Auto-oscillatory system based on dielectric resonator with whispering-gallery modes

Abstract

In recent years, vacuum electronics technology has exhibited a trend toward moving to millimeter and submillimeter wavelength range. Use of traditional approaches to designing and constructing these elec tronic devices encounters considerable difficulties related, in particular, to small geometric dimensions of the main elements that generate and stabilize electro magnetic oscillations. Solution of this problem leads to the use of superdimensional (relative to wavelength) electrodynamic structures operating in multimodal regimes. The generation of electromagnetic oscilla tions with stable frequency is closely related to the excitation and selection of high order modes in these structures.The possibility of exciting weakly decaying oscilla tions in dielectric resonators with cylindrical and spherical surfaces using high order whispering gallery modes (WGMs) [1-5] accounts for their wide use in vacuum electronic devices for millimeter and submil limeter wavelength range, where the aforementioned technological problems can be solved. However, the output power level in radiation sources of traditional design sharply drops upon passage to submillimeter wavelengths [6]. Therefore, there arises a need for high energy oscillators excited by electron beams. It should be noted that the use of superdimensional elec trodynamic structures with electromagnetic oscilla tions excited by high current relativistic electron beams also eliminates the problem of electric break down.The present study was aimed at assessing the possi bility of creating electromagnetic radiation sources operating in the millimeter wavelength range, which would pose no limitations on passage to the terahertz frequency range. The approach to construction of the proposed source is based on the use of electrodynamic properties of a quasi optical cylindrical dielectric res onator (CDR) [2,7], which serves as the main element in the resonant auto oscillatory system.We have employed a fluoroplastic (Teflon) CDR with a radius of ρ 0 = 3.9 cm and length of L = 0.9 cm. Table 1 gives the values of eigenfrequencies /2π (p ≡ msl) and Q E for the E type modes with indices m = 36 (azimuthal), s =1 (radial), and l = 0, 1, 2 (axial). Cal culations were performed using formulas from [2,7]. The choice of CDR dimensions and working modes was determined by the desired frequency range of the auto oscillatory system described below and the mode type was determined by the method of resonator exci tation. Figure 1 shows the structures of fields of the E type eigenmodes of the CDR employed. As can be seen, the fields of weakly decaying WGMs are concentrated ω p ' Abstract-A new method of microwave generation in a system with high Q quasi optical cylindrical dielec tric resonator (CDR) excited by an azimuthal periodic electron beam current is proposed. Characteristic parameters of a cylindrical fluoroplastic CDR have been determined. Data on microwave generation in a sys tem based on a CDR with whispering gallery eigenmodes excited by a relativistic azimuthal periodic elec tron b...

Whispering gallery mode resonators in microwave physics and technologies

“…The possibility of exciting weakly decaying WGMs in the WGM resonator gives rise to hopes of using them in mm and submm vacuum electronic devices [76][77][78], where the above-mentioned technological problems can be solved. The output power of traditional radiation sources drops sharply in the submm range [79].…”

“…Therefore, a need arises for highenergy oscillators excited by electron beams. It should be noted that the use of oversized structures with oscillations excited by high-current REBs also eliminates the problem of electric breakdown [76][77][78]. The proposed source design is based on the use of the electrodynamic properties of the resonator [9,11], which serves as the main element in the autooscillatory system [78].…”

“…The proposed auto-oscillatory system was experimentally investigated on a high-current linear electron accelerator "Temp A" (Fig. 17), the parameters of which are listed in [78]. The accelerator generated a pulse of REB with energy of 300 keV and a pulse duration of 3 ms at half-maximum power level.…”

“…The authors [78] used a Teflon resonator with a radius of ρ 0 = 3.9 cm and a length of L = 0.9 cm. Table 2 gives the values of the eigenfrequencies f msl and Q -factors for the resonator with HE modes where the azimuth n and radial s indices are equal to 36 and 1, respectively, and the axial l index equals 0, 1, or 2.…”

Experimental Conditions for the Excitation of Thin Disk Whispering-Gallery-Mode Resonators

“…Whispering gallery mode (WGM) resonators (dielectric disks, cones, spheres, toroids, and other structures [1,2]) are known for their exceptional performance as nearly perfect frequency filters, resonators for oscillation sources, dielectric resonator antennas, etc. [3,4]. They possess record-breaking characteristics in a broad frequency range extending from optics to millimeter waves (e.g., quality factor Q exceeding 850 millions has recently been achieved in optics [5]).…”