New-Tech Europe Magazine | August 2017

75+ an ideal candidate for isolating upstream and downstream paths in Full Duplex DOCSIS 3.1 systems. Conclusion: One Piece of a Complex Puzzle Full Duplex DOCSIS 3.1 presents a number of new challenges that cable operators and suppliers are working diligently to overcome. Isolating the forward and return signal paths at the node is one of the key challenges unique to full duplex communication, requiring innovative problem solving at the component level. Mini- Circuits’ SYDC-8-122-75+ enables system architects to effectively isolate forward and return signals at the same frequency and prevent signal leakage that would otherwise lead to systemic problems. The successful implementation of Full Duplex DOCSIS 3.1 ultimately depends on a wide and complex variety of factors. Mini-Circuits is proud to contribute one piece in the puzzle and play a role in the collaborative efforts of the broadband industry to bring the market faster connectivity. The SYDC- 8-122-75+ high-directivity directional coupler is an example of our ability to respond to challenging, application- specific system requirements with technical expertise, flexibility and fast turnaround.

Figure 1: Simplified schematic of high isolation directional couplers (SYDC-8-122-75+) isolating upstream and downstream signal traffic in Full-Duplex DOCSIS 3.1 system.

develop broadband, high-isolation 75Ω directional couplers to prevent leakage between forward and return signal within network nodes. In the forward direction, downstream signal is injected through the coupled port onto the mainline toward subscriber premises. In the return direction, upstream signal is injected onto the mainline toward the head end. The difficulty is designing a wideband coupler with sufficient isolation between the coupled port and the in/ out ports to prevent leakage of the injected signal into the opposing path. System requirements call for input/ output operating frequency from 5 to 1218 MHz, coupled frequency range from 40 to 780 MHz and typical isolation (In/Out – Coupled Port) of roughly 30 to 35 dB or better up to 780 MHz. Achieving this level of isolation over a frequency range this wide is challenging, but Mini- Circuits leveraged our in-house design expertise to develop model SYDC-8-122-75+, a surface-mount, transformer-type 75Ω directional coupler to support the requirements for Full Duplex DOCSIS 3.1 systems. Test data for this coupler exhibits isolation greater than 40 dB up to 1000 MHz and greater than 30 dB up to 1220 MHz at the upper limit of the DOCSIS 3.1 application band. This design has a coupling ratio of 8.9 dB with ±0.5 dB flatness over the 5 to 750 MHz range and ±0.9 dB flatness over the 5 to 1218 MHz range. It provides

Figure 2: SYDC-8-122-75+ case style 1W RF input power handling, 1.4 dB typical mainline loss, and 18 dB typical return loss (input/output/coupling). It comes housed in a miniature plastic package (0.38 x 0.50 x 0.25”) mounted on printed wiring laminate base with a wraparound terminations for excellent solderability. Its exceptional isolation of over wide frequency range, flat coupling and combination of other performance characteristics, make the SYDC-8-122-

Figure 3: Curves of measured test data for SYDC-8-122-75+ for Coupling, Isolation and Directivity, swept over DC to 1500 MHz.

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