Antenna Arrays Prof. Girish Kumar Electrical Engineering - PowerPoint PPT Presentation

Antenna Arrays Prof. Girish Kumar Electrical Engineering Department, IIT Bombay gkumar@ee.iitb.ac.in (022) 2576 7436 1

Linear and Planar Arrays  Arrays of Two Isotropic Sources  Principles of Pattern Multiplication  Linear Array of N Elements with Uniform Amplitude  Broadside  Ordinary Endfire  Increased Directivity Endfire Array (IDEA)  Scanning Array  Linear Arrays with Non-Uniform Amplitude  Planar Arrays 2

Array of Two Isotropic Point Sources        2 j r j r    E E e E e 1 2 k P o o   d    r r r cos  2 1 2      r d , 90 >> d  r cos   d 2    r  r r cos 1 2  2    d d      1 2 j cos j cos   d / 2     j r 2 2 E E e e e o   d        j j       j r 2 2 E e e e  o   2 d         d cos cos   2 d           d = dsin sin         E 2 E cos 2 E cos cos  o o     2 3

Two Isotropic Point Sources of Same Amplitude and Phase Normalized E: 0 ° 90 ° 60 ° ф E 0 1 HPBWs = 60 ° in one plane and 360 ° in another plane 4

ORIGIN AT ELEMENT 1 5

Two Isotropic Point Sources of Same Amplitude and Opposite Phase HPBW = 120 ° 0 ° 90 ° 60 ° ф E 1 0 HPBWs = 120 ° in both orthogonal planes 6

Two Isotropic Point Sources of Same Amplitude with 90 0 Phase Difference at λ /2 0 ° 60 ° 90 ° 120 ° 180 ° ф E 0 1 7

Two Isotropic Point Sources of Same Amplitude with 90 0 Phase Difference at λ /4 Spacing between the sources is reduced to λ /4 0 ° 90 ° 120 ° 150 ° 180 ° ф E 0 0.924 0.994 1 HPBW = 180 ° 8

Two Isotropic Point Sources Of Same Amplitude with Any Phase Difference 9

Two Same Dipoles and Pattern Multiplication Horizontal Dipole: For δ = 0, Array Factor (AF) will give max. radiation in Broadside Direction Dipole Final Pattern AF 10

PATTERN MULTIPLICATION Dipole E-Field for Vertical Orientation: Combined E-Field Array of two vertical dipole antennas Dipole Pattern AF Product of Patterns 11

N Isotropic Point Sources of Equal Amplitude and Spacing where As Ψ 0, E max = n, E norm 12

Radiation Pattern of N Isotropic Elements Array Array Factor First SLL = 20log0.22 = -13.15dB Radiation Pattern for array of n isotropic radiators of equal amplitude and spacing. 13

Broadside Array (Sources In Phase) and n = 4 ф Ψ E 0 ° π 0 60 ° π /2 0 90 ° 0 1 Field pattern of 4 isotropic point sources with the same amplitude and phase. Spacing =  /2. 14

Ordinary Endfire Array For d =  /2, ϕ = 0 0 and Ψ = 0 BWFN=120 ° Field pattern of ordinary end-fire array of 4 isotropic point sources of same amplitude. Spacing is  /2 and the phase angle  = -  . 15

Increased Directivity Endfire Array (IDEA) For endfire array For increased directivity endfire array Parameter Ordinary end Increased Directivity fire array endfire array 69 ° 38 ° HPBW 106 ° 74 ° FNBW Field patterns of end-fire arrays of 10 isotropic point sources of equal amplitude spaced  /4 apart. Directivity 11 19 (a) Phase for increased directivity (  = - 0.6  ), (b) Phase of an ordinary end-fire array (  = - 0.5  ). 16

Array with Maximum Field in any Arbitrary Direction For Beam Maxima at ϕ = 60 ° For d = λ / 2, d r = π Field pattern of array of 4 isotropic point sources of equal amplitude with phase adjusted to give the maximum at ф = 60 ° for spacing d = λ /2 17