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Automotive Windscreen Antenna Analysis

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Windscreen antenna definition
as part of CAD model creation

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Analysis of gain patterns for
windscreen antenna reception abilities

Introduction

Vehicle manufacturers are incorporating an increasingly wide variety of antennas into vehicles for AM, FM, television and GPS reception, for GSM communication, for automated tolling, and so forth. To find a combination of antenna topologies and locations, which is both functional and aesthetically acceptable, is a very challenging task. Integration of antennas into windscreens has become a popular solution. However, the design of such antennas is a complex procedure, requiring the ability to analyse electromagnetic interactions between thinly layered dielectrics, thin embedded wires, and the surrounding vehicle body. FEKO provides accurate and efficient solutions to analyse complex integrated windscreen antennas.

Solver Features

The dedicated windscreen antenna analysis feature of FEKO allows the user to analyse the electromagnetic behaviour of integrated windscreen antennas within their operating environment. The analysis can take all physical features of windscreen antennas and their surroundings into account, including:

  • Finite sized windscreens
  • Arbitrarily curved windscreens
  • Multiple dielectric windscreen layers (glass, plastic, etc.)
  • Mutual coupling between antenna elements
  • Multiple windscreens in a vehicle
  • The vehicle body
  • The presence of a real ground

FEKO provides the user with innovative tools for the specification of windscreen antenna CAD.  A constrained surface tool can be used for the construction of a work surface in the shape of the windscreen in a model.  This work surface can be placed at an offset to the windscreen and an antenna can be defined in the work surface by using wires, Bézier curves and regularly spaced wires.

The analysis of the windscreen is based on the method of moments (MoM). Only the vehicle body and metallic windscreen antenna elements are included in the MoM mesh, which makes the analysis very efficient. Although windscreen surfaces are meshed into flat or curvilinear triangles, these elements are not used in the solution phase but only as reference elements that represent the geometry of the windscreen.  Various electromagnetic characteristics of the windscreen antenna can be computed, including:

  • Current distribution on the antenna and vehicle
  • Input impedance bandwidth and scattering parameters
  • Near‐field distributions and far‐field radiation patterns

Apart from the dedicated windscreen antenna analysis feature, FEKO also supports the inclusion of dielectrically coated wires in its models. This feature can alternatively be used to model windscreen antenna wires by assigning coating properties to represent the effect of the windscreen dielectric sheet, but the approach breaks down for closely spaced wires where mutual coupling effects are strong.

Validation Example

Consider a flat, rectangular, framed glass panel with integrated antenna, above a finite ground plane. The glass is 3 mm thick, with tan(δ) = 0.02 and εr = 7. The response of this antenna was simulated with the rigorous FEM‐MoM approach as well as with the efficient windscreen analysis approach, and the results compared with a measurement. The FEM-MoM required 1.79 GBytes of memory, while the windscreen analysis method required only 280 Mbytes, with dramatically reduced run time. These results show that the windscreen analysis approach is very accurate as well as computationally very efficient.


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FEM-MoM Model Windscreen Method Model



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Comparison of Reflection Coefficient Results

 

Automotive Example

Now consider a complex antenna integrated into the rear window of a car. The glass is 3.15 mm thick, with tan(δ) = 0.01 and εr = 6.85. The antenna wire radius is 0.3 mm. As can be seen, the window is generally curved and the antenna consists of wire sections which will couple strongly with each other, as well as with the vehicle body. The windscreen analysis‐based reflection coefficient results again show excellent agreement with measured results, especially considering the complexity of this model.

windscreen antenna model w=378 h=300
Integrated Windscreen Antenna in Car with Detailed View


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Magnitude Phase


Simulated vs. Measured Windscreen Antenna Reflection Coefficient