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Description:
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Novel microwave transmitter and receiver circuits have been developed for
implementing UWB (Ultra -Wideband ) impulse radar imaging sensor operating in
frequency band 0 .2 to 4 GHz . with tunable operating frequency band . The fundamental
system design parameters such as the required transmitting pulse power and the pulse
duration were estimated for a presumed specific application , the pavement assessment .
The designed transmitter is the tunable monocycle pulse generator with tuning capability
for the output pulse duration from 450 - to 1200 - ps , and has relatively high transmitting
pulse power from 200 to 400 mW . Tuning of the pulse duration was implemented by
novel PIN diode switch configuration and decoupling circuit , and boosting of
transmitting pulse power was made possible by using a high power pulse driving circuit
and SRD coupling circuit .
The synchronous sampling receiver system was designed by using the integrated
sampling mixer and two reference clock oscillators placed in the transmitter and receiver
respectively for timing control . A novel integrated CSH (Coupled -Slotline Hybrid )sampling mixer has been developed along with the design of the strobe pulse generator
appropriate for the impulse radar system . The integrated sampling mixer has
unprecedented conversion loss of 2 .5 dB for the pulse signal , bandwidth 5 .5 GHz , and
dynamic range 50 dB . The introduced UWB LNA (Low Noise Amplifier ) design
operating up to 4 GHz should be useful for weak signal detection applications .
The design of the UWB microstrip quasi -horn antenna was optimized for short pulse
transmission with respect to the input return loss and the pulse stretching effect . For
signal detection in the signal processing stage , the background subtraction technique and
B -scan data format were used . A novel signal monitoring technique was introduced in
the signal processing to compensate the frequency modulation effect of the reference
clock . The test results for the complete system with respect to some sample multi -layer
structures shows good receiving pulse waveform with low distortion , enough pulse
penetration depth for 13Â pavement sample structure , and minimum 1 -in of range
resolution . |