A coaxial RF and Microwave cables are a type of coaxial cable which is used in RF and microwave systems to send or receive radio frequency signals through it. RF and Microwave Coaxial cable is a transmission line, which is used to carry RF electrical signals through it with low loss.
RF coaxial cables differ from other normal shielded cables because, for the efficient function of the transmission line, it needs a precise and constant conductor spacing within it.
The design of the Coaxial cable was patented in 1880 by English physicist, mathematician, and engineer Oliver Heaviside (British patent No. 1407).
In this article about RF cables, we will share the following details.
The fundamental construction of RF cable consists of
Flexible RF cables would possess a Jacket, which is made of FEP or PUR, and Ruggedisation such as Aramid (if any).
Cable with Solid Center conductor would be preferable for Static applications and Strand Center conductor would be preferable for Dynamic application.
In radio-frequency and microwave applications the wave propagates primarily in the transverse electric magnetic (TEM) mode (electric and magnetic fields propagate perpendicular to each other).
Even though twin-lead lines can be used to propagate the electromagnetic wave down the line, but it causes to extend the propagation into the space surrounding it. This propagation may induce currents in the nearby conductors and cause detuning of the line by unwanted radiations. Another drawback of twin lines is, they cannot be bent, or tightly twisted, which may cause to change in the characteristic impedance, and cause reflection of the signal back toward the source.
Coaxial lines can solve the above 2 problems by confining all of the electromagnetic waves to the inside area of the cable. Coaxial lines are more flexible and can be bent and moderately twisted without any internal reflections. RF cables can be strapped to conductive supports without any induction of unwanted currents in them.
The ends of RF coaxial cables need to terminate with RF connectors to connect to other RF devices by maintaining their coaxial form and impedance. RF Connectors are usually plated with metals such as silver or tarnish-resistant gold, which have high conductivity. RF connectors will be available in different types with both gender and polarities.
General connector options: BNC, N, TNC, SMA, QN, QMA, 7/16, 3.5mm, 2.92mm, 2.4mm, 1.85mm, etc.
The prime application of the RF Coaxial cable is for the transmission line for radio frequency and microwave signals.
Rf cable is classified into different types on the basis of the flexibility of the RF coaxial cable assemble. Following are a few of the main classifications.
Sem-Rigid is known for its excellent Screening Effectiveness about ≥ 120 dB up to 18 GHz and it is a conventional cable used in precise & undisturbed installation applications up to 70 GHz frequency.
Equivalent co-axial cable with a flexible option known as Minibend/Micro bend, which is having a ‘Bend to End’ feature (with comparable electrical performance to semi-rigid cables).
Hand-Formable coaxial cables offer distinct mechanical advantages over semi-rigid cables. Bending is possible without any tools, and quick and easy assembly for design and manufacture.
Flexible Cables are used in commercial and military RF and microwave airborne systems, communication systems, cellular base stations, satellite, and ground systems.
Applicable in frequencies up to 70GHz. Options available with Resistant to chemicals, oils lubricants, and humidity.
Flexible cables are available as normal RF cables and High-performance microwave RF cables.
Normal RF Cables:
Normal RF Cables are optimized for frequencies up to 6GHz operation. These include flexible low-loss cables such as RG, Spuma/LMR, etc. Low Smoke-Free of Halogen (LSFH) jacketing can be used for fire retardant applications.
Defence, railway, telecom (wireless infrastructure), etc.
High-Performance Microwave Cable Assemblies:
High-Performance Microwave Cable Assemblies offer Stable system performance, a Large product selection for customized applications, a Long lifetime, fewer maintenance costs, etc. Generally applicable for frequencies up to 70GHz. Sucoflex cable series is known for precision.
Aviation, Space and Defense, Test & Measurement, Medical.
The Major specification that needs to be considered in the selection of the right cable is its application (Ground/Airborne/Testing/Any specific/Static or Dynamic/Indoor or Outdoor).
Once the cable is selected as per the application, need to select the cable meeting Operating Frequency (in GHz), Impedance (in Ohm), Insertion and Return Loss (of Cable Assembly- in dB) Screening Effectiveness (in dB), Static /Dynamic Bending Radius (in mm), Power handling (in Watt), Weight (in gram), Phase Matching or Delay Matching if any (in Degree or picosecond respectively).
In addition, Environmental Specification (Vibration, Operating Temperature range, Humidity, etc) and Velocity of Signal propagation (in %) need for the specific application.
Frequency measured in Hz (Hertz). RF and Microwave frequencies range of the cable and associated connector need to select for the suitable operation. RF cables are available from low frequency to very high frequency.
Insertion loss of the RF cables increases with frequency, it indicates the amount of RF power loss in the RF cables. Need to select a cable with lower insertion loss.
Voltage Standing Wave Ratio (VSWR) increases with the frequency of the RF cables. It indicates the efficiency of the RF cable to transmit the RF signal from a source, to the load side through a transmission line. A cable with lower VSWR needs to select.
Impedance is measured, in Ohms. It shows the resistance of the RF signal to the flow through the cable. 50 & 75 ohms cable is available.
The dielectric material is insulating material between the outer and inner of a coaxial cable. Good Dielectric material offers higher insulation and avoids the leakage of the signal.
The Bend Radius of the RF cable indicates the minimum radius, a RF coaxial cable can bend without degrading the electrical performance like VSWR and insertion loss. If the bend radius is more, the cable can be used for rough installations, where need to bend the cable for installations.
Another critical parameter that needs to consider is the number of the mating cycle of the RF and Microwave connectors associated with the RF cables. There are RF connectors designed for the lower number of mating to a larger number like 10K cycles of meeting without failure
Each type of RF and microwave co-axial cable has its own advantages and disadvantages, hence the selection should be based on the application, cost, in addition to the type and Radio Frequency range of signals, need to transmit.
As there are many cable manufacturers available, if you need support in the selection of suitable manufacturers, comment below in the comment box, with your application and design constraints, RFMWC is ready to support the designers in their design needs.
If you feel to recommend any specific cables and manufacturers, please feel free to reach us over the contact us or the article submission button.
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