Radar Laboratory – Interactive Radar Phenomenology

Radar can feel abstract because the important behavior happens in places you cannot easily see: time delay, Doppler shift, antenna patterns, noise, clutter, detection thresholds, and line-of-sight geometry. Radar Laboratory was created to make those invisible ideas visible. Use the modules below to build intuition first, then connect what you see to the equations and deeper theory.

Three-Step Learning Approach

1. Learn visually: Each module pairs a simple simulation with plots so you can see how radar behavior changes in real time.
2. Move one control: Change one slider at a time and compare the scene, plot, and readouts. That is the fastest way to build intuition.
3. Then go deeper: The explanations and theory sections connect the visuals to the math, assumptions, and real radar challenges.

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MODULE 01: EM Waves & Propagation

Electromagnetic waves carry energy at the speed of light. The frequency you choose shapes every performance parameter that follows – beamwidth, Doppler shift, ambiguity, and antenna size.

Typical System Values (IEEE Bands):

• L-band (1 GHz): λ = 30 cm · Surveillance
• S-band (3 GHz): λ = 10 cm · ATC / Weather
• X-band (10 GHz): λ = 3 cm · Fire control
• Ku-band (15 GHz): λ = 2 cm · Imaging

Atmospheric Absorption:

Water vapor (H2O) peaks at 22 GHz and 183 GHz. Oxygen (O2) dominates at 60 GHz and 119 GHz. Atmospheric windows at 35, 77, and 94 GHz are exploited by automotive and military radars.

MODULE 02: Range Measurement

Radar times the two-way travel of a pulse. Electromagnetic waves travel at c = 3×10⁸ m/s, which is 150 m/μs (one-way).

• Maximum Unambiguous Range (Ru): The radar must receive the previous pulse's echo before firing again. If the Pulse Repetition Interval (PRI) is too short, a distant echo arrives after the next transmission and is reported at a false closer range.

MODULE 03: Range Resolution & Pulse Compression

Two targets closer than ΔR cannot be separated – their echoes overlap in the receiver.

• Pulse Compression: A chirp sweeps frequency across bandwidth B. The matched filter compresses the pulse to width 1/B, breaking the energy–resolution trade-off.
• Matched Filter SNR: The matched filter is optimal – it maximizes SNR for any given waveform. The output SNR depends on signal energy and noise spectral density.

MODULE 04: Doppler & Velocity

A moving target compresses or stretches the reflected wavefront, shifting the echo frequency.

• PRF Ambiguity: PRF simultaneously sets both Ru and vu in opposite directions. No single PRF can simultaneously maximize both. Staggered PRF techniques are used to resolve these ambiguities by alternating PRFs.

MODULE 05: Antennas & Beamforming

• Beamwidth: It is always the ratio λ/D that matters. A larger aperture or higher frequency produces a narrower beam, improving angular resolution.
• Phased Array: A progressive phase shift steers the main beam. Element spacing must satisfy d ≤ λ/2 to prevent grating lobes (ambiguous returns at wrong angles).

MODULE 06: Detection Theory

Every range cell is tested against two hypotheses: H0 (noise only) vs H1 (target + noise). The threshold sets the trade-off between false alarm probability (Pfa) and detection probability (Pd). Real radar receivers use envelope detection, making the noise Rayleigh-distributed.