Изучение принципов построения широкополосной колебательной СВЧ системы на примере резонатора Фабри-Перо

Abstract

In telecommunications and radar systems of the centimeter and millimeter wave ranges, span klystrons are widely used as medium and high power amplifiers. The use of high-quality resonators makes it possible to realize high efficiency and amplification factors. However, typical designs of 2 - 4 resonator klystrons have a bandwidth of 0.1 - 0.5 % due to the need to use resonators with a high Q – factor. The well-known method of expanding the amplified frequency band in the centimeter range up to 7 – 12 % and in the millimeter range up to 1 - 2 % consists in tuning the frequency of the intermediate klystron resonators by several percent of the central amplification frequency. But in this case, it is required to use 10 - 12 resonators. The authors of the work discovered that when a millimeter range electromagnetic wave is reflected from an electrodynamics system in the form of a metal film on the surface of a semiconductor layer, the input resistance phase-frequency characteristic of this system consists of a chain of frequency intervals with turnings from a positive phase-frequency characteristic to a negative one and vice versa. The possibility of constructing a phase shifter with a negative phase frequency response based on this phenomenon is demonstrated and its application for expanding the resonant frequency band is considered on the example of the Fabry - Perot interferometer model. This resonator contains a phase shifter in the form of a semiconductor layer F with a thickness DF, a conductivity σF, a relative dielectric eF and a magnetic mF permeability. The outer surface of the layer F contains a metal mirror, and the inner surface is adjacent to the layer W. The layer W which has the thickness of DW, eW, mW forms the internal space of the resonator. The external environment I with mI and eI. adjoins the layer W. A plane electromagnetic wave propagates in I media so that it excites the resonator at a wavelength of l0. The use of a phase shifter makes it possible to increase the resonant wavelength band Δl/l0 by 2 - 4 times and with an electromagnetic field amplification coefficient |G(l)| in the W layer by 10 - 20 times (the value of Dl/l0 corresponds to 0.707 max |G(l0)|). An increase of σF leads to an amplitude-frequency characteristic transforming of the field gain function G(l0) from two maxima to one maximum form with a transition through a flat top. In this case max |G(l0)| decreases and Dl/l0 increases. For the case, when the function |G(l)| has a flat top, an increase in the wave resistance ρW of the layer W with a corresponding decrease in sF and optimal values of DW leads to an increase in |G(l0)|. When this occurs, Dl/l0 becomes lower.