The Ultimate Guide to mmWave Presence Sensor Technology & mmWave Antenna Design (2025)

In the rapidly evolving world of smart technology, mmWave presence sensor systems are emerging as a powerful force, revolutionizing how we interact with our environments. Unlike traditional motion detectors, these sophisticated radar-based sensors offer unparalleled sensitivity, environmental robustness, and privacy preservation. Coupled with advancements in mmWave antenna technology, they are unlocking new possibilities in smart homes, automotive safety, industrial automation, healthcare, and beyond.

This comprehensive guide delves into the core technology, key specifications, diverse applications, and market landscape of mmWave presence sensor solutions, including crucial details about mmWave antenna design.

1- Understanding mmWave Presence Sensing Technology: Beyond Simple Motion

What is a mmWave Presence Sensor?

A mmWave presence sensor is a type of radar system operating in the millimeter-wave frequency spectrum (typically 30 GHz to 300 GHz). It utilizes short-wavelength electromagnetic waves to detect the presence, motion, distance, velocity, and even the angle of objects, with a particular focus on human subjects.

Crucially, mmWave presence sensor technology distinguishes itself from traditional Passive Infrared (PIR) sensors through its incredible sensitivity. While PIR sensors react mainly to larger body movements, mmWave can detect subtle motions like breathing, typing, or even the stillness of a sleeping person. This ability to detect static presence and micro-motions fundamentally changes the game, enabling continuous occupancy monitoring and nuanced automation where PIR sensors often fail.

How does it work? The Magic of FMCW Radar

Most commercial mmWave presence sensor units employ Frequency-Modulated Continuous Wave (FMCW) radar. Here’s a simplified breakdown:

1. Chirp Transmission: The sensor continuously emits a signal (“chirp”) whose frequency increases linearly over time via its transmit (TX) mmWave antenna.
2. Reflection: This signal bounces off objects (like a person) in its path.
3. Reception: A time-delayed version of the chirp is captured by the receive (RX) mmWave antenna(s).
4. Mixing: The transmitted and received signals are mixed, creating an Intermediate Frequency (IF) or “beat” signal.
5. Signal Processing: Sophisticated algorithms analyze the IF signal:
   • Range (Distance): The frequency of the IF signal is proportional to the object’s distance. A Fast Fourier Transform (FFT) reveals distance peaks.
   • Velocity: The phase change of the IF signal between consecutive chirps reveals the object’s radial velocity (Doppler effect). A second FFT across chirps resolves velocities.
   • Angle of Arrival (AoA): Using multiple RX mmWave antennas, the slight phase difference of the signal arriving at each antenna allows the system to calculate the direction (angle) of the object.

This FMCW approach allows a single, compact mmWave presence sensor to extract rich information (range, velocity, angle) simultaneously.

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Frequency Spectrum: The 24 vs. 60 vs. 77 GHz Landscape

mmWave presence sensor technology primarily operates in these bands:

• 24 GHz: Initially popular, but regulatory phase-outs (FCC/ETSI) of its Ultra-Wide Band (UWB) portion by 2022 have largely relegated it to a narrow 250 MHz band (ISM). This severely limits its range resolution (approx. 60 cm). Low-cost modules (like HiLink LD2410) still utilize this band for basic presence/motion.
• 60 GHz: The current sweet spot for industrial and consumer applications requiring high resolution. This unlicensed band offers significantly wider bandwidth (up to 7 GHz globally, practically often 4 GHz used by chipsets like TI’s). This wider bandwidth enables much finer range resolution (e.g., 3.75 cm with 4 GHz BW), crucial for object classification, dense point clouds, and vital signs. Recent regulatory updates (e.g., FCC 23-35) further support its use.
• 77 GHz (and 79 GHz): Predominantly used for automotive radar (ADAS) due to its very wide bandwidth (4 GHz+) enabling high resolution and long range needed for driving applications. Its use in industrial settings is often restricted but employed for specific high-accuracy tasks like level sensing.

Key Takeaway: The regulatory shift away from 24 GHz UWB has been a major catalyst, pushing innovation and market focus towards the 60 GHz band for non-automotive high-performance mmWave presence sensor applications. Higher frequencies generally allow smaller mmWave antennas and better resolution but may have slightly reduced penetration through some materials compared to 24 GHz.

2. Diving Deep into mmWave Antenna Technology

The mmWave antenna is not just an accessory; it’s a critical component dictating the sensor’s performance – its range, field of view, angular resolution, and overall efficiency.

Why mmWave Antenna Design is Crucial

At millimeter-wave frequencies, antenna design requires precision. Factors like feedline losses, manufacturing tolerances (substrate material, etching), and impedance matching become highly significant.

Common mmWave Antenna Architectures

• Microstrip Patch Antennas: Planar, low-profile antennas fabricated directly onto the Printed Circuit Board (PCB). They are ideal for integration.
• Patch Arrays: Multiple patches grouped to increase gain and directivity. They can be series-fed or parallel-fed (corporate-fed). More patches in an element increase gain but narrow the Field of View (FoV).
• Phased Arrays: Multiple antenna elements where the signal phase to each is controlled to electronically steer the beam – essential for tracking.
• Virtual Antenna Arrays (MIMO): Using multiple transmit (TX) and receive (RX) antennas creates a larger “virtual” array. The number and spacing of these elements determine the sensor’s angular resolution. Spacing at half-wavelength (λ/2) typically maximizes the unambiguous FoV.

The Rise of Integrated Antennas: AiP and AoP

A major trend is Antenna-in-Package (AiP) or Antenna-on-Package (AoP). Here, the mmWave antenna elements are integrated directly into the semiconductor package alongside the radar chip (e.g., TI’s IWR6843AOP, Infineon’s BGT series).

Benefits of AiP/AoP:

• Simplified Design: Users don’t need deep RF/antenna design expertise.
• Compactness: Enables much smaller sensor modules.
• Consistency: Pre-characterized and reliable antenna performance.
• Potentially Lower Cost: Reduces PCB complexity.

This integration significantly lowers the barrier to adopting mmWave presence sensor tech, especially for IoT and consumer markets, though it sacrifices the customization flexibility of external mmWave antenna designs.

3. Key Performance Characteristics of mmWave Presence Sensors

• Detection Range & Field of View (FoV):
  • Range: Varies hugely by application and sensor. Smart home sensors might offer 5-15m (e.g., HiLink LD2410: ~5-8m; Aqara FP2 likely higher), while automotive long-range radar reaches 250m+. Range depends on transmit power, mmWave antenna gain, target size (RCS), and processing.
  • FoV: The angular coverage (horizontal/azimuth and vertical/elevation). Room sensors often need wide FoV (e.g., 100°-120° horizontal), while long-range sensors might have narrower beams for higher gain. There’s a trade-off: higher mmWave antenna gain often means narrower FoV.
• Precision: Accuracy & Resolution:
  • Range Resolution: Ability to separate close objects. Crucially dependent on bandwidth. 4 GHz BW (60/77 GHz) yields ~3.75 cm resolution, while 250 MHz BW (24 GHz ISM) only allows ~60 cm.
  • Velocity Resolution: Ability to separate objects with slightly different speeds. Improves with longer observation time (frame time) and higher frequency.
  • Angular Resolution: Ability to separate objects at the same range/velocity but different angles. Improves with a larger virtual mmWave antenna array (more elements, wider spacing) and higher frequency.
  • Accuracy: How close the measured value is to the true value. Influenced by resolution, SNR, calibration. High-end systems claim millimeter-level range accuracy.
• Power Efficiency: Critical for battery-powered devices. Consumption varies widely:
  • Low-cost modules: ~0.15W – 0.8W (e.g., HiLink LD2420 ~50mA, EP1 ~160mA).
  • Ultra-low-power chips (with duty cycling): Average < 2mW – 5mW (e.g., TI IWRL6432, Infineon BGT60TR13C/LTR11AIP).
  • Power Saving Strategies: Advanced chip technology (e.g., TI 45nm RFCMOS, Infineon SiGe BiCMOS), sophisticated sleep/idle modes, heavy duty cycling (waking periodically), and optimized Power Management ICs (PMICs) are key.

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4. Applications Across Industries: Where mmWave Shines

The unique capabilities of the mmWave presence sensor enable diverse applications:

• Smart Homes & Buildings: Reliable occupancy detection (even static presence) for lighting/HVAC control, energy savings, people counting, gesture recognition for contactless control, and smart appliance integration.
• Automotive:
  • ADAS (77/79 GHz): Adaptive Cruise Control (ACC), Autonomous Emergency Braking (AEB), Blind Spot Detection (BSD), Cross-Traffic Alerts.
  • In-Cabin Monitoring (60 GHz): Child Presence Detection (CPD – crucial for Euro NCAP), occupant detection/classification, intruder alerts, gesture control, driver monitoring.
• Industrial Automation & Robotics: Obstacle detection (even through dust/smoke), human safety zones around robots (SIL-rated sensors available), AGV/AMR navigation, level sensing in tanks, and machine vibration monitoring.
• Security & Surveillance: Privacy-preserving intrusion detection (can see through drywall), perimeter monitoring, people flow analysis, augmenting cameras (triggering recordings reliably in poor conditions), and threat detection (body scanners).
• Healthcare & Wellness: Contactless vital signs monitoring (breathing/heart rate via chest motion detection), fall detection for elderly care, sleep monitoring, and activity tracking.
• Emerging Uses: Complex Human Activity Recognition (HAR), micro-Doppler analysis for gait/gestures, through-wall sensing, Integrated Sensing and Communication (ISAC/JCS) with 5G/6G.

Sensor Fusion: Combining mmWave presence sensor data with cameras, LiDAR, or PIR often yields the most robust solutions, leveraging the strengths of each modality.

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5. mmWave vs. the Alternatives: Choosing the Right Sensor