D38999 Connectors and Cable Assemblies in Military Applications

Named for MIL-DTL D38999N, the applicable military standard, the “D38-Triple-9” cable assemblies have played an important role in various military applications, from communication systems to radar and electronic warfare equipment since World War II. These robust and versatile RF and microwave single-action interconnects are critically important for engaging and disengaging multiple lines of communication in the field of battle. Long used as rugged, high performance connectors in military and aerospace applications, D38999 connectors and cable assemblies are resurging as dependable favorites in high frequency multi-port/multi-signal applications. The D38999 design capably meets the demanding requirements of high frequency performance, multi-signal management, flexibility and durability in tough land and sea environments.

High Frequency Performance

Military operations often rely on high frequency communication and data transfer capabilities, especially in emerging warfare scenarios. D38999 cable assemblies are designed to deliver exceptional performance up to Ka-Band. The D38999’s ability to handle high frequencies with minimal signal loss ensures reliable and secure communication channels for military personnel in the field. Figure 1 shows individually terminated cables in (a) and examples of populated D38999 shells in (b).

Table 1 shows applications for D38999 connectors and cable assemblies.

Figure 1 ConductRF terminated cables (a) and ConductRF D38999 shells (b).

Benefits

Multi-Signal Management

Military settings commonly require simultaneous transmission of multiple signals and signal types. D38999 cable assemblies excel in managing these complex signal configurations, whether it involves combining data, voice and video streams or integrating various sensor inputs into a centralized system. Their advanced design and shielding capabilities prevent signal interference while maintaining signal integrity and accuracy even in highly dynamic operational environments.

Application Flexibility

D38999 assemblies can be customized to accommodate specific multi-signal interconnection requirements. These requirements may address connector and cable styles, along with distance specifications, to ensure seamless integration with existing military equipment and infrastructure. Their flexibility extends to harsh environmental conditions, with options for ruggedized and water-resistant designs that withstand extreme temperature, vibration and mechanical stress.

Challenges

For the untrained specifier/purchaser, ordering D38999 cable assemblies can be tricky. Housings are offered in nine different shell sizes and each size has many insert arrangements. Users can fully or partially load them with coax, twinax, quadrax, signal, power, fiber and more. These technologies can be mixed within a single interface or keyed to the same interface in four different ways. This level of customization requires a trusted and experienced supplier to assist and ensure best practices in the ordering/production stages of assembly. Additionally, material and plating choices offer more options that can be tailored to various mechanical and environmental needs.

D38999 coax solutions come in standard contact sizes: #8 (largest), #12 and #16 (smallest). The standard back shell solutions are more diverse than the insert arrangements and shell options. These options include straight, angled, clamp, crimp and strain relief styles. There are also several material and plating options to consider.

Ordering D38999 Connectors and Cable Assemblies

A D38999 connector and cable assembly integrates, bundles or harnesses multiple signals to allow single-action connections and disconnections in the field. If the required assembly mates to a predetermined configuration, much of the specification is defined. In these cases, electrical parameters on the mating side of the solution and factors like loss and power handling capability of the cable and assembly still need to be defined.

If the entire solution needs to be specified, the designer must consider the performance of each signal in the combined interconnect uniquely. This is important because each strand of cable that gets terminated in the final integration carries a signal. Each of these signals is terminated with a D38999 socket or pin contact that is inserted into the shell in a specifically keyed position.

To properly specify the assembly, the following performance requirements are important:

• Operating frequency range
• Insertion loss
• Maximum CW power
• VSWR
• Return loss
• Attenuation
• Impedance (50, 75 or 95 Ohm)
• Shielding requirements.

In addition to these parameters, ConductRF can assist designers with specifying cable type and size and selecting the best cable contact or termination style and size from a variety of options. Additional requirements to consider include phase matching, passive intermodulation (PIM) testing and other RF-related testing of key performance characteristics. It is also important to consider the need for strain relief, further wrapping and/or ruggedization, environmental sealing, thermal management and EMI/RFI protection.

Figure 2 Standard D38999 contacts.

Figure 2 shows examples of standard D38999 RF contacts. In this example, there are two pin-type contacts and one socket-type contact. It is important to note that not every RF cable style can be terminated to all the RF contact styles. This is a common miscue when specifying assemblies. Custom-designed contact solutions are possible but uncovering any potential cable/contact incompatibility early is important.

Conclusion

D38999 connectors and cable assemblies continue to be indispensable in military applications due to their versatility and reliability. Since ordering the connectors and cable assemblies can be complex, this article has highlighted tips to simplify this process for users. With proper education and in collaboration with an experienced RF cable assembly provider, users can specify key electrical, mechanical, environmental and assembly parameters and constraints to configure the appropriate D38999 connector and assembly solution. ConductRF will help users configure the best solutions for each unique challenge. The company also has a range of D38999 RF plug-in assembly solutions that provide field replacements in existing systems or turnkey solutions for users who want to avoid specifying a custom solution.