350lect12 - 12 Interference, antenna arrays contd. E H We...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
12 Interference, antenna arrays — cont’d. We continue with our study of interference eFects and antenna arrays. x y z θ φ r ˜ E = ˆ θ ˜ E θ ˜ E × ˜ H * θ ± d r - ˆ zd d cos θ 2 d 3 d Beam patterns of N -element antenna arrays examined last lecture were isotropic in φ direction — the main eFect of increasing the array size Nd appeared to be narrowing the mainlobe of the pattern in θ direction. New vocabulary: Broadside arrays Array axis Broadside direction These so-called broadside arrays —mean ingtha ttheyma in lyra - diate in the “broadside direction” of the “array axis” — are good for broadcasting purposes at relatively high frequencies ω 2 π in the ±M band ( 100 MHz), where array sizes Nd ,inexcesso fmany λ ’s, become practicable (as opposed to in AM band where ω 2 π 1MHzand λ 300 m). They may also be used as “elements” of arrays built along x -or y -axis directions which we will consider next. In that case it will be possible to produce antenna beam patterns anisotropic in the azimuth plane (in φ direction).
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
y z θ φ r ˜ E = ˆ θ ˜ E θ ˜ E × ˜ H * d d cos θ x 2 d 3 d r - ˆ xd θ x Consider an array of elements polarized in ˆ z -direction positioned along the x -axis as shown above. Our initial analysis of this array will assume equal input currents I o for all the elements. Let ˜ E 0 ( r ) e - jk | r | | r | denote the Feld at the observation point r due to the element at the origin. Then, using the paraxial approximation, the Feld phasor at a dis- tant observation point due to the next element at ( d, 0 , 0) can be expressed in terms of ˜ E 0 ( r ) as ˜ E 1 ( r ) ˜ E 0 ( r ) e jkd cos θ x where θ x is the angle between vectors r and ˆ x ,i .e . , cos θ x r ·
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 09/27/2011 for the course ECE 450 taught by Professor Staff during the Fall '08 term at University of Illinois, Urbana Champaign.

Page1 / 9

350lect12 - 12 Interference, antenna arrays contd. E H We...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online