Filters
Filters are highly resonant structures that can be found in any communication channel. The frequency domain solvers within CST MICROWAVE STUDIO® are ideal for their design and analysis. The eigenmode solver provides a specialized solution for cavity design. Both solvers support curved tetrahedral elements, which means that curved structures can be analyzed more accurately and efficiently.
A key design step is the tuning of a filter, which might be a challenge because of the high sensitivity of the tuning parts. CST provides several unique features to make the design process as simple as possible. An estimation of the sensitivity of the filter response to small geometric or material property variation can be obtained from a single simulation. In addition EM/circuit co-simulation allows for a very efficient manual tuning process.
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Electromagnetic simulation of anechoic chambers is a very difficult task. Gwenaël Dun, R&D Engineer for Siepel, used a variety of different electromagnetic simulation tools to address this challenge in the past but ran into problems with both poor accuracy and long compute times. He then worked with the developers of CST MICROSTRIPES™ electromagnetic simulation software, to implement a feature that makes it possible to model the ferrite absorbers used in the chamber as a boundary condition rather than part of the computational domain. This change made it possible to increase mesh size by a factor of 15, reducing compute time by more than 95%. The simulation results provided a near-perfect match to physical testing.
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This application note describes the use of CST MICROWAVE STUDIO® in optimising the geometry of a free standing nested annular slot type Frequency Selective Surface (FSS). An isolation of better than 20 dB between the 316.5-325.5 GHz and 349.5-358.5 frequency bands was achieved in both the TE and TM planes for a 45 degree incident plane wave, while the insertion loss was below 1 dB.
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Linear Accelerators (Linacs) are widely employed in accelerator facilities. Linear acceleration is the method of choice for light particles as synchrotron radiation effects limit the usability of circular accelerators for these particles. Industrial applications require compact linacs for the acceleration of electrons with target energy in the range between 1 and 25 MeV. CST MWS and PS can be used to investigate the high frequency behaviour of linac structures as well as the interaction between particles and the accelerating field.
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This article demonstrates how properties of the resonant modes of photonic crystal (PhC) point defect cavities are obtained from transient solver simulations using CST MICROWAVE STUDIO®. In this example a single point defect in a triangular lattice of air holes in a high refractive index slab is used. Properties of particular interest are: the resonance frequency, intrinsic Q factor and field distribution of the resonant modes. The cavity is excited using discrete ports, and the spectral features are recorded with point probes. The Q factor is determined from the energy decay rate and using auto regressive filtering. 2D and 3D field monitors record the field distributions.
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Stefan Prorok, Hamburg University of Technology
We present an overview of our current research activities in silicon photonics and thermal barrier coatings. Doing so, we will comment on how CST Microwave Studio can be used to design strip waveguides, micro ring resonators, as well as 2-D and 3-D photonic crystal structures. Particularly we will concentrate on the discussion of photonic crystal micro cavities which can be used as electro-optic modulators. It will be shown that MWS provides all the functionality to optimize and characterize optical micro cavities. The appearance of resonant modes is adjusted through eigenmode calculation of the photonic crystal waveguide modes. Time domain simulation with discrete port excitation is applied to calculate the intrinsic Q-factor of the cavity. Waveguide ports are used to model experimental conditions of excitation with strip waveguide modes. Field monitors help to understand the mechanism of energy loss from the cavity. The simulation results are compared to measurements on fabricated structures. As possible application we will show a hybrid silicon organic hetero structure cavity for GHz electro-optic modulation.
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The CST EM STUDIO™ Thermal Solver has been applied to simulate the temperature distribution of a dual-mode filter. The current density distribution inside the lossy conductive metals is precomputed by CST MICROWAVE STUDIO® acting as the thermal source.
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Tuning of a coupled-resonator filter is performed in this article by using the group delay response of the input reflection coefficient of sequentially tuned resonators containing all the information necessary to design and tune filters. To achieve high out-of-band rejection losses a single transmission zero is introduced producing a pair of finite frequency poles.
CST MICROWAVE STUDIO® is used to optimize and/or tune the bandpass filter resonse in a complete model by applying the new, fast MOR-Frequency Domain Solver. To speed-up the tuning process the entire model is split up into several sections and recombined in CST DESIGN STUDIO™ to get the overall filter response.
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The Bragg Reflector implemented in the coaxial technology is an example for setting up simulations of periodic structures. The simulation is performed with CST MICROWAVE STUDIO® and compared to measurements.
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Ad Reniers, Technical University Eindhoven
High-data-rate wireless communications need wide bandwidths. In the Ultra-Wideband (UWB) frequency band from 3.1 GHz to 10.6 GHz, information may be spread over a large bandwidth at low power levels thus creating the possibility to share the spectrum with other users. To prevent interference with existing wireless systems, like IEEE 802.11a WLAN, stop band characteristics are required from 5 GHz to 6 GHz*. The notch filter function is designed in a low-cost circular planar dipole antenna based on the ‘two-penny’ dipole. To achieve the required specifications for this notch function we used first the CST optimizer. After that we optimized systematic the design. In this presentation we want to show the results of both approaches to achieve a maximum result and try to understand the working of this notch and spur function in this compact UWB antenna.
* Paper: Low-cost, compact UWB antenna with frequency band-notch function. H.J. Visser.
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This structure for mobile communication in LTCC technology combines a diplexer for the GSM and DCS frequency bands with a low pass filter for each band.
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This application has been succesfully simulated using the powerful Eigenmode Solver in CST MICROWAVE STUDIO® with the aid of the Modal Analysis Module.
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The dichroic filter is an example for setting up simulations of frequency selective surfaces. The simulation is performed with CST MICROWAVE STUDIO® and compared to measurements.
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This waveguide filter has been simulated with CST MICROWAVE STUDIO® general purpose frequency domain solver applying a tetrahedral mesh.
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New, compact configurations for RF/microwave bandstop and lowpasss filters are presented. Compact footprints are achieved by folding the transmission lines in a microstrip platform. The effect of mutual coupling between the transmission lines, curved line sections, interconnecting lengths of the sections are taken into account to obtain the network parameters for the folded line filters. The folded line filters have practical dimensions for a wide range of electrical specifications, making physical implementation realizable. The filter designs have been validated by using full wave 3D EM simulation using CST MICROWAVE STUDIO®, as well as by comparison with the measurements. The new designs presented should prove useful for a host of embedded passive and RFIC applications in the 1-10 GHz range.
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The example design is a classic hairpin filter with a bandwidth of 3.6 to 4.3 GHz. The hairpin filter was designed for a return loss better than -20dB across the band.
CST DESIGN STUDIO™ was used to design and tune the filter, the resulting layout was then verfied with the 3D- EM simulation software CST MICROWAVE STUDIO®.
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Shown is the discretised model of a dielectric two circuit filter with coaxial input and output couplers.
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The dual mode filter was developed, measured, and simulated by ESA (European Space Agency).
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A monotron is a simple microwave tube which converts DC energy into RF energy. The simulation of such a two-cavity monotron with CST PARTICLE STUDIO® is performed and compared to published results.
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