Design of high-frequency pulse subsurface penetrating radar for pavement assessment

High-frequency subsurface penetrating pulse radar (SPR) has been developed for pavement assessment applications, such as measuring the thickness and dielectric constant of a layer. SPR transmits a monocycle pulse having 333-ps width and receives a signal reflected from the pavement through wide-band antennas. The developed SPR is composed of a receiver, transmitter, antennas, and data acquisition device. Each subsystem has been designed and fabricated using microwave integrated circuit (MIC) technology.; The integrated sampling receiver has its own pulse generator, local oscillator (LO), and IF amplifier. The internal pulse generator uses a step recovery diode (SRD) together with a unique ultra-wideband hybrid junction to generate sub-nanosecond balanced pulses for gating the sampling bridge diodes. The receiver has been designed for detecting the DC to 6-GHz signal. The receiver shows a 15-dB return loss at the RF port over this RF bandwidth, a 50-dB dynamic range, and a 1-dB compression point at 5dBm input power.; The transmitter operates in the sub-nanosecond regime and employs a Schottky diode, SRD, MESFET, and simple charging and discharging circuitry. It is completely fabricated using a microstrip line. The monocycle pulse generator produces a monocycle pulse having a 333-ps pulse width and more than 2 Volts from an input square wave of 10-MHz repetition rate. The generated monocycle pulses have very symmetrical positive and negative portions and a low ringing level.; A wide-band antenna has been designed based on a cosine-tapered microstrip line and forms a quasi-horn structure. The measured results show a return loss of better than 10-dB from 0.2 to more than 20-GHz, gain from 7.5-dB at 2.6-GHz to 17.6-dB at 18-GHz. Measured transient responses of the antenna confirm its feasibility for use in ultra wide band (UWB) time-domain systems.; Finally, these SPR sub-systems are integrated in each transmit and receive microwave substrate with antennas to achieve a compact structure and seamless electrical connections.; Various samples have been tested for verifying the prototype radar performance. The received data was stored and processed by Labview® and Matlab®. The analysis results show usefulness of the prototype SPR to estimate material parameters and thickness of layers. This developed high frequency SPR prototype can be used for pavement assessment applications with low cost and higher resolution.