RF coaxial connector is a subdivision of electronic connector and also a hot field. Next, engineers of Cankemeng will make a professional introduction to the knowledge of RF coaxial connector.
Overview of RF coaxial connectors:
Coaxial connectors, (Some people also call it RF connector or RF connector. In fact, RF connector is not exactly the same as coaxial connector. RF connector is classified from the perspective of the use frequency of the connector, while coaxial connector is classified from the structure of the connector. Some connectors are not necessarily coaxial, but also used in the field of RF, and coaxial connector can also be used in low frequency, for example, very common audio headphone plug, The frequency shall not exceed 3MHz From the traditional point of view, RF refers to the MHz category. Nowadays, coaxial connectors are often used in the microwave field. In the GHz category, the word “RF” has been used all the time and overlaps with the word “microwave”), which is a branch of connectors. There are similarities and differences between connectors. Coaxial connectors have inner conductors and outer conductors. The inner conductor is used to connect the signal line. The outer conductor is not only the ground wire of the signal line (reflected on the inner surface of the outer conductor), but also plays the role of shielding the electromagnetic field (shielding the interference of the internal electromagnetic wave to the outside through the inner surface of the outer conductor, and shielding the interference of the external electromagnetic field to the inside through the outer surface of the outer conductor), This feature gives the coaxial connector great space and structural advantages. The outer surface of the inner guide and the inner surface of the outer guide of the coaxial connector are basically cylindrical surfaces – in special cases, they are often required for mechanical fixation and have a common axis, so they are called coaxial connectors. Among the several forms of transmission lines, coaxial cable is widely used because of its outstanding advantages (simple structure, high space utilization, easy manufacturing, superior transmission performance…), resulting in the need to connect coaxial cable, and coaxial connector is applied. Due to the advantages of coaxial structure, the continuity of characteristic impedance of (coaxial) connector (compared with other connectors) is more easily guaranteed, the transmission interference and interference (EMI) are very low, and the transmission loss is small, so it is almost exclusively used in radio frequency and microwave fields. Because it is almost absolutely used in high frequency, some electrical performance requirements are different from other connectors
Performance index of RF coaxial connector
The electrical performance of the RF coaxial connector should be like the extension of the RF coaxial cable, or the impact on the transmitted signal should be minimized when the coaxial connector is connected with the coaxial cable. Therefore, the characteristic impedance and voltage standing wave ratio are important indicators of the RF coaxial connector. The characteristic impedance of the connector determines the impedance type of the cable connected with it The voltage standing wave ratio reflects the matching level of the connector
A. Characteristic impedance: an inherent characteristic of the transmission line determined by the capacitance and inductance of the transmission line, reflecting the distribution of electric and magnetic fields in the transmission line. As long as the medium of the transmission line is uniform, the characteristic impedance is a constant. During wave transmission, E/H is constant. The transmission line itself determines its characteristic impedance, and the characteristic impedance is the same everywhere on the transmission line. In coaxial cables or coaxial connectors, the characteristic impedance is determined by the inner diameter of the outer conductor, the outer diameter of the inner conductor and the dielectric constant of the medium between the inner and outer conductors. There is the following quantitative relationship.
B. Reflection coefficient: the ratio of reflected voltage to input voltage. The higher the value, the less reflected energy, the better the matching, the closer the characteristic impedance, and the better the continuity
C. Voltage standing wave ratio: there will be two kinds of waves propagating on the mismatched transmission line, one is the incident wave and the other is the reflected wave. In some places, two kinds of waves are superimposed. The superimposed waves do not propagate along the transmission line, but stagnate. In other words, there is always a maximum or minimum voltage on any reference plane. Such waves are called standing waves. The VSWR is the ratio of the sum of the input voltage and the reflected voltage to the difference between the input voltage and the reflected voltage. This value is greater than or equal to 1, the smaller the better, and has a quantitative relationship with the reflection coefficient.
Post time: Feb-18-2023