Antennas · Volume 18
Passive Splitters, Combiners & Couplers
Wilkinson, hybrid (quadrature, rat-race, 180°), resistive, ferrite-core, directional couplers — the passive RF distribution catalogue with isolation, insertion loss, and bandwidth tradeoffs
Contents
1. About this volume
A splitter divides one RF signal into multiple outputs. A combiner does the reverse — combines multiple signals into one. A coupler is a splitter with deliberately unequal outputs, typically with one “main” path (low loss) and one “coupled” path (small fraction tapped off for measurement).
These three operations dominate the passive RF distribution catalog and are essential for:
- Sharing one antenna among multiple receivers (a discone feeding a HackRF + RTL-SDR + scanner) — a 4-way splitter
- Combining outputs of multiple amplifiers for higher TX power — a combiner
- Measuring SWR and return loss in test instruments (NanoVNA, Bird wattmeter) — a directional coupler
- Powering masthead amplifiers over the same coax as the RF — a bias-T (RF/DC splitter)
- Sampling RF for monitoring or calibration without disrupting the main signal path — a directional coupler
This volume covers the passive members of the family — devices that don’t need power and that handle the RF entirely through transmission-line and ferrite-core geometry. The active family (LNAs, distribution amplifiers, masthead preamps) lives in Vol 19 (Active splitters, distribution amplifiers & preamps).
The dividing question: do you need to replace the lost signal, or just live with the loss? A 4-way passive split costs ~6 dB (3 dB inherent + ~1 dB resistive/insertion). If the system’s pre-split signal level is strong enough to tolerate 6 dB loss, passive splitting is the simpler and more reliable choice. If the system can’t afford the loss (weak-signal applications, distant beacons), an active distribution amp (Vol 19) is the right answer.
2. Splitter vs combiner vs coupler — what each is for
2.1 Splitter
A splitter divides one input into N equal outputs. Each output sees:
- 1/N of the input power (for an N-way split)
- Equal phase at all outputs (for a Wilkinson) or 90°/180° phase relationships (for hybrid couplers)
- High isolation between outputs (20-30 dB typical for Wilkinson, less for resistive)
For an N-way Wilkinson splitter:
- Inherent loss = 10·log₁₀(N) — i.e., 3 dB for 2-way, 6 dB for 4-way, 9 dB for 8-way
- Insertion loss = ~0.5 dB (the resistor losses)
- Total loss per output port = 3.5 dB (2-way) to 9.5 dB (8-way)
2.2 Combiner
A combiner is physically identical to a splitter but operated in reverse. N inputs → one output. Common use: combining the outputs of two amplifiers to get higher TX power.
The reciprocity rule: any passive splitter can be used as a combiner with the same characteristics. The 3 dB-per-doubling rule applies in reverse: 2 amplifier outputs combined = 0 dB increase in output power per amplifier (the combining process is lossless if the inputs are in-phase) but +3 dB total over a single amp’s output.
2.3 Coupler
A coupler is a splitter with unequal outputs: one “main” path at low loss (typically -0.5 dB) and one “coupled” path at -10 to -30 dB. Used for:
- SWR measurement: the coupled port samples the forward (or reflected) wave; the main port carries the signal
- Frequency monitoring: a coupler taps a small sample of the TX signal for a spectrum analyzer or counter
- Sequence detection: monitoring forward/reverse waves to determine SWR and detect mismatches in real time
The coupler’s directivity (how well it discriminates between forward and reverse waves) determines measurement accuracy. Good directional couplers achieve 30+ dB directivity.
3. Resistive splitter — the simplest, most lossy option
The simplest 2-way splitter uses three equal resistors in a Y configuration. For 50 Ω input and 50 Ω outputs:
Resistive splitter:
Input (50 Ω)
●
│
● R1 = 16.67 Ω
│
●─────────────●
│ │
● R2 ● R3
│ │
● ●
Output 1 Output 2
(50 Ω) (50 Ω)
R1 = R2 = R3 = 16.67 Ω for 50 Ω system3.1 Resistive splitter properties
- Insertion loss: 6 dB total per output (3 dB inherent + 3 dB resistive loss)
- Isolation between outputs: ~0 dB (the resistor network doesn’t isolate)
- Bandwidth: DC to many GHz (essentially flat across all frequencies — the resistors don’t have frequency-dependent behavior)
- Power handling: limited by the resistor wattage (typically 2-10 W for amateur use)
- Cost: ~$5 in parts
3.2 When to use a resistive splitter
The resistive splitter wins when:
- Bandwidth is the dominant requirement — covers DC to microwave
- Cost is the dominant requirement — three resistors in a box
- Isolation between outputs doesn’t matter — receivers that are isolated by other means (different LO frequencies, for instance)
It loses when:
- Signal strength matters (6 dB total loss per output is severe)
- Output isolation matters (reverse coupling between receivers causes feedback)
- High power is involved (resistor wattage limits)
3.3 The 6 dB loss math
A 2-way resistive splitter loses 6 dB per output because:
- 3 dB is the inherent split loss (half the power to each output)
- 3 dB is the resistive dissipation (the resistor network drops the impedance from 50/2 = 25 Ω back up to 50 Ω at each output)
The resistive splitter is unable to deliver the theoretical minimum 3 dB inherent loss; the resistors add another 3 dB. Wilkinson splitters (next section) achieve the theoretical minimum loss.
4. Wilkinson — equal-split with isolation
The Wilkinson power divider (Ernest Wilkinson, 1960) is the canonical low-loss splitter. It uses two quarter-wave 70.7 Ω transmission lines + a 100 Ω bridging resistor between the outputs.
Wilkinson 2-way splitter:
Input (50 Ω)
●
│
●─────────────●
│ │
│ │
70.7 Ω line 70.7 Ω line
λ/4 long λ/4 long
│ │
●─────────────●
│ │
● 100 Ω │
│ bridging │
│ resistor │
│ │
Output 1 Output 2
(50 Ω) (50 Ω)4.1 Wilkinson properties
- Insertion loss: 3 dB inherent + ~0.3-0.5 dB resistive = ~3.5 dB per output
- Isolation between outputs: 20-25 dB (the bridging resistor dissipates reverse currents)
- Bandwidth: ~25% (typical 2-way design); wider bandwidths possible with multi-section designs
- Power handling: limited by the bridging resistor (low — typically 1-2 W) and the transmission-line conductors
- Cost: $10-30 in parts for HF/VHF
4.2 The 70.7 Ω line and the 100 Ω resistor
The two key components:
- 70.7 Ω transmission line: this is
sqrt(50 × 100) = 70.7 Ω— the geometric mean of the input (50 Ω) and the bridging resistor (100 Ω). The quarter-wave length transforms the 100 Ω parallel pair at the input back to 50 Ω. - 100 Ω bridging resistor: provides isolation between the two outputs. Reverse currents from output 1 see 100 Ω at the bridging point; output 2 sees them as a 100 Ω termination, so they don’t couple through.
The geometry works because at the design frequency, the quarter-wave lines invert impedance: 100 Ω at the output looks like (70.7²/100) = 50 Ω at the input. Two of these in parallel = 25 Ω. The series 50 Ω input sees 25 Ω in parallel with 50 Ω = 16.67 Ω, but the geometry is also feeding through the 70.7 Ω lines, so the impedance match math is more complex than this simplified explanation captures. The net result: 50 Ω at all three ports, 3.5 dB loss per output, 20-25 dB isolation.
4.3 Wilkinson scaling to N ways
For N-way Wilkinson splitters:
| N (ways) | Line impedance | Insertion loss per port |
|---|---|---|
| 2 | 70.7 Ω | 3.5 dB |
| 3 | 86.6 Ω | 5.3 dB |
| 4 | 100 Ω | 6.5 dB |
| 8 | 141 Ω | 9.5 dB |
| 16 | 200 Ω | 12.5 dB |
Higher N requires higher line impedance, which becomes mechanically harder to realize (high-Z lines need very thin conductors or wide separation). Practical Wilkinson splitters are typically 2- or 4-way.
4.4 PCB Wilkinson construction
For frequencies above 100 MHz, Wilkinson splitters are conveniently built as microstrip on PCB:
- FR-4 substrate (or Rogers for low-loss) — ~1.6 mm thick
- Microstrip traces sized for 70.7 Ω characteristic impedance
- 100 Ω SMD resistor as the bridging element
- Three SMA connectors
The KiCad / JLCPCB design flow makes these straightforward to build. A 2.4 GHz Wilkinson PCB is about 4 cm × 3 cm and costs ~$10 at JLCPCB for 5 boards.
5. Quadrature hybrid (90° hybrid) — the 3 dB / 90° workhorse
A quadrature hybrid produces two outputs at equal magnitude but 90° apart in phase. The geometry is three quarter-wave transmission lines arranged in a ring.
5.1 The branch-line geometry
Quadrature hybrid (branch-line topology):
Input 1 (in-phase port)
●
│
λ/4 (35.4 Ω)
│
●─────────● Output 1 (0°)
│ │
λ/4 λ/4
(50 Ω) (50 Ω)
│ │
●─────────● Output 2 (-90°)
│
λ/4 (35.4 Ω)
│
●
Isolation port (resistor-terminated)5.2 Quadrature hybrid properties
- Insertion loss: 3 dB inherent (theoretical minimum for 2-way split)
- Isolation: 25-30 dB
- Phase relationship: 90° between outputs (Output 1 leads Output 2 by 90°)
- Bandwidth: ~20% (narrowband; multi-section designs achieve wider)
- Applications: single-ended-to-balanced conversion, image-reject mixers, balanced amplifiers, dual-feed antenna arrays
The quadrature hybrid is the canonical “split with phase” device. The 90° phase relationship is used in:
- Single-sideband (SSB) generation: I/Q quadrature mixing in digital radios
- Balanced amplifiers: Two amplifiers driven 90° out of phase, with output combining hybrid
- Image-reject receivers: Two mixers driven 90° out of phase
- Dual-feed antennas: feeding a vertical and horizontal antenna 90° apart for circular polarization
5.3 Commercial quadrature hybrids
| Model | Frequency | Power | Price (USD) |
|---|---|---|---|
| Mini-Circuits ZX10-2-12+ | 800-1200 MHz | 5 W | $50 |
| Mini-Circuits ZAPDQ-1 | 0.1-1 GHz | 1 W | $40 |
| Pasternack PE-Q12-2400 | 2.4 GHz | 25 W | $200 |
| MECA 822 series | 30 MHz-3 GHz | 100 W | $400 |
6. Rat-race / 180° hybrid
A rat-race (or “ring”) hybrid produces two outputs at equal magnitude but 180° apart in phase. The geometry is a 1.5λ ring with 4 ports at specific positions.
6.1 The rat-race geometry
Rat-race 180° hybrid:
Output 1
●
┌─────┴─────┐
╱ ╲
╱ ╲
╱ ╲
Input ● ● Isolation port
╲ ╱
╲ ╱
╲ ╱
└─────┬─────┘
●
Output 2
Ring circumference: 1.5λ at design frequency
Port positions: at 0, λ/4, λ/2, 3λ/4 (90° spacing for 4 ports)6.2 Rat-race properties
- Insertion loss: 3 dB inherent
- Phase: 180° between outputs in one configuration; 0° in another
- Isolation: 25-30 dB
- Bandwidth: ~15% (narrower than Wilkinson; narrower still than quadrature)
- Applications: differential signal generation, balanced mixer drivers
The rat-race is less common in amateur use than the Wilkinson or quadrature hybrid. Its 180° phase relationship is sometimes used in differential I/Q processing.
7. Ferrite-core transformer splitter — wideband, low loss
For HF and lower-VHF where physical quarter-wave lines are huge (a quarter-wave at 1 MHz = 75 m), Wilkinson splitters become impractical. The solution: ferrite-core transformer splitters built with TLT-style windings on ferrite toroids.
7.1 The TLT splitter geometry
A ferrite-core 2-way splitter uses:
- A bifilar (or trifilar) winding on a ferrite toroid
- Common-mode chokes to ensure isolation
- 50 Ω terminations at the bridging resistor location (similar to Wilkinson’s 100 Ω)
The exact winding depends on the splitting ratio and the impedance ratio. Sevick’s “Transmission Line Transformers” (5th ed.) covers the design in detail.
7.2 Ferrite-core splitter properties
- Insertion loss: 3 dB inherent + 0.5-1.0 dB ferrite/resistor loss = ~3.5-4 dB per output
- Isolation: 18-25 dB (lower than Wilkinson — the ferrite has less ideal impedance behavior)
- Bandwidth: 10:1 or wider (1.8-30 MHz on one design)
- Power handling: up to several kW with appropriately-sized ferrite
- Size: a 4-way HF splitter fits on a 50 mm × 50 mm × 25 mm chassis
The ferrite-core splitter is the dominant HF/low-VHF passive splitter. Commercial parts (Mini-Circuits ZN2PD2-50, MECA 802 series) are TLT-based.
7.3 Commercial ferrite-core splitters
| Model | Frequency | Ports | Power | Price |
|---|---|---|---|---|
| Mini-Circuits ZN2PD2-50+ | 0.5-50 MHz | 2 | 0.25 W | $50 |
| Mini-Circuits ZN4PD-642+ | 0.5-50 MHz | 4 | 0.25 W | $80 |
| Mini-Circuits ZB16PD2-S+ | 1.5-3 GHz | 2 | 1 W | $35 |
| MECA 802-2-1.500V | 1.5-1500 MHz | 2 | 5 W | $150 |
| MECA 802-4-1.500V | 1.5-1500 MHz | 4 | 5 W | $250 |
8. Directional couplers — for SWR/return-loss measurement
A directional coupler has two output ports with different coupling levels:
- Main port: -0.5 dB loss (most power passes through)
- Coupled port: -10 to -30 dB (a small fraction is tapped off)
Directional coupler (basic schematic):
Input ●─────────●─────────● Main output
│
│ coupled section
│ (-20 dB typical)
│
● Coupled port
│
● Isolation port (terminated)8.1 Where directional couplers are used
The most-common amateur use: inside SWR meters and watt meters. A Bird wattmeter has a coupler inside that samples the forward (or reflected) wave; the coupled port goes to the meter movement (or RF detector).
Other applications:
- Return-loss bridges (NanoVNA front end): two couplers measure incident and reflected signals
- Signal sampling: tap a portion of the TX signal for spectrum monitoring
- Power monitoring: continuous sampling for SWR alarms
- Antenna calibration: known-power injection through a directional coupler
8.2 Directional-coupler specs
| Parameter | Typical value | Notes |
|---|---|---|
| Coupling | -10 to -30 dB | The fraction tapped off |
| Insertion loss | 0.2-0.5 dB | Main-path loss |
| Directivity | 20-40 dB | How well it discriminates forward vs reverse |
| Isolation | Directivity + coupling | The reverse-path attenuation |
| Bandwidth | 1-3 octaves typical | Some special designs cover 10:1 |
The directivity is the key spec for measurement applications. A directivity of 30 dB means the coupler distinguishes forward from reverse waves at the 30 dB level — adequate for SWR measurements down to 1.1:1 accuracy.
8.3 NanoVNA’s internal couplers
The NanoVNA’s reflection bridge uses two directional couplers plus a reference oscillator. The two couplers extract the forward signal (incident wave) and the reflected signal (reflected wave); the NanoVNA’s DSP computes their ratio to determine S11 (reflection coefficient) and SWR.
The NanoVNA’s directional couplers are PCB-embedded with directivity of ~35 dB across 100 MHz – 1.5 GHz. This is the foundation of its measurement accuracy.
9. Bias-T — splitting RF from DC for masthead amplifiers
A bias-T is a special-purpose splitter that separates RF signals from DC power on the same coax cable. Used to power a remote LNA (masthead amplifier) over the same coax that carries the RF signal back to the receiver.
9.1 The bias-T topology
Bias-T:
DC + RF RF only
Coax to Coax to
masthead receiver
amplifier
● ●
│ │
│ │
● RF capacitor ●
╱ (passes RF, blocks DC) ╱
●─────────────────●───────────────●
│ │
│ ●─DC inductor─●
│ │ │
│ │ │
│ ● DC supply │
│ │ │
● ● ●
DC ground RF ground DC groundThe key insight: a capacitor passes RF and blocks DC; an inductor passes DC and blocks RF. The bias-T uses one of each, in the right topology, to separate the two on a common coax line.
9.2 Bias-T applications
- Masthead amplifiers: LNA at the antenna, DC power delivered up the coax
- Active antennas: powered loop antennas, active receive arrays
- GPS preamps: GPS LNA powered through the SMA connector
- Satellite TV LNB: low-noise block at the dish, powered via coax
- Active GPS antennas: 3.3-5V DC up the coax to the LNA
9.3 Bias-T specs
| Parameter | Typical value | Notes |
|---|---|---|
| Insertion loss (RF) | 0.3-0.5 dB | Capacitor’s series loss |
| DC voltage drop | < 0.5 V | At rated current |
| DC current rating | 100 mA - 1 A | Depends on inductor wire gauge |
| RF range | DC blocking from 1 MHz - 6 GHz | Wider with multi-element designs |
| Cost | $20-100 (commercial); $10 DIY |
9.4 Commercial bias-Ts
| Model | Frequency | DC | Power | Price |
|---|---|---|---|---|
| Mini-Circuits ZFBT-282-1.5+ | 0.1-2 GHz | 30 V / 1.5 A | 30 W | $70 |
| Mini-Circuits ZFBT-352+ | 0.5-7 GHz | 50 V / 1 A | 1 W | $120 |
| Pasternack PE7600 | 10 MHz - 18 GHz | 12 V / 0.5 A | 0.5 W | $300 |
| Stridsberg BT-300 | 0.1-3 GHz | 28 V / 1 A | 25 W | $250 |
| DX Engineering BT-1500 | 1.8-30 MHz | 12 V / 0.5 A | 50 W | $100 |
10. Insertion loss, isolation, bandwidth — the spec triangle
These three specs are in tension; you can have any two:
Insertion Loss
●
(low loss)
│
│
│
│
│
●───────────────────────────────●
Isolation Bandwidth
(high isolation) (wide bandwidth)
"Pick two of three"10.1 The tradeoff
- Low loss + high isolation = narrowband: a 0.3 dB / 30 dB combination is typically 5-15% bandwidth
- Low loss + wideband = low isolation: a 0.3 dB / 50%-bandwidth combination has 10-15 dB isolation
- High isolation + wideband = high loss: a 30 dB / 50%-bandwidth combination has 1-3 dB extra loss
10.2 Typical real-world combinations
| Splitter type | Loss | Isolation | Bandwidth |
|---|---|---|---|
| Resistive 2-way | 6 dB | 0 dB | DC-microwave |
| Wilkinson 2-way (single section) | 3.5 dB | 25 dB | 25% |
| Wilkinson 2-way (3-section) | 3.6 dB | 25 dB | 80% |
| Ferrite-core 2-way | 3.5-4 dB | 20 dB | 10:1 |
| Quadrature hybrid | 3.0 dB | 28 dB | 20% |
| Rat-race hybrid | 3.1 dB | 28 dB | 15% |
| Directional coupler (-20 dB) | 0.3 dB | 35 dB | 1-3 octaves |
| Bias-T | 0.5 dB | DC blocking | 1.8 MHz-6 GHz |
11. Best-case use
The passive distribution family wins when:
- Splitting an antenna among multiple receivers (HackRF + RTL-SDR + scanner from one discone) — a 4-way passive splitter delivers all three receivers from one antenna with 6 dB loss per port
- Combining the outputs of two amplifiers for higher TX power — 2-way combiner gives +3 dB at the antenna
- SWR/return-loss measurement in NanoVNA, Bird-meter, and tuner front ends — directional couplers are essential
- Powering masthead amplifiers via bias-T over coax — LNA at the antenna, DC up the coax
- Test signal injection for receiver alignment — a coupler taps a known signal into the receive chain
- Branch combining in repeater systems — multiple inputs combined at one antenna feedpoint
- Multi-feed antenna arrays — splitting one source across multiple feed points with specific phase relationships (Wilkinson for in-phase, quadrature hybrid for 90° feeds)
12. Worst-case use
The passive distribution family is the wrong answer for:
- Splitting TX signal among multiple antennas — usually a bad idea. The phase relationship matters, isolation matters, return-loss matters; passive splitters can mess all three up. Use an active distribution amp (Vol 19) for serious TX splitting.
- Operating outside the design band — insertion loss climbs, isolation collapses. Passive splitters have specific band ranges; outside them, performance degrades catastrophically.
- Weak-signal applications — 6 dB of 4-way split loss is fatal if the signal is already at the receiver’s noise floor. Use an active distribution amp with masthead LNA.
- High-power operation through narrowband splitters — Wilkinson resistor heating is a real issue at 100+ W.
- Direct splitting of a noisy signal — passive splitters don’t filter; the noise propagates equally to all outputs.
13. Power handling
| Splitter type | Typical max power | Limit |
|---|---|---|
| Resistive 2-way | 2-10 W | Resistor wattage |
| Wilkinson 2-way (PCB) | 5-25 W | Trace heating + bridging resistor |
| Wilkinson 2-way (cast / industrial) | 100-1000 W | Resistor + cable |
| Ferrite-core 2-way (small toroid) | 1-10 W | Ferrite saturation + resistor |
| Ferrite-core 2-way (large toroid) | 100-1000 W | Same |
| Quadrature hybrid | 1-25 W | Resistor + ferrite |
| Bias-T | 0.5-30 W | RF cap + DC inductor |
| Commercial high-power (ENI, MECA) | 1-10 kW | Custom for broadcast/military |
For amateur receive applications, 1-10 W splitters are sufficient. For TX applications, 100 W minimum splitters are needed; 1-2 kW for amplifier work. Commercial broadcast splitters reach kilowatts.
14. DIY build — a Wilkinson 2-way splitter for 100-1000 MHz
About 4 hours of work (mostly PCB design + assembly time). Total cost ~$25 + PCB fab.
14.1 BOM
| Part | Specification | Source | Mid-2026 price |
|---|---|---|---|
| FR-4 PCB (or Rogers RO4003 for low-loss) | 70 × 30 mm, 1.6 mm | JLCPCB (5 boards minimum) | $10 |
| 100 Ω SMD resistor | 1206 package, 1/4 W | DigiKey | $0.10 |
| 3× SMA edge-mount connectors | Standard 50 Ω | DigiKey | $9 |
| Solder + flux | Standard | Local | $2 |
| Total | ~$22 |
14.2 PCB layout (KiCad)
The PCB has three SMA edge-mounts (Input, Output 1, Output 2) and a 100 Ω resistor bridging Output 1 to Output 2 at their feedpoints.
Microstrip line dimensions for 70.7 Ω characteristic impedance on 1.6 mm FR-4:
- Trace width: ~1.4 mm
- Length: λ/4 at center frequency (e.g., 75 mm at 1 GHz; 750 mm at 100 MHz)
For a 100 MHz design, the λ/4 lines are 75 mm long — fits comfortably on a 90 × 60 mm PCB. For a 1 GHz design, the λ/4 lines are 75 mm long — same length! (because the velocity factor in FR-4 dielectric gives λ at 1 GHz of ~150 mm, with λ/4 being 37.5 mm — but typical Wilkinson uses 75 mm at 1 GHz for the 100 MHz – 1 GHz coverage with one design)
For a wider bandwidth (100 MHz – 1 GHz, 10:1), use the 3-section Wilkinson design with three pairs of λ/4 lines and three bridging resistors. The 3-section design extends bandwidth to ~80% at the cost of two extra resistors.
14.3 Construction
Order the PCB. Submit the KiCad design to JLCPCB or OSHPark. 5 boards typically arrive in 5-10 days for $10-30.
Solder the SMA connectors. Mount the three SMA connectors on the PCB edges, solder the center conductors to the PCB pads.
Solder the bridging resistor. A single 100 Ω 1206 SMD resistor bridges Output 1 and Output 2 at their feedpoints. Solder with a fine-tip iron.
Test with NanoVNA. Sweep across the design band:
- Input port (S11): should be < -15 dB across the design band (SWR < 1.4)
- Output 1 to Output 2 isolation (S12): should be > 20 dB
- Input to Output 1 (S21): should be -3.5 ± 0.3 dB across the design band
14.4 Verification
A successful build shows:
- SWR < 1.5:1 at all three ports across 100 MHz – 1 GHz
- 3.0-3.5 dB insertion loss to each output
- 20-25 dB isolation between outputs
- Pattern roughly flat across the band (small ripple ±0.5 dB)
15. DIY build — a ferrite-core 4-way splitter for HF
About 6 hours of work plus testing. Total cost ~$45.
15.1 BOM
| Part | Specification | Source | Mid-2026 price |
|---|---|---|---|
| FT240-43 ferrite core | Mix 43, 2.4″ OD | DigiKey | $8 |
| #14 enamel wire | 4 m total (for 4 bifilar windings) | Local | $5 |
| 100 Ω bridging resistors (3×) | Non-inductive, 5 W | DigiKey | $9 |
| Hammond 1591-XL enclosure | 6″ × 4″ × 2″ | DigiKey | $15 |
| 5× SO-239 chassis connectors (1 input + 4 outputs) | DigiKey | $20 | |
| Hardware (screws, washers) | Local | $5 | |
| Total | ~$62 |
15.2 Construction
The 4-way ferrite-core splitter uses a two-stage Wilkinson architecture:
- Stage 1: input → two outputs (each at -3.5 dB)
- Stage 2: each of those two outputs → two more outputs (each at -3.5 dB more)
Total: 4 outputs at -7 dB each (theoretical 6 dB inherent + 1 dB resistive).
For HF (1.8-30 MHz), the bifilar transmission lines wind through the FT240-43 core. The 100 Ω bridging resistors connect between stage outputs.
15.3 Specifications
- Frequency range: 1.8-50 MHz (one design)
- Insertion loss per output: ~7 dB
- Isolation between outputs: 18-22 dB
- Power handling: 100 W SSB
- Mechanical: 4-port distribution in a 6″ × 4″ enclosure
This 4-way splitter handles a discone receiving 25 MHz – 1.3 GHz and distributes the HF portion (1.8-30 MHz) to 4 different SDR receivers simultaneously.
16. Commercial buys — Mini-Circuits, MECA, ENI, Anaren
Sorted by tier (USD, mid-2026):
| Tier | Model | Type | Frequency | Power | Price | Notes |
|---|---|---|---|---|---|---|
| Budget | Mini-Circuits ZFSC-2-1+ | 2-way Wilkinson | 1-1000 MHz | 1 W | $35 | The amateur reference |
| Budget | Mini-Circuits ZN2PD2-50+ | 2-way TLT | 0.5-50 MHz | 0.25 W | $50 | HF specialty |
| Budget | Mini-Circuits ZX10-2 family | Quadrature hybrid | various | 5 W | $50-100 | Wi-Fi to UHF |
| Budget | Mini-Circuits ZFBT-282-1.5+ | Bias-T | 0.1-2 GHz | 30 W | $70 | Standard bias-T |
| Mid | Mini-Circuits ZN4PD-642+ | 4-way TLT | 0.5-50 MHz | 0.25 W | $80 | HF 4-way |
| Mid | MECA 802 series | 2-way TLT | 1.5-1500 MHz | 5 W | $150 | Higher-power 2-way |
| Mid | MECA 802-4 series | 4-way TLT | 1.5-1500 MHz | 5 W | $250 | 4-way version |
| Mid | Stridsberg MCA20 series | 4-way passive | 0.5-2 GHz | 25 W | $200 | Modular distribution |
| Mid | DX Engineering DXE-DP-4-1 | 4-way HF | 1.8-30 MHz | 50 W | $180 | Amateur HF specialty |
| Premium | ENI 4061-2 | 2-way industrial | DC-1 GHz | 2 kW | $1500 | Industrial-grade |
| Premium | MECA broadband | 2-way | various | 1 kW+ | $800+ | Broadcast/industrial |
| Premium | Anaren custom couplers | Custom | various | various | $500+ | Custom-fab |
| Premium | Pasternack PE-W7150 horn coupler | Directional | 1-18 GHz | 15 dBi | $400 | Microwave |
| Premium | Pasternack PE-W18-N | Directional coupler | 6.5-18 GHz | 22 dBi | $1500 | Premium directional |
What to avoid:
- Cheap eBay “1-2.4 GHz splitters” with no published S-parameters — the specs are usually wishful thinking
- “Multi-band miracle splitters” claiming 100 MHz – 6 GHz with 0 dB insertion loss — physically impossible
- Resistive splitters marketed as “Wilkinson” — they’re not; verify the topology before buying
- Used splitters with bridged resistor failure — visible carbonization on the resistor is a permanent damage indicator
17. Common gotchas and myths
-
“Resistive splitter has 3 dB loss” — no, 6 dB loss including the resistive cost. The 3 dB is the inherent split loss; another 3 dB is the resistor network’s dissipation.
-
“Splitter with no resistor is lossless” — false in the passive case. T-junctions without a Wilkinson resistor have 0 dB isolation and 100% reflective interaction between branches; the resulting standing-wave pattern wastes power and corrupts both outputs.
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“Splitter = combiner” — physically yes (same device), electrically: in a Wilkinson, the resistor only “lossless” combines the signal if the inputs are in-phase. Mismatched-phase signals heat the resistor (the energy that would otherwise be wasted as reflection).
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“Directivity = isolation” — distinct specs. Directivity is the coupler’s ability to discriminate between forward and reverse waves. Isolation is the reverse-path attenuation between two output ports (in a splitter). Both matter; they measure different things.
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“Higher coupling = better directional coupler” — false. A -10 dB coupler has lower insertion loss in the main path than a -30 dB coupler, but provides less reverse-path discrimination. The “right” coupling depends on application: -10 dB for general sampling, -20 dB for SWR meters, -30 dB for precision measurement.
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“Bias-T blocks all DC and passes all RF” — only over the design frequency range. Outside the band, the capacitor’s reactance changes (lower at low f) and the inductor’s reactance changes (higher at high f) — the separation degrades.
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“My SWR meter is bidirectional” — true for crossed-needle meters that show both forward and reverse simultaneously; false for single-needle meters that read either forward or reverse selectively. Verify which type before relying on the reading.
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“Coupling and insertion loss are unrelated” — false. For a fixed coupler topology, lower coupling (= more main-path power) means higher coupled-port loss. The tradeoff is a property of the coupler design.
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“All quadrature hybrids are 90° phase” — true at the center frequency, false at the band edges. Phase response is frequency-dependent; the 90° spec is at the design center, with ±10° variation across the band typical.
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“Splitters are reciprocal” — true for the passive ones. A 2-way Wilkinson works equally well as a combiner. Active devices (LNAs, amplifiers) are not reciprocal — they have specific signal-flow directions.
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“Power handling is the same for splitting and combining” — usually yes, but the resistor dissipation is different. Combining mismatched-phase signals dumps the difference into the resistor; splitting just splits the power. The combining application can stress the resistor more.
18. Resources
- Pozar, Microwave Engineering (4th ed.) Ch. 7 (power dividers and directional couplers) — the canonical reference.
- Mini-Circuits app notes (AN-10-005, AN-10-006 — power splitter basics; AN-50-009 — Wilkinson splitter design) — vendor-published design tutorials.
- MECA passive RF device handbook — comprehensive product family.
- Sevick, Transmission Line Transformers (5th ed.) — covers ferrite-core splitter design.
- Wilkinson’s 1960 original paper — “An N-Way Hybrid Power Divider,” IRE Transactions on Microwave Theory and Techniques.
- ARRL Antenna Book Ch. 25 (matching and power dividers) — amateur-focused treatment.
- Microwaves101 articles on Wilkinson, quadrature, and rat-race designs — community reference.
- Pasternack catalog — high-end commercial splitter reference.
- JLCPCB / OSHPark — PCB-fab options for DIY Wilkinson and Vivaldi designs.