Data Sheet

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RFbeam Microwave GmbH | Schuppisstrasse 7 | CH-9016 St. Gallen | www.rfbeam.ch | K-LD 2 | data sheet 02 / 2020 – Revision C | Page 7 / 25
Sampling and FFT calculation
The K-LD2 works with an internal I/Q doppler signal
sampling and a computation of a 256 point wide com-
plex FFT. I/Q doppler signals are phase shifted by+ 90°
or - 90° depending on the direction ofa movement in
the front of the sensor.
The signal processing unit samples the I/Q data
with a configurable sampling rate (see parameter S04)
Figure 5: I/Q doppler signals of an approaching movement (left) and a receding movement (right)
and computes a complex FFT. The sampling rate is
animportant parameter ofthesensor because itdirec-
tly estimates the speed resolution, the maximal speed,
and the response time of the system. The response
time is doubled if the FFT average feature (described
below) is used.
Parameter
S04
Sample rate
[Hz]
Resolution
[Hz]
Max. frequency
[Hz]
Resolution
[km/h]
Max speed
[km/h]
Response time
[ms]
01 1280 5 640 0.11 14.3 200 / 400
02 2560 10 1280 0.22 28.6 100 / 200
03 3840 15 1920 0.34 43.0 67 / 134
04 5120 20 2560 0.45 57.3 50 / 100
05 6400 25 3200 0.56 71.6 40 / 80
06 7680 30 3840 0.67 85.9 33 / 66
07 8960 35 4480 0.78 100.2 29 / 58
08 10240 40 5120 0.89 114.5 25 / 50
09 11520 45 5760 1.01 128.9 22 / 44
0A 12800 50 6400 1.12 143.2 20 / 40
Table 2: Sampling rate vs. speed resolution vs. maximal speed vs. response time
The sampled I/Q doppler signals are transformed
with a complex FFT into the frequency domain with
256 bins. Those signals appear either in the real (right)
plane for an approaching move ment or in the imagi-
nary (left) plane for a receding movement. Thesignal in
the centre is the DC offset caused by the amplifier and
the analogue to digital conversion.
To reduce random noise, the sensor features a FFT
average option (see parameter S0A) which is enabled
in the factory settings. It is an average over two
FFT frames.