RF power dividers and splitters

01

Separate the split loss from excess loss, and set isolation

Mini-Circuits' application note defines a 0° splitter's ideal outputs as equal in amplitude, 0° apart in phase and highly isolated, with theoretical insertion loss of 3.0 dB for 2 ways, 4.8 dB for 3, 6.0 dB for 4, 7.8 dB for 6, 9.0 dB for 8, 10.0 dB for 10, 12.0 dB for 16, 13.8 dB for 24 and 16.8 dB for 48 ways. It explains that a simple T has poor isolation and a 25 Ω input impedance in a 50 Ω system, which the transformer-and-resistor design corrects. [1]

RFTYT's 16-way dividers list, by model, 0.5–6.0 GHz at 3.2 dB maximum insertion loss, 1.80 VSWR, 18 dB minimum isolation and 20 W input; 0.8–2.5 GHz at 1.5 dB, 1.40 VSWR, 22 dB and 30 W with N-female connectors; and 6.0–18.0 GHz at 1.8 dB, 1.80 VSWR, 16 dB and 10 W. [3]

Editorial calculation and note: RFTYT's 1.0–3.8 dB figures are far below the 12.0 dB theoretical split for 16 ways, so they read as excess loss above the split; on that reading, the 0.5–6.0 GHz model's total loss from input to each output would be up to about 12.0 + 3.2 = 15.2 dB. Confirm with the supplier whether a quoted insertion loss includes the theoretical split. [1] [3]

Give the supplier the number of ways, frequency band, maximum insertion loss (and whether it includes the split), minimum isolation, VSWR at each port, amplitude and phase balance, input power as splitter and as combiner, impedance, connector type and any environmental rating.

02

Check port matching and power rating as a combiner

Mini-Circuits stresses that the “common” (sum) port must be properly matched to keep isolation: in its example a −10 dB reflection at the sum port cuts isolation to 16 dB, whereas a mismatch at an output port is not critical when the sum port is matched. With one output of a two-way splitter shorted, half the reflected power is dissipated in the internal resistor and half returns to the input. [1]

On power, Mini-Circuits says the rating is set by the internal resistor and the transformer's core and wire size: the core may saturate at the low end of the band if the rating is exceeded, and as a combiner the internal resistor must, in a two-way unit, be able to dissipate half the power applied to each port. Isolation is measured with the “common port” terminated in the correct impedance; Mini-Circuits uses a termination of VSWR 1.05:1 for isolation tests. [1]

Mini-Circuits' companion note describes a two-way splitter as a divider section, a matching section, an isolation resistor and a capacitor, with the divider and matching sections realised on magnetic cores in its low-cost series. [2]

Editorial calculation: splitting 20 W ideally into 16 ways gives 1.25 W per output before any excess loss; with 3.2 dB excess loss each output would receive about 1.25 × 10^(−0.32) ≈ 0.6 W.

03

Size the isolation resistor in a Wilkinson combiner

A Hitachi Kokusai Electric patent application, US 2018/0053984 A1, gives worked figures for a two-way Wilkinson combiner in a 50 Ω system: two quarter-wave matching lines of 70.7 Ω, a 50 Ω output line and a 100 Ω isolation resistor between the two input branches. If 100 W enters one input and the other input has none, 50 W reaches the sum port and 50 W is absorbed in the isolation resistor, so the resistor must be rated for the maximum load plus a margin. The application then shows the catch: a resistor with a large rated power carries a larger parasitic component, which degrades matching, loss and isolation at 500–700 MHz in its simulations. [4]

This matches Mini-Circuits' point that, as a combiner, the internal resistor of a two-way unit must dissipate half the power applied to each port. [1] Editorial note: when a divider will also combine signals, ask the supplier for the isolation resistor's rated dissipation, the combiner power rating with one input absent, and measured isolation and loss of the high-power version across the band, not only figures from the low-power model.

04

Compare what suppliers offer

The suppliers linked to this page list RF power dividers or splitters; their cards link to the pages reviewed.

Ask any supplier for measured insertion loss (stating whether the split is included), isolation, VSWR, amplitude and phase balance across the band, power rating as splitter and combiner, connector type, housing and environmental tests, and test data for the units shipped.

05

Trace the divider parts

This is a functional reference built from the sources cited; it is not one maker's specification.

06

Fill the specification fields with values for your system

A power divider quotation needs values for your RF system. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the RF and mechanical data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

RF: [ways; band; loss; isolation; VSWR; balance]
Power: [as splitter; as combiner]
Interface: [impedance; connectors]
Environment: [temperature; humidity; IP]
Quantity: [units; test data]

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