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MM8130 RF Calibration Kit

A 1‑ and 2‑port VNA calibration kit presented at the Murata MM8130‑2600RA2 SWF‑type microwave coaxial switch‑connector interface (DC–6 GHz). Use it to calibrate a cable + Murata probe assembly (or a fixture that uses the SWF/MM8130 probe interface) to the probe tip, so the reference plane lands at the connector's center contact.

Status: V1, 2‑layer, ready for OSH Park. Design‑rule clean (0 DRC, 0 ERC, 0 schematic‑parity).

⚠️ AI‑generated design. This schematic and PCB layout were produced with AI assistance. Review every connection, value, footprint, and dimension against the datasheets before ordering or trusting it. The schematic and the board silkscreen carry the same warning.

Standards included (SOLT)

All standards sit on one non‑separable board. Each is an MM8130 receptacle with the standard element placed right at the RF contact. The Murata probe, when inserted, opens the connector's internal switch and contacts pin 1 (IN) — so every standard is defined between IN and GND.

The switched OUT pin (pin 2) of every connector is intentionally left unconnected — the internal switch isolates it from IN while a probe is inserted, so loading it would only add a stub.

The connector (MM8130‑2600RA2)

• Murata SWF‑type microwave coaxial connector with switch, 50 Ω, DC–6 GHz, 2.5 × 2.5 × 1.4 mm.
• Normally the internal mechanical switch connects IN→OUT (signal passes through). Inserting a Murata probe breaks that path and connects the probe to IN. That is why all standards are referenced to IN.
• Pinout: 1 = IN (center RF contact, probe‑contacted), 2 = OUT (switched), 3 = GND (shell, 4 lands).
• LCSC C167503, DigiKey 490‑4981‑1‑ND, Mouser 81‑MM8130‑2600RA2.

Footprint

Custom footprint MM8130:MM8130-2600RA2 (in the project's MM8130.pretty), built from Murata catalog O30E ("Standard Pattern Dimension") and cross‑checked pad‑for‑pad against the vendor land pattern (LCSC C167503). Copper lands: two 0.50 × 0.58 mm signal pads (IN/OUT) on the center axis at ±1.16 mm, and four 0.75 × 0.80 mm ground lands at (±1.025, ±0.95) mm — reproducing the catalog's 2.80 mm ground span / 1.30 mm signal gap / 2.90 mm signal span.

Board / fabrication — OSH Park 2‑layer

• Board size ≈ 46.5 × 15.0 mm, rounded rectangle with 3 mm corner fillets. Connector pitch is ~8 mm; the Thru pair is ~7.5 mm apart. Standards are probed one at a time during a cal, so the tighter spacing is fine — just confirm your specific Murata probe body clears a neighbour when inserted.
• 2 × M3 mounting holes (3.2 mm, non‑plated) at the lower‑left and lower‑right corners (H1, H2), centred in the corner fillets, in a clear band below the connectors so screw heads/standoffs stay out of the probe area.

Using the kit (SOLT)

1. Terminate your VNA cable with the mating Murata SWF probe (Murata O30E p.23 lists the probes).
2. In the VNA's cal‑kit definition, enter the standard models:
   • Open: characterize the open capacitance (C0…C3) — the MM8130 open is not an ideal open.
   • Short: offset‑short with the small residual inductance of the via/copper.
   • Load: 50 Ω; the Stackpole RNCQ 0603 HF resistor is good but not a perfect broadband load — characterize if you need <‑30 dB return loss near 6 GHz.
   • Thru: one‑way delay ≈ 30 ps for the 5.18 mm CPW line (plus the two connector transitions). Measure it for the exact electrical length/loss.
3. PCB standards are secondary standards — for best accuracy, characterize each one against a known‑good reference and store the measured models.

Next‑version ideas / caveats

• The load uses an 0603 (chosen for easy hand‑soldering). It has more parasitic reactance than an 0402/0201, so characterize the load if you need high accuracy near 6 GHz; drop to 0402/0201 and shorten the stub for a better HF load.
• If you want tight Thru impedance, a 4‑layer controlled‑impedance build (thin top dielectric) is the better route; on 2‑layer, keep the Thru as a characterized reference rather than a precise standard.
• Characterize and label each standard with its measured model.

Sources

• Murata Microwave Coaxial Connectors catalog O30E (SWF type, land pattern, probe lineup).
• Murata SWF product page.
• Stackpole RNCQ HF thin‑film resistor datasheet (50 Ω 0603 load, RNCQ0603BKE50R0).
• OSH Park design rules (2‑layer: 6 mil trace/space, 10 mil drill, 1.6 mm FR4).
• Footprint geometry cross‑checked against LCSC C167503.