Which mechanism explains signal attenuation in a microwave waveguide operating near its cutoff frequency?

💡 Explanation

When a microwave frequency approaches cutoff, evanescent modes become dominant because the waveguide can no longer effectively propagate electromagnetic waves, leading to reactive power that is not radiated, causing signal attenuation. Therefore attenuation from evanescent mode results, rather than simple resistive, dielectric or scattering losses, which are independent of the frequency.

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