Microstrip Filter Harmonic Suppression
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Solution Overview
Problem
Traditional parallel-coupled microstrip bandpass filters suffer from spurious passbands at harmonics of the center frequency, limiting their use in broadband communication systems, and there is a need for compact, reliable, and efficient filters that can suppress these harmonics without increasing complexity or size.
Innovation Solution
Incorporating half-wavelength microstrip resonators strategically positioned relative to other resonators to enhance attenuation in specific frequency ranges, allowing for the suppression of second and third harmonic passbands without altering the filter's size or complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional parallel-coupled microstrip bandpass filters are used, then the filter structure is simple and compact, but spurious passbands appear at harmonics of the center frequency
Solution Approach 1:
The filter is divided into multiple resonator sections with different electrical path lengths. The first resonator has a different even-mode electrical path length than odd-mode electrical path length, creating distinct frequency responses for different modes. This segmentation allows independent control of passband and stopband characteristics without increasing overall structural complexity
Solution Approach 2:
Different resonators are designed with specific local characteristics - the first resonator has asymmetric coupling for fundamental mode suppression, while the second resonator has specific electrical path length ratios to suppress second harmonics. Each resonator section has optimized local properties to achieve global spurious passband suppression
2Reliability
If filters are designed to attenuate harmonic frequency ranges, then spurious passbands are reduced, but the filter size increases
Solution Approach 1:
The resonators utilize dynamic electromagnetic field distribution at different frequencies. By designing resonators with specific electrical path length ratios (e.g., 2:1 ratio between fundamental and second harmonic wavelengths), the filter dynamically responds to different frequency components, achieving high attenuation at harmonics while maintaining compact physical dimensions at the fundamental frequency
3Reliability
If multiple resonators with different electrical path lengths are used, then harmonic suppression is achieved, but the device complexity increases
Solution Approach 1:
Each resonator section serves multiple functions simultaneously - the first resonator both passes the fundamental frequency and suppresses the second harmonic through its asymmetric coupling structure. The second resonator provides both bandpass filtering and second harmonic rejection. This multi-functionality reduces the need for additional dedicated suppression elements, maintaining device simplicity
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 integration of half-wavelength resonators significantly increases attenuation in targeted frequency ranges, improving filter performance by reducing spurious signals while maintaining the bandpass characteristics, resulting in a more efficient and compact filter design scalable for various microwave applications.
Implementation Method 1
a first microstrip resonator operatively connected to a first feed point, a second microstrip resonator operatively connected to a second feed point, and a third microstrip resonator operatively connected to the first or second resonator wherein the third resonator is a half wavelength (1/2λ) resonator
Data Source
AI summary
An apparatus and method for attenuating selected frequency bands in a microstrip filter having a plurality of microstrip resonators. The filter comprises plural resonators, a first of the plural resonators is operatively connected to a first feed point and a second of the plural resonators is operatively connected to a second feed point. A third of the plural resonators is a half wavelength resonator and may be operatively connected to the first, second and/or other plural resonators. The third resonator may also comprise a plurality of resonators whereby the position and number of the third resonator is a function of a predetermined rejected frequency range.