Transmission Line Reflectionless Filters for Absorptive Stop-Band Rejection
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Solution Overview
Problem
Conventional filters reflect unwanted frequency components back to the source, leading to harmful interactions and limitations in frequency range, especially when trying to implement absorptive filter designs using transmission lines.
Innovation Solution
A reflectionless electronic filter design using a symmetric two-port circuit with transmission lines and lossy elements, where even-mode and odd-mode equivalent circuits are duals of each other, allowing for conversion from lumped element prototypes to transmission line form using Richard's Transformations and Kuroda's Identities, facilitating easier manufacturing and extended frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional filters are used to reject unwanted frequency components, then filtering function is achieved, but harmful interactions occur due to signal reflection
Solution Approach 1:
The patent converts the harmful reflected signals into beneficial absorbed energy by using lossy elements (resistors) in the filter structure. The unwanted frequency components that would normally be reflected back to the source are instead dissipated as heat in the lossy elements, eliminating harmful interactions while maintaining the filtering function.
Solution Approach 2:
The patent introduces lossy elements as intermediary components between the signal paths. These elements act as mediators that absorb the unwanted signals before they can cause harmful interactions, effectively decoupling the filtering function from the harmful reflection effect.
2Object-generated harmful factors
If absorptive filter topology is used to absorb unwanted signals, then harmful interactions are reduced, but frequency range is limited to cm-wave and below
Solution Approach 1:
The patent replaces lumped element mechanical structures with transmission line structures. This substitution enables the absorptive filter topology to operate at higher frequencies (submillimeter-waves) because transmission lines maintain their distributed parameter characteristics at higher frequencies where lumped elements would fail due to parasitic effects.
Solution Approach 2:
The patent changes the fundamental parameters of the filter structure by transitioning from lumped elements to transmission lines. This parameter change includes using distributed inductance and capacitance along the transmission lines instead of discrete lumped elements, which allows the filter to maintain its absorptive characteristics at much higher frequencies.
3Speed
If transmission line form is used for absorptive filters, then frequency range is extended, but manufacturing complexity increases
Solution Approach 1:
The patent segments the transmission line structure into modular sections with standardized configurations. Each section can be independently designed and manufactured, then assembled into the complete filter. This segmentation reduces manufacturing complexity by breaking down the complex transmission line network into manageable, repeatable units.
Solution Approach 2:
The patent employs nested transmission line structures where smaller transmission line sections are embedded within larger structural frameworks. This nesting approach allows for compact integration of multiple filter functions within a single manufactured component, reducing overall manufacturing complexity while maintaining extended frequency range capabilities.
Data Source
AI summary
Reflectionless transmission line filters, as well as a method for designing such filters is disclosed. These filters preferably function by absorbing the stop-band portion of the spectrum rather than reflecting it back to the source, which has significant advantages in many different applications. The insertion of additional transmission line sections that change the phase response of the circuit without altering the amplitude response preferably allows follow-up transmission line identities to be applied in order to arrive at a more easily manufacturable filter topology. This facilitates their application over a higher frequency range the solely lumped-element circuits.