Dielectric-loaded Resonators Research Articles

Vortex dynamics in NbTi films at high frequency and high DC magnetic fields

We report on the characterization of NbTi films at sim 11 GHz and in DC magnetic fields up to 4 T, performed by means of the coplanar waveguide resonator technique, providing quantitative information about the penetration depth, the complex impedance, and the vortex-motion-induced complex resistivity. This kind of characterization is essential for the development of radiofrequency cavity technology. To access the vortex-pinning parameters, the complex impedance was analyzed within the formalism of the Campbell penetration depth. Measurements in this frequency range allowed us to determine the complete set of vortex-pinning parameters and the flux flow resistivity, both analyzed and discussed in the framework of high-frequency vortex dynamics models. The analysis also benefits from the comparison with results obtained by a dielectric-loaded resonator technique on similar samples and by other ancillary structural and electromagnetic characterization techniques that provide us with a comprehensive picture of the material. It turns out that the normalized flux flow resistivity follows remarkably well the trend predicted by the time dependent Ginzburg-Landau theory, while the pinning constant exhibits a decreasing trend with the field which points to a collective pinning regime.

Design and Test of a New Dielectric-Loaded Resonator for the Accurate Characterization of Conductive and Dielectric Materials.

The spread of additive manufacturing techniques in the prototyping and realization of high-frequency applications renewed the interest in the characterization of the electromagnetic properties of both dielectric and conductive materials, as well as the design of new versatile measurement techniques. In this framework, a new configuration of a dielectric-loaded resonator is presented. Its optimization, realization, and use are presented. A measurement repeatability of about one order of magnitude lower than the commonly found values (10-3 on the Q-factor and 15×10-6 on the resonance frequency, given in terms of the relative standard deviations of repeated measurements) was reached thanks to the design of a closed resonator in which the samples can be loaded without disassembling the whole measurement fixture. The uncertainty levels, the ease of use, and the versatility of the realized system make its use of potential interest in numerous scenarios.

A Dielectric Loaded Resonator for the Measurement of the Complex Permittivity of Dielectric Substrates

A new configuration of dielectric-loaded resonator (DR), particularly versatile for the complex permittivity measurement of substrates for microwave circuits, even in the presence of back metal plates, is shown here. To test this technique in a wide interval of the values of the complex permittivity, the versatility of 3-D printing is exploited to print samples with different densities, thus artificially changing the effective permittivity in the interval (1.7–3.1) for the real part and (0.02–0.06) for the imaginary part. The designed resonator, tuned at ~12 GHz, is experimentally validated by the comparison of measurements obtained on these samples with a split ring resonator (SRR) and standard transmission/reflection waveguide methods. Then, the versatility of the designed resonator is shown in the characterization of FR4-fiberglass and Kapton polyimide samples.

Proposal: Apparatus for Sensing the Effect of Surface Roughness on the Surface Resistance of Metals

The root mean square surface roughness Rq of metals is detrimental in several microwave applications. Rq characterization methods are thus largely used and of great interest. In this work, a new dielectric loaded resonator (DR) design is proposed to evaluate the surface resistance variations of samples with different Rq. The new design is thought to make the measurement accuracy, usually strongly affected by the measurement repeatability, suitable for this study. We analyze the measurement method's sensitivity and accuracy in order to assess the possibility of using this new DR design for highly accurate surface resistance measurements sensitive to Rq variations.

Characterisation of dielectric 3D-printingmaterials at microwave frequencies

<p class="Abstract">3D-printer materials are becoming increasingly appealing, especially for high frequency applications. As such, the electromagnetic characterisation of these materials is an important step in evaluating their applicability for new technological devices. We present a measurement method for complex permittivity evaluation based on a dielectric loaded resonator (DR). Comparing the quality factor <em>Q</em> of the DR with a disk-shaped sample placed on a DR base, with <em>Q</em> obtained when the sample is substituted with an air gap, allows a reliable determination of the loss tangent.</p>

Microwave investigation of pinning in Te- and cubic-BN- added MgB2

MgB2 has great potential for many applications, thanks to its relatively high critical temperature and low fabrication cost. Large efforts are done to improve the current carrying capabilities of bulks and tapes in view of different application fields, e.g. with the addition of Te and cubic-BN to MgB2. To elucidate the vortex pinning physics exploiting a different dynamic regime, we present here a microwave study of the pinning properties of spark plasma sintered bulk MgB2 with and without the addition of 0.01 % at. Te or cubic-BN. We show the surface resistance Rs of the MgB2 samples measured with a dielectric-loaded resonator at ~ 16.5 GHz and ~ 26.7 GHz in the 10 K-Tc temperature range at fields up to 1.0 T. Then, the MgB2 Rs is studied with high frequency vortex motion models in order to obtain the pinning constant (Labusch parameter) and the depinning frequency. Finally, the microwave behavior of MgB2 in the mixed state is compared with the recent results obtained on Nb3Sn.

WAKEFIELDS AND DRIVE ELECTRON BUNCHES DYNAMICS IN THREE-ZONE DIELECTRIC RESONATOR AT ASYMMETRICAL INJECTION

A numerical study of the wakefield excitation in a rectangular dielectric-loaded resonator by a sequence of relativistic electron bunches in the case of non-axial injection is carried out. The effect of the shift of injected bunches on the particle dynamics, as well as on the spatial distribution of the components of the bunch-excited fields, is studied. The current losses of a sequence of relativistic electron bunches due to the particles deposition on the surface of the dielectric is determined.

Spurious stopband improvement of dual‐mode dielectric resonator filters using T‐shaped coupling probe

This work presents a new design technique for dual-mode dielectric-loaded resonator filter operating at 2.18 GHz by using T-shape coupling probe. A cylindrical dielectric puck is suspended in the middle of metallic cavity and short-circuited on the side walls. Four vertically etched-slots through the dielectric puck from the top to the base of the ceramic puck offer a high unloaded quality factor of 4300 at the fundamental TE 11δ mode and allows the T-shape coupling to be located close to the centre of the dielectric puck. The size reduction ratio in this resonator was 11% compared with air-filled coaxial resonator. Fourth-poles Chebyshev bandpass filter with planar configuration was designed and implemented by employing two dielectric-loaded cavities. The experimental results show that the spurious-free window of ~820 MHz from the fundamental frequency of 2.18 GHz and the operational bandwidth of 77 MHz were achieved.

Sensitivity limits comparison of surface resistance measurements based on dielectric loaded resonators

We present a study of the uncertainties on the measures of the surface resistance, obtainable with different measurement methods based on the use of dielectric-loaded resonators. We consider the so-called round robin rotation method versus the single measurement technique and we evaluate the respective uncertainties. This comparison is done in the case of samples with surface resistance near that of the resonant cavity walls. We establish the limits of application of the round robin technique versus those of the single measurement.

Modeling of couplings between double-ridge waveguide and dielectric-loaded resonator

Full-wave modeling of the coupling structure between a double-ridge waveguide and dielectric-loaded resonator in a rectangular cavity through an iris is presented. Eigenmodes of the double-ridge waveguide, and the discontinuities of the structures are obtained by rigorous mode-matching method. By applying the cascading procedure, the reflection coefficients of the coupling structure can be obtained. From the phase variation of the reflection coefficient and circuit theory, resonant frequency and input/output coupling of the structure are accurately determined. An equivalent circuit model of the resonant structure is established. The computed results are compared with those obtained by other methods and shown to be in good agreement, which verifies the theory.

Tuning effect analysis of cylindrical dielectric-loaded resonators

Tuning effect analysis of cylindrical dielectric-loaded resonators

Resonant frequencies of dielectric resonators containing guided complex modes

It is shown that unless complex modes are included in the mode-matching analysis to determine the resonant frequencies of dielectric-loaded resonators, some resonant frequencies could be missed. Field distributions, mode charts, and mode coefficients of dielectric-loaded resonators in which complex modes exist are presented. Experimental measurements for the verification of the computed results are presented and show good agreement with theory. >

New Results in Dielectric-Loaded Resonators (Corrections)

In the above paper, an error was made in plots. The corrected plots are shown below.

New Results in Dielectric-Loaded Resonators

Analysis of cylindrical dielectric-loaded resonators is reviewed. The fields within the dielectric-loaded region are postulated as the superposition of hybrid, TE, or TM modes of the infinite dielectric-loaded waveguide, while the fields in the end regions of the resonators are described by the superposition of the normal modes of a homogeneously filled waveguide. Numerical results are presented which reveal that accurate representation of the fields in the resonant structure generally require several modes. Hence, the resonant modes cannot be correlated directly with single waveguide modes. A new method for mode identification is proposed. For a wide range of parameters, the resonant frequencies, mode charts, field expansion coefficients, field intensity, and distributions are presented. Excellent agreement of the mode charts with resonant frequency measurement results are obtained.

Loss Mechanisms in Dielectric-Loaded Resonators

Analysis is presented of resonators consisting of a section of a dielectric-loaded waveguide shorted at both ends. The analysis includes resonant frequency calculations, mode charts, and unloaded Q computations. Numerical results are presented for the unloaded Q's of various modes, as a function of the resonator parameters. Effects of losses in different parts of the resonator wall on the unloaded Q are discussed, and methods of improving these Q's are explored. Experimental verification of the theoretically derived results is made for a number of resonators, and the measurements agree closely with theory.