Tunable Bandpass Filter With Constant Absolute Bandwidth
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Solution Overview
Problem
Conventional 3D microwave filters require multiple bandpass filters for different frequency bands, leading to size and logistical challenges in wireless base stations, and existing tunable filters face issues with maintaining constant bandwidth and loss performance due to varying inter-resonator and input/output coupling.
Innovation Solution
A tunable bandpass filter design using tunable resonators with mechanical or piezoelectric motors, coupled with balanced electromagnetic coupling structures that do not require additional tuning elements, maintaining constant absolute bandwidth across the tuning range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional bandpass filters are installed for each frequency band, then each frequency band can be suppressed independently, but the base station size increases and hardware resources are not efficiently managed
Solution Approach 1:
The patent implements a single tunable bandpass filter that can operate across multiple frequency bands by adjusting its center frequency. The filter is designed with adjustable resonators that can be tuned to different frequencies, allowing one filter to replace multiple fixed-frequency filters. This multi-functional approach enables the base station to support different wireless standards and frequency bands without increasing hardware quantity or physical size.
2Reliability
If tuning elements are added to control inter-resonator and input/output coupling, then bandwidth can be maintained, but device complexity and design difficulty increase significantly
Solution Approach 1:
The patent applies different design approaches to different parts of the filter system. The resonators are made fully adjustable with tuning elements to maintain center frequency, while the inter-resonator and input/output coupling structures are designed with fixed geometries that inherently maintain constant coupling characteristics. This localized differentiation allows bandwidth constancy to be achieved without adding complex tuning mechanisms to the coupling structures.
Solution Approach 2:
The coupling structures are designed with specific geometric configurations that automatically maintain constant coupling values across the tuning range. The inter-resonator coupling structures use optimized spacing and orientations, while input/output coupling structures use specifically designed probe positions and lengths. These self-adjusting geometric designs eliminate the need for additional tuning elements in the coupling paths.
3Device complexity
If tuning elements are used for resonators only, then device complexity is reduced, but inter-resonator and input/output coupling variation causes bandwidth deterioration
Solution Approach 1:
The patent changes the geometric parameters of the coupling structures to achieve frequency-independent coupling. The inter-resonator coupling structures are designed with specific spacing and orientation parameters that compensate for frequency variations. The input/output coupling structures use optimized probe lengths and positions that maintain constant coupling coefficients across the tuning range. These parameter optimizations allow the system to maintain constant bandwidth without requiring active tuning of the coupling structures.
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 allows for a compact, cost-effective, and efficient filter with a wide tuning range and constant bandwidth, reducing the number of filter elements and enabling easy upgrades for future wireless standards without adding new hardware.
Implementation Method 1
tunable resonators with tuning screws or piezoelectric motors as the tuning elements
Implementation Method 2
tuning screws or piezoelectric motors as the tuning elements
Implementation Method 3
inter-resonator and input/output coupling structures that do not require any tuning elements
Data Source
AI summary
A tunable bandpass filter to provide a constant absolute bandwidth across the entire tuning range. The filter comprises of a plurality of tunable resonators, each having an enclosure. A resonating structure extending upwardly from the bottom surface of the enclosure and a tuning screw with a flat head extending downwardly from the top surface of the enclosure, wherein the resonating structure and the flat head of the screw face each other and form a gap. The height of the tuning screw can be adjusted to change the gap between the resonating structure and the flat head. The adjustable gap of the present filter allows for tunable filter operation.