Effective Antenna Design Using EM and Circuit Co-Simulation in
WIPL-D MicrowaveIntroduction
The EM simulation of complex antenna systems
presents a challenge for modern computationalsoftware. The goal of a circuit-EM co-simulation is toalleviate the computational complexity decomposing
the complete system into parts that need to be simulatedusing full-wave approach, and parts that would bemodeledbypredefinedlibrarycomponents.
Encapsulation of proven parameterized antenna models
and their reuse within the same or another project isessential in rapid development of complex systems.

Co-Simulation in WIPL-D Microwave
The microwave (MW) circuit is composed of models oflumped elements, transmission lines and discontinuities
which are characterized by relatively simple analyticalequations based on physical and material properties ofcomponents. The circuit solver uses these models tocalculate S-parameters of components, and finally
S-parameters of the circuit (in reference to its ports).
Main benefit of using circuit analysis is the speed inwhich results are obtained. The circuit analysis is much
faster than full-wave EM analysis, even if done over awide frequency range because of simple component
models. Simulation time does not depend on the size ofthe circuit (in wavelengths).

optimization cycle. EM models allow investigation of
wanted or unwanted radiation and couplingmechanisms. Parts of the system whose radiation or EM
coupling to other parts of the system are not crucial canbe modeled analytically. Moreover, measured data overa frequency range can be imported as a component.
Finally, a model of any antenna or antenna componentof interest can be included and electromagneticallysimulated, on-the-fly, at the circuit simulation runtime.
Hence, antennas can be excited in ways that are closer
to how the structures are used in practice.
WIPL-D Microwave offers all the possibilities
mentioned above, as well as some additional features:
1. Radiation pattern produced by all the radiating
components in the circuit (Fig. 1),
2. A WIPL-D designed EM model of circuitcomponents in the library (see Fig. 2) withde-embedded S-parameters calculation,
3. Mode-matching models of the most important
rectangular waveguide discontinuities,
4. Library EM models of basic antennas and mostoften encountered implementation technology
transitions (see Fig. 3),
5. An impedance calculator built into eachcomponent specification window (Fig. 3).

However, the validity range of analytical models is
often small which significantly limits their applications.
Besides, such a circuit model takes into accountconductor and substrate losses in a typical circuit, but
not radiation mechanisms. It is also difficult to include
enclosure effects, since there may be box resonances or
waveguide modes in our physical implementation.
Furthermore, parasitic coupling between various circuitcomponents is not accounted for.
The most significant drawback of the approach is that
there is no possibility to model a device that can’t bedescribed by standard library analytical models.
Therefore, there is a clear benefit from inclusion of EM
simulation capabilities into the circuit simulation. EM
models imported into the circuit can be parameterized
and treated as any other circuit components in anFigure 1. Microwave circuit schematic

Simulation Example
MW circuit shown in Fig. 1 is analyzed using WIPL-D
Microwave. The circuit consists of two microstrip patch
antennas and a feeding network: microstrip lines,
microstrip T-junction and bends. All of the circuit
parameters are optimized in order to achieve matchingwww.wipl-d.com
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at 10 GHz. Patch antennas are physically separated by adistance which is also forwarded from the circuit, as aparameter. We specified this distance to be 25 mmalong x-axis. We specified that the only radiating
components in the circuit are patch antennas, although
there was a possibility to account radiation from othercomponents as well.

Figure 4. S11 parameter

Figure 2. Full-wave microstrip patch antenna model

Figure 5. Gain in 3D

Figure 6. Near field
Figure 3. Library microstrip patch antenna dialog box

Full-wave model of the library patch antenna is shownin Fig. 2. Its definition dialog box is shown in Fig. 3.
The circuit is analyzed in the frequency band from 9 to
11 GHz in nine uniformly distributed points. ParameterS11 is calculated in order to analyze matching, andshown in Fig. 4. Gain and near field from both antennas
are calculated at 10 GHz, and shown in Figs. 5 and 6.
Each EM model was simulated separately so gain andnear fields were obtained by superposition of theseresults. The simulation speed-up is significant since twosimulations of individual antennas are faster thensolving the whole problem at once. The more antennas
in an array we have, the speed-up is larger.

Conclusion
EM and circuit co-simulation offers a very effective
way of designing antennas. Including antenna EM
models into the circuit design environment provides
greater flexibility in modeling of accompanying
circuitry without decreasing the overall simulation
speed. Parameterization and reuse of antenna models
facilitates complex designs. Automation andoptimization tools offer further increase of design
productivity. The overall result is better system
performance achieved in less time, at a lower cost.

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