Miniaturized Half-Wave Balun Using Capacitive Loading
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Solution Overview
Problem
Conventional half-wave baluns are too large for commercial cellular and W-LAN applications, and existing compact balun designs, such as the LC balun, suffer from high insertion loss and unsuitable common mode response, making them inadequate for applications requiring high signal-to-noise ratios and compact form factors.
Innovation Solution
A miniaturized half-wave balun is designed using a combination of transmission lines and capacitors, allowing for fabrication with high dielectric constant materials and enabling a DC bias to be applied to both signal carrying terminals, resulting in a significant reduction of common mode response and improved differential mode performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional half-wave balun is used, then the differential mode signal conversion is achieved, but the device size becomes too large for commercial applications
Solution Approach 1:
The patent changes the electrical length parameter of transmission line sections from the conventional 90 degrees to substantially less than 90 degrees (e.g., 45 degrees), enabling miniaturization while maintaining balun functionality through capacitive loading that compensates for the reduced electrical length
Solution Approach 2:
Capacitors are introduced as intermediary elements to load the transmission line sections, enabling the use of shorter transmission lines while achieving the required electrical performance for differential mode signal conversion
2Volume of moving object
If compact balun designs like LC balun are used, then the device size is reduced, but insertion loss increases and common mode response becomes unsuitable
Solution Approach 1:
The patent uses readily available capacitor components to load the transmission lines, achieving compact size without the high insertion loss and common mode response problems of LC balun designs
Solution Approach 2:
By changing the electrical length parameter to substantially less than 90 degrees and using capacitive loading, the patent achieves compact size while maintaining low insertion loss and suitable common mode response
3Volume of moving object
If transmission line sections with electrical length substantially less than 90 degrees are used, then the balun size is reduced, but the common mode response increases
Solution Approach 1:
Capacitors are used as intermediary elements to load the transmission line sections, suppressing the harmful common mode response that would otherwise increase with reduced electrical length
Solution Approach 2:
The patent changes the electrical length parameter to substantially less than 90 degrees and uses capacitive loading to simultaneously achieve miniaturization and suppress common mode response
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 miniaturized half-wave balun achieves a differential mode component that is substantially greater than the common mode component, with a common mode response at least 14dB lower in power, and maintains low insertion loss and improved impedance matching across a wide frequency range.
Implementation Method 1
connected to a second circuit node 53B via a second transmission line section 54B which has substantially identical physical properties to first transmission line section 54A
Implementation Method 2
A first end of transmission line section 54A is connected to a shunt capacitor 56A at a first circuit node 53A
Data Source
Figure 1~2
Figure 3
Figure 4A~4B
AI summary
A miniaturised half-wave balun comprises a single-ended I/O port comprising a first signal carrying terminal for connection to a source impedance and a differential I/O port comprising second and third signal carrying terminals for connection to a load impedance. First and second transmission line sections of equal length and characteristic impedance are connected together at a common end and at opposite ends to the second and third terminals. The first signal carrying terminal is coupled to the first transmission line section. The combined length of the first and second transmission line sections is substantially less than one half of the wavelength of an RF signal at the operating frequency. First and second loading shunt capacitors are connected to respective first and second transmission line sections. A shunt capacitive element is connected at the common end of the transmission line sections. The capacitance of the shunt capacitive element is chosen so that the common mode impedance of said differential I/O port at a selected frequency is substantially zero Ohms.