Bhatnagar, Deepak

Sharma, K B

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Indian J. Phys. 68B (3). 283 -  290 (1994)U P  B--- an iiiiemational journalOn radiations from microstrip patch in two component warm ionized plasma mediumDeepak Bhatnagar and K B Sharma*Microwave Laboratory. Department o f  Physics, University o f Rajasthan. Jaipur-302 fXM, Rajasthan, India*Department o f  Physics, S S Jain Subodh College, Jaipur, Rajasthan, India Received 17 October 1993, accepted 14 February 1994A b stra c t : Presence o f  electron-ion plasma medium likely modifies radiation properties o f  microstrip patch antenna to a great extent. With variation o f plasma to source frequency, different radiation properties o f patch antenna are observed theoretically by using hydrodynamic theory coupled with vector wave techniqueK e y w o r d s  ; Microstrip patch, plasma, radiation conductance, efficiency P A C S  N o s . : 41.20.Jb, 52.40.Fd, 84 .40 .G fMicrostrip antennas are becoming more and more popular in these days due to their light weight, low manufacturing cost and better aerodynamic properties [1,2]. An antenna radiates electroacoustic waves in addition to usual electromagnetic waves during its voyage in ionized plasma media [3]. Presence of electro-acoustic waves is likely to modify the overall radiation properties of antenna structure. Different workers [4,5] have studied radiation properties of linear antennas immersed in ionized plasma medium. The purpose of this paper is to study the effect of ion electron plasma medium on the radiation properties of microstrip rectangular patch antenna fed through a narrow strip. Hydrodynamic theory coupled with vector wave technique is used in the present study.The geometry and coordinate system of the patch antenna is shown in Figure 1. A microstrip patch of length / = (where Xg is guide wavelenjgth), width height A, substrate relative permittivity and permeability of £,. > 1 and = 1 respectively, is fed through a narrow strip of very low impedance. The waves guided by the microstrip are©1994IACS284 D eepak Bhatnagar and K  B  Shartnaassumed to be transverse electromagnetic waves which are concentrated under the strip and incident on each aperture, where some power is radiated and remainder is reflected back asSUBSTRATEGROUNDPLANEF igu re 1. Geometry o f  microstrip patch.guided waves. The reflection coefficient \r\ is assumed to bte unity. End effects are taken to be negligible for the purpose of simplification [6] because it produces only second order effects in the radiation patterns.Present analysis is carried out by assuming plasma as warm, homogeneous, lossless, non-drifting continuum of electrons and equal number of singly charged ions. Collisions of electrons with neutral particles, effect of sheath formation around the antenna and the presence of an external magnetic field are disregarded to make derivation simpler. It is also assumed that only aperture portion of the antenna encounters the plasma. This is possible by covering the remaining portion of structure by protective layer like beryllium oxide, polystyrene and ice. When antenna is covered with a protective layer, alteration in resonant frequency takes place. This causes detuning which may seriously degrade performance of the system. For thin protective layers {d ^  1 mm), fractional change in resonant frequency is only about 0.7% at resonant.frequency 1.2 GHz which will not make any serious change in results [7].The electric field at the aperture is assumed to beE = E^x  (1)Following image theory and an established method [8] expressions for far zone field pattern factors are derived.On radiations from microstrip patch etc (i) Field nattem factor in electromaenetic mode:r ( I >1= [ 2 ^  sinecosj^^, -  sinesin^Jsin X sin Y ~ X  Y~hereand2 4 0 nX  = A sin decs 0 ),Y = A cos0)/2F,e = 0.(ii) Field pattern factor in electroacoustic mode:h b(\ -  Of, ) ) (ot2 + M) cos /^3^^’’ \ 2 ^ n  w Eq [a^ -  0 2 ) {q  ^ -  \A A C l - a j )  (i3^j) ( a ,  + A / )  ^ s i n d s i n ^ j120;r w Eq ( a ,  -  a j )  {Q^ - 1  -  Af)here285(2)(3)(4)sin^ j3^ y Asindcos^l ^ (/3p^  Asinffcos^) x ycos© )j  = 1 , 2Q  = M = m jm .  and = p^A,Po and Pe are propagation constants of E.M. wave in free space and plasma respectively while Wpf and Wpi are angular plasma frequency of electrons and ions respectively. A is known as plasma parameter which can be defined asH> WA = 1 -  ^w~ w2 l>/2The wave numbers pp\ and Pp2 of eq. (4) are the roots of the equation-  (T„ *  T n ) f „  + (T n 'h , -  V „ )  .  0and are related to ay byPIj = 7’,, + Tj, a j,wb«B 0  ^ are the roots of equation+ ( r„ - T2 2 ) a ^  -  r.j  = 0,(5)(6)(7)68B(5)-I2here286 Deepak Bhatnagarand K B Sharma7’u =T’2. =w1 -2 2T s s  _______0 > * 22 '>Tn =vv£L2In these expressions, uq and are the r.m.s. thermal velocity of electrons and ions respectively. The values of F^^(£-plane patterns with 6  » jtH) and Fp are calculated using b = 0.081 m, / =s 0.125 m, A = 0.00158 m and resonant frequency /;. = 1.2 GHz to compare results with some other structures working at the same frequency [9,10].Values of b and A are very small (A < Ao» A «  Aq) to a good approximation and reduces to 1 in eq. (2). On the other hand, / « Aq/ 2 makes cos(j3  ^ ^sin Osin 0) asFigure 2. Variation of with plasma parameter A.dominant term in the equation. Due to the presence of this factor, a two lobe pattern appears in free space which reduces to a single lobe on increasing plasma to source frequency.The power radiated by an antenna through an upper half space can be obtained by integrating the complex poynting vector over a closed surface [11]. Using above relations, the radiation conductance in two modes reduces toOn radiations from  microstrip patch etc 287F ig u re  3 . Variation o f  Fp with angle 9 for A 0.198  (i) In electromagnetic mode:P.r ==0 0t  c A P(\ b sm 6 2/^ /'UT ‘  i f  — ^sin^X sin^KdO d(l>. (8)hereV ^ ^ E ^ h .(ii) In electroacoustic mode:= "ijr = S4 b^{\ -  a^ \ w?/ V2* K ^X J  J  ^sin0sin0jX^^sin0 (9)0 0hoeM  =Variation of the radiation conductance with plasma parameter A is calculated and tabulated for both electromagnetic mode and electroacoustic mode in Table 1.288T ab le  1. Variation o f  radiation conductance and efficiency with plasma parameter A.Deepak Bhatnagar and K B SharmaPlasma parameter ARadiation conductance (u )  G, CpEflictency(%)0.1 3.589 X 1(T* 81.0839 —0.2 2.224 X KT* 1.2347 —0.3 2.403 X  10-5 6.96 X 10-2 0.030.4 1.2530x10-* 3.37 X 10-2 0.370.5 4.347 X 10^ 9.50 X 10-* 31.390.6 1.157 x ir^ 5.83 X 10-* 66.490.7 2.558 X 10-5 6.10 xlO-* 80.740.8 4.929 X 10-5 2.57 X 10-* 95.040.9 8.576 X 10-5 2.50 X ir5 99.711.0 1.389 X 10-2 — 100.00The radiation efficiency of an antenna in plasma medium can be defined as the ratio of useful power output in plasma to the total power input77 =  X 1 0 0  ( % ) ,P e + P p( 10)here Pg and Pp are the radiated power in electromagnetic mode and electroacoustic mode respectively. Radiation efficiency of some other microstrip structures in plasma medium is also plotted for comparison puipose. Their nomenclatures are tabulated in Table 2.T ab le 2 . Nomenclatures o f  som e microstrip antennas.Rectangular patch antennaOpen circuit rectangular microstrip resonatorCircular patch microstrip antennaDimensions (i) length (/) 0.125 m and 0.12 42 m *0.048 m —(ii) radius (a ) — — 0.021 m and 0.022 m*(iii) width (6) 0.08 Im 0.047 m —(iv) thickness {h) 0.00158 m 0.00158 m 0.00158 mResonant frequency (fr)1.2 GHz 1.2 GHz 1.2 GHzo f  substrate 2.31 2.31 2.31^considering end effects.Radiation patterns of a rectangular patch antenna indicates that the presence of plasma medium affects them to a great extent. Electromagnetic mode pattern indicates that with theincrease of plasma to source frequency ratio, directivity of antenna decreases while 3 db beamwidth increases. Plasma mode radiation pattern shows discrete multilobe pattern, whichOn radiations from  microstrip patch etc 289F ig u re  4 . Variation o f  radiation efficiency with plasma parameter .4 for different radiators.is different from that of linear antenna [12,13]. Radiation conductance of present antenna structure in E.M. mode is maximum in free space and becomes negligible for lower A values. On the other hand, plasma mode radiation conductance shows a reverse behaviour. The net result of these two is a continuous decrease in radiation efficiency with decreasing A values although it is still higher than the radiation efficiency of two other antennas working at the same frequency. An interesting feature regarding efficiency is that it becomes almost zero for all antennas under consideration for values of A lower than 0.3.The effect of plasma medium on radiation properties is quite significant and needs experimental verification though simulation of plasma medium in laboratoiy is difficult.AcknowledgmentThe authors are indebted to University Grants Commission, Delhi for providing financial help to one of them (DB) to work on this project. The authors also express their gratitude to Prof Raj Kumar Gupta and Mrs Charulata for their suggestions and encouragement and to Dr Yogesh Vijay for providing computer facilities.References[1] R  E  Post and  D  T  S tephenson IEEE Trans. Ante. Propag. 29 129(1981)[2] K R C a r v e r a n d J  W  M i n k / £ £ £ r r a r i i .  Anie. P ro /w x -2 9 2 (1 9 8 1 )[3J K  M  C h en  Proc. IEEE 112 1668 (1964)290 Deepak Bhatnagar and K B Sharma.[4] R R Burman Electron. Lett. 2 102 (1965)[5] V L Talekar and S S Rawat J. Inst. Electron. Telecomn. Engrs. 17 334 (1971)[6] J R James and G J Wilson Microwaves, Opt. Acous. 1 165 (1977)m  IJ Bahl. P Bhaitiya and S S Stuchly IEEE Trans. Ante. Propag. 30 314 (1982)[8] A Kumar and R K Gupta Indian J. Radio Space Phys. II 247 (1982)[9] D Bhatnagar and K B Sharma Indian J. Phys. B66 1 (1992)f 10] D Bhatnagar and R K Gupta Indian J. Radio Space Phys. 14 113(1985)fl 1] IL Fteeston and R K Gupta Proc. IEEE 118 633 ( 1971)(12] K M Chen, H Judson and Lin Proc. IEEE 55 1656 (1967)(13] V L Talekar and R K Gupta Int. J. Electron. 25 101 (1968)

On Radiations From Microstrip Patch in Two Component Warn Ionized Plasma Medium

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On Radiations From Microstrip Patch in Two Component Warn Ionized Plasma Medium

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