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RF Multiplexers
In complex RF environments, managing multiple frequency bands over a shared path is key to keeping systems smaller, lighter, and performing well. Multiplexers are designed to separate and route different bands with minimal interference, making multi-band operation much easier.
Using a precise set of filters, such as the suspended-substrate design shown to the right, multiplexers allow multiple transmitters and receivers to share a single antenna or transmission line while maintaining high isolation, low loss, and reliable performance across all channels.
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At the heart of any multiplexer is one key objective: isolation. A multiplexer separates incoming signals into their respective frequency bands and maintains isolation so each can be processed independently without interference.
Multiplexers manage four or more frequency bands simultaneously using a network of bandpass filters and multiple ports to control signal routing. This allows multiple transmitters and receivers to share a single antenna or transmission line, reducing system size and weight.
In crowded RF environments, signals can overlap, distort, or bleed into adjacent channels. A well-designed multiplexer prevents these issues by tightly controlling each frequency band and maintaining signal integrity across all channels.
Spectrum Control focuses on ultra-low insertion loss (as low as 0.1 dB) and steep rejection between bands. The result is efficient signal management and dependable operation in demanding applications such as electronic warfare, radar, targeting systems, and next-generation communications, including 5G and emerging 6G frequencies.
Multiplexer Selectivity vs. Insertion Loss
When designing multiplexers, one of the biggest balancing acts is the trade-off between selectivity and insertion loss. The goal is to separate multiple frequency bands while keeping loss as low as possible; improving one almost always impacts the other.
Selectivity allows a multiplexer to cleanly separate adjacent bands and reject unwanted signals. To achieve sharper skirts between bands, RF engineers add more filter sections to each channel. This produces steeper roll-off, higher rejection, and better isolation, which is especially important when signals are closely spaced or operating in a crowded RF spectrum.
However, there is a trade-off. As more poles are added to improve selectivity, insertion loss tends to increase. Every added reactive element—inductors and capacitors—introduces some loss due to real-world limitations such as finite Q and resistance. While higher-order designs improve isolation and rejection, they also make it more difficult to minimize signal loss through the multiplexer.
As multiplexer designs become more complex, sensitivity to tolerances and parasitics also increases. Even small mismatches between poles can create reflections that lead to additional loss and reduced performance. What may be negligible in a simple LC design becomes much more significant in a high-order multiplexer.
Because each channel interacts with adjacent channels to some degree, small variations—whether from machining tolerances, component values, or temperature shifts—can affect impedance and overall performance. In higher-order designs, tight control of component values is essential to avoid passband ripple, center-frequency shifts, and excess loss.
Filter response also influences the balance between selectivity and insertion loss. Butterworth designs generally favor lower loss and a smooth passband, while Chebyshev and elliptic responses provide sharper rejection at the expense of ripple. Ultimately, multiplexer design is about managing trade-offs and finding the optimal balance between channel separation and efficient RF performance.