Abstract. Use of OFDM signals with central frequency sweep in radars
offers some advantages over conventional radiolocation systems based on chirp
signals or short impulses, including increased time-domain resolution and
dynamic range. The implementation of such a system is described in the article.
The results of measurements demonstrating obtained range resolution of 10 cm
Increasing of the signal bandwidth is one of the main tendencies in
radiolocation nowadays. Ultra-wideband location offers centimeter-range
distance resolution and less sensitivity to jamming. If implemented using
traditional approach with chirp or video or radio impulse ultra-wideband
signals, the radar system experiences a number of problems, including less
dynamic range due to the ADC (typical ENOB of 5-20 Gsps ADC is about 8-5 bits),
requirements to the precision analog circuitry with linear phase and constant
amplitude frequency response (otherwise ripples in time-domain signal appear),
incompatibility with standard phase antenna arrays (PAR), limitations in time
resolution due to RF switches for the short pulse approach.
A frequency-domain radar is free of the abovementioned problems. The
measured quantity is the channel complex frequency response, which is then
converted to analytic signal by FFT. This approach is quite similar to one used
in vector network analyzers (VNAs) with time-domain option. However, the method
is modified in this article for the use of OFDM signals instead of sinusoid
signals used in VNAs. This allows orders of speed increase compared to sinusoid
With OFDM signals ensemble, the dynamic range of the radar is kept high
due to the use of 14-16 bits ADCs, the requirements to the analog circuitry are
simple since the non-linearities are calibrated for each OFDM subcarrier, the
PAR frequency dependence is taken into account using a specific phase shift on
each subcarrier, and the RF switches limiting the time resolution are not used.
Keywords: radiolocation, OFDM.
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