Doppler Radar analogRead() - arduino

Question

I've been doing a project on reading doppler speed and creating velocity data. I don't have a firm background on electric engineering / signal processing but I've researched quite a bit so far. Please bear with me if I get things wrong in my explanation.
I am currently using HB100 and CDM324 breakout model. The objective in this project is to get the voltage reading from the module and create a spectrogram though FFT in MATLAB. I got a sample data from BlackCatScience with the hand moving towards the Sensor at a fast speed. Its plot is shown below:
Hand Speed Using Doppler Radar
And I've assembled my arduino kit like the picture below:
Arduino-HB100_kit
Connections are:
VCC -> 5V GND -> GND FOUT -> Pin 8 VOUT -> Pin A5
So far, I found out that HB100 supports pulse/CW usage and used the code below to measure the frequency using HB100.
#include <MsTimer2.h>
#include <FreqMeasure.h>
//--------------GlOBAL VARIALBES---------------------
double raw_data = FreqMeasure.read();
double sum = 0;
int count = 0;
double raw_data_array[10];
unsigned long timeStamp = 0;
//---------------------------------------------------
void setup() {
Serial.begin(115200);
FreqMeasure.begin();
Serial.print("Time (ms)");
Serial.print("\t");
Serial.println("Hz");
}
void loop() {
timer();
freq_measure();
}
void timer() {
timeStamp+=1;
}
void freq_measure() {
while (timeStamp < 101) {
if(FreqMeasure.available()) {
//average readings
sum += FreqMeasure.read();
count ++;
if (count > 2) {
float frequency = FreqMeasure.countToFrequency(sum/count);
// Serial.print(timeStamp);
// Serial.print("\t");
Serial.println(frequency);
timeStamp++;
sum = 0;
count = 0;
}
}
}
}
The problem with this code is that, I want to measure the voltage reading at every, say for example, 1 millisec. However, this code is similar to using pulseIn function and the rate at which the data is out differs on whether I'm moving my hand to/from the sensor or not. When I'm not moving, the data output become slow, and when I'm moving, the data output rate is fast.
Hence, I decided to use some other code and use analogRead function like below:
//-----------------------------------------------------------------
#define RADAR A5 //pin number for VOUT
//--------------------GLOBAL VARIABLES-----------------------------
unsigned long timeStamp;
//-----------------------------------------------------------------
void setup() {
Serial.begin(115200);
pinMode(RADAR, INPUT);
Serial.println(F("Settings Complete" ));
}
void loop() {
// 1 millisec == 0.001 second --> 1000 millisec == 1 second
// we want about 5 seconds of data, hence the loop runs for 5000 millisec
while (timeStamp < 5000){
showReading();
}
}
void showReading() {
// timeStamp = millis();
// Serial.print(timeStamp);
// Serial.print("\t");
//Read input on analog pin 5:
int sensorData = analogRead(RADAR);
// float voltage = sensorData * (5.0 / 1023.0);
Serial.println(sensorData);
}
This time, the serial monitor is giving me a value between 0 and 1023 and that's great, but even if I move my hand in front of the sensor, the values change but minimally. What should I do to correct this and get a plot like the graph above?
Thanks for reading such a long question. Have a great day!