Impedance matching is a critical technology for ensuring signal transmission quality; the characteristic impedance of a connector must align with that of the connected coaxial cable and the overall system to prevent signal reflection and energy loss, thereby maintaining signal integrity. Common system impedances include 50Ω and 75Ω. For instance, an SMA connector has a characteristic impedance of 50Ω; using it in a 75Ω system would result in performance degradation.
In precision multi-channel systems, manufacturing tolerances can lead to inconsistencies in phase and impedance across channels. To address this, the industry employs selective assembly methods based on predicted electrical performance.
Rigorous signal integrity testing is required to ensure connector performance in high-frequency, high-speed applications. Key tests include characteristic impedance, insertion loss, return loss, far-end crosstalk (FEXT), near-end crosstalk (NEXT), and eye diagram analysis. These tests adhere to various international and industry standards, such as USCAR-17 for the automotive sector and IEC 60512 for general applications.
To keep pace with the evolution of communication technology toward higher frequencies and greater densities, coaxial connectors are advancing in terms of miniaturization, higher frequency capabilities, lower loss, and lower Voltage Standing Wave Ratio (VSWR). Operating frequencies have expanded from the traditional GHz range into the millimeter-wave band; for example, the SMPM series supports frequencies up to 65 GHz and the SMPS series reaches 100 GHz, while millimeter-wave connectors with upper limits of 50–110 GHz are also under development. Simultaneously, connector sizes are shrinking-seen in series such as SMP and MMCX-to enable higher board-level mounting densities.
A connector's electrical performance, mechanical durability, and environmental adaptability depend largely on its materials and surface plating. Common plating types and their characteristics include: silver plating, which offers superior electrical and thermal conductivity, low contact resistance, and excellent intermodulation performance-making it ideal for inner conductors in low-intermodulation and high-power applications, though it is prone to sulfidation; gold plating, characterized by chemical stability, corrosion resistance, and low contact resistance-with wear resistance depending on thickness-commonly used for inner conductors and PCB connectors requiring high reliability; nickel plating, often used as an underlayer or for housings to provide good mechanical strength and corrosion resistance; and ternary alloy plating, which performs similarly to silver, offering excellent non-magnetic properties and corrosion resistance that help improve passive intermodulation performance, commonly used for outer conductors.