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The Challenges of High-Frequency Accuracy in RF Connectors

Author Cadence System Analysis

Key Takeaways

  • RF coaxial connectors are the most frequently used type of high-frequency connector in professional or commercial RF and microwave systems. 

  • Types of commonly-used RF connectors include UHF, BNC, Type N, TNC, Reverse Polarity TNC (RPTNC), SMA, and Reverse Polarity SMA (RPSMA). 

  • When choosing RF connectors to provide high-frequency accuracy, factors such as attenuation, VSWR, electromagnetic interference, and crosstalk need to be thoroughly studied to reach an optimal connector solution. 

RF connectors

In microwave and RF systems, connectors and cables are precision components that influence the performance of microwave and RF systems. To increase the reliability and performance of these systems, highly sophisticated RF connectors and cables are needed. However, even with these cables, high-frequency accuracy is a challenge.

In this article, we will discuss RF connectors, cables, and the challenges of high-frequency accuracy. 

RF Connectors

RF connectors are used in radio, digital, cellular, and satellite communication systems for transmitting high-frequency signals. RF coaxial connectors are the most frequently used type of high-frequency connector, used for transmitting signals or for providing screening.

Types of RF Connectors

There are a wide array of RF connectors available, with a wide range of sizes. These connectors are selected depending on the application and parameter considerations such as frequency, power, impedance, and physical size. 

Common RF connector types include:   

  1. UHF connectors - Ultra high frequency (UHF) connectors are a type of RF connector used for transmitting signals of frequencies up to 100MHz. These connectors have non-constant surge impedance. They are commonly used for radio applications such as amateur radio, marine VHF radio, and ham radio.

  2. BNC - This type of connector is used in video devices, oscilloscopes, laboratory equipment, and RF systems within the 2GHz frequency range. In RF applications, BNC connectors are utilized in transmitters, receivers, and test equipment. 

The main advantage of BNC  connectors is its connect and disconnect feature. The bayonet fixing in BNC connectors prevents accidental disconnection. Considering the most important electrical parameter—characteristic impedance—the BNC connector provides a constant value throughout. Typically 50 and 75 ohm versions are available in BNC connectors.

  1. Type N connectors - The type N connector is a high-performance RF coaxial cable that is threaded. The threaded coupling in Type N connectors is used to ensure the cable mates perfectly. These cables are available in 50-ohm and 75-ohm characteristic impedance. These cables are larger than BNC connectors and have a higher power handling capacity as well. These cables are compliant with MIL-STD-348 standards and handle frequencies up to 11GHz. Due to them being medium sized, rugged, cheap, durable, and weather-proof, these cables are used in lower-band microwave systems.   

The Challenges of High-Frequency Accuracy in RF Connectors  

In the RF market, there is a continuous demand for high-frequency connectors with a reduced cross-sectional area. As the frequency of operation increases in high-speed digital systems, accuracy is one of the attributes that can be compromised. Precision RF connectors used in high-speed systems face the challenges of high-frequency accuracy.

Signal Integrity

Signal integrity is a major concern in high-frequency RF connectors. With shorter rise times and faster clock frequencies, the signal integrity of transmitted signals through RF connectors are significantly affected. When choosing RF connectors to provide high-frequency accuracy, factors such as attenuation, VSWR, electromagnetic interference, and crosstalk should be considered to select an optimal connector solution. 

Signaling Scheme

The signaling scheme used affects the RF connector’s performance. When the signaling scheme is single-ended and a differential connector is connected, then high-frequency accuracy is affected. When the RF connector type is not optimal for the signaling scheme, the speed rating of the RF connector decreases, affecting the frequency accuracy expected in a particular application.

Parasitic Elements

As the operating frequency increases, the influence of parasitic inductance and capacitance becomes more predominant in RF connectors. Maintaining a constant characteristic impedance is important in RF connectors to achieve high-frequency accuracy. However, parasitic reactances offer a hindrance in managing high-frequency accuracy in RF connectors.

The weave effect, waveguide modes, and trace radiation are other challenges of high-frequency accuracy in RF connectors. However, with proper designs, most challenges of high-frequency accuracy can be mitigated. Cadence software can help with the design of RF systems utilizing RF connectors.

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