Radar systems- Beam Forming, Beam Steering, Beam Width Changes

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This Presentation tries to cover Beam forming, beam steering & beam with changes subtopic for RADAR systems.

This PPT was made for Internal Assessment seminar for 18ECOE07- Open Elective I- Introduction to Radar systems- 7th semester, Jain (Deemed-to-be) University, Bengaluru India by Chaitanya Shukla (19BTRAS051)

1. Innovative Assessment: Seminar Seminar topic #33- Beam Steering & Beam width changes (Unit 5- 18ECOE07) Chaitanya Shukla (19BTRAS051), 7 TH Semester, Aerospace

2. Introduction & Prerequisite concepts 01 Prerequired concepts to understand core topic Beam Steering 02 Brief discussion on core idea about beam steering TABLE OF CONTENTS B eam width Changes 03 Brief discussion on core idea of Beam Width changes Conclusion 04 The advantages, disadvantages and future trends

3. 1.1 Brief Introduction & Prerequisite concepts: Generation of EM waves through dipole oscillators

4. Dipole a pair of equal and opposite electric charges or magnetic poles of opposite sign separated especially by a small distance How can it propagate EM waves? Assume the dipole is oscillating

5. Dipole generating waveform The charges will keep interchanging position and this will affect the electric field around it as show below for different time intervals. At t=T/4 they will cross each other and the field will separate as shown in next slide.

6. Dipole generating waveform

7. Practical application: Antenna What is antenna? Antenna is a radiating element which converts our current/voltage into EM radiation. Antenna will propagate that radiation into the space. At receiving end, vice versa happens.

8. Practical application- Antenna

9. 1.2 Brief Introduction & Prerequisite concepts: Three types of propagation modes

10. Uniform intensity in all directions like a light bulb. Isotropic Propagation in just two directions. Biaxial Directed beam in single direction often focused on a single target. Unidirection / directive Wave propagation types

11. Waterdrop Analogy Comparison Can be compared to isotropic propagation. We can see the waves are travelling uniformly in all direction. Can be compared to directive propagation. We can see the waves are travelling uniformly in all direction.

12. 1.3 Brief Introduction & Prerequisite concepts: Array based antennas: Need, Classification, Assumptions

13. Problems with conventional isotropic antenna Energy is radiated in 3-D sphere. Some part is received and majority is wasted. Range requirements have increased for military applications. Also we want to direct energy in specific direction without making antenna bulky and continuously moving bulky antenna. Conventional isotropic antenna: Problems

14. This constructive & destructive interference is used mathematically to get precise narrow beam, uni -directional beam, beam steering and changing width of beam. It will be discussed in further slides. Solution to problems: Array based antenna When single isotropic element (assuming point source ) is arranged in an array of n number of similar isotropic elements placed equidistance from each other , have same impendence ; it is observed that the individual waveforms from each element constructively or destructively interfere with each other to give a directional focused beam of Electromagnetic radiation. Single elemental antenna in an array- isotropic Array Array Array Types What is an Array? Linear, Planar, Conformal

15. 1.4 Brief Introduction & Prerequisite concepts: Beam forming, main lobe & Polar Diagrams

16. What is Beam Forming?

17. What is Beam Forming? Main Lobe

18. We have a dipole and inductor We can view them from above, they look like dots. A wave leaving antenna reaches reflector 1/4 th of wavelength later. Due to inductance, wave of opposite polarity is produced. When it reaches antenna, it is in phase with wave being created and the pattern can be seen. Unidirectional Beam forming has taken place here as one side reenforces constructively and other as destructively. Unidirectional Beam Forming

19. Polar Diagrams Isometric elemental radar Polar & Reflector patter- Directive / uni -directional 180 out of phase two dipoles- Bi-directional Polar Diagram Increase number of dipoles to aid this lobe.

20. Two types of array based on beam propagation Both dipoles 180deg in phase. Radiation pattern perpendicular to antenna axis This type is called “Broadside array” Both dipoles -180deg in phase. Radiation pattern is along the antenna axis This type is called “Endfire array”

21. 2.1 Beam Steering What is beam steering? Why we need it?

22. What is beam steering? Beam steering Is changing direction of main lobe of antenna radiation pattern What is need of beam steering? We discussed previously that there exists Broadside array & Endfire array that radiate either perpendicular or parallel to the axis of antenna. Beam steering is used if we want to radiate in some other angle between. We cannot always steer entire bulky antenna and we should have an easy option.

23. 2.1 Beam Steering How to achieve it?

24. How is it achieved? Beam steering is achieved by either means as follows Mechanical (conventional)- Servos / Motors move the array. Not efficient method. Electrical (Modern)- The current gain is varied

25. How is it achieved?

26. Comparing to waterdrop analogy

27. 2.3 Beam Steering Mathematical Equn . & Notes

28. Mathematical Equation & Notes Mathematically we need radiation pattern in angle of We know that, phase angle between 2 antenna elements is: Where beta is Propagation angle, d is distance between antenna elements inn array, theta is phase angle and alpha is phase shift. Changing alpha we can steer antenna pattern One application is Phased array antenna for receiving or sending EM waves. When we have steered to required direction theta_0, we say Hence, equation becomes: Hence now, Which proves that antenna angles changed by changing alpha  

29. 3.1 Beam width Changes Introduction

30. 3. 2 Beam width Changes Half Power Beam Width

31. 3. 3 Beam width Changes First Null Beam Width

32. 3.4 Beam width Changes Relation between directivity and Beam Width

33. 3.5 Beam width Changes Notes

34. Notes

35. THANKS ! This PPT will be available to download at https://slideshare.net/ChaitanyaShukla10 Please keep this slide for attribution Chaitanya Shukla | LinkedIn [email protected]