Testing and Optimizing of 16-element Antenna Array

Transcription

1 PIERS ONLINE, VOL. 5, NO. 5, Testing and Optimizing of 16-element Antenna Array A. Jeziorski 1, W. Kolosowski 1, P.Gajewski 1, E. Sedek 2, and Z. Bielecki 1 1 Military University of Technology, Poland 2 Telecomunication Research Institute, Poland Abstract The objective of this study is to test and optimize the design of a 16-element antenna array made up of radiating elements in the form of Tapered Slots Antenna (TSA). Optimization of array construction and results of measurement of radiating characteristic of antenna is presented in the paper. The results from the needs to develop broadband antenna elements suitable for a variety of application in the UWB systems. 1. INTRODUCTION TSA elements represent now one of the antenna technology areas that develop at the highest rate. This results from the needs to develop broadband antenna elements suitable for a variety of applications on the one hand, and on the other hand from the TSA elements capacity to meet numerous requirements that are specific to the needs. The aforementioned applications include dynamically developing UWB (Ultra Wide Band) systems and georadars, but also traditional radiolocation and telecommunication systems, a broadening of the antenna bandwidth of which may result in increased data throughput rate and significant improvement of radar system performance. A TSA antenna design should feature a low wave standing coefficient over as wide frequency band as possible, with a symmetrical radiation characteristic retained at minimum side-lobes. A significant requirement was also suitability to transmission operation, i.e., with a high microwave power. Also important were antennas design simplicity and low manufacturing cost. A traditional tapered slot antenna (initially called the Vivaldi antenna) was developed on a laminate with appropriately etched fields and power supply paths. Authors of this study have developed a number of such antenna s varieties. It was maintained in the published at that time literature that an antenna developed on a dielectric base (a laminate) may not be used as a transmitting antenna meant to radiate large powers. Therefore a concept was devised of a metal antenna made up of two slots cut in two parallel metal walls and an activation loop set perpendicular to the slots. 2. APPLICATION OF WIPL-D SOFTWARE IN TSA ELEMENT DESIGNING Analysis of measurement results has shown that the TSA elements presented on Fig. 1. are the most promising, so it was decided to choose it for multi-element aerial arrays. The computer model of analysed TSA antenna is presented in Fig. 2. The slot activation loop (a half-loop in fact), supplied from a coaxial line, is opened at its end. Attempts were made at development of a solution with a line closed at its end. This would contribute to the loop s rigidity. The main factors of antenna performance include the slot s shape, as well as the supply loop s design, size, and position. Therefore the designers focused on solving just this problem. For this purpose a computer analysis was completed using WIPL-D software [4]. For full accomplishment of the adopted objective it was necessary to familiarise with WIPL-D software that would enable computer simulation and selection of the ultimate solution. With the Figure 1: Examples of TSA elements.

2 PIERS ONLINE, VOL. 5, NO. 5, Figure 2: TSA antenna model in WIPL-D. Figure 3: Designed TSA antenna geometry. slot shape already determined, development was attempted of a transmitting array that would by far outperform the earlier designed antenna model with a broad bandwidth at the same time retained. The slot shape and supply line dimensions were calculated using WIPL-D software. The TSA element was developed in a few stages. First the shape presented on Fig. 3 was cut of 1 mm brass sheet. The applied cutting technology enabled cutting a shape in a dozen or so packs of the sheet stacked one on another. Then openings were drilled for (SMA-type) supply seat, and plates were bent according to the dotted lines shown on the drawing. The last stage involved fixing the seat and loop. With the slot shape already determined, development was attempted of a transmitting array that would by far outperform the earlier designed antenna model with a broad bandwidth at the same time retained. The best matching course achieved is presented on Fig. 4. The loop-shape and size have become the designed antenna s geometric specifications.

3 PIERS ONLINE, VOL. 5, NO. 5, WFS < 1,3 WFS < 1,2 2,51 2,57 3,65 3,77 Figure 4: WFS of TSA antenna supplied from half-wave loop. Figure 5: The 4 4 antenna element s layout. Figure 6: The 4 4 antenna matrix view. 3. MULTI-ELEMENT ANTENNA SYSTEM The model of antenna with TSA elements so developed is designed for operation in the S-band. The elements layout is presented on Fig. 5, whereas the view of a ready antenna is presented on Fig. 5. It was decided that at this stage of R&D works the distances between elements would be selected according to traditional criteria, i.e., ca. 0.5λ. Combined with cophasal and equal activation of

4 PIERS ONLINE, VOL. 5, NO. 5, individual elements it produced an antenna of performance far away from that required of operable items. The point was to check suitability of the idea of multi-element antenna with TSA radiators. 4. RESULTS OF MULTI-ELEMENT ANTENNA MEASUREMENT The multi-element antenna s radiation characteristics were measured in the planes of both vectors E and H, and the results are presented on Fig. 7 and Fig. 8. Figure 7: The radiation characteristics measured in E-plane vector. Figure 8: The radiation characteristics measured in H-plane vector. 5. SUMMARY AND CONCLUSIONS The objective of this study was to design a multi-element antenna using radiating elements in the form of tapered slot elements. Both the individual element and the entire array are innovative solutions that may provide alternatives to the solutions so far applied in the radiolocation engineering. The basis for simulation and design of the TSA aerial array was analysis of the existing solutions and properties of both narrow slot as well as multi-element antennas. In the next stage following familiarisation with WIPL-D software the TSA antenna design methodology was presented that enabled relatively quick development of even quite complex antenna structures by the software future users. The WIPL-D software was used in the study to present the characteristics of simple arrays made up of TSA antennas. With the aid of the software the designed array s parameters were selected to be subsequently used for building its physical model. The objective of the study, i.e., development and testing of an aerial array suitable for operation in a broad frequency band with symmetrical radiation characteristics and a narrow main lobe, has been fully accomplished, and the study results have justified the claim that the aerial arrays may provide in the future an alternative to the antenna systems used so far in the S-band of frequencies. Features of the examined elements include the following: antenna bandwidth at SWR < %, antenna bandwidth at SWC < %, symmetrical radiation characteristic, see Figs. 7 and 8, fixed radiation characteristic shape throughout bandwidth, stable input impedance throughout bandwidth, simple design, small antenna size, low manufacturing cost, damage-proof design. Subsequent R&D efforts should focus on further performance improvements of both the individual element and arrays made up thereof. Subsequent solutions that would feature even broader bandwidth than those of existing solutions should be sought after with the use of WIPL-D software and modelling the element s slot. Whereas modelling the elements positioning on-screen and the

5 PIERS ONLINE, VOL. 5, NO. 5, screen itself even more directional characteristics should be sought after of the side lobes lower level. However, the studies so far completed fully confirm growing interest in TSA antennas and their operation in phased aerial arrays and encourage continued works so aimed. These may also provide some interesting material to be used in laboratory exercises as familiarisation with TSA antennas and their advantages compared to the hitherto recognised solutions. This work may be continued by designing a TSA antenna model of even better performance, a broader bandwidth in particular. Such a new model will have a changed slot shape and size, as well as a better way of slot activation. Based on the performance of the already developed TSA antenna and the algorithm of programming in the WIPL-D environment a design, development, and computer simulation should be possible of a new TSA antenna and an aerial array made up of eight radiating elements. This should result in better radiation characteristics and broader bandwidth than those of the TSA antenna model hereby presented. REFERENCES 1. Prasad, S. N. and S. Mahapatra, A new MIC slot-line aerial, IEEE AP, Vol. 31, No. 3, May Janaswamy, R. and D. H. Schaubert, Analysis of the tapered slot antenna, IEEE AP, Vol. 35, No. 9, September Ko losowski, W., H. Grucha la, M. Wnuk, and A. Jeziorski, Antena z rozszerzaj aca siȩ szczelin a zasilana z linii komplanarnej, KKRRiT 2003, Wroc law, Ko losowski, W., M. Wnuk, and A. Jeziorski, New construction of tapered slot antennas, ICAP 2003, Exeter, Ko losowski, W., P. Gajewski, A. Jeziorski, and A. Sedek, The dielectric-free tapered slot antennas array, EuMW, Manchester, Kolundzija, B. M., J. S. Ognjanovic, and T. K. Sakar, WIPL-D: Electromagnetic modeling of composite metallic and dielectric structures, Software User s Manual, Artech House, Boston, London, 2000.