Waveguide taper cross section and coordinate system definition. The waveguide dimensions a and b vary in z according to Eqs. (9) and (10) for the HC taper or Eqs. (B1) and (B2) for the linear taper.
Plots of three basic forms of coupling coefficient κ and the corresponding approximate wave solutions according to Eq. (8). Constant values of γ1 = j1.679 mm−1 and γ2 = j0.756 mm−1 were assumed (see discussion below Eq. (8)).
Magnitude of the coupling coefficient from Eqs. (A1)–(A9) for the largest coupled and reflected modes (TE12, TE10, and TM12) through the HC taper. Plots are shown for values of the inflection point d in Eqs. (9) and (10) of 2 mm (red), 5 mm (orange), 8 mm (green), 11 mm (blue), and 14 mm (purple) and at a frequency of 94 GHz.
Magnitude of the coupled and reflected modes predicted by Eqs. (1) and (2) corresponding to the coupling coefficients of Fig. 3 through the HC taper.
Ansoft HFSS simulation of the electric field magnitude in a pair of tapers with a 132 mm length of WR28 waveguide between. Only the left side is shown in order to view the field profile more clearly. (a) Brass linear tapers off resonance, 94 GHz. (b) Brass linear tapers on resonance, 95.048 GHz, transmission coefficient 0.7 dB below non-resonance. (c) Cu HC tapers off resonance, 94.1 GHz. (d) Cu HC tapers on resonance, 95.694 GHz transmission coefficient 0.015 dB below non-resonance. See also Secs. III B, III C, and IV C.
(a) Transmission and (b) and (c) reflection coefficients of a pair of tapers with a 132 mm length of WR28 waveguide between. The colored lines show network analyzer measurements (Sec. IV C), and the black lines indicate Ansoft HFSS simulations (Sec. III C). Blue indicates HC tapers and red linear tapers. The measurement averages and standard deviations are (a) − 0.105 ± 0.015 dB for HC and − 0.68 ± 0.16 dB for linear, and (b, c) − 37.1 ± 5.6 dB for HC and − 32.1 ± 6.7 dB for linear. The comb-like dips in T due to resonance of higher order modes between the tapers are less than −0.03 dB for HC compared to −0.8 dB for linear tapers.
Photographs of the HC taper pair. (a) End detail showing, from left to right, UG-599 WR28 flange (Ref. 12), custom high-precision WR28 flange (Sec. IV B), ALMA WR10 flat flange (Ref. 11). (b) Assembled taper pair with 132 mm WR28 oversize waveguide section.
Transmission and reflection coefficient comparison between 96 mm HC tapers with 711 mm section of WR28 (blue) and 902 mm section of WR10 (red). (a) T. (b) R. (c) R with slightly detuned LGR (Ref. 8) with 38 mm section of WR10. The measurement averages and standard deviations are (a) − 0.44 ± 0.02 dB for WR28 and − 2.80 ± 0.03 dB for WR10, and (b) − 38.5 ± 5.1 dB for WR28 and − 40.4 ± 4.8 dB for WR10.
Coupling coefficients and corresponding wave amplitudes in linear taper. (a) Magnitude of the coupling coefficient from Eqs. (A1)–(A9) for the largest coupled and reflected modes (TE12, TE10, and TM12) at frequencies of 92 GHz (red), 94 GHz (green), and 96 GHz (blue). (b) Magnitude of the coupled and reflected modes predicted by Eqs. (1) and (2) corresponding to the coupling coefficients of (a).
Taper single-pass reflection and transmission coefficients.
Taper reflection and transmission coefficients predicted by Ansoft HFSS at 94 GHz.
Wavelengths and attenuation lengths for Cu waveguide at 94 GHz.
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