CST – Computer Simulation Technology

Modal Analysis of a Dielectric 2 Port Filter

The discretized model of a dielectric two circuit filter with coaxial input and output couplers is shown. The two dielectric discs act as coupled resonators such that the entire device becomes a high quality band pass filter. This device has been calculated by using the Eigenmode Solver of CST MICROWAVE STUDIO® (CST MWS) together with Modal Analysis. In combination with the transient solver and AR filter analysis it is an ideal tool for filter design.

Figure 1: Filter structure

View of the filter structure. Purple: Dielectric discs (permittivity of 38). Blue: Metal parts. Light gray: Resonator chamber, filled with air.

Figure 2: S-Parameters

S-Parameters calculated with Modal Analysis in the band pass region. Calculation time: 2 minutes and 40 seconds on a Pentium PII 400 MHz.

Figure 3: 3D vector plot of the first mode (magnetic field) at 4.079 GHz...

Figure 4: 3D vector plot of the second mode (magnetic field) at 4.079 GHz

Figure 5: 3D vector plot of the third mode (magnetic field) at 4.577 GHz

This mode is related to the first peak in the spectrum shown above. Please notify, that the S-Parameters have been calculated with external coupling, whereas the modes have been calculated without external coupling. This explains the frequency shift of approx. 20 MHz.

Figure 6: 3D vector plot of the fourth mode (magnetic field) at 4.604 GHz

It is related to the second peak of the spectrum shown above. Again the frequency shift of approx. 20 MHz has been caused by external coupling.

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