Published on 10/13/2026
For a 24 to 40 GHz coax interconnect, specify the complete assembly through its highest required frequency, with a suitable precision interface and defined insertion-loss and matching limits. A 2.92 mm interface is rated to 40 GHz as a connector family, but that does not guarantee every cable termination, bend or assembly meets your requirement.
A 28 GHz prototype may work with a short bench lead and then lose repeatability after the cable is routed around a bracket. At these frequencies, reference planes, connector condition and the agreed routing deserve as much attention as the bulk-cable selection.
This guide explains what to buy and what drives the quote. It does not assign an invented price or promise a universal 40 GHz cable performance figure.
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A 2.92 mm connector is a common choice through 40 GHz. The 2.4 mm family supports higher frequency capability, but it is not directly interchangeable with the SMA/3.5 mm/2.92 mm mating group. Use a correctly specified adapter when transitioning between different mating systems.
| Interface | General family context | Procurement check |
|---|---|---|
| 2.92 mm | Operation through 40 GHz | Exact connector and cable termination qualification |
| 2.4 mm | Operation through 50 GHz | Correct mating system and calibration hardware |
| SMA | Part-dependent microwave capability | Do not assume 40 GHz from thread compatibility |
| 3.5 mm | Part-dependent upper frequency | Check exact part, not only compatibility with 2.92 mm |
Mechanically mateable interfaces can still have different electrical limits. A lower-rated SMA device connected to a 2.92 mm cable does not become a 40 GHz port. Inspect and gauge precision interfaces according to the equipment procedure; a damaged contact can harm a valuable port.
Specify insertion loss over the entire operating band, not only at 28 GHz if the design reaches 40 GHz. The maximum permitted loss depends on the signal-chain budget and installed length. A short assembly can use a different construction from a moving bench cable even when both operate at the same frequency.
| Requirement | Define it explicitly | Avoid |
|---|---|---|
| Insertion loss | Maximum dB versus frequency | One vague low-loss claim |
| VSWR or return loss | Limit across the required band | Confusing matching with through loss |
| Phase or delay | Tolerance and reference planes if needed | Assuming equal cut lengths prove phase match |
| Routing | Bend geometry and movement conditions | Qualifying straight then sharply bending in service |
Key idea: VSWR and insertion loss answer different questions. Specify both where needed; a well-matched lossy cable is still a lossy cable.
Calibrate the VNA to the agreed reference planes using appropriate hardware for the interface and band. State whether the measured assembly includes adapters. A calibration before an extra adapter is not equivalent to a calibration at the assembly mating face.
Step 01
Control the interface
Inspect for debris, bent contacts and worn mating surfaces. Use the exact torque requirement from the connector or instrument documentation rather than a generic family value.
Step 02
Control the route
Measure in the agreed configuration and avoid unnecessary movement afterward. If flex stability matters, specify how much movement and the allowed change.
Step 03
Control the acceptance record
Request frequency span, S21/insertion-loss data, matching data and the stated calibration reference planes. Include phase data only when it is an agreed test requirement.
Specify the loss you can afford, not only the cable name
Send SigmaRF your frequency band, connector interfaces, installed length and insertion-loss target. Every assembly is VNA-swept for VSWR and insertion loss before shipment.
Specify a Custom AssemblyPrecision interfaces, suitable cable construction, controlled termination and full-band verification add cost. Tight phase, flex or loss tolerances add work beyond a basic static jumper. These costs do not vanish just because the assembly is only 100 mm long.
| Cost driver | What changes | How to avoid unnecessary expense |
|---|---|---|
| Frequency ceiling | Connector and test hardware requirements | Specify the actual upper band edge |
| Loss target | Cable diameter and construction | Use the system budget, not an arbitrary lowest-loss demand |
| Phase/flex stability | Selection and additional verification | State a measurable tolerance and movement test |
| Routing and shape | Fixtures or forming constraints | Supply a clear installed drawing |
| Reporting and traceability | Test data and identification work | Name the required deliverables in the RFQ |
Do not compare quotes by GHz label alone. Ask whether the same length, interface grade, acceptance limits, routing and test record are included. A cheaper assembly with a different requirement is not an equivalent quote.
If a long coax run consumes too much budget, consider whether the RF source or receiver can move closer to the antenna or device. At fixed installations, another transmission approach may be worth evaluating, but it brings its own transitions, mechanics and test requirements. Do not assume a coax replacement is drop-in.
Read SigmaRF's RF Connector Frequency Limits for interface context, RF Interconnects for Test Labs for bench handling, and Phase-Matched Cable Assemblies for phase procurement. This guide focuses on the 24 to 40 GHz purchasing and acceptance boundary.
Illustrative 40 GHz budget: 300 mm cable path, 1.0 dB maximum complete insertion loss, assumed 0.2 dB interface allowance. These are design assumptions, not catalog ratings.
The extra interface crosses this example target even though every component may be described as 40 GHz capable. Replace the assumed loss allowances with verified complete-path data and qualify the installed configuration.
Can 2.92 mm connectors operate at 40 GHz?
The 2.92 mm family is intended for operation through 40 GHz. Confirm the exact connector, cable termination and finished assembly limits across your required band.
Can I mate 2.92 mm with SMA?
The interfaces are mechanically mateable, but the SMA part may have a lower electrical limit. Check condition, dimensions and exact ratings before mating precision hardware.
Is 2.4 mm directly compatible with 2.92 mm?
No. They are different mating systems. Use a correctly specified precision adapter where a transition is required.
Why are mmWave cables expensive?
Precision interfaces, cable construction, termination control and full-band tests add work. Phase, flex and tight loss requirements can add further cost; request equivalent specifications when comparing quotes.
Do I need phase-stable cable at 28 GHz?
Only if the measurement or system needs controlled phase under movement or temperature change. State the phase tolerance and conditions; a frequency rating alone does not prove stability.
What should a 40 GHz cable test report include?
At minimum, the agreed frequency span, insertion loss, matching results and reference-plane information. Include phase, flex and other data when they are specified acceptance requirements.
Buy a measured assembly, not only a connector family and a GHz label. Define the upper frequency, loss and matching limits, routing, reference planes and required handling stability before asking for a quote.
SigmaRF VNA-sweeps every assembly for VSWR and insertion loss before shipment. Its requirements range reaches 40 GHz from 100 MHz, with Vadodara volume and Cleveland-area precision facilities. Lead times can be as short as 2 days for suitable builds; precision interfaces and extra qualification may affect the final schedule.
Specify the loss you can afford, not only the cable name
Send SigmaRF your frequency band, connector interfaces, installed length and insertion-loss target. Every assembly is VNA-swept for VSWR and insertion loss before shipment.
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