Ultra-Wideband Micro-Coaxial Dual Directional Coupler Covering DC to 145 GHz
YUSNTECH | RF & Microwave Components
As RF and microwave systems continue to move toward higher frequencies, wider bandwidths and greater integration, conventional directional couplers often face increasing challenges in bandwidth coverage, directivity, insertion loss and physical size.
YUSNTECH has developed a miniaturized ultra-wideband micro-coaxial dual directional coupler designed to address these challenges. The technology supports frequency coverage from DC to 120 GHz with a 1.0 mm coaxial connector configuration, and up to DC to 145 GHz with a 0.8 mm coaxial connector configuration.
The design combines two ultra-wideband single directional couplers with continuously tapered coupled lines, optimized Y-junction structures and a compact three-dimensional port arrangement.
Ultra-Wideband Performance in a Miniaturized Structure
The core of the design is a micro-coaxial coupled-line structure with continuously varying impedance. Instead of using abrupt impedance transitions, the coupled line adopts a multi-section continuous taper, allowing the even- and odd-mode impedances to change smoothly along the coupling path.
This approach helps reduce discontinuities and higher-order mode excitation while maintaining broadband coupling performance.
The two single directional couplers are integrated using a compact Y-junction topology. Their first ends are connected through narrow-side Y-junctions, while the opposite ends form the input, output, coupled and isolated ports of the dual directional coupler.
The first section of the coupled line features a smaller spacing and cross-sectional dimension than the second section, creating a gradual transition between the two regions.
This geometry enables broadband operation while maintaining a compact physical footprint.
C-Shaped Nested Topology for Size Reduction
A key feature of the design is the C-shaped nested topology used for the two single directional couplers.
The coupling structures are bent inward and partially nested with each other. Rather than relying on long straight coupled lines, the continuously curved topology makes more efficient use of the available chip area.
At the same time, the curved structure reduces the aspect ratio of the coupling line, which can improve manufacturing yield and reduce fabrication difficulty.
The resulting coupler can be designed within a chip footprint of approximately 1 cm × 2 cm or smaller, providing a significant size advantage for high-frequency test and measurement and RF front-end applications.
Micro-Coaxial Architecture with Integrated Dielectric Supports
The dual directional coupler consists of an inner conductor, outer conductor and dielectric support structures.
The outer conductor forms a hollow transmission environment, while the inner conductor is suspended inside the outer conductor by multiple axially distributed dielectric support bars.
The dielectric supports are fabricated using SU-8 photosensitive organic material and periodically positioned between the inner and outer conductors.
To compensate for the electromagnetic discontinuity introduced by the dielectric supports, the inner conductor width is locally reduced at the support locations. This compensation structure helps maintain impedance continuity throughout the transmission path.
The combination of micro-coaxial transmission lines, dielectric supports and impedance compensation enables the structure to maintain broadband electrical performance within an extremely compact package.
Optimized Y-Junction Design
The Y-junction is another critical element of the ultra-wideband structure.
The outer conductor of the narrow-side Y-junction incorporates a three-layer stepped matching structure, while the inner conductor gradually increases in width with an approximately 45° transition.
This geometry is designed to improve impedance matching and reduce higher-order mode excitation over the extremely wide operating frequency range.
The result is a smoother electromagnetic transition between the coupled-line sections and coaxial ports.
Two Connector Configurations: DC–120 GHz and DC–145 GHz
YUSNTECH offers two implementation configurations based on different high-frequency coaxial connector sizes.
1.0 mm Coaxial Connector Configuration
The 1.0 mm version is based on an eight-layer micro-coaxial forming process, with an overall structure thickness of approximately 0.8 mm and an average layer height of approximately 100 μm.
All six ports can be directly connected to 1.0 mm coaxial connectors.
Key specifications:
- Frequency Range: DC–120 GHz
- Input Return Loss: >19 dB
- Directivity: >20 dB
- Insertion Loss: <2.5 dB
0.8 mm Coaxial Connector Configuration
The 0.8 mm version is based on an eight-layer micro-coaxial transmission-line process, with approximately 100 μm forming height per layer.
The micro-coaxial coupled line has a cross-sectional height of approximately 0.2 mm.
This configuration extends the operating frequency range to DC–145 GHz, making it suitable for applications requiring extremely wideband millimeter-wave and sub-THz measurement capability.
Key specifications:
- Frequency Range: DC–145 GHz
- Input Return Loss: >14 dB
- Directivity: >18 dB
- Insertion Loss: <3 dB
Compact Three-Dimensional Port Configuration
The coupler incorporates a three-dimensional port arrangement to further reduce package size.
The load-port axes are arranged perpendicular to the plane containing the four main coaxial ports. The complete six-port structure therefore includes:
- Input Port
- Output Port
- Coupled Port
- Isolated Port
- Two Load Ports
This arrangement allows four ports to be positioned horizontally and two ports vertically, creating a compact package suitable for dense RF and microwave assemblies.
The package can be implemented using either a flange-type connector structure or a locator-type structure.
Both approaches use mechanical positioning between the upper and lower covers. Standard coaxial connectors can directly contact the corresponding ports, eliminating the need for soldering and simplifying assembly.
Integrated Loads and GSG Interfaces
For applications requiring further miniaturization, the load ports can incorporate integrated micro-coaxial terminations, reducing external package volume.
The input, output, coupled and isolated ports can also be configured with GSG interfaces. Gold-wire bonding can then be used to integrate the coupler directly with MMIC-based RF systems.
This provides a practical pathway for integrating the ultra-wideband directional coupler into high-frequency RF front ends, test fixtures and advanced microwave modules.
Additive Manufacturing for High-Frequency Micro-Coaxial Structures
The micro-coaxial structure is fabricated using a metal additive manufacturing process with an eight-layer forming approach.
The multi-layer manufacturing method enables the formation of extremely small three-dimensional conductor geometries while maintaining controlled dimensional transitions.
Compared with conventional machining approaches, the process is particularly suitable for compact high-frequency structures where conventional manufacturing can become increasingly difficult as the operating frequency approaches the millimeter-wave and sub-THz ranges.
Key Advantages
The YUSNTECH ultra-wideband micro-coaxial dual directional coupler combines several key advantages:
Ultra-wide frequency coverage: DC–120 GHz and DC–145 GHz configurations reduce the need to use multiple couplers for different frequency bands.
High directivity: Directivity greater than 20 dB is available in the 1.0 mm configuration, supporting accurate forward and reverse power measurement.
Miniaturized footprint: The nested C-shaped topology enables the coupler to be implemented within approximately 1 cm × 2 cm.
Low insertion loss: The optimized coupled-line and Y-junction structures provide insertion loss below 2.5 dB for the 1.0 mm version.
Solderless assembly: Direct mechanical contact with standard coaxial connectors simplifies installation and reduces assembly complexity.
MMIC integration: GSG interfaces and gold-wire bonding enable direct integration with high-frequency semiconductor circuits.
Scalable manufacturing: The eight-layer micro-coaxial process provides a repeatable manufacturing platform for compact high-frequency components.
Applications
The ultra-wideband dual directional coupler can be considered for a wide range of high-frequency applications, including:
- Millimeter-wave and sub-THz test and measurement
- Vector network analyzers and calibration systems
- RF power monitoring and measurement
- High-frequency signal generation and analysis
- Radar and advanced sensing systems
- Satellite and space communication
- 6G and future wireless communication research
- MMIC and RF front-end development
- Wafer-level and package-level RF testing
- High-frequency laboratory instrumentation
Engineering and Customization Support
Beyond standard configurations, YUSNTECH can support customization of frequency range, coupling level, directivity, connector configuration, package dimensions, port orientation, GSG interfaces and integrated loads according to specific application requirements.
For high-frequency RF and microwave systems operating into the millimeter-wave and sub-THz range, the ultra-wideband micro-coaxial dual directional coupler provides a compact approach to broadband signal sampling and forward/reverse power monitoring.
YUSNTECH — RF & Microwave Components from DC to 110 GHz and beyond, with customized solutions for advanced high-frequency applications.