mmW Radar: A Technical Guide to Millimeter Wave Radar Technology

mmW radar (millimeter wave radar) is a radio detection and ranging technology that uses electromagnetic waves with wavelengths of 1–10 mm (corresponding to frequencies of 30–300 GHz) to detect objects, measure their distance and velocity, and in some cases identify their nature by analyzing the reflected signal. The most common commercial mmW radar bands are 24 GHz (24.0–24.25 GHz), 60 GHz (57–64 GHz), and 77 GHz (76–81 GHz), with each band offering different trade-offs between range, resolution, antenna size, regulatory environment, and chipset cost. The 60 GHz band has become the dominant frequency for indoor presence detection because it provides 7 GHz of unlicensed bandwidth, which enables 2.1 cm range resolution and micro-Doppler detection of human breathing at 0.2–0.5 Hz from ranges of 6–8 meters. The 77 GHz band is primarily used for automotive radar and long-range industrial applications, while the 24 GHz band is used for cost-sensitive motion-only applications.

This guide provides a comprehensive technical overview of mmW radar, covering the physics, the frequency bands, the FMCW processing, the antenna design, and the major applications.

mmW Radar: The Physics

The physics of mmW radar is governed by the same electromagnetic principles as lower-frequency radio systems, but the short wavelength and the wide bandwidths available in the mmW frequency range give the technology capabilities that are not achievable at lower frequencies.

mmW Radar: Wavelength and Frequency Bands

The wavelength of an electromagnetic wave is inversely proportional to its frequency. At 24 GHz, the wavelength is approximately 12.5 mm; at 60 GHz, it is approximately 5.0 mm; at 77 GHz, it is approximately 3.9 mm. The shorter wavelength at higher frequencies allows smaller antennas for a given gain.

The three major commercial mmW radar bands are:

• 24 GHz band (24.0–24.25 GHz): the oldest and most mature mmW band, with a narrowband ISM allocation of 250 MHz. Suitable for motion detection and basic FMCW range resolution.
• 60 GHz band (57–64 GHz): the dominant band for indoor presence detection, with 7 GHz of unlicensed bandwidth. Provides 2.1 cm range resolution and micro-Doppler detection of human breathing.
• 77 GHz band (76–81 GHz): the primary automotive radar band, with 5 GHz of bandwidth. Suitable for long-range radar (20–30 m) and fine angular resolution.

mmW Radar: Bandwidth and Range Resolution

The range resolution of a radar system is determined by the bandwidth: c / (2 × B), where c is the speed of light and B is the bandwidth. At 24 GHz with 250 MHz of bandwidth, the range resolution is approximately 0.6 m. At 60 GHz with 7 GHz of bandwidth, the range resolution is approximately 2.1 cm. At 77 GHz with 5 GHz of bandwidth, the range resolution is approximately 3 cm.

The wide bandwidth at 60 GHz and 77 GHz is what enables these systems to detect the micro-motion of human breathing. A person breathing produces a chest wall displacement of 5–20 mm at a frequency of 0.2–0.5 Hz, and detecting this motion requires a range resolution on the order of 5 mm or better.

mmW Radar: Atmospheric Attenuation

The atmospheric attenuation of mmW radar signals varies significantly by frequency. At 24 GHz and 77 GHz, the atmospheric attenuation is relatively low (typically 0.5–1 dB/km). At 60 GHz, the atmospheric attenuation is much higher (~15 dB/km) due to the oxygen absorption resonance at this frequency.

For indoor sensing applications where the maximum range is typically 8–12 m, the atmospheric attenuation at any of these bands is negligible. However, the high attenuation at 60 GHz does have a beneficial side effect: it prevents 60 GHz signals from propagating between rooms, which is a privacy advantage for hotel and residential deployments.

mmW Radar: FMCW Processing

The most common waveform used in commercial mmW radar is the frequency-modulated continuous wave (FMCW) chirp.

mmW Radar: The FMCW Chirp

In an FMCW radar, the transmitter emits a signal whose frequency sweeps linearly across a defined bandwidth over a short period called the chirp duration (typically 50–200 microseconds). The transmitted signal is mixed with a copy of itself (the local oscillator signal), and the reflected signal from a target is also mixed with the local oscillator signal. The result is a beat signal whose frequency is proportional to the range of the target.

By performing a Fast Fourier Transform (FFT) on the beat signal, the radar processor can determine the range of every target in the detection zone with a resolution of c / (2 × B). For a 60 GHz system with 7 GHz of bandwidth, the range resolution is approximately 2.1 cm.

mmW Radar: Doppler Processing

In addition to range, an FMCW radar can determine the velocity of a target by analyzing the phase of the beat signal across multiple chirps. A stationary target produces a beat signal with a constant phase across chirps; a moving target produces a beat signal whose phase shifts from chirp to chirp, with the phase shift proportional to the target's velocity.

By performing a second FFT across the chirps of each range bin (a "Doppler FFT"), the radar processor can determine the velocity of every target in the detection zone. The velocity resolution is determined by the wavelength and the frame duration. For a 60 GHz system with a 50 ms frame duration, the velocity resolution is approximately 0.05 m/s.

mmW Radar: Micro-Doppler Analysis

The micro-Doppler effect is the phenomenon where the micro-motion of parts of a target produces distinctive Doppler signatures. In human presence detection, the most important micro-Doppler signature is the breathing signature: the periodic chest wall motion at 0.2–0.5 Hz produces a Doppler modulation that is distinct from the background noise and from the Doppler signatures of inanimate objects.

A well-designed mmW radar presence sensor uses signal processing techniques to extract the breathing signature from the radar return. The processing typically involves:

1. Range FFT: determine the range of every target in the detection zone.
2. Doppler FFT: determine the velocity of every target at every range.
3. Range-Doppler map: produce a 2D map of range vs. velocity.
4. Micro-motion extraction: for each range bin that contains a target, analyze the time-varying Doppler signature to identify periodic components (breathing, heartbeat) that indicate a human presence.
5. Classification: use a machine learning model (or a rule-based classifier) to classify the target as "human present," "no human present," or "ambiguous."

mmW Radar: Antenna Design

The antenna design determines the angular resolution, the field of view, and the form factor of the mmW radar system.

mmW Radar: MIMO Antenna Arrays

Modern mmW radar systems use multiple-input multiple-output (MIMO) antenna arrays to determine the angular position of targets in the detection zone. A 2×2 MIMO array (two transmit, two receive) provides basic angular resolution in one dimension. A 3×3 MIMO array provides angular resolution in two dimensions with finer resolution. A 4×4 MIMO array provides the finest angular resolution.

For a ceiling-mounted presence sensor, a typical antenna array is a 2×2 or 3×3 MIMO configuration that provides a field of view of approximately ±60° azimuth and ±40° elevation.

mmW Radar: Field of View

The field of view of an mmW radar system is the angular range over which the antenna can effectively transmit and receive signals. A wide field of view is desirable for a ceiling-mounted presence sensor that needs to cover an entire room. A narrow field of view is desirable for a long-range sensor that needs to focus on a specific zone.

mmW Radar: Performance Metrics

The performance of an mmW radar presence sensor is characterized by several key metrics.

mmW Radar: Stationary-Occupant Detection

The stationary-occupant true positive rate (TPR) is the percentage of time that a stationary human occupant is correctly reported as present. For a 60 GHz mmW radar, the TPR is above 99% in controlled testing and above 95% in real-world deployment.

mmW Radar: False Positive Rate

The false positive rate is the percentage of time the sensor reports presence when the room is actually empty. For a well-designed mmW radar, the FPR is below 1% over a 24-hour period.

mmW Radar: Detection Range

The detection range of a 60 GHz mmW radar is 6–8 m for stationary occupants and 8–12 m for moving occupants when ceiling-mounted at 2.5–3.0 m.

mmW Radar: Detection Latency

The detection latency is the time between an occupant entering the detection zone and the sensor reporting the change. For an mmW radar, the latency is typically 0.5–3 seconds.

mmW Radar: Applications

The mmW radar has a wide range of applications across multiple industries.

mmW Radar: Presence Detection

The most common application of mmW radar in 2026 is presence detection for hotels, offices, healthcare facilities, and residential smart homes. A 60 GHz mmW radar can detect both moving and stationary occupants, enabling true presence detection rather than just motion detection.

mmW Radar: Automotive

The 77 GHz mmW radar is the dominant technology for automotive radar, used for adaptive cruise control, collision avoidance, blind spot detection, and other advanced driver assistance systems (ADAS).

mmW Radar: Industrial Sensing

The mmW radar is used in industrial applications for level sensing (liquids and powders in tanks and silos), conveyor monitoring, and robotic collision avoidance.

mmW Radar: Healthcare

The mmW radar is used in healthcare for fall detection, patient monitoring, and vital signs measurement (heart rate, respiration rate).

mmW Radar: Final Recommendation

The mmW radar is the dominant technology for presence detection in 2026, and the 60 GHz band is the default choice for most indoor applications. The technology provides reliable stationary-occupant detection, an excellent privacy profile, and a compact form factor, making it suitable for hotel rooms, offices, healthcare facilities, and residential smart homes.

For a procurement team or a consumer selecting an mmW radar product, the right approach is to start with a clear definition of the application requirements, then evaluate the available products against those requirements, then select a vendor with a proven track record in the target vertical. The recommended products for most applications are the ceiling-presence-sensor-zigbee, ceiling-presence-sensor-wifi, and ceiling-presence-sensor-matter from vendors with strong product portfolios and proven deployment track records.

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