An N-bit digitally variable ultra wideband pulse generator for GPR and UWB applications

This paper presents a low-cost Ultra Wideband (UWB) pulse generator that can vary the pulse duration digitally by using a Step Recovery Diode (SRD), microstrip transmission lines and PIN diodes. First, a sharp edge is generated by using a SRD circuitry. Then a pulse is formed from the sharp edge through the use of transmission lines and the PIN diodes. Based on the number of transmission lines (N), the duration of the pulse can be varied in steps. The UWB pulse generator circuits are implemented on an FR-4 substrate using microstrip line technology and UWB pulses with durations of 550 to 2400 psec are measured. N2 Ke

Comparison of Time Domain Reflectometry Performance Factors for Several Dielectric Geometries: Theory and Experiments

We propose three nontraditional dielectric geometries and present an experimental and theoretical analysis and comparison of time domain reflectometry (TDR) performances for them. The traditional geometry (the probes inserted in material of essentially infinite extent) is compared to three nontraditional geometries where the probes are affixed outside of a core sample, inside of a bore, or flat on the surface of a semi‐infinite solid. Our derivation relates the velocity of electromagnetic wave propagation to the complex permittivities and permeabilities of the media and the geometry for the three nontraditional configurations. Experimental results for air, styrofoam, dry sand, wet sand of varying water content, nylon, dry wood, and ferromagnetic steel are obtained for the three proposed configurations and are in fair agreement with the literature within the experimental uncertainties. Through experiments and theoretical analysis, the TDR performance is found to be the same within the experimental uncertainties for the three nontraditional geometries. The proposed geometries yield slightly lower sensitivities compared to the traditional geometry. Advantages and disadvantages of the geometries compared to the traditional geometry are also discussed

An All-Harmonic Coupling-Band Hybrid

A description is given of a microstrip, branch-arm hybrid which exhibits 3-dB coupling at all harmonics of a fundamental frequency as compared to the odd-harmonic coupling exhibited by conventional branch-arm hybrid structures. Copyrigh

A Nanosecond Impulse X-Band Radar

A description is given of a high spatial resolution (< 10 cm) X-band nanosecond impulse radar incorporating a transmitter noise suppression technique. The performance of the radar as a thickness sensor for thin layers of floating fresh-water ice is described. The basic system is suitable for other microwave carrier frequency time-domain reflectometry applications requiring high spatial resolution. Copyrigh

Recent Advances in Broad-Band VHF and UHF Transmission Line Methods for Moisture Content and Dielectric Constant Measurement

Recent advances in VHF and UHF transmission line methods for determining either the complex permittivity or moisture content of bulky or film-like materials, or the thickness of film-like materials are discussed. These methods include TDR, CW phase, and |S21| transmission methods and employ a time-domain reflectometer (TDR), a vector voltmeter, and a network analyzer, respectively. Each technique involves monitoring the change of the transmission line parameters of a balanced open line, or of an unbalanced coaxial transmission line, when loaded with the material under test. Particular attention is given to the frequency range 10 to 1000 MHz and to broad-band methods. Experimental results are presented for several common materials, viz, concrete, asphalt, Plexiglas, moist paper, and moist soil. Copyrigh

An Open Transmission Line UHF CW Phase Technique for Thickness/Dielectric Constant Measurement

A description is given of a system which employs open-balanced transmission line structures and UHF CW phase measurement techniques to determine either the thickness or dielectric constant or moisture content of film or slab-like materials in the thickness range of 1 to 400 mil and the relative dielectric constant range of approximately 2 to 20. Both experimental and analytical results are presented. Copyrigh

Equivalent Circuits of Microstrip Impedance Discontinuities and Launchers

Experimental results obtained indicate that an excess phase shift is the most pronounced high-frequency parasitic effect resulting from a microstrip quarter-wave transformer impedance discontinuity. An empirically derived design-oriented model describing the dominant parasitic reactances associated with a microstrip impedance discontinuity at X-band frequencies is described. A description is also given of the dominant parasitic reactances associated with a number of commercially available coaxial-to-microstrip launchers. Copyrigh