Efficient design of a Cband aperturecoupled stacked microstrip

Efficient design of a C-band aperture-coupled stacked microstrip array using Nexxim and Designer Alberto Di Maria German Aerospace Centre (DLR) – Microwaves and Radar Institute – Oberpfaffenhofen (DE)

Outline Synthetic Aperture Radar (SAR) range resolution synthetic aperture and azimuth resolution image retrieval Antenna specifications Patch design Array setup Feeding networks Antenna assembly feeding networks optimization Solver-On-Demand configuration refining the model HFSS complete antenna model Conclusions ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 2

Synthetic Aperture Radar (SAR) range resolution range height (z) frequency W t phase v t Courtesy of Matteo Nannini ground-range (y) swath ra ng e azimuth (x) range resolution cell ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 3

SAR: synthetic aperture azimuth resolution height (z) r(x) x 0 x Synthetic Aperture chirp r(x) Courtesy of Matteo Nannini ground-range (y) x 0 azimuth (x) ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 4

Synthetic Aperture Radar (SAR) image retrieval height (z) A Synthetic Aperture Radar (SAR) system allows the retrieval of reflectivity images of the observed scene with high spatial resolution. range (y) azimuth (x) SLC Nominal Resolution: 1 x 1. 5 m E-SAR (L-band) 1998 ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 5

Antenna specifications Carrier frequency 5. 3 GHz (C-band) Frequency range 5. 05 GHz – 5. 55 GHz Bandwidth 500 MHz (up to 800 MHz desirable) Polarization Dual linear polarization (h, v) Geometry Planar Power 1. 5 k. W (peak) Gain 17 d. Bi min Input adaptation (S 11) > 10 d. B for 5. 05 GHz – 5. 55 GHz > 12 d. B for 5. 1 GHz – 5. 5 GHz Azimuth beam width (θ 3 d. B) 12 deg ± 1 deg Azimuth Side Lobe Level (SLL) > 15 d. B Elevation (range) beam width (θ 3 d. B) 34 deg ± 2 deg Elevation Side Lobe Level (SLL) > 15 d. B Crosspolarization insulation Critical requirements for SAR are: ≥ 25 d. B Bandwidth Azimuth beam width ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 6

A 0 x A 0 y Aw Ls W 1 x W 2 x Patch design Aw ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 7

Patch design impedance matching The impedance matching has been optimized for bandwidth. S 11 < -20 d. B over the bandwidth. ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 8

Patch design radiation pattern Patch antenna gain = 8. 5 d. B Front to back ratio = 20 d. B ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 9

Array setup patch_offset ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 10

Array setup radiation pattern Patches distance: optimized to obtain the required beamwidth (12 deg). Feed voltage tapering: using Dolph-Chebyshev to obtain the required SLL (-20 d. B). ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 11

Feeding network schematic H Special components are created in Designer and inserted in Nexxim. V ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 12

Feeding network layout Special components are created in Designer and inserted in Nexxim. ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 13

Feeding network A full parameterization and the use of Position Relative function assure the layout consistency over the variables variations. ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 14

Antenna assembly schematic The array of six patches and the two feeding networks are combined together in a top level circuit in order to create the entire antenna. ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 15

Antenna assembly layout ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 16

Antenna assembly Feeding network optimization As the parameterization is retained through the hierarchy, it is possible to set-up optimization of the feeding networks directly in the top level circuit. ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 17

Solver-On-Demand configuration The Solver-On-Demand lets you choose the simulation engine. Then each antenna part can be simulated either as circuit or with full wave analysis. ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 18

Solver-On-Demand refining the model – step 1 Here a full wave analysis has been done. But the three components (feeding networks H and V and the array) are still independent i. e. no mutual coupling between them is considered. ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 19

Solver-On-Demand refining the model – step 2 8 d. B Simulation shows that, when the entire antenna is simulated at once, the matching is up to 8 d. B worse than what we obtained with optimization at the circuit level. What can be done? ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 20

Solver-On-Demand Simulation shows that, when the entire antenna is simulated at once, the performance is up to 8 d. B worse than what we obtained with optimization at the circuit level. What can be done? Through Solver-On-Demand (as the parameterization is retained) it is possible to optimize again the antenna matching, running the simulation with Planar. EM engine. The entire antenna can be exported in one click to HFSS, retaining all the variables and parameters. The final optimization can be run in HFSS. Other elements can be taken in account (connectors, screws, vertical elements) ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 21

HFSS complete antenna model The model is electrically large and complex ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 22

HFSS complete antenna model Distributes mesh sub-domains to networked processors and memory ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 23

HFSS complete antenna model Domain Decomposition Solver Profile 8 Domains ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 24

HFSS complete antenna model Field Animation: Antenna, feed and enclosure Vertical Polarization ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 25

HFSS complete antenna model Field Animation: Antenna, feed and enclosure Horizontal Polarization ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 26

HFSS complete antenna model ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 27

Conclusions The design of an array antenna suitable for an airborne SAR system, operating at C-Band has been presented. Every antenna component has been designed separately with a fully parameterized model and has been easily tuned and optimized with Designer, to meet the dimensional and frequency requirements. The individual components are then assembled and interconnected in the Nexxim circuit simulator to form the entire array. The assembly is tuned and optimized using the speed capability of Nexxim. The Solver-On-Demand feature lets us choose which part of the antenna will be solved with a full wave analysis and which part will be solved with a fast circuit simulation. The entire antenna has been then exported in HFSS. The final tuning is hence done in a very detailed model. ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 28

Thank you ANSYS Conference & 27. CADFEM Users’ Meeting 2009 – Nov. 19 th - 29