Space-Time Modulated Band-Pass Filter for One-Way RF Propagation
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Solution Overview
Problem
Existing non-reciprocal circuits and devices, such as radar systems and isolators, rely on bulk magnetic materials that are not suitable for integrated chip designs, and nonmagnetic alternatives are needed for compact integration and efficient signal propagation in one direction.
Innovation Solution
A non-reciprocal band pass filter using a transmission line with finite unit cells, where the ratio of unit cell length to modulation signal wavelength is engineered to allow signal propagation in one direction while blocking it in the opposite direction, utilizing space-time modulation and varactors to control capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bulk magnetic materials are used to break spatial symmetry and control RF energy flow, then non-reciprocity is achieved, but device size increases and integration becomes difficult
Solution Approach 1:
The patent changes the fundamental parameter of material selection from bulk magnetic materials to nonmagnetic materials with engineered dispersion characteristics. By modifying the dispersion relation through periodic modulation and finite unit cell structures, the patent achieves non-reciprocity without relying on magnetic materials, thereby reducing device size and enabling integration.
Solution Approach 2:
The patent employs a composite structure consisting of periodically modulated transmission line segments with specific impedance variations. This composite structure creates engineered dispersion characteristics that enable non-reciprocal behavior, replacing the need for bulk magnetic materials while maintaining the desired RF energy flow control.
2Volume of moving object
If nonmagnetic materials are used for reciprocity breaking, then device size is reduced and integration is enabled, but achieving sufficient non-reciprocity becomes more difficult
Solution Approach 1:
The patent introduces dynamic modulation of the transmission line parameters through periodic variation of impedance along the transmission path. This dynamic structuring creates time-varying dispersion characteristics that produce strong non-reciprocal effects in nonmagnetic materials, compensating for the weaker intrinsic non-reciprocity compared to magnetic materials.
Solution Approach 2:
The patent applies periodic modulation to the transmission line impedance with a specific spatial period. This periodic action creates band structure effects and engineered dispersion relations that enhance non-reciprocal behavior, allowing sufficient isolation performance to be achieved using nonmagnetic materials with reduced device footprint.
3Device complexity
If continuous transmission line theory is used, then analysis is simplified, but dispersion effects and finite unit cell dimensions are neglected
Solution Approach 1:
The patent divides the continuous transmission line into discrete periodic segments with specific impedance characteristics. This segmentation allows the explicit inclusion of finite unit cell dimensions in the analysis, capturing dispersion effects that are neglected in continuous theory while maintaining manageable analytical complexity through periodic structure assumptions.
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
Achieves compact integration and efficient one-way signal propagation without bulky magnetic materials, enabling higher speed and power circuitry in integrated receivers.
Implementation Method 1
A non-reciprocal band pass filter including a transmission line having a plurality of repeating finite unit cells, where a ratio between a length of the unit cells and the wavelength of a modulation signal are selected to provide propagation modes that allow a transmission signal to propagate within the pass band along the transmission line in one direction, but prevent the transmission signal within that band from propagating along the transmission line in the opposite direction
Implementation Method 2
utilizing space-time modulation and varactors to control capacitance
Data Source
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Figure 6~7
AI summary
A non-reciprocal band pass filter including a transmission line having a plurality of repeating finite size unit cells, where each unit cell has a predetermined length and includes an inductor and a varactor. The filter also includes a signal source providing a transmission signal that propagates on the transmission line, and a modulation source providing a modulation signal that modulates the varactor. A ratio between the predetermined length of the unit cells and a frequency of the modulation signal is selected to provide propagation modes that allow the transmission signal to propagate along the transmission line in one direction in a controlled pass band, but prevent the transmission signal from propagating along the transmission line in the opposite direction in the controlled pass band.