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Open and Short-Circuited Lines

Due to the model used in the calculation engine, the transmission lines that are considered to exist in the simulation are those that have both ports connected to wire segments. Therefore, if you want to have an open-circuited line connected to a certain segment, the opposite port must also be connected to another wire segment. Create a short wire with only one segment that is no longer than 1% of the wavelength (its radius can be one-tenth of its length) and connect it to the open circuit transmission line port. This short wire should be disconnected from the rest of the structure, and the shunt admittance of the port it’s connected to should be zero, Fig. 1.

Fig. 1: Open circuit transmission line. The port that is open circuited is connected to a short wire that has only one segment and has a null shunt admittance.

On the other hand, if you need a transmission line with a short-circuited port, connect that port to any other segment and set a shunt admittance at that end that is very large, for example, 1E6 [S]. At this end, you could connect a short wire segment created for this purpose, as is done for an open-circuited line, Fig. 2.

Fig. 2: Short circuited transmission line. The port that is short circuited is connected to a short wire that has only one segment and has a large shunt admittance.

When creating short wires to connect open or short circuit transmission line ports, it is advisable to move these wires away from the rest of the structure to minimize interaction with it. Enter the length of the transmission line as indicated in Adding Transmission Lines. Remember that the length of the line is not necessarily related to the actual distance between the segments where it is connected.

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