Presentation is loading. Please wait.

Presentation is loading. Please wait.

Chapter 4. Antenna Synthesis

Similar presentations

Presentation on theme: "Chapter 4. Antenna Synthesis"— Presentation transcript:

1 Chapter 4. Antenna Synthesis
4.1 Basic principle for antenna synthesis 4.2 Line source synthesis (Fourier transform, woodward-lanson sampling) 4.3 Linear array synthesis (Fourier series, woodward-lanson sampling) 4.4 Low sidelobe synthesis (Dolph-Chebyshev, Taylor)

2 Synthesis Problems Given affordable SLL, No. of elements,
how to synthesize? Ideal case: narrow beam, constant side-lobe envelope Approaches: Dolph-Chebyshev, Taylor Line Source…. Secret behind: to synthesize a polynomial like pattern….

3 Dolph-Chebyshev Linear Array
The Chebyshev polynomials: Property used:

4 Chebyshev Polyminals

5 Symmetrically Excited Array
, P odd , P even Property: is P-1 th polynomial of Let Choose appropriate to match the coefficients to those in Chebyshev polynomial, we obtain,

6 Chebyshev Polynomial Example

7 Synthesis Standards SLL=-20log R (dB) so Optimum spacing, Endfire:
Broadside: Endfire: , where

8 Beamwidth and Directivity
(broadside) In general, (endfire) , where An approximation for the broadside: Beambroadening factor: Directivity:

9 Example No.1 Five element array (P=5), -20dB Side-Lobe,
Half-Wavelength Spaced Dolph-Chebyshev Array

10 Synthesized Array Factor

11 Example No.2 Optimum Spaced 10-Element, -30dB Side Lobe,
Dolph-Chebyshev Endfire Array

12 Taylor Line Source Method
Transform: where a is a constant and, So the pattern maximum is, For the side-lobe region: Main beam region:

13 Transformed Chebyshev Polynomial

14 Basic Properties of Zeros
Zeros of the transformed function in the side-lobes are given by: For the main beam, Introduce A so that, and For large N,

15 Selection of Constant a
a is selected so that the first zero location remains fixed as N increases, Then The pattern should have the following format,

16 Ideal Pattern Factor Normalizing the pattern to unity at x=0,
(side lobes) (main beam)

17 Realistic Pattern Factor
where In format of w,

18 Woodward-Lawson Equivalent
for The source current is

19 Beamwidth and Directivity
(ideal Taylor) (realistic Taylor)

20 Example A 10-Wavelength Taylor Line Source with –25 dB side lobes and

21 Pattern and Current Source

Download ppt "Chapter 4. Antenna Synthesis"

Similar presentations

Ads by Google