How to Select the Right Circular Connector for Avionics and Radar Systems

Together, avionics and radar systems support safe navigation, mission-critical communication, and situational awareness in aviation operations. These sophisticated systems rely on uninterrupted connectivity and signal transmission, and among the many components enabling this are connectors. These versatile devices ensure stable electrical links across avionics modules, sensors, radar arrays, processing equipment, and more.

As there are a vast range of connector types available for these purposes, selecting the most suitable and compatible option is an imperative, but challenging, task. In this blog, we will specifically focus on circular connectors for avionics and radar applications, examining the most common types and some important considerations for integrating them.

Circular Connector Types to Consider

MIL-DTL-38999 Connectors

The MIL-DTL-38999 series represents one of the most widely adopted families of circular connectors in aerospace and defense. Designed for high-density interconnects, these connectors deliver excellent electromagnetic interference (EMI) shielding, environmental sealing, and mechanical durability. Depending on their material and configuration, many variants are also rated for continuous operation at temperatures up to 200°C.

These connectors come in four primary options:

• Series I features a bayonet coupling mechanism that allows for quick mating and unmating, perfect for field-level maintenance and serviceability.
• Series II offers a low-profile bayonet coupling with a shorter shell design for applications with limited mounting depth or tight packaging constraints.
• Series III employs a self-locking, threaded coupling mechanism that provides the highest resistance to vibration and mechanical stress.
• Series IV uses a push-pull coupling system with anti-decoupling retention, allowing fast connection and disconnection while still maintaining resistance to accidental disengagement.

MIL-DTL-38999 shells are manufactured from aluminum, stainless steel, or composite materials. To meet specific corrosion resistance, conductivity, and shielding performance needs, consumers can also choose from finishes such as cadmium plating, electroless nickel, and olive drab zinc cobalt. Meanwhile, many variants support rear-release crimp contacts, fiber optic termini, or coaxial inserts for flexible signal and power configurations.

Use Cases

MIL-DTL-38999 connectors are equally suited for both airborne and ground-based radar platforms, as they boast resistance to moisture, vibration, dust, and electromagnetic interference (EMI). For instance, they are extensively deployed in avionics line-replaceable units (LRUs), cockpit displays, radar signal processors, engine control modules, flight control systems, and power distribution units. However, these connectors may introduce challenges in weight-sensitive applications such as within unmanned aerial vehicle (UAVs), space systems, or compact payloads due to their heavier shell materials and dense construction.

MIL-C-5015 and MIL-DTL-5015 Connectors

The MIL-C-5015 connector series, originally developed for general-purpose military use, are foundational in legacy aerospace and defense systems. Its more recent successor, MIL-DTL-5015, introduced tighter manufacturing tolerances, improved environmental sealing, and enhanced mechanical durability to better align with modern aerospace requirements. Both versions are appropriate for transmitting electrical power and low-frequency signals, particularly in environments that require high current handling.

These connectors are available in a broad range of sizes and employ a threaded coupling mechanism. Although this option is slower to engage and disengage compared to others, it excels in applications exposed to continuous vibration, shock, and mechanical stress. Moreover, their shells are typically constructed from aluminum alloy or stainless steel, while they are finished with materials like cadmium plating, anodizing, or zinc chromate for corrosion protection. Most configurations also accommodate backshells that offer strain relief, cable clamping, and environmental sealing to adapt to various installation needs.

Use Cases

MIL-C-5015 and MIL-DTL-5015 connectors serve non-flight-critical areas or where system compatibility with existing infrastructure is required, including avionics wiring harnesses, engine monitoring units, and ground control stations. Their high current-carrying capacity also makes them an apt choice for power distribution units, transmitter electronics, and maintenance platforms in radar applications.

However, as they lack the EMI shielding, contact density, and lightweight construction found in more advanced connector systems, these types may be less suitable for newer platforms with tight space constraints or strict weight limitations. Still, for retrofits, repairs, or standardization purposes, they remain a cost-effective and technically reliable solution.

BNC Connectors

The Bayonet Neill–Concelman (BNC) connector is a miniature radio frequency (RF) connector type. Known for their bayonet-style coupling, BNC connectors allow for quick connect and disconnect cycles. Although they are not designed for harsh environmental exposure like MIL-spec connectors, they offer consistent impedance—usually 50 ohms—to maintain signal fidelity in RF and video applications.

Constructed primarily from brass with nickel or chrome plating, BNC connectors provide moderate corrosion resistance and mechanical durability. While their environmental sealing is limited, BNC connectors can be overmolded or enclosed for added protection in semi-controlled environments. Additionally, they are compatible with an array of coaxial cables and available in both 50-ohm and 75-ohm versions to meet different demands.

Use Cases

BNC connectors are present in radar diagnostics, avionics test benches, and RF monitoring setups, where they enable quick, repeatable connections for signal injection, extraction, and analysis. Their low-loss performance makes them ideal for calibration and ground testing, especially in radar systems where they can support intermediate frequency (IF) or baseband stages by providing access to analog signal paths during development and maintenance.

BNC connectors are not typically used in flight due to their limited vibration resistance and environmental sealing, but they are indispensable and easy to use in ground-based systems and maintenance functions for radar and avionic platforms.

General Considerations for Selecting Circular Connectors

While connector type sprovide the framework for selection, additional criteria must be evaluated to ensure optimal performance and compliance in aerospace environments.

Electrical Performance

Connectors need to be tailored to the voltage, current, and signal frequency ranges specific to the avionics or radar system. Signal degradation can compromise radar accuracy or disrupt avionics communication, so impedance matching and shielding are also essential to take into account.

Durability

Aerospace connectors may face extreme temperatures, pressure fluctuations, and even chemical exposure. As such, sealing ratings like IP67/IP68 and corrosion-resistant materials—such as electroless nickel-plated aluminum or passivated stainless steel—are essential for connectors exposed to external elements or high-heat zones.

Shock and vibration tolerance are particularly important when it comes to in-aircraft connections. Threaded and bayonet coupling mechanisms offer secure retention for such conditions, with locking features and backshell accessories further enhancing strain relief and cable integrity during dynamic operation.

Standards Compliance and Compatibility

Connectors must comply with relevant aerospace and defense standards such as MIL-DTL-38999, ARINC 600/404, or SAE-AS specifications. Beyond certification, physical compatibility with existing mating interfaces, mounting systems, and cable assemblies is imperative to support seamless integration. This extends to choosing a connector’s size and weight to best use the space that it is placed in, with high-density insert arrangements or lightweight composite shells being particularly prized in UAVs, satellites, and tightly packed avionics bays.

Integration and Installation Considerations

• Even an appropriate connector can underperform if installation and system integration are not carefully planned, so some integration factors to keep in mind include:
• Employ backshell and strain relief options to protect wiring from pull-out forces.
• Secure contact plating for improved conductivity and corrosion resistance.
• Use color coding and keying for easy identification and secure mating.
• Encapsulating the connector or cable termination in a protective material—typically a thermoplastic (overmolding) or epoxy resin (potting)—to seal out moisture, dust, vibration, and other environmental hazards.

Technicians and engineers also have a responsibility to ensure proper torque settings during connector installation, as under- or over-tightening can lead to compromised sealing, thread damage, or unreliable coupling. After mating, insulation resistance and continuity testing should be performed to verify dielectric integrity, detect potential short circuits, and confirm proper contact engagement.

ASAP Purchasing: Providing Comprehensive Solutions for Your Connector Needs

If you are seeking a dependable source of circular connectors and other aerospace-grade components, ASAP Semiconductor is prepared to serve you through its procurement platform ASAP Purchasing. Here, we offer access to a diverse range of industry-compliant connector solutions and many other products from reputable manufacturers, all of which are subjected to stringent quality control measures prior to shipment. Furthermore, we are committed to helping customers secure competitive and swift fulfillment options while accommodating their unique requirements and restrictions alike. To learn more about our parts and services, we welcome you to peruse our inventory and get in touch with a member of our staff over phone or email.

1. randolph gills
2. Posted on July 2, 2025
3. connectors