RFID Tag Notch Filter Using Printed Transmission Line
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Solution Overview
Problem
RFID tags used in harsh rail environments fail due to high power air-traffic control radar signals, requiring costly limiter diodes and discrete filters to protect against high power microwaves, leading to increased production costs.
Innovation Solution
A notch filter with a printed transmission line length is used as a shunt component, providing high impedance at the operating frequency (around 915 MHz) and low impedance at the stop-band frequency (1300 MHz), connected between the antenna and the matching circuit to suppress the 1300 MHz signal without significant cost increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If limiter diodes and discrete filters are used to protect RFID tags from high power radar signals, then reliability is improved, but manufacturing cost increases
Solution Approach 1:
The patent combines the filtering function with the existing transmission line structure by creating a notch filter using printed circuit board traces. This integrates the protective function into the existing antenna matching circuit rather than adding separate discrete components, thereby reducing manufacturing cost while maintaining protection against high power radar signals at 1300 MHz
Solution Approach 2:
The patent replaces expensive limiter diodes and discrete filter components with a low-cost printed transmission line notch filter that can be manufactured using standard PCB techniques. This significantly reduces the bill of materials cost while providing the necessary protection function
2Reliability
If discrete component band pass filter is used to protect RFID tags, then protection effectiveness is improved, but device complexity increases
Solution Approach 1:
The patent merges the filter function with the transmission line structure used in the antenna matching circuit. The notch filter is implemented using printed circuit board traces that are integrated into the existing circuit layout, eliminating the need for separate discrete filter components and reducing overall device complexity
Solution Approach 2:
The transmission line structure serves dual purposes: it provides the necessary impedance matching for the antenna while simultaneously functioning as a notch filter to protect against radar signals. This multi-functionality reduces the total number of components and simplifies the overall device design
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 notch filter effectively attenuates the 1300 MHz signal, ensuring RFID tag functionality at the desired frequency band while reducing production costs by eliminating the need for costly limiter diodes and discrete filters.
Implementation Method 1
The transmission line for this invention strays from conventional approaches by using a transmission line length determined such that the filter impedance is very high at the operating frequency range and very low at the stop frequency range
Implementation Method 2
a notch filter with a printed transmission line length is used as a shunt component, providing high impedance at the operating frequency (around 915 MHz) and low impedance at the stop-band frequency (1300 MHz)
Data Source
AI summary
A transponder includes a notch filter to suppress the 1300 MHz at minimal product cost increase. The notch filter utilizes a printed transmission line length adjusted to a correct length. This notch filter will connect to the antenna matching circuit at a junction between the antenna and an ASIC as a shunt component with high impedance (e.g., greater than 500 Ohms) at 915 MHz and low impedance (e.g., less than 10 Ohms) at 1300 MHz. Since the operating impedance of the junction is about 200 ohms, the 915 MHz signal from the antenna will feed the ASIC without any attenuation with a high shunt impedance component, while the 1300 MHz signal will be attenuated significantly by a low shunt impedance component. The transponder is applicable for all types of RFID tags (e.g., passive, semi-passive, active, read only, read-write, read first, tag-talk first) and is well suited for tags operating at radio frequencies, including microwave frequencies (e.g., 902 MHz to 928 MHz) in the U.S.