Directional Coupler Recess for High Directivity
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Solution Overview
Problem
Existing directional couplers face challenges in achieving high directivity while maintaining a compact size, particularly in high-power applications like digital television transmitters, where the length required for optimal directivity in the UHF band results in large circuits, and shorter coupled lines lead to degradation in directivity.
Innovation Solution
A directional coupler design featuring a main line and sub-line with an optimized opening through the dielectric substrate, allowing the phase velocities of even and odd modes to be approximated, thereby improving directivity without increasing size, by using a suspended line structure and microstrip configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a quarter-wavelength coupled line is used to achieve optimal directivity, then directivity is improved, but the circuit size becomes large
Solution Approach 1:
The invention changes the physical parameters of the coupled line by introducing a recess structure that modifies the effective dielectric constant and phase velocity. This allows the coupled line length to be shortened below the conventional quarter-wavelength while maintaining the necessary electrical length for optimal directivity, thus resolving the contradiction between compact size and high directivity
Solution Approach 2:
The invention transitions from a planar microstrip structure to a three-dimensional structure by forming a recess in the dielectric substrate. This vertical dimensionality change allows modification of the electromagnetic field distribution and phase characteristics without increasing the planar footprint, enabling compact size while maintaining directivity performance
2Area of stationary object
If a shorter coupled line is used to reduce circuit size, then circuit size is reduced, but directivity deteriorates
Solution Approach 1:
By modifying the effective dielectric constant through the recess structure, the invention changes the phase velocity characteristics of the coupled line. This parameter change compensates for the shortened physical length, maintaining the electrical length required for high directivity while achieving a compact physical size
3Area of stationary object
If a compact directional coupler is designed for high-power applications, then space utilization is improved, but achieving high directivity becomes difficult
Solution Approach 1:
The invention applies local quality modification by creating a recess structure at specific locations along the coupled line. This localized structural change affects the electromagnetic field distribution in critical regions, enabling high directivity performance in a compact overall structure suitable for high-power applications
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 proposed design achieves a significant improvement in directivity of up to 20 dB compared to conventional designs, enabling a compact high-directivity coupler even when the coupled line is shorter than a quarter-wavelength, suitable for high-power applications like digital television transmitters.
Implementation Method 1
A directional coupler design featuring a main line and sub-line with an optimized opening through the dielectric substrate, allowing the phase velocities of even and odd modes to be approximated, thereby improving directivity without increasing size
Data Source
Figure 1
Figure 2(a)~2(b)
Figure 3~4(b)
AI summary
A directional coupler according to the present embodiment includes a dielectric substrate (10), a main line (11) formed on the front surface of the dielectric substrate (10), a sub-line (12) formed on the front surface or the rear surface of the dielectric substrate (10) and placed with a predetermined gap from the main line (11) in the plan view of the dielectric substrate (10), and an opening (14) provided between the main line (11) and the sub-line (12) through the dielectric substrate (10).