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The 25th International Symposium on Space Terahertz Technology , 27 ­ 30 April 2014, Moscow, Russia

Capillary quasioptical highpass filter
Valerian S. Edelman , Mikhail A. Tarasov and Artem M. Chekushkin . P.Kapitza Institute for Physical Problems Email: edelman@kapitza.ras.ru V.Kotelnikov Institute of Radio Engineering and Electronics Email : tarasov@hitech.cplire.ru
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Single below-cutoff circular waveguide as a high-pass filter was studied earlier in [1], it was obtained attenuation of 6-12 dB in the pass-band and attenuation of 30-60 dB in the stop-band. Such filter requires input and output horns and adapters if using in quasioptical systems and makes construction rathe r complicated, of big size, with nonuniform spectral characteristics. Matrix of capillaries can operate as a high pass filter at millimeter and submillimeter waves without additional adapters. At lower frequencies each capillary can be viewed as a below-cutoff circular waveguide. Array of capillaries do not need any adapters, they are thin and can be inserted in any quasioptical beam -guide. They can be alternative to perforated plates (grids) that should be arranged as 4-6 parallel layers and this pseudo high pass filter is rather a bandpass filter with a bandwidth of about one octave [2]. Industrial manufacturers of multimesh Terahertz filters such as QMC Instruments and TYDEX do not offer high performance highpass filters that are required for cryogen ic radiation sources intended for calibration of superconducting bolometers. We fabricated series of capillary matrix fi consists of following steps: electroplating 10 mm inner diameter tubewith as many electro-erosion cutting pieces of 1, 2, 3, 4 lters with different diameters and lengths of capillaries. Fabrication of stainless or nickel-copper capillaries with Ni, filling short piece of capillaries as possible, soldering of such package with tin -lead alloy, mm long, final cleaning in ultrasonic bath.

Filters were placed in the waist of a quasioptical beam -guide comprising Backward Wave Oscillator (BWO) radiation source, corrugated horn, four Teflon lenses, and Goley cell detector. Transmission was measured in the frequency range 150-550 GHz. For inner diameter of capillary of 0.7 mm and length of 3 mm the attenuation of such filter was over 40 dB at frequencies below 200 GHz. At frequencies above 350 GHz attenuation does not exceed 5 dB.

References

1. V.S.Syzranov, A.S.Ermolov, S.P.Lebedev, V.N.Murzin, Design and studies of terahertz and sub-terahertz waveguide filters, PriboryiTekhnikaExperimenta, 2012, No 5, pp. 1-8. 2. R.Ulrich, Interference filters for the far infrared, Applied Optics, vol.7, No 10, pp. 1987 -1996 (1968).

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