How to connect RF antenna cable connector
As an important part of passive components, RF antenna cable connector has good broadband transmission characteristics and a variety of convenient connection modes. Therefore, it is widely used in test instruments, weapon systems, communication equipment and other products. Because the application of RF antenna cable connector has penetrated almost all sectors of the national economy, its reliability has attracted more and more attention. In this paper, the failure mode of RF antenna cable connector is analyzed, and how to improve its reliability is discussed.
Although there are many kinds of RF antenna cable connectors, the connection principle is basically the same whether it is threaded connection type such as n-type, SMA and 3.5mm, bayonet connection type such as BNC and C, or push connection type such as SMB, SSMB and McX. Taking n-type connector as an example, the failure forms and methods to improve reliability are analyzed.
After the n-type connector pair is connected, the outer conductor contact surfaces (Electrical and mechanical reference surfaces) of the connector pair are pressed against each other by the tensile force of the thread, so as to achieve small contact resistance (< 5m Ω). The pin part of the conductor in the pin is inserted into the hole of the conductor in the socket, and good electrical contact between the two inner conductors at the mouth of the conductor in the socket is maintained through the elasticity of the wall of the insertion hole (contact resistance < 3M Ω). At this time, the step surface of the conductor in the pin and the end face of the conductor in the jack are not pressed tightly, but a gap of < 0.1mm is left, which has an important impact on the electrical performance and reliability of the coaxial connector. The ideal connection state of n-type connector can be summarized as follows: good contact of outer conductor, good contact of inner conductor, good support of dielectric support to inner conductor, and correct transmission of thread tension. Once the above connection status changes, the connector will fail. Next, we will start with these key points to analyze the failure principle of the connector, so as to find the correct way to improve the reliability of the connector.
Failure caused by poor contact of outer conductor
In order to ensure the continuity of electrical and mechanical structures, the force between the contact surfaces of outer conductors is generally large. Taking the n-type connector as an example, when the tightening torque MT of the screw sleeve is the standard 135n. Cm, the formula MT = kp0 × 10-3n. M (k is the tightening torque coefficient, here k = 0.12), it can be calculated that the axial pressure P0 on the outer conductor can reach 712n. If the strength of the outer conductor is poor, it may cause serious wear and even deformation and collapse of the connecting end face of the outer conductor. For example, the wall thickness of the connecting end face of the male outer conductor of SMA connector is relatively thin, only 0.25mm. Most of the materials used are brass, with weak strength and slightly large connecting torque. The connecting end face may be excessively extruded and deformed, damaging the inner conductor or medium support; Moreover, the surface of the outer conductor of the connector usually has a coating. A large contact force will destroy the coating on the connecting end face, resulting in an increase in the contact resistance between the outer conductors and a decline in the electrical performance of the connector. In addition, if the RF antenna cable connector is used in a bad environment, a layer of dust will be deposited on the connecting end face of the outer conductor after a period of time, which will increase the contact resistance between the outer conductors, increase the insertion loss of the connector and reduce the electrical performance index.