Tunable Microwave Filter With Cascaded Subfilters

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Solution Overview

Problem

Existing microwave filters lack the ability to independently control center frequency and bandwidth, leading to unacceptable bandwidth changes when frequency is adjusted, which is critical for precise satellite communications, and conventional tuning methods increase complexity, weight, and cost.

Innovation Solution

A cascaded series of pseudo high pass and pseudo low pass subfilters with voltage-controlled capacitors allows for separate control of bandwidth and center frequency, maintaining a fixed bandwidth over a tunable range of frequencies by adjusting voltage inputs to the capacitors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If conventional tuning methods are used to adjust the center frequency of the filter, then the center frequency is tunable, but the bandwidth changes substantially which is unacceptable for satellite communications

Engineering Contradiction:

Improvecenter frequency tunabilityVSAvoidbandwidth control precision

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The filter is divided into multiple resonant circuits (at least three), each with its own voltage-controlled capacitor. This segmentation allows independent control of different frequency components, enabling separate tuning of center frequency and bandwidth through different voltage control strategies applied to different resonant circuits.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent uses voltage-controlled capacitors (varactors) to dynamically change the capacitance values in the resonant circuits. By applying different voltage levels to different capacitors, the system can independently adjust the center frequency and bandwidth parameters without affecting each other, resolving the trade-off between frequency tunability and bandwidth stability.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If additional microwave components are added to control bandwidth separately, then bandwidth control is improved, but the device complexity, volume, weight, and cost increase

Engineering Contradiction:

Improvebandwidth control precisionVSAvoidfilter structure complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The voltage-controlled capacitors serve dual functions: they control both the center frequency and bandwidth of the filter depending on which capacitor is adjusted. This multi-functionality eliminates the need for separate bandwidth control components, reducing overall device complexity while maintaining precise control over both parameters.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent merges the frequency control and bandwidth control functions into a single filter structure by using the existing resonant circuits and voltage-controlled capacitors for both purposes. This consolidation avoids adding separate microwave components for bandwidth control, thereby reducing complexity, volume, weight, and cost.

Inventive Principle:

Principle #5Merging (Combining)

3Manufacturing precision

If fixed low pass and high pass filters with wide bandwidth are used, then bandwidth control is achieved, but many resonator elements are required increasing volume, mass, and cost

Engineering Contradiction:

Improvebandwidth control precisionVSAvoidfilter mass

Core Design Contradiction:

Manufacturing precisionVSWeight of stationary object

Solution Approach 1:

The patent transforms fixed filters into dynamically controllable filters by incorporating voltage-controlled capacitors in each resonant circuit. This dynamic control allows the filter to achieve precise bandwidth control with fewer elements, as the electrical tuning capability replaces the need for multiple physical resonator elements that would be required in a fixed filter design.

Inventive Principle:

Principle #15Dynamics

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

This configuration enables precise control of bandwidth and frequency, reducing complexity and weight while maintaining constant bandwidth over a significant frequency range, suitable for satellite communications, with the ability to tune center frequency by 85% to 115% of a nominal frequency.

Implementation Method 1

each subfilter including at least one voltage-controlled capacitor. Tuning of the filter may be accomplished by adjusting a voltage input to one or more of the voltage-controlled capacitors

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS9019039B1Frequency and bandwidth tunable microwave filter

Publication Date: 2015.04.28 LANTERIS SPACE LLC

AI summary

An RF bandpass filter includes a cascaded series of a first subfilter and a second subfilter. Each subfilter includes a respective inverter, voltage-controlled capacitor and inductor. A first selected one of the first subfilter and the second subfilter is a pseudo low pass filter and a second selected one of the first subfilter and the second subfilter is a pseudo high pass filter. The RF bandpass filter is configured to separately control a bandwidth and center frequency of output RF energy. The bandwidth may be controlled to be substantially fixed over a significant substantial range. The center frequency and bandwidth are controlled by adjusting a voltage input to one or more of the voltage-controlled capacitors.