1,368 research outputs found

    New achievements and configurations of helical resonator filters for space applications - theory and design

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    The satellite for communication uses frequencies from UHF band (300MHz to 3 GHz) up to Ka band (40GHz). The dimensions of the components in the satellite transponder, usually decrease with the frequency increment. For the Ka band typical dimensions of the microwave components are in the order of 10mm while for lower frequencies such as UHF band, the dimensions are in the order of 100mm. For this last case, there is the necessity of the reduction of the size of the component to save mass and minimize the footprint in the satellite transponders. This work focuses on the filters that compose the input and output multiplexer (IMUX and OMUX) for the UHF band applications. In particular, the OMUX manage several hundred of watts of RF power, so, in this case, the filters has to be designed for high power, maintaining the small dimensions and low mass. In the thesis, prototypes waveguide filters loaded by single helical resonator were designed and manufactured. The prototypes were tested for high power in ESA-VSC High Power RF Laboratory in Valencia to verify their power handling characteristics. For the IMUX, the thesis concentrates on the mass and dimensions saving due to the fact that, for UHF band, typical size of waveguide filters is higher than 100mm. the proposed solution is to use a dual mode concentric helices filters. The novelty of this kind of solution required the development of the mathematical background for the first dimensioning and analysis of filter characteristics. All the theory developed is reported in this work. The output of this procedure is the design and simulation of a very compact dual mode concentric helices filter (28.08mmx28.08mmx10.36mm). A prototype is produced using 3D additive manufacturing technique and the test campaign is in progress. In conclusion, for the helical resonator filter in OMUX, the high power test confirms that this technology is promising for power handling purposes and gives some suggestions for future development such as changing the helix geometry and loading the helices with dielectrics. For the dual mode concentric helices filter, the hope is that the test campaign will confirm the designed results and after, the possible next step is to improve the design for high power applications

    Crescent Waves in Optical Cavities

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    We theoretically and experimentally generate stationary crescent surface solitons pinged to the boundary of a micro-structured vertical cavity surface emission laser by using the intrinsic cavity mode as a background potential. Instead of a direct transition from linear to nonlinear cavity modes, we demonstrate the existence of a symmetry-breaking crescent waves without any analogs in the linear limit. Our results provide an alternative and general method to control lasing characteristics as well as to study optical surface waves.Comment: 3 figure

    Miniaturised bandpass filters for wireless communications

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    The wireless industry has seen exceptional development over the past few decades due to years of sustained military and commercial enterprise. While the electromagnetic spectrum is becoming increasingly congested, there is a growing tendency to strive for higher bandwidths, faster throughputs, greater versatility, compatibility and interoperability in current and emerging wireless technologies. Consequently, an increasingly stringent specification is imposed upon the frequency utilization of wireless devices. New challenges are constantly being discovered in the development and realization of RF and microwave filters, which have not only sustained but fuelled microwave filter research over the many years. These developments have encouraged new solutions and techniques for the realization of compact, low loss, highly selective RF and microwave bandpass filters. The theme of this dissertation is the realization of planar compact performance microwave and RF bandpass filters for wireless communication systems. The work may be broadly categorised into three sections as follows. The first section presents a novel compact planar dual-mode resonator with several interesting and attractive features. Generally, planar microwave dual-mode resonators are known to half the filter footprint. However, it is found that the proposed resonator is capable of achieving further size reductions. In addition the resonator inherently possesses a relatively wide stopband as the lowest spurious harmonic resonance is observed at thrice the fundamental frequency. Properties of this resonator, such as these and more are explored in depth to arrive at an accurate electrical equivalent circuit, which is used as the basis for high order filter design. The application of these resonators in the design of bandpass filters is the subject of the second section. A general filter design procedure based on the equivalent circuit is presented to assist the design of all-pole filters. Alternatively, it is shown that generalised Chebyshev filters with enhanced selectivity may be developed with cross coupled resonator topologies. The discussions are supplemented with detailed design examples which are accompanied by theoretical, simulated and experimental results in order to illustrate the filter development process and showcase practical filter performance. The third section explores the possibility of employing these resonators in the development of frequency tunable bandpass filters. Preference is given to varactor diodes as the tuning element due to the numerous qualities of this device in contrast to other schemes. In particular, interest is paid to center frequency tuned filters with constant bandwidth. Tunable filters constructed with the dual-mode resonator are shown to have a relatively wide tuning range as well as significantly higher linearity in comparison to similar published works. In line with the previous section, experimental verification is presented to support and supplement the discussions

    High-Q Tuneable 10-GHz Bragg Resonator for Oscillator Applications

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    This paper describes the design, simulation, and measurement of a tuneable 9.365-GHz aperiodic Bragg resonator. The resonator utilizes an aperiodic arrangement of non (λ/4) low-loss alumina plates (εr = 9.75, loss tangent of 1×10−5 to 2 × 10−5) mounted in a cylindrical metal waveguide. Tuning is achieved by varying the length of the center section of the cavity. A multi-element bellows/probe assembly is presented. A tuning range of 130 MHz (1.39%) is demonstrated. The insertion loss S21 varies from −2.84 to −12.03 dB while the unloaded Q varies from 43 788 to 122 550 over this tuning range. At 10 of the 13 measurement points, the unloaded Q exceeds 100 000, and the insertion loss is above −7 dB. Two modeling techniques are discussed; these include a simple ABCD circuit model for rapid simulation and optimization and a 2.5-D field solver, which is used to plot the field distribution inside the cavity

    Reconfigurable optical spectra from perturbations on elliptical whispering gallery resonances

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    Elastic strain, electrical bias, and localized geometric deformations were applied to elliptical whispering-gallery-mode resonators fabricated with lithium niobate. The resultant perturbation of the mode spectrum is highly dependant on the modal indices, resulting in a discretely reconfigurable optical spectrum. Breaking of the spatial degeneracy of the whispering-gallery modes due to perturbation is also observed

    Towards achieving strong coupling in 3D-cavity with solid state spin resonance

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    We investigate the microwave magnetic field confinement in several microwave 3D-cavities, using 3D finite-element analysis to determine the best design and achieve strong coupling between microwave resonant cavity photons and solid state spins. Specifically, we design cavities for achieving strong coupling of electromagnetic modes with an ensemble of nitrogen vacancy (NV) defects in diamond. We report here a novel and practical cavity design with a magnetic filling factor of up to 4 times (2 times higher collective coupling) than previously achieved using 1D superconducting cavities with small mode volume. In addition, we show that by using a double-split resonator cavity, it is possible to achieve up to 200 times better cooperative factor than the currently demonstrated with NV in diamond. These designs open up further opportunities for studying strong and ultra-strong coupling effects on spins in solids using alternative systems with a wider range of design parameters.Comment: 20 pages, 9 figure

    Design of Distributed Spiral Resonators for the Decoupling of MRI Double-Tuned RF Coils

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    © 1964-2012 IEEE. Objective: A systematic analytical approach to design Spiral Resonators (SRs), acting as distributed magnetic traps (DMTs), for the decoupling of concentric Double-Tuned (DT) RF coils suitable for Ultra-High Field (7 T) MRI is presented. Methods: The design is based on small planar SRs placed in between the two RF loops (used for signal detection of the two nuclei of interest). We developed a general framework based on a fully analytical approach to estimate the mutual coupling between the RF coils and to provide design guidelines for the geometry and number of SRs to be employed. Starting from the full-analytical estimations of the SRs geometry, electromagnetic simulations for improving and validating the performance can be carried out. Results and Conclusion: We applied the method to a test case of a DT RF coil consisting of two concentric and coplanar loops used for 7 T MRI, tuned at the Larmor frequencies of the proton (1H, 298 MHz) and sodium (23Na, 79 MHz) nuclei, respectively. We performed numerical simulations and experimental measurements on fabricated prototypes, which both demonstrated the effectiveness of the proposed design procedure. Significance: The decoupling is achieved by printing the SRs on the same dielectric substrate of the RF coils thus allowing a drastic simplification of the fabrication procedure. It is worth noting that there are no physical connections between the decoupling SRs and the 1H/23Na RF coils, thus providing a mechanically robust experimental set-up, and improving the transceiver design with respect to other traditional decoupling techniques

    Design of Distributed Spiral Resonators for the Decoupling of MRI Double-Tuned RF Coils

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    OBJECTIVE: A systematic analytical approach to design Spiral Resonators (SRs), acting as distributed magnetic traps (DMTs), for the decoupling of concentric Double-Tuned (DT) RF coils suitable for Ultra-High Field (7 T) MRI is presented. METHODS: The design is based on small planar SRs placed in between the two RF loops (used for signal detection of the two nuclei of interest). We developed a general framework based on a fully analytical approach to estimate the mutual coupling between the RF coils and to provide design guidelines for the geometry and number of SRs to be employed. Starting from the full-analytical estimations of the SRs geometry, electromagnetic simulations for improving and validating the performance can be carried out. RESULTS AND CONCLUSION: We applied the method to a test case of a DT RF coil consisting of two concentric and coplanar loops used for 7 T MRI, tuned at the Larmor frequencies of the proton (1H, 298 MHz) and sodium (23Na, 79 MHz) nuclei, respectively. We performed numerical simulations and experimental measurements on fabricated prototypes, which both demonstrated the effectiveness of the proposed design procedure. SIGNIFICANCE: The decoupling is achieved by printing the SRs on the same dielectric substrate of the RF coils thus allowing a drastic simplification of the fabrication procedure. It is worth noting that there are no physical connections between the decoupling SRs and the 1H/23Na RF coils, thus providing a mechanically robust experimental set-up, and improving the transceiver design with respect to other traditional decoupling techniques
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