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A minimalistic nonlinear dynamic model, which still reflects the main aspects of the devices response to baseband pulse signals, is considered. The model is built as “black-box” and does not require knowing the structure and physical properties of the device. Since the model should reflect the exponential-type transient response, it is based on a nonlinear recursive filter. In the recursive loops the integrators are placed, because the main effect in the response of the simulated devices is the smoothing of the signal edge. The model reflects the nonlinear amplitude characteristic of the device (at the flat top of pulse), the dependence of the transient process duration on the input signal, and the nonlinear properties of the overshoot at the flat top of the pulse. We consider the realization of this model in CAD system and the methods for extracting the model parameters. The simulation error with the proposed model is 2-10% depending on the similarity of the test signal and signal at which the parameters were extracted.

A model of the p–n junction that adequately describes the non-quasi-static effects of accumulation and relaxation of nonequilibrium charge carriers is considered. In this case, the diffusion charge equation is written in a closed form resolved with respect to the diffusion charge. This allowed computer programming of this model to be performed without user-defined recursion resolving the differential equation with respect to the diffusion charge. As a result, the non-quasi-static model of the p–n junction has been realized as an equivalent circuit containing only conventional quasi-static elements of computer-aided design systems.

It is shown that in baseband pulse nonlinear radars a preselector based on the bridge circuits can be used (instead of filter’s preselectors in harmonic radars). An original design of the bridge preselector is considered, in which the balun transformer is combined with the magnetic antenna. Based on the simulation results (taking into account a deviation of elements parameters), was obtain that the preselector suppresses the test signal by 46 dB.

The effectiveness of short electric and magnetic dipoles is compared when they are used as an antenna for a nonlinear baseband pulse near-field radar. It is shown that a magnetic dipole provides a four times larger nonlinear response from a test semiconductor object than an electric dipole at seven times smaller dimensions of magnetic dipole.

It is noted that there are significant distortions in the measured current-voltage characteristics of Gunn diodes presented in the literature: self-heating effects and/or smoothing of the discontinuity in the current-voltage characteristic. It is indicated that the self-heating effects are eliminated at the short-pulse measurement of the I-V characteristics, but such measuring systems, as a rule, have an output resistance that comparable (or greater) to the resistance of a Gunn diode. It is shown that an increased output resistance of the measuring system leads to a smoothing of the discontinuity in the I-V curve. A requirement for the output impedance of the meter based on the permissible distortion of the I-V characteristics is establish.

A modeling and experimental investigation on the detection of a dipole with a nonlinear semiconductor inclusion by baseband pulse test signals is carried out. It is shown that step signals give an advantage in sensitivity at limited amplitude of the transmitter output signal.

Theoretical and experimental investigations have been carried out to study the possibility of electric contact diagnostics by the method of nonlinear reflectometry with allowance for thermoelectric effects. The characteristics of the nonlinearity of high- and low-quality electric contacts caused by their response to test signals are presented. The possibility is demonstrated of determining the intrinsic parameters of electric contacts specifying their quality from the nonlinearity characteristics.

A brief description of methods for the investigation of nonlinear transformations of ultra-wideband (UWB) signals at their impact on circuits is provided. The experimental setups implementing such methods for the investigation of nonlinearity microwave circuits nonlinearity characteristics under the action of UWB signals are described.

The nonlinearity of signal transformation by an object is investigated via sensing of the object by two successive test signals and determining the nonlinearity characteristic in terms of the difference between the convolutions of the test signals and the object responses. It is shown that, in such an approach, there is no need to prespecify the relationship between the test signals and predetermine the signal waveforms. An approach that takes into account the nonlinear signal distortions in a receiver is described. In an experimental investigation of the nonlinearity of the transformation of the test signal (magnetic field) by metal objects, it is shown that the considered nonlinearity characteristic is several times greater than the nonlinearity characteristic of signal transformation that can be obtained via determination of sideband spectral components.

The linearity is one of the more difficult challenges of receiver in ultra wideband (UWB) communication systems (Green & Roy, 2003). When testing UWB receivers, one should use UWB signals as nonlinear signal distortion caused by a device dependant on the waveform of a signal. The investigation of nonlinear distortions of UWB signals run across considerable difficulties. They are caused by a continuous spectrum of UWB signals. In this case, it is impossible to observe harmonics or intermodulation products. In addition, application of UWB signals practically has no alternative in subsurface radars. However, such radars remain linear today. It can be explained by the same reason as stated above (difficulties in observing nonlinear transformation products). The same situation can be observed in reflectometry of wire transmission lines. Lately Agilent Technologies Company has been using X-parameters (Verspecht, 1996; Verspecht & Root, 2006) in Advanced Design System (ADS) and PNA-X measuring devices. It is assumed that object characteristics depend only on the first harmonic of test signal and dc bias. Therefore, X-parameters are adequate only when narrow-band test signals are used. The methods described, which allow using the UWB test signals, have some failings. There is a method, which allows identifying parameters of nonlinear object model by means of testing the object by pulse signal with level sweep (Sobhy et al., 1996). However, such model includes recursive (or nonrecursive) filter and the order of this filter is prespecified. Therefore, if complexity of the object transfer function is not limited, the method is not suitable. The equivalent gain concept (Arnstein, 1979; Arnstein et al., 1992; Chen et al., 1996) implies finding the difference between the object response and the test signal. In this case it is required that the effective width of the test-signal spectrum should be inside the horizontal segment of the frequency response of the object under test. Otherwise, it is necessary to compensate linear distortions of the test signal produced by the object. In practice, this compensation can be accomplished only for time-independent linear distortions with simple frequency dependence. The problem of observing nonlinear transformation products of UWB signals can be solved by using the test signal with local null (or nulls) of spectrum (E. Semyonov, 2002, 2004; Lipshitz et al., 2002) or by means of rejection of narrow frequency band in the test-signal

It is shown that an approach included investigation of the nonlinearity characteristics of signals transformation by an element is preferable to quality diagnostics of nonlinear models of elements. The software tools and measuring device which allow carrying out such diagnostics for baseband pulse signals are specified.

The results of the research and development of the instrumentation for measurement of UWB nonlinear distortion are shown. Calculations of application of measuring systems with limiting frequency 1.5 and 18 GHz are presented.