Ultrawide Band Electromagnetic Pulses
Development of New Calculation-Theoretical and Metrologic Approaches in Technology of Ultrawide Band Electromagnetic Pulses, Elaboration and Investigation of Standard Field-Forming Systems of Subnanosecond Pulse Field
Tech Area / Field
- INS-MEA/Measuring Instruments/Instrumentation
- PHY-RAW/Radiofrequency Waves/Physics
3 Approved without Funding
Scientific Research Institute for Optophysical Measurements, Russia, Moscow
- Institute of Strategic Stability, Russia, Moscow
- Metatech Corporation, USA, CA, Goleta\nUniversität Hannover / Institut für Grundlangen der Electrotechnik und Messtechnik, Germany, Hannover
Project summaryAn intensive development of the technique of generation, radiation and measurement of subnanosecond UWB EMP poses new problems in investigating the irregular waveguide lines with metallic walls where UWB EMP are formed, restructurized, applied or transmitted [1, 2].
Some of such problems are presented below.
1. The transformation efficiency of the pulses of diametrical electromagnetic waves (TEM - waves) to the pulses with a structure of longitudinal waves (TM - waves) proves to be determining influence for the operation quality of a number of devices. This phenomenon takes place when pulse propagating from the coaxial lines with biconnected cross sections where the pulses are formed to irregular waveguides with singly connected cross sections. In particular the phemenon takes place in the devices with longitudinal interaction, fir example, in the switching tubes  and in the pulse radiating antennas . Satisfactory quantitative theory of the above mentioned pulse structure transformation so far is absent. The main reason is the mathematical modelling difficulty of pulse operation modes of irregular lines. Particularly the lines containing both distributed irregularities and concentrated ones such as a topologic discontinued joints. Nearby the joints the structure transformation is particularly effective and has "collapse" behaviour.
2. The problem of mathematical model development and calculation method with controllable accuracy of irregular transmission lines with open radiating ends in pulse mode is very important and so far satisfactory solution of this problem is absent. The results of investigations of pulse radiating antennas presented in  contain uncontrollable methodical error. This error is greater when the pulse is shorter. Origin of the error is connected with the method of separation of time dependence in field representation in radiating aperture as separate cofactor [4, (2.5)] applied for calculations is permitted by the Maxwell's equations only in some special cases and certainly in monochromatic (but not in pulse) modes.
The models and methods of numerical investigation of irregular lines for monochromatic (~e-iwt) operation modes when investigating for UWB EMP developing throughout last decades proved to be inapplicable in practice for next reason. Numerical transformation of Fourier integrals from numerically monochromatic field components UWB EMP obtained for irregular waveguides is connected with difficulties to reach satisfactory calculation accuracy because of highly considerable width of frequency spectra. This results in necessity of development of new more general calculation methods with high accuracy and possibility of error control. The frequency representations are not applied.
At the same time the calculation methods of transient electromagnetic fields in irregular waveguide transmission lines of TEM - waves on the basis of approximate telegraph equations model are not known to guarantee the required accuracy of calculation, and the methods can result in qualitative discrepancies as well. In matched discontinuous line (that is at constant characteristic impedance along its length) the pulse with TEM structure in accordance with the single mode model. When the losses are absent the pulse shape should be saved. However both experiment  and calculations [7, 8] made on the basis of more rigorous model of "connected strings"  show the possibility of considerable qualitative deviations from these representations. The difference of the results is accounted for the calculation methods on the basis of single mode model do not take into consideration the mechanism of mutual mode transformation and, in particular, the transformation of undispersive TEM wave to dispersive modes (and vice versa).
The feature of the model of connected strings  proposed for calculations is the result evidence and its adequacy to strict electrodynamic approach. Uncontrollable methodical error usually resulting from the simulation is excluded. This results in of principle possibility of calculation accuracy control and its increase. As our last calculations have shown [9, 10] the achievement of relative error of intensity determination ~ 10-4 – 10-5 is not difficult. This permits, in particular, application the model of connected strings to calculate the field-forming systems of metrologic devices.
On the basis of the recommendations for development of standard field-forming systems of subnanosecond pulses obtained in executing of the ISTC Project #1573 one proposes to investigate the system "cone over plane". Step exciting signal with the front up to 40 ps will be used. The strip transducers will be used as measuring instruments. The transducers permit the recording of step signals with a front of the same order [11-14].
Both theoretical and experimental parts of proposed Project are the development of the working results of the ISTC Project #1573 of the same participating organizations.
The purpose of the Project is the elaboration of the high accuracy calculation methods of new problems and investigation of the phenomena accompanying propagation and formation of UWB EMP in irregular waveguide transmission lines of devices and sets and calculated and experimental investigation of models of standard field-forming subnanosecond system.
The participants of the project have much work already done [5-16] to execute the investigations.
The results of the work to be expected are as follows:
1. Development of the model of connected strings and its extension to the description of pulse operation modes of transmission lines with combined distributed-concentrated discontinuities. As a result of the simulation the method for transient electromagnetic fields calculation in irregular waveguide transmission lines with rotation symmetry with controllable error (~ 0.1% and higher) will be developed. The efficiency of mode transformation of UWB pulses by topologic discontinued joints in irregular lines will be investigated.
2. Mathematical modelling, development calculation method and investigation of irregular transmission lines with open radiating ends in pulse mode.
3. Calculated-theoretical investigation of waveguide lines of coaxial-horn pulse-radiating antennas and efficiency of their operation.
4. Theoretical investigation of the excitation phenomena of standard field-forming system (SFS) "cone over plane" by step UWB electromagnetic pulses.
5. Experimental investigation of the reproduction process of standard UWB electromagnetic pulses in SFS "cone over plane".
Scientific importance. As a distinctive feature of the proposed model of connected strings, is its adequacy to a strict electromagnetic approach, which excludes the uncontrollable methodical error usually appearing in simulation. Besides possibility of calculation accuracy control and its increase this will allow an investigation of the phenomena, whose theory lies outside application of the conventional approximate models. Calculations and experimental investigations carried out will allow a creation of the standard of pulse electromagnetic fields in subnanosecond range and to provide the unity of the measurements in new field of electromagnetics of short UWB EMP.
Technical Approach. Technically, a considerable amount of work for mathematical and physical simulation, programming, calculations, design and production of field-forming systems and transducers and electromagnetic measurements should be carried out.
Methodology. As a basis of the theoretical and calculational part of the project we shall use a further development of the proposed connected string model. This will eliminate the uncontrollable methodical error that usually appears when simulating and have to provide, in principle to increase calculation accuracy.
For less exact calculations the method of specified currents will be used.
The project experiment is based on measurements by means of the transducers. Since the specific character of transducer application in subnanosecond range measurements has not yet studied enough, we assume that investigations should be carried out in this field as well.
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