Ferrite Antenna With Parallel Ferromagnetic Rods for Impedance Matching
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Solution Overview
Problem
Ferrite antennas face challenges in achieving suitable impedance matching, particularly at 50 Ω, leading to reduced efficiency and limited frequency agility due to high reactive impedance and space constraints on ferromagnetic rods, which affects their performance across a wide range of frequencies.
Innovation Solution
A ferrite antenna design featuring a main resonant contour with a tuning system and a non-resonant secondary contour, where the secondary coil is electrically separated and wound around a distinct ferromagnetic rod, allowing magnetic coupling and enabling efficient impedance matching and multi-resonance, with adjustable capacitance and ferromagnetic rod positioning for frequency tuning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a tuning capacitor is used to reduce the reactive component of impedance, then the reactive part of the impedance disappears, but the impedance remains very high (tens-hundreds of kΩ)
Solution Approach 1:
The antenna is divided into two independent resonant contours, each with its own ferromagnetic rod and coil winding. The first contour operates at the tuning frequency with high impedance, while the second contour provides a second resonance at a different frequency with lower impedance, enabling impedance transformation and better matching to standardized impedances like 50 Ω.
Solution Approach 2:
The invention changes the operational parameters by introducing a second resonant frequency through an additional LC contour. This allows the antenna to operate at two different impedance states: high impedance at the first resonance and lower impedance at the second resonance, providing flexibility for impedance matching without sacrificing gain.
2Device complexity
If the number of turns of the winding is reduced to obtain a lower impedance, then the impedance decreases, but the gain of the antenna is reduced
Solution Approach 1:
The antenna system segments the winding function across two separate contours. The first contour maintains a high number of turns for high gain at the tuning frequency, while the second contour provides an alternative resonance path that allows impedance reduction without requiring a reduction in the number of turns of the main winding, thus preserving gain.
Solution Approach 2:
The second resonant contour acts as an intermediary mechanism that enables impedance transformation. By coupling the two contours through magnetic interaction between the ferromagnetic rods, the system can achieve lower effective impedance at the second resonance without reducing the number of turns in the main winding, thereby maintaining antenna gain.
3Ease of operation
If two windings are wound side by side on the same ferromagnetic rod, then impedance matching improves, but the maximum potential efficiency is reduced because the main contour cannot occupy the entire length of the ferromagnetic rod
Solution Approach 1:
Instead of placing two windings on the same ferromagnetic rod, the invention segments them onto two separate rods. This allows each rod to be fully utilized by its respective contour, maximizing the effective length and efficiency of the main contour while still achieving impedance matching through the coupled resonant system.
Solution Approach 2:
The invention transitions from a single-rod spatial arrangement to a multi-rod configuration, effectively using an additional spatial dimension. This allows both contours to have optimal winding lengths on their respective rods while maintaining magnetic coupling, thereby preserving the efficiency of the main contour and achieving impedance matching simultaneously.
4Ease of operation
If the two windings are wound above each other on the same ferromagnetic rod, then impedance matching is achieved, but the antenna quickly loses its second resonance
Solution Approach 1:
The invention segments the two windings onto separate ferromagnetic rods, which prevents the degradation of the second resonance that occurs when windings are stacked on the same rod. This segmentation maintains magnetic coupling sufficient for impedance matching while preserving the independence of each resonant contour, thereby maintaining frequency agility and the integrity of both resonances.
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 design achieves efficient impedance matching at 50 Ω, maximizes radiation efficiency, and extends the frequency band, allowing for high gain beyond the main resonance frequency, making it suitable for various applications including RFID systems and direction-finding functions.
Implementation Method 1
each main ferromagnetic rod and the secondary ferromagnetic rod are arranged parallel to each other so as to allow magnetic coupling of each main winding with the secondary winding, so as to create a second resonant frequency distinct from the tuning frequency
Data Source
Figure 1a~2c
Figure 3~5
Figure 6~8
AI summary
The invention relates to a ferrite antenna having at least one main contour, comprising at least a first coil, termed the main coil (1), at least one ferromagnetic rod, termed the main ferromagnetic rod (4), and a tuning system (3), each main coil (1) being wound around a main ferromagnetic rod (4) and connected to the tuning system (3) comprising a capacitor connected in parallel with the coil (1). The ferrite antenna is characterised in that it further comprises a non-resonant secondary contour, comprising a secondary coil (2) electrically separated from each main coil (1) and a secondary ferromagnetic rod (5) around which the secondary coil (2) is wound, and in that each main ferromagnetic rod (4) and the secondary ferromagnetic rod (5) are arranged in parallel with one another in such a way as to allow a magnetic coupling of each main coil (1) with the secondary coil (2).