Modernizing A Legacy 16-Way Receiver Multicoupler With Mini-Circuits Parts

Many RF systems require distribution of an input signal from an antenna to feed multiple individual receivers. System designers use multi-couplers to accomplish this while multiplexing different paths into different bandwidths, maintaining the desired signal power levels, and circumventing unwanted effects depending on the specific system.

Imagine the challenges of designing and building a worthy 16-way receiver multicoupler in the 1990s.  For those of us interested in history, or perhaps old enough to remember designing in the 1990s, some of the best silicon bipolar transistor MMICs were supplied by Avantek (acquired by HP in 1991) and the most popular design software was a program called Touchstone, supplied by EEsof (acquired by HP in 1993). Reactive splitters had long been the prevailing signal distribution component for receiver multicouplers because of their low loss, broadband and rugged nature.¹  These quarter-wavelength reactive devices could be designed to split HF, VHF and UHF frequencies evenly and contiguously to the output ports with very low intermodulation distortion due to their high power handling capability.  Many of the MMIC amplifier devices available in that day and age exhibited too great a noise figure and lower linearity than required for most receiver applications. Consequently, discrete transistors were often designed into the multicoupler to meet a given combination of specifications.

About three decades since that time, a customer approached Mini-Circuits with a project to redesign just such a 16-way receiver multicoupler for a SATCOM application originally produced in the ‘90s. The system was still in service, but many of the components in the assembly were obsolete and the workforce no longer knew how to build the clunky, magnetic splitter that underpinned the legacy design.

Moreover, vast improvements in RF components had been achieved in Mini-Circuits’ product line and the industry at large. MMIC amplifiers that exhibit 1 dB or less noise figure and IP3 levels greater than +30 dBm are now commonplace. Matched amplifier pairs integrated on the same die and combined with baluns in push-pull configurations can routinely achieve IP2 levels of +60 dBm or greater across more than a decade of bandwidth. These innovations had taken place at Mini-Circuits across so many product lines that the receiver multicoupler redesign effort that ensued needed only focus almost exclusively on Mini-Circuits’ components.