Compact Circular Polarized Antenna With Cavity For RFID Systems
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Solution Overview
Problem
Current circularly polarized antennas for RFID systems face challenges in achieving compact size, low VSWR, wide frequency bandwidth, and high front-to-back ratio while maintaining good polarization quality and axial ratio, making them unsuitable for portable and wearable applications.
Innovation Solution
The design incorporates elongated side radiating elements oriented at angles between 10° and 80° from a perpendicular plane, with a cavity defined by non-radio frequency-transparent sidewalls, and a feeding circuit that distributes signals with equal amplitudes and specific phases to concentrate energy in the boresight direction, reducing back radiation and increasing realized gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional circularly polarized antennas are designed to be compact, then the antenna size is reduced, but the frequency bandwidth and radiation efficiency deteriorate
Solution Approach 1:
The antenna is segmented into multiple radiating elements (first and second radiating elements) arranged in a specific geometric configuration. This segmentation allows each element to contribute to different aspects of the radiation pattern, enabling compact size while maintaining wide bandwidth through the combined effect of multiple elements with controlled orientations and feed phases
Solution Approach 2:
The patent transitions from planar antenna designs to three-dimensional configurations by orienting radiating elements at specific angles (e.g., 45 degrees) relative to the substrate normal and incorporating vertical spacing. This dimensional transition enables the antenna to achieve wide bandwidth and circular polarization in a compact volume by utilizing spatial distribution of current paths
2Adaptability or versatility
If the antenna is designed for wide frequency bandwidth, then the frequency range is expanded, but the antenna size increases
Solution Approach 1:
The antenna employs asymmetric feeding networks with different transmission line lengths and impedance transformations for each radiating element. This asymmetry, combined with specific element orientations, creates frequency-independent radiation characteristics that achieve wide bandwidth without requiring large antenna dimensions, as the asymmetric current distribution maintains consistent radiation patterns across frequency variations
3Reliability
If the antenna achieves low VSWR, then the impedance matching is improved, but the structural complexity increases
Solution Approach 1:
The patent achieves low VSWR by carefully controlling electrical parameters including transmission line characteristic impedances (e.g., 50 ohms, 70.7 ohms), line lengths (e.g., λ/8, λ/4 at center frequency), and radiating element dimensions. These parameter optimizations provide broadband impedance matching without requiring complex matching networks, as the inherent distributed capacitance and inductance of the compact 3D structure provide natural broadband matching
4Reliability
If the antenna concentrates energy in boresight direction, then the front-to-back ratio is improved, but the radiation pattern becomes more directional
Solution Approach 1:
The antenna design achieves multiple functions simultaneously: the specific geometric configuration and phase feeding of radiating elements create constructive interference in the boresight direction for high front-to-back ratio, while the circular polarization and broadband characteristics maintain versatility for RFID applications. The cavity structure provides both directional focusing and broadband operation through its resonant modes
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 enhances the antenna's ability to concentrate energy in the preferred direction, achieving higher realized gain and improved front-to-back ratio, while maintaining low VSWR and wide frequency bandwidth, making it suitable for portable and wearable RFID systems.
Implementation Method 1
a feeding circuit, each output of the feeding circuit being electrically connected to a corresponding one of the radiating elements
Implementation Method 2
a cavity defined by at least one non-radio frequency-transparent sidewall
Data Source
AI summary
According to one embodiment, an antenna comprises a plurality of elongated side radiating elements having longitudinal axes oriented at angles of between about 10° and about 80° from a line perpendicular to an imaginary base plane extending across ends of the side radiating elements, and a cavity positioned between the side radiating elements defined by at least one non-radio frequency-transparent sidewall. In another embodiment, a system comprises a plurality of elongated side radiating elements each lying along a unique side plane and having longitudinal axes oriented at angles of between about 10° and about 80° from a line perpendicular to an imaginary base plane extending across ends of the side radiating elements, and a cavity being positioned between the side radiating elements defined by at least one non-radio frequency-transparent sidewall, wherein the at least one sidewall has sides each lying along a plane about parallel to the unique side plane.