Accurate simulation and experimental validation of a 4-by-4 antenna array for Ka band

Transcription

1 Accurate simulation and experimental validation of a 4-by-4 antenna array for Ka band CST EUC Strasbourg B. Lesur, M. Thévenot, T. Monédière, C. Mellé

2 Outline Introduction Context Objectives Design and modeling of the array Antenna element Radiating panel Feeding Network Combination of [S] matrices Measurements Return loss Radiation pattern Gain / Efficiency Conclusions

3 Zodiac Data Systems Tracking / telemetry products : Receivers Recorders Modems High gain reflector antennas : RF & Antenna Department Xlim Research Institute 6 Departments : Components Circuits Signals and High Frequency Systems Mathematics and Computer Sciences Micro & Nanotechnologies for optoelectronics and microwave components Waves and Associated Systems : Multifunction Antennas Team

4 Objective Designing a large array for internal tests on a SATCOM link (Ka-Sat) Specifications : Bandwidth : 19,7-20,2 GHz Linear polarization Broadside beam : Half power beamwitdths of 1,1 (H-plane) & 4,4 (E-plane) Antenna size : 680 mm x 170 mm => 1024 antenna elements Satellite Ka-band antenna with mechanical positioner

5 Objective Designing a large array for internal tests on a SATCOM link (Ka-Sat) Specifications : Bandwidth : 19,7-20,2 GHz Linear polarization Broadside beam : Half power beamwitdths of 1,1 (H-plane) & 4,4 (E-plane) Antenna size : 680 mm x 170 mm => 1024 antenna elements [S] matrices of feed and panel need to be known in order to synthesize resulting radiation pattern and return loss a 1 b 1 a 2 Φ 1 => Accurate modeling of such a big array is a difficult task [S feed ] b 2 a 3 b 3 [S panel ] Φ 2 Φ 3 First step : design and modeling of a 4-by-4 array to secure simulation results before proceeding with the full array

6 Outline Introduction Context Objectives Design and modeling of the array Antenna element Radiating panel Feeding Network Combination of [S] matrices Measurements Return loss Radiation pattern Gain / Efficiency Conclusions

7 Design and modeling of the array : antenna element Element spacing : d = 10,625 mm (0,72 λ f max ) => Grating lobe free broadside pattern Type of element : aperture coupled patch Feed line : stripline Low loss teflon substrate (Rogers RT5880) Aperture coupling + stripline feed radiating panel and feeding network can be studied separately Periodic Boundary Condition (x) + Symmetry plane (y) Infinite array approach (with F solver) Patch Gnd plane w/ aperture Feed line Bottom gnd

8 Design and modeling of the array : antenna element Antenna element is simulated with frequency solver Addition of an air box on top of the patch Local meshing on feed line, slot, patch and air box Adaptive meshing Result of adaptive meshing : Air box Patch Gnd plane w/ aperture Feed line Bottom gnd

9 Design and modeling of the array : antenna element Addition of shorting vias between the two ground planes Removal of undesired resonances Suppression of surface waves propagations

10 Design and modeling of the array : antenna element Convergence between Frequency and Transient solvers : Frequency solver : Adaptive meshing tetrahedrons Total solver time : 8 min Transient solver : Local meshing (line, slot, patch) Substrate grid to align mesh cells on vias mesh cells Total solver time : 13 min

11 Design and modeling of the array : radiating panel E Repetition of the cell obtained after convergence between Frequency and Transient solvers Transient solver : 16 ports Total solver time : 23 h 64 Go RAM, 2x Intel Xeon GHz + GPU acceleration (Tesla K40 12 Go RAM) Panel : Reflected powers b i = j S ij. a j Imperfections due to finiteness of the panel

12 Design and modeling of the array : radiating panel E Repetition of the cell obtained after convergence between Frequency and Transient solvers Transient solver : 16 ports Total solver time : 23 h 64 Go RAM, 2x Intel Xeon GHz + GPU acceleration (Tesla K40 12 Go RAM) Panel : Couplings Couplings are much more important in the E plane

13 Design and modeling of the array : feeding network Design of a uniform excitation network Stripline technology Shorting vias Frequency solver : 17 ports Total solver time : 18h (64 Go RAM, 2x Intel Xeon GHz) Dispersion < 0,1dB Magnitudes and phases of transmission coefficients

14 Design and modeling of the array : feeding network Design of a uniform excitation network Coupling between neighbor ports is only due to line coupling : no direct coupling => circuit is well shielded Reflection coefficient is below -26 db over the required frequency band

15 Design and modeling of the array : combination of [S] matrices a b CST Design Studio Probes => monitor steady state voltages (U) and currents (I) Calculation of injected and reflected powers at the border of feed and panel : a = U + Z 0I 2 Z O b = U Z 0I 2 Z O

16 Design and modeling of the array : combination of [S] matrices a b 2 db Powers reflected by the patches Inhomogeneity of injected powers => perturbations due to interactions between [S] matrices of feed and panel

17 Design and modeling of the array : combination of [S] matrices a b N 1 M 1 jkd(n.sin θ.cos φ +m.sin θ.sin φ ) Φ Tot (θ, φ) = A n,m. Φ n,m (θ, φ). exp n=0 m=0 «AC, Combine result» task : automatically combines each radiation pattern and complex weights to synthesize resulting pattern «S-Parameters» task : computes return loss of cascaded matrices

18 Summary Design of an antenna element : Periodic approach : active reflection coefficient Frequency solver Modeling of a radiating panel : Repetition of the antenna element Transient solver => full-wave study of the radiating panel Modeling of a feeding network: Uniform amplitude/phase excitation Stripline technology Frequency solver Combination of [S] matrices Actually injected and reflected powers Resulting radiation pattern and return loss

19 Outline Introduction Context Objectives Design and modeling of the array Antenna element Radiating panel Feeding Network Combination of [S] matrices Measurements Return loss Radiation pattern Gain / Efficiency Conclusions

20 Measurements

21 Measurements : Return loss and radiation pattern A second resonance appears at GHz It is also slightly noticeable in simulation Probably due to connection / soldering Measured patterns : very good agreement with simulations in both planes

22 Measurements : Gain and efficiency Measured gain is really close to simulation Gold/Nickel finish is lossier Total efficiency of the array varies between 80% and 65% at the end of the band

23 Outline Introduction Context Objectives Design and modeling of the array Antenna element Radiating panel Feeding Network Combination of [S] matrices Measurements Return loss Radiation pattern Gain / Efficiency Conclusions

24 Conclusions Design of an antenna array with detailed analysis at each step of the design Antenna element => active reflection coefficient Radiating Panel => reflected powers and couplings Feeding network => transmission coefficients and couplings Combination of [S] matrices => radiation pattern, reflection coefficient and injected/reflected powers => The design meets the specifications Measurements : good agreement with simulations Observed complex weightings are really applied on each element => nulls and side lobes positions and levels Predicted interactions between [S] matrices are confirmed Simulations accuracy is validated

25 Thank you for your attention