Expanding Bandwidth in HFC Networks The Role of 1.8 GHz Diplex Filters

As hybrid fiber-coaxial (HFC) networks evolve toward higher bandwidth and faster data rates, components that support extended frequency ranges are becoming increasingly important. The move from 1.2 GHz to 1.8 GHz spectrum marks a significant upgrade in broadband infrastructure, enabling operators to deliver more capacity without a full system overhaul.
One key component in this transition is the CATV diplex filter, which separates upstream and downstream signals within a shared transmission path.

Why the Diplex Filter Matters
In cable and broadband systems, both forward (downstream) and return (upstream) signals travel through the same network but occupy different frequency ranges.
To prevent interference, a diplex filter acts as a frequency divider — it passes one range while blocking the other. This ensures that each direction of communication remains isolated, maintaining signal clarity and network stability.
As the industry expands toward 1.8 GHz, traditional filters are no longer sufficient. Wider bandwidth demands improved isolation, lower insertion loss, and greater mechanical precision to ensure compatibility with upgraded amplifiers and optical nodes.

Design Considerations for 1.8 GHz Networks
When designing or upgrading CATV systems for 1.8 GHz operation, engineers typically look at three key aspects:

Crossover Frequency (Split Point)
Depending on the system architecture, different frequency splits are used — such as 5–85 MHz https://www.sanlandtech.com 102–1794 MHz, or 5–204 MHz https://www.sanlandtech.com 258–1794 MHz. Each combination serves different upstream bandwidth requirements.

Isolation & Insertion Loss
The filter must maintain high isolation between return and forward paths while keeping insertion loss minimal. Poor performance in either metric can lead to distortion, cross-talk, or reduced network efficiency.

Mechanical and Environmental Factors
Compact “plug-in” designs simplify maintenance and integration in dense network environments. At the same time, RoHS compliance and robust mechanical structure ensure long-term stability in the field.
A Practical Example: 1.8 GHz CATV Diplex Filters
A good example of such design evolution can be seen in the 1.8 GHz CATV Diplex Filter series by Sanland.
This series includes several band-split options (e.g., 5–85 MHz https://www.sanlandtech.com 102–1794 MHz, 5–204 MHz https://www.sanlandtech.com 258–1794 MHz, 5–396 MHz https://www.sanlandtech.com 492–1794 MHz) to support diverse network plans.
Each model is optimized for low insertion loss, high isolation, 75 Ω impedance, and a slim plug-in structure suitable for compact modules and headend applications.
Future Outlook
As operators continue extending HFC bandwidth toward 1.8 GHz and beyond, diplex filters will remain essential in ensuring reliable upstream and downstream coexistence.
Developments in filter topology, materials, and precision manufacturing will further enhance performance and enable smooth migration to next-generation networks.

For more technical details about 1.8 GHz filter solutions, Click here!