help regarding 3db divider

hello sir,

i want to design a 3db divider for the cosine output, which is formed from the equation IF = a(t) cos[(2πfc t +φ (t)] .carrier frequency of IF is fc with a time varying amplitude a(t) and time varying phaseφ (t).so please help me in this issue.and also how we can create a time varying amplitude and phase.i wrote a code for this waveform which we can enter values through the keyboard

% if singnal

clc; close all; clear all;

data_bits_i(1,(1:2:2000)) = zeros(1,1000)+1; data_bits_i(1,(2:2:2000)) = ones(1,1000);

fc = input('carrier frequency\n'); Fs = 16*fc; a=input('amplitude\n'); t = 0:1/Fs:15/Fs; angle=input('angle\n');

IF = a* cos(2*pi*fc*t + angle)

In_Signal=[];

for ii = 1:1:2000 In_Signal = [In_Signal data_bits_i(ii)*IF]; end

x_lenth = 1:1:200; figure; plot(x_lenth,In_Signal(1,1:200));

this output must enter to 3db divider to give the output so that it is applied to low pass filter.