Coupled Line: Frequency Range DC to 40 GHz, VSWR <1.5:1

Q: What is the primary function of a coupled line in a directional coupler?

To sample a controlled portion of signal power from the main transmission line without significantly disrupting the signal flow, enabling applications like power monitoring, measurement, and signal splitting.

Q: How does a coupled line achieve directionality?

Through specific geometric designs, such as asymmetric spacing or multi-line configurations, that preferentially couple signals traveling in one direction (e.g., forward) while minimizing coupling in the opposite direction, enhancing isolation and performance.

Q: What factors affect the coupling factor of a coupled line?

The coupling factor is influenced by the physical proximity of the lines, their length, the dielectric constant of the substrate, and the operating frequency, with tighter spacing and longer lines generally increasing coupling.

Component Specifications

Definition

A coupled line consists of two or more parallel transmission lines placed in close proximity, enabling electromagnetic coupling between them. In directional couplers, this configuration allows a fraction of the signal power traveling along the main line to be transferred to a secondary coupled line, facilitating signal monitoring, measurement, or power splitting while maintaining signal integrity and directionality.

Working Principle

Operates based on electromagnetic coupling between adjacent transmission lines. When a signal propagates along the main line, a portion of its electromagnetic field interacts with the coupled line, inducing a proportional signal in the coupled port. The coupling factor depends on the physical dimensions, spacing, and dielectric properties, with directionality achieved through specific geometric arrangements that favor forward or backward wave coupling.

Materials

Typically made from conductive materials like copper or aluminum for the traces, with substrates of PTFE (Teflon), FR4, ceramic, or other low-loss dielectrics. May include plating with gold or silver for enhanced conductivity and corrosion resistance in high-frequency applications.

Technical Parameters

Parameter	Typical range	Notes & selection driver
VSWR	<1.5:1
Impedance	50 ohms or 75 ohms
Directivity	>20 dB
Insertion Loss	<0.5 dB
Coupling Factor	3 dB to 30 dB
Frequency Range	DC to 40 GHz

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

ISO 9001, IEC 61169, MIL-PRF-39012

Parent Products

This component is used in the following industrial products

Directional Couplers

Passive microwave/RF components that sample a portion of signal power from a transmission line in a specific direction while maintaining isolation from signals traveling in the opposite direction.

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Engineering Analysis

Risks & Mitigation

Impedance mismatch leading to signal reflections
Poor directivity causing measurement inaccuracies
Material degradation at high frequencies or temperatures
Manufacturing tolerances affecting performance consistency

FMEA Triads

Trigger: Insufficient spacing between lines
Failure: Excessive coupling or signal leakage
Mitigation: Implement precise design rules and quality control during fabrication to maintain specified dimensions.

Trigger: Substrate material imperfections
Failure: Increased insertion loss or frequency drift
Mitigation: Use certified low-loss dielectric materials and conduct regular material testing.

Trigger: Environmental exposure to moisture or contaminants
Failure: Corrosion or electrical shorting
Mitigation: Apply protective coatings or encapsulation and ensure proper storage and handling.

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

±0.1 mm for line width and spacing, ±5% for electrical parameters like coupling factor

Test Method

Vector network analyzer (VNA) measurements for S-parameters, including insertion loss, return loss, and directivity, per industry standards like IEC 61169.

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

Verify equipment lists, process limits, capacity, and representative production evidence.

Inspection readiness

Confirm test methods, calibrated equipment, sampling plans, and traceable reports.

Supplier transparency

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Manufacturers of Coupled Line

Manufacturer profiles associated with Coupled Line.

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Frequently Asked Questions

What is the primary function of a coupled line in a directional coupler?