A Dielectric Filter is an optical fiber that selectively transmits one wavelength and reflects others based on Interference inside the structure. Also called interference filter. Microwave dielectric effects ceramics improve the size of devices and the packaging density of microwave integrated circuits. For this reason, it is widely used for the microwave filters and circuit boards in the base station of mobile communication and satellite communication systems especially in 5G.
Rapidly-developed 5G technology will bring considerable market space to 5G base station as well as dielectric filter for 5g base station.
Design Principle
A symmetric model of a dielectric resonator filter [1] is analyzed using the Scattering parameters module of HFWorks to determine its pass-band, the attenuation in and out of the band, and the electric field distributions for various frequencies. The result shows a perfect match with those presented in [2]. The cables have a lossy conductor, and have a Teflon inside part. HF Works gives the possibility to plot variouScattering Parameters on 2D and Smith Chart plots. Besides, the electric field can be spotted in vector and fringe 3D plots for all studied frequencies.
Simulation
To simulate the behavior of this filter (insertion and return loss...), we will create a Scattering Parameters study, and specify the relevant frequency range at which the antenna operates (in our case 100 frequencies uniformly distributed from 4 GHz to 8 GHz).
Solids and Materials
In figure 1, we have shown the discretized model of a dielectric circuit filter with coaxial input and output couplers. The two dielectric discs act as coupled resonators such that the entire device becomes a high-quality bandpass filter.
Load/ Restraint
Two ports are applied at the sides of the two coaxial couplers. The bottom faces of the air box are treated as Perfect Electric Boundaries. The structure profits the horizontal symmetry plane and therefore, we only need to model one half. Consequently, we should announce that to the HFWorks simulator by applying a PEMS boundary condition; whether it is a PECS or PEMS, depends on the orientation of the electric field near the boundary of symmetry. If tangential, then it is PEMS; if orthogonal then it is a PECS.
Meshing
The mesh has to be concentrated on the ports and PEC faces. Meshing these surfaces helps the solver refine its precision on the eddy parts, and take their particular forms into account.
Results
Various 3D and 2D plots are available to exploit, depending on the nature of the task and on which parameter the user is interested in. As we are dealing with a filter simulation, plotting the S21 parameter sounds like an intuitive task.
As mentioned at the beginning of this report, HFWorks plots curves for electrical parameters on 2D plots as well as on Smith Charts. The latter is more suitable for matching issues, and is more relevant when we deal with filter designs. We notice here that we have sharp pass-bands and that we reach great isolation outside the band.
The 3D plots for the scattering-parameters studies cover a wide range of parameters: the following two figures show the electric field distribution for two frequencies (one is inside the band and the other is outside the band)
The model can be simulated using the resonance solver of HFWorks too. We can detect as many modes as we wish. It is easy to derive such a study from the S-Parameter simulated study : HFWorks allows drag and drop erations to quickly set up the resonance simulation. The resonance solver takes into consideration the model's EM matrix and delivers the various Eigen mode solutions. The results match very well the former studies' results. We show here the result table :
References
[1] Microwave Filter Analysis Using a New 3-DFinite-Element Modal Frequency Method, John R. Brauer, Fellow, IEEE, and Gary C. Lizalek, Member, IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 45, NO. 5, MAY 1997
[2] John R. Brauer, Fellow, IEEE, and Gary C. Lizalek, member, IEEE " Microwave Filter Analysis Using a New 3-D Finite-Element Modal Frequency Method."IEEE Transactions on Microwave Theory and Techniques, Vol45, No. 5, pp.810-818, May 1997.
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Post time: Oct-25-2021
