Available online European Journal of Advances in Engineering and Technology, 2018, 5(9):

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1 Available online wwwejaecom European Journal of Advances in Engineering and Technology, 8, 5(9): 77-7 Research Aricle ISSN: X Increasing he Level of he Refleced Signal of a Broadband Pulse Locaor by Changing he Pulse Duraion of he Shock Exciaion of a Broadband Anenna Vladimir Arisov Insiue of Elecronics and Compuer Science, Riga, Lavia vladimirsarisovs@edilv ABSTRACT Is invesigaed possibiliy increasing he level of he refleced signal a he se frequency a a choice of opimum duraion of an impulse of exciemen of locaor wih shock exciemen of he anenna Key words: specral densiy as a funcion of pulse s duraion, he opimal duraion of exciaion pulse, rapezium s shaped impulse, specral densiy of rapezium s shaped impulse INTRODUCTION In locaors wih shock exciaion of ulra-wideband (UWB) anennas, shor pulse are used for ransmiers Depending on he purpose of he locaor, hese pulses can be ampliude from a few vols o hundreds or even housands of vols and duraion from ens of picoseconds o several nanoseconds The crierion for selecing he marked parameers is he assignmen of a locaor, wheher for subsurface sounding of a medium wih large aenuaion or for a displacemen sensor for small-sized arges in a room In any case, when he acive elemen [,, ] is seleced, wih he help of which impulses are formed, he developers end o ge he maximum reurn from i Namely - he maximum ampliude of he signal, refleced from he arge This can be achieved in various ways For example, careful maching of all nodes of he signal pah: he driver of he exciaion pulse - he ransmission line of he pulse o he anenna - he anenna of he ransmier - he anenna of he receiver - he line - he receiver's inpu [4] Or o seek he possibiliy of increasing he ampliude of he exciaion pulse However, is unconrolled increase causes addiional noise in he recepion pahs of he locaor [5] Anoher way is possible, namely, raising he level of he specrum in he impulse of he anenna exciaion a is cenral frequency by changing he shape of he pulse, in paricular by changing he pulse widh As a rule, developers ry o reduce he duraion of he exciaion pulse fron, missing he opporuniy o vary he pulse duraion The ool for changing he pulse widh is he change in he duraion of is verex SUBSTANTIATION INCREASING THE LEVEL OF THE REFLECTED SIGNAL As experimen has shown ha in mos cases a pulse is used o excie broadband anennas, characerized by parameers such as: ampliude, duraion of he fron, duraion of he fla par (verex), and duraion of he decay Form such an impulse can be represened as a rapezoid wih he corresponding duraions The ypical described above real impulse and is analogue - rapezium are presened in Fig Fig Typical impulse, used in mos cases for shock exciaion of broadband anennas (a) Trapezium is he equivalen of he exciaion pulse shape (b) 77

2 In he specral represenaion in he limied frequency range, when he parameers are equal, hese pulses are pracically equivalen Sudies [6] in which he pulses are represened in he form of a rapezium wih smoohed angles approximaing he rapezoid o he real pulses gave equivalen resuls Therefore, furher reasoning and research will be performed wih an exciaion pulse in he form of a rapezium We represen a rapezoidal pulse of uni ampliude in he form of a piecewise funcion: a and UT and b( ) and () Fig Trapezoidal impulse (a) and is specral densiy module (b) as frequency disribuion of ampliudes Is specral densiy is found by he classical formula: j f S UTe d For example pulse (Fig a) wih parameers, where he limi of inegraion 5 ns; 7 ns; 4ns he disribuion of he modulus of is specrum is shown in Fig b Now le us ake some fixed frequency f and find he dependence of he ampliude (specrum S a frequency f ) on he duraion of he fla par of he rapezoidal pulse To avoid confusion, we denoe his A ( ) As shown in [6], his dependence can be represened in he form of a dependence (ampliude disribuion) as periodic funcion: jw, () A( ) K K e K, K - consan complex coefficiens, deermined respecively by he values of where dependence of he module A ( ) is shown in Fig The period of he and The ypical Fig Typical dependence of he module A ( ) a a fixed frequency on he duraion of he fla par of he rapezoidal funcion is T / f pulse ( f = 8GHz, 78 5 ns; 5ns ) We will execue our research on he inerval of he firs period As follows from he figure and he analysis of he curve A ( ), he laer has exreme values for he duraion : he opimal value of he duraion op a which he maximum value of he specrum module is reached, he criical value of he duraion cr a which he value of he specrum modulus is minimal The found expressions for hese quaniies are:

3 5( ) ; op f cr () f The values of he opimum and criical duraions of he fla par of he exciaion pulse of an anenna, calculaed from hese formulas, allow in pracice o achieve a gain in he refleced signal or o explain he reason for he low level of he refleced signal in he presence of exciaion pulses a he ransmiing anenna An example is he oscillograms, obained on he layou of he locaor and shown in Fig These signals correspond o reflecions from a meal shee locaed a a disance of 5 m from he anennas For he exciaion pulse =ns Fig 4 Oscillogram, corresponding o reflecions from a meal shee when he anenna is excied by pulses wih he fla par duraion equal o: a) - zero; b) - op ; c) - cr The cener frequency in he specrum of he refleced signal is f =GHz Wih an error no exceeding %, he values of he calculaed and criical duraions coincided ( op = 5ns, cr = 8ns) In he complex shape of he rapezoidal exciaion pulse (see Fig a), i is necessary o have he experience of correcly assigning values,, and selecing he cener frequency f in he specrum of he refleced broadband signal A small values of he exciaion pulse duraion ( example RG-58, RG-6, RG-45) used o ransfer he pulse from he generaor o he anenna " sreches" he fron and he decay of pulses Therefore, when calculaing, one mus ake hose values of he duraions ha are measured for he cable used, <ns), one should keep in mind ha mos of he common cables (for PRACTICAL USE OF RESEARCH RESULTS In addiion o he abiliy o adjus he ransmier by adjusing he duraion of he fla par of he exciaion pulse, for example, by he mehods proposed in [7, 8, 9], a which he maximum ampliude in he received signal is reached, i is necessary o noe he following possibiliies, resuling from formulas () For pracical use, a family of graphs is useful (Fig 5), for which you can quickly deermine op for given f and ( ) Fig 5 A family of graphs for he pracical deerminaion of he pulse duraion op from given f and ( ) I should no be forgoen ha research was conduced o opimize he duraion of he fla par of he exciaion pulse for any fixed frequency in he signal specrum If we are dealing wih an ulra-wideband signal, for example, one ha is aken for he layou of a pulsed locaor, hen i is necessary o choose for ourselves wha frequency o calculae In general, i is recommended o ake he cener frequency of he refleced signal specrum Earlier in he pracical example of finding he relaionship A ( ), we se he fixed values of he duraions and of exciaion pulse However, heir value affecs he opimum duraion of he fla par () As follows from he analysis of 79

4 he maximum modulus max A for op, boh of hem have he greaes value wih he minimum duraion of he fron (decay) and decrease wih is growh (Fig 6) From which i follows ha for a genly sloping fron (for example, > 8 A ( ) ns), he maximum of he funcion approaches o he zero mark of duraion op In his case, for excie he anenna, here is no need o opimize he duraion of he pulse fla par because of he small gain obained in his case Fig 6 Influence of he pulse fron duraion on he value of he opimum fla par duraion for he frequency f = 8GHz and f = 4 ps CONCLUSIONS As shown by heoreical and pracical sudies, in mos cases, when he broadband anenna is excied by rapezoidal pulses, i is possible o raise he level of he refleced signal by adjusing he duraion of he fla par of he pulse wih he approach of he laer o he opimum value For example, when he exciaion pulse is rebuil, having a fron and a decay of 5 ns from zero verex duraion o 5 ns a a frequency of f = 8 GHz, he ampliude is increased by 5 percen a his frequency The periodic characer of he behavior of he dependence of he level of he specrum on he duraion of he verex of he exciing pulse makes i possible o choose he duraion of he verex of he pulse no only equal o he opimum value, bu also, if he echnical realizaion of his varian is impossible, a muliple of he period of he above dependence The period is inversely proporional o he frequency f under sudy If he rapezoidal exciaion pulse has a genly sloping a fron or a decay, he gain o be achieved when choosing he opimal pulse verex duraion is negligible This indicaes ha i is no advisable o adjus he duraion of he verex for he above-menioned fron or decay For example, for a varian of he firs conclusion wih decay duraion of 5ns, he gain is only 5 percen REFERENCES [] Vladimirs Arisovs, Modris Greiāns, Evalds Hermanis Pikosekunžu impulsu formēājs ar impa diodi Reģisrēs LR paens Nr 48 g [] Greians Modris, Krumins Karlis, Arisov Vladimir Ulra-wideband sharpener for exciaion a symmeric anenna Paen Inernaional Applicaion No: PCT/LV/7 g [] Modris Greiāns, Vladimirs Arisovs, Gais Šūpols Simeriskas ulra-plajoslas (UWB) anenas riecienierosmes impulsa formēājs Reģisrēs LR paens Nr 4767 g [4] Johanna Rosenlind The Impulse-Radiaing Anenna Engineering Physics, Maser Thesis Karlsads universie 9 [5] Копейкин ВВ К вопросу об истории и перспективах развития георадиолокации Институт земного магнетизма, ионосферы и распространения радиоволн Российской академии наук им НВПушкова (ИЗМИРАН), ООО ВНИИСМИ hp://wwwgeo-radarru/ariclesphp 9 [6] V Arisov Opimizaion of he Transmier Pulse Duraion by he Crierion of he Radiaion Specrum Maximizaion a a Given Frequency Auomaic Conrol and Compuer Sciences, 6, Vol 5, No 4, pp 5 Alleron Press, Inc, 6 [7] Serac Yilmaz and Ibrahim Tekin Ulra-Wideband N-Bi Digially Tunable Pulse Generaor Sabanci Universiy, Isambul, Turkey 6 [8] Jeongwoo Han Ulra-wideband elecronically unable pulse generaors IEEE Microwave and Wireless Componens Leers, Volume4, Issue, March 4 7

5 [9] M Zahn Subnano second pulse generaor wih variable pulse widh using avalanche ransisors Ruhruniversia Bochum Insiu fur Elecronik 46 Bochum, Posfach 48, Germany, 974 7