1063-7842/00/4506- $20.00 © 2000 MAIK “Nauka/Interperiodica” 0747 Technical Physics, Vol. 45, No. 6, 2000, pp. 747–752. Translated from Zhurnal Tekhnicheskoœ Fiziki, Vol. 70, No. 6, 2000, pp. 78–83. Original Russian Text Copyright © 2000 by Belyantsev, Kozyrev. INTRODUCTION The possibility of the direct and efficient transfor- mation of video pulses into radio pulses during their propagation along a nonlinear transmission line (TL) with spatial dispersion was considered in [1–3]. The method is based on the instability of the front of an electromagnetic shock (EMS) interacting with a syn- chronous wave (v s = v p (ϖ), where v s is the EMS veloc- ity and v p (ϖ) is the phase velocity of the wave). The efficiency of transformation of an EMS propagating in synchronism with a forward wave (v p v g > 0, where v g (ϖ) is the group velocity, v g < v s ) was studied with account of high-frequency losses for various dispersion properties of the TL. In our previous paper [2], we have demonstrated that both the duration of a quasi-steady train of the generated oscillations and the TL length necessary for its formation depend on the choice of a “working point” at the TL dispersion curve upon satu- ration of nonlinearity. In particular, it was shown that, in the case of the generation of RF oscillations at the frequency corresponding to a minimum of v g , when the dispersion broadening of the radio pulse is minimal, both the TL length that is necessary for the generation of a given number of oscillations and the damping rate of these oscillations depend strongly on the difference v p – v g . In the case of synchronism with a forward wave, this difference can be slightly increased by changing the TL dispersion. The situation changes drastically when v p and v g have opposite signs, i.e., when the EMS is in synchronism with either a back- ward harmonic of a periodic system or a normal backward wave (v g v p < 0). In this paper, we study the distinctive features of the generation of RF oscillations in a TL with ferrite in the case when the EMS is in syn- chronism with a backward wave or backward spatial harmonic and compare the results obtained with those for synchronism with a forward wave. Obviously, each particular electrodynamic system requires special study of spatial harmonics or normal waves and the efficiency of their excitation by a traveling source (EMS front). However, the main features of the synchronism between the EMS and a backward harmonic (or wave) can be establish based on general considerations using the simplest equivalent schemes of a TL with nonlinear ferrite elements. The analysis of the processes in such lines shows that, in the case of synchronism of an EMS with a backward spatial harmonic (or backward wave), the above mechanism can be used to generate longer radio pulses in a higher frequency range. THE MODEL OF AN ELECTRODYNAMIC SYSTEM WITH FORWARD AND BACKWARD WAVES It is well known that backward waves can exist in the media with anomalous spatial dispersion [4] and in various periodic systems, in particular, slow-wave elec- trodynamic systems (see, e.g., [5]), in which the propa- gating wave is spatially modulated. Such a wave can be considered as a wave group consisting of spatial har- monics whose amplitudes are coupled. The harmonics travel with different phase velocities, but the group velocity is the same for all of them. Some of the har- monics are forward, and some are backward. In differ- ent slow-wave systems, the fundamental (or zero) spa- tial harmonic, which has the largest absolute value of the phase velocity, can be either forward or backward [5]. If the wavelength is much longer than the period d of the system (λ  d), then the backward zero harmonic is dominating in the wave group [5]. This fact some- times allows one to consider the wave group of a peri- odic system as a quasi-normal backward wave analo- gous to the backward wave in a system with anomalous spatial dispersion. The waves with zero backward har- monic propagate in slow-wave systems only within a RADIOPHYSICS Generation of RF Oscillations in the Interaction of an Electromagnetic Shock with a Synchronous Backward Wave A. M. Belyantsev and A. B. Kozyrev Institute for Physics of Microstructures, Russian Academy of Sciences, Nizhni Novgorod, 603600 Russia Received April 7, 1999 Abstract—A new mechanism for the transformation of video pulses into radio pulses during their propagation along a nonlinear transmission line with spatial dispersion—synchronism with a backward wave—is consid- ered. Numerical simulations demonstrate that a substantial advantage of this mechanism over the interaction with a forward wave is the possibility of generating longer radio pulses at higher frequencies. © 2000 MAIK “Nauka/Interperiodica”.