Import/load data arc tangent demodulation

The goal of the whole code(not included here) is too use arctangent demodulation on the I&Q channels of a dobbler radar to get theta. If relevant ffilt is the result of my fft I and Q signals from a doubler motion sensor. I get the error, "Dot indexing is not supported for variables of this type. Error in arctangentdemodulationcode (line 9) z1=filter(B,1,d.data(:,2)); % I channel signal"

 clear all; close all; clc;
load d_1318_12JUN2020.mat

d='ffilt';                       % import data options 
fs=100;                                       % Sampling frequency
fc=40;                                         % carrier frequency (corner frequency) 
fc_n = fc .* 2 /fs;                            % normalized frequency
B = fir1(10000,fc_n);                          % filter basics 
z1=filter(B,1,d.data(:,2));                    % I channel signal
z2=filter(B,1,d.data(:,4));                    % Q channel signal 

 
 I=z1;                                         % I data filtered
 Q=z2;                                        % Q data filtered 

[Sriram Tadavarty]

As seen in the code, d is a character vector 'ffilt'. Thus, accessing it as a structure or object with dot indexing for a field or property data, causes an error. Replace d equals ffilt with someother variable. I assume d is a variable from your import file.

Hope this helps. Regards, Sriram