Transmission Line (TL)
In our previous article, we talked about the parasitic capacitance and inductance of circuits designed in lumped element. With majority of device and applications operating in high frequencies, especially with the introduction of 5G at millimeter wave, it is unfeasible to design filters using lumped elements. This is where transmission line type filters come in. Another name for it is called distributed line filters. Whereas the characteristic of the device are concentrated (lumped) in components such as inductors and capacitors for lumped filters, distributed have the characteristic distributed evenly across the whole transmission line. The design concept of distributed basically revolves around manipulating a transmission line by introducing gaps and bends that will impact the wave propagation through the line.
Filter designs usually starts in the lumped element, which can be synthesized from the transfer functions. Transfer functions are basically mathematical models which define a type of filter. By using the transfer functions, a filter can be designed that will manifest the characteristic of the transfer functions. Talking about translating something invisible such as math to something tangible like a filter! The Richard’s Transformation is the theory that will transform a lumped filter to a distributed line filter.
In this week article, watch this video on how we design a lumped lowpass filter and transform it into a transmission line filter using Richard’s Transformation. We are sure this video will provide you some insight on how to design your own transmission line filter! Who knows, maybe with the information you learnt, you might wanna join a rewarding design challenge?