Can Radar Detect Tennis Balls?
By: Dr Damien Clarke
Lead Consultant, Plextek
7th December 2022
Large and expensive military radar systems, such as the Artisan Radar, are capable of detecting objects as small as tennis balls at great distances even while moving at high speeds:
Capable of detecting objects as small as a tennis ball and travelling at three times the speed of sound more than 25km away, Artisan can monitor more than 900 objects simultaneously from 200 to 200,000 metres and cut through radio interference equal to 10,000 mobile phone signals.
In contrast, can small and cheap consumer radar systems also be used to perform such feats? Not for long range air defence purposes of course, but perhaps for short range sports related ball detection applications.
In this blog post we explore the use of a low Size, Weight, Power and Cost (SWaP-C) radar solution for the detection of small moving objects such as balls. In particular, the Texas Instruments IWR6843 single-chip mmWave radar operating in the 60 – 64 GHz frequency band. The IWR6843ISK evaluation board uses three transmitters and four receivers to provide a 120° azimuth field of view and 30° elevation field of view, though other configurations are possible.
The first step in assessing the performance of this radar for ball detection applications is to confirm that the radar can indeed detect such small moving objects. This was achieved by hitting and/or throwing balls at the radar, though from a range of a few metres rather than 25 km. Different balls were investigated (e.g. golf balls) but the example below will use a table tennis ball as it is small, lightweight and hollow, so might be considered a challenging target.
Raw data from the radar was then processed to calculate both range and velocity (via the Doppler effect) of the scene within the radar’s field of view. This can be presented as a heatmap image where the x-axis represents the distance from the radar, the y-axis represents the radial velocity as observed from the point of view of the radar and the pixel intensity is the strength of the radar return of the target. Note that negative velocity represents range decreasing over time as an object moves towards the radar. Data from sequential measurements can then be used to produce a video.
The person can be seen as the large “blob” on the right-hand side at constant range. This blob is approximately symmetric about zero velocity as they are not walking towards the radar. Since parts of their body are moving towards or away from the radar (e.g. their arms) some radar reflections measure small positive and negative velocities. This can potentially be used to analyse the motion of people playing sport (e.g. a golf swing) as a training aid perhaps.
In addition, the table tennis ball can be seen in the radar image moving to the left (towards the radar) at a mostly constant radial velocity before slowing down and stopping or moving outside the field of view.
While this video does resemble the trajectory of the ball, it only shows range and velocity. It is possible for this radar to measure the 3D position of the ball over time for tracking purposes but that has not yet been investigated in depth.
This work demonstrates that the radar evaluation board can be used to detect even small objects like lightweight table tennis balls at useful ranges. Developing a viable product using this low-cost radar is now a reality and we are supporting multiple partners to bring low SWAP-C technologies to market.
For better performance at longer ranges a higher performance device with a custom antenna design can be produced to meet customer requirements. If you are interested in this sort of detection application, then please do contact us so that we can discuss your specific performance requirements.