Cavity Multiplexers

A cavity multiplexer is a type of RF (radio frequency) filter network that uses resonant cavities to separate or combine multiple frequency channels. It’s commonly used in communication systems, especially in satellite, radar, and cellular base stations.

It works by using a series of cavity resonators—metallic enclosures that resonate at specific frequencies—to allow desired frequencies to pass while rejecting others. Each “port” corresponds to a frequency band, allowing the system to multiplex (combine) or demultiplex (split) signals.

• High Q-factor (narrow bandwidth, low loss)

• Excellent out-of-band rejection

• High power handling capability

• Mechanical and thermal stability

These traits make cavity multiplexers ideal for high-performance and mission-critical RF systems.

• Satellite transponders

• Wireless base stations (e.g., 5G)

• Radar systems

• Broadcast transmitters

• Aerospace and defense communication systems

• A multiplexer combines or separates multiple frequency channels.

• A duplexer is used to separate transmit and receive paths operating on different frequencies but often through the same antenna.

A duplexer is a special case of a multiplexer with only two bands.

Cavity multiplexers are tuned using adjustable screws or plungers that change the resonant frequency of each cavity. Precision tuning is critical to match the desired frequency response and minimize insertion loss.

Insertion loss refers to the amount of signal power lost due to the multiplexer. In high-quality cavity multiplexers, this is typically low (under 1 dB), but it depends on design, frequency, and quality of materials.

Cavity multiplexers usually provide very high isolation between channels, often 60–100 dB or more. High isolation prevents channel-to-channel interference and is critical in dense, high-power RF systems.

Lower frequencies require physically larger cavities due to longer wavelengths, resulting in larger and heavier multiplexers. Higher-frequency cavity multiplexers can be more compact but may be more sensitive to manufacturing tolerances.

Return loss or VSWR indicates how well the multiplexer matches the system impedance (typically 50 ohms). Poor matching causes signal reflections, increased loss, and potential transmitter stress. High-quality cavity multiplexers typically have VSWR better than 1.3:1.

Both options exist. Off-the-shelf cavity multiplexers are available for common frequency bands, while custom designs are often used for specialized applications requiring unique channel spacing, power levels, or environmental specifications.

Generally, cavity multiplexers are low-maintenance, but periodic inspection and retuning may be required in high-power or outdoor installations. Mechanical shock, temperature cycling, or aging can cause slight frequency drift.

Yes. Due to their mechanical robustness, they are often used in military, aerospace, and outdoor telecom applications, including environments with high temperature variations or vibration.

• Maintaining low insertion loss and high isolation

• Minimizing size and weight

• Ensuring temperature stability

• Achieving tight frequency tolerances in multi-channel configurations

• Mechanical complexity in tuning and manufacturing

Typical cavity multiplexers support 2 to 16 channels, but more complex systems can go higher. The number of channels depends on system requirements, available space, and acceptable performance trade-offs.

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