An optimal realization of heterodyne receiver for SFCW UWB radar system
Damodar V Kadaba1, SA Subhan1, VK Bansal1, Subhadra Singh1, Gowtham G2
1
Central Research Lab, BEL, Bangalore – 560013, 2D&E (Military Radar), BEL, Bangalore-560013
Abstract
Realization of a heterodyne receiver for step frequency continuous wave (SFCW) through wall radar
(TWR) is discussed in this paper. As the Doppler bandwidth of signals reflected from slow moving objects such as human beings illuminated by SFCW TWR sensor is negligible compared to transmit bandwidth, the received signal can be heterodyned with a signal offset from transmitted one by an intermediate frequency, and the echo signal at IF is passed through a band pass filter with very narrow pass band centered…show more content… The synthetic range profile is a time domain approximation of the frequency response of a combination of the medium, through which the electromagnetic radiation propagates, and any targets or dielectric interfaces present in the beam width of the radar.
It is constructed by sequentially transmitting a series of n frequencies, fi = f0 + i∆f, where 0 ≤ i ≤ n −
1 and for each measuring the amplitude and phase shift of the received signal with respect to the transmitted signal
Fig 2. SFCW waveform in time vs. frequency
Fig (2) shows the time-frequency characteristic of the transmitted waveform for a stepped frequency radar where T is known as the pulse repetition time.
The phase shift in the received signal is a proportional to the transmitted frequency and the range to the target. This is shown in following equation for a point target stationary relative to the radar. 2
=2
Differentiating,
=
4 +
4
The above equation illustrates the fact that received signal’s rate of phase change is a function of both derivatives of range, and frequency. Range rate phenomenon is used in estimation of target