Design of Sectoral Horn Antenna with Low Side Lobe Level (S.L.L)

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1 Volume 117 No , ISSN: (printed version); ISSN: (on-line version) url: doi: /ijpam.v117i9.16 ijpam.eu Design of Sectoral Horn Antenna with Low Side Lobe Level (S.L.L) Chandana Viswanadham 1, Senior Member, IEEE and Prof. Prudhvi Mallikarjuna Rao 2 1PhD student Andhra University, Visakhapatnam, Andhra Pradesh, India , Phone # , ( viswanadhamch@bel.co.in) 2Professor, Department of ECE, Andhra University, Visakhapatnam, Andhra Pradesh, India , Phone # , ( pmraoauece@yahoo.com) Abstract Modern electronic systems like Radars, jammers, satellite transponders, trackers, etc., were designed with phased array antennas in their transmitter and or receiver sections, to provide electronically steered beam with very high gain in the required direction. Linear array of horns is one of the antennas used for high power radiation applications like jamming. H- plane sectoral horn antennas are used as element in the array to cater for wide bandwidths and high power handling capability. However, the S.L.L is high and need to be reduced for many applications including jamming. In this paper a simple and novel technique is proposed to reduce the side lobe level in Elevation plane. Key words: Bandwidth ratio, Flare Angle, Impedance, Side lobe level, Slant length, V.S.W.R, Waveguide 1 Introduction Many antenna engineers had developed wide band pyramidal horns suitable for reflector feed and mono-pulse tracking systems. In recent times, the applications of these antennas were expanded to Radar and E.W fields, where these antennas are considered in the areas of direction finding, tracking and multi-beam jammers [1-2]. The authors have designed, simulated and measured the performance of H-plane sectoral horns in the frequency range of 2-7 GHz and 7-18 GHz. The main application of H-plane sectoral horn antenna is receiving the radio frequency signals for estimation of direction of arrival and tracking systems. Also, H-plane sectoral horn antenna is used as element in the phased array antenna and exhibits higher S.L.L, which is not suitable for many applications. Hence, in this paper, the techniques for reducing S.L.L have been studied and implemented and the results are presented. 2 Design equations of sectoral horns The horn is considered as an aperture antenna and the fields at the aperture of the horn are found by treating the horn as radial waveguide. The geometry of H-plane horn antenna is shown at Fig. 1 [8-13, 15]. Fig. 1: Geometry of H-plane sectoral horn The following equations [21] are relevant for the geometry of sectoral horn antenna shown at Fig A lh R 0 2 (1) 1 A H tan 2R0 (2) lh 1 RH A a A 4 (3) Where l H Slant length of the horn, R0 Straight length of the horn, A Aperture height, H Flare angle, R H Flare length, a Waveguide height The directivity of the H-plane sectoral horn is calculated as per the following procedure [7, 9]. Step-1: Calculate X using formula A X 50 l H (4) 89

2 Step-2: Using this value of X, calculate the GH value from Fig. 5. If the value of X is smaller than 2, then G we need to compute H using 32 GH X (5) D Step-3: Calculate H using the formula DH b GH 50 lh (6) 3 Specifications and Design Calculations 3.1 Specifications The specifications of 7-18 GHz H-plane sectoral horn antenna are given at Table-1. Table-1 Sl. No. Parameter Targeted Specifications 1. Frequency range 7 18 GHz 2. V.S.W.R Max. 2.5:1 (95% band) 3. Side Lobe Level (S.L.L) < -20 db Min (El) 4. Gain (Min.) 6 dbi 5. 3-dB E.P. Beam width 35 Max dB A.P Beam width 120 Max. 7. Connectors S.M.A (F) 3.2 Design Calculations Based on the above requirements, the calculated design values are DH =5.46, GH=88, b=8.2mm, X=9.39 mm, A= mm, Ro=215.7 mm and lh= mm. 3.3 Design Simulations The H-plane sectoral horn antennas is modeled in solid works using the design values obtained in section 3.2, exported to C.S.T studio Ver.2 for analysis of all electrical parameters, viz. V.S.W.R, radiation patterns, S.L.L and directive gain. The model is shown at Fig. 2. Fig. 3: Simulated V.S.W.R Radiation patterns The Radiation patterns obtained from the simulation for each frequency from 7 to 18 GHz are shown at Fig. 4 to Fig. 5. Radiation GHz Fig. 4: Simulated radiation pattern (Az & EL) at 7 GHz Radiation GHz Fig. 5: Simulated radiation pattern (Az & EL) at 18 GHz Fig. 2: Solid model of H-plane sectoral horn 3.4 Simulation results V.S.W.R The V.S.W.R obtained from the simulation is shown at Fig. 3. The maximum S.L.L obtained in the simulation is -3.5 db at 14 GHz. 4 Fabrication and measurements The antenna is manufactured on C.N.C machine with 0.1 mm accuracy and assembled and tested for various parameters using network analyzer and anechoic chamber with antenna measurement facilities as per the procedures [6]. 4.1 Measured results Radiation patterns The radiation patterns for E.P & A.P are measured and shown below from Fig. 6 to Fig

3 172 mm 107 mm Fig. 6: Measured radiation pattern (Az & El) at 7 GHz Fig. 8: Dielectric lens (172 mm X 107 mm X 8 mm thick) used in sectoral horn 6 Fabrication and measurements The H-plane sectoral horns in the frequency range of 7-18 GHz are, manufactured with the above improvements i.e., hybrid tapering and parabolic dielectric lens and the results are shown in the subsequent paragraphs. The photographs of the manufactured H-plane sectoral horn with dielectric parabolic lens inserted are shown at Fig. 9. Fig. 7: Measured radiation pattern (Az & El) at 18 GHz S.L.L measurements The S.L.L of the antenna is calculated from the radiation patterns and -18 db is achieved at 18 GHz. 4.2 Comparison of Simulated and Measured results The simulated and measured results are shown at Table-2. Table-2 Comparison of simulated and measured results Sl. No. Parameter Simulated results Measured results 1. Frequency range 7 18 GHz 7 18 GHz 2. S.L.L in -3.5 db -18 db Min Elevation plane Fig. 9: Picture of H-plane sector horn antennas with Dielectric parabolic lens inserted in the antenna 6.1 Measured results The V.S.W.R and radiation diagrams are shown at Fig 10 to Fig.12. The measured S.L.L from radiation patterns is -20 db at 7 GHz. 5 Techniques for S.L.L improvement Many improvement techniques were available for narrow band application [5-8] and new techniques are evolved, simulated, implemented, tested and presented in the subsequent paragraphs [7,11,15]. The proposed improved techniques for S.L.L reduction is through introduction of parabolic dielectric lens inside the horn body. The dimensions of the dielectric lens is shown at Fig. 8 Fig. 10: Measured V.S.W.R 91

4 Fig. 11: Measured radiation pattern at 7 GHz Fig. 12: Measured radiation pattern at 18 GHz 7 Conclusions It is clearly evident that the modified sectoral horn antenna i.e., with hybrid aperture and parabolic dielectric placed inside the horn body showed better S.L.L results than simulated and unmodified antenna. Hence it is concluded that the placement of parabolic dielectric lens at optimum distance in the horn has improved the performance without degrading the gain and V.S.W.R. In each case the simulated and measured results are in agreement. References [1] Richard G. Wiley, Electronic Intelligence in the title of Electronic Intelligence: The interception of Radar signals, 2nd edition, 1985, Artech publications [2] Stephen E. Lipsky, Microwave passive direction finding in the title of Microwave Passive Direction Finding, 2004, Scitech publishing Inc [3] Hans Schantz, Antenna as Transducers and Antennas as transformer, in the title of Art and Science of Ultra Wide Band antennas 1st edition, 2005, Artech publications [4] Ch Viswanadham, Prof P Mallikarjuna Rao, Experimental Results of Structurally Modified High Power Ultra Broadband Phased Array Antenna for Extending the Operating Frequency Range and Improving the V.S.W.R, Feb 2016, presented at ATMS India. [5] Pues H.F, An impedance-matching techniques for increasing the bandwidth of micro strip antennas, Antennas and Propagation, IEEE transactions Vol. 37, issue 11, pages , ISSN: X, 06 Aug [6] Licul, S., Ultra wideband characterization and measurement," PhD Thesis, Faculty of Virginia Polytechnic Institute & State University, September [7] Constantine A Balanis, Antenna Theory Analysis and design with multimedia CD, 3rd edition, Wiley India, reprint [8] A. W. Love, Electromagnetic Horn Antennas, IEEE Press, New York, [9] C. A. Balanis, Horn Antennas, Chapter 8 in Antenna Handbook: Theory, Applications and Design (Y. T. Lo and S. W. Lee, eds.), Van Nostrand Reinhold Co., New York, [10] A. W. Love, Horn Antennas, Chapter 15 in Antenna Engineering Hand book (R. C. Johnson and H. Jasik, eds.), New York, [11] R. F. Harrington, Time-Harmonic Electromagnetic Fields, McGraw-Hill, New York, 1961, pp [12] S. Silver (ed.), Microwave Antenna Theory and Design, MIT Radiation Laboratory Series, Vol. 12, McGraw-Hill, New York, 1949, pp [13] C. A. Balanis, Advanced Engineering Electromagnetic, John Wiley and Sons, New York, [14] M. J. May bell and P. S. Simon, Pyramidal Horn Gain Calculation with Improved Accuracy, IEEE Trans. Antennas Propagat., Vol. 41, No. 7, pp , July 1993 [15] K. Liu, C. A. Balanis, C. R. Bircher and G. C. Barber, Analysis of Pyramidal Horn Antennas Using Moment Method, IEEE Trans. Antennas Propagat., Vol. 41, No. 10, pp , October [16] M. Abramowitz and I. A. Seguin (eds.), Handbook of Mathematical Functions, National Bureau of Standards, United States Dept. of Commerce, June [17] J. Boersma, Computation of Fresnel Integrals, Math. Comp., Vol. 14, p. 380, [18] Y.-B. Cheng, Analysis of Aircraft Antenna Radiation for Microwave Landing System Using Geometrical Theory of Diffraction, MSEE Thesis, Dept. of Electrical Engineering, West Virginia University, 1976, pp [19] E. V. Jull, Gain of an E-Plan e Sect oral Horn A Failure of the Kirchhoff Theory and a New Proposal, IEEE Trans. Antennas Propagat., Vol. AP-22, No. 2, pp , March [20] R. E. Lawrie and L. Peters, Jr., Modifications of Horn Antennas for Low Side Lobe Levels, IEEE Trans. Antennas Propagat., Vol. AP-14, No. 5, pp , September [21] R. S. Elliott, On the Theory of Corrugated Plane Surfaces, IRE Trans. Antennas Propagat., Vol. AP-2, No. 2, pp , April [22] C. A. Mentzer and L. Peters, Jr., Properties of Cutoff Corrugated Surfaces for Corrugated Horn Design, IEEE Trans. Antennas Propagat., Vol. AP- 22, No. 2, pp , March

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