Fast Modeling of a Transmission Line Low-Pass Filter
Application ID: 41681
One way to design a filter is to use the element values of well-known filter prototypes, such as maximally flat or equal-ripple low-pass filters. It is easier to fabricate a distributed element filter on a microwave substrate than a lumped element filter, since it is cumbersome to find off-the-shelf capacitors and inductors that are exactly matched to the frequency-scaled element values of the filter prototype.
This tutorial model demonstrates the design process of a distributed element filter using Richard’s transformation, Kuroda’s identity, and the Transmission Line interface. This approach is very fast compared with solving Maxwell’s equations in 3D. The model simulates a three-element 0.5-dB equal-ripple low-pass filter that has a cutoff frequency at 4 GHz. The resulting S-parameter plot shows a low-pass frequency response that is also periodically observed at a higher frequency range.
This model example illustrates applications of this type that would nominally be built using the following products:
however, additional products may be required to completely define and model it. Furthermore, this example may also be defined and modeled using components from the following product combinations:
The combination of COMSOL® products required to model your application depends on several factors and may include boundary conditions, material properties, physics interfaces, and part libraries. Particular functionality may be common to several products. To determine the right combination of products for your modeling needs, review the Specification Chart and make use of a free evaluation license. The COMSOL Sales and Support teams are available for answering any questions you may have regarding this.