User Guide (Version 2.2) of the
SiRad Simple® Evaluation Kit
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4.2.14
There are too many targets. The CFAR operator does not work.
You may experience that there are no targets detected by the CFAR operator although there are
plenty of targets visible in the FFT output. If there are too many targets adjacent to each other in
the field of view, the CFAR operator may treat those targets like noise floor and calculates an
envelope around those targets. Increasing the number of guard cells may help in such a scenario.
4.2.15
How is the distance information calculated?
All calculations are done on the microcontroller on the SiRad Simple® sensor, so that the reported
target distance is already in millimeters. The distance formula used is
d = n
Bin
* acc,
where d is the distance to the target, n
Bin
is the FFT bin of the target, and acc is the accuracy (see
Section 3.3.2 for the formula).
4.2.16
The update rate of the sensor is very low. How can I improve it?
The update rate is dependent on the chosen parameters in the ‘BB Processing’ tab, in particular, on
the ramp time, number of samples, number of ramps, and FFT size. Further, the amount of data
that has to be transferred is important. You can select the transmitted frames in the ‘System
Configuration’ tab. Using only the target list output, the sensor can reach about 50 Hz update rate.
4.3 Sensor Behavior, Range & Lens
4.3.1 How is the resolution defined?
We define the resolution as the ability to separate two targets in range. The resolution is only
dependent on the selected bandwidth. With 1 GHz bandwidth the resolution is 15 cm, 6 GHz
bandwidth equals 2.5 cm resolution. In practice, target recognition works from twice the resolution.
4.3.2 How is the accuracy defined?
We define accuracy as the maximum error of the measured distance to a single target. It is
dependent on the number of samples, the bandwidth, the downsampling and the FFT size. If the
FFT size is twice the number of samples, the accuracy is two times less than the resolution. We
can reach about 1 mm accuracy, also see Section 3.3.2 for the formula.
4.3.3 Is there a minimum range / blind spot when using the SiRad Simple®?
The minimum range depends on the selected bandwidth. 1 GHz bandwidth works from about
30cm, 6 GHz bandwidth works from about 7cm. The blind spot is approximately as wide as once or
twice the resolution.
4.3.4 Can something be detected within the minimum range / blind spot?
Going below the bandwidth-dictated minimum range leads to an increased DC-offset in the FFT
output. It could be used to detect ‘something is nearby’ but this is very application-specific.
4.3.5 What is the maximum range of the SiRad Simple®?
The maximum range is dependent on the target. The SiRad Simple® Evaluation Kit reaches about
40 m with strong targets like buildings.
4.3.6 Can the range of the sensor be increased?
You can increase the range by assembling the lens delivered with the SiRad Simple® Evaluation
Kit, however, the opening angle will decrease. Larger detection distances are possible using bigger
lenses or well-designed patch array antennas.