Coaxial cables and waveguides differ in typical frequency ranges, loss mechanisms, and power handling. Which statement is correct?

Coaxial cables and waveguides differ in typical frequency ranges, loss mechanisms, and power handling. Which statement is correct?

• A. Coax is for lower to medium frequencies; waveguides for higher frequencies; coax has conductor and dielectric losses; waveguides have higher power handling and lower loss
• B. Coax is for higher frequencies; waveguides for lower frequencies; waveguides have more loss
• C. Coax and waveguides have the same loss mechanisms and power handling
• D. Waveguides are always smaller and cheaper

Answer: (A)

The main idea here is how the transmission medium behaves differently with frequency, and how that affects losses and power handling. Coaxial cables are a compact way to carry signals at lower to mid frequencies. The signal travels in a TEM mode along the center conductor with an outer shield and a dielectric between them. Losses come from two main sources: the conductor resistance (which gets worse with frequency due to the skin effect) and dielectric losses in the insulating material. As you push to higher frequencies, these losses rise, making coax less efficient. Waveguides are hollow metal tubes that carry signals in TE/TM modes. They have a cutoff frequency set by their dimensions, so they’re used at higher frequencies where practical, microwave-scale sizes exist. They typically exhibit much lower attenuation per unit length than coax at these frequencies and can handle higher RF power because there’s no lossy dielectric in the signal path and the metal walls can support large surface currents without breakdown of the dielectric. So the statement aligns with experience: coax is typical for lower-to-mid frequencies with conductor and dielectric losses present, while waveguides suit higher frequencies with lower loss and greater power handling. The other ideas conflict with how waveguides function (they’re not used for low frequencies due to impractically large sizes and cutoff) and with the differing loss mechanisms and power capabilities.

The main idea here is how the transmission medium behaves differently with frequency, and how that affects losses and power handling.

Coaxial cables are a compact way to carry signals at lower to mid frequencies. The signal travels in a TEM mode along the center conductor with an outer shield and a dielectric between them. Losses come from two main sources: the conductor resistance (which gets worse with frequency due to the skin effect) and dielectric losses in the insulating material. As you push to higher frequencies, these losses rise, making coax less efficient.

Waveguides are hollow metal tubes that carry signals in TE/TM modes. They have a cutoff frequency set by their dimensions, so they’re used at higher frequencies where practical, microwave-scale sizes exist. They typically exhibit much lower attenuation per unit length than coax at these frequencies and can handle higher RF power because there’s no lossy dielectric in the signal path and the metal walls can support large surface currents without breakdown of the dielectric.

So the statement aligns with experience: coax is typical for lower-to-mid frequencies with conductor and dielectric losses present, while waveguides suit higher frequencies with lower loss and greater power handling. The other ideas conflict with how waveguides function (they’re not used for low frequencies due to impractically large sizes and cutoff) and with the differing loss mechanisms and power capabilities.