% echo_r_mtx: range processing echo data
% target_list_RD: target list include range and doppler information
% d: antenna spacing
% fc: carrier frequency
% acc: angle estimation accuracy

% target_list_RDA: target list include range, doppler and angle information
% RA_map: range-angle map
% THETA: scale of angle


function [ target_list_RDA, RA_map, THETA ] = angle_est(echo_r_mtx, target_list_RD, d, fc, acc)

    % parameters
    if nargin < 5
        acc = 181;
    end
    [lenA, lenR, lenP] = size(echo_r_mtx);
    c = 3e8;      
    lambda = c / fc;
    
    % initialization
    echo_mtx = squeeze(echo_r_mtx(:, :, 1));
    
    % CBF
    THETA = linspace(-90, 90, round(acc));
    RA_map = zeros(length(THETA), lenR);
    for i = 1: length(THETA)
        a = exp((0: lenA - 1)' * -1j * 2 * pi / lambda * d * sin(THETA(i) / 180 * pi)); 
        RA_map(i, :) = a'* echo_mtx;  
    end
    RA_map = transpose(RA_map);
    
    % calculate angle
    range_angle = zeros(1, lenR);
    for j = 1: lenR
        [v, num] = max(abs(RA_map(j, :)));
        range_angle(j) = THETA(num);
    end
    targets_angle = range_angle(target_list_RD(:, 2));
    target_list_RDA = [target_list_RD, transpose(targets_angle)];

end