Abstract: This paper attempts to overcome the limitations of the parametric curves that characterize the performance of the Log Periodic Dipole Array Antenna (here after referred to as the LPDA). For instance, the parametric curves in design handbooks e.g. ARRL antenna handbook and other relevant literature e.g. Peixeiro do not contain those giving the relationship between the boom-length 'L' and the number of dipole element 'N' for any given bandwidth, even when it is known that these two parameters are the main cost determinants of a LPDA Antenna. The concept of convergence is introduced to aid cost optimization of the LPDA Antenna in terms of number of dipole element 'N'. Although 'N' is used as the minimization criterion, the criteria for establishing convergence encompass all the main electrical characteristics of the LPDA antenna, such as VSWR, gain and radiation patterns.

The thesis is focused on the design of a measuring antenna for 1 – 6 GHz band. It deals with the types of log periodic antennas with the the detailed elaboration of log periodic dipole antennas (LPDA). One can find the description of their functions, maximum features and the possibilities to use the asymmetrical feeder. Also there is the procedure of LPDA design and the realization of the design itself including simulation in 4NEC2 programme. In the next part there is a planar LPDA realization with the microstrip-to-balanced stripline balun symmetrization. This design was simulated and tested within the frames of Zeland IE3D programme. The last part contains the measuring results of S parametres as well as beam characteristics of the planar version of LPDA.

Abstract Whether an Open Area Test Site (OATS) is qualified is based on the Normalized Site Attenuation (NSA). The purpose is to eliminate the influence of Antenna Factor (AF). Usually the AF provided by the manufacturer adopts the Standard Site Method (SSM) and is quoted from measurements at a 10-m range. In practice, the AF varies with the measurement conditions. This uncertainly will translate into error in NSA measurements. Currently radiated electromagnetic interference measurement mostly adopts the broadband antennas, and LPDA is one of the antennas used extensively. However, the AF provided by the manufacturer does not consider shifts in the phase center of LPDA with frequency. In the meantime the radiation pattern of LPDA is different from that of a short dipole. The investigation of this thesis will focus on these two parts. In determining the phase center of LPDA antenna we adopt the average shift of phase center to improve the AF. The numerical simulation results show that such an arrangement can result in improvement. We also use the method of PCPM (Phase Center and Pattern Matching) to modify the AF under different conditions of measurement when a ground plane is present. Our study, by using the numerical simulation and measurement, shows that this indeed improves the variation of AF over that obtained by SSM. In addition, efforts are also made to have a detailed discussion in mutually coupling effects between the LPDA antenna and the ground plane, in order to distinguish the impact on AF due to the coupling of the LPDA antenna and its image. Our numerical simulation results indicate that it does not have a significant effect.

No description available.

Student Number : 9713144D - MSc Dissertation - School of Electrical Engineering - Faculty of Engineering and the Built Environment / The performance of the Log Periodic dipole array antenna has been characterized, in the form of parametric curves available in most antenna design handbooks and other relevant literature. These characteristic curves are often limiting in scope, as for instance they do not contain parametric curves giving the relationship between the boom-length 'L' and the number of dipole element 'N' for any given bandwidth, even when it is known that these two parameters are the main cost determinants of a LPDA Antenna. The concept of convergence is introduced to aid cost optimization of the LPDA Antenna in terms of number of dipole element 'N'. Although 'N' is used as the minimization criterion, the criteria for establishing convergence encompass all the main electrical characteristics of the LPDA Antenna, such as VSWR, gain and radiation patterns. Lastly, the effects of boomimpedance 'Zo' and length to diameter ration 'Ln/Dn', on the performance characteristics of the LPDA Antenna was investigated with the view to determining if neglecting the effects of these two parameters were responsible for the disparity in the directive gain values obtained by R. L Carrel compared to those obtained by later researchers. The investigation indicates that if an LPDA Antenna is converged, then the effects of Zo and Ln/Dn ratio though significant can not alone account for the fairly large disparity in the gain values. In other to perform these investigations, a modern scientific tool in the form of numerical modeling by method of moments based, Super Numerical electromagnetic code version2 was utilized. The numerical modeling tool was first validated by agreement between measured values and the values as predicted by the modeling tool. Next, simulation of the performance of LPDA antennas under variations of their number of elements was done. Thereafter, the means and standard deviations of the gain were extracted from the simulated numerical models. Trends in the pattern of variation of the means and standard deviations of the gain are used as the basis for deciding the value of number of element at which the antenna can yield acceptable performance (convergence criteria). These are presented as convergence curves, which gives for any given boom-length and operating bandwidth, the minimum number of elements required for the antenna to yield acceptable performance. Finally, the effect of length to diameter ratio and boom-impedance on the gain of optimized LPDA antennas are presented as parametric curves.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: This thesis is about the design, simulation and measuring of ultra wide band antennas for use in the Square Kilometre Array (SKA). The SKA is a radio astronomy project with one of the aims of detecting hydrogen particles in deep space. Several thousand antennas over a wide band of frequencies are needed to receive the radiation from these particles. This motivates the need for a low-cost ultra wide band antenna with the focus on the low frequency part of the SKA. In this thesis we present two design strategies: The first design strategy is for a printed LPDA on a substrate and design curves are generated. A scale model was built and measurements did not correlate with simulation results. This is due to manufacturing tolerances and assembly of the pyramidal structure. The second design strategy is for a full scale zig-zag antenna and design curves were also generated. The aim here is to produce a low-cost prototype by using brazing rods for the wire structure and mount it on a wooden frame. A full scale model was built and measurements on the roof produced much interference for the radiation pattern, but the reflection coefficient was good. We suggest doing measurements in an interference free environment in order to achieve the needed results. To conclude we suggest using the zig-zag antenna for the SKA. Some issues do however need more attention as the transformer has some losses, the cross polarisation is probably not good enough and the beamwidth does not reach the specification. We demonstrated a low cost prototype and there is the possibility of low-cost large scale manufacturing but this needs to be addressed. This has however not been analysed as many factors for large scale manufacturing are very difficult to predict beforehand and lies outside the scope of this thesis. / AFRIKAANSE OPSOMMING: Hierdie tesis gaan oor die ontwerp, simulasie en opmeting van ultrawyebandantennas vir gebruik in die SKA ("Square Kilometre Array"). Die SKA is ’n radioastronomie projek met die doel om waterstof partikels op te spoor in die ruimte. Duisende antennas wat oor ’n wye band van frekwensies strek is nodig om die energie van die partikels op te vang. Hieruit is daar ’n aanvraag vir lae-koste ultrawyebandantennas met die fokus op die lae frekwensie deel van die SKA. In hierdie tesis word twee ontwerpstrategieë voorgestel: Die eerste ontwerpstrategie is vir ’n gedrukte logaritmies periodiese dipool reeks (LPDR) op ’n substraat tesame met ontwerpskurwes wat gegenereer word. ’n Skaal model is gebou en die gemete resultate stem nie ooreen met die simulasie nie. Dit kan toegeskryf word aan vervaardigingstoleransies en die aanmekaar sit van die piramide struktuur. Die tweede ontwerpstrategie is vir ’n vol skaal sigsag ("zig-zag") antenna met ontwerpskurwes wat ook gegenereer word. Die doel is om ’n lae-koste prototipe te bou deur sweissoldeerdraad te gebruik vir die draadstruktuur en dan op ’n hout raam te plaas. ’n Vol skaal model is gebou en metings op die dak het baie interferensie veroorsaak vir die stralingsveld, maar tog was die weerkaatskoëffisient goed. Ons stel voor om die metings te herhaal in ’n steuringvrye omgewing om sodoende die korrekte resultate te verkry. Om af te sluit stel ons voor om die sigsag antenna vir die SKA te gebruik. Sekere kwessies soos die transformator wat verlieserig is, die kruispolarisasie wat moontlik nie goed genoeg is nie en die bundelwydte wat nie die spesifikasie haal nie moet nog aandag geniet. Ons het ’n lae-koste prototipe gedemonstreer en daar is die moontlikheid om dit op grootskaalse vervaardiging ook goedkoop te doen, maar dit moet nog uigesorteer word. Dit was wel nie geanaliseer nie, siende dat vele faktore ’n rol speel by grootskaalse vervaardiging wat uiters moeilik is om voor die tyd te voorspel en buite die omvang van die tesis lê.