A complete introduction to coaxial wires (RF coaxial cables) for aerospace applications
Aerospace coaxial cable is a radio frequency transmission cable designed specifically for extreme working conditions of airborne, missile borne, satellite, and deep space aircraft. Its core function is to stably transmit radio frequency/microwave signals in environments with wide temperature, vacuum, vibration, irradiation, and strong electromagnetic interference. Unlike civilian coaxial cables, it uses special fluoroplastic, silver plated conductors, and high shielding structures, strictly following aerospace specific standards. It focuses on five core performance characteristics: low loss, phase stability, lightweight, extreme environment resistance, and high shielding
Classification of coaxial cables
(1)Basic coaxial structure (aerospace grade layered design)
Five layers from inside to outside, each layer has special requirements for military aerospace materials, and it is strictly prohibited to use ordinary copper, PE, PVC and other civilian materials:
Inner conductor
Material: High purity oxygen free copper silver plated (coating ≥ 1 μ m, high-end aerospace ≥ 2 μ m); The satellite in orbit products are made of silver plated copper-clad steel/anti atomic oxygen alloy to resist the erosion of space atomic oxygen.
Structure: Single strand solid (semi-rigid)/ultra-fine multi strand precision twisted (flexible, resistant to millions of bending vibrations); High frequency and low loss require a super smooth surface of the conductor to reduce skin effect losses.
Dielectric insulation layer (core performance layer)
Civilian PE is completely prohibited, and aerospace is divided into three levels:
General airborne: solid PTFE/FEP, temperature resistance -55~200 ℃;
Lightweight/Low Loss: Expanded Polytetrafluoroethylene (ePTFE) with extremely low dielectric constant, reduced weight by 30%, and minimal phase fluctuations across a wide temperature range;
Satellite vacuum grade: high-purity foamed PTFE, no small molecule volatilization, avoiding vacuum precipitation pollution of optical and RF devices, resistant to high-energy space irradiation Jekano (J...).
Shielding layer (EMI anti-interference core)
Single layer braided shielding is only used for ordinary airborne applications, while high-end radars/satellites use composite shielding:
Double layer silver plated copper weaving: coverage rate of 95%~98%, shielding effectiveness ≥ 90dB;
Foil tape+double-layer braided composite shielding: shielding efficiency of 120dB+, dedicated for phased array radar and electronic countermeasures;
Semi rigid: Seamless silver plated copper tube outer conductor with optimal phase stability and extremely low leakage.
Outer sheath
Mainstream FEP and PFA fluoroplastics; Low smoke halogen-free special sheath is used for civil aviation aircraft, resistant to corrosion from aviation hydraulic oil (Skydrol), de icing fluid, and fuel; Vacuum satellites have no outer sheath or ultra-thin FEP weight reduction design.
(2)Three mainstream product types (classified by rigidity)
1. Flexible aviation coaxial (most commonly used onboard, RG series/European EN4604 series)
Suitable for cabin wiring, frequent bending, narrow space penetration, and anti vibration fatigue.
Classic military RG model (MIL-DTL-17 US military standard)
RG179:75 Ω, outer diameter 2.54mm, micro lightweight, GPS, Internal wiring of navigation receiver, -55~200 ℃, 1GHz attenuation ≤ 0.52dB/m, yellow page 88 shift ..;
RG316: 50 Ω, PTFE insulation, higher temperature resistance than RG174, universal avionics and satellite antenna short wire;
RG400: 50 Ω double shielded standard airborne cable, radar and satellite communication feeder, long distance low loss, standard configuration for aircraft on military aircraft;
RG142: Coarse diameter and low loss, used for airborne high-power RF transmitters.
European aviation standard EN4604 series (Airbus, Boeing, domestic large aircraft)
WD, WM, KX lightweight series, mainly 50 Ω, maximum operating frequency of 6GHz, temperature range of -65~200℃, lightweight design, reducing weight by 20%~60% compared to traditional RG, in line with FAR25 aviation flame retardant low smoke requirements analysis and testing .
2. Semi rigid/semi flexible coaxial (radar, phased array, satellite payload)
The outer conductor is seamless silver plated copper tube, which can be manually bent and fixed after shaping. The phase temperature drift is extremely small and the shielding leakage is extremely low, making it a must-have for high-precision microwave systems
Specifications: 0.86mm, 1.19mm, 2.2mm, 3.0mm outer diameter;
Frequency band coverage DC~40GHz (X/Ka band radar);
Application: Airborne active phased array radar, satellite RF payload, missile seeker, high-precision testing equipment;
Advantages: Full temperature range phase change<0.3 °, resistance to external electromagnetic interference, no weaving gap signal leakage micro coax.
3. Ultra lightweight micro coaxial (weight reduction for unmanned aerial vehicles, commercial aircraft, deep space satellites)
Gore and Kesley high-end products, foam ePTFE medium, thin-walled structure, reduce weight by 60% compared to RG400 under the same energy; The replacement of a single large passenger aircraft can reduce weight by more than 20kg, directly reduce fuel consumption, support up to 12GHz RF transmission, and is widely used for onboard entertainment and satellite communication antenna feeders.
(3)Two standard impedances with clear division of labor
50 Ω (used in 90% of aerospace scenarios): matched with RF power amplifier, radar, satellite communication, electronic countermeasures, airborne VHF/UHF radio, balancing power capacity and low loss, RG400,EN4604, Semi rigid all 50 Ω.
75 Ω: Navigation, GPS satellite reception, onboard video transmission, civil aviation onboard entertainment system, representative model RG179, lightweight 75 Ω foam coaxial.
(4)Strict aerospace grade environmental performance indicators (distinguishing from civilian cores)
1. Temperature tolerance
Conventional onboard: -55℃~+200℃;
Deep space/polar spacecraft: extended to -65℃, short-term peak temperature of 260℃; Impedance and attenuation fluctuations of ≤ 3% after hundreds of high and low temperature cycles.
2. Mechanical reliability
Vibration: 10~2000Hz random vibration, simulating the impact of engine and rocket launch, with millions of bends and no broken strands;
Pressure resistant and wear-resistant: resistant to body compression, friction of cabin wiring harness, and corrosion of aviation chemicals on the protective sheath;
Flame retardant: Civil aviation meets FAR Part 25 Appendix F, low smoke, halogen-free, low toxicity, and does not release highly toxic gases when ignited.
3. Space exclusive performance (satellites, manned spacecraft)
Vacuum low exhaust: Total material mass loss TML<1%, condensable volatile matter CVCM<0.1%, does not contaminate the lens and sensor;
Radiation resistance: able to withstand proton and electron radiation in space, with insulation not powdering and loss not soaring;
Anti atomic oxygen: Silver plated alloy conductor for low orbit satellites to prevent corrosion and failure of the outer conductor.
4. RF electrical core indicators
Strict impedance tolerance: 50 Ω± 2 Ω, only ± 5 Ω for civilian use;
Ultra low attenuation: Foam PTFE medium significantly reduces high-frequency losses;
High shielding effectiveness: ordinary airborne ≥ 90dB, radar/satellite composite shielding ≥ 120dB;
Phase stability: Temperature changes and minimal phase shift after bending meet the precise control of phased array radar beams.
(5)Mainstream execution standards
US military standard (military aircraft, satellite): MIL-DTL-17 (formerly MIL-C-17) RG series coaxial specification; GJB1215A Domestic Military RF Cable Component Standard;
European civil aviation standards (Airbus, domestic large aircraft): ASD EN4604 series, WD/WM/KX lightweight high-temperature coaxial;
NASA Space Standard: SP-8007 Vacuum Low Gas, Atomic Oxygen Protection Specification;
Domestic aerospace standards: HB aerospace cable standard, QJ aerospace cable specification, supporting manned spaceflight, satellite, and launch vehicle models.
(6)Typical application scenarios
1. Civil aircraft/general aviation: GPS navigation, satellite communication SATCOM, VHF communication radio, onboard entertainment IFE, weather radar, collision warning system, priority lightweight EN4604 low smoke halogen-free coaxial.
2. Military aircraft, missiles, drones: airborne active phased array radar, electronic countermeasures ECM, data link, seeker RF components; A large number of RG400, semi-rigid, and ultra lightweight micro coaxial cables are used to balance weight reduction and anti-interference.
3. Satellites, manned spacecraft, deep space probes: onboard communication payloads, onboard radar, remote sensing RF receivers; Vacuum low exhaust, radiation resistant foam PTFE coaxial, semi-rigid for high-precision microwave loading.
4. Launch Vehicle: Equipped with telemetry, RF communication, and guidance systems, capable of withstanding strong launch impacts and high-temperature tail flame radiation.
(7)Industry Development Trends
Ultimate lightweighting: Expanded ePTFE and thin-walled composite structure continuously reduce weight, lowering aircraft load and fuel consumption;
High frequency: Developing low loss Ka/Ku band special coaxial cables for 6-40GHz millimeter wave radar and high-throughput satellites;
Integrated: coaxial+high-speed differential composite wiring harness, simplifying the layout of wiring harnesses inside the cabin;
Upgraded to withstand extreme environments: Expansion -85-260 ℃ ultra wide temperature range, stronger atomic oxygen, radiation tolerance, suitable for deep space exploration;
Low smoke and halogen-free environmental protection: Civil aviation mandates the promotion of fluorine free and low toxicity protective sheaths to enhance fire survival.
