Absorptive Coupled-Line Bandpass Filter Design
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Solution Overview
Problem
Existing reflectionless bandpass filters face challenges such as limited bandwidth, large circuit size, high insertion loss, and absorptive behavior limited to a specific frequency range, particularly when aiming for well-matched input and output ports.
Innovation Solution
The design of an absorptive coupled-line bandpass filter with absorptive stubs and a coupled-line bandpass section comprising parallel strip line resonators, which appear as open circuits at the center frequency and matched loads outside the passband to absorb out-of-band signals, along with cross-coupling for enhanced signal cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional reflective-type filters are used to achieve out-of-band rejection, then stopband signals are rejected through impedance mismatch, but reflection signals deteriorate the performance of adjacent non-linear devices
Solution Approach 1:
The patent converts the harmful reflected signals into beneficial absorbed signals by transforming the conventional reflective filter structure into an absorptive filter structure. The filter uses resistive loading to dissipate out-of-band signals as heat, converting the harmful reflection into a beneficial absorption effect that protects adjacent devices while maintaining filtering functionality.
Solution Approach 2:
The patent introduces an intermediary absorptive mechanism (resistive loading) between the filter and adjacent devices. This intermediary absorbs the reflected signals before they can reach and deteriorate adjacent non-linear devices, acting as a buffer that protects the system while maintaining signal integrity.
2Object-affected harmful factors
If non-reciprocal devices such as isolators or circulators are inserted to re-direct reflected signals, then reflection impact is reduced, but the devices become bulky, expensive, bandwidth limited, and difficult to integrate
Solution Approach 1:
The patent extracts the non-reciprocal devices (isolators, circulators) from the filter structure and replaces them with a planar absorptive mechanism. By removing these bulky three-dimensional components and substituting them with a two-dimensional resistive-loaded filter structure, the patent achieves the same reflection mitigation function with significantly reduced size and improved integrability.
Solution Approach 2:
The patent substitutes the mechanical/non-reciprocal device system with an electrical/resistive system. Instead of using physical isolators or circulators that require complex mechanical or magnetic structures, the patent uses resistive loading to achieve signal absorption, replacing a mechanical system with an electrical field-based solution that is more compact and easier to integrate.
3Object-affected harmful factors
If existing reflectionless bandpass filter designs are used, then absorptive behavior is achieved, but bandwidth is limited, circuit size is large, and insertion loss is high
Solution Approach 1:
The patent applies local quality by implementing resistive loading only at specific locations within the filter structure (at the resonant elements) rather than throughout the entire circuit. This localized absorption approach achieves the necessary out-of-band rejection while minimizing the impact on passband performance, thereby reducing insertion loss and maintaining wider bandwidth compared to uniform absorptive designs.
Solution Approach 2:
The patent uses partial action by applying absorption only where necessary (at the resonant elements and out-of-band frequencies) rather than excessive absorption across all frequencies. This selective absorptive approach maintains good impedance matching in the passband while providing effective rejection in the stopband, avoiding the excessive insertion loss that would result from uniform absorptive loading throughout the entire filter.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design achieves improved passband flatness, increased out-of-band rejection, and good impedance matching across both in-band and out-of-band frequencies, addressing the limitations of existing filters by providing a compact, high-order quasi-reflectionless filter with enhanced performance.
Implementation Method 1
the non-transmitted stopband signals in a reflectionless filter are dissipated within the filter itself
Implementation Method 2
the first and second absorptive stubs appear as matched loads to ground and contribute to absorption of out-of-band signals
Implementation Method 3
the coupled-line bandpass section comprises a set of one or more parallel strip line resonators
Data Source
AI summary
The disclosed embodiments provide an absorptive coupled-line bandpass filter. This bandpass filter includes a first port, which is coupled to a first absorptive stub, and a second port, which is coupled to a second absorptive stub. The bandpass filter also includes a coupled-line bandpass section coupled between the first and second ports, wherein the coupled-line bandpass section comprises a set of one or more parallel strip line resonators, which are coupled together in series and are coupled to the first and second ports through overlapping coupled-line sections, wherein at a center frequency of a passband for the absorptive coupled-line bandpass filter, the first and second absorptive stubs appear as open circuits, and outside of the passband, the first and second absorptive stubs appear as matched loads to ground and contribute to absorption of out-of-band signals.