Waveguide Couplers: Principles, Types, and Applications

Waveguide couplers are indispensable in RF and microwave systems, facilitating power distribution and signal monitoring. This guide explains their principles, types, and significant applications in modern communication technologies.

The device which couples the Electro-Magnetic Signal from main path of the waveguide is called waveguide directional coupler or waveguide coupler. This is required for monitoring purpose as well as to feed the signal to some other place.

Usually it will have 4 ports viz. input, output, coupled and terminated ports. The function of waveguide coupler is similar to RF directional coupler. Refer RF Directional Coupler for more information. Figure-1 depicts waveguide coupler.

Working principle : It works by creating an intentional interaction between two waveguides or ports through apertures, slots, or loops. This interaction allows a portion of the electromagnetic power traveling in one waveguide to be transferred to another, enabling signal sampling, monitoring, or splitting while maintaining high isolation between ports.

waveguide coupler

Following technical specifications need to consider for rectangular type of waveguide coupler.
• Operating frequency band
• Coupling value: 10 dB, 20 dB, 30 dB or 40 dB as desired
• Return Loss or VSWR: should be better
• Directivity: vary based on dimension, typical values are 10, 15, 20 and 25 dB
• Dimension: It should be choosen as per cutoff frequency needed as well as system with which it need to be interfaced.

Types of Waveguide Couplers

Waveguide couplers are devices that transfer a portion of the power from one waveguide to another. They are essential for signal monitoring, power splitting, and signal combining in RF and microwave systems. The main types of waveguide couplers are as follows.
1. Directional Couplers : Couplers that transfer power directionally, typically to a secondary waveguide or port. Applications are Signal monitoring, power measurements, and network analysis. Key Features are High directivity and isolation. Types include following.
• Single hole Coupler: Transfers power through a single aperture between two waveguides.
• Multi hole Coupler: Uses multiple apertures for broader bandwidth and better coupling efficiency.
2. Hybrid Couplers : Split power equally or unequally between two output waveguides while maintaining phase relationships.
3. Crossguide Couplers : Consist of two waveguides crossing at a specific angle, with coupling achieved through apertures at the intersection.
4. Branch-Line Couplers : Uses branching waveguide sections to couple power.
5. Bethe-hole Couplers : Based on small apertures or holes, designed to provide specific coupling levels and frequency selectivity.
6. Loop Couplers : Use a small loop structure inside the waveguide to extract or inject signals.

Manufacturers

• The Waveguide Solution Limited, United Kingdom. Website: www.waveguidesolution.co.uk
• FLANN Microwave, Website: www.flann.com
• Connecticut Microwave Corporation, Website: connecticutmicrowave.com

Conclusion

Waveguide couplers enhance functionality in RF systems, offering precise power distribution and signal handling. Choosing the right type ensures system efficiency and reliability.

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