Bend Radiuses of Coaxial Cable Types for U.FL Cables

Using very thin and flexible coax for U.FL cables is often necessary in compact wireless devices, even though the more flexible options typically exhibit higher signal attenuation compared to thicker coaxial cable types.

In IoT, embedded wireless, cellular, WiFi, GPS, and Bluetooth applications — which are core focus areas of Data Alliance Inc. — selecting the correct coaxial cable type for a U.FL cable assembly is critical to maintaining reliable RF performance while accommodating tight mechanical constraints.

Why Very Thin Coax is Often Required for U.FL Cable Assemblies

The more flexible the coax, the more signal loss among the available options. However, very thin and flexible coaxial cable is frequently required for two main reasons:

1. Tight Space Constraints Inside Enclosures

In compact devices such as:

• IoT gateways
• Embedded Linux boards
• Mini-PCIe cellular modems
• M.2 wireless modules
• Industrial controllers
• Drones and robotics systems
• Asset tracking devices

A thin coax option is often essential. Limited internal routing space and tight RF port spacing frequently require the use of:

• 1.13 mm coax
• 1.32 mm coax
• 1.37 mm coax

These are commonly referred to as micro-coax or mini-coax cable types. Their small diameter allows clean routing inside enclosures without stressing the PCB-mounted U.FL jack.

2. Preventing U.FL Connector Detachment

Thicker coaxial cables can exert mechanical force on the U.FL connector when routed in confined spaces. Because U.FL connectors are extremely small and low-profile (mated height approximately 2.5 mm), excessive cable stiffness can:

• Cause the connector to lift or pop off the PCB jack
• Place torque stress on the RF pad
• Damage the PCB trace or connector

For mini-PCIe or M.2 radio cards, where clearance is minimal, thin coax (1.13, 1.32, or 1.37 mm) allows the U.FL plug to snap securely onto the jack without mechanical strain.

Data Alliance frequently assists customers in selecting the proper cable type to avoid mechanical failures in IoT deployments.

Coaxial Cable Types Compatible with U.FL Connectors

Only specific small-diameter coaxial cables can be terminated with U.FL connectors. Larger coax types exceed the connector’s crimping and dielectric capacity.

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 it can be bent without physical damage or impairing its performance. It is usually around five times the outer diameter of the coax (though this is not hard and fast).

The five commonly used coax types compatible with U.FL connectors are:

All thicker coax types (such as RG-58, LMR-100, LMR-195, etc.) are too large in diameter to be terminated with U.FL connectors.

For applications requiring transition to larger coax, Data Alliance manufactures custom U.FL to SMA, RP-SMA, MMCX, N-Type, and other RF adapter cable assemblies.

What Happens When Bend Radius Is Exceeded?

Exceeding the bend radius limit can cause:

• Kinking of the cable
• Disruption of the concentric layered structure
• Displacement of the inner conductor
• Warping or separation of the braided shield
• Micro-cracks in the dielectric
• Impedance discontinuities
• Increased VSWR (Voltage Standing Wave Ratio)
• Higher insertion loss
• Signal reflections
• Reduced antenna efficiency
• Degraded overall RF system performance

Even if visible damage is not apparent, impedance shifts along the cable length can negatively impact sensitive RF circuits.

For IoT and industrial wireless applications, this may result in:

• Reduced signal strength (RSSI)
• Lower data throughput
• Intermittent connectivity
• Increased retransmissions
• Reduced cellular or WiFi range

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 it is not adequately flexible. The table at the top of the page compares the bend radius of the five coax cables and the diameter and maximum frequency range for a quick comparison.

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

Flexibility vs. Signal Loss Tradeoff

There is always a tradeoff between:

• Mechanical flexibility
• Cable diameter
• Shielding effectiveness
• Attenuation (signal loss)

Micro-Coax (1.13 / 1.32 / 1.37 mm)

Advantages:

• Very flexible
• Ideal for tight routing
• Prevents connector stress

Disadvantages:

• Higher attenuation per foot
• More susceptible to shielding degradation

RG-174

Advantages:

• Better shielding
• Lower loss than micro-coax
• Higher durability

Disadvantages:

• Larger diameter
• Less flexible

RG-178

Advantages:

• PTFE dielectric
• Good temperature resistance
• Smaller than RG-174

Disadvantages:

• Lower max frequency rating (typically 3 GHz)
• Slightly stiffer than micro-coax

Data Alliance technical support often recommends using the thinnest cable possible only for the short internal jump, then transitioning to a lower-loss coax for longer external runs.

Shielding Characteristics and EMI Considerations

Shielding effectiveness becomes increasingly important in:

• Industrial IoT environments
• High EMI settings
• Cellular installations near switching power supplies
• Multi-radio devices

Micro-coax typically uses lighter shielding compared to RG-174. For environments with:

• High RF noise
• Long cable runs
• Outdoor exposure

RG-174 or RG-178 may provide better long-term performance.

Data Alliance can assist in selecting cable assemblies based on EMI conditions and frequency bands.

U.FL Connector Overview

The U.FL connector, originally developed by Hirose, is a micro-miniature RF connector designed for:

• Surface-mount PCB applications
• Space-constrained wireless modules
• High-frequency performance up to 6 GHz

Key characteristics:

• Mated height: approx. 2.5 mm
• Snap-on coupling mechanism
• Compact footprint
• Lightweight design
• Reliable microwave-frequency performance

It consists of:

• A PCB-mounted jack
• A cable-mounted plug

The tactile “click” confirms proper engagement.

Because of its small size, U.FL connectors are rated for limited mating cycles (typically around 30 connections). For applications requiring frequent connect/disconnect cycles, an external SMA or RP-SMA bulkhead connection is recommended.

Common Applications for U.FL Cable Assemblies

Data Alliance supplies U.FL cable assemblies for:

• LTE/4G/5G routers
• WiFi modules
• GPS receivers
• LoRaWAN devices
• Embedded IoT boards
• M2M industrial equipment
• Drones and robotics
• Smart city infrastructure

Custom lengths, connector combinations, and bulkhead options are available to match specific antenna integration requirements.

Best Practices for Routing U.FL Coaxial Cables

To ensure optimal performance:

1. Avoid sharp 90-degree bends.
2. Maintain bend radius above minimum specification.
3. Do not pinch cables under enclosure lids.
4. Avoid repeated flexing once installed.
5. Secure cables to prevent vibration stress.
6. Use strain relief when transitioning to bulkhead connectors.

Proper routing significantly extends cable life and preserves RF integrity.

Compliance and Quality

All coaxial cable assemblies supplied by Data Alliance Inc. are manufactured in compliance with:

• European Union RoHS directives
• International hazardous substance regulations
• Conflict Minerals legislation
• Section 1502 of the Dodd-Frank Act

This ensures environmentally responsible manufacturing and global regulatory compatibility.

Technical Support from Data Alliance Inc.

Selecting the correct coaxial cable type for a U.FL assembly requires balancing:

• Frequency band
• Cable length
• Available space
• Mechanical stress
• Environmental conditions
• Signal loss tolerance

Data Alliance provides technical assistance to help customers choose the proper cable type and connector configuration for their specific IoT or wireless application.

If you are designing a wireless device or integrating antennas into an enclosure, our team can help determine:

• Optimal coax type
• Appropriate connector transition
• Bulkhead mounting solutions
• Strain relief methods

• Shielding considerations

Conclusion

When working with U.FL connectors, the smallest and most flexible coax types — 1.13 mm, 1.32 mm, and 1.37 mm — are often necessary for internal routing within compact wireless devices. However, flexibility comes at the cost of increased attenuation and sometimes reduced shielding.

Understanding bend radius limitations and respecting them during installation is critical to preserving impedance stability and minimizing RF performance degradation.

By selecting the appropriate coaxial cable type and following proper routing practices, reliable wireless performance can be maintained even in highly constrained IoT and embedded applications.

For more information about U.FL cable assemblies, RF adapters, and antenna integration solutions, consult Data Alliance Inc.’s technical resources or contact our support team for guidance tailored to your specific wireless design.