Switchable Bandpass Filter Using Stepped-Impedance Resonators
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Solution Overview
Problem
Conventional switchable bandpass filters suffer from poor band selectivity and spurious responses due to wideband designs, leading to inadequate isolation in both ON and OFF states, and existing designs are either large in layout size or difficult to implement at high orders.
Innovation Solution
A switchable bandpass filter using stepped-impedance resonators loaded with diodes, where the diodes adjust resonance frequencies by changing bias conditions, allowing for flexible resonant frequency arrangement and spurious frequency rejection, integrating bandpass filtering and switching functionality into a single component.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If wideband switch design is used, then switching functionality is achieved, but band selectivity deteriorates
Solution Approach 1:
The patent combines the bandpass filter and switch into a single integrated structure where the stepped-impedance resonator serves dual purposes: providing filtering functionality through its resonant characteristics and switching functionality through diode loading. This merging eliminates the need for separate filter and switch components, achieving both band selectivity and switching capability in one device.
Solution Approach 2:
The patent introduces diodes as variable loading elements on the stepped-impedance resonator that can dynamically change the resonant frequency and impedance characteristics based on bias conditions. This dynamic adjustment allows the filter to switch between different operational states (ON/OFF) while maintaining sharp band selectivity through controlled resonance.
2Ease of manufacture
If conventional planar filter design is used, then fabrication ease is improved, but spurious responses worsen
Solution Approach 1:
The patent applies stepped-impedance sections with different characteristic impedances at different locations along the resonator structure. This local variation in impedance creates specific resonance conditions that suppress spurious responses while maintaining the desired passband characteristics, all within a planar fabrication-compatible structure.
Solution Approach 2:
The patent modifies the electrical parameters (impedance values and lengths) of different sections of the resonator to create a stepped-impedance profile. By carefully selecting these parameters, the design achieves sharp cutoff characteristics and suppresses upper stopband spurious responses while remaining compatible with standard printed circuit board fabrication techniques.
3Adaptability or versatility
If ring resonator with p-i-n diodes is used, then switchable filtering is achieved, but layout size increases
Solution Approach 1:
The patent divides the resonator into multiple stepped-impedance sections rather than using a continuous ring structure. This segmentation allows for more compact arrangement of the resonator elements and reduces the overall layout area while maintaining the switchable filtering functionality through diode loading on the segmented sections.
Solution Approach 2:
The patent transforms the traditional ring resonator geometry into a more compact planar configuration using stepped-impedance transmission lines. This dimensional reorganization maintains the resonant functionality while significantly reducing the layout footprint compared to conventional ring structures.
4Ease of operation
If quarter-wavelength resonators are used, then switching capability is achieved, but stopband rejection worsens
Solution Approach 1:
The patent changes the electrical length and impedance parameters of the resonator sections from conventional quarter-wavelength designs to optimized stepped-impedance configurations. This parameter optimization extends the stopband rejection beyond the immediate vicinity of the center frequency to cover wider frequency ranges in both ON and OFF states.
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
The solution achieves wide stopband rejection in the ON state and high isolation performance across multiple octaves in the OFF state, while maintaining a compact design, effectively addressing the limitations of previous switchable filters.
Implementation Method 1
stepped-impedance resonators loaded with diodes, where the diodes adjust resonance frequencies by changing bias conditions
Data Source
AI summary
A switchable bandpass filter includes a first stepped-impedance resonator, a second stepped-impedance resonator wirelessly coupled to the first stepped-impedance resonator, and a first diode connected to one end of the second stepped-impedance resonator.