write a matlab code which plots tschebyscheff co-efficients and array factor of

Question

write a matlab code which plots tschebyscheff co-efficients and array factor of linear array antenna with number of elements =127 and sidelobe level=-25db

Explanation / Answer

% dolph.m - Dolph-Chebyshev array weights % % Usage: [a, dph] = dolph(d, ph0, N, R) % % d = element spacing in units of lambda % ph0 = beam angle in degrees (broadside ph0=90) % N = number of array elements (even or odd) % R = relative sidelobe level in dB, (e.g. R = 30) % % a = row vector of array weights (steered towards ph0) % dph = 3-dB beamwidth in degrees % function [a, dph] = dolph(d, ph0, N, R) if nargin==0, help dolph; return; end N1 = N - 1; % number of pattern zeros Ra = 10^(R/20); % sidelobe level in absolute units x0 = cosh(acosh(Ra)/N1); % scaling factor dmax = acos(-1/x0)/pi; % maximum element spacing if d>dmax, fprintf('maximum allowed spacing is dmax = %.4f ', dmax); return; end i = 1:N1; x = cos(pi*(i-0.5)/N1); % N1 zeros of Chebyshev polynomial T_N1(x) psi = 2 * acos(x/x0); % N1 array pattern zeros in psi-space z = exp(j*psi); % N1 zeros of array polynomial a = real(poly2(z)); % zeros-to-polynomial form, N1+1 = N coefficients a = steer(d, a, ph0); % steer towards ph0 x3 = cosh(acosh(Ra/sqrt(2))/N1); % 3-dB Chebyshev variable x psi3 = 2*acos(x3/x0); % exact 3-dB frequency dps = 2*psi3; % 3-dB width dph = bwidth(d, ph0, dps); % 3-dB width in phi-space

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