Technical Documentation

Radar vs PIR: selecting the right solution
BackgroundAs radar capabilities advance, the level of information obtainable increases.
Per the image below, radar now provides a more broader range of capabilities which means where previously passive infrared (PIR)
may have been the only viable solution, you now need to understand if the advantages radar brings over PIR could benefit your specificapplication further.
The objective of this material is to take a closer look at both technologies to ensure you chose the technology that will bring most value
to your specific requirements.

Image: range of information obtainable from radar

Speed/velocity››Derived from Doppler shift in frequency

Range/distance to target››Derived from measurement of electromagnetic wave

Angle/direction to target››Derived from phase difference at the antennas

Position of object››Derived from FMCW

www.infineon.com/24GHz

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Comparison of some example use cases
Before we move further into the details of two solutions, the chart below lists some of the advantages that radar brings against some of
the challenges of PIR.

Use case

Indoor lighting

Automaticopening system

Advantages of radar

Challenges of PIR››Increased detection range››Energy efficient by turning lights off››Limited range compared to radar››Limited coverage means more sensors››Can be discretely designed behind casing››Unsightly design means PIR needs to be visible

automaticallyrequired››Detects direction of travel so only opens when ››Only detects movement, irrespective of person
Automatic door

necessary››Keeps the building energy efficient throughreduced door opening

Smart streetlighting››Increased detection range››Precision object identification››24GHz works independent of hot weather

Intruder alarm››Increased detection range››Reduce false alarms››Detection sensitivity is adjustablecoming into building››Cannot distinguish between people andanimals››Can be unreliable and impacted in harshweather conditions››Lack of object identification means falsetriggers››No directional measurement››Unsightly design means PIR needs to be visible››Can be unreliable and impacted in harshweather conditions››Limited range/coverage means more sensors
requiredPIR

Passive InfraredRadarTechnical Documentation

Kim Lee – Applications Engineering Manager
RF and Sensors Products, PMM Division, Infineon
When designing sensor systems for detecting proximity or motion information, designers must consider flexibility and cost of
the type of technology they utilize.

Is radar the correct technology for my application? The answer depends on the system requirements with respect to functionality andcosts, and to fully answer this question, let’s quickly review how each of these sensors behaves. Traditional motion sensors have been
designed using PIR. This has been an inexpensive and simple detection of objects using the object’s heat signature when the object
comes within the range of the sensor. The PIR sensor detects changes in the amount of infrared radiation it sees and converts thischange into a voltage. This voltage is compared to a threshold limit to trigger a signal that enables a light or activates an alarm.
Radar uses the Doppler principle to determine the object’s motion, speed and even direction, given the complexity of the radar’s implementation. For the simple case of object detection, the radar transmits a 24 GHz waveform and reflects off an object that is in thesensor’s field of view. This reflected waveform is received by the radar transceiver. The received signal will have a frequency difference
referred to as the Doppler frequency. The Doppler frequency is then used to detect movement along with velocity. Depending if the24GHz transceiver is fed with a Continuous Wave (CW) Doppler or Frequency Modulated CW (FMCW), other parameters of the object canbe realized such as distance to the sensor and given an additional antenna, the exact position or coordinates of the object in the field ofview.

“Factors such as range, object sensitivity and environmental factors can influence
the sensor performance.”
Getting back to the question of whether radar is best suited fora particular application; the designer must determine criticalfeatures versus cost for this design. Factors such as range, object
sensitivity and environmental factors can influence the sensor
performance.

PIR is inexpensive, although radar technologies are decreasing in cost and are more compact and simple to design. Radar can be as
simple as a PIR sensor detecting motion or as complex as an imaging radar where complex algorithms and multiple antennas can rendera map of geographic terrain.

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Technology comparisonFeatures

24GHz sensor

InfraredUltrasonicLaser

Application flexibility

ll

l

l

Resistance to moisture, dirt and temperature

ll

l

l

Speed detectionllllAccuracy sensitivity

ll

l

l

Resolution

ll

l

l

Direction capability

ll

l

l

Distance measurement

ll

l

l

Penetration of materials

ll

l

l

Size of solution

ll

l

l

Costl

l

l

l

l Bestl Goodl WeakSensor features will dictate technology choice. Is distance important? If so, consider that PIR sensors are roughly 10 meters maximum,and found in places like in-home motion detectors or driveway lights. Radar can range from within 10 meters to over 50 meters depending on the radar signature of the object. This opens the door for radar as a sensing solution for various applications where PIR traditional
has limitations. Sensing for outdoor lighting for streets, parking lots or campuses can be extended to cover a larger area depending on
the antenna scheme.
As inexpensive as PIR is, there are limitations in performance. For example, the PIR sensor monitors change in the infrared radiation ofan object. This means that if the object is stationary, PIR sensors cannot detect the motionless object. Environmental factors also should
be considered. If the sensor is intended for an outdoor application; snow, dirt and other outdoor conditions can degrade the performance of the PIR sensor. Heat is a well-known limitation. For example, if the ambient temperature is around 98–99 degrees (F), it will
not detect human movement since the body registers 98.6° typically. If an aesthetic design is desired, then consider that PIR requires aplastic radome or cover that is semi-transparent in order for the infrared energy to pass. This cover should be clean from dust or dirt inorder to maximize performance. This is more difficult for an outdoor application. There are also issues with false detection when non­human objects come into the sensor’s view.

“Environmental factors also should be considered...snow, dirt and other outdoor
conditions can degrade the performance of the PIR sensor.”
When starting a new sensor design, one may consider an intelligent sensor that has positive tradeoffs that justify some minimal cost
increase. The 24GHz radar sensor can be a simple Doppler-based motion detector, and a simple algorithm can determine if the object iscoming closer or moving away from the sensor. Even with a Doppler implementation, speed calculation comes for free as the Doppler
shift (frequency) can be used to calculate speed. The Doppler shift itself is made available by the radar transceiver to the processing unit
where the processor uses this frequency to determine movement. For a slightly more complex implementation, an FMCW scheme would
monitor stationary and moving objects as well as track these objects. This allows a radar to also measure range and can update the object’s movement and distance real-time to the user. Design freedom is also an important factor and can include the ability to adjust thefield pattern of the sensor as well as the appearance of the sensor to the end users. Radar sensors can be designed aesthetically behinda wall or a fixture so that there is no visible sensor seen. This could be useful for security sensors that can monitor motion behind a wall.
Radar sensors can be combined with optical cameras where radar serves as a longer distance activator for the camera.

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To experiment with a radar solution and determine if it addresses the needs of their specific application, engineers can obtain different
reference designs and development platforms such as those available from Infineon Technologies. The Sense2Go is an example of asimple and compact development platform that can be used for an intelligent motion sensor.
The Sense2Go platform allows the user to implement and test several sensing applications at the 24 GHz ISM band such as Doppler
based movement detection, Doppler based direction of movement detection, Doppler based speed estimation and Frequency-Modulated Continuous Wave (FMCW) based distance measurement of stationary targets.

For additional support and information

Collaterals and brochures››Product briefs››Selection guides››Application brochures››Presentations››Press releases, ads
www.infineon.com/24GHz-Radar

Technical material››Application notes››Radar FAQ››Technical articles››Simulation models››Datasheets, MCDS files

Evaluation boards››Evaluation boards››Demoboards››Reference designs

www.infineon.com/evaluationboards

Videos››Technical videos››Product information videos

www.infineon.com/mediacenter

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