Tag Archives: simulation

Designing and simulating a Multi-Coupled Resonator Microwave Diplexer with High Isolation

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By Nadia Gary, Application Engineer, EMWorks.

Diplexer is a device used for either splitting a frequency band into two sub-bands or for combining two sub-bands into one wide band. It is popularly used in satellite communication systems to combine both the Tx and the Rx antennas on space craft. Microwave diplexer is commonly used in the Radio Frequency (RF) front end of cellular radio base stations to separate the Tx and the Rx channels.

Conventionally, microwave diplexers are achieved by connecting two separately designed filters together via an external energy distribution device. This connecting device could be a T-junction,  a Y-junction, a circulator, a manifold  or a common resonator. In this article, we present without an external junction a microwave diplexer [1], and replacing it with resonators which provide resonant poles in the diplexer response.

Here is a design flow and a simulation of a 10-pole (10th order) diplexer that has been successfully designed and simulated. The diplexer is composed of 2 poles from the dual-band filter, 4 poles from the Tx bandpass filter, and the remaining 4 poles from the Rx bandpass filter. The design was implemented using asynchronously tuned microstrip square open-loop resonators. Figure 1 shows the design of the diplexer using SolidWorks.

Figure1- Geometry of Multi-Coupled Resonator Microwave Diplexer

Fig. 2 shows the diplexer layout which consists of a multi-coupled resonator designed using SolidWorks. The diplexer fed by a 50 microstrip-line (width WF = 1.1 mm) for each port, the center frequency is 1.84 GHz, The RT/Duroid 6010LM substrate with a dielectric constant of 10.8, a loss tangent of 0.0023, and a substrate thickness of 1.27 mm was used for the simulation. The geometrical parameters of the multi coupled resonator diplexer (S1, S2, S3, S4, S5, S6, S7, S8, S9, t1 and t2) are defined in a file and they will be imported to SolidWorks as equations in order to facilitate and accelerate the workflow.Diplexer layout and fabricated model

Figure2 – Diplexer layout and fabricated model [1]

The table below summriazes the diffrent dimensions (global variables) to be imported into SolidWorks.

Dimension Value(mm)
S1 1.5
S2 2
S3 2
S4 1.6
S5 0.9
S6 1.65
S7 1.95
S8 2
S9 1.45
t1 1.45
t2 1.35

Table1 – summarizes the list of dimensions to be imported into SolidWorks 

The diplexer circuit model was simulated using HFWorks S-Parameters analysis. Figure 3, depicts the distribution of the electric field and figure 4 shows the simulated results S-parameters  of the geometry of Multi-Coupled Resonator Microwave Diplexer.

Distribution of the electric field at 1.9GHz

Figure3 – Distribution of the electric field at 1.9GHz

Simulation responses of the diplexer circuit model with HFWorks

Figure4 – Simulation responses of the diplexer circuit model with HFWorks

 Measured and simulated (with ADS) results of the diplexer circuit model

Figure5 – Measured and simulated (with ADS) results of the diplexer circuit model

The measured results and the EM loss simulation results with HFWorks are presented, in Fig.4 and indicated that the isolation between the Tx and Rx bands is about 40 dB. The graphs clearly show a good agreement between the simulation and measurement.

REFERENCES

[1] Augustine O. Nwajana, Kenneth S. K. Yeo, ” Multi-Coupled Resonator Microwave Diplexer with High Isolation”, 2016 European Microwave Conference, pp. 1167-1170, 4–6 Oct 2016, London, UK.

The concept of air region in EM Simulation

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In all EM simulation, the empty spaces (or volumes) within a model and around a model are important. This is because we are interested in computing and plotting the magnetic and electric fields in these regions. Imagine a magnet lying on a table, there is magnetic field inside the magnet (of course) but there is also a magnetic field in the air region surrounding the magnet and also in the table. In order to capture these fields, one must model these empty spaces as 3D geometry along with the components of interest.

If you are using EMS for SolidWorks, creating air geometry inside SolidWorks is extremely easy (see video linked below). You first have to create a new part in the assembly you want to simulate. Remember that all EMS models have to be SolidWorks assembly to be simulated. In the new part, you can sketch and extrude any arbitrary shape as long as you make sure that this shape sufficiently encloses all the other parts of the assembly. Next you must use the Cavity feature in SolidWorks to subtract out all the inner components. Now your model is ready for EM simulation (see Figure 1). Please note that you are not just limited to a box region as shown in the figure. For some designs which are cylindrical in nature, it is more appropriate to create a cylindrical air geometry (see Figure 2).Air region in EM Simulation

Figure 1- Air region created around a C core inductor using SolidWorks cavity feature

Air region cylindrical in EM Simulation

Figure 2- One can create a cylindrical air region as well for models that are cylindrical in nature

Video explaining how to create air region in SolidWorks:

When you create the air region, make sure that it is sufficiently big so that the results at the extremities of the air region is negligible compared to the ones closer to the model. For example, plot the magnetic flux density on the boundary faces of the air region and compare those values to the maximum value of the magnetic flux density. Also the magnetic flux density should be fairly uniform in these boundary faces.

This blog post is a part of Learn EMS for SolidWorks series. To learn more about EMS, visit www.emworks.com.