Experimental Verification of Low-Loss TM Modes in Dielectric-Lined Waveguide

Recent analytical studies 1-3 of the heat loss characteristics of the normal modes in oversized dielectric-lined circular waveguide indicate that modes other than those of the circular electric type have low loss ( 1 0 dB/km). Specifically, in 51-mm diameter waveguide lined with a 200-/im layer of polyethylene, the T M n mode was predicted to have a theoretical attenuation coefficient which decreases with increasing frequency and achieves values less than 10 dB/km over the 80- to 110-GHz frequency range. This paper reports some recent experimental results which confirm the decreasing heat loss versus frequency trend predicted for the T M n mode in lined waveguide. The differential phase constant (A/3) for the TE 0 i and T M n modes, A/3 s hn - h0h (1)