Hyperbolic-cosine waveguide tapers and oversize rectangular waveguide for reduced broadband insertion loss in W-band electron paramagnetic resonance spectroscopy
Hyperbolic-cosine waveguide tapers and oversize rectangular waveguide for reduced broadband insertion loss in W-band electron paramagnetic resonance spectroscopy
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DOI：
10.1063/1.3607432
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发表时间：
2011-07-01
影响因子：
1.6
通讯作者：
Hyde, J. S.
中科院分区：
文献类型：
--
作者：
Mett, R. R.;Sidabras, J. W.;Hyde, J. S.
在W波段（94 GHz），电子顺磁共振（EPR）谱仪在1 m长波导上的双向插入损耗在4%带宽上比WR 10波导降低了近5 dB。波导具有市售矩形WR 28的超大部分和根据双曲余弦（HC）函数随轴向位置变化的截面的一对新颖的锥形。锥形连接传统的矩形WR 10波导到WR 28。为了使损耗最小，主模电场平行于WR 28的长边。利用模式耦合理论，针对与高阶模的耦合和主模的反射，优化了锥形中最大耀斑（拐点）的位置。最佳的拐点位置是从锥形的小端开始的锥形长度的十分之一。反射和耦合相对于相同长度的锥形（线性）锥体减少约20 dB。梳状下降的透射系数产生的谐振的高阶模式在超大部分约为0.03分贝。特别设计的高精度，可调WR 28法兰对准约5 μ m，需要保持高阶模式的振幅从法兰可比的HC锥。最小回波损耗约为30 dB。本文为进一步优化提供了基础。方法不特定于EPR或微波频段。(C)2011年美国物理学会。[doi 10.1063/1.3607432]
The two-way insertion loss of a 1 m length of waveguide was reduced by nearly 5 dB over a 4% bandwidth at W-band (94 GHz) for an electron paramagnetic resonance (EPR) spectrometer relative to WR10 waveguide. The waveguide has an oversize section of commercially available rectangular WR28 and a novel pair of tapers that vary in cross section with axial position according to a hyperbolic-cosine (HC) function. The tapers connect conventional rectangular WR10 waveguide to the WR28. For minimum loss, the main mode electric field is parallel to the long side of the WR28. Using mode coupling theory, the position of maximum flare (inflection point) in the taper was optimized with respect to the coupling to higher order modes and the reflection of the main mode. The optimum inflection point position is about one-tenth of the taper length from the small end of the taper. Reflection and coupling were reduced by about 20 dB relative to a pyramidal (linear) taper of the same length. Comb-like dips in the transmission coefficient produced by resonances of the higher order modes in the oversize section were about 0.03 dB. Specially designed high-precision, adjustable WR28 flanges with alignment to about 5 mu m were required to keep higher order mode amplitudes arising from the flanges comparable to those from the HC tapers. Minimum return loss was about 30 dB. This paper provides a foundation for further optimization, if needed. Methods are not specific to EPR or the microwave frequency band. (C) 2011 American Institute of Physics. [doi:10.1063/1.3607432]