Where To Find This Example
Coax Fed Patch Antenna with Waveport at Different Locations
This example demonstrates the modeling of a coaxial probe-fed rectangular microstrip patch antenna. Analyst finite element wave ports are used to drive the antenna. Radiation patterns and feed return loss and input impedance are calculated.
A coaxial probe-fed rectangular microstrip patch antenna on a finite dielectric substrate and a finite ground plane is modeled. Perfectly Matched Layer (PML) boundary conditions are used on the 3D enclosure except for a circular region through which the coax line feeds the antenna. Principal plane radiation patterns at Phi equals 0 and 90 degrees are plotted at 7.8 GHz along with the feed return loss and input impedance.
This example demonstrates two important aspects of Analyst's wave ports:
- Wave ports can be defined on the face of 3D subcircuit that extends outside of the enclosure space of the parent EM structure.
- When a wave port meets an enclosure wall it replaces the boundary condition for that entire enclosure face with the 2D port solution
This example also demonstrates how the finite dielectric substrate is setup in the 2.5D layout editor in the AWR Design Enviroment. This is done by mapping the drawing layer "+LAY_3_SubFinite_COND" with a dielectric material "SubFinite". It should also be noted that the finite ground is drawn with a circular hole. Move the "Coaxial_Feed" in 2D layout view to see the hole. Without this hole, the Coax feed would be short circuited.
Understanding Analyst Wave Port Calculations in the EM Structures
In the "ExtendedCoax" EM structure the wave port solution includes only the cross-section of the coax line with its TEM mode. Since the lower boundary of the 3D structure is a PML the radiating fields fringe around the bottom face resulting in a significant back lobe in the radiation pattern graph.
The "TouchingBoundary" EM structure is drawn so that the wave port is coplanar with the bottom face of the enclosure boundary. Here the PML boundary condition specified on the bottom face of the enclosure where the coax enters is overridden by the Analyst wave port. Consequently, the 2D wave port solution is calculated on the entire bottom face. The fields inside the coax are calculated and also calculated outside the 2D cross-section of the coax, where there the fields are very small. Since the bottom face no longer has a PML boundary condition on it, but rather the 2D port solution, the radiating fields from above fringe only around the sides of the enclosure resulting in only a small back lobe.
The "ExtendedCoax" setup is therefore a better real-world arrangement, whereas the "TouchingBoundary" document shows the behavior of the Analyst wave port solution.
Radiation Pattern Measurements
The total power far field radiation pattern measurement is found under Electromagnetic > Antenna > Sweep Theta > PPC_TPwr. Phi=0 gives the XZ plane cut, and Phi=90 gives the YZ plane cut. The graphs show the directivity patterns as none of the two options for including losses is checked.