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An efficient demodulation method designed for FMCW (Frequency-Modulated Continuous Wave) radar is presented. It is a kind of modified DFT (IDFT) algorithm; the spectrum segment of interest can be easily extracted from the original signal without calculating the whole DFT/FFT. It provides fast demodulation and extraction of desired frequency bands in our HFSWR (High-Frequency Surface Wave Radar) system. The proposed approach enhances the performances of radar system and reduces the computing complexity. The new structure could also be inversely used for signal modulation. And also arbitrary sampling rate conversion could be achieved with the combination of forward and backward structure.

FMCW is a radar system where a known stable frequency continuous wave radio energy is modulated by a triangular modulation signal so that it varies gradually and then mixes with the signal reflected from a target object with this transmit signal to produce a beat signal. With the advent of modern electronics, the use of Digital Signal Processing is used for most detection processing. The beat signals are passed through an Analog-to-Digital converter, and digital processing is performed on the result [

Frequency-Modulated Continuous Wave mechanism has been widely used in modern radar system. The waveform parameter of the mechanism is described as follows:

The time delay

Sketch of transmit and receive signal of FMCW.

As shown by Barrick, and others [

As discussed above, the frequency information can be extracted from Fourier Transform (FT) of

The new structure is described as follows: we expand (

If we separate the result of total FT of

Structure of proposed demodulation method.

In high frequency (3–30 MHz) ground (surface) wave radar, electromagnetic wave propagates along the ocean surface, in the lower frequency, the radar can reach a distance of 450 kilometers [

HF surface wave radar (IFM, University of Hamburg).

As discussed above, appropriate sampling rate and repetition time are determined. In our HF radar system,

Spectrum of processing results with proposed method.

Frequency points (1–8192)

Frequency points (1–512)

Frequency points (513–1024)

If there is also a target at 1000th frequency point in the spectrum, the probable distance (propagating path) is nearly 3000 km. This might happen in Sky-wave Radar system, in which a certain range of distance is concerned. For example, Using once ionospheric reflection, an OTH (Over The Horizon) radar covers the range interval between about 1000 and 3500 km, as shown in Figure

Demonstration of OTH Radar.

The proposed algorithm is more efficient than the whole FFT calculation, the computing complexity of FFT is

The conventional SRC method could also derive a certain frequency band from original signal, but the shape of digital filters (anti-imaging and anti-aliasing) is not as optimal as the proposed structure. When using conventional SRC method, with higher performance of roll-off characteristics, pass-band ripples and stop-band attenuation, higher stage number of filters is demanded [

The structure can be inversely used for modulation (interpolation), as shown in Figure

Structure of the proposed interpolation method.

And also we can input two or even more sequences, for example, we input two sequences

Demonstration of proposed modulating interpolation.

Frequency points (1–512)

Frequency points (1–512)

Frequency points (1–8192)

Combining with the decimation and interpolation methods, Arbitrary sampling rate conversion could be achieved, we define

Structure of decimation and interpolation.

This paper describes a demodulation method to extract the desired frequency band in FMCW Radar, which is an efficient method in some periodic transceivers like radar and sonar systems. It also provides a flexible method for the demodulation. Different frequency bands can be derived from input signal by setting corresponding