II. Array Antennas

1. II. Array Antennas

2. Array of Radiating Elements -Higher Directivity: arrange the radiating elements in space Linear Array Planar Array Conformal Array -Phased Array for Electronically Scanning: change the phase of the exciting current of each element -Element Pattern: Pattern of each radiating element -Array Factor: Pattern of Arrayed isotropic elements

4. Array of 2 Isotropic Elements

9. Equally Spaced Uniform Array

13. Uniformly Excited, Equally Spaced Linear Array (UE,ESLA) Current amplitudes are all equal

14. As N increases, the main lobe narrows • As N increases, there are more side lobes: # of SL/period = • Width of minor lobe = half of that of main lobes • As N increases, the side lobe peak decreases • is even function

15. Ex) 4-element UE, ESLA

16. Main beam maximum direction can be controlled by changing the phase difference between adjacent elements Main Beam Scanning and Beam-width Main Beam Scanning

17. Visible Region and Radiation pattern

18. Beam-width 1. BWFN (Beam Width between First Nulls) a) Broad Side:

19. b) End Fire:

20. 2. HPBW (Half Power Beam Width) a) Near Broad Side: b) end-fire:

21. One major lobe at direction Two major lobes at directions Endfire Array 1. The Ordinary Endfire Array One main, and one grating lobe For only one main lobe

22. 2. Hansen-Woodyard Endfire Array To obtain narrower beamwidth than the Ordinary case Visibleregion are not included in Visible Region Optimum phasing and spacing for maximum directivity

24. Pattern Multiplication Far-zone field of uniform array of identical elements is equal to the product of the field of a single element at a reference point and the array factor of that array Ex) collinear array of short dipoles

26. Ex) half wave length spaced collinear array of 2 short dipoles

27. Ex) half wave length spaced parallel array of 2 short dipoles Pattern of short dipole parallel to x-axis E-Plane Pattern H-Plane Pattern

28. half wave length spaced parallel array of 2 short dipoles E-Plane Pattern 3-D Pattern H-Plane Pattern

29. Directivity of UE_ESLA Beam Solid Angle Radiated Power Directivity

30. Beam Solid Angle of UE_ESLA Max. in the visible region for Hansen-Woodyard

31. Another main lobes appear Directivity is decreased Broadside Case

32. Broadside Endfire Endfire

33. Nonuniformly Excited, Equally Spaced Linear Array (NE,ESLA) Array Factor is Z-Transform of Amplitude Distribution and has N-1 Zeros (Pattern Nulls) 1) Uniform Excited

34. By tapering the current amplitude Tapering toward the ends decrease the side lobe level increase HPBW Tapering toward the center increase the side lobe level decrease HPBW

35. 2) Binomial Distributed 3) Triangular Distributed

36. 4) Dolph-Chebyshev Distributed

37. Tapering toward the center (inverse taper)

38. Directivity of NuE,ESLA

39. Array Pattern Synthesis Fourier Series Method: -.Fourier series expansion of desired array pattern -.Least-mean-square error approximation to the desired pattern

40. Binomial Arrays: -.Binomial expansion of desired array pattern -.complete absence of side lobes but low directivity

41. Array Polynomial: • The array factor of an (N+1)-element array is the product of the array of N 2-element arrays superimposed to produce nulls at the zeros of AF • 2. Any polynomial of degree N can be interpreted as an (N+1)-element array • 3. The product of 2 polynomials is the array factor for an array whose pattern is the product of patterns associated with each polynomial by itself

44. Multi-dimensional Array 2-dimensional Planar Array If the currents separable

45. Uniform Excited

46. Principal plane pattern,

47. Circular Array

49. Phased Array Scan Principle Beam broadening: scanned off broadside the main beam widens Grating Lobe: if visible region is wider than , there are more than one main lobe For avoiding grating lobes

50. Feed Networks for Beam Scanning Beam Forming Network Frequency Scanning Parallel Feed (Corporate feed) Parallel-series Feed Electronically phase control