Abstract

We describe a method to determine the crosstalk between two adjacent transmitter and receiver antennas using ANSYS High frequency simulation software (HFSS) and ANSYS circuit. The antennas used, emit waves carrying orbital angular momentum (OAM). However, the method can be generalized for other antennas. The OAM antenna consists of a circular array of eight rectangular patch antennas. The input signal is split into 8 to feed each of the patches. To generate an OAM wave, the signal to each patch is phase shifted by 45 degrees from the adjacent patch, increasing in the anti-clockwise direction for mode +1, and in the clockwise direction for mode -1. The experimental setup consists of adjacent transmitter and receiver OAM antennas. To determine the decrease in crosstalk due to OAM modes, crosstalk S12 is measured between the two antennas with receiver mode varied between -1 and +1, and transmitter mode fixed at +1. The difference in crosstalk is calculated to determine ΔS12, for varying distances. In HFSS, each patch is fed by a lumped port, and the excitation voltage is to be increased by 45 degrees across the array in a clockwise or anticlockwise direction. This is not possible in HFSS, in the case of the receiver, so ANSYS circuit is employed. The HFSS project consisting of two adjacent patch arrays is embedded in ANSYS circuit as a subcircuit model to create a dynamic link. An input signal is split into 8 using a 1 to 8 divider to provide excitation to the transmitter pins, via phase shifters. The phase shifts are sequentially incremented by 45 degrees. Similarly, receiver pins are connected to phase shifters and then combined using an 8 to 1 combiner which is connected to an output port. Therefore, the crosstalk between the transmitter and receiver ports can be determined in ANSYS circuit.