Patch antenna

tags

coaxial waveguide, modal surface, lossy dielectric, metallization, radiation pattern, reflection coefficient

Patch antenna fed by a coaxial waveguide

Description

This model, inspired from [1], is made of a coaxial waveguide feeding a patch antenna on a lossy dielectric substract.

We wish to compute radiation diagrams as well as the reflection coefficient around the resonance frequency about 5.02 GHz.

The PSHELL of the model are named after its different objects.

Volumic domains

In this model there are three homogeneous volumic dielectric domains:

  • SUBSTRACT: the substract on which the metallic patch is printed

  • GUIDE: the coaxial waveguide

  • EXT: the exterior domain (unbounded)

There is one perfect volumic metallic domain:

  • CORE: the core of the coaxial waveguide

Surfacic interfaces

The gain is the perfect conducting (PEC) metallization between the waveguide and the exterior domain:

  • GUIDE/EXT interface

There are PEC metallizations between the substract and the exterior domain:

  • the ground

  • the patch

There are dielectric interfaces between:

  • the substract and the exterior domain

  • the waveguide and the substract

There are interfaces between dielectric and perfect metallic domains:

  • the core and the waveguide

  • the core and the substract

  • the core and the exterior domain

CAD and Mesh tips

Waveguide

It is important to ensure that the length of the waveguide is not too small compared to the wavelength in the waveguide domain. In this model it is about half of the largest wavelength.

One has to imagine that the modal surface is the interface to a semi-infinite domain. Hence the end of the core next to the modal surface is not a metallic/dielectric interface and must be ignored.

Mesh rules

The mesh is globally set to be equal to approximately \(\lambda/10\) in the dielectric domain. It is refined:

  • on the modal surface for a good representation of the TEM mode

  • around patch border where the current can vary rapidly

  • around ground and substract singularties

Simulation setup

Physical properties

You can use the following values for relative permittivity and permeability of the volumic domains:

Name

\(\varepsilon'\)

\(\varepsilon''\)

\(\mu'\)

\(\mu''\)

air

1.0

0.0

1.0

0.0

substract

4.34

0.08681

1.0

0.0

waveguide

2.2

0.0

1.0

0.0

Warning

ASERIS works in \(e^{-i\omega t}\) time convention. Hence imaginary part of lossy materials must be positive.

Illumination

The coaxial transmission line is illuminated by its first TEM mode.

We consider a frequency sweep around 5.02 GHz from 4.92 GHz to 5.12 GHz with a step of 20MHz.

Observation

We wish to compute the radiation pattern for all directions, that is for \(\theta\) in [-180° 180°] and \(\phi\) in [0 180°], with an angular step of 3°.

We can also access the reflection coefficient inside the modal surface.

Results

Below are some representations of the solution in terms of current density, far field diagram and reflection coefficient.

Current density at 5.02 GHz

Current density at 5.02GHz. One can see the patch resonance at patch border. The waveguide is visible by transparency.

Directivity diagram at 5.02 GHz

Directivity diagram of the total far field at 5.02 GHz. While the far field has been computed for all frequencies and all directions, one can draw slices for fixed angles, e.g. here at \(\phi=0\) °.

Reflection coefficient

Reflection coefficient. The minimum is obtained around 5.02 GHz.