Bend Radiuses of U.FL Cables' Coax Types: 1.13, 1.32, 1.37, RG174, RG178

rg178-coax-for-ufl-cables

Coaxial cable Bend radius (mm/in) Diameter (mm/in) Max. frequency (GHz)
1.13 aka 1.13mm  4.5 / 0.177 1.13 / 0.04 6
1.32 aka 1.32mm 5.5 / 0.216 1.32 / 0.051 3
1.37 aka 1.37mm 9 / 0.354 1.37 / 0.053 6
RG 174 coax 9.9 / 0.393 2.79 / 0.11 1
RG 178 coax 10.16 / 0.4 1.83 / 0.072 3

It is often necessary to use very thin and flexible coax for U.FL cables, even though the more flexible options have the most signal loss.

The more flexible the coax, the more signal loss it has among the options. However, it is often required or important to use very thin and flexible coax for two reasons:

  1. In tight spaces (inside of cases and enclosures), a thin coax option is often necessary. Sometimes limited size of ports, requires the use of the most flexible 1.13 coax, or 1.32 or 1.37.
  2. Thicker coax may make the U.FL connector pop off the jack: When connecting U.FL connector to a jack on a mini-PCI card or board, often the tight space requires the use of 1.13,1.32 or  1.37mm coaxial cable, because it is very thin and flexible. Very thin cable is typically needed in tight spaces inside of enclosures, so that the uFL connector will snap down on the jack without popping off.

The five coax types in the table above are the only five types that can be used with U.FL connectors. All thicker coax types are too large in diameter to be used with U.FL. 1.13 coax, or 1.32 or 1.37 are known as micro or mini-coax.

Flexibility and bend radius will affect the performance of U.FL cable assemblies when they are routed and used in radio frequency circuits. The minimum bend radius of a coaxial cable is the minimum radius at which the cable can be bent without physical damage or impairment of its performance. It is usually around five times the outer diameter of the coax (though this is not hard and fast). 

Exceeding the bend radius limit will cause:

  • The cable to become kinked
  • Disruption of the concentric layered structure of the cable
  • Displacement of the inner conductor
  • Warping of the outer braided shielding
  • Impedance changes within the cable
  • Discontinuities along the length of the cable that cause an increase in VSWR, signal loss, and reflections
  • Degraded overall performance of the radio frequency circuit in which the bent cable is used

This means that coaxial cable with increased flexibility is a favorable selection in settings where a low bend radius is critical for reliable routing. As the cable is passed it often has to bend around fixed structures that can create a corner in the cable if is not adequately flexible. The table at the top of the page compares the bend radius of the five coax cables along with the diameter and maximum frequency range for a quick comparison.

See list of all of our articles about U.FL cables and connectors

The U.FL connector by Hirose is a lightweight micro-miniature coaxial cable connector known for its low profile (mated height of only 2.5 millimeters) and consistent performance at microwave frequencies up to 6 GHz. It consists of a male jack which is usually PCB-mounted and a female plug that forms a reliable mechanical and electrical connection that is confirmed by a tactile click sensation. The small mounting area of this ultra-small surface-mounted coaxial connector makes it ideal for applications where wireless connectivity is required within a device.

All coaxial cable featured is manufactured in compliance with the European Unions Restriction of Hazardous Substances (RoHS) legislation and its international equivalents as well as existing Conflict Minerals legislation, including Section 1502 of the Dodd-Frank Act.

Posted by George Hardesty on 22nd Nov 2020


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