Bragg reflectors

Chong, C.K.; McDermott, D.B.; Razeghi, M. M.; Luhmann, Neville C.; Pretterebner, J.; Wágner, D.; Thumm, M.; Caplan, M.; Kulke, B.

doi:10.1109/27.142841

Cited by 111 publications

(53 citation statements)

References 9 publications

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“…Calculated and measured transmission of the multifrequency notch filter. Calculations were done using the mode matching method (scattering matrix calculations) [5,6]. Measurements were performed with the Rohde&Schwarz Vector Network Analyzer (ZVA24).…”

Section: Resultsmentioning

confidence: 99%

A Multifrequency Notch Filter for Millimeter Wave Plasma Diagnostics based on Photonic Bandgaps in Corrugated Circular Waveguides

Wágner

Bongers

Kasparek

et al. 2015

EPJ Web of Conferences

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Abstract. Sensitive millimeter wave diagnostics need often to be protected against unwanted radiation like, for example, stray radiation from high power Electron Cyclotron Heating applied in nuclear fusion plasmas. A notch filter based on a waveguide Bragg reflector (photonic band-gap) may provide several stop bands of defined width within up to two standard waveguide frequency bands. A Bragg reflector that reflects an incident fundamental TE 11 into a TM 1n mode close to cutoff is combined with two waveguide tapers to fundamental waveguide diameter. Here the fundamental TE 11 mode is the only propagating mode at both ends of the reflector. The incident TE 11 mode couples through the taper and is converted to the high order TM 1n mode by the Bragg structure at the specific Bragg resonances. The TM 1n mode is trapped in the oversized waveguide section by the tapers. Once reflected at the input taper it will be converted back into the TE 11 mode which then can pass through the taper. Therefore at higher order Bragg resonances, the filter acts as a reflector for the incoming TE 11 mode. Outside of the Bragg resonances the TE 11 mode can propagate through the oversized waveguide structure with only very small Ohmic attenuation compared to propagating in a fundamental waveguide. Coupling to other modes is negligible in the non-resonant case due to the small corrugation amplitude (typically 0.05·λ 0 , where λ 0 is the free space wavelength). A Bragg reflector for 105 and 140 GHz was optimized by mode matching (scattering matrix) simulations and manufactured by SWISSto12 SA, where the required mechanical accuracy of ± 5 μm could be achieved by stacking stainless steel rings, manufactured by micro-machining, in a high precision guiding pipe. The two smooth-wall tapers were fabricated by electroforming. Several measurements were performed using vector network analyzers from Agilent (E8362B), ABmm and Rohde&Schwarz (ZVA24) together with frequency multipliers. The stop bands around 105 GHz (-55dB) and 140 GHz (-60dB) correspond to the TE 11 -TM 12 and TE 11 -TM 13 Bragg resonances. Experiments are in good agreement with theory.

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Section: Resultsmentioning

confidence: 99%

A Multifrequency Notch Filter for Millimeter Wave Plasma Diagnostics based on Photonic Bandgaps in Corrugated Circular Waveguides

Wágner

Bongers

Kasparek

et al. 2015

EPJ Web of Conferences

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“…Therefore, it is beneficial to increase the diameter of the tunnel through which the electron beam may propagate whilst hindering the transport of oncoming radiation. A Bragg reflector [14] is a waveguide structure with radial periodicity which can be used as a method of providing frequency selective feedback. A review of a Bragg reflector design in the W-band is presented in [15].…”

Section: Coaxial Input Coupler Designmentioning

confidence: 99%

TE10R–TE11c input coupler for a low-THz gyro-TWA

Garner

Zhang

Donaldson

et al. 2015

2015 8th UK, Europe, China Millimeter Waves and THz Technology Workshop (UCMMT)

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Abstract-The design of a fundamental rectangular-tocircular coaxial cavity input coupler for a low-THz gyrotraveling wave amplifier (TWA) is presented. Theoretical and numerical approaches to the design of the coaxial cavity input coupler are introduced. The design is optimized for operation between 360 -384 GHz, achieving a transmission bandwidth of 7.5% (358 -386 GHz). A comment on the manufacturability of sub-mm waveguide channels is included.

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“…As an example, the calculated reflection as a function of frequency for a Bragg reflector with 200 periods (p=λ Bragg =5.27mm) of rectangular corrugation with a constant corrugation amplitude of 0.25 mm in a circular waveguide with I.D.=27.79 mm is given in Fig.3. Tapering of the corrugation amplitude profile strongly reduces resonance overlaps and side bands in the frequency response [6,7]. …”

Section: Bragg Reflector In Oversized Circular Waveguidementioning

confidence: 99%

“…The resonant frequencies where k z2 =k Bragg -k z1 are indicated by the rectangles. Since the Bragg reflector can be composed by a series of radial step discontinuities, an accurate method to calculate the reflectivity of this structure is the scattering matrix formalism where both propagating and evanescent modes are taken into account [6,7]. The spectral width of the Bragg reflection depends on the number of periods N, corrugation amplitude h and aspect ratio w/p , where w is the width of the grooves.…”

Section: Bragg Reflector In Oversized Circular Waveguidementioning

confidence: 99%