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Practical considerations on train antenna design

CSEM

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Document Properties

Document Title Practical considerations on train antenna design

Document Number CAP-0268

Author (s) Q. Xu

Date 28.02.2005

Participant (s) (short names) L. Zago

Workpackage(s) WP3.2

Total number of slides (including title and this slide)

12

Security level (PUB, RES, CON)

Internal confidential

Description / Abstract

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: 25255 cm

Scan angle and speed:180° semi-sphere by mechanical steering system0.4°/s for train running at 500 Km/h

Scan angle precision0.8° for 5° HPBW0.32° for 2° HPBW

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Theoretical investigation (1)

Theoretical gainApproximation of maximum directivity D0 using HPBW of 5°:

D0 = 32400/(55) => 31.13 dBi

Maximum effective aperture (Aem) of any antenna is related to its maximum

directivity (D0):

Without considering conduction dielectric losses, reflection losses and polarization losses, an array of dimensions 2020 cm leads to a maximum D0 of 37 dBi.

How many elements in the array to get 30 dBi?16 elements => 18 dBi element antennaIssues: element spacing, mutual coupling, grating lobe level, antenna efficiency.256 elements => 5.9 dBi element antennaIssues: feeding network loss, phase errors.

0

2

4DAem

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Theoretical investigation (2)

Techniques to generate CPSingle 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 networkBeam direction: boreside

Progressive phase = 0

Power distribution for beam shape

0°

90°

RHCP LHCP

L

W

RH LH

x

y

45°

RH LH

x

y

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An example in simulation (1)

Circularly polarized stacked truncated patch working at 2.4 GHz

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

1.8 2.0 2.2 2.4 2.6 2.81.6 3.0

-15

-10

-5

-20

0

Frequency

Mag. [

dB

]

Readout

m1

Readout

m2

S11

1.8 2.0 2.2 2.4 2.6 2.81.6 3.0

-100

-50

0

50

100

-150

150

Frequency

Phase

[deg]

S11

freq (1.700GHz to 3.000GHz)

S11

Mon Feb 21 2005 - Dataset: inverted_patch1_mom_a

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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 2nd 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 computationTarget field visualization, balloon detectionBalloon position tracking

Possible optical autoguided tracking as a backup solution

And if all the above processes failed……

Manual tracking available