BASIC PRODUCT DETAILS

RF & Microwave Cables:

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 cable consists of three elements, centre conductor, surrounded by the outer conductor, and finally an insulating spacer (dielectric material) between the inner and outer 
• Most of the Coaxial RF cables have a protective outer sheath or jacket in addition to the outer conductor material.
• The inner conductor and the outer shield of the RF cable is sharing the same geometric axis.

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.

• What are RF Cables?
• Construction of RF cables.
• Types of RF
• Prime applications of
• The Specifications that need to consider in the RF cable selection process?
• RF and Microwave Cables manufacturers.

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Design and Application

Construction of RF and Microwave cable:

The fundamental construction of RF cable consists of

• The Center conductor (at the center of the cable assemble ) is made of Copper material.
• The dielectric material is an insulator between the inner and outer conductor, which is usually made of PTFE. 
• Outer Conductor which is generally made of Copper material.

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.

Twin-lead lines Vs Co-axial RF Cables.

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.

Advantages of Co-axial Cable:

• In an ideal coaxial RF cable, the electromagnetic field exists only in the space between the outer and inner conductors.
• RF Co-axial cable can install next to any metal objects without power losses.
• RF Co-axial cables are more flexible, so they can bend within the limit.
• RF Coaxial cable provides protection from external electromagnetic interference.

Connector for RF Cables:

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.

Gender and Polarity of RF Connectors:

• RF connectors are available in both polarity modes(standard and reverse).
• For standard polarity, RF and microwave standard male RF connectors have threads on the inside of the shell and for RF female connectors, have threads on the outside of the shell.
• For a reverse polarity, in the RF connector the male plug has a socket in the middle and the plug’s shell has threads on the inside to receive the pin from the female connector.

Applications of RF & Microwave Connectors:

The prime application of the RF Coaxial cable is for the transmission line for radio frequency and microwave signals.

Industrial applications: 

• Feedlines connecting antenna to RF trans receiver at the base station.
• Distribution of cable television signals, digital audio, computer network, etc.
• Telephone trunk lines, broadband internet networking cables.
• Connecting different systems in RF and microwave industry.
• Connecting instruments to DUT in RF & microwave lab testing.

Types of RF Cables:

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 RF Cables:

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.

• Semi-Rigid cable is unique in that it is easily bent to the desired finished shape using tools, however, it shouldn’t be returned to the previous shape once bent.

Minibend/Microbend RF cables:

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).

• This gives the liberty to the user to bend the cable at the connector-cable junction so as to use the straight connector as well as the Right Angle connector.

Hand-Formable coaxial 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.

• Hand-Formable cable lies in between Semi-rigid and Flexible cables in terms of performance & cost.

Flexible RF Cables:

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 RF cables are used in the majority of indoor & outdoor applications and are preferable by users because of their convenience & user-friendliness.

Flexible Cable Types:

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.

• Spuma & RG categories would be cost-effective and widely used.

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.

Applications:

Aviation, Space and Defense, Test & Measurement, Medical.

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Basics & Selection Feature

Selection Criteria of RF Connectors:

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:

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:

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.

VSWR:

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:

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.

Dielectric:

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.

Bend Radius:

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.

RF cable Connector Mating Cycles:

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

Conclusion:

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.

Thanks & Regards

RFMWC:-RF & Microwave Community

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