Folded Cavity RF Filter With Notch Coupling for Thin PCB Layouts
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional radio frequency filters face challenges in size reduction due to the extension of resonators in the thickness direction and require additional conductive components for coupling, leading to increased weight and limited usability of both sides of the printed circuit board.
Innovation Solution
A filter design using a folding method to form a cavity with notch-forming portions, including L-notch and C-notch structures, which are formed inside the cavity to enable multi-pass coupling and reduce thickness while allowing frequency tuning on both sides of the passband.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If resonators are extended in the thickness direction inside the cavity, then resonance characteristics are improved, but the filter size in the thickness direction increases
Solution Approach 1:
The resonators are reconfigured to extend primarily in the lengthwise direction rather than the thickness direction. The folding method creates a compact three-dimensional structure where the resonant path is folded back on itself within the cavity, achieving effective resonance without increasing the filter's thickness dimension.
Solution Approach 2:
The resonator structure is nested within the cavity by folding the resonant element back on itself. The resonator extends from one end of the cavity, folds back through the cavity space, and connects to the other end, effectively nesting the resonant path within the available cavity volume without protruding in the thickness direction.
2Reliability
If additional conductive components are installed for coupling between resonators, then inductive and capacitive coupling characteristics are improved, but the filter weight increases
Solution Approach 1:
The coupling functions are merged into the resonator structure itself. The resonator is designed with integrated coupling sections that directly provide both inductive and capacitive coupling to adjacent resonators, eliminating the need for separate conductive coupling components.
Solution Approach 2:
The resonator structure serves multiple functions simultaneously: it provides resonance at the desired frequency, establishes inductive coupling with adjacent resonators through its conductive paths, and provides capacitive coupling through its geometric configuration. This multi-functionality eliminates the need for dedicated coupling components.
3Length of moving object
If ceramic filters are used to minimize thickness, then the filter thickness is reduced, but both sides of the printed circuit board cannot be utilized
Solution Approach 1:
The filter design transitions from a thin-film ceramic approach to a three-dimensional folded structure that achieves compactness through spatial folding rather than reducing thickness to minimal dimensions. This allows the filter to maintain a thickness that does not prevent dual-sided PCB utilization while still achieving overall size reduction.
Solution Approach 2:
The resonator is segmented into multiple sections that are folded and arranged within the cavity. This segmentation allows the resonant path to be distributed through the three-dimensional cavity space rather than requiring a single thick layer, enabling the filter to be thin enough for dual-sided PCB use while maintaining resonance characteristics.
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 design achieves a compact filter with improved frequency characteristics and enhanced usability of both sides of the main board by eliminating the need for ceramic filters and additional conductive components.
Implementation Method 1
a resonant element fixed inside the filter housing and including an input port terminal connected to the input port and an output port terminal connected to the output port, wherein the resonant element includes: a base portion disposed to be elongated in the lengthwise direction on a lower side of the cavity in a thickness direction; a resonant leg portion folded from the base portion to extend toward an upper side of the cavity in the thickness direction
Implementation Method 2
a notch-forming portion formed to extend in a predetermined direction from any one of the base portion, the resonant leg portion, or the resonant plate to enable multi-pass coupling
Implementation Method 3
a notch-forming portion, configured to form an L-notch portion through inductive coupling and a C-notch portion through capacitive coupling at both ends of a band-pass
Data Source
Figure 1
Figure 2
Figure 3(a)~3(c)
AI summary
The present disclosure relates to a filter for a communication device including: a notch-forming portion formed to extend in a predetermined direction from any one of resonant elements: a base portion, a resonant leg portion, or a resonant plate, particularly to enable multi-pass coupling, wherein at least the resonant elements are provided to be fixed to a filter housing after being manufactured from a single base material plate through press and folding processes, thereby reducing the complexity of the filter and enabling implementation of various filter functions.