Are You Measuring the DUT — or the Cable?
The Junkosha MWX8 Series is a metrology-grade VNA test cable assembly designed for engineers who need bounded, documentable phase and amplitude stability at microwave and mmWave frequencies.
The Role of the Cable in a VNA Measurement
A Vector Network Analyzer measures how RF energy behaves as it passes through or reflects from a device — parameters such as insertion loss, return loss, VSWR, phase, group delay, gain, and impedance.
After calibration, the VNA should remove the errors of the test system and measure only the device under test. In practice, this works only if the measurement setup remains stable after calibration.
When a cable is bent, moved, twisted, or repositioned after calibration, its electrical behavior can change. At microwave and mmWave frequencies, even small mechanical changes become significant measurement errors. Calibration cannot correct errors that happen after calibration — they appear directly as DUT measurement data.
Why Standard RF Cables Create Measurement Errors
A standard coaxial cable may transfer signal from point A to point B, but that does not mean it is stable enough for precision measurement. Engineers move cables to connect different DUTs, bend cables to reach fixtures, and reposition cables inside chambers or probe stations. Each movement can slightly change the conductor geometry, dielectric position, and connector interface.
Phase drift after calibration — cable movement changes electrical length, so the error appears as DUT behavior.
Amplitude instability — connector and cable movement introduce variability in insertion loss.
False pass/fail results — production test limits crossed because of cable variation, not the DUT.
Wasted debug time — engineers troubleshoot the DUT when the cable is the actual source of variability.
What Makes the MWX8 Series Different
The MWX8 Series is designed specifically as a VNA test assembly — not just as a general-purpose RF cable. Its main advantage is phase and amplitude stability during flexure: the cable maintains predictable electrical performance even when bent or moved during normal testing.
Model Overview
| Model | Max Frequency | DUT Connector | VNA Port | VSWR (typ) |
|---|---|---|---|---|
| MWX821 | 26.5 GHz | 3.5 mm (f) straight | NMD 3.5 mm | 1.29:1 |
| MWX851 | 50 GHz | 2.4 mm (f) straight | NMD 2.4 mm | 1.43:1 |
Both models available in 635 mm (25 in) and 965 mm (38 in). NMD ruggedized connectors are standard on the VNA port side — not an option.
NMD Ruggedized VNA Port (Standard)
Standard on all MWX8 assemblies. Protects the high-value VNA port from repeated connection wear and mechanical strain during daily lab use.
Phase Stability in Flexure
Specified and bounded phase change when the cable is moved — not just a general transmission rating. Critical for S-parameter repeatability.
Flex Life
Exceeds 40,000 tick-tock cycles at 180° bend on a 57 mm radius mandrel. Designed for realistic lab use where the cable is repositioned frequently.
Cable Properties
50 Ω · 79% velocity of propagation · >90 dB shielding to 18 GHz · 14.2 mm OD · Operating temperature 23 ±5°C (lab bench, not thermal cycling).
Performance Specifications
All stability specifications below are measured during cable flexure — the conditions that matter in a real VNA setup where the cable is moved between measurements.
Phase Stability in Flexure
| Model | Test Frequency | 635 mm (25 in) | 965 mm (38 in) |
|---|---|---|---|
| MWX821 | 26.5 GHz | ±3.9° | ±7.1° |
| MWX851 | 50 GHz | ±4.5° | ±9.0° |
Amplitude Stability in Flexure
| Model | 635 mm (25 in) | 965 mm (38 in) |
|---|---|---|
| MWX821 | ±0.08 dB | ±0.15 dB |
| MWX851 | ±0.08 dB | ±0.15 dB |
Insertion Loss
| Model | Length | Typical | Maximum |
|---|---|---|---|
| MWX821 | 635 mm | 1.75 dB | 2.1 dB |
| MWX821 | 965 mm | 2.45 dB | 2.8 dB |
| MWX851 | 635 mm | 3.6 dB | 4.5 dB |
| MWX851 | 965 mm | 5.1 dB | 6.2 dB |
Typical Applications
VNA Port Extension
Extends the calibrated measurement plane from the VNA front panel to fixtures, probe stations, chambers, or antenna test environments — without adding uncontrolled error.
S-Parameter Measurements
S11, S21, S12, S22, return loss, insertion loss, phase, group delay, and VSWR all benefit from a cable that introduces bounded, documentable uncertainty.
Component Characterization
Filters, amplifiers, attenuators, couplers, switches, connectors, RF modules, and PCB test fixtures — stable cables reduce measurement uncertainty and improve confidence in simulation data.
Antenna and Feed Testing
Swept-frequency antenna measurements, feed-line testing, and mmWave antenna development — where cable movement must not appear as antenna behavior.
5G / 6G mmWave R&D
At 26.5 GHz and 50 GHz, phase stability becomes critical. The MWX851 is well suited to 5G NR FR2 component and module characterization as well as 6G research.
Calibration Verification
A stable cable provides a reliable baseline for system checks, helping confirm that a measurement setup is still performing as calibrated between test sessions.
Why It Matters More at Higher Frequencies
At higher frequencies, wavelength becomes shorter. A very small change in electrical length creates a noticeable phase shift. A cable that seems stable at lower frequencies may not be stable enough at mmWave frequencies.
For example, at 50 GHz a single degree of phase error corresponds to roughly 55 femtoseconds of timing uncertainty. Phase-stable cables become more important as systems move into higher frequency bands used in 5G, 6G research, radar, satellite communication, automotive radar, high-speed digital validation, and advanced RF component development.
The Cost of Using the Wrong Cable
The risk is not only poor signal transmission. The larger risk is false confidence — believing the DUT has changed when the measurement error actually came from the cable.
- Non-repeatable measurements across test sessions
- Phase drift after calibration due to cable repositioning
- Insertion loss variation caused by cable flexure
- Ripple in reflection or transmission measurements
- False pass/fail results in production test systems
- Incorrect S-parameter data fed into simulation tools
- Connector wear on expensive VNA front-panel ports
- Engineering time spent debugging the setup instead of the DUT
MWX8 Selection Guide
MWX82126.5 GHz · 3.5 mm
Choose MWX821 for RF and microwave VNA testing up to 26.5 GHz with 3.5 mm connector interfaces. Suitable for component testing, board-level validation, filter and amplifier characterization, and general precision RF measurements up to K-band.
Not for mmWave applications above 26.5 GHz or 2.4 mm connector systems.
MWX85150 GHz · 2.4 mm
Choose MWX851 for mmWave VNA testing up to 50 GHz with 2.4 mm connector interfaces. Suitable for 5G NR FR2 component characterization, mmWave module testing, high-frequency amplifier and filter measurement, and automotive radar R&D.
Higher cost than MWX821 — specify only if the application genuinely requires 50 GHz coverage.
Choosing Cable Length
Both models are available in 635 mm (25 in) and 965 mm (38 in). The shorter assembly gives better stability specifications. The longer assembly offers more physical reach on the bench. Select the shortest length that comfortably reaches the DUT without placing mechanical stress on the connectors.
Operating Temperature: 23 ±5°C
The MWX8 Series is optimized for laboratory bench use at near-room temperature. It is not rated for thermal cycling, TVAC, or environments outside this range. For wide-temperature applications, see the EMF-06 (high-temperature) or EMF-07 (ruggedized) series.
Order the MWX8 Series Through Koto Electronics
Koto Electronics is the exclusive authorized distributor of Junkosha in Israel. We carry the MWX821 and MWX851 with local technical support, application consultation, and fast delivery to Israeli customers. Contact us for pricing, availability, and specification assistance.