Abstract
Frequency-modulated continuous-wave (FMCW) radar systems send known frequency signals to moving targets and receive the signal back to detectors. FMCW systems can be used to measure exact heights of landing aircrafts. In addition, they are used in early warning radar systems and in proximity sensors. The advantage of using these radar signals is that the object target velocity and range can be quickly calculated using fast Fourier transforms (FFT). Taking the row-wise FFT of the signal matrix gives range information in form of range bins. Then taking column-wise FFT enables displaying the velocity for each range bin. The three-dimensional graph of the resulting matrix gives a signal power plot with respect to both the range bin numbers and their velocity.
TopIntroduction
This chapter details the steps taken to simulate the FMCW radar system using FFT. One should be able to follow these steps with the specified set of hardware and software to get the same configuration. This project was implemented under the supervision of NASA scientists and faculty advisors in dedicated NASA labs. Following lessons learned here and authors’ previous experiences in data visualization and signal processing research and training relevant labs were designed to enhance the Engineering programs at the Virginia State University (VSU) and Elizabeth City State University (ECSU) (Sheybani, 1992, 2002, 2006, 2007, 2008, 2010, 2011, 2012, 2013, 2017; Javidi, 2008, 2010, 2014, 2015, 2017; Ouyang, 2010; Garcia-Otero, 2011; Badombena-Wanta, 2010; Ettus, 2014, 2015; Luttamaguzi, 2017; Mathworks, 2014).
Some of the most recent advances in applications of microwave radiometry and specialty radar systems are due to the new developments in high-speed integrated circuits developed in digital signal processing as well as radio frequency (RF) and microwave technologies. As an example, the FMCW (frequency modulated continuous wave) maritime radar transmits a continuous radio frequency that varies gradually with time. When an object reflects the signal, the received waveform will build up a delayed replica of the transmitted waveform, with the time delay as a measure of the target range. If the target is moving, the radar system will register a Doppler shift within the received signal. The amount of Doppler shift is directly proportional to the radial speed of the target and can be determined after performing the range fast Fourier transform (range FFT). Performing a second FFT gives a two dimensional complex valued matrix, whose spectral peak corresponds to the Doppler shift of the moving target (Sediono, 2013).
Key Terms in this Chapter
DSP: It is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The signals processed in this manner are a sequence of numbers that represent samples of a continuous variable in a domain such as time, space, or frequency.
Continuous-Wave Radar: It is a type of radar system where a known stable frequency continuous wave radio energy is transmitted and then received from any reflecting objects. Continuous-wave (CW) radar uses Doppler, which renders the radar immune to interference from large stationary objects and slow-moving clutter.
Communications Satellite: It is an artificial satellite that relays and amplifies radio telecommunications signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. Communications satellites are used for television, telephone, radio, internet, and military applications. There are over 2,000 communications satellites in Earth’s orbit, used by both private and government organizations.