A Miniaturized Non-ResonantLoaded Monopole Antenna for HF-VHF Band. Mehdi KarimiMehr, Ali Agharasouli

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1 Iteratioal Joural of Scietific & Egieerig Research, Volume 8, Issue 4, April ISSN A Miiaturized No-ResoatLoaded Moopole Atea for HF-VHF Bad Mehdi KarimiMehr, Ali Agharasouli Abstract I this paper, a ew techique for widebad impedace matchig of short moopole ateas i the HF- VHF bads is proposed. This techique is motivated by the challege of obtaiig low VSWR values i small ad low frequecy ateas. The proposed etwork topology cosists of two lumped elemets: a iductor cascaded with a trasformer. A aalytical model is provided to obtai the proper values of these lumped elemets. The small moopole atea is desiged, fabricated, ad tested i the HF-VHF bad ad a good agreemet betwee the simulated ad measured results is achieved. Moreover, it is also show that a critical improvemet of the atea matchig is obtaied by addig a pure resistor i the middle of the atea, without sigificatly reducig the atea gai. Idex Terms loaded moopole ateas, impedace matchig, small ateas. are ot applicable whe the badwidth required is 0% or 1 INTRODUCTION higher. I geeral, matchig circuits ca be classified ito two gieers have had a great challege to desig desired groups. Passive circuits ad active or switchig circuits [10,11 Ematchig circuits to match a o-resoat (i.e., relatively ]. I passive circuits, the aalytical approach requires a short) moopole or dipole atea over a wide frequecy approximatio of the atea s iput impedace (the load), bads. Small ateas are beig widely used i may but it has bee developed for simple load circuits oly. A applicatios [1] specifically i moopole ad dipole atea thorough treatmet of the aalytical approach for differet [].For istace, i low-frequecy liks, where robustess types of load is available i [1]. The Carli s RFT gaibadwidth optimizatio approach is a umerical techique with respect to blockage ad multipath is more importat tha large data throughputs [3]. I some papers that does ot require a load model. Sice the mai radiatio metamaterials are used to desig VHF atea but these type of moopoles is fixed at λ/4, ed loadig is a well-kow ad of the ateas caot hadle high RF power. Curret very commo techique that has bee employed to reduce impedace matchig techiques ivolve modifyig the the resoat legth of ateas [13,14]. We sidestep these two atea structure. Although this is quite popular, such approaches ad prefer to itroduce the equalizer topology up ateas are sometimes complicated to desig, build, ad frot: the equalizer s first sectio is the sectio with two aalyze. Some desigers use helix ateas to obtai iductors. This sectio is adopted from the aalysis of whip widebad frequecy resposes [4-6], but these structures moopoles. This sectio is cascaded with a high-pass -sectio caot be used i VHF or HF bad. The commo way to comprisig a shut iductor ad two capacitors, iteded to compesate for the capacitive behavior of short ateas is broade the arrowbad respose of the sectio. This usig passive elemets with iductive behavior. Stadard matchig etwork topology ca be used for all dipole-like arrowbad impedace matchig techiques iclude ateas. I this paper a simple moopole atea has bee itroducig some sectios of reactive lumped circuit divided i two sectios ad to improve the matchig elemets, which are cascaded with some resistive elemets. respose, a resistor has bee embedded betwee two upper However, typically this is ot sufficiet to obtai VSWR ad uder rods as well as a exteral matchig circuit is values below 3.5 ad these stadard approaches are ot added. This atea ca hadle high RF power (about 80 applicable whe the badwidth required is 0% or higher. Watt) because there is o active elemet for the matchig This paper attempts to solve the problem of widebad etwork ad may fid its applicatio i the desig of small matchig for short o-resoat moopoles by usig lumped ad low frequecy ateas. elemet matchig etworks, which we believe would miimize the complexity. This approach could also serve as a ANTENNA SCHEMATIC OVERVIEW basis for costructig appropriate matchig etworks that modifies the atea respose dyamically. The stadard I Figure 1 the schematic diagram of the frequecy arrowbad impedace matchig techiques iclude some recofigurable atea is depicted. sectios of reactive lumped circuit elemets which are As show i Figure 1, two sectio moopole atea have cascaded with some resistace elemets [7-9]. Former circuits bee mouted o a square groud plae with dimesios of

2 Iteratioal Joural of Scietific & Egieerig Research, Volume 8, Issue 4, April ISSN meter. A lumped elemet coects two sectios of the moopole atea. From the begiig to ed of the story dimesios of the two sectios of the moopole ad the resistor value are mai purpose to desig.i this paper we use a matchig circuit to improve atea matchig (see Figure ) ad the fial value of the atea dimesios are metioed i Table 1. TABLE 1. PHYSICAL PARAMETERS AND DIMENTIONS OF SHORT MONOPOLE PRESENTED IN FIGURE 1 Parameter L1 L L3 Value (mm) Parameter L4 L5 a Value (mm) Figure 3. Simulated ad measured reflectio coefficiet with/without matchig circuit 3 ANTENNA DESIGN PROCEDURES For a wire or strip dipole, the iput impedace ca be approximated with a high degree of accuracy as Figure 1. Geometry of the proposed o-resoat short moopole with lumped elemet Z A = Rat ( ω) + jx at ( ω) (1) Figure. The schematic model of the moopole atea with proposed widebad matchig etwork For small ateas capacitor behavior should be compesated ad iductor matchig circuit is used. We describe how chose values for the iductor ad trasformer as follows. At the first glace it is clear that how matchig circuit improved the VSWR. From 50MHz to 80MHz ad 30MHz to 35MHz the VSWR is improved dramatically. Every atea has a iput impedace or admittace which is depedet o the operatig frequecy of the atea. The imagiary part of a short moopole iput impedace is egative (capacitive behavior), so we ca use the iductor for elimiatig capacitive properties of short wire atea. As it show i Figure, parallel iductor delivers positive reactace to the atea i low frequecies because i higher frequecies impedace of the iductor is very high ad does ot sigificat effect o the atea. If we used a series iductor it had a sigificat effect o higher operatio frequecies ad it was ot proper for the atea matchig. To compesate the differece level of impedace betwee the atea ad trasmissio lie a RF trasformer is used. Usig the RF trasformer ca icrease degree of freedom to get the best result. After some mathematical calculatio the Ri( ω), X i( ω) of the moopole atea with the matchig circuit i Figure are give by the followig equatios. Z = jω L ( R + jx ) () i ( at at

3 Iteratioal Joural of Scietific & Egieerig Research, Volume 8, Issue 4, April ISSN R X i i ωl = ωl Rat + ( X at + ) (3) ωl ωl ( Rat + X at ) + X at = ωl Rat + ( X at + ) (4) Therefore, the real part of output impedace of matchig etwork should be equaled to 50Ω ad the imagiary part of it should be equaled to zero to achieve perfect matchig. The followig equatio must be satisfied. Figure 5. Differet values of the ferrite (: 1) trasformer turs for perfect matchig parameters versus frequecy. Ri = Z0 (5) I this step of desigig procedure, we should choose the X i = 0 proper values of trasform turs ad matchig iductace from the obtaied diagrams, which have bee preseted i After some mathematical calculatios the values of Figure 4 ad 5. I these diagrams the values of L ad for iductace ad trasformer turs are derived. It is obvious perfect matchig coditio are illustrated. It is importat for a that the values of them versus frequecy ca be obtaied desiger to choose aappropriate value to reach the fial from the Rat ( ω), jx at ( ω) matrixes which have bee purposes. I this paper, good matchig at the middle of the bad has take priority over the other frequecy bad. The, calculated by CST software. It is iterestig to metio that with respect of the trasformer turs diagram (Figure 5), the we caot obtai costat values for L ad because the R at ad X at trasformer tur value ca be chose betwee 0.4 to 0.6 (at are ot costat versus the frequecy operatio. the rage of the frequecies betwee 50MHz to 80MHz). Therefore, they have bee plotted at the first step. Theaverage value of 0.4 ad 0.6 is 0.5, which is applied for our desig. Fortuately, the stadard trasformers at this Z0Rat L = (6) rages are available. I this step we should choose a proper ω. X at trasformer to match the atea with lie. At first Z0R trasformer should be able to hadle high RF power. About at = (7) 80Watt RF power is trasferred by the trasformer, therefore ( Rat + X at ) the Quality Factor (Q) of the trasformer must be high. Secod, frequecy badwidth is aother importat factor for choosig RF trasformer. Third, trasformer size ca be cosidered sice very large trasformers are ot practical. I this matchig circuit, ADT-1T-1P trasformer has bee utilized. 4RESULTS ANALYSIS Figure 4. Differet values of matchig circuit iductor for perfect matchig parameters versus frequecy. To measure the atea radiatio patter, we istalled the moopole atea ad receiver atea mouted o the special tower. This is ofte doe for very large ateas or at low frequecies (VHF ad below, <100 MHz) where idoor measuremets would be itractable. The source atea (the moopole) is ot ecessarily at a higher elevatio tha the test atea, but it is better to set o higher elevatio to get patter higher tha 90 i elevatio plae (E-Plae). The source atea must be placed i the far field of the test atea. The reaso is that the wave received by the test atea should be a plae wave for maximum accuracy. The photo of the fabricated atea prototype ad matchig circuit is show i Figure 7 ad Figure 8, respectively. As show these radiatio patters are almost omidirectioal

4 Iteratioal Joural of Scietific & Egieerig Research, Volume 8, Issue 4, April ISSN ad there is o deep ull iside them. Whe the operatio frequecy icreases the mai beams tred to tur upward because as the legth of the dipole icreases beyod oe wavelegth (l/λ) the umber of lobes begi to icrease. I upper frequecy bad (100MHz), radiatio patter shape is like a butter fly. The miimum value for the ull is about - 5dB (see Figure 6(c)). This value is acceptable for a short moopole atea. The resistor i the atea has ot itesive effect o the atea gai sice the curret pick o the moopole atea is ot o the resistor locatio. The maximum value for atea gai ca be achieved at higher frequecies ad i this case at 100MHz. As show i Figure 6(c) the maximum gai is.1db. At lower frequecies (about 30MHz), atea gai is -4dB. The mai reaso for low atea gai at lower frequecy bad is radiatio resistace value. Size of the atea for lower frequecies is small ad caot be cover by eve λ/8 operatio frequecy curret. The, it is ormal to have atea gai lower tha 0dB. This (b) atea is used for portable applicatios. Therefore, it should be istalled o the roof of the cars or truck bodies. It is clear that the groud plae for the atea will be icreased whe atea groud is coected to cars body. So, the mai lobs at upper frequecy bad are pulled up. Therefore, the lower lobs will be vaished. At lower frequecy bad, movig of the mai lobs happes, but the movemet is egligible. The reaso is that at lower frequecy, vehicle body legth is about oe or less tha wavelegth. (c) Figure 6. The radiatio patter of the atea at the three frequecy bads. Simulated ad measured atea realized gai (a) 30MHz (b) 60MHz (c) 100MHz. (a)

5 Iteratioal Joural of Scietific & Egieerig Research, Volume 8, Issue 4, April ISSN REFERENCES [1]F. Farzami, K. Forooraghi ad M. Norooziarab, "Miiaturizatio of a Microstrip Atea Usig a Compact ad Thi Mageto-Dielectric Substrate," i IEEE Ateas ad Wireless Propagatio Letters, vol. 10, o., pp , 011. [] F. Farzami; S. Khaledia; B. Smida; D. Erricolo, "Patter Recofigurable Prited Dipole Atea Usig Loaded Parasitic Elemets," i IEEE Ateas ad Wireless Propagatio Letters, vol.pp, o.99, pp.1-1 [3] H. G. Schatz, A. H. Ude, M. A. Nikrava, ad D. -H. Kwo, "Simple formulas for ear-field trasmissio, gai, ad fields." I Proc. 013 Atea Appl. Symp, pp [4] O. Maoochehri, S. Abbasiiazare, ad K. Forooraghi, "Desig of a tapered dielectric loaded helical atea array for INMARSAT M satellite system," Microwave ad Optical Techology Letters, vol. 55, pp , 013. [5] S. Abbasiiazare, K. Forooraghi, A. Torabi, ad O. Maoochehri, "Mutual couplig compesatio for a 1 short helical atea array usig split-rig resoators," Electromagetics, vol. 33, pp. 1-9, 013. [6] Daddish, S. M., R. A. Abd-Alhameed, ad P. S. Excell. "New desigs for dual bad ateas for satellite-mobile commuicatios hadsets." Applied Computatioal Electromagetics Society Joural 15.3 (000): [7] D.C.Youla,"A ewtheory of broadbad matchig,"ieee Tras. Circuit Theory,vol.CT-11,pp.30-50,March1964. [8] E. H. Newma, "Real frequecy wide-bad impedace matchig with omiimum reactace equalizers,"ieeetras.ateas ad Propagatio, vo1.53,o.11,pp ,nov.005. [9]Iyer, V.; Makarov, S.N.; Harty, D.D.; Nekoogar, F.; Ludwig, R., "A Lumped Circuit for Widebad Impedace Matchig of a No-Resoat, Short Dipole or Moopole Atea," Ateas ad Propagatio, IEEE Trasactios o, vol.58, o.1, pp.18,6, Ja. 010 [10] S. Abbasiiazare, O. Maoochehri, K. Forooraghi "A recofigurable prited dipole atea usig RF PIN diodes," Microwave ad Optical Techology Letters, vol. 56, pp , 014 [11] Ojaroudi, S., Y. Ojaroudi, ad N. Ojaroudi. "Multi-Resoace Moopole Atea with Iverted Y-Shaped Slit ad Coductor-Backed Plae." Applied Computatioal Electromagetics Society Joural 9.9 (014). [1] R.GudipatiadW.-K.Che," Explicit formulas for the desig of broadbad matchig badpass equalizers with Chebyshev respose," 1995 IEEE Iteratioal Symposium o Circuits ad Systems, ISCAS 1995,8April-3 [13] J. S. Petko ad D. H. Werer, "Miiature recofigurable three-dimesioal fractal tree ateas," Ateas ad Propagatio, IEEE Trasactios o, vol. 5, pp , 004. [14] Zehforoosh, Y., ad M. Naser-Moghadasi. "CPW-Fed Fractal Moopole Atea for UWB Commuicatio Applicatios." Applied Computatioal Electromagetics Society Joural 9.9 (014). Figure 7. Photo of the fabricated atea prototype 5 CONCLUSION To sum up, i this paper a ovel simple matchig circuit, which ca be applied for every short atea, is desiged ad fabricated. Because of capacitive behavior of short moopole ad dipole ateas, matchig etwork with iductor ad RF trasformer is practicable. By the use of the aalytical solutio ad calculatio of obtaied graphs, the appropriate values of lumped iductor ad trasformer have bee gaied. The values of these elemets ca be achieved for other ateas coveietly. Also, to improve VSWR of proposed atea a resistor is located i somewhere betwee the two parts of the atea. The simulated ad measured results showed good agreemet.