Coaxial RF connectors are important RF transmission components in the microwave field and are widely used in various microwave devices/components, microwave communication equipment, instruments and radar systems.
RF coaxial connector types: With the rapid development of wireless communications and radar technology in recent years, increasing system transmission range requires increasing system transmission power. As part of the entire microwave system, RF coaxial connectors must be able to withstand high-power transmission requirements. RF engineers also frequently perform high-power testing and measurement, and various microwave devices and components used for testing also require high-power capabilities. This creates increasingly high demands on the power capacity of RF coaxial connectors, a key indicator of RF coaxial connector quality. So, how much do you know about the power capacity of RF coaxial connectors? The power capacity of RF coaxial connectors is a complex issue, influenced by numerous factors, some of which interact with each other. These factors primarily include connector size (including pinhole size), operating frequency, body material, insulation material, contact reliability, contact resistance, voltage standing wave ratio (VSWR), ambient temperature, and altitude. The figure below shows Megaphase's recommended power capacity values for different RF connectors at different frequencies. When designing RF products, you can select the appropriate connector based on the product's operating frequency and power handling capacity.
Next, we will provide a detailed explanation of the factors that influence the power capacity of RF coaxial connectors. For RF signals of the same frequency, larger connectors have higher power handling capabilities. For example, connector pinhole size is related to the connector's current capacity, which is directly related to power. Among commonly used RF coaxial connectors, 7/16 (DIN), 4.3-10, and N-type connectors are relatively large, corresponding to larger pinhole sizes. Generally, the power handling capability of an N-type connector is approximately three to four times that of an SMA. This increased popularity of N-type connectors explains why the majority of passive components sold on the market, such as attenuators and loads with a power rating of over 200W, use N-type connectors. RFbuy (www.rfbuy.com) provides convenient access to high-power loads, attenuators, and other passive microwave components. The power handling capability of RF coaxial connectors decreases with increasing signal frequency. Changes in transmitted signal frequency directly affect transmission loss and voltage standing wave ratio (VSWR), which in turn affect transmission power capacity. Furthermore, skin effects can also be present. For example, a typical SMA connector has a power handling capability of approximately 500W at 2GHz, but an average power handling capability of less than 100W at 18GHz. According to the RFbuy RF Mall (www.rfbuy.com), most passive components, such as attenuators and loads, operating at frequencies above 18 GHz have an average power rating of less than 100 W. For millimeter wave frequencies, a 1.85mm 67 GHz fixed attenuator has an average power rating of less than 10 W, and a 1.85mm 67 GHz load has an average power rating of less than 22 W. A wider selection of 2.92mm attenuators and loads are available, with average power ratings up to 100 W. RF connectors are designed with a specified electrical length. In a finite-length line, when the characteristic impedance and load impedance are unequal, a portion of the voltage and current from the load is reflected back to the power supply. This wave is called the reflected wave, while the voltage and current from the power supply to the load are called the incident wave. The combined wave of the incident and reflected waves is called the standing wave. The ratio of the maximum and minimum voltage values of the standing wave is called the voltage standing wave ratio (also known as the standing wave coefficient). Reflected waves occupy channel capacity, reducing transmission power capacity. Insertion loss (IL) refers to the power loss in the line caused by the introduction of the RF connector. It is defined as the ratio of output power to input power. Many factors contribute to connector insertion loss, including characteristic impedance mismatch, assembly precision errors, mating end-face clearance, axis tilt, lateral offset, eccentricity, machining accuracy, and plating. Loss creates a difference between input and output power, which also affects power handling. Air pressure changes at altitude cause variations in the dielectric constant of air segments, and at low pressures, air is more susceptible to ionization, producing corona. The higher the altitude and the lower the air pressure, the lower the power handling capacity. Contact resistance: The contact resistance of an RF connector refers to the resistance at the contact point between the inner and outer conductors when the connector is mated. It is generally measured in milliohms and should be kept as low as possible. It primarily assesses the mechanical properties of the contacts, and the effects of bulk resistance and solder joint resistance should be eliminated during measurement. Contact resistance causes heating at the contacts, making it difficult to transmit high-power microwave signals. Connector materials: The power handling capacity of the same connector can vary depending on the materials used.