Push-On vs Threaded SMPM Microwave Connectors

Introduction : To pack dozens of coaxial cable assemblies into single module, designers frequently turn to Sub Miniature Push on Micro (SMPM) connector. However, traditional push-on designs come with inherent EMI (Electromagnetic Interference) vulnerabilities. To solve this, manufacturers have introduced the Threaded SMPM. Let us understand key difference between these SMPM microwave connector types.

Standard Push On SMPM Connectors

The standard push-on SMPM connector is engineered to maximize board space and simplify installation. Instead of a bulky threaded coupling nut, the SMPM socket features a slotted outer conductor. These slotted fingers flex inward when pressed onto a mating pin connector, using radial outward force to maintain the electrical connection. It has outer diameter of around 0.125 inches typically.

Advantages :

• Incredibly small center to center spacing
• Allows to densely pack ports on PCB or Panel
• Allows for quick and tool free installation

Limitations:

• Push-on connectors are highly susceptible to human error during blind mate or tight space installations.
• The slotted fingers that make the push-on action possible also act as windows for RF leakage.
• A misaligned push-on SMPM can see its shielding effectiveness plummet to as low as 40 dB, while also suffering from severe VSWR (Voltage Standing Wave Ratio) degradation and insertion loss.

Threaded SMPM Connectors

To overcome the EMI and mechanical retention issues of the push-on interface without reverting to large, traditional threaded connectors such as 2.92mm or SMA, the Threaded SMPM was developed.

This design utilizes the standard SMPM mating interface but integrates a highly compact, external threaded coupling nut.

Advantages:

• When the coupling nut is threaded onto the mating pin and torqued with a calibrated wrench, it physically covers the exposed slots of the socket conductor. This provides an continuous ground path that locks external noise out and internal signals in. Shielding effectiveness is restored to levels comparable to traditional threaded connectors.
• The threaded nut guarantees a standardized, consistent engagement force.
• While slightly larger than a pure push-on SMPM, the threaded SMPM remains remarkably compact.

Key differences

Summary

If your system demands the absolute smallest footprint and you can manage the resulting RF crosstalk, the Standard Push-on SMPM remains the go to choice. However, if your system is failing EMC compliance tests, suffering from erratic VSWR due to cable routing angles or being deployed in high vibration aerospace environments, upgrading to a Threaded SMPM provides the electrical reliability of a traditional connector while preserving critical board space.