Workshop national graduate school for space technology, Omid Sotoudeh Omid Sotoudeh Antenna group Innovative solutions for Multibeam antenna feeds

Workshop national graduate school for space technology, Omid Sotoudeh Overview  Examiner: Prof. Per-Simon Kildal, Chalmers, Head of Antenna Group  Industrial supervisor: Dr. Per Ingvarson, Chief Engineer Antennas, Saab Ericsson Space  ESA/ESTEC project ”Innovative solutions for muti-beam antenna feeds”  August 2002 – September 2003  Principal investigator: Omid Sotoudeh  Supervisors: Per-Simon Kildal (Chalmers) Per Ingvarson (SES)  Contacts from ESTEC: Antoine Roederer, Head of Electromagnetics Division Cyril Magenot, Head of Antenna and Sub-Millimeter Wave Section Arturo Martin-Polegre, Antenna and Sub-Millimeter Wave Section  Teknisk Licentiat: O. Sotoudeh, ”Hard horns for cluster-fed multi-beam antennas”, National Graduate School of Space Engineering & Chalmers University of Technology, Sweden, February  Final work in analysis, optimization and design of single and multi-mode hard horns for cluster fed multi-beam antennas.

Workshop national graduate school for space technology, Omid Sotoudeh  New generation of satellite networks operating in the Ka-band (20/30 GHz)  Two way high-speed communications  A broad range of voice, data and video communications  Large coverage area (ex Europe, Asia)  Low Cost Source: EuroSkyWay program: Ka – band multimedia satellites

Workshop national graduate school for space technology, Omid Sotoudeh Footprint 30 GHz 20 GHz One of four antennas Hard horns proposed as feed Cluster-fed multi-beam antennas for Ka-band 4 reflector system 17.7 – 20.2 GHz downlink 27.5 – 30.0 GHz Uplink

Workshop national graduate school for space technology, Omid Sotoudeh  Max relative co- and x-pol. between the neighboring beams  Max x-pol. in own beam f1f1 f1f1 f1f1 f1f1 f1f1 f1f1 f1f1 f2f2 f2f2 f2f2 f2f2 f4f4 f4f4 f4f4 f4f4 f3f3 f3f3 f3f3 f3f3 Beam isolation: 4 cell reuse scheme  Directivity and directive gain at the weakest point of the footprint (EOC)  Minimum directive gain level Coverage: 4 reflector system Δ  = 1   d4 = 2 

Workshop national graduate school for space technology, Omid Sotoudeh System requirements given by ESTEC Downlink Tx: 17.7 – 20.2 GHz Uplink Rx: GHz End of Coverage directivity 39.5 dBi XPD within own beam < -27 dB Co-polar beam isolation relative to weakest useful point >25 dB Cross-polar beam isolation relative to weakest useful point >27 dB Reflection coefficient at feed port< -27 dB Polarization between frequency bands Dual polarization system, individual beams remain single polarized. Polarization within each band Dual, linear or circular Operating frequency band Tx and Rx

Workshop national graduate school for space technology, Omid Sotoudeh Tools used for the analysis and design of horns Theoretical formulas based on modes Rotational symmetric problems Very fast solution Rather accurate for design of single mode horns Mode-Matching technique 2D solver – rotational symmetric problems Very accurate and fast Used for design of horns traditionally Commercial 3D SW’s: (FDTD) Slow and demanding Accurate Used for verification

Workshop national graduate school for space technology, Omid Sotoudeh Smooth walled, TE 11 mode Corrugated soft Ideal soft or dual mode Corrugated hard Ideal hard H-planeE-plane Aperture distribution Horn types Horn types and their radiation patterns at center frequency Hard horns as feeds in CF-MBA Hard horns: Dielectric in the corrugations, ε r = 2.44 Wall thickness ~ 0.21 d = 5 at 30 GHz

Workshop national graduate school for space technology, Omid Sotoudeh Potter/dual mode horns  TE 11 + TM 11 modes  Equal E - and H – planes: Low X - pol  Low efficiency  Narrow bandwidth R.H. Turrin, 1966 TE 11 TM 11 += Potter Smooth walled horns  TE 11 mode  Difference in E- and H-plane  High X-pol  Medium efficiency  Wide bandwidth

Workshop national graduate school for space technology, Omid Sotoudeh High efficiency horns  Multimode  Complex step geometry  High efficiency (ex. 90 %)  Low X - pol  Narrow bandwidth Bhattacharyya et al 2002

Workshop national graduate school for space technology, Omid Sotoudeh Hard and Soft surfaces direction of propagation Conductor direction of propagation Corrugations filled with dielectric Conductor (blue region) More on these surfaces I recommend: P-S, Kildal, “Artificially soft and hard surfaces in Electromagnetics”, IEEE transactions on Antennas and Propagations, Vol. 38, No. 10, Oct Soft surface: Stops field propagation Hard surface: Enhances field propagation

Workshop national graduate school for space technology, Omid Sotoudeh The hard horn: using longitudinal corrugations  High efficiency  Low X – pol  Wide bandwidth  Complex geometry direction of propagation Corrugations filled with dielectric Conductor (blue region)

Workshop national graduate school for space technology, Omid Sotoudeh Single and multimode hard horns ab c d a.Single mode horn with corrugations of constant depth b.Single mode horn with linearly increasing thickness c.Multimode horn with hard wall in an outer section d.Multimode horn combined with a step-shaped mode exciter to improve the performance at high frequencies

Workshop national graduate school for space technology, Omid Sotoudeh Simple single mode hard horns Analysed using asymptotic models LHLH LELE Har wall region d t

Workshop national graduate school for space technology, Omid Sotoudeh Co Cross 19 GHz23 GHz27 GHzTEM 30 GHz 30.5 GHz31 GHz The corrugation period p << Classical-type model: Dominant TE z mode field distribution Example: d = 5λ at 30 GHz ε r = 2.5 f TEM = 30 GHz εrεr d = 50 mm t = 2 mm Study of hard horns: Analysis tools

Workshop national graduate school for space technology, Omid Sotoudeh Multimode hard horns: Initial studies Based on simple manufacturing – very simple geometry Direct transition from PEC to hard surface Cylindrical or slightly conical hard surface Only part of the horn is corrugated Smaller D/t gives shorter L1 Possible for small radii < 4-5λ Larger apertures need a long PEC section

Workshop national graduate school for space technology, Omid Sotoudeh Dual band multimode horn Designed using parametric studies and Genetic algorithm optimization EM solver: Mode-matching Tested with FDTD: QW-V2D and QW3D

Workshop national graduate school for space technology, Omid Sotoudeh Calculated at 29 GHz Rx band Calculated at 19 GHz Tx band

Workshop national graduate school for space technology, Omid Sotoudeh Horn performance: 2D simulations Aperture efficiency (%)Return-loss (dB) Max cross-polar level (dB) Frequency (GHz)

Workshop national graduate school for space technology, Omid Sotoudeh Total antenna performance in BOR reflector Directive gain Co polar BI Cross polar BI Max rel. cross pol in own beam

Workshop national graduate school for space technology, Omid Sotoudeh Hard horn measurements at SES

Workshop national graduate school for space technology, Omid Sotoudeh Horn performance: measurements and MM → High sidelobes in E- plane

Workshop national graduate school for space technology, Omid Sotoudeh Horn performance: measurements and MM and 3D FDTD (40 corrugations) →The 3D simulations agree with the measurements

Workshop national graduate school for space technology, Omid Sotoudeh Horn performance: measurements and MM and 3D FDTD N = 40 and 80 corrugations →The 3D simulations of N = 40 agree with the measurements → N = 80 and tooth thickness 0.4 mm agrees with asymptotic design

Workshop national graduate school for space technology, Omid Sotoudeh Comparison of designs Best single mode design L tot = 47 cm, corrugated L corr = 47 cm Best multi-mode design L tot = 30 cm, corrugated L corr = 22 cm

Workshop national graduate school for space technology, Omid Sotoudeh Conclusions Studies of hard walled horn antennas: –The hard walls may be used in horn antennas in order to enhance their performance. –They can be designed as single mode hard horns or multimode hard horns. A dual band multi-mode hard horn has been built and measured for 20/30 GHz Ka- band operation. –Horn designed using fast Mode-Matching. –Present design is smaller than previous single mode horns and much more simple to manufacture. –Discrepancies with measurements have been explained. –For present design: we need more than 40 corrugations and < 0.5 mm corrugation tooth thickness. We can use the fast mode-matching codes in the future for design of these horns. Future work: More on the effect of corrugations on the hard horn performance and their optimal dimensions for our hard horn design is being studied at the moment.

Workshop national graduate school for space technology, Omid Sotoudeh

Horn parameters

Workshop national graduate school for space technology, Omid Sotoudeh BOR reflector model  Rotationally symmetric reflector, and neglected feed blockage (offset reflectors)  Horns in the focal point of reflector  Aperture integration method  Short computational time  Very fast for parametric studies  Quite accurate and relevant results

Workshop national graduate school for space technology, Omid Sotoudeh Theory of BOR, Body of revolution Aperture fields: vertical polarization Total: BOR 1 component:

Workshop national graduate school for space technology, Omid Sotoudeh Far-fields: vertical polarization Theory of BOR, Body of revolution Total: BOR 1 component:

Workshop national graduate school for space technology, Omid Sotoudeh BOR 1 relations for RHCP Far-field functions Aperture field functions Theory of BOR, Body of revolution (see e.g. Kildal’s textbook, Foundations of Antennas)

Workshop national graduate school for space technology, Omid Sotoudeh Hard horn analysis: Performance as a function of frequency Ex: d = 5λ TEM, L H = 15 λ TEM, f TEM = 31.8 GHz ε r = 1.25, t = 4.5 mm ε r = 5, t = 1.2 mm ε r = 1.5, t = 3.2 mm ε r = 2.5, t = 1.9 mm TE 11 Frequency (GHz) e ap (%) TE 11 Frequency (GHz) Max xp level (dB) ε r = 1.25, t = 4.5 mm ε r = 1.5, t = 3.2 mm ε r = 5, t = 1.2 mm ε r = 2.5, t = 1.9 mm Frequency (GHz)

Workshop national graduate school for space technology, Omid Sotoudeh Hard horn analysis: Performance as a function of length Ex: d = 5λ TEM, f = f TEM = 31.8 GHz ε r = 1.25, t = 4.5 mm ε r = 5, t = 1.2 mm ε r = 1.5, t = 3.2 mm ε r = 2.5, t = 1.9 mm TE 11 e ap (%) TE 11 Length (mm) Max xp level (dB) ε r = 1.25, t = 4.5 mm ε r = 1.5, t = 3.2 mm ε r = 5, t = 1.2 mm ε r = 2.5, t = 1.9 mm Length (mm)

Workshop national graduate school for space technology, Omid Sotoudeh Comparison mode-matching – classical-type ε r = 1.25, d = 5λ at 17.7 GHz, f TEM = 30.5 GHz L H = 25λ at 17.7 GHz ≈ 424 mm L E = 376 mm Frequency (GHz) Max XP (dB) e ap (%) Frequency (GHz) Max XP (dB) e ap (%) Ideal design Realizable design

Workshop national graduate school for space technology, Omid Sotoudeh Horn patterns Reflector patterns Optimum D = 1.25 m, F ≈ 1.86 m, subtended semi angle ~19˚