Short-Circuited Quarter Wavelength Cylindrical- Rectangular Microstrip Patch Antenna

Transcription

1 NTNTN JUN F CV ND TC TCHNGY V. 3, N., 8 Shrt-Circuited Quarter avelength Cylindrical- ectangular icrstrip atch ntenna eena ant*, radyt Kala, S. S. attnaik and. C. Saraswat 3 *Department f & ngineering, J hilkhand University, Bareilly-ND. mail: pradyt_bly@yah.c.in Department f C,... Deemed University, llahabad-nd mail: pradyt_bly@yah.c.in Department f C, NTTT, Chandigarh-ND. mail: shyampattnaik@yah.cm 3 Department f C, S.G.S..T.S., ndre-nd. mail: rcswat@yah.cm bstract: The bjective f this wrk is t develp a simple methd t calculate the input impedance and radiatin pattern f shrt-circuited quarter wavelength lng cylindrical-rectangular micrstrip patch antenna. t is als t study the effect f the size f cylinder as well as the parameters f dielectric substrate. n this study we wuld like t take int accunt the prblems f resnance and radiatin f a shrt-circuited quarter wavelength cylindrical-rectangular micrstrip patch antenna. Transmissin line mdel is used t calculate the input impedance f the patch, while the cmbinatin f array thery and cavity mdel is used t calculate its radiatin pattern. The vlume cvered by electric and magnetic walls change with radius f the magnetic plane. t is bserved that the beam-width, resnant frequency, and resnant resistance decrease with cylinder radius. eak radiated pwer increases with cylinder radius, but beynd the critical angle, radiated pwer decreases with cylinder radius. Critical angle increases with cylinder radius and substrate permittivity. t is als bserved that difference f peak radiated pwer decreases with substrate permittivity, and pwer radiatin beynd 9 is pssible fr cylindrical rectangular patch. The bandwidth is nt sensitive t curvature but it decreases as substrate permittivity increases. ndex Terms: Cmpact micrstrip antenna, Cylindrical-rectangular patch, Shrted wall, Quarter wave patch. NTDUCTN ne f the majr advantages f micrstrip antennas is that they can be made cnfrmal t the surfaces n which they are munted because f their lw prfile. st current investigatins f micrstrip antennas have been cncentrated n planar structures. Hwever, ften this plane surface is either distrted r antenna elements are intentinally placed n a curved surface. Cylindrical micrstrip antennas find many applicatins pertaining t high-speed aircrafts, because f their cnfrmability with the aerdynamical structure f such vehicles. n recent research wrk, much attentin has been fcused n the develpment f small antennas n a cylindrical surface fr applicatins where limited antenna real state is available, which is imprtant in many cmmercial and military applicatins. mng several small antennas, the shrted micrstrip patch has been a ppular candidate []. The resnant frequency f a micrstrip antenna can be significantly reduced by intrducing a shrt-circuited plane r a partly shrt-circuited plane where the electric field f the resnant mde is zer. S the length f the patch is half f the riginal length and resnant frequency f the patch remains unchanged []. hile such antennas have been used in many applicatins, basic studies f the effect f curvature are rather scarce [3]-[8]. JT ST

2 NTNTN JUN F CV ND TC TCHNGY V. 3, N., 8 Sme wrk has been devted t the analysis f micrstrip patch antenna munted n cylindrical surface. This structure was first prpsed by Krwne []. Using a cavity mdel, he bserved that resnant frequency changes with surface curvature. u and Kaufman [3], calculated the radiatin patterns using cavity mdel in cnjunctin with the methd f images, but this methd is nt applicable when the grund plane is nt flat. n the paper by Fnseca and Giarla [4], the radiatin frm the wraparund cylindrical micrstrip element was cmputed frm a magnetic wall cavity mdel. n the paper by shkenazy et al. [6], the radiatin frm the wraparund and the rectangular patches was cmputed by assuming an electric surface current distributin n micrstrip patch antenna. shkenazy et al. [6], shw an analysis f micrstrip antennas n cylindrical substrates fr a given current distributin n the patches. Dahele et al. [7], investigated the effect f curvature n the characteristics f rectangular patch antenna theretically and experimentally. They fund that fr T mde, the resnant frequency is nt affected by curvature. Hwever, as curvature increases the pattern bradens, the resnant resistance decreases, and bandwidth increases. uk et al. [9], cnsidered the case when the substrate thickness is much smaller than the wavelength and the radius f curvature. Based n the cavity mdel, they fund that the resnant frequencies and electric field under the patch were nt affected by curvature. Hwever, the patterns, Q factrs, and input impedances are affected. Habashy et al. [], calculated the input impedance and radiated field frm the cylindrical-rectangular and the wraparund elements excited by a prbe using mment methd. The mment methd has been widely used fr the calculatin f the input impedance f micrstrip patch antennas fed by means f prbe n cylindrical substrate. re recently, full wave apprach was applied t micrstrip patch antennas []-[]. n thse wrks, nly the single rectangular patch was studied. The methd f mments [] and the general transmissin line mdel have been used t analyze micrstrip patch antennas n spherical and cylindrical supprts. ng and Ke [3] investigated the curvature effect n aspect rati and circular plarizatin cnditins fr cylindrical-rectangular micrstrip patch antennas. Kashiwa et al. [4], calculated the rectangular micrstrip patch antennas munted n the curved surface wave analyzed using curvilinear FD-TD methd. Since a micrstrip patch antenna is a highly resnant structure, its current distributin and input impedance at resnance are mainly determined by internal structures such as the shape f the patch, the thickness, and the dielectric cnstant f the substrate and superstrate. rvided that a patch antenna is placed n a lcally flat surface r surface with small curvature, the shape f the hst cylinder (external structure) has little effect n its current distributin and input impedance, as demnstrated in Kempel [5]. Tam et al [6], calculated the mutual cupling fr a prbe fed cylindrical-rectangular micrstrip array using Green's functins which incrprate the effect f the size f cylinder as well as the parameters f dielectric substrate. utual cupling between tw rectangular micrstrip antennas n cylindrical surface has been studied by [7] []. utual cupling between tw triangular micrstrip patch antennas munted n a cylindrical surface was first calculated by an and ang []. Zaid et al. [], investigated the input impedance, the resnant frequency, the current density maps n the surface f each resnatr and far field radiatin patterns f stacked quarter wavelength micrstrip patch antenna. The different radiating elements cnsidered are end-shrted alng ne edge. n end-shrted element presents the advantage f the smallest size with a length f λ/4, a brad beamwidth and a bandwidth which is reduced cmpared with a half element. Gue et al. [3], presented a cmpact dual-band patch antenna design using slt-laded and shrt-circuited size reductin techniques Thus t determine the crrect mdel field slutin t the electrmagnetic cavity prblem, which can be used t find the radiatin field slutin, this curvature shuld be taken int accunt. The bjective f this wrk is t develp a simple methd t calculate the input impedance, VS, and radiatin pattern f shrt-circuited quarter wavelength lng JT ST

3 NTNTN JUN F CV ND TC TCHNGY V. 3, N., 8 cylindrical-rectangular micrstrip patch antenna. t is als t study the effect f the size f cylinder as well as the parameters f dielectric substrate. THTC FUTN n this paper we reprt n the resnance and radiatin prblems f a shrt-circuited quarter wavelength cylindrical-rectangular micrstrip patch antenna (C). Transmissin line mdel is used t calculate the input impedance f the patch, while the cmbinatin f array thery and cavity mdel is used t calculate its radiatin pattern.. Calculatin f ffective ength and idth f the atch The gemetry f a shrt-circuited quarter wavelength cylindrical-rectangular micrstrip patch antenna is shwn in Fig.. The straight edge f the patch has a dimensin f (=λ/4) and the curved edge has a length f ' [=(+h)ψ], where ψ is the angle subtended by the curved patch and is cylinder radius. The width f the patch may be find as [4] ' = c f d ε r + () c = l 4 f ε (3) d eff here C is speed f light in free space and l is the fringing field length Shrt circuited edge h Feed int ' Fig. : shrt-circuited rectangular patch munted ver cylindrical surface. where ε r is relative permittivity f substrate and f d is designed frequency f antenna. Frm Fig., it is clear that the vlume cvered by electric and magnetic walls change with radius f the magnetic plane, which results the change in the effective dimensins f the patch. S the effective width f the patch may be find as +h/ +h + h + h ' =. ; () and the effective length f the patch may be calculate as [4] ε efff ψ ε + h r ε r = + + / B. Ccalculatin Fig. f : rbe ffective sitin width. (5) JT ST

4 NTNTN JUN F CV ND TC TCHNGY 3 V. 3, N., 8 l =.4h ( ε eff +.3) ( ε.58) eff +.64 h +.8 h (4) where h is substrate thickness and ε eff is the effective relative permittivity f the substrate material The patch impedance at any pint (x,y ) may be given as [4] ( πy ) rad c = rad p cs (6) where rad c = radiatin resistance f feed prbe. This frmula is valid n the cnditin that the feed psitin y is lcated alng side and x is at / (Fig: ), and rad p = edge fed resnant resistance f the patch, which is given by [4] λ rad p = 9 fr <<λ λ rad p = fr >>λ (7) D. Calculatin f nput mpedance Frm Fig. 3, the input impedance ffered by the patch (Z in ) may be given by Z = jω + Z Z (9) in p in in where ω is perating angular frequency, and p is self inductance ffered by the prbe, and Z in and Z in are the impedance ffered by the right and left hand sectin f T.. respectively. n cmputing the self-impedance f the prbe, the nnzer radius f the prbe has t be cnsidered. Hwever, this will lead t a cmplicated expressin fr the self-impedance in the cylindrically stratified medium case. n apprximate expressin has t be cmputed, by neglecting the curvature f the cylinder structure and assuming the prbe t be embedded in a planar stratified medium. This is a reasnable apprximatin if the radius f curvature f the cylindrical structure is sufficiently large as cmpared t the substrate thickness and the perating wavelength [9]. C. Calculatin f esnant Frequency Fr the case f h much smaller than ne wavelength, the cavity mdel r mdalexpansin apprximatin can be adpted fr analyzing the patch antenna n a thin substrate. n this case the resnant frequencies f the T mn mdes fr the cylindrical-rectangular micrstrip patch antenna under the additinal cnditin h<<, are given as [4] G+JB p y λ /4 Shrting wall f mn c m n ( ) = + ε + h ψ r (8) quatin (7) shws that if the dimensin f the patch, i.e., (+h)ψ and, are fixed, the resnant frequencies f T ρ mdes are nt affected by curvature. This cnclusin is valid fr thin substrate satisfying h<<. Zin Zin Zin Fig. 3: quivalent circuit f shrt-circuited rectangular patch munted ver cylindrical surface. JT ST

5 NTNTN JUN F CV ND TC TCHNGY 4 V. 3, N., 8 Frm transmissin line thery Z in and Z in = Z ( G + j B) + j Z tan ( β y ) Z + j ( G + j B) tan ( β y ) tan β λ y () 4 = j Z here G and B are cnductance and suseptance f fringing field respectively, Z is characteristic impedance f patch as transmissin line, and β is phase cnstant.. adiatin attern ath difference θ ρ φ ψ eference line h array where all element f the array are in same phase and f equal amplitude but their alignment is fllwed by the curvature f the hst surface. Because these array elements are nt pint surce, therefre they behave as nn-istrpic elements, leading an additinal factr t cme int existence sin α, where α is the inclinatin angle f far-field pint frm the plane nrmal t the element and passing thrugh its center. Frm Fig. 4, α may be determined as α=9-(θφ). Using the array thery, ttal far-field electric field may be written as = e t + j ( δ + β d ) cs e j ( φ θ ) ( δ + β d ) cs( φ θ ) n e j ( δn + β d n ) cs φ θ ( ) n () where n is electric field strength f n th element, δ n is phase difference f the n th surce element with reference surce, and d n is the path difference f the n th element with reference surce, φ is the angle f reference line frm vertical axis, and θ n is the angle f n th element line frm vertical axis. Here = = n =, δ =δ =δ n =, and d n = [-cs (φ-θ n )] () Fig. 4: ay diagram f patch antenna. n rder t calculate the far-zne fields, the prbe t be a ρ directed unit-amplitude current ribbn has been mdeled [Fig. 4]. n this case the electric fields under the curved patch have nly ρ cmpnent, which is independent f ρ. Frm Fig. 4, cnsider the slt as an antenna But, nly that part f the curved patch will cntribute n radiatin, which face t far-field pint and rest will nt because grund f the patch reflect the field. Substituting the abve values in (4), far-field field may be written as θ j β j β cs t = e e θ ( φ θ ) cs ( φ θ ) dθ (3) where θ and θ are the left mst and right mst inclinatin angle f the elements frm the reference line which cntribute n radiatin and JT ST

6 NTNTN JUN F CV ND TC TCHNGY 5 V. 3, N., ε r = T V [db] - ngle [degree] ngle [degree] (a) ε r = T -9 V [db] - - ngle ngle [degree] (b) ε r = 4.5 (c) T V [db] - nglee [degree] ngle [degree] ε r = 9.8 (d) T -9 V [db] - ngle ngle [degree] = cm = 4 cm = 8 cm = 6 cm = 3 cm Fig. 5(a)-(d): Variatin f radiated pwer fr different substrate permittivity and cylinder radii. JT ST

7 NTNTN JUN F CV ND TC TCHNGY 6 V. 3, N., D N C H S 55 ε r =. (a) D N C H S ε r =. (b) 3 3 F requency [GH z] F requency [GH z] D N C H S 55 ε r = 4.5 (c) D N C H S ε r = 9.8 (d) 3 F requency [GH z] F requency [GH z] = cm = 4 cm = 8 cm = 6 cm = 3 cm Fig. 6(a)-(d): Variatin f impedance with frequency fr different substrate permittivity and cylinder radii. JT ST

8 NTNTN JUN F CV ND TC TCHNGY 7 V. 3, N., 8 is the vltage acrss the slt and may be given as [4] = s k n= m= m m= m n= + π s ( k K ) π 4 m ( k k ) 8 n m nπ cs y + mπ cs y + mπ m cs x ( ) k k mn SUTS ND DSCUSSN (4) Frm Fig. 5(a)-(d) it is bserved that (a) the beamwidth increases with radius f curvature (b) peak radiated pwer increases with radius f curvature (c) it is bserved that beynd the critical angle, radiated pwer decreases with radius f curvature and increases with radius f curvature fr angle less than critical angle (d) pwer radiatin beynd 9 is pssible fr cylindrical rectangular patch. Frm Fig. 6(a)-(d) it is bserved that the resnant resistance increases as radius f curvature decreases fr different substrate permittivities. t is als bserved that resnant frequency increases as radius f curvature decreases, but the change in the resnant frequency is nt significant (maximum change is.3%). lmst same results were bserved by ng & Ke [5] fr cylindrical-rectangular patch. The bandwidth is nt sensitive t curvature but it decreases as substrate permittivity increases. V FNCS. C.. Krwne, "Cylindrical rectangular micrstrip antenna radiatin efficiency based n cavity Q factr," ntennas rpagat. Sc. nt. Symp. Dig., pp. -4, June 98.. C.. Krwne, "Cylindrical-rectangular micrstrip antenna," Trans. ntennas rpagat., vl. p-3, pp , January K. Y. u and J. F. Kaufman, "adiatin pattern cmputatins fr "Cylindrical-rectangular micrstrip antenna," ntennas rpagat. Sc. nt. Symp. Dig., pp. 39-4, S. B. Fnseca and. J. Giarla, "nalysis f micrstrip wraparund antennas using dyadic Green's functins," Trans. ntennas rpagat., vl. p-3, pp , N. G. lexpuls,... Uslenghi, and N. K. Uzunglu, "icrstrip diples n cylindrical structures," rc. 98 ntenna ppl. Symp., Univ. llinis, Sept J. shkenazy, S. Shtrikman, and D. Treves, "lectric surface current mdel fr the analysis f micrstrip antennas n cylindrical bdies," Trans. ntennas rpagat., vl. p-48, pp. 95-3, arch J. S. Dahele,. J. itchell, K.. uk, and K. F. ee, "ffect f curvature n characteristics f rectangular patch antenna," lectrn. ett., vl. 3, pp , July S. inhas and S. Shtrikman, "Cmparisn between cmputed and measured bandwidth f quarter-wave micrstrip radiatrs," Trans. ntennas rpagat., vl. p-36, pp , K.. uk, K. F. ee, and J. S. Dahele, "nalysis f cylindrical-rectangular micrstrip patch antenna," Trans. ntennas rpagat., vl. p-38, pp , February T.. Habashy, S.. li, and J.. Kng, "nput impedance and radiatin pattern f cylindricalrectangular and wraparund micrstrip antennas," Trans. ntennas rpagat., vl. p-38, pp. 7-73, ay 99.. F. C. Silva,. J. Giarla, S. B. D.. Fnseca, and. J.. Sares, "ffect f dielectric cver in a icrstripline n a circular cylindrical substrate," ntennas rpagat. Sc. nt. Symp. Dig., pp. 58-5, 99.. F. C. Silva, S. B. D.. Fnseca, and. J.. Sares, "icrstrip antenna n a circular cylindrical substrate with a dielectric cver," ntennas rpagat. Sc. nt. Symp. Dig., pp , ndn, ntari, June K.. ng and S. Y. Ke, "Cylindrical-rectangular micrstrip antenna fr circular plarizatin," Trans. ntennas rpagat., vl. p-4, pp. 46- JT ST

9 NTNTN JUN F CV ND TC TCHNGY 8 V. 3, N., 8 49, February T. Kashiwa, T. nishi, and. Fkai, "nalysis f micrstrip antennas n a curved surface using a cnfrmal grids FD-TD methd," Trans. ntennas rpagat., vl. p-4, pp , arch C. Kempel, "adiatin and scattering frm cylindrically cnfrmal printe antennas," h. D. dissertatin, univ. ichigan, nn rbr, Y. Tam,. K. Y. ai, and K.. uk, "utual cupling between cylindrical rectangular micrstrip antennas," Trans. ntennas rpagat., vl. p-43, pp , ugust K.. ng, Y. H. iu, and C. Y. Huang, "Generalized transmissin line mdel fr cylindrical-rectangular micrstrip antennas," icrwave pt. Technl. ett., vl. 7, pp , K.. ng, S.. ang, and S. Y. Ke, "easured input impedance and mutual cupling f rectangular micrstrip antennas n a cylindrical surface," icrwave pt. Technl. ett., vl., pp. 49-5, C. Y. Huang and K.. ng, "nput impedance and mutual cupling f prbe-fed cylindricalcircular micrstrip patch antennas," icrwave pt. Technl. ett., vl., pp. 6-63, C. Y. Huang and Y. T. Chang, "Curvature effects n the mutual cupling f cylindrical rectangular micrstrip antennas," lectrn. ett., vl. 33, pp. 8-9, June S. C. an and K.. ng, "utual cupling between triangular micrstrip antennas n a cylindrical bdy," lectrn. ett., vl. 33, pp. 5-6, June Zaid, G. Kssiavas, J. Y. Dauvignac, J. Cazajus, and. apiernik, "Dual-frequency and brad-band antennas with stacked quarter wavelength elements," Trans. ntennas rpagat., vl. p-47, pp , pril Y. X. Gu, K.. uk and K. F. ee, "Dual-band slt-laded shrt-circuited patch antenna," lectrn. ett., vl. 36, pp. 89-9, February. 4.. J. Bahl and. Bhartia, icrstrip ntennas, rtech Huse, nc, Dedham,, 98. JT ST