Using Alternative Aperture Geometry Horn Antennas in Wide-Band Multifrequency Measurements

Application of horn antennas in non-destructive testing by multifrequency reflectivity measurements has several advantages in comparison with simple antennas such as open-ended waveguide, in particular, higher gain and narrower directional characteristic. However, having two reference discontinuitie...

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Date:	2002
Main Authors:	Drobakhin, O.O., Kondratyev, Y.V.
Format:	Article
Language:	English
Published:	Радіоастрономічний інститут НАН України 2002
Series:	Радиофизика и радиоастрономия
Online Access:	http://dspace.nbuv.gov.ua/handle/123456789/122342
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Cite this:	Using Alternative Aperture Geometry Horn Antennas in Wide-Band Multifrequency Measurements / O.O. Drobakhin, Y.V. Kondratyev // Радиофизика и радиоастрономия. — 2002. — Т. 7, № 4. — С. 385-388. — Бібліогр.: 3 назв. — англ.

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spelling	irk-123456789-1223422017-07-03T03:02:57Z Using Alternative Aperture Geometry Horn Antennas in Wide-Band Multifrequency Measurements Drobakhin, O.O. Kondratyev, Y.V. Application of horn antennas in non-destructive testing by multifrequency reflectivity measurements has several advantages in comparison with simple antennas such as open-ended waveguide, in particular, higher gain and narrower directional characteristic. However, having two reference discontinuities hinders from using them for the purpose because of superposition of echoing characteristics being retrieved. General solution lies in extracting single echoing characteristic whether by mathematical post-processing measurement results or by strong reducing one of reference discontinuity reflectivity levels by altering discontinuity's geometry, that is the subject of this paper. Применение рупорных антенн для неразрушающего контроля посредством измерения многочастотных характеристик отражения имеет ряд преимуществ по сравнению с простыми антеннами (такими как открытый конец волновода), а именно: более высокий коэффициент усиления и более узкие характеристики направленности. Однако, наличие двух стандартных неоднородностей приводит к многократным переотражениям и препятствует использованию этих антенн. Основное решение состоит в выделении отдельных характеристик отражения либо путем математической обработки результатов измерений, либо за счет значительного снижения уровня отражений от одной из стандартных неоднородностей изменяя геометрию этой неоднородности, что и является предметом исследования в настоящей статье. Застосування рупорних антен для неруйнівного контролю за допомогою вимірювання багаточастотних характеристик відбиття має низку переваг у порівнянні з простими антенами (такими як відкритий кінець хвилеводу), зокрема: вищий коефіцієнт підсилення та вужчі характеристики спрямованості. Однак, наявність двох стандартних неоднорідностей приводить до багаторазового перевідбиття і перешкоджає застосуванню цих антен. Основне рішення полягає у виділенні окремих характеристик відбиття або за допомогою математичної обробки результатів вимірювань, або за рахунок значного зниження рівня відбиття від однієї зі стандартних неоднорідностей змінюючи геометрію цієї неоднорідності, що і є предметом дослідження у даній статті. 2002 Article Using Alternative Aperture Geometry Horn Antennas in Wide-Band Multifrequency Measurements / O.O. Drobakhin, Y.V. Kondratyev // Радиофизика и радиоастрономия. — 2002. — Т. 7, № 4. — С. 385-388. — Бібліогр.: 3 назв. — англ. 1027-9636 http://dspace.nbuv.gov.ua/handle/123456789/122342 en Радиофизика и радиоастрономия Радіоастрономічний інститут НАН України
institution	Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection	DSpace DC
language	English
description	Application of horn antennas in non-destructive testing by multifrequency reflectivity measurements has several advantages in comparison with simple antennas such as open-ended waveguide, in particular, higher gain and narrower directional characteristic. However, having two reference discontinuities hinders from using them for the purpose because of superposition of echoing characteristics being retrieved. General solution lies in extracting single echoing characteristic whether by mathematical post-processing measurement results or by strong reducing one of reference discontinuity reflectivity levels by altering discontinuity's geometry, that is the subject of this paper.
format	Article
author	Drobakhin, O.O. Kondratyev, Y.V.
spellingShingle	Drobakhin, O.O. Kondratyev, Y.V. Using Alternative Aperture Geometry Horn Antennas in Wide-Band Multifrequency Measurements Радиофизика и радиоастрономия
author_facet	Drobakhin, O.O. Kondratyev, Y.V.
author_sort	Drobakhin, O.O.
title	Using Alternative Aperture Geometry Horn Antennas in Wide-Band Multifrequency Measurements
title_short	Using Alternative Aperture Geometry Horn Antennas in Wide-Band Multifrequency Measurements
title_full	Using Alternative Aperture Geometry Horn Antennas in Wide-Band Multifrequency Measurements
title_fullStr	Using Alternative Aperture Geometry Horn Antennas in Wide-Band Multifrequency Measurements
title_full_unstemmed	Using Alternative Aperture Geometry Horn Antennas in Wide-Band Multifrequency Measurements
title_sort	using alternative aperture geometry horn antennas in wide-band multifrequency measurements
publisher	Радіоастрономічний інститут НАН України
publishDate	2002
url	http://dspace.nbuv.gov.ua/handle/123456789/122342
citation_txt	Using Alternative Aperture Geometry Horn Antennas in Wide-Band Multifrequency Measurements / O.O. Drobakhin, Y.V. Kondratyev // Радиофизика и радиоастрономия. — 2002. — Т. 7, № 4. — С. 385-388. — Бібліогр.: 3 назв. — англ.
series	Радиофизика и радиоастрономия
work_keys_str_mv	AT drobakhinoo usingalternativeaperturegeometryhornantennasinwidebandmultifrequencymeasurements AT kondratyevyv usingalternativeaperturegeometryhornantennasinwidebandmultifrequencymeasurements
first_indexed	2025-07-08T21:32:42Z
last_indexed	2025-07-08T21:32:42Z
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fulltext	Radio Physics and Radio Astronomy, 2002, v. 7, No. 4, pp. 385-388 USING ALTERNATIVE APERTURE GEOMETRY HORN ANTENNAS IN WIDE-BAND MULTIFREQUENCY MEASUREMENTS O.O. Drobakhin, Y.V. Kondratyev* Dnepropetrovsk National University Nauchnaya str., 13, Dniepropetrovsk, Ukraine E-mail: ) odr@ua.fm, *) ce@ua.fm Application of horn antennas in non-destructive testing by multifrequency reflectivity measurements has several advantages in comparison with simple antennas such as open-ended waveguide, in particular, higher gain and narrower directional characteristic. However, having two reference discontinuities hinders from using them for the purpose because of superposition of echoing characteristics being retrieved. General solution lies in ex- tracting single echoing characteristic whether by mathematical post-processing measurement results or by strong reducing one of reference discontinuity reflectivity levels by altering discontinuity's geometry, that is the subject of this paper. 1. Introduction Wide-band multifrequency measurements of reflec- tivity in free space allow testing the internal structure of complex multi-layered materials containing dis- continuities of different kinds (both inter-layer bor- ders and defects of different kinds). Due to applying the method of synthesising radio-pulse envelope [1] spatial distribution of insertion reflectivity may be obtained, which then is used to locate the defects and/or derive dependency of dielectric constant and other parameters of structure under test on the dis- tance along the measurement axis. Existing real-time measurement systems [2] use waveguide reflectometric circuit for acquiring reflec- tivity data. Reflectivity is obtained as ratio of re- flected to incident wave power, correspondingly re- ceived and radiated by a probe. The most frequently used probes are open-ended waveguide (OEW) and different types of horn antennas. Every probe represents one or more discontinui- ties serving as references, thus spatial echoing char- acteristic appears a superposition of similar reflectiv- ity characteristics, corresponding to cross-correlation of reflection signals of structure under test with that of each reference discontinuity. Superposing hinders clear interpreting reflectivity signals and estimating structure's parameters, so only characteristics derived with OEW may be used directly for this purpose. Horns, though of higher gain and narrower direc- tional diagram than OEW, have two discontinuities (throat and aperture), so the superposition may be avoided whether by mathematical filtering raw echo- ing data, or/and by strong reducing the minor discon- tinuity (i. e. having lower reflectivity, typically, aper- ture) by special designing its geometry. 2. Alternative Aperture Design Modified horn may be derived from usual horn by framing its aperture in cylindrical metal surface, as it is shown in Fig. 1. Outer diameter (D ) of the cylin- der lies in range 0.5-1 wavelength at minimum fre- a b D D Fig. 1. Alternative design of horn antenna O.O. Drobakhin, Y.V. Kondratyev 386 Radio Physics and Radio Astronomy, 2002, v. 7, No. 4 quency [3]. We have tested such a design with three pyramidal-shaped horns having square aperture (one for 8-12.5 GHz band with aperture of size 93a b= = mm, and two for 17-26 GHz band with same parameters of 42 and 82 mm respectively). 3. Using Modified Horns Studying alternative geometry horns as probes showed that some of their properties, essential for wide-band testing, differ from that of their conven- tional analogues. First, insertion reflectivity of any discontinuity obtained with an alternative geometry horn decreases non-monotonously with the distance along the prob- ing axis (further – distance). In particular, the de- pendence suffers oscillations with period of 1/2 aver- age wavelength (Fig. 2), taking place as (mainly) in the near-field, so (insignificantly) in the far-field re- gion. Maximum amplitude of oscillations depends on own value of discontinuity's reflectivity, so their na- ture may be supposed to be an interaction of reflect- ing surface with aperture of the horn, which influ- ences the EM field distribution in the system probe- structure under the test. Thus the system should be considered (especially for near-field measurements) as the whole. For example, when finding out dielec- tric constant for single layer structure by calculating the ratio of insertion reflectivity of the structure and that of metal surface, correct result may be obtained only if oscillations' “spatial phases” for both surfaces' reflectivities are equal. It must be said that for usual horns and even open-ended waveguide probes the dependency ( )r z has similar oscillations at very low amplitude. They can hardly be detected on the noise background and are anyway incomparable with common levels of informative signals. Second, inter-influence of the probe and struc- ture under the test leads to strong non-linear depend- ency of ratio of insertion reflectivities, corresponding to cross-correlation with signals of aperture and throat of the horn (for conventional horns it is linear at least in whole far-field and usually in the most part of the near field region, see Fig. 3). At farther dis- tances the ratio stabilises at considerably low level (typically 0.12-0.14). Thus modifying a horn reduces aperture-referenced reflectivity by 2-3 times. Phase difference and distance between mentioned insertion reflectivity peaks are also constant, so estimating parameters of multi-layered structures having electric lengths equal to or greater than that of the horn used 0 0.01 0.02 0.03 0.04 0.05 300 400 500 600 700 800 z, mm \|r (z )\| a b Fig. 2. Spatial oscillations of reflectivity character- istics of metal plate moving along probe axis, derive with horn’s throat (a) and aperture (b) 0 0.2 0.4 0.6 0.8 1 1.2 200 300 400 500 600 700 z, mm a b Fig. 3. Aperture-to-throat reflectivity module ratio for usual horn (a) and the same horn with altered aperture geometry (b) 0 20 40 60 80 100 120 0 200 400 600 800 1000 z, mm L (z ), m m Fig. 4. Locality of testing 0z = at the aperture Using Alternative Aperture Geometry Horn Antennas in Wide-Band Multifrequency Measurements Radio Physics and Radio Astronomy, 2002, v. 7, No. 4 387 as probe becomes possible, especially in combination with special mathematical filter deleting aperture constituent of structure's reflectivity characteristic (high quality of filtering is possible only at low and constant aperture-throat reflectivity ratios). Finally, some words may be said about locality of testing. Locality is the characteristic that shows minimal distance (across the probe axis) between two discontinuities, which allows their clear discrimina- tion. Up to the present this question could not be completely solved due to enormous amount of meas- urements in the scanning mode, needed to learn how reflectivity dependency, measured along the cross axis, and thus the locality, changes along the probe axis. Now it is observed that locality is a linear direct ratio dependency from the distance along probe axis tending to a zero at aperture, though near the aperture it takes a super-linear character, taking at aperture the value of half its size (see Fig. 4). Linear behaviour may be explained by existence of concrete directional diagram, which at considerably large distances does not depend on structure under test, so there is certain sector, within which the reflectivity changes between its maximum and half the maximum values. Angle 2ϕ , determining size of the sector, binds the locality (L ) with distance (d ) to the discontinuity: sinL d ϕ= . For example, the horn used for study- ing the locality has sector width 2 14.8ϕ = ° , so 0.129L d= , or 0.134L z= , where z is the dis- tance along probe axis. Next, the non-linear locality dependency near the aperture is due to non-zero size of the aperture, so the locality value anyway cannot be lower than half the size of the aperture. As for resolution, or minimal size of discontinu- ity, which can be discovered by measurements within certain frequency range, it is, in general, not re- stricted by anything save sensitivity of measurement system and other like factors, but strongly depends on its spatial orientation and electric properties. For example, testing in 17-26 GHz band allows sure de- tecting cavities in the dielectric structures having size of about 0.5 mm (see Fig. 5 for example) along the probe axis (average wavelength makes about 15 mm). Existing measurement system allows deter- mining position of a small local discontinuity with error less than 20 % average wavelength in all direc- tions (see Fig. 6 for example). 4. Conclusion Described properties of modified horn antennas al- low recommending their use in relatively remote part of far-field region for measuring echoing characteris- tics of thick multi-layered dielectric structures and estimating their parameters, such as dielectric con- stants and widths provided that remaining minor ap- erture reflection constituent is removed by additional digital filtering. Using modified antennas for meas- urements in the near-field and adjacent part of the far-field region is undesirable because of high non- linearity of probe-structure system's parameters: usual horns with or without (for thin structures) addi- tional filtering or the open-ended waveguide (for the shortest distances) should be used instead. a b c Fig. 5. Fragment of raw echoing characteristic of two-layer organic glass: a – layer 1 front surface signal, c – layer 2 rear surface signal, b – signal of thin gap due to loose contact between layers 0 0,25 0,5 0,75 1 -100 -50 0 50 100 150 200 x, mm Fig. 6. Normalized reflection signal of a defect (small metal plate) within dielectric layer moving across the probe axis. 0x = corresponds to edge of the dielectric crossing the probe axis O.O. Drobakhin, Y.V. Kondratyev 388 Radio Physics and Radio Astronomy, 2002, v. 7, No. 4 References 1. O.O. Drobakhin. Realisation of the method of synthe- sising radio pulse envelope using amplitude measure- ment data derived with a horn antenna. // Russian Non-destructive Testing Journal. – 1999. – No. 7.– pp. 67-74. 2. O.O. Drobakhin, Y.V. Kondratyev, V.G. Korotkaya. Computerised measurement installation for non- destructive testing of dielectric products: hardware and software // System Technologies. – 2001. – No. 5(16).– pp. 29-32. (In Russian). 3. D.E. Baker, C.A. van der Neut. Reflection measure- ments of microwave absorbers. // Microwave Jour- nal. – 1988. – 31 No. 12.– pp. 95-104. ИСПОЛЬЗОВАНИЕ РУПОРНЫХ АНТЕНН С АЛЬТЕРНАТИВНОЙ ГЕОМЕТРИЕЙ АПЕРТУРЫ ДЛЯ ШИРОКОПОЛОСНЫХ МНОГОЧАСТОТНЫХ ИЗМЕРЕНИЙ О.О. Дробахин, Е.В. Кондратьев Применение рупорных антенн для неразрушаю- щего контроля посредством измерения многочастот- ных характеристик отражения имеет ряд преимуществ по сравнению с простыми антеннами (такими как от- крытый конец волновода), а именно: более высокий коэффициент усиления и более узкие характеристики направленности. Однако, наличие двух стандартных неоднородностей приводит к многократным переотра- жениям и препятствует использованию этих антенн. Основное решение состоит в выделении отдельных характеристик отражения либо путем математической обработки результатов измерений, либо за счет значи- тельного снижения уровня отражений от одной из стандартных неоднородностей изменяя геометрию этой неоднородности, что и является предметом исследова- ния в настоящей статье. ЗАСТОСУВАННЯ РУПОРНИХ АНТЕН З АЛЬТЕРНАТИВНОЮ ГЕОМЕТРІЄЮ АПЕРТУРИ ДЛЯ ШИРОКОСМУГОВИХ БАГАТОЧАСТОТНИХ ВИМІРЮВАНЬ О.О. Дробахін, Є.В. Кондратьєв Застосування рупорних антен для неруйнівного контролю за допомогою вимірювання багаточастотних характеристик відбиття має низку переваг у порівнян- ні з простими антенами (такими як відкритий кінець хвилеводу), зокрема: вищий коефіцієнт підсилення та вужчі характеристики спрямованості. Однак, наявність двох стандартних неоднорідностей приводить до бага- торазового перевідбиття і перешкоджає застосуванню цих антен. Основне рішення полягає у виділенні окре- мих характеристик відбиття або за допомогою матема- тичної обробки результатів вимірювань, або за раху- нок значного зниження рівня відбиття від однієї зі стандартних неоднорідностей змінюючи геометрію цієї неоднорідності, що і є предметом дослідження у даній статті.

Using Alternative Aperture Geometry Horn Antennas in Wide-Band Multifrequency Measurements

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