Multi-layered Submillimetre FSS of Shifted Crossed Slot Elements for Applications in Radio Astronomy Ge Wu , Volkert Hansen , Hans-Peter Gemuend and Ernst Kreysa Chair of Electromagnetic Theory, University of Wuppertal, Rainer-Gruenter-Str. 21, 42119 Wuppertal, Germany, Tel: +49-202-439-1935, E-Mail: [email protected]Max Planck Institute for Radioastronomy, Bonn, Germany Abstract — Thi s pape r deal s with th e desi gns and perf or - manc es of the multi -lay ere d FSS structu res propose d as band- pass filter s in spac e applic ation s. The so calle d shift ed crossed slot elemen ts are utili zed as res onant meshe s, with the help ofwhic h two type s of 4-resonan t-me sh- filters are real ized eith er with air spac ers or diele ctri c sepa ratio ns, possessi ng a shar p roll-off frequency response. The method of moment (MoM) used in a spec tral domain analysis and some numeri cal result s are presented. The production technology is also described. I. INTRODUCTION The advances in frequency selective surfaces (FSS) technol- ogy have led to their use as high-grade filters for submillimetre wave app lic ati ons [1], [2]. In thi s pap er , we report on the des igns and per for man ces of FSS ban d-pass filters which fulfill the special requirement of bolometer systems for radio astronomy. The proposed filters shall, on the one hand, exhibit a selectivity as high as possible, so it is often necessary to have a frequency separation ratio of 1.05:1 or less; on the other hand possess a broad stop band - a good attenuation is necessary par tic ula rly at hig her fre que ncies because of the the rma l radia tion risin g with , from tele sco pe and atmosp her e at ambient temperature [3], [4]. Fig. 1. Cascading of a high-pass, a low-pass and a band-pass A sharp roll-off frequency response can only be achieved by making use of the interference effects between two or more FSS screens. We prese nt one 4-res onant -mesh -filter with air spacer at a cut-off frequency of 290 GHz, and one with 4 mesh layer s embe dded in diele ctric material (polyprop ylene ), at a cut-off frequency of 370 GHz. The so called shifted crossed slot elements are applied as resonant mesh structure. To supp ress the high order propa gatin g modes, a low-pass filter consisting of layers of metallic square patches is applied for making a sufficient wide stop band. On the other hand, a circular waveguide is employed as a high-pass which cuts out the und esi red low fre que nc y ban d to mee t the requir ed bandwidth. Fig. 1 indicates schematically this combination. It is easy to realize these types of low-pass and high-pass filters, the ref ore , the entir e pro ble m is led to the essen tia l tas k ofdeveloping the band-pass filters with a sharp roll-off on the edge of interest (cut-off). II. DESIGN OFF SS BAND- PASS FILTERS In simple mesh filters, metal meshes (either free-standing or supported by dielectric sheets) are mounted with separating dista nces typically less than one wavele ngth. The dista nces between thes e mesh es provi de the reso nant elements . More advanced designs use meshes that are resonant in themselves thus reducing the accuracy of spacing required [5], [6]. Fig. 2 shows a capacitive mesh, an inductive mesh and a resonant mesh of crossed slot structure. Fig. 2. (a) Capacitive mesh, (b) Inductive mesh and (c) Resonant Mesh In thi s stu dy , we tak e advant age of the so cal led shifted crossed slot elements to realize the band-pass filters because of the ir exc ellent res ona nt beh avior. Fig . 3 ill ust rates the geo met ry of this res ona nt mes h and its equ iv ale nt cir cuit from lumped elements. Fig. 3. (a) Shifted crossed slots elements and (b) Equivalent circuit It has to be taken into account during the design process that compared to the normal crossed slots elements (Fig. 2. 128 GeMiC 2005
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Multi-layered Submillimeter Fss of Shifted Crossed Slot Elements for Applications in Radio Astronomy
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7/27/2019 Multi-layered Submillimeter Fss of Shifted Crossed Slot Elements for Applications in Radio Astronomy
Tel: +49-202-439-1935, E-Mail: [email protected]¾ Max Planck Institute for Radioastronomy, Bonn, Germany
Abstract — This paper deals with the designs and perfor-mances of the multi-layered FSS structures proposed as band-pass filters in space applications. The so called shifted crossedslot elements are utilized as resonant meshes, with the help of which two types of 4-resonant-mesh-filters are realized eitherwith air spacers or dielectric separations, possessing a sharproll-off frequency response. The method of moment (MoM) usedin a spectral domain analysis and some numerical results arepresented. The production technology is also described.
I. INTRODUCTION
The advances in frequency selective surfaces (FSS) technol-
ogy have led to their use as high-grade filters for submillimetre
wave applications [1], [2]. In this paper, we report on the
designs and performances of FSS band-pass filters which
fulfill the special requirement of bolometer systems for radio
astronomy. The proposed filters shall, on the one hand, exhibit
a selectivity as high as possible, so it is often necessary to have
a frequency separation ratio of 1.05:1 or less; on the other hand
possess a broad stop band - a good attenuation is necessary
particularly at higher frequencies because of the thermal
radiation rising with
¾ , from telescope and atmosphere at
ambient temperature [3], [4].
Fig. 1. Cascading of a high-pass, a low-pass and a band-pass
A sharp roll-off frequency response can only be achieved by
making use of the interference effects between two or more
FSS screens. We present one 4-resonant-mesh-filter with air
spacer at a cut-off frequency of 290 GHz, and one with 4 mesh
layers embedded in dielectric material (polypropylene), at a
cut-off frequency of 370 GHz. The so called shifted crossed
slot elements are applied as resonant mesh structure.
To suppress the high order propagating modes, a low-pass
filter consisting of layers of metallic square patches is appliedfor making a suf ficient wide stop band. On the other hand,
a circular waveguide is employed as a high-pass which cuts
out the undesired low frequency band to meet the required
bandwidth. Fig. 1 indicates schematically this combination. It
is easy to realize these types of low-pass and high-pass filters,
therefore, the entire problem is led to the essential task of
developing the band-pass filters with a sharp roll-off on the
edge of interest (cut-off).
II . DESIGN OF FSS BAND-PASS FILTERS
In simple mesh filters, metal meshes (either free-standing or
supported by dielectric sheets) are mounted with separating
distances typically less than one wavelength. The distances
between these meshes provide the resonant elements. More
advanced designs use meshes that are resonant in themselves
thus reducing the accuracy of spacing required [5], [6]. Fig.
2 shows a capacitive mesh, an inductive mesh and a resonant
mesh of crossed slot structure.
Fig. 2. (a) Capacitive mesh, (b) Inductive mesh and
(c) Resonant Mesh
In this study, we take advantage of the so called shifted
crossed slot elements to realize the band-pass filters because
of their excellent resonant behavior. Fig. 3 illustrates the
geometry of this resonant mesh and its equivalent circuit
from lumped elements.
Fig. 3. (a) Shifted crossed slots elements and (b) Equivalent circuit
It has to be taken into account during the design process
that compared to the normal crossed slots elements (Fig. 2.
128 GeMiC 2005
7/27/2019 Multi-layered Submillimeter Fss of Shifted Crossed Slot Elements for Applications in Radio Astronomy
Fig. 8. Computed and measured transmission of the4-resonant-mesh-filter (type 1).
Air separation:Ð ¿ ¼ ¼ Ñ
. Grid parameters are:
¿ Ñ ¼ Ñ Û Ñ
.
Fig. 9. Computed and measured transmission of one free-standingresonant mesh of type 2.
Grid parameters are: ¾ Ñ ¼ ¼ Ñ Û ¾ Ñ
.
Fig. 10. Computed and measured transmission of the4-resonant-mesh-filter (type 2).
Dielectric separation:Ð ½ ¿ ¿ Ñ
. Grid parameters are:
¾ Ñ ¼ ¼ Ñ Û ¾ Ñ
.
V I. CONCLUSION
The work presented in this paper describes design and
performance of submillimetre band-pass filters, which are
realized by shifted crossed slot elements meshes. Some nu-
merical results are presented, which agree quiet well with
the experimental measurements. The performance of a multi-
layered FSS with dielectric spacer material is limited by theinsertion loss, which has negative influence on the transmission
roll-off rate. Further developments are in progress to reduce
this loss component.
REFERENCES
[1] Hook, M., Vardaxoglou, J.C., Ward, K. Applications of FrequncySelective Surfaces, 27th ESA-WPP-222, pp. 299-309 2004.
[2] Irwin, P.G.J., Ade, P.A.R., Calcutt, S.B. Taylor, F.W., Seeley, J.S.,Hunneman, R. and Walton, L. Investigation of dielectric spaced resonantmesh filter designs for PMIRR, Infrared Physics, Vol. 34, pp. 549-5631993.
[3] Aroudaki, H., Hansen, V., Gemuend, H.P., Kreysa, E. Analysis of Low-pass Filters Consisting of Multiple Stacked FSS’s of DifferentPeriodicities with Applications in the Submillimeter Radioastronomy,