RG402 is the 0.085-inch semi-rigid coaxial cable that populates precision RF assemblies: test equipment, communication systems, radar-adjacent hardware, and any application where signal integrity at radio frequencies justifies a cable you must form by hand. Semi-rigid construction trades convenience for performance — this guide covers what you gain, and the discipline it demands.
Construction and Specifications
RG402: 0.085-inch OD, solid copper outer conductor (the semi-rigid defining feature), solid or semi-solid PTFE-class dielectric, silver- or copper-plated center conductor. The solid outer conductor is the performance secret: 100% shield coverage with zero braid leakage, phase stability through temperature, and consistent impedance (50 ohm) along the formed path. Frequency performance reaches well into the tens of GHz for short runs — the cable's electrical ceiling sits far above most applications' needs, which is why RG402 remains the precision default. Jacket-less by design (the copper tube is the jacket), with plating options (silver for conductivity and solderability, copper for economy) matched to the application.
Why Semi-Rigid Instead of Flexible
Flexible coax (braid shields) leaks: braid coverage tops out below 100%, and braided shields' transfer impedance grows with frequency — measurable as signal leakage and ingress at the frequencies RF assemblies care about. Semi-rigid's solid tube eliminates the braid problem entirely and adds phase/mechanical stability (the cable holds its formed shape — RF path lengths stay where you formed them). The trade is exactly what the name says: the cable doesn't flex. Routing is done by forming the tube — deliberately, once, correctly.
Forming Discipline
RG402 is hand-formed with tooling (bending fixtures or a forming jig): minimum bend radius respected (typically ~10x OD for safe forming — tighter radii deform the dielectric and compromise impedance), smooth continuous bends (no kinks — a kinked RG402 is scrap; the deformation is permanent and electrical), and forming before connector attachment where possible (connector ends are the fragile regions). Planning the formed path on a template before touching the cable is the professional practice — measure twice, form once, because formed mistakes don't un-form.
Connector Termination
Semi-rigid terminates in SMA, SMP, N and precision RF connector families — typically by solder attachment of the outer conductor (the tube solders to the connector body: excellent electrical bond, demanding clean soldering) with the center conductor prepared to dimension (the connector's pin or the cable's core directly). Termination quality decides the assembly: dimensional precision (center-conductor length and dielectric setback are specified), clean solder without dielectric damage, and verification (VNA-class testing for demanding assemblies — insertion loss, VSWR). This is the class where RF test certificates ship with the parts.
Applications
- Test and measurement interconnects (the dominant use — VNA and signal-chain internal cabling).
- Communication and radar system assemblies.
- Aerospace and defense RF payloads (phase-stability-critical paths).
- Medical RF-adjacent equipment (MRI-adjacent and therapy systems).
Kaweei RF Assembly Capability
Kaweei manufactures semi-rigid RF assemblies — RG402-class constructions, formed and terminated to drawing, VNA-verified for precision classes — supporting communication and equipment customers from our Dongguan facility. Contact our engineering team with your frequency range and path requirements; our coaxial and communication guides cover the broader cabling classes.