Variable Resonant Circuit Antenna Impedance Matching
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Solution Overview
Problem
Existing multiband antenna devices face challenges in maintaining impedance matching across different frequency bands, particularly when switching between low frequency bands and high frequency bands, leading to high return losses and inefficient operation.
Innovation Solution
An antenna device with a variable resonant circuit that switches between two resonance characteristics, allowing for impedance matching in both low frequency bands and maintaining matching in the high frequency band, achieved by inserting a variable resonant circuit between the feeding point and the ground conductor, which includes a switch between an LC series resonant circuit and an LC parallel resonant circuit, or an LC series resonant circuit, to adjust capacitance and inductance for optimal impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the resonance frequency of the reactance changing section is varied to switch the low frequency band, then the radiating element can operate in different low frequency bands, but the impedance matching in the high frequency band is affected and may be lost
Solution Approach 1:
The antenna device is divided into functionally independent sections: a reactance changing section for low frequency band switching and a matching section for high frequency band impedance matching. Each section operates independently with its own resonant circuit, allowing low frequency band switching without affecting high frequency band performance.
Solution Approach 2:
The matching section acts as an intermediary between the feeding circuit and the reactance changing section. It provides impedance transformation and matching specifically for the high frequency band, isolating the high frequency performance from variations in the reactance changing section.
2Adaptability or versatility
If a reactance changing section and matching section are both defined by parallel resonant circuits, then multiple bands can be supported, but the complexity of the circuit increases and precise control of resonance frequencies becomes difficult
Solution Approach 1:
Different resonant circuit configurations are applied to different sections based on their specific functions: the reactance changing section uses a parallel resonant circuit for low frequency band switching, while the matching section uses a series resonant circuit for high frequency band impedance matching. This localized optimization simplifies each section's design.
Solution Approach 2:
The invention changes the circuit configuration parameter from both parallel resonant circuits to a combination of parallel and series resonant circuits. This parameter change simplifies the overall circuit complexity while maintaining multiband operation capability through independent resonance frequency control.
3Adaptability or versatility
If the radiating element operates in multiple low frequency bands by varying resonance frequency, then band selection is achieved, but return loss increases in non-selected bands making efficient operation difficult
Solution Approach 1:
The reactance changing section dynamically changes its resonance frequency to match the desired low frequency band, while the matching section remains tuned for the high frequency band. This dynamic adjustment allows efficient operation in the selected band while minimizing return loss in non-selected bands through proper impedance matching.
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 solution ensures sufficient impedance matching in both low frequency bands and maintains low return losses in the high frequency band, allowing the antenna device to operate efficiently across the desired frequency ranges without the need for additional matching circuits.
Implementation Method 1
The variable resonant circuit switches between at least two resonance characteristics, a first resonance characteristic and a second resonance characteristic
Implementation Method 2
including a switch between an LC series resonant circuit and an LC parallel resonant circuit, or an LC series resonant circuit
Implementation Method 3
including a switch between an LC series resonant circuit and an LC parallel resonant circuit
Implementation Method 4
The variable resonant circuit may include an inductor and a variable capacitor connected in series to each other, and may switch between the first resonance characteristic and the second resonance characteristic by varying a capacitance of the variable capacitor
Data Source
AI summary
A variable resonant circuit is inserted between a feeding point of a radiating element and a ground conductor. When the variable resonant circuit is not inserted, an input impedance of the radiating element is lower than about 50Ω and capacitive in a first low frequency band, lower than about 50Ω and inductive in a second low frequency band, and close to about 50Ω in a high frequency band. When the variable resonant circuit exhibits a first resonance characteristic, the variable resonant circuit is inductive in the first low frequency band, and its impedance in the high frequency band is higher than that in the first low frequency band. When the variable resonant circuit exhibits a second resonance characteristic, the variable resonant circuit is capacitive in the second low frequency band, and its impedance in the high frequency band is higher than that in the second low frequency band.