1 Practical considerations on train antenna design CSEM

2 Document Properties

3 Antenna specification Frequency range and BW: down link GHz, up link GHz -> 13% BW Half power beam width (HPBW): 5° (best result 2°) Gain:30 dBi Polarisation: circular polarisation (CP) Size: 25255 cm Scan angle and speed: 180° semi-sphere by mechanical steering system 0.4°/s for train running at 500 Km/h Scan angle precision 0.8° for 5° HPBW 0.32° for 2° HPBW

4 Theoretical investigation (1) Theoretical gain Approximation of maximum directivity D 0 using HPBW of 5°: D 0 = 32400/(5  5) => dBi Maximum effective aperture (A em ) of any antenna is related to its maximum directivity (D 0 ): Without considering conduction dielectric losses, reflection losses and polarization losses, an array of dimensions 20  20 cm leads to a maximum D 0 of 37 dBi. How many elements in the array to get 30 dBi? 16 elements => 18 dBi element antenna Issues: element spacing, mutual coupling, grating lobe level, antenna efficiency. 256 elements => 5.9 dBi element antenna Issues: feeding network loss, phase errors.

5 Theoretical investigation (2) Techniques to generate CP Single point (microstrip or coax) excited patch Two-point (microstrip or coax) excited patch Microstrip-slot coupled excitation Coax (or microstrip) excited cavity fed patch (slot) Travelling wave excited patch (or slot) Others… Beam forming network Beam direction: boreside Progressive phase = 0 Power distribution for beam shape

6 An example in simulation (1) Circularly polarized stacked truncated patch working at 2.4 GHz HFSS model ADS Momentum model

7 An example in simulation (2) HFSS simulation results

8 An example in simulation (3) ADS simulation results

9 Technical challenges and proposed solutions Microstrip loss at high frequency solutions: special low-loss substrate, stripline, multilayer structure [8] Required high gain with small size solutions: multiple superstrates [1], high permittivity superstrate [2,3], coupling and shielding [4]  attention: the gain should NOT compromise the antenna efficiency Large impedance BW for printed antenna solutions: stacked patch [5], slot excitation Purity of the CP within very large BW solutions: sequential rotation feeding network [6], polarisation transformer [7] At high frequency, phase error very sensitive to substrate planarity

10 2-axis Antenna Mount The purpose of this development is twofold: 1.Mobile active mount for antenna tests 2.Concept development for eventual product Main capabilities: Pointing range: azimuth (0-360), altitude (0-180) Speed and stability compatible with train antenna requirements Active tracking: closed loop on signal intensity System components Electromechanical 2-axis system: base, motors, bearings, mobile structures, sensors, connectors, wiring Electronic controller Tracking software

11 References [1] H. Y. Yang and N. G. Alexópoulos, “Gain Enhancement Methods for Printed Circuit Antennas Through Multiple Superstrates”, IEEE Trans. AP, vol. AP-35, No. 7, pp , July [2] W. Choi, Y. H. Cho, C.-S. Pyo and J.-I. Choi, “A High-Gain Microstrip Patch Array Antenna Using a Superstrate Layer”, ETRI Journal, vol. 25, No. 5, pp , October [3] Patent US 2004/ A1, “Microstrip Patch Antenna and Array Antenna Using Sperstrate”, June. 3, [4] X. Zhang, S. Kado, T. Hiruta, Y. Miyane, “Development of a 26GHz band High Gain Flat Antenna for FWA Systems”, Hitachi Cable Review, No. 22, pp , August [5] R. B. Waterhouse, “Stacked Patches Using High and Low Dielectric Constant Material Combinations”, IEEE Trans. AP, vol. 47, pp , December [6] W. Choi, C. Pyo and J. Choi, “Broadband Circularly Polarized Corner-truncated Square Patch Array Antenna”, /02, 2002 IEEE, pp [7] L. Young, L. A. Robinson and C. A. Hacking, “Meander-Line Polarizer”, IEEE Trnas. AP, May, 1973, pp [8] D. Pozar

12 Mechanical mount for the ground antenna for the 2 nd test The main active mount (motors, controllers and an optical telescope) has been delivered. Start to work on the dedicated software and user interface including three modules GPS data processing and antenna orientation computation Target field visualization, balloon detection Balloon position tracking Possible optical autoguided tracking as a backup solution And if all the above processes failed…… Manual tracking available