In IoT wireless systems, performance evaluation is often focused on the communication module or the antenna itself, while the RF cable assembly connecting the two is frequently treated as a secondary component. In practical deployments, however, the choice of cable type, connector interface, and assembly quality directly affects signal attenuation, link stability, and long term system reliability an impact that is especially pronounced in compact platforms such as ESP32 based designs, LoRa nodes, and NB IoT terminals.This guide compares commonly used coaxial cables and RF connectors to help engineers and system integrators make informed technical decisions based on their applications.
Common IoT Wireless Technologies Overview
WiFi and Bluetooth Low Energy, commonly used on ESP32 platforms, operate mainly in the 2.4 GHz ISM band and support relatively high data rates over short to medium distances. At this frequency, coaxial cable attenuation increases quickly with length, making short cable runs, low-loss constructions, and compact connectors such as U.FL or I-PEX particularly important in device design.
LoRa and LoRaWAN are designed for low power, long range communication and typically operate in Sub GHz frequency bands. Compared with 2.4 GHz systems, Sub GHz signals experience lower path loss and reduced cable attenuation, allowing greater tolerance in cable loss. However, outdoor and remote deployments make mechanical durability and environmental resistance key considerations for RF cable assemblies.
NB IoT and LTE Cat M are cellular based IoT technologies operating in licensed frequency bands. They are optimized for wide area coverage, deep indoor penetration, and long device lifecycles. Because cellular IoT modules often support multiple frequency bands, RF cable assemblies used in these systems must maintain stable impedance and consistent performance across a wider frequency range.
From an RF interconnect perspective, the key difference between Sub GHz and 2.4 GHz systems lies in their sensitivity to cable loss and discontinuities. Higher frequency IoT designs benefit from shorter cable assemblies, tighter connector tolerances, and lower loss coaxial cables, while Sub GHz applications can prioritize mechanical robustness and environmental suitability with less impact on RF performance.
Core Components of an IoT RF Cable Assembly
Coaxial Cable
The coaxial cable forms the RF transmission path within an IoT cable assembly. It consists of a center conductor, dielectric insulator, shielding layer, and outer jacket, a structure designed to maintain controlled impedance and limit electromagnetic interference.
In IoT devices, commonly used coaxial types are selected based on frequency range, attenuation characteristics, flexibility, and size constraints. Thinner coaxial cables offer routing flexibility for compact modules, while lower loss constructions become increasingly important at higher frequencies or longer cable lengths.
RF Connectors
RF connectors provide the mechanical and electrical interface between the coaxial cable, the wireless module, and the antenna. In IoT applications, these connectors must maintain impedance continuity while accommodating repeated mating, limited PCB space, and vibration or environmental exposure.
Compact board level connectors such as U.FL or I-PEX are widely used on IoT modules, while SMA type connectors are often employed on external antenna interfaces. Adaptor components may be introduced when interfacing different connector standards, but each additional transition can introduce insertion loss and potential impedance discontinuities.
Common Coaxial Cable Types Used in IoT Projects
In IoT devices, coaxial cable selection is driven by a balance between electrical performance and mechanical constraints. Unlike traditional RF infrastructure, IoT platforms often require short cable runs, tight bending paths, and compact routing inside enclosures. As a result, cable diameter, attenuation characteristics, and flexibility are typically more critical than maximum power handling.
RG 178 Coaxial Cable
RG 178 is a thin, flexible coaxial cable widely used in compact IoT and wireless modules. It features a small outer diameter and PTFE dielectric, making it suitable for high frequency operation while maintaining good flexibility.
In IoT applications, RG 178 is commonly selected for short internal connections where tight routing and repeated bending may be required. While its attenuation is higher than that of thicker cables, the impact is typically acceptable due to the short cable lengths used in ESP32, LoRa, or cellular IoT devices.
RG 316 Coaxial Cable
RG 316 is a low loss coaxial cable compared with RG-178, offering improved attenuation performance while retaining flexibility. It uses a PTFE dielectric and silver plated conductors, which contribute to stable RF performance across a wide frequency range.
For IoT systems where cable loss margin is tighter such as higher frequency designs or applications requiring slightly longer internal or external cable runs RG 316 is often preferred. Its balance of low attenuation and mechanical robustness makes it suitable for industrial and long life IoT deployments.
RG 174 and Similar Small Diameter Coaxial Cables
RG 174 is another commonly used coaxial cable in IoT systems, characterized by its small diameter and relatively high flexibility. It is often selected for applications where routing space is limited and mechanical handling is a concern.
However, RG 174 exhibits higher attenuation compared with RG 316, particularly at higher frequencies. As a result, it is typically used in short cable assemblies or jumper cables, where mechanical convenience outweighs the need for minimum signal loss.
Micro Coax and Miniature Coaxial Cables
Micro coaxial and miniature coaxial cables are increasingly used in highly compact IoT devices, especially where space constraints are extreme. These cables offer very small bending radii and excellent routing flexibility, enabling integration within dense PCB layouts and small enclosures.
The trade off is higher attenuation and reduced mechanical robustness compared with standard RG series cables. Therefore, micro coax solutions are best suited for very short internal interconnects where minimizing size is the primary design objective.
Common RF Connector Types Used in IoT Devices
U.FL / I-PEX / MHF Series Connectors
U.FL, I-PEX, and MHF connectors are miniature RF connectors designed for direct mounting on wireless modules or PCBs. They are widely used in IoT devices due to their extremely small footprint and suitability for internal antenna connections.
These connectors are typically rated for limited mating cycles and are intended for controlled assembly environments rather than frequent field reconnection. Their compact size makes them ideal for ESP32 modules, cellular IoT modules, and other space constrained designs, where short jumper cables are required.
SMA and RP SMA Connectors
SMA connectors are threaded RF connectors commonly used for external antenna connections in IoT devices, offering robust mechanical retention and stable RF performance across a wide frequency range. RP SMA connectors share the same mechanical interface but differ in internal pin configuration, which prevents accidental mating with standard SMA connectors.
In IoT applications, SMA or RP SMA connectors are typically used when antennas must be externally accessible, such as in gateways, industrial IoT devices, or enclosures requiring field installation. Proper connector selection and polarity matching are essential to avoid impedance mismatches or installation errors.
To learn more about the differences between SMA and RP SMA connectors, please refer to our article Differences Between SMA and RP-SMA Explained.
MMCX and MCX Connectors
MMCX and MCX connectors are snap-on RF connectors used in certain industrial and modular IoT designs. Compared with threaded connectors, they allow faster connection and disconnection while maintaining relatively stable RF performance.
MMCX connectors are smaller and more compact, while MCX connectors provide slightly greater mechanical strength. These connector types are often selected for applications where modularity, serviceability, or vibration resistance is required, though their use in IoT is generally less common than U.FL or SMA interfaces.
To learn more about the structural differences and application considerations of MCX and MMCX connectors, please refer to our article MCX & MMCX RF Cable Assemblies Guide.
How to Select the Right RF Cable Assembly for IoT Projects
If the Connection Is Inside the Module or Enclosure
For internal connections within an IoT device, such as between a wireless module and an internal antenna, compactness and routing flexibility are typically the primary concerns. Short cable length, small connector size, and tight bend radius compatibility are often more important than achieving the lowest possible attenuation.
Thin coaxial cables combined with miniature connectors are commonly used in these scenarios, as long as impedance continuity is maintained and the cable length remains short enough to limit signal loss.
If an External Antenna Is Required
When an IoT device uses an external antenna, the RF cable assembly becomes part of the exposed signal path, and additional factors must be considered. Mechanical retention, connector durability, environmental resistance, and consistent RF performance across the operating frequency range are all critical.
In these applications, slightly thicker coaxial cables and robust connector interfaces are often selected to balance attenuation control with long term reliability, especially in industrial or outdoor deployments.
When a Custom RF Cable Assembly Is Preferable to a Standard One
Standard RF cable assemblies are suitable for many IoT applications, particularly during prototyping or low volume production. However, custom cable assemblies become preferable when specific length tolerances, connector combinations, routing constraints, or environmental requirements cannot be met by off the shelf solutions.
From a procurement standpoint, custom assemblies also help improve consistency across large production volumes, reduce installation variability, and support long term product scalability in IoT deployments.
FAQ
Conclusion
In IoT systems, RF cable assemblies are a critical but often overlooked part of the wireless link. As shown throughout this guide, selecting the right combination of coaxial cable, connector type, and assembly approach depends on frequency band, mechanical constraints, deployment environment, and production scale. By aligning cable choices with application specific requirements and long term supply considerations, engineers and system integrators can improve link stability, reduce integration risk, and support scalable IoT deployments across diverse use cases.