Radio Frequency Filter Using Acoustic Impedance Elements
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Solution Overview
Problem
High frequency radio frequency filters face challenges in achieving reproducible band pass and notch or band rejection characteristics while minimizing physical space and addressing the variability in inductance values at high frequencies.
Innovation Solution
A radio filter design incorporating coupled transmission lines with acoustic impedance elements, such as SAW or FBAR devices, connected between a ground layer and transmission lines, which provides both band pass and stop band filtering functions without the need for discrete inductors, utilizing a combline structure on a piezoelectric substrate to enhance reproducibility and reduce space requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If discrete inductors are used in high frequency filters, then band pass and notch filtering functions can be achieved, but inductance values become variable and reproducibility deteriorates
Solution Approach 1:
The patent replaces discrete mechanical inductor components with an acoustic wave resonator that provides inductive functionality through acoustic wave propagation. The resonator is electrically connected between the transmission line and ground, substituting the need for separate inductor elements while maintaining the filtering function through acoustic resonance rather than magnetic inductance.
Solution Approach 2:
The acoustic wave resonator serves multiple functions simultaneously: it provides the inductive element for band pass filtering, creates the notch filtering function through its resonant characteristics, and acts as an impedance matching element. This multi-functionality eliminates the need for separate inductor and capacitor components, improving reproducibility by reducing the number of discrete elements.
2Reliability
If traditional LC-filter circuits are used, then filtering functions can be achieved, but physical space requirements increase
Solution Approach 1:
The patent merges the functions of multiple discrete LC-filter components into a single integrated acoustic wave resonator structure. The resonator combines inductive and capacitive elements in one component, and the transmission line structure integrates multiple filtering stages, reducing the overall physical footprint while maintaining filtering performance.
Solution Approach 2:
The patent transitions from a planar arrangement of discrete LC components to a three-dimensional acoustic wave resonator structure that utilizes vertical spacing and acoustic wave propagation paths. This dimensional transition allows compact integration of multiple filtering functions in a smaller footprint by exploiting the acoustic wave's interaction with the resonator's three-dimensional structure.
3Measurement precision
If acoustic resonators are used to create notch filters, then sharp notches with high Q-factor are achieved, but the filter structure becomes more complex
Solution Approach 1:
The patent extracts the notch filtering function from a separate component and integrates it directly into the acoustic wave resonator that already provides band pass filtering. By taking out the need for additional notch-filtering elements and incorporating the resonator's natural resonance to create the notch, the structure is simplified while maintaining sharp notch 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 solution achieves stable and reproducible high-frequency filtering with improved reproducibility and reduced physical space, effectively attenuating undesirable frequencies while maintaining desired signal bands, particularly beneficial for high-frequency applications like space communication.
Implementation Method 1
Another approach to obtaining notch filters based on Surface Acoustic Wave (SAW) devices have been explained in U.S. Pat. No. 4,126,837.
Implementation Method 2
It has been demonstrated that notches in the responses of such filters may be obtained using acoustic resonators in place of capacitors.
Implementation Method 3
utilizing a combline structure on a piezoelectric substrate to enhance reproducibility and reduce space requirements.
Data Source
AI summary
A radio filter has a band pass filter for passing a desired band of signal frequencies and a band stop filter for reducing the passing of a band of undesired signal frequencies. The filter comprises an input terminal, an output terminal, and a filter having a multiple of transmission lines arranged between said input and output terminal which filters input signals through said input terminal to pass signals of a given frequency band. A ground is connected to said transmission lines at first ends of said multiple of transmission lines and acoustic impedance elements are connected between said ground layer and second ends of said multiple transmission lines for providing a stop band filter function of the input signals, and whereby the input signal after band pass filtering and stop band filtering is provided at said output terminal.