Suppression Of Parasitic Modes Research Articles

Suppression of Parasitic Modes in a Cylindrical Gyrotron Beam Tunnel by a Wall Corrugation With Schroeder Diffuser Structures

Suppression of Parasitic Modes in a Cylindrical Gyrotron Beam Tunnel by a Wall Corrugation With Schroeder Diffuser Structures

Design and Analysis of 55–63-GHz Fundamental Quad-Core VCO With NMOS-Only Stacked Oscillator in 28-nm CMOS

This article presents a 55–63-GHz fundamental multicore voltage-controlled oscillator (VCO) in a 28-nm bulk CMOS process. The single-core VCO utilizes stacking and magnetic coupling of two NMOS-based resonators, which increases the tank energy for phase noise reduction while maintaining low voltage swings for reliability. In the multi-core configuration, the oscillators are coupled in a way that also simplifies LO distribution toward the transmitter and receiver. The potential parasitic modes that occur both in single-core and multi-core configurations are suppressed by design. The implicit common-mode (CM) impedance control is utilized to reduce phase noise without any large extra tail inductor as used in a conventional complementary oscillator. The distributed nature of energy restoring elements in the proposed stacked oscillator also offers robust parasitic mode suppression compared to alternative implementation based on a conventional complementary oscillator. The working range of the prototype is between 55 and 63 GHz corresponding to a tuning range of 13.4% with power consumption varying from 15.3 to 12 mW across the tuning range. The prototype achieves the best phase noise of −95 and −121.7 dBc/Hz at 1- and 10-MHz offsets from the carrier at 55GHz. The corresponding peak figure of merits (FOMs) achieved are 178 and 185 dBc/Hz at 1- and 10-MHz offsets from the carrier.

Suppression of parasitic modes in a YAG:Nd slab laser using selective coating

The use of selective coating for suppression of parasitic modes in a slab laser with a YAG:Nd active element is investigated. Various designs of selective coatings are analyzed and optimized, based on the phenomenon of total internal reflection. The possibility of implementing a selective coating based on thin-film materials titanium, silicon dioxide, and aluminum oxide is demonstrated.

Selective excitation of eigenmodes in a multilayer thin film resonator on bulk acoustic waves

We consider a method of control over the operating frequency of a resonator on bulk acoustic waves, which is based on the selective excitation of eigenmodes. The frequency switching is achieved by using several layers of a ferroelectric in the paraelectric state and applying a control voltage of appropriate magnitude and polarity to each layer. The principle of selectivity is formulated and the criterion function is defined, which ensure the most effective excitation of a selected eigenmode with the possible suppression of parasitic modes. An example of using this function for a resonator switched between four eigenmodes is presented.

Densely-tiled metal-insulator-metal metamaterial resonators with quasi- monochromatic thermal emission.

Metal-insulator-metal metamaterial thermal emitters strongly radiate at multiple resonant wavelengths. The fundamental mode, whose wavelength is the longest among resonances, is generally utilized for selective emission. In this paper, we show that parasitic modes at shorter wavelengths are suppressed by newly employed densely-tiled resonators, and that the suppression enables quasi-monochromatic thermal emission. The second-order harmonics, which is excited at half the fundamental wavelength in conventional emitters, shifts toward shorter wavelength. The blue-shift reduces the amplitude of the second-order emission by taking a distance from the Wien wavelength. Other parasitic modes are eliminated by the small spacing between resonators. The densely-tiled resonators are fabricated, and the measured emission spectra agree well with numerical simulations. The methodology presented here for the suppression of parasitic modes adds flexibility to metamaterial thermal emitters.

Free-space beam shaping for precise control and conversion of modes in optical fiber.

We consider the general problem of free-space beam shaping for coupling in and out of higher order modes (HOMs) in optical fibers with high purity and low loss. We compare the performance of two simple phase structures - binary phase plates (BPPs) and axicons - for converting Gaussian beams to HOMs and vice versa. Both axicons and BPPs allow for excitation of modes with high purity (>15 dB parasitic mode suppression), or conversion of HOMs to near-Gaussian beams (M2 < 1.25). Axicon coupling in single-clad fibers allows for lower loss (0.85 ± 0.1 dB) conversion than BPPs (1.7 ± 0.1 dB); but BPPs are compatible with any fiber design, and allow for rapid switching between modes. The experiments detailed here use all commercial components and fibers, allowing for a simple means to investigate the unique properties of multi-mode fibers.

Experimental study on parasitic mode suppression using FeSiAl in Relativistic Klystron Amplifier.

Experimental study of parasitic mode suppression using electromagnetic attenuate material FeSiAl in an S-band Relativistic Klystron Amplifier (RKA) is presented in this paper. The FeSiAl powder is coated and sintered onto the inner surface of a drift tube which locates between the input and the middle cavity of the RKA. Cold tests show that the attenuate rate of the tube against parasitic mode TE11 is about 50%. Experiments carried out on the Torch-01 accelerator present that the tube is effective in suppressing the parasitic mode. Two typical outputs are obtained. When the diode voltage is on a moderate level, the RKA operates well and the parasitic mode is totally suppressed. The pulse length of the High Power Microwave (HPM) almost equals the electron beam pulse length and the HPM average output power is about 300 MW, with a power efficiency of 10%. When the diode voltage is on a higher level, the output power and efficiency rise but the parasitic mode oscillation occurred and the pulse length is shortened. By contrast, the parasitic mode oscillation is too strong for the RKA to operate normally with un-sintered drift tube. The experimental study implies that FeSiAl is effective in suppressing the parasitic mode oscillation in a certain extent. However, total suppression needs a deeper attenuate rate and further investigation.

New method of parasitic mode suppression in lateral-field-excited piezoelectric resonator

A new method of parasitic mode suppression in piezoelectric resonators with transverse (lateral) electric field is described, which employs the partial coverage of electrodes by a damping layer. The potential of the proposed method is demonstrated for a resonator based on an X-cut lithium niobate plate. It is experimentally confirmed that an acoustic wave with transverse electric polarization exhibits stiffening, the degree of which depends on both the electromechanical coupling coefficient and the wave aperture

Highly efficient design of spectrally engineered whispering-gallery-mode microlaser resonators

We present an accurate, reliable and versatile method for studying the effect of deformations on the characteristics of the high-Q whispering gallery (WG) modes supported by two-dimensional dielectric resonators (DR). An eigenvalue problem is formulated in terms of contour integral equations and further discretised with the method of analytical regularisation. Such a procedure significantly reduces the number of unknowns whilst providing high and controllable accuracy. Natural frequencies, Q-factors and field patterns of elliptical, flower- and egg-shaped DRs are calculated. Methods to enhance the Q-factors, provide directional light output, and parasitic mode suppression are discussed. The identification of WG modes is simplified by the symmetrical/asymmetrical mode separation included into the formulation of the problem and solution algorithm.

Simulations of the build-up of transverse and longitudinal structures of the microwave field in the Fusion FEM

The interaction of longitudinal and transverse modes in the Dutch Fusion FEM is studied, taking the characteristics of the feedback system, provided by quasi-optical stepped reflectors, into account. The simulations predict that the stable single-frequency operation is possible basically due to the frequency dispersion of the feedback system. As for the transverse mode interaction, the selective properties of the feedback system, as well as the effect of the suppression of parasitic modes by the operating mode at the output of the interaction region lead to a very pure transverse structure of the output microwave radiation.

Stability analysis of relativistic gyro-traveling wave devices

The stability of parasitic modes in gyro-traveling wave tubes is studied, both with and without the operating mode present. Using a Hamiltonian formalism, linear equations are derived which describe the spatial evolution of parasitic modes in the absence of the operating mode. Complications such as a nonuniform waveguide and tapered magnetic field are taken into account. As an example, the linearized equations are applied to a 10 GHz, 430 kV, gyro-traveling wave tube to determine the start current in the absence of the operating mode. Included in the analysis is the effect of frequency-dependent reflection from the output window. A relatively low start current is found, well below the nominal operating current of 240 A. Multi-mode equations are then derived which can be used to analyze the suppression of parasitic modes by the operating mode. An algorithm is developed that allows efficient computation of the nonlinear start current in this regime. The algorithm is applied to the 10 GHz, 430 kV device mentioned above, and a stable configuration is found.