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Practical considerations on train antenna design

CSEM

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Document Properties

Document Title Document Number Practical considerations on train antenna design CAP-0268 Author (s) Date Q. Xu 28.02.2005 Participant (s) (short names) L. Zago Workpackage(s) Total number of slides (including title and this slide) Security level (PUB, RES, CON) Description / Abstract WP3.2 12 Internal confidential After having reviewed the antenna specification, different technical aspects influencing the antenna design are discussed. Simulation results of one example are shown using both HFSS and ADS Momentum.

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Antenna specification

Frequency range and BW: down link 27.5-28.35 GHz, up link 31-31.3 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

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Theoretical investigation (1)

Theoretical gain Approximation of maximum directivity D 0 D 0 = 32400/(5  5) => 31.13 dBi using HPBW of 5 ° : Maximum effective aperture (

A em

) of any antenna is related to its maximum directivity (

D 0

):

A em

  2 4 

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.

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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… RHCP 0° 90° LH 45° y RH x LHCP LH L W y RH x Beam forming network Beam direction: boreside Progressive phase = 0 Power distribution for beam shape

An example in simulation (1)

Circularly polarized stacked truncated patch working at 2.4 GHz

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HFSS model ADS Momentum model

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An example in simulation (2)

HFSS simulation results

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An example in simulation (3)

ADS simulation results Mon Feb 21 2005 - Dataset: inverted_patch1_mom_a S11 0 -5 -10 -15 m1 m2 -20 1.6

1.8

2.0

2.2

2.4

Frequency 2.6

2.8

3.0

S11 S11 150 100 50 0 -50 -100 -150 1.6

1.8

2.0

2.2

2.4

Frequency 2.6

2.8

3.0

f req (1.700GHz to 3.000GHz)

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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

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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

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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. 860-864, July 1987.

[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. 407-411, October 2003.

[3] Patent US 2004/0104852 A1, “Microstrip Patch Antenna and Array Antenna Using Sperstrate”, June. 3, 2004.

[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. 16-19, August 2003.

[5] R. B. Waterhouse, “Stacked Patches Using High and Low Dielectric Constant Material Combinations”, IEEE Trans. AP, vol. 47, pp. 1767-1771, December 1999.

[6] W. Choi, C. Pyo and J. Choi, “Broadband Circularly Polarized Corner-truncated Square Patch Array Antenna”, 0-7803-7330-8/02, 2002 IEEE, pp. 220-223.

[7] L. Young, L. A. Robinson and C. A. Hacking, “Meander-Line Polarizer”, IEEE Trnas. AP, May, 1973, pp.376-378.

[8] D. Pozar

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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