17.5 ft-long multiconical taper for TE01 mode in 29.7 in-diameter waveguide at X band

An X band TE01-mode taper to connect circular waveguides with diameters of 2.25 and 29.7 in was designed, fabricated and evaluated. The 29.7 in circular aluminium waveguide for the TE01 mode had an attenuation of 2.1 × 10¿6dB/ft at 8.35GHz. To obtain a taper of short length that would be economical to fabricate, a multiconical type was selected. The four mode-converting junctions in the multiconical taper were designed to cancel the first higher-order TE02 mode. The taper was 17.5 ft long and comprised 12 sections. The larger-diameter sections were fabricated by using a thin sheet of aluminium alloy, rolled and longitudinally welded. Circular flanges and stiffening rings provided the desired degree of circularity. By using a spinning dipole mode analyser, the TE02 and TE03 modes due to the taper were measured to be about 25 dB below the TE01 mode.