Range and Doppler Measurement of RADAR (Basics, Range & Doppler Calculation) Explained

Summary

In this video, the speaker explains the fundamentals of range and Doppler measurement in radar systems, specifically focusing on deriving the radar range equation using range frequency. The discussion covers pulse and CW radar systems, emphasizing how frequency drift helps identify target velocity. The core explanation centers around FMCW radar, which combines both range and velocity detection using frequency-modulated continuous waves. The video includes a step-by-step derivation of the range equation based on beat frequency, considering scenarios where the target is stationary and Doppler frequency is zero.

Takeaways

• 📡 The video explains the range and Doppler measurement in radar systems.
• 🛠️ The presenter derives the radar range equation based on range frequency, different from the time-delay method used in pulsed radar systems.
• 🎯 Pulsed radar measures range using time delay, while CW radar measures velocity using frequency drift between transmitted and received signals.
• 🚀 FMCW radar can measure both range and velocity simultaneously, using frequency-modulated continuous waves.
• 🔄 The range is identified through the time delay between transmitted and received signals, with a round trip distance represented by 2r/c.
• 📊 Beat frequency (FB) is a combination of Doppler frequency (FD) and range frequency (FR). If the target is stationary, FD becomes zero, making FB equal to FR.
• 📈 A triangular wave is used to represent frequency modulation in FMCW radar, showing the relationship between frequency deviation and time.
• 📏 The range is calculated by the equation: Range = c * FR / (4 * deltaF * FM), where deltaF is the total frequency deviation and FM is the modulation rate.
• 📉 The presenter breaks down the beat frequency graph, showing how transmitted and received signals converge and diverge, indicating range information.
• 📖 In future videos, the presenter will cover how FMCW radar can measure both range and velocity of a moving target.

Q & A

What is the main difference between pulsed radar and CW radar?

The main difference is that pulsed radar calculates range based on the time delay between transmitted and received signals, while CW radar calculates velocity or motion based on the frequency drift between the transmitted and received signals.

What is FMCW radar and what are its benefits?

FMCW (Frequency Modulated Continuous Wave) radar transmits a frequency-modulated signal that changes over time, allowing it to measure both the range and velocity of a target, combining the functions of pulsed radar and CW radar.

How is range calculated in FMCW radar?

In FMCW radar, range is calculated based on the frequency deviation between the transmitted and received signals. The round-trip delay is related to the distance traveled by the signal, and the range equation is derived using the beat frequency and modulation parameters.

What is the significance of beat frequency (FB) in FMCW radar?

Beat frequency (FB) is the difference between the transmitted and received signal frequencies. It is a combination of Doppler frequency (FD) and range frequency (FR). In the case of a stationary target, the beat frequency equals the range frequency.

What happens to the Doppler frequency when the target is stationary?

When the target is stationary, the Doppler frequency (FD) is zero, meaning that the beat frequency equals the range frequency, as there is no motion to cause a frequency shift.

How does the transmitted signal in FMCW radar change over time?

In FMCW radar, the transmitted signal is a frequency-modulated continuous wave where the frequency increases linearly over time. This is typically represented as a triangular wave when plotted against time.

What is the role of frequency deviation (Δf) in FMCW radar?

Frequency deviation (Δf) represents the total change in the transmitted signal's frequency over a given period. It is a key factor in determining the beat frequency and thus the range of the target.

How is range frequency (FR) related to the time delay (T) in FMCW radar?

The range frequency (FR) is related to the time delay (T) by the equation T = FR / (df/dt), where df/dt is the rate of frequency change over time. This relationship allows the range to be calculated using the beat frequency and modulation parameters.

How is the range of a target calculated from the time delay in FMCW radar?

The range is calculated using the equation R = (C * T) / 2, where T is the time delay and C is the speed of light. Substituting the time delay (T) in terms of range frequency gives the final equation: R = (C * FR) / (4 * Δf * FM).

Why is the triangular wave used in the derivation of the range equation?

The triangular wave represents the linear change in frequency of the transmitted signal over time. It is used in the derivation because it simplifies the calculation of beat frequency and allows for a clear understanding of the relationship between transmitted and received frequencies.