Multiplexer
Understanding Multiplexers
Multiplexers are complex filter assemblies that handle the simultaneous routing of multiple frequency bands. In a satellite transponder, a multiplexer divides the total received bandwidth into individual channels for separate amplification, then a second multiplexer recombines them for transmission.
| Antenna Type | Gain (dBi) | Beamwidth | Bandwidth |
|---|---|---|---|
| Dipole | 2.1 | 360° (H) | Moderate (~10%) |
| Patch | 5-8 | 60-90° | Narrow (2-5%) |
| Horn | 10-25 | 10-60° | Wide (>50%) |
| Parabolic | 25-45 | 1-10° | Wide |
Multiplexer Types
- Input multiplexer (IMUX): Divides wideband input into individual channels. Low insertion loss, high isolation.
- Output multiplexer (OMUX): Combines individually amplified channels onto one feed. Must handle high power.
- Manifold-coupled: Filters connected via a common transmission line (manifold). Best performance but complex design.
- Circulator-coupled: Filters connected through circulators. Simpler design, moderate performance.
Key Specifications
- Channel count: 4 to 16+ channels typical for satellite multiplexers.
- Channel bandwidth: 27 MHz, 36 MHz, 54 MHz, 72 MHz standard satellite channels.
- Insertion loss: 0.3-1.5 dB per channel.
- Adjacent channel isolation: 25-40 dB between neighboring channels.
Frequently Asked Questions
What is a multiplexer in RF?
An RF multiplexer combines or separates three or more frequency bands on a common port. It is an extension of the diplexer (2 bands) to multiple channels. Satellite transponders use input and output multiplexers to process individual channels.
How does a satellite multiplexer work?
The input multiplexer divides the full received bandwidth into individual channel filters. Each channel is separately amplified by its own traveling-wave tube or solid-state amplifier. The output multiplexer then combines all amplified channels back onto the satellite antenna feed for transmission.
What is the difference between a multiplexer and a switch?
A multiplexer handles multiple frequency bands simultaneously through frequency-domain separation (filtering). A switch routes signals in the time domain, selecting one path at a time. Multiplexers are passive and handle all bands continuously; switches are typically active and handle one band at a time.