FREQUENCY RECONFIGURABLE MICROSTRIP SLOT ANTENNA LOADED WITH VARACTOR DIODE

Transcription

1 Intenational Jounal o Advanced Technology in Engineeing and Science FREQUENCY RECONFIGURABLE MICROSTRIP SLOT ANTENNA LOADED WITH VARACTOR DIODE RitikaTandon 1, Tejbi Singh 1 M.Tech Schola, Subhati Univesity, Meeut, U.P. (India) Assistant Poesso, EC Depatment, Subhati Univesity, Meeut, U.P. (India) ABSTRACT This pape pesents the simulated esults o a compact vaacto diode integated conventional cicula patch antenna and also compaes the esults with a simila patch antenna. Poposed micostip patch antenna (MSA) was designed and simulated using HFSS.V.13 and CST MWS and its vaious paametes such as etun loss, VSWR and iut impedance wee detemined, and shape o this MSA was modiied by cutting vaious slots in it at appopiate positions. The diode is modeled as a switch o the equency band om.85 to 3.0 GHz. The poposed antenna also gives CP adiation with slots. In addition to it is obseved that the poposed antenna shows equency agility behavio in the equency anges.85 to 3.0 GHz with bias voltage vaying om 0 to 5V o in ON and OFF state. A bandwidth enhancement and miniatuization is also achieved. Keywods: Bandwidth enhancement; Cicula polaization(cp); Vaacto diode I. INTRODUCTION Micostip patch antenna consists o a metallic adiating patch backed up by a dielectic substate and a gound plane below that. Now days, MSAs is widely used in many applications due to thei advantages such as low poile, lightweight, plane coniguation and ease o abication. Howeve the main limitation o MSAs is thei inheently naow BW [1]. In ode to impove the BW o MSA, the idea o integating active devices has been implemented o last many yeas. Such types o antennas ae known as active integated antenna. The active integated antenna (AIA) has been a gowing aea o eseach in ecent yeas. An AIA can be egaded as an active micowave cicuit in which the output o iut pot is ee space instead o a conventional 50 Ω inteace. Active antennas educe size, weight and cost ove conventional designs which ae vey useul in micowave systems [-4]. Active antennas ovecome seveal limitations o taditional micostip antennas [5]. They ae almost equency independent that is thei bandwidth is depends on the active cicuity athe than the adiating element. Also a caeul design o the connected ampliie may ensue boadband chaacteistics o the antenna. Similaly the gain o the antenna can also be contolled by using the ampliies. Since the active antenna is electically small compaed to the passive one, the oveall length is much less than the conventional antenna, and thus can be used in places whee thee is limitation o space. Integated Antennas and Active integated antennas (AIAs) ae widely used in the aea o wieless communications, both o civilian and militay puposes. In paticula, AIAs ae devices in which a passive antenna element and an active cicuity ae integated togethe on the same substate. The integation o active solid state devices like oscillatos, vaacto diode, gun diode, ampliies,and mixes gants geate compactness, lowe costs and highe powe eiciencies with espect to conventional passive layouts[6-11]. 0 P a g e

2 Intenational Jounal o Advanced Technology in Engineeing and Science In this pape, a vaacto diode has been modeled in CST MWS and integated with a hexagonal micostip patch antenna with unequal side to om an active antenna latte which is modeled in HFSS and CST. The eason behind selecting the hexagonal micostip antenna that, it has smalle size compaed to the squae and cicula micostip antennas, as well as bette impedance bandwidth ove ectangula and squae micostip antennas o a given equency. Theeoe, authos have designed a coaxial ed hexagonal patch antenna and ciculaly polaized adiation has been achieved by adjusting the position acoss the antenna. It is ound that the obtained esults ae encouaging o pactical applications. As it enhances BW o HMSA a compaative analysis o the vaious geometies o MSA obtained by cutting slots inside the adiating patch indicate consideable impovement in BW without much saciice on othe peomance paametes o MSA such as etun loss, VSWR and its iut impedance. Also when slots ae inside the adiating patch it shows the good cicula polaization Fequency agility is the ability o a ada system to quickly shit its opeating equency to account o atmospheic eects, jamming, mutual inteeence with iendly souces, o to make it moe diicult to locate the ada boadcaste though adio diection inding [1]. Fequency agility behavio o the poposed antenna will also be used in these applications. II. CALCULATIONS (i )Resonant equency The esonance equency o a CMSA is obtained using the given omula [3]. K mn c o whee K nm is the mth oot o the deivative o the Bessel unction o ode n. Fo the a e e undamental TM 11 mode, the value o K nm is The a e and ε e ae the eective adius and the eective dielectic constant o the MSA, espectively. The inging ields along the cicumeence o the given MSA ae taken into account by eplacing the patch adius a by the eective adius a e. h a h a e a 1 ln a h a The value o ε e is obtained using ε e = C(a, h, ε e, ε )/C(a, h, ε e ) (7) 1 whee C(a, h, ε e, ε ) and C(a, h, ε e ) ae the total capacitances o the dominant TM 11 mode o MSA with and without a dielectic substate espectively. These can be calculated as [3] o a C ( a. h, o, ) 0. 5C h (8) In (8), the ist tem is the main capacitance o the disc and the second tem is the inging capacitance, C, which is given by C a h a ln o h a C(a, h, ε e ) is calculated by putting ε = 1 in (8) and (9). Fo thin substates, ε should be used instead o ε e in (6.1), and o thick substates (h > 0.05λ o ), ε e should be used. (ii) Actual adius o the Patch Using equations 6 to 9 and taking the values o dieent paametes as ollows, we can calculate the value o actual adius o the patch. K mn = ; c=3x10 8 m/s; (9) (6) 03 P a g e

3 Intenational Jounal o Advanced Technology in Engineeing and Science ε o = 8.86x10-1 F/m; ε =4.; h=1.6 mm; Fequency( o )=.1GHz We can now calculate the value o the inging capacitance C, C(a, h, ε e, ε ), C(a,h, ε e ), ε e and eective adius a e ollowed by the value o the actual adius a which come out to be 4mm. III. DESIGN OF CIRCULAR MSA The geometical coniguations o top and side views o the cicula patch antenna ae shown in Fig 1 & Fig. The esonant equency o the dominant as well as o the highe ode modes can be calculated om the omula o the cicula disc by eplacing adius a by equivalent adius a eq [6-7] i.e. X '. c (1) a eq Whee X ae the zeos o the deivative o the Bessel unction J n (x) o the ode n and the equivalent adius a eq is detemined by compaing aeas o a egula hexagon and a cicula disk o adius a eq i.e. 3 3 S a eq () a eq= S Thus the esonant equency o a hexagonal element may be expessed as: X '. c 1.1 X '. c (3) ( S ). S. And o the lowest ode mode TE 11 X = Hence =.8 GHz IV. DESIGN SPECIFICATIONS AND CALCULATIONS Design speciications o the poposed patch antenna ae as ollows. Paamete Value Substate FR4 Thickness 1.6 Radius o Patch 4 mm Slot (1x1.5)x11 in x and y diection Diode/SW position (,,1.6) and (-,-,1.6) V. RESULTS AND DISCUSSION Using these design paametes and mathematical expessions, the poposed antenna has been designed and peomances ae examined using HFSS and CST MWS, and the obtained esults ae descibed in the ollowing sections. 04 P a g e

4 Intenational Jounal o Advanced Technology in Engineeing and Science Radius=4mm Diode/SW Fig1. Top View o Reconiguable Patch Fig. Bottom View Hee a eed location point is to be ound out on the conducting patch whee patch impedance is 50 Ω. This eed point gives maximum adiation because o pope matching with 50 Ω coaxial eed. At ist the eed position is vaied and its eect on the iut impedance, S 11 and VSWR ae measued. The vaiation in etun loss with equency is shown in Fig 3,4 and 5 which shows that the vaacto diode/switch is in ON and OFF state. Fig3. Retun Loss when diode/sw is in OFF State Fig4. Retun Loss when diode/sw is in ON State Fig. Compaative Retun Loss when diode/sw is in OFF/ON State The adiation patten nea the esonant band equencies shows that with an incease in equency, the adiation patten vaies and the coss pola level inceases signiicantly to the extent that the adiation becomes maximum along Φ = 0 at.7 GHz. The adiation patten o the antenna also shows that it is Omni diectional as well as ciculaly polaized with small levels o coss polaization. The othe paametes ae also ound as given in 05 P a g e

5 Intenational Jounal o Advanced Technology in Engineeing and Science Table Chaacteistics Diode/SW Diode/SW ON OFF Resonance Feq.91GHz.94 GHz Axial atio (db) BW(GHz) Gain (dbi) VI. CONCLUSION In this pape, design, simulation o conventional and vaacto integated cicula patch antenna has been pesented. The active device and the patch antenna have been consideed as a composite unit instead o taking them as independent units wheeas in conventional wieless o othe communication systems antenna and cicuit they ae being consideed as sepaate element. The antenna has been designed at.45ghz (ISM Band) and excited using coaxial eeding techniques and its peomance chaacteistics such as etun loss, axial atio, VSWR, iut impedance and adiation patten has been calculated. The antenna with slots gives cicula polaization (AR < 3 db) as compaed to the antenna without slots in addition to gain and bandwidth impovement. The dieential bandwidth o antenna system when SW/Diode is in OFF state is 0.17 GHz wheeas it becomes 0.13 GHz when the SW/diode is in ON position. The esonance equency is also shited om.94 GHz to.91 GHz clealy showing the popety o antenna miniatuization. REFERENCES [1] S.K. Behea, Novel tuned ectangula patch antenna as a load o phase powe combining", Ph.D. Thesis, 007. [] C. M. Montiel, F. Lu and K. Chang, Active-notch antennas stabilized with a slot line ing esonato o wieless applications, IEEE Tans. on Antennas and Popagation, Vol. 46, No. 6, 945{946, 1998}. [3] J. A. Navao and K. Chang, Integated Active Antennas and Spatial Powe Combining, Wiley, New Yok, 1996, 110 PIERS Poceedings, Kuala Lumpu, MALAYSIA, Mach 7-30, 01. [4] C. M. Montiel, L. Fan, and K. Chang, A novel active antenna with sel-mixing and wide-band vaactotuning capabilities o communications and vehicle identiication applications," IEEE Tans. Micowave Theoy Tech., Vol. 44, pp , Dec [5] S. Sodagam, Active eceive antennas as sensos o adas", Technical Repot CRSIS TR 107, Aug. 17, 006 [6] R.K.Yadav, J. Kisho and R.L. Yadava, Compensation o Dielectic Cove Eects on CP Hexagonal Micostip Antenna, IJECET Volume 4, Issue 1, pp , Januay- Febuay (013). [7] R.K.Yadav, J. Kisho, and R.L. Yadava, Design o Hexagonal Patch Antenna o Mobile Wieless System, IEEE IJSTM, Vol. Issue 4, Decembe 011. [8] R.E. Collin, Foundations o Micowave Engineeing, nd Edition, 484, Wiley, 000. [9] G. Kuma and K.P. Ray, Boadband Micostip Antenna, Atech House Publication, pp.1-91, 003. [10] T. Noo, and Y. Kazama, A novel wideband cicula polaization micostip antenna - combination o dieent shaped antenna element, Antennas and Popagation Society Intenational Symposium, P a g e

6 Intenational Jounal o Advanced Technology in Engineeing and Science IEEE Volume: 3, pp , 005. [11] Y.K. Gupta, R.K. Yadav and R.L. Yadava, Ciculaly polaized tuncated pentagonal shaped Micostip patch antenna, Volume, Intenational Jounal o Micowaves Applications, No.6, pp , 013. [1] N. Zhu and W. Zhang, A Novel Fequency-tunable Antenna with a Wide Tuning Range, Pogess In Electomagnetic Reseach Symposium Poceedings, Stockholm, Sweden, pp , Aug. 1-15, P a g e