Design of a Low-Cost UWB Time-Domain Radar System for Subcentimeter Image Resolution

The design and development of a hybrid Gaussian pulse radar transceiver, including transmitter and receiver, is presented. The transmitter is realized using a transistor-based square pulse generator, a tunable step recovery diode (SRD) Gaussian pulse-shaping network, and a differentiator. The SRD circuit design is modified using a high-pass filter to have a low ringing and narrow pulsewidth. The output pulse with a broadband amplifier has a power of 500 mW, at a pulse repetition frequency (PRF) of 10 MHz, and tunable pulsewidth ranges from 56 to 300 ps. A 90° coupler is configured to convert the Gaussian pulse into a monopulse. Then, a transmitter antenna is used to radiate the pulse, and a separate receiving antenna is used to receive the reflected pulse. The receiver is comprised of a local Gaussian pulse generator, a radio frequency mixer (RF-mixer) accompanied by a low-pass filter (LPF), a low-frequency amplifier (LFA), and an analog-to-digital converter (ADC). The RF-mixer is used for expanding the receiving pulse from the receiving antenna by a factor of 100000. The LPF and LFA are used to detect the envelope of the output of the RF-mixer and amplify it. The ADC is interposed between the LFA and a processor to digitize the expanded pulse for data processing. The validity and reliability of the digitized expanded pulse compared to those received using a sampling oscilloscope are 93% in agreement, which is remarkable. A version of the system is also developed for a single-antenna operation by utilizing an ultrawideband (UWB) coupler as a semicirculator. Both the systems are compared, and the benefits of each are illustrated. The flexibility and performance of the designs are analyzed. The proposed system demonstrates subcentimeter imaging capabilities.

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