Vertical Interdigital Coupler for Compact RF Systems
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Solution Overview
Problem
Conventional RF and microwave couplers face challenges in achieving desired coupling values and compact form factors, with existing designs experiencing phase velocity imbalances, limited bandwidth, and manufacturing difficulties, particularly in producing high coupling values like 3 dB couplers using interdigital edge coupled transmission lines.
Innovation Solution
A vertical interdigital coupler structure with three or more broadside coupled transmission lines, where alternating layers of transmission lines are vertically aligned on different dielectric materials, allowing for adjustable coupling and compact design, enabling the achievement of any desired coupling value within a smaller volume and area compared to standard broadside or interdigital edge couplers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If interdigital edge coupled transmission lines are used to achieve tight coupling, then coupling value improves, but manufacturing precision deteriorates due to difficulty in producing high coupling values like 3 dB couplers
Solution Approach 1:
The patent transitions from planar edge-coupled interdigital transmission lines to vertically stacked broadside-coupled transmission lines. This dimensional change from 2D to 3D configuration allows electromagnetic fields to couple through the dielectric substrate between stacked layers, achieving tight coupling (3 dB and higher) with relaxed manufacturing tolerances compared to edge-coupled designs that require precise lateral spacing control.
2Volume of moving object
If conventional broadside or interdigital edge couplers are used, then coupling functionality is achieved, but device volume and area increase
Solution Approach 1:
By stacking transmission lines vertically across multiple layers separated by dielectric substrates, the patent achieves tight coupling in a compact volume. The vertical stacking configuration reduces the planar footprint compared to conventional broadside or interdigital edge couplers while maintaining coupling functionality through controlled electromagnetic field interaction between stacked layers.
Solution Approach 2:
The patent enables coupling adjustment by varying multiple parameters including the number of stacked transmission line pairs, dielectric substrate thickness, conductor width, and spacing between layers. This provides flexibility to achieve different coupling values (3 dB, 6 dB, 10 dB, 20 dB and higher) within a compact form factor, enhancing adaptability without increasing device volume.
3Area of moving object
If transmission lines are meandered tighter to reduce area, then area decreases, but even/odd mode phase velocity imbalance increases negatively impacting performance
Solution Approach 1:
The patent uses vertically stacked broadside-coupled transmission lines instead of planar meandered lines. This vertical stacking configuration maintains larger effective coupling area without requiring tight lateral meandering, thereby avoiding the even/odd mode phase velocity imbalance that plagues meandered line designs. The electromagnetic fields couple through the dielectric between stacked layers rather than requiring tight lateral proximity.
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 vertical interdigital coupler structure achieves tight coupling and compactness, providing improved performance by minimizing even and odd mode phase velocity imbalances and reducing the volume and area required for equivalent coupling values, while allowing for flexible coupling adjustments.
Implementation Method 1
two conductors in relative proximity to each other such that an RF signal propagating along a main conductor is coupled to a secondary conductor
Implementation Method 2
An electromagnetic field is coupled to the secondary conductor and the coupled RF signal is directed into a third port
Implementation Method 3
the incident signal and the coupled signal reinforce each other
Implementation Method 4
the two incident signal and the coupled signal are substantially out of phase with each other and cancel each other
Implementation Method 5
Each first transmission line is disposed on a first dielectric material between the first port and the second port
Data Source
AI summary
The present invention is directed to a coupler structure that includes a first port, a second port, a third port, and a fourth port. L first transmission line layers are disposed in the structure. Each first transmission line layer includes a first transmission line conforming to a predetermined geometric configuration. The first transmission line is disposed on a first dielectric material between the first port and the second port. L is an integer. M second transmission line layers are disposed in alternating layers with the L first transmission line layers to form a total of N transmission line layers within the structure. M and N are integers and N is greater than or equal to three. Each second transmission line layer includes a second transmission line substantially conforming to the predetermined geometric configuration. The second transmission line is disposed on a second dielectric material between the third port and the fourth port. Each second transmission line is disposed in a predetermined position relative to a corresponding first transmission line within the structure.