Tunable All-Pass Bandstop Filter for Wideband Absorptive Rejection

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Solution Overview

Problem

Current bandstop filters lack the ability to provide an absorptive, electronically tunable solution with a wide tuning range, particularly over an octave bandwidth, and fail to simultaneously tune both rejection frequency and bandwidth, while also being bulky and slow in tuning speed.

Innovation Solution

A tunable bandstop filter design utilizing a pair of power dividers joined by two branches of all-pass filter networks, allowing for electrical control of the phase difference between the branches to achieve a wide tuning range, with the flexibility to control rejection bandwidth and featuring low insertion loss and high power handling, implemented on a planar monolithic substrate.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If YIG based tunable bandstop filters are used, then wideband tuning with minimal insertion loss is achieved, but the device becomes bulky and tuning speed becomes very slow

Engineering Contradiction:

Improveinsertion lossVSAvoidtuning speed

Core Design Contradiction:

Loss of energyVSSpeed

Solution Approach 1:

The patent replaces the mechanical YIG (Yttrium Iron Garnet) tuning mechanism with an electrical field-effect transistor (FET) based switching system. The FETs are controlled by digital signals to electronically switch between different resonator configurations, achieving fast tuning speeds comparable to digital switching while maintaining the absorptive bandstop filter performance with minimal insertion loss.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Adaptability or versatility

If YIG based tunable bandstop filters are used, then wideband tuning is achieved, but the device becomes bulky

Engineering Contradiction:

Improvetuning rangeVSAvoiddevice size

Core Design Contradiction:

Adaptability or versatilityVSVolume of moving object

Solution Approach 1:

The patent divides the bandstop filter into multiple independently controllable resonator sections, each with its own FET switching mechanism. This segmentation allows the filter to achieve wide tuning range by selectively activating different resonator segments while maintaining a compact planar structure suitable for integration on small substrates.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent transitions from the three-dimensional bulky YIG crystal structure to a two-dimensional planar microstrip resonator design. The resonators are implemented as flat conductive patterns on a substrate, enabling wide tuning range through electrical control while dramatically reducing the device volume and enabling high integration.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Adaptability or versatility

If conventional bandstop filters are used, then filtering is achieved, but the ability to electronically tune over an octave bandwidth is not provided

Engineering Contradiction:

Improveelectronic tuning capabilityVSAvoidfilter structure

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent designs a universal resonator structure that can operate across a wide frequency range by changing the effective electrical length through FET switching. The same physical resonator can be electronically reconfigured to different resonant frequencies, providing octave-bandwidth tuning capability without requiring multiple different filter structures.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 enables a bandstop filter with a rejection center frequency tuning ratio of more than 3.5:1, flexible bandwidth control, and low insertion loss, suitable for high integration and high-speed wireless applications, while being compact and efficient.

Implementation Method 1

electrical control of the phase difference between the branches to achieve a wide tuning range

Methodology Applied

Scientific EffectPhase shift:

Implementation Method 2

an input power divider for splitting the input signal and passing approximately half of the input signal power through each the branch of the all-pass filter networks, and an output power divider for recombining the signal power from each the branch

Methodology Applied

Scientific EffectSignal splitting and recombination:

Implementation Method 3

absorptive bandstop filter... to reject but absorbing selected frequencies

Methodology Applied

Scientific EffectAbsorption: Absorption (EM radiation)

Data Source

PatentUS8981873B2Absorptive tunable bandstop filter with wide tuning range and electrically tunable all-pass filter useful therein

Publication Date: 2015.03.17 HITTITE MICROWAVE LLC

AI summary

This invention features an absorptive tunable bandstop filter with a wide tuning range including first and second branches of all-pass filter networks, an input power divider for splitting the input signal and passing approximately half of the input signal power through each branch of the all-pass filter networks, and an output power combiner for recombining the signal power from each branch of the all-pass filter networks, at least one of the branches of the all-pass filter networks being electrically tunable to provide an approximately 180° phase difference with similar amplitudes of the split signal power to be recombined at the output power combiner for rejecting but substantially absorbing selected frequencies.