In ADS EM setup, in addition to the classic EM Simulation/Model, you will also see an option Setup Type-> EM Cosimulation. Many students do not understand the difference between it and traditional EM simulation. This article attempts to use a Gysel power divider example to introduce the use of EM Cosimulation.

Task objective: Design a one-to-two Gysel power divider:

• Frequency range: 9-11 GHz
• Output port: < -3.3dB@9-11 GHz
• Return loss: < -20dB@9-11 GHz
• Isolation between output ports: < -20dB@9-11 GHz

Substrate and process selection:

According to the task objectives, we chose the ALS996 ceramic substrate manufactured by Shenzhen Aoli Electronics. The basic parameters are shown in the figure:

Because the device frequency is around 10GHz, we use a high-precision processing technology with a processing accuracy of 5um.

According to the characteristics of the Gysel power divider, the designed circuit schematic is shown in the figure:

Because the isolated port needs to add a 50 Ohm isolation resistor, we choose resistors R16 and R17 with a package of 0603. Therefore, it is necessary to add a 0.8*0.4mm microstrip line at both ends of the resistor as a pad. At the same time, it is connected to the RF ground on the back through the ground hole.

At the input and output ports, add 200*200um microstrip lines as pads for gold wire bonding.

The simulation results are shown in the figure, which fully meet the design requirements:

Generate a layout based on the schematic diagram, as shown in the figure:

If you choose traditional EM Simulation, you need to delete all devices and then add ports at the ports. If the device package is large, you also need to align the ports and leave space for components. If there are many components, the workload will be unacceptable. After setting the Substrate and Frequency Plan, you need to perform a simulation to create the Model and Symbol.

When choosing Cosimulation, it is not as complicated as traditional EM Simulation. As can be seen from the Layout, the position and size of the 50 Ohm resistor are retained, and there is no need to add a port. Next, we will demonstrate the process of Cosimulation.

In the 3D view, you can also see that the resistor and ground via are well connected.

Click EM Setup, and select Setup Type -> EM Cosimulation, EM Simulator -> Momentum Microwave in the interface. Then, during schematic simulation, ADS will call the Momentum Microwave simulator.

According to the board manufactured by Shenzhen Aoli Electronics, the selected parameters are ALS996, dielectric constant 9.7, and thickness 10mil.

In the Partitioning tab, you can see that the Rule of R16 and R17 is Circuit, not EM. This means that the resistor components will be simulated according to the circuit model. This setting is consistent with the classic operation of adding ports in the layout , adding components in the schematic, and simulating the results.

In the ports setting, we can also see that only three ports are enough. In classic operation, ports must be set for each component, and a more complex circuit often requires 20-40 ports.

Follow the steps of Momentum simulation and set the Frequency Plan and options

Finally, in the Cosimulation option, click View-> Go in the lower right corner. This will create a View without performing a simulation. Then, click the Open Symbol Editor button in the figure to create a Symbol.

In the Source View of the Symbol Generator, select Layout:

After that, select Look- alike

In this way, you can create a symbol similar to a graphic on a board. The created symbol is shown in the figure

Create a new schematic, drag the Symbol into the schematic, and add the S parameter simulation control. At this point, there is no need to add component or substrate controls. Simply click the simulation button to perform a schematic-layout joint simulation.

The simulation data for this example is as follows:

It can be seen that the simulation results meet the design requirements.

In addition, we can add HB sweep controls, input a single-tone signal of 0dBm@10GHz, and set the voltages of the output port and the isolation port to Vout_2 and Vdiss_2 respectively.

Through the calculation formula, we can see that at the 10GHz frequency point, the power of the output port is -3.09 dBm, and the power of the isolation port is -36.1 dBm. In other words, based on the 20dBm power capacity of the 0603 resistor, the power that can be obtained at the output port is about 53dBm. If a larger power load is used, the Gysel power divider can withstand a larger power capacity.

This example mainly introduces the usage of Cosimulation in ADS EM simulation. If you are interested in Gysel power dividers, you can contact us privately to discuss the design of Gysel power dividers with relative bandwidth > 30%.

Finally, it should be emphasized that this design is designed under the condition of 5um processing accuracy, which exceeds the commonly used design accuracy of ordinary thin-film ceramic processes. Therefore, if ordinary thin-film ceramic processes are used for design, simulation, and processing, the results will be much worse.

The machining accuracy is set to 50um, and the schematic simulation results are as follows:

By turning on the History option and comparing it with the 5um accuracy, it was found that S11, S21, and S32 had all deteriorated significantly.

Considering that the circuit performance will decline after layout processing, it is obvious that the performance improvement can be achieved by adopting high-precision process design and processing.

Students who are interested in ADS EM simulation and Gysel power divider can contact the blogger to discuss and exchange ideas!

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