Radar Basics including mmWave, pulse radar

basic working of Radar

1. Radar block diagram

2. Range : Distance to the target (Round – trip time) Size : Size of the target (Radar Cross Section) Speed : Speed at which the target is moving (Doppler Analysis) Frequencies used : Hertz Here, C = Speed of the electromagnetic wave (Speed of light = 3 x ) = Wavelength (in meters, inversely proportional to frequency) Frequency : 30 Gigahertz to 300 Gigahertz (Giga = ) Wavelength : 1 millimetre to 10 millimetre The Radars working in this range are called millimetre wave radar (mm wave) The international telecommunication union has categorized these radars in these bands. Ku : 12 – 18 Gigahertz K : 18 – 27 Gigahertz Ka : 27 – 40 Gigahertz W : 40 – 100+ Gigahertz   Radio Detection and Ranging

3. Radar Equation Signal to Noise Ratio (SNR) = Normally this is represented in terms of decibel (db)(it’s a logarithmic scale) 0.01 = -20 db 0.1 = -10 db 0 = 1 db 10 = 10 db 100 = 20 db   Received Power ( ) = Here, : Transmitted Power : Gain of the receiver antenna : Gain of the transmitted antenna : Wavelength of the electromagnetic signal : Target’s Radar cross section : Transmitter antenna aperture : Transmitter antenna aperture R : Distance between Radar and Target L : Losses   Noise Power = K Here, K : Boltzmann constant (1.380×10 −23 J/K) : Noise Bandwidth of the receiver : System Noise  

4. Doppler Effect Transmitted signal Transmitted signal Echo signal Echo signal The received signal's frequency increases when the target is moving towards the Radar. Whereas the frequency reduces when the target is moving away from the Radar. This is the Doppler effect. Relative velocity of the target is calculated based on the change in frequency.

5. Continuous Wave Radar (CW) on period off period : Period for which the Radar Transmitter is on. : Period for which the Radar Transmitter is off (Waits for echo). Duty Cycle = For the < - figure Duty Cycle is 25 % So, when the Duty Cycle is 100%, meaning the transmitter is constantly emitting pulses, we refer such radars as Continuous Wave (CW) Radar .   on period Inside the "on" period, multiple pulses can be transmitted; it's not like a single pulse will only be transmitted during the "on" period

6. Frequency Modulated Continuous Wave Radar (FMCW) on period The frequency of the transmitted signal is continuously varied in a known and linear fashion over time. FMCW radars are well-suited for measuring target velocities due to the frequency modulation. The Doppler shift induced by moving targets can be precisely analyzed, providing information about the speed of the targets. So FMCW radars are good for observing moving targets By doing this, the bandwidth of the Radar is increased. This gives better range resolution. 

7. Constant False Alarm Rate (CFAR) This is a signal processing technique used to detect targets in the presence of varying levels of noise or clutter. The key idea behind CFAR is to adaptively adjust the detection threshold based on the local statistical properties of the received signal. Average Noise (Noise Floor) Threshold Valid Target Detections In scenarios with assumed constant noise floor, preset thresholds may work well, particularly in the case of white noise following a normal distribution. However, real-world situations can introduce deviations, such as variations in the noise floor. In these cases, the adaptability of Constant False Alarm Rate (CFAR) algorithms becomes crucial. They dynamically adjust detection thresholds, ensuring accurate target identification amidst changing noise conditions.

8. Array of Antennas An array of antennas can be used to increase the gain. It enables the Radar system to focus its energy in a specific direction. This improves target detection, tracking, and discrimination capabilities. By changing the phase of the transmission signals, the Radar system with an array of antennas achieves steering capabilities. This increases the complexity and cost. It helps reduce noise’s impact by focusing energy on a desired direction. The distance between the antennas must be less than half the wavelength of the signal.  This prevents grating lobes. 

9. Compared to a traditional single-antenna radar, an array antenna radar gives higher flexibility, higher capacity, several radar functions simultaneously and increased reliability, and makes new types of signal processing possible which give new functions and higher performance

10. Range profile: Obtained by taking the Fast Fourier Transform of the Intermediate-Frequency signal. It depicts the relative reflected power from the target as a function of range. Targets with large cross section reflects more power, targets nearer to the sensor also reflects more power.  Range-Doppler heat map: displays multiple targets with their speeds as a function of range.  Stationary targets have zero Doppler while moving targets have a range–Doppler map with non-zero Doppler values. This essentially provides dynamic information about the targets, such as their velocity and range

11. UWB VS MM wave radars Frequency Range: UWB Radar: Operates typically in the frequency range of 3.1 GHz to 10.6 GHz, although it can extend beyond this range. mmWave Radar: Operates in the millimeter-wave frequency range, typically from 24 GHz to 100 GHz or higher. mmWave radar uses much shorter wavelengths compared to UWB radar. Resolution: UWB Radar: Offers excellent range resolution due to its short pulse duration. It can distinguish between closely spaced objects with high precision. mmWave Radar: Also provides high resolution, especially in terms of angular resolution , which is beneficial for applications requiring precise localization and tracking. Penetration and Reflection: UWB Radar: Excels in penetrating materials such as walls, foliage, and clothing, making it suitable for through-wall imaging, ground-penetrating radar, and indoor positioning systems. mmWave Radar: Works well for short-range applications and line-of-sight scenarios. Its shorter wavelengths make it less effective at penetrating obstacles compared to UWB radar. Applications: UWB Radar: Commonly used for indoor positioning and tracking, automotive radar, healthcare monitoring, and through-wall imaging. mmWave Radar: Widely employed in automotive radar for advanced driver assistance systems (ADAS), industrial sensing, gesture recognition, and short-range communication systems. Cost and Complexity: UWB Radar: Generally simpler and less expensive to implement compared to mmWave radar systems. mmWave Radar: More complex and costly due to the higher frequencies involved and the need for sophisticated antenna arrays and signal processing algorithms.

12. Reference  MIT introduction to Radar concepts lecture series: https://youtube.com/playlist?list=PLUJAYadtuizA8RC2Qk8LfmiWA56HZsk9y&si=J2MNv_XiO632qD7K