CHAPTER 2 DESIGN OF PLANAR MICROSTRIP ANTENNA ARRAYS AND MUTUAL COUPLING EFFECTS

Transcription

1 CHAPTER DESIGN OF PLANAR MICROSTRIP ANTENNA ARRAYS AND MUTUAL COUPLING EFFECTS In patch antennas, chaacteistics such as high gain, beam scanning, o steeing capability ae possible only when discete patch elements ae combined to fom aays. The elements of an aay may be spatially distibuted to fom a linea, plana, o volume aay. Plana aays have elements distibuted on a plane. Plana aay configuations ae extensively used in both communication and ada systems whee a naow pencil beam is equied [51]. Individual elements can be positioned along a ectangula gid to fom a plana aay fo bette contol of beam shape and position in space. Plana aays of pinted adiating elements ae potentially good candidates fo low cost scanning aay applications [5]. Micostip patch aays ae vesatile as they can be used to synthesize a equied patten that cannot be achieved with a single element. In addition, they ae used to incease the diectivity and pefom vaious othe functions, which would be difficult with any one single element [53]. The chapte pesents the basic chaacteistics and stuctue of a micostip antenna, modeling and analyzing the behavio of a fou and a six element ectangula micostip patch antenna aay. Configuations of a symmetical and asymmetical 3 patch aay have been analyzed and an optimum fequency ange of the patch antenna aay has been aived at. It is infeed that fo any plana aay configuation, optimized antenna chaacteistics can be obtained, depending upon element spacing. The effects of suface waves and mutual coupling can be minimized by optimizing the inte element spacing in both the planes. The antenna povides fequency close to the designed opeating fequency with an acceptable Diectivity and Gain. When antenna stuctue is closely spaced, the etun loss impoves in the E plane. It has been shown that with the inceasing aay spacing, the gain of the antenna gets educed significantly..1 Micostip Antennas As discussed in Chapte1, conventional antennas and micostip antennas ae cucial fo application in moden communication and navigation systems. Unlike 6

2 conventional micowave antennas, micostip antennas can confom to both plana and non-plana sufaces. Militay o civilian applications such as space and weight esticted aeospace vehicle stuctue micostip antennas ae bette suited in compaison to conventional antennas..1.1 Applications of Micostip Antennas The design and analysis of micostip antenna to suit in applications elated to aeospace viz. high pefomance aeoplane, satellite fo militay pupose, spacecaft and missile may necessitate citical examination of the following aspects. Antenna adiation patten i.e. adiated field. Related to antenna adiation patten ae impotant paametes such as diectivity, gain, adiation efficiency and powe output. Retun loss which ensues that thee is impedance match between the feeding netwok and the micostip patch antenna. Patten and impedance bandwidth. Low impedance bandwidth esults due to use of thin dielectic substate, altenatively use thick dielectic but it will enhance suface wave and deteioate adiation patten and efficiency..1. Advantages and Limitations of Micostip Antennas It is woth mentioning the advantages as well as the limitations of micostip antennas. Well known facts which highlight the micostip antenna as compaed to conventional micowave antenna ae: Because of its size, light weight, ease of installation and thin pofile configuations it can be made confomal. Integation with micowave integated cicuits is elatively easie. It is vesatile as fa as esonance fequency, polaization, adiation patten and impedance bandwidth is concened. Along with the micostip antennas stuctue, associated feed lines and matching netwok can be simultaneously fabicated. Can be made mechanically obust when confomed on igid sufaces. Limitations o disadvantages of micostip antenna as compaed to conventional antenna ae: High Q esulting in naow bandwidth, geneally a few pecent. 7

3 Undesied adiation fom the feed. Low gain and efficiency, in addition to high levels of coss polaization. Can handle low powe of the ode of tens of watts. It is difficult to achieve polaization puity. Thicke substate esults in excitation of suface waves. Most micostip antennas adiate into half space..1.3 Why Micostip Antennas? Despite the above stated limitations of the micostip antennas, it is these popeties of low pofile, light in weight, confomable to both plana and non plana stuctue, easy to fabicate and integation to MIC that makes it supeio to conventional flush mounted antennas. Hence in pactice, micostip antennas ae extensively used in seveal applications meet the challenging system equiement due to the above stated facts. In addition effot to develop micostip antennas configuation with accuate and ugged analytical model needs undestanding of its limitations as well as impove design and optimize its pefomance [5]..1.4 Pefomance Impovement Techniques Thee ae techniques to ovecome some of these limitation/disadvantages. Techniques exists to impove Q facto and hence enhancement of bandwidth. Micostip antenna aays can ovecome the lowe gain and lowe powe handling capacity. Use of photonic gap stuctue can ovecome limitations such as poo efficiency, degaded adiation patten and lowe gain pimaily by educing the suface waves [54].. Constuction of Micostip Antenna Figue.1: Constuction of micostip patch antenna. Micostip antenna, shown in Figue.1 consists of a metallic patch, placed above a gound plane with a dielectic substate sandwich between them. The thickness t of the metallic patch is vey small compaed to fee space wavelength λ, i.e. t << λ. 8

4 The height h of the substate above the gound plane on which patch is placed is vey much less than λ. Geneally ange of h lies within.3λ h.5λ...1 The Pemittivity Limitations of Micostip Antennas In the design of a micostip patch antenna,, the elative pemittivity of the dielectic substate, which sepaates the patch fom the gound plane, is geneally taken to be in the ange of. and 1 i.e.. 1. To achieve bette efficiency and lage bandwidth one must use low pemittivity and thick substate. Howeve, if smalle patch elements ae equied it may be necessay to use thin substate with high pemittivity that will esult in low efficiency and smalle bandwidth. The impedance bandwidth may lie between 1% to few tens of pecent fo substate satisfying the citeia h/λ <.3 fo =1. to h/ λ <.7 fo =.3 [5]... Impact of Patch Dimension on Micostip Antennas As explained above in Section.1, suitability of micostip antenna in aeospace elated applications is pimaily due to limitation of space available in the paent stuctue. It is well known that lage patch width esults in geneation of gating lobes in addition to space equiements. Coss polaization is also an impotant chaacteistic elated to the patch width. Theefoe in addition to achieving good adiation efficiency, the patch width selection should be based on the space equiement, suppession of gating lobes and avoidance of coss polaization. In the following section and subsections the theoy elated to the chaacteistics, design consideations of micostip antennas on the basis of bandwidth, adiation chaacteistics and antenna patten ae discussed..3 Chaacteistics and Design Aspects of Micostip Antennas.3.1 Theoetical Model of a Micostip Antenna Theoetical model of a micostip antenna s can be explained as in Figue. [54]. At the esonant fequency significant adiation is poduced due to stong field inside the cavity and stong cuent on the bottom suface of the patch. E = and E = aˆ E ( x, y) t z z Tangential component of the electic field on the patch and gound plane is zeo and the electic field is expessed as given above. Sepaation h between micostip patch 9

5 antenna and the gound plane esults in close poximity between them thus E has z component. E = jωµ H E = 1 E jωµ 1 1 = ( aˆ E ( x, y) ) = ( aˆ E ( x, y) ) jωµ 1 H ( x, y) = z z y jωµ ( aˆ E ( x, )) z z jωµ Using Maxwell s equation, H is detemined as shown above. z z Figue.: Theoetical model of micostip antenna The mode is TM z and the magnetic field is puely hoizontal. As can been seen above the vecto field H has only x y components in the egion bound by the patch and the gound plane. Fo the egions mentioned above, field is independent of z-coodinates. J s aˆ n = J s is the suface cuent and on the edges of the patch we have J s = ( aˆ z H ) ; H t = aˆ n H( x, y) = aˆ aˆ E ( x, y) = n ( ) z aˆ = z ( aˆ E ( x, y) ) n z z E o z = n 3

6 On lowe suface of the patch thee is no electic cuent component nomal to the edges of the patch; hence tangential H component does not exist, i.e. Pefect Magnetic Conducto (PMC) [14]..3. Design Consideations Micostip antenna can be called a esonant antenna [55]. System equiement specifies the opeating fequency of antenna, and to meet the goal, appopiate antenna geomety is decided upon consideing a ectangula patch, eithe used as a single element o numbe of elements foming an aay. Design pocedue is based on specific system equiements. The following design consideations ae woth mentioning: Geomety of the patch antenna consists of a dielectic substate sepaating the patch and the gound plane. Suitable dielectic mateial of height h, having a elative pemittivity and a specified loss tangent needs to be selected. Selected substate having highe loss tangent effect the antenna efficiency. f = c L (.1) Dimension of the ectangula patch of width W and length L has effect on pefomance of the antenna. Resonant fequency f of the ectangula patch antenna is dependent on the length L and elative pemittivity. Fo TM 1 mode, f is given by equation (.1). 1/ h e = W (.) Since the finging field that esults in incease of effective length of the patch, it can be accounted fo by consideing effective dielectic constant e given by the equation (.) [5]. L =.41h W ( e +.3) +.64 h (.3) W ( e.58) h The incease in length of the patch L due to finging field is given by equation (.3) [5]. 31

7 c L = Leff L = L f e The actual length of the patch is given by equation (.4) [5], whee L is the effective length of the patch. eff (.4) c = f It is impotant to note that width W has insignificant effect on the esonant fequency f and the adiation patten of the antenna. Nevetheless, input impedance and hence the bandwidth is affected by the width of the patch..3.3 The Bandwidth of Micostip Antennas The bandwidth of micostip antennas can be impoved by inceasing patch width W. Due to incease in W the esonant esistance is educed and as a esult powe output inceases. Futhe, with pope excitation, W>L is esoted to in ode to achieve the desied mode and suppession of undesied modes. Howeve, lage W in antenna aays, unlike a single patch antenna, may not suit the system equiements and in addition esult in poduction of gating lobes. It has been suggested [56], [57] that fo the limitation mentioned above, one must choose 1<W/L <. e λg W = hλ g ln 1 (.5) h To obtain 5Ω input impedance patch width W can be found using the equation (.5) [58], whee λ =. It is significant to mention that the facto is due to λg loading by the substate and stictly valid fo a vey wide patch fo TM 1 mode [5]..3.4 The Radiation Chaacteistics of Micostip Antennas Radiation chaacteistics detemine the adiation patten of the antenna. Futhe, adiation chaacteistics not only includes beam patten i.e. beamwidth, sidelobe level, but also includes diectivity, powe output and polaization chaacteistics. The potential function may be used to deive the adiation patten [5]. F = 4π s M ( ' ) jk o ' e ' ds ' (.6) 3

8 Let F be the vecto electic potential which is expessed as shown in equation (.6), whee M(' ) is the suface magnetic cuent density vecto at a point ' fom the oigin and ds ' is the element suface shown in Figue.3. Figue.3: Detemination of adiation chaacteistic of a ectangula patch jk o ' µ e A = J ( ' ) ds ' (.7) 4π ' s Similaly, the vecto magnetic potential is given by equation (.7), whee J (' ) is the suface electic cuent vecto. Since the adiation chaacteistics of micostip antennas may be studied by consideing the expessions fo electic and magnetic field components, it is necessay to conside the expessions fo these components. 1 1 E( ) = (. A) jω A ( F ) jωµ 1 1 H( ) = (. F) jω F ( A) jωµ µ 33 (.8) (.9) The total electic and magnetic fields due to electic and magnetic cuent souces ae given by equation (.8) and (.9) espectively [5]. Hθ = jω F θ and Hφ = jω Fφ (.1) Fa field components that ae tansvese to the diection of popagation ae θ and φ components. Consideing magnetic field components which ae function of electic vecto potential is given in the equation (.1) [54]. E = η ( H) = η ( ϕ H E = jωη ( ϕ F θ F ) θ H θ ϕ θ ϕ ) (.11) (.11(a)) Eθ = jω A θ and Eϕ = jω Aϕ (.1)

9 The electic field in the fee space thus can be obtained as shown in equation (.11) and (.11(a)), whee η is the fee space impedance, the electic field component Eθ and ϕ H = E may be expessed as given in equation (.1). E η jk e F = ( ) M ( ' ) e 4π s jk µ e jk A = ( ) J ( ') e 4π s jk'cosϕ 'cosϕ ds' ds' (.13) (.14) (.15) Since cosϕ = xsinθ cosϕ + y sinθ sinϕ (.16) The H in fee space may be expessed as in equation (.13). Fo the fa field condition >> ' and ' = 'cosϕ in the numeato and ' = in the denominato, we have expession fo vecto electic and magnetic potential as given by equation (.14) and (.15) espectively [5]. e F = ( 4π ) M ( x', y') e jk L / W / jk ( x'sin θ cosϕ + y'sin θ sin ϕ ) L / W / x ( x ', y ') x+ M y ( x ', y ') dx' dy'. (.17) M ( x ', y ') = ( M y (.18) jk L / W / e jk ( x'sinθ cosϕ+ y'sinθ sinϕ ) Fx = ( ) M x ( x', y') e dx' dy 4π L / W /.19(a)) F y e = ( 4π jk L / W / jk ( x'sinθ cosϕ+ y'sinθ sinϕ) ) M y ( x', y')( e L / W / ) dx' dy' (.19(b)) F = (.19(c)) z Fom equation (.14) and (.16), integating ove two dimensional suface aea between L/ to L/ and -W/ to W/, fa fields of a ectangula magnetic cuent souce is obtained in equation (.17). The suface magnetic cuent density defined in equation (.18) and the coesponding components of electic potential given in equation (.19(a)) to equation (.19(c)) [5]. E E θ ϕ = jωη ( F x sin ϕ F y cos ϕ ) (.(a)) = jωη ( F x cos θ cos ϕ F y cos θ sin ϕ )... (.(b)) 34

10 Coesponding electic field components in pola coodinates obtained in equation (.(a)) and ((b)) [5]..3.5 Radiation patten based on two slots model: Similaly using two slots-model adiation pattens fo the TM 1 mode can be detemined. Howeve adiation patten gets affected due to gound plane and the substate. cosθ sin θ F3 ( θ ) = sin θ j cosθ cot( kh sin θ ) (.1) Applying ecipocity theoem to two infinitesimal dipoles, one located on the suface of the substate and the othe in fee space at a fa distance esults in a facto F3 ( θ ) which needs to be included is [5]. F4 ( θ ) = cosθ j cosθ sin θ cot( k h sin θ ) o o Similaly, fo the E plane patten ( ϕ = ). Fo H-plane patten ϕ = 9 E E ϕ θ ( ) ( ) sin ( jk ) (, ) θ ϕ ϕ e J θ ϕ F ( θ ) (.) jωµ = (.3) 4π, 4 jωµ = (.4) 4π ( ) ( ) cos ( jk ) (, ) θ ϕ ϕ e J θ ϕ F ( θ ), 3 V J ( x, y) = xˆ sin( βx) fo < x < L, < y < W (.5) Z W J ϕ cos π sinθ cos V ( ) = (.6) Z k (sin θ cos ϕ ) e e ( θ ϕ ) sinc (.5k W sinθ sinϕ ), e Radiation patten based on the model whee suface cuent eplaces the metallic patch and taking into account gounded substate as given in equation (.3) and equation(.4) [5], whee J ( θ,ϕ ) is the Fouie tansfom of the patch cuent. Patch cuent fo the TM 1 mode is given by equation (.5). Whee β= e k and Z is the chaacteistic impedance coesponding to width W. J ( θ, ϕ) is obtained as shown in equation (.6). V is the voltage acoss eithe adiating slot. Patch length L fo the TM 1 mode is given by L=λ g / 35

11 k L = θ E ( θ ) (.7) E ( θ ) ϕ β e = = e λg π = λ g 1 e [ 1 + cot ( k h )] λg = e π e cos ( θ k Lsin )( sin θ ) cos 3 ( e sin θ ) + cos θ cot ( kh sin θ ) cos θ sinc [ ( )] ( kw sinθ ) 1 + cot k h e ( sin θ ) cot ( k h sin θ ) + cos θ e (.8) E-plane patten coesponding to ϕ = plane E = is obtained in equation (.7) [5], and H-plane which coesponds to = 9 o plane E θ = is given in equation (.8) [5]. P ( Eθ Eϕ ) sinθ dθ dϕ π π / 1 = η + (.9) cos π sinθ cos ϕ π π / V = 6 ( ) e e P sinc Z π (sin θ cos ϕ e ) cos θ sin ϕ + ( sin θ ) cot ( kh sin θ ) + cos θ ϕ ( k W sinθ sinϕ / ) θ sinθ dθ dϕ ( ) ( ) ( ) sin θ cos θ cos ϕ sin θ + cos θ cot kh sin θ Hence the adiated powe P can be obtain substituting equation (.7) and equation (.8) in equation (.9). Hence we have the adiated powe. P = ( E h) Aπ 34 A A B 1 B A A πw L whee A = and B = λ λ Simple expession is obtained by neglecting the effect of the substate [59]. R V Z = = e is valid fo h.3λ and є fo an accuacy of 1% [6]. P 1I whee, I = ( k h) I = I L / 1 kw fo 5 e I fo

12 and I = ( k h) L 4.53 k W / 3.57h and 1 ( 1) 1.9 / 9 I = λ Radiation esistance R is as given above. π x f R = R in cos L If the patch is fed at a distance x fom one of the adiating edge, the input esistance is obtained as given above. The facto dominant mode. ( Eθ + Eϕ ) f π x f cos is due to field vaiation fo the L D = η θ = (.3) P 4π Now we obtain the Diectivity of the patch antenna is given by equation (.3) ( k W ) G 4 D. π η Fo a ectangula patch antenna, the diectivity can be appoximated as [5], whee G =1/R is the adiation conductance of the patch. G = kd Gain of an antenna is defined as G, whee k = adiation efficiency of the antenna <k <1 sin 7.3 1/ 1 θ E = (.31(a)) 3k L + k h 1 1/ 1 θ H = sin (.31(b)) + kw The half powe beamwidth θ E and θ H fo E and H plane may be expessed espectively by the empiical elationship in tems of equations (.31(a)) and (.31(b)) [5]. 37

13 .4 Micostip Antenna Aays Single micostip patch antenna may not be suitable fo application, which needs high gain, beam scanning o enhance bandwidth. In ode to enhance gain and to achieve beam steeing capability the aays fomation of micowave antenna is esoted to. The same concept of aay fomation may theefoe be used with the micostip patch antenna as well. Antenna aays may be linea, plana o confomal. In applications elated to ada and communication systems naow beam is desied and hence plana aay configuation may be used fo such a equiement..4.1 Micostip Plana Aays Consideing that edge effects ae subjected to all the elements, the design of finite aays necessitates gouping of the patches in a symmetical patten so that adiation in the desied diection is obtained. This can be achieved only when fields due to individual patches get combined in phase in the desied diection and cancel each othe in all othe diections. In othe wods each patch output is combined to obtain the fields adiated by the aay. It is impotant to note that adiation patten of individual patch in the aay is the same when it is in stand-alone mode. Hence the oiginal patten of the individual patch gets multiplied by the aay facto that takes into consideation the amplitudes and phases of the feed cuent [61]. Howeve due to close poximity between patches in the aay thee is inteaction between the elements. Since each patch element induces cuents to the othe adjacent patches, it leads to coupling among the adiating patches [6]. Inte element location and spacing between the aays affects the adiation patten as well as antenna paametes. Momentum, an Advanced Design System Softwae (ADS), based on the Method of Moments may be used to detemine the adiation patten, cuent distibution and associated antenna paametes fo the micostip antenna aay system. The system equiement necessitates that spacing between the patch elements in the aay, in tems of wavelength in both H and E planes, be specified in ode to obtain the desied adiation patten. Simple design steps of plana aays with the schematic shown in Figue.4 ae 38

14 1. Pope choice of spacing between patch elements pimaily to minimize the gating lobes.. Pope selection of substate mateial viz. its thickness, elative pemittivity and inte element spacing within the scan volume can eliminate scan blindness. 3. In ode to minimize spuious adiation, the feed netwok should be suitably designed o isolated fom the adiating elements. Figue.4: Schematic of a Plana Aay.4. Micostip Resonant Aays Peiodically sepaating the patch elements fed by an open o shot cicuit teminated feed line esults in a esonant aay. As shown in the equivalent cicuit of a esonant aay of Figue.5, the inte element spacing lies between λg and λg/. The esonant feed esults in the geneation of boad side beam and in naow VSWR bandwidth. Figue.5: Resonant Aays The spacing λg and λg/ between elements esults in high etun loss due to eflection fom the patch adiating elements. 39

15 N y = g n= 1 n + j = 1 The nomalized input admittance y of the aay fo N adiating elements may be expessed in tems of g n,, the nomalized conductance of the n th element.[5]. In othe wods matching of the feed line chaacteistic admittance with the input admittance of the aay must be ensued [63], [64]. Resonating fequencies of micostip antenna depends on modes. Antenna chaacteistics such as esonant fequency, adiation patten, polaization etc. ae diffeent fo each mode. Since a squae patch suppots modes (1, ) and (, 1) with hoizontal and vetical polaization, it is pefeed ove a ectangula patch. In view of this the design of the pesent wok is based on the squae patch aay..5 Single Patch Design Paametes Patch unde consideation is designed to opeate in X-band. RT Duoid 588 is the substate chosen having thickness =.747 mm, pemittivity =. and the substate loss tangent tanδ=.9. Figue.6 shows the ADS Momemtum layout of the single micostip patch antenna. Figue.6: ADS Momemtum layout of single micostip patch antenna. Squae patch designed having length and width of 9.6mm to esonate at a fequency of 1 GHz. Details of micostip antenna patch paametes and substate details ae 4

16 shown in Figue.7 and Figue.8 espectively. Figue.7: Squae Micostip Patch Antenna Paametes Figue.8: Details of Substate consideed in the design. 41

17 Calculations of feed design ae given in the following subsections:.5.1 Impedance Calculation The Patch Impedance is calculated fom knowledge of R. 1 R in = ( G + ) 1 G1 W π sink cosθ 3 sin θ θ cosθ d G 1 = (.3(a)) 1π W π sink cosθ 3 ( J ( klsinθ )) sin θ θ cosθ d G 1 =.3(b)) 1π Expessed in tems of self conductanceg 1 and mutual conductance G 1 of the patch unde consideation as given above [54], whee G1 and G 1 ae espectively expessed π by equations (.3(a)) and (.3(b)), whee k =. Using the values obtained fo λ G1 and G1 fom equations (.3(a)) and (.3(b)), we obtain G1 + G1 =.14mho, e hence the input impedance of the patch is found to be ohm. Impedance of the matching tansfome line is ohm; impedance of the feed line is ohm. (Tansfome Matching Impedance) Calculated Patch Impedance = Feed line Impedance Using the fomula fo patch impedance calculation is as shown above. Theefoe, calculated patch impedance is ( ) = ohm, which is close to ohm hence impedance match, is ealized. in 4

18 .5. ADS Momentum Results The esults obtained based on ADS Momentum ae as follows. Figue.9 shows the etun loss S 11, at fequency of esonance 9.93 GHz is db. Figue.9: Retun loss S 11 obtained fo the Patch The feed design can be consideed matched to the patch input impedance. Figue.1 and.11 espectively shows the adiation plot of the micostip patch antenna in both θ and φ plane espectively. The plot shows adiation patten with pefect null and no sidelobes. Figue.1: Both font and back E θ plot 43

19 Figue.11: Both font and back E φ plot. Table.1 shows the antenna paametes. The antenna adiates mw powe with diectivity of db and gain db. The antenna efficiency is 94.84%. Table.1: Antenna Paametes.6 *Fou Element x Antenna Aay Design Fou element plana aay is designed fo the study of effect of mutual coupling in both E and H Plane. The squae antenna element patch length and width is 9.6 mm, height of the substate unde consideation is.747 mm, having pemitivity =.. In 44

20 both E and H plane the sepaation kept at λ/= 15 mm. Figue.1 shows the layout schematic of the plana fou element antenna aay unde consideation..6.1 Calculation of Impedance fo the Plana Aay Calculation of the Feed Line Impedance Z = 1π log h W 1 ( A + B).5.5 π ( + 1) e 1 (.33) whee W e = W + W and e W e = W eff Chaacteistic impedance of the stip is obtained based on the equations (.33) [65]. Figue.1: Schematic of fou element plana antenna aay. 45

21 = log t W h t e t W π π We obtain W fom the following equation. + = e eff W h A and = π eff A B Also the paametes A and B ae obtained using the above equations. Based on the calculation we obtain the value of Z= ohm, hence the impedance can be 15 ohm appoximately. Figue.13 validates the calculations, as the value obtained using ADS Momentum is 15 ohm. Figue.13: Stipline Impedance calculated using ADS Momentum Theefoe the feed impedance is taken half the impedance of the feed line i.e. 6.5 ohm [54], [66], [67].

22 Calculation of the Patch Impedance Next we calculate the patch impedance consideing the effect of mutual coupling due the close poximity of the patches [54]. ( ) ( ) = π θ θ π λ θ π λ θ π λ θ θ θ λ π µ π sin sin sin sin cos cos sin 1 d L x J L x J x J W G E Plane (.34) Using the equation fo conductance due to effect of mutual coupling espectively in E and H plane based on equations (.34) and (.35). Along the E plane ( ) ( ) + + = π θ θ π λ θ π λ θ θ θ λ π µ π sin cos cos sin cos cos sin 1 d L J z W G H Plane (.35) ( ) = G G G G R Plane H EPlane in (.36) Along the H plane and then in R using equation (.36), whee G 1 is the self conductance and G 1 is the mutual conductance of the patch itself. Expession of G 1 and G 1 ae expessed by equation (.3(a)) and (.3(b)) espectively, the same along with equation (.34) and (.35) may be put in equation (.36) to detemine in R of the plana aay. Using in R, the value of the impedance of the patch is found out. The value of EPlane G 1 (due to mutual coupling in the E-Plane) is found to be x1-4 mho, Plane H G 1 (due to mutual coupling in the H-Plane) woks out to be 6.377x1-4 mho and EPlane G G of the patch itself is.14 mho. Hence impedance of the patch comes out to be ohm. Hee we have not consideed the conductance due to mutual coupling between the diagonally opposite patch. Assuming the mutual

23 conductance of the diagonally opposite patch is in the ange of the mutual conductance of the E-Plane ( G 1 ) along with patch G EPlane 1 + G1 + G1 + G EPlane H Plane 1 i.e. taking the value of the mutual conductance of the diagonally opposite patch to be x1-4 mho we get the input impedance of the patch as ohm. Altenatively we may also conside by taking the mutual conductance of the diagonally opposite patch to be to mutual conductance of the H-Plane patch i.e x1-4 mho along with patch G1 + G1 + G1 + G EPlane H Plane 1, we get the input impedance of the patch as ohm which comes faily close to the feed impedance. Figue.14 shows the ADS Momentum based value of input impedance obtained fo the plana aay. The input impedance obtained is ohm which nealy same as calculated taking into consideation the effect of mutual coupling and found to be ohm. * The wok epoted in this chapte is based on the following eseach pape contibutions [68]: Gupta S.D., Singh A., Design of Micostip Plana Antenna Aay and Study of Effect on Antenna Paametes due to Mutual Coupling in both E and H Planes, Intenational Jounal of Communication Engineeing Applications (IJCEA), vol., Issue 6, Aug. 11. Figue.14: Input Impedance obtained using ADS Momentum. 48

24 .7 Effect of Mutual Coupling in E plane and H plane Figue.15: Layout of the x micostip patch antenna aay. Figue.15 shows the layout of the x, fou element micostip patch antenna plana aay. Figue.16: Stipline Impedance fo the Aay calculated using ADS Momentum Figue.16 shows the stip line impedance fo the aay calculated using ADS Momentum. The impedance of the feed obtained is ~157 ohm, which is less 49

25 than ohm found based on calculations and which is expected as seen to be same that matched the esult obtained using the fomula. Diagonal patch Figue.17: Schematic showing Mutual Coupling due to Diagonal Patch. Hee we have consideed the self conductance of the patch (same as obtained) along with conductance due to mutual coupling in the E Plane and conductance due to mutual coupling in the H- Plane patch but not the conductance due mutual coupling due to diagonal patch, efe schematic shown in Figue.17. Incopoating the mutual conductance of the diagonal patch will futhe decease the patch impedance value..7.1 Effect of Mutual Coupling on Antenna Paametes Analysis of Antenna Paametes Vaiation in E Plane Refe Table. which consides inte element spacing vaiation in E plane stating fom.5 λ in steps of.5 λ upto maximun ange of.7 λ. The paametes unde consideation include etun loss S 11, adiated powe output, gain, diectivity and antenna efficiency at a deviated esonant fequency due to effect of mutual coupling. Table shows at.7λ the antenna diectivity and gain is the maximum. It is obseved that etun loss of -4.7 db is the minimum value at.65λ. At.5λ adiated output powe and antenna efficiency is maximum at a esonant fequency of GHz which is the closest to the design value of 1 GHz. 5

26 Table.: Effect of Mutual Coupling in E-Plane on Antenna Paametes E-Plane Sepaation S 11 (db) Powe Radiated (mw) Gain (db) Diectivity(dB) Resonant Fequency (f ) (GHz) Efficiency (%).5λ λ λ λ λ Analysis of Antenna Paametes Vaiation in H Plane Refeing Table.3 consideing inte element spacing vaiation in H plane in the same ange fom.5λ in steps of.5λ upto maximun value of.7λ. Hee too we study vaiation in etun loss S 11, adiated powe output, gain, diectivity and antenna efficiency at a changed esonant fequency due to effect of mutual coupling. We obseve fom the Table that at.5λ the antenna diectivity, gain, powe output and the antenna efficiency is the maximum. It is seen that at.55λ etun loss of db is the minimum value. At.5λ H plane spacing antenna esonates at fequency of GHz same as that seen at E plane. With 1.95 mw powe adiated at.55λ, a typical adio fuze application of employing such an antenna aay is envisaged. Table.3: Effect of Mutual Coupling in H-Plane on Antenna Paametes H-plane Sepaation S 11 (db) Powe Radiated (mw) Gain (db) Diectivity(dB) Resonant Fequency (f ) (GHz) Efficiency (%).5λ λ λ λ λ Effect of Mutual Coupling in E and H Plane on Radiation Patten Effect on adiation patten both E θ and E φ due to inte element spacing espectively in E and H plane ae shown in Figue.18 and Figue.19. In E plane at antenna 51

27 element sepaation.55λ and fo H plane at.5λ we obseve adiation patten with nulls and without sidelobes in both E θ and E φ. In both the planes as the inte element spacing is inceased the effect on E θ adiation patten is dominant in tems of incease in sidelobe level. Howeve E φ adiation patten shows maginal distotion and incease in sidelobe levels.7λ specifically in E plane. E-Plane Sepaation E θ E φ.5λ.6λ.65λ 5

28 E-Plane Sepaation E θ E φ.7λ Figue.18: Effect of Antenna Element Sepaation in E Plane on Radiation Patten H-Plane Sepaation E θ E φ.5λ.55λ 53

29 H-Plane Sepaation E θ E φ.6λ.65λ.7λ Figue.19: Effect of Antenna Element Sepaation in H Plane on Radiation Patten Effect of Mutual Coupling in E and H Plane on Retun Loss Figue. shows effect of mutual coupling in both plane on etun loss S 11. Relative compaision of etun loss due to mutual coupling in E plane vis-à-vis H plane shows significant deteoiation in S 11 in the latte afte spacing is inceased fom.6λ onwads. This attibutes to dop in diectivity, gain, hence antenna efficiency along 54

30 with adiated powe output. It can be concluded that in H plane effect of mutual coupling is moe dominant as compaed to mutual coupling in E plane. Sepaation E-Plane H-Plane.5λ.55λ.6λ.65λ 55

31 .7λ Figue.: Plot Showing Effect of Mutual Coupling on Retun Loss S 11 Plot shown by the Figue.1(a) consists of combined plot depicting vaiation in S 11 with inte element spacing changes in both E and H plane. At.6λ, we obseve that etun loss in both plane ae closest, an impotant paamete fo plana antenna aay design. Figue.1(a): Plot showing on vaiation in Retun Loss S 11 due to Mutual Coupling Effect of Mutual Coupling in E and H Plane on Diectivity, Gain, Efficiency, Resonant Fequency and Powe Output Plots shown in Figue.1(b) to Figue.1(f) consides mutual coupling in both E and H plane due change in inte element spacing and its effect on antenna paametes viz. diectivity, gain, efficiency, esonant fequency and powe output. We obseve at.5λ identical antenna paametes in both E and H plane. But as the spacing in both E 56

32 and H planes ae vaied in steps of.5λ, fom the initial value of.5λ following obsevations ae made, consideing mutual coupling effect in E and H plane. Figue.1(b): Plot showing Vaiation in Diectivity due to Mutual Coupling Figue.1(c): Plot showing Vaiation in Gain due to Mutual Coupling Efficiency (%) Figue.1(d): Plot showing on vaiation in Antenna Efficiency due to Mutual Coupling 57

33 Resonant Fequency (GHz) Figue.1(e): Plot showing on Deviation in Antenna Efficiency due to Mutual Coupling Deviation At.55λ both the diectivity and gain in E and H plane ae of the ode of appoximately 11 db, howeve antenna efficiency is of the ode 97.5% at.7λ. in both the plane. Also at.55λ, the antenna esonating fequency matches. At.6λ, the antenna adiated powe output is almost of the ode of 1.9 mw in both the planes. Powe Radiated (watt) Figue.1(f): Plot showing on vaiation in Powe output due to Mutual Coupling.8 Pototype x Plana Antenna Aay Figue. shows the fabicated pototype x plana antenna aay. The pototype is used to validate the effect of mutual coupling on the antenna esonant fequency obseved in the simulation esult shown in figue.1 (e). 58

34 Figue.: Fabicated Pototype x Plana Micostip Antenna Aay. Figue.3 shows the set up to measue the etun loss S 11 at the esonant fequency. The fou element aay is seen to esonate at f =9.731 GHz with inte element spacing in H and E plane coesponding to.55λ and.65λ espectively. Measued etun loss S 11 is found to be -17 db. Figue.3: Setup showing the measuement of Retun Loss S 11 and Resonant Fequency f of the Pototype x Plana Micostip Antenna Aay. 59

35 Figue.4(a): Pola Plot E θ. Figue.4(b): Pola Plot E φ. Figue.4(a) and Figue.4(b) shows the pola plot coesponding to adiation patten E φ and E θ espectively. The pola plot shows diective adiation patten expected out of the plana micostip antenna aay meeting the equiement of aicaft applications. The fabicated fou element antenna aay gain measued coesponds to 16 db which is 5 db above than obseved in the simulation esults. Figue.5(a) and Figue.5(b) shows the f 1 =9.5 GHz and f =1. GHz espectively coesponding to fequencies measued at -1dB on eithe side of esonant fequency f =9.731 GHz. Hence the impedance % bandwidth obtained is = ( f f ) ( ) 1 = 1 = f 5.14%. Figue.5(a): Measuement setup f 1 =9.5 GHz 6

36 Figue.5(b): Measuement setup f =1. GHz.9 ** Six Element x3 Antenna Aay Design.9.1 Modeling of the Plana Aay Figue.6 shows x3 configuation of six element micostip antenna aay designed to opeate in lowe S band at a fequency of esonance of.3 GHz. Squae patches of width and length of a single patch element ae taken as 3mm using commecially available FR4 ( =4.7, thickness =1.57 mm), taken as the substate. dx dy Figue.6: Configuation of six element micostip antenna aay. ** The wok epoted in this chapte is based on the following eseach pape contibutions [69]: Gupta S.D., Rahul, "Optimization of Plana Micostip Patch Antenna Aay Designed fo Lowe S-Band, Eleventh URSI Commission F Tiennial Open Symposium on Radio Wave Popagation and Remote Sensing at Rio de Janeio, Bazil, pp , 3 Oct. to Nov

37 .9. Citeia fo the Substate Selection The Figue.7 shows the schematic depicting suface, space and eflected waves. Figue.7: Schematic depicting suface space and eflected waves. Micostip line feed has been used to feed the patch. The citeion fo the selection of substate with specific dielectic constant and thickness impacts the micostip patch antenna design necessitates the following consideations: Substates with highe thickness and high dielectic constant esults in smalle bandwidths and lowe efficiencies due to possibility of suface-wave excitation. Highe dielectic constant mateials with longe length of feed line esults in inceased losses and chances of spuious adiation [7]. In ode to eliminate multiple suface waves the substate thickness should be made as thin as possible. A height of.1λ o to.5λ o is consideed ideal in this egad. It is pefeable to use low dielectic constant mateial and also a substate of optimum thickness fo containing the spuious feed adiation to minimum. Fo simplicity of analysis a 5Ω efeence system is used with the micostip feed lines of same impedance. In the analysis pesented, the etun loss S 11 is consideed to depend on hoizontal spacing S e (dx) between the elements, the width W, elative pemittivity є and the esonance fequency f and may be expessed by the following elation [71]. 6

38 I m [ Z ] in S S 11 =, Zin = Z c (.37) 1 S11 whee Z c is equal to 5Ω, the chaacteistic impedance of the system..1 Pefomance Analysis of the Micostip Plana Aays in H plane On the basis of the analytical discussion on the pefomance analysis, the etun loss, esonant fequency, diectivity, gain and the adiation patten of the micostip plana aays ae pesented in the following subsections: dx= 1λ dx=.9λ S11 M ag. [db] Fequency Mag. [db] Fequency Figue.8(a) Figue.8(b) dx=.8λ S11 dx=.7λ S Mag. [db] Mag. [db] Fequency Fequency Figue.8(c) dx=.6λ Figue.8 (d) dx=.55λ S11 S11-5 Mag. [db] Mag. [db] Fequency Figue.8(e) Fequency Figue.8(f) 63

39 dx=.5λ S11 dx=.4λ -5 M ag. [db] Fequency Figue.8(g) Figue.8(h) dx=.3λ S11-5 dx=.5λ S11 M ag. [db ] -5-1 M ag. [db] Fequency Fequency Figue.8(i) Figue.8(j) Figue.8(a)-(j): Plots of Retun Loss S 11 vs. Fequency.1.1 Retun Loss Limiting the distance at dx=.5λ, the esonance fequency of the patch aay is obseved at aound. GHz with a etun loss of 1 db. As the spacing is educed, we obseve the following esults. At.45λ the esonance fequency shifts by 9 MHz, with a etun loss of db, which is not significant. At spacing dx=.4λ the etun loss impoves consideably to 36 db. Futhe educing the antenna element spacing to.3λ, the etun loss falls to 14 db at.31 GHz. At.5λ the antenna tunes to.35 GHz with a good etun loss of 7 db. This is attibuted to mutual coupling and can be obseved fom the elation expessed by equation (.37). Z in 1+ S = Zc 1 S Figues.8(a)-.8(j) shows Retun Loss against Fequency. Closely spacing the antennas shifts the input impedance at esonance to a lowe value, which in tun affects the etun loss [7]. 64

40 .1. Resonant Fequency Inte element sepaation dx less than.5λ, esults in space eduction between patches. The esonance fequency educes by 6 MHz at.4λ (Figue.9). At sepaation.3λ, stong coupling is obseved, which inceases the esonant fequency by MHz and by 6 MHz at.5λ. The analysis has been epoted in [7]. Resonance fequency ises at close inte element spacing. This shift up in f can be attibuted to the paallel line coupling which educes e, as a esult, esonance fequency inceases slightly ( nal f α 1 ) [31]. e RESONANT FREQUENCY BEHAVIOUR Retun Loss Behaviuou in H Plane Resonant fequency dx(λ) Seies1 Retun Loss dx (λ) Seies1 Figue.9: Plot of Resonant Fequency vs. dx(λ) Figue.3: Plot of Retun Loss vs. dx(λ) At inte element spacing geate than half wavelength (dx >.55λ), coupling is due to combined effect of suface and space waves [73], [74]. At dx=.5λ and dx=.55λ, the antenna has fequency esponse at.35 GHz and.9 GHz with etun loss of 3 db and 7 db espectively (Figue.9 and Figue.3). Between.7λ and 1λ, at incements of.1λ thee ae inconsistencies in etun loss. It has been obseved specifically at.6λ and.8λ that etun loss is poo to what has been achieved at.7λ and.9λ. Howeve, a shift of 1 MHz and 35 MHz at.7λ and.9λ espectively is obseved fom the tuned fequency of.35 GHz. Thus, no specific infeence can be dawn about the etun loss at dx >.55λ..1.3 Diectivity and Gain No significant effect is obseved in the diectivity and gain of patch aay antenna due to mutual coupling. The maximum deviation of db is obseved in the diectivity as shown in Figue.31. Similaly no significant deviation in gain is obtained except at vey close spacing (about.5λ) the gain falls dastically to.95 db as shown in Figue.3. 65

41 VARIATION IN DIRECTIVITY ANTENNA GAIN VARIATION Diectivity(db) dx(λ) Seies1 GAIN(db) dx(λ) Seies1 Figue.31: Plot of Diectivity vs. dx(λ) Figue.3: Plot of Gain vs. dx(λ).1.4 Optimum Radiation Patten Figue.33 and Figue.34 espectively shows plana antenna adiation plot at dx=.55λ in Catesian and pola coodinates. As seen in the Figue.33 and.34 a shap null is obseved at -4 db fo dx =.55λ. Figues.35 and.36 shows the pola plots fo two exteme cases, i.e.at dx =.5λ and dx=1λ espectively. The patten is highly distoted in the fome case due to mutual coupling. At spacing of 1λ the null is not shap and the enegy is distibuted in the side lobes. Figue.33: Catesian Plot of Radiation at dx=.55λ 66

42 Figue.34: Pola Plot of Radiation at dx=.55λ Figue.35: Pola Plot of Radiation at dx=.5λ Figue.36: Pola Plot of Radiation at dx=1λ 67

43 .1.5 Aay Elements diven though a Phase Shifte It is always desied to excite the patch in its fundamental mode (TM 1 ), so that the antenna is tuned to the fundamental esonant fequency and thee ae no dominant highe ode modes. Figue.37 shows the cuent distibution at dx=.55λ. It has been obseved that the electic field vectos in the diametically opposite patch elements cancel each othe and hence no hot egions ae seen. Compaing this with the spacing dx=.5λ and dx =1λ (Figues.38 and Figue.39 espectively), the patch elements ae well excited and hot egions ae obseved. The solution is to add a 18 degee phase shifte which shall evese the diection of the electic field vecto; hence, thee will be constuctive intefeence. This seves anothe impotant pupose as well. It will ensue that the patch elements ae excited only in the fundamental mode and no highe ode hamonics ae geneated. As the absence of hot egions with the phase shifte is indicative of the antenna being excited in some othe highe ode modes. Figue.37: Antenna cuent distibution at dx=.55λ Figue.38: Antenna cuent distibution at dx=.5λ 68

44 Figue.39: Antenna cuent distibution at dx=1λ.11 Results As pe the esults discussed above an optimum design is achieved fo linea spacing of.55λ. It is found at this spacing the antenna is woking closest to the designed opeating fequency with a good etun loss of 3 db. The Diectivity and Gain is also found to acceptable at 7.7dB and 6.9dB espectively. Powe Radiated by the patch aay is 9 mw, which is a decent powe level, expected of a patch antenna..1 *** Optimization of Plana Micostip Patch Antenna Aay Opeating at Lowe S-Band based on Analysis in both H and E Plane Using 3 geomety, the behavio of a six element ectangula micostip patch antenna aay may be optimized fo the design paametes - gain, diectivity, adiated powe and adiation patten in both E and H plane at Lowe S-band [75]. To achieve this, the inte element spacing is vaied in eithe hoizontal o vetical plane at a time keeping the spacing at othe plane constant. *** The wok epoted in this chapte is based on the following eseach pape contibutions [75]: Gupta S.D., Rahul, "Design and Optimization of Plana Micostip Patch Antenna Aay Opeating at Lowe S-Band Based on Analysis in both H and E Plane, 11th Intenational Symposium on Micowave and Optical Technology (ISMOT 7) Italy at Monte Pozio Catone, Roma ITALY, pp , Dec.17-1, 7. This appoach is based on the fact that optimized antenna chaacteistics can be obtained fo any plana aay configuation, depending upon inte element spacing. The antennas have been modeled using micostip feed line and S-paamete data 69

45 fom individual single element. The design paametes ae fist calculated fo squae patch antenna using tansmission line model equation. With configuation of a 3 patch aay, optimum chaacteistics of the patch antenna aay ae obtained though momentum simulation using ADS softwae povided by Agilent Technologies. The effects of suface waves and mutual coupling have been minimized by optimizing the inte element spacing in both the plane. It is obseved that fo obtaining optimum antenna chaacteistics fo any aay configuation, tadeoff between vaious antennas paametes ae to be aived at [76]. The poposed appoach is conceptually simple, pactical, and efficient fo designing wide-band micostip antennas. It takes into account two majo aspects in configuations of micostip antennas fo impoved electical pefomance and manufactuability, and in the analytical modeling of micostip antennas and aays Mutual Coupling Consideations in Design The mutual coupling affects has on the esonant fequency f, esonant input impedance R and the fa field adiation patten. It has been shown that the mutual coupling effect on f is about 1% o a fequency shift of 1 MHz at 1 GHz, the effect on R is about 5% and the effect on adiation patten is about 3% Mutual coupling affects the esonance fequency of the antenna elements in the aay and needs to be taken into account while tuning the elements to esonance at the desied fequency [31], [71]. A.R.Sindois and C.M.Kowne [3] has epoted that closely spacing the antenna (showing coupling) inceases esonant fequency by 7.7 MHz and shifts the input impedance at esonance to a lowe value. The coupling is vey fequency sensitive anging fom about 3 db at the fist esonant fequency to less than 3 db appoximately half way between the fist and second esonance and it also vey shaply peaked about the fist esonance. Futhe, the mutual coupling between micostip patches may be due to both space wave and suface wave.suface wave contibutes significantly to the mutual coupling, especially in E-plane [3]. The mutual coupling in the H-plane is smalle than in E-plane and the inceasing of d/λ futhe o the distance d between adiating elements educes the mutual coupling [31]. Fo excitation of suface wave a distance d (.5.7) λ is necessay [3]. In this 1 zone the suface wave has a small magnitude. The distance d 1 is dependent on and h (thickness of the dielectic). Howeve, it is difficult to detemine analytically the 7

46 effect of mutual coupling between adiating elements because of the influence of a vaiety factos such as eflected and suface wave excited in the impedance stuctue and the dielectic above the metal plane [3]. This difficulty is ovecome by employing ADS Momentum softwae. Its effect has been effectively incopoated in the aay design using the softwae..1. The Pefomance Analysis The pefomance of the designed micostip antenna in tems of the etun loss, plot of S 11, esonant fequency, gain and Optimum Radiation Patten in both E and H plane ae next discussed Retun Loss and plots of S 11 Figues.4 and.41 show Retun Loss less than -35 db coesponding to vaiation of inte element spacing in H plane (dx=.4λ, dy=.5λ) and E Plane (dy=.4λ, dx=.5λ) espectively. Figue.4: Vaiation in H- Plane with dx=.4λ, dy=.5λ & S 11 =-37dB Figue.41: Vaiation in E-Plane with dy=.4λ, dx=.5λ & S 11 =-33dB Figue.4 and.43 show plots of S 11 vaiation in E and H plane espectively fo diffeent values inte element spacing. 71

47 Figue.4: S 11 vs. dy Figue.43: S 11 vs. dx.1.. Resonant Fequency While consideing mutual coupling in both E & H plane simultaneously fo spacing dx less than.5λ, thee is eduction in esonance fequency at.4λ in accodance with easoning, given in section.1.1. Resonant fequency vesus dx Resonant fequency dx Seies1 Figue.44: Resonant fequency vs. dx 7

48 At sepaation of.3λ, stong coupling is obseved, which inceases esonant fequency by MHz and by 6 MHz at.5λ as shown in Figue.44. The analysis has been epoted in [31]. At inte element spacing geate than half wavelength (dx >.55λ), coupling is due to combined effect of suface and space waves [7], [73]. At dx=.55λ, the antenna has fequency esponse at.9 GHz with etun loss of 7 db espectively. The Resonant fequency was achieved to be.7 GHz at.4λ. Thee is a shift in the fequency when dy is vaied fom.4λ to.6λ Figue.45. This may be due to fact that the change in the feed length intoduces a physical notch, which in tun intoduces a junction capacitance [77]. The notch and its coesponding junction capacitance influence slightly the esonant fequency [54]. Figue.45: Resonant fequency vs. dy Figue..46 (a): Gain vs. dx 73

49 .1..3 Gain Figue.46 (b): Gain vesus dy No significant effect is obseved in the gain of patch aay antenna due to mutual coupling (Figue.46(a)) (within 1 to db). Simila esults ae obtained fo gain, howeve, at vey close spacing (.5λ); the gain falls dastically to.95 db. Figue.46 (b) suggests that a fai amount of gain between 7-8 db is achieved when the spacing dy is vaied between.4λ and.5λ.this is emakable achievement fo micostip patch antenna aays Optimum Radiation Patten As obseved in Figue.33 and.34, a shap null is obseved at -4 db fo dx=.55λ and dy=.5λ and fo dx=.5λ and dy=.55λ, in the Catesian and pola plot of the adiation patten a null is obseved at 35 db as shown in figue.47 ((a) & (b)) and.48 ((a) & (b)). Figue.47(a): Catesian Plot in H Plane 74

50 Figue.47(b): Pola Plot in H Plane Figue.48(a): Catesian Plot in E Plane 75

51 Figue.48(b): Pola Plot in E Plane.13 Conclusions In E plane at antenna element sepaation.55λ and fo H plane at.5λ in case of symmetical x aay, adiation patten with nulls and without sidelobes in both E θ and E φ is obseved. With the inte element spacing in both the planes inceased, the effect on E θ adiation patten is dominant in tems of incease in sidelobe level. Similaly in x3 assymetical aay an optimum design fo linea spacing of dx =.55λ and dy =.5λ and similaly dx =.5λ and dy =.55λ, is aived at. It is found at this spacing the antenna is woking closest to the designed opeating fequency with a good etun loss of 3 db. The Diectivity and Gain is also found to acceptable at 7.7 db and 6.9 db espectively. Powe Radiated by the patch aay is 9 mw, which is a decent powe level, expected of a patch antenna. When antenna stuctue is closely spaced, the etun loss impoves by a facto of.3 fom.5λ-.4λ in the E plane. It is maximum at.4λ (-33.6 db). A significant impovement in the gain of patch aay antenna aound 7-8 db when the spacing is maintained aound.4λ-.55λ. Howeve if the aay spacing is inceased, it educes by 5%. The distance dy is kept constant at about.5λ, while the inte element spacing dx has been vaied fom.5λ (closest possible spacing) to 1λ, to study the antenna paametes. Next the study is E Plane spacing being kept constant at.5λ, while the H Plane spacing is vaied fo analysis. 76