Power splitters - advantages, etc  - Page 1
Forum section: electronics / rf-microwave

author: cncjerry
author_rank: Unknown
timestamp: December 01, 2020, 09:03:56 pm
content: Can someone explain to me the considerations for using a resistive RF power splitter vs a Wilkinson type? Are splitters like the Minicircuits PSC-2-2+ Wilkinson type? They don't use the term resistive like they do with the ZFRSC-42. I think having an 'R' in the part number implies resistive.According to wikipedia, "...the Wilkinson Power Divider is a specific class of power divider circuit that can achieve isolation between the output ports while maintaining a matched condition on all ports. The Wilkinson design can also be used as a power combiner because it is made up of passive components and hence reciprocal." The resistive splitters can also be used as a combiner and being purely if not mostly resistive, I don't see why they wouldn't be close to the same as far as matching and load goes. Since both are splitter/combiners, I don't see how the reverse isolation on either or return loss could be anywhere near the Wilkinson type.The splitters I have considered for this project are the PSC-2-2+ (used by the author of the project) and the ZFRC-42. The first, PSC-2-2+ is, I assume, to be a Wilkinson model. The latter, ZFRC-42, is described as a "2 Way, 0° Resistive 50Ω DC to 4200 MHz." Note the term resistive so can I assume that means they are resistive type, and not Wilkinson type. Taking it apart makes it clear that it is a resistive type. Anyone that spends a small fortune on this one will be very disappointed it they ever open it up as I did. Just a triangle of 49r9 resistors between the ports.The PSC-2-2 and another used, the ZMSC-2-1, both have much better isolation at 40dB vs 6dB for the resistive type; insertion loss is much better on both Wilkinson type. I think that answers my question but I want to understand if I'm not too narrowly focused on those two parameters.Application is for splitting 5Mhz and 10Mhz oscillators for phase noise testing prior to being digitized by a 125Msps ADC.ThanksJerry

author: ejeffrey
author_rank: Super Contributor
timestamp: December 01, 2020, 09:38:15 pm
content: Wilkinson splitters are ideally lossless, whereas resistive splitters have 3 dB or more excess loss. However, they are narrow bandwidth compared to resistive splitters: the classic wilkinson splitter is less than an octave while multi-stage splitters can be broad bandwidth. Note that unlike a directional coupler, a wilkinson splitter is still amplitude and phase matched outside its bandwidth but suffers from mismatch.Wilkinson splitters also provide good isolation between the two output ports, but not from the output to input which only has 3 dB isolation.Wilkinson splitters can act as a power combiner if fed in phase. Out of phase signals will be absorbed by the internal load resistor so you have to be wary of the power handling.Resistive splitters can be extremely broad band -- from DC to the limit of your resistor technology. However, they don't provide meaningful isolation: all 3 ports are identical.Resistive splitters can act as signal combiners, but the excess loss means they can't actually function as a _power_ combiner -- the excess loss will always drop the output power down to no more than the individual inputs.

author: fourfathom
author_rank: Super Contributor
timestamp: December 01, 2020, 09:40:10 pm
content: Isolation is the factor here, and when you are doing noise and IMD testing you don't want reflections returning to your input port, or having one source couple into another source. This can cause IMD in the source driver, which can mask any IMD in the DUT (usually an amplifier or mixer). I'm not sure if you are using these as dividers or combiners, but the same factors apply as these are generally passive, symmetrical devices.Plain resistive dividers have no isolation. All ports are coupled together.Wilkinson dividers do have good isolation, but are designed for a specific frequency. Away from this frequency they will not work as desired. I think there are some Wilkinson dividers that are designed for a frequency range, but it's still going to be fairly limited.The Minicircuits PSC-2-2+ is probably a "hybrid" transformer design, not a Wilkinson. Hybrid splitters/couplers will have one or more wide-band transformers and perhaps some resistors. These can have many decades of good performance.Here's a random discussion of various types of combiners/splitters:https://www.electronics-notes.com/articles/radio/rf-combiner-splitter-coupler-hybrid/splitter-divider-combiner.php