponse. Howeve, cuently available metamateial-loaded antennas at RF and micowave fequencies ae esticted in thei oveall miniatuization due to limitation in packing seveal metamateial inclusions in a small volume, in pat due to having metallization on both sides of the dielectic slab. Moeove, multiple scatteing fom such inclusions causes impuities in polaization. Being able to employ a single DNG mico-esonato instead of an aay would addess both of these issues while adding ease of implementation. In this pape a single DNG DDR metamateial inclusions is poposed to induce changes in a conventional micowave antenna behavio. The micostip antenna is based on a 1.5 mm thick substate % Delta-SWR 1. 1 1 1.1 1. 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.1 x 1 1 Figue 5. SWR compaison. Standing Wave Ratio % Change 15 1 5-5 -1-15 - 1 1.1 1. 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.1 x 1 1 Figue 6. SWR pecentage change.
-4. Intenational Jounal of Electomagnetics and Applications 1, (): 6-1 9..4..6.4 Input Impedance.8.6.8 1. 1.. 3.. 4. 5. Swp Max 11.5 Conventional 3. DNG 1. 4. 5. 1. topic and DNG dielectic was caied out. Fom the esults it can be highlighted that by using the DNG substate a miniatuization is achievable with an impovement in weight and pefomance; also, the expeimental esults shown a etun loss impovement of 73.9%. The benefits of using DNG mateials in antenna design ae also confimed by othe measued paametes such as VSWR and input impedance. The poposed technique allows achieving pefomance impovement in a vey simple way. -1. -. -5. -.4 Figue 7. Input impedance compaison. Numeical analysis and expeimental measuements have been pefomed using a single unit of the DDR to load seveal plana micowave antennas. A micostip antenna woking in the X-band fequency ange was simulated, fabicated and tested with the DDR esonato collocated on top of the patch. Numeical esults showed an impovement in the impedance matching of 8.8%. Futhemoe, the bandwidth of the esonant fequency was almost unaffected by the DDR. Expeimental esults confimed the positive ect of the DDR showing a measued etun loss of -34.54 db that, compaed with the antenna without the DDR, poduces a damatic 73.9% impovement in its pefomance (Fig. 4). Howeve, the pesence of the DDR metamateial caused a shift in the esonance fequency of the dipole antenna of 83 MHz. Anothe impotant paamete that can be used to detemine the antenna iciency is the voltage-standing-wave-atio (VSWR). Figue 4 shows the measued VSWR fo the conventional and DNG-loaded antenna. As a ule-of-thumb an antenna is consideed pefoming if the VSWR is < :1. Fom the pictue In Fig. 5 it can be noticed that this value is achieved ove a 95 MHz band poviding a matched VSWR bandwidth appoximately equal to 94% consideing the antenna esonating at 1.7 [19]. The SWR pecentage change is also shown (Fig. 6). It can be noticed that the use of the DNG single esonato impoved the antenna SWR of about 13-14%. Finally Fig. 7 epots the expeimental input impedance compaison fo the two antennas. Remakably the DNG-loaded antenna shows a matching impovement with a nomalized value at 1.7 as low as 1.1-j. confiming the benefit associated to the use on non-conventional mateials in antenna design. 7. Conclusions -.6 -.8-1. The pefomance of a micostip antenna on DNG laye was investigated using the commecial softwae HFSSTM and expeimental measuements using a single DDR. The etun loss was consideed and a compaison between iso- -. -3. Swp Min 9.5 REFERENCES [1] Y. Rahmat-Samii, Metamateials in antenna applications: classifications, designs and applications, IEEE Intenational Wokshop on Antenna Technology Small Antennas and Novel Metamateials, Mach 6-8, 6, pp.: 1-4. [] Tam, W.Y.; Kuisong Zheng;, "Tansmission line model fo ectangula micostip antennas with -negative metamateials," Antennas and Popagation Society Intenational Symposium (APSURSI), 1 IEEE, vol., no., pp.1-4, 11-17 July 1. [3] Mitta, R., Li, Y. and Yoo, K. (1), A compaative study of diectivity enhancement of micostip patch antennas with using thee diffeent supestates. Micow. Opt. Technol. Lett., 5: 37 331. [4] Zheng, K.S.; Tan, W.Y.; Ge, D.B.;, "Impedance Matching of Rectangula Micostip Antennas patially loaded with DNG metamateials," Micowave Confeence, 8. EuMC 8. 38th Euopean, vol., no., pp.678-681, 7-31 Oct. 8. [5] G. Singh, "Double Negative Left-Handed Metamateials fo Miniatuization of Rectangula Micostip Antenna," Jounal of Electomagnetic Analysis and Applications, Vol. No. 6, 1, pp. 347-351. [6] Ma, J.J.; Cao, X.Y.; Liu, T.;, "Design the size eduction patch antenna based on complementay split ing esonatos," Micowave and Millimete Wave Technology (ICMMT), 1 Intenational Confeence on, vol., no., pp.41-4, 8-11 May 1. [7] F. Ubani, and Y. Zhou, Design of a Compact Dual-Band Micostip Antenna Loaded with Anisotopic Substate, Poceedings of the 8th Annual Symposium of the Antenna Measuement Techniques Association (AMTA) Octobe -7 6, Austin, Texas. [8] F. Ubani, and L. Vegni, Analysis of Fequency Selective Sufaces Loaded by Chial Substates, Poceedings of the 5 IASTED Intenational Confeence on Antennas, Rada, and Wave Popagation (ARP5), Banff, Albeta, Canada, July 19-1, 5. [9] Constantine A. Balanis, "Antenna Theoy: Analysis and Design," Wiley-Intescience, 3d Edition, 5. [1] F. Ubani and C. Gacia, Design of Miniatuized Double-Negative Micostip Antennas using Electomagnetic Paamete Retieval, IEEE Intenational Wokshop on Antenna Technology: iwat9. [11] C. A. Kyiazidou, H. F. Contopanagos, W. M. Meill, and N.
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