Tunable Bandpass Filter Harmonic Suppression
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Solution Overview
Problem
Conventional microwave filters are ineffective in suppressing second, third, and fourth harmonic signals, and require additional lowpass filters that increase size and signal loss, or use multiple filters for different pass frequencies, which is inefficient and expensive.
Innovation Solution
A tunable bandpass filter with a dielectric substrate, conductive ground plane, and microstrip conductive trace pattern featuring T-shaped and TL-shaped conductor portions, varactor diodes, and bias control circuitry to adjust impedance and phase velocity, or a piezoelectric transducer to change the effective dielectric constant, allowing for harmonic suppression and frequency tuning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a lowpass filter is added at the two ends of a bandpass filter to suppress harmonic signals, then the suppression of harmonics is improved, but the filter structure becomes bigger and signal loss increases
Solution Approach 1:
The patent combines the bandpass filter and lowpass filter functions into a single integrated filter structure. The microstrip transmission line is designed with specific impedance transformations that simultaneously achieve bandpass filtering at the fundamental frequency and lowpass filtering to suppress harmonics, eliminating the need for separate filter components and reducing overall size.
Solution Approach 2:
The filter structure is designed to perform multiple functions: it acts as a bandpass filter for the fundamental frequency while simultaneously functioning as a lowpass filter for harmonic suppression. The impedance transformation section enables the same structure to provide both filtering functions, making the filter multi-functional and reducing the need for additional components.
2Object-generated harmful factors
If a lowpass filter is added at the two ends of a bandpass filter to suppress harmonic signals, then the suppression of harmonics is improved, but signal loss increases
Solution Approach 1:
The patent combines the bandpass filter and lowpass filter functions into a single integrated filter structure. The microstrip transmission line is designed with specific impedance transformations that simultaneously achieve bandpass filtering at the fundamental frequency and lowpass filtering to suppress harmonics, eliminating the need for separate filter components and reducing overall size.
Solution Approach 2:
The patent uses impedance transformation along the microstrip transmission line to achieve different filtering functions at different frequency ranges. By carefully controlling the characteristic impedance and physical dimensions of the transmission line sections, the filter achieves effective harmonic suppression while maintaining low insertion loss for the fundamental frequency.
3Adaptability or versatility
If multiple separate filters are used for different pass frequencies, then the need for frequency tuning is met, but the system becomes more expensive and inefficient
Solution Approach 1:
The patent employs varactor diodes that can be electrically tuned to change the resonant frequency of the filter. This dynamic tuning capability allows a single filter structure to operate at multiple different pass frequencies by adjusting the capacitance of the varactor diodes through applied voltage, replacing the need for multiple fixed-frequency filters.
Solution Approach 2:
The filter structure is designed to perform multiple functions: it acts as a bandpass filter for the fundamental frequency while simultaneously functioning as a lowpass filter for harmonic suppression. The impedance transformation section enables the same structure to provide both filtering functions, making the filter multi-functional and reducing the need for additional components.
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 tunable bandpass filter effectively suppresses harmonics with low loss and high return loss, providing a wide tuning range and compact design, reducing the need for multiple filters and minimizing signal degradation across settings.
Implementation Method 1
a piezoelectric transducer attached to the tunable substrate, wherein the tunable substrate is configured to move when a voltage is applied to the piezoelectric transducer
Implementation Method 2
at least one varactor diode coupled to a first T-shaped conductor portion of the series of T-shaped conductor portions and to the conductive ground plane, and bias control circuitry coupled to the first T-shaped conductor portion, wherein the bias control circuitry is configured to control the at least one varactor diode
Data Source
AI summary
Tunable bandpass filters are provided. In one embodiment, the invention relates to a tunable bandpass filter including a dielectric substrate having a first surface opposite to a second surface, a conductive ground plane disposed on the first surface, a microstrip conductive trace pattern disposed on the second surface, the trace pattern defining a phase velocity compensation transmission line section including a series of spaced alternating T-shaped conductor portions, at least one varactor diode coupled to a first T-shaped conductor portion of the series of T-shaped conductor portions and to the conductive ground plane, and bias control circuitry coupled to the first T-shaped conductor portion, wherein the bias control circuitry is configured to control the at least one varactor diode.