Near-field Characterization of a GHz Branchline Coupler Using a THz Microscope

The design of microwave circuits is usually based on simulations, which can be supported by S-parameter measurements to evaluate the circuit’s performance after fabrication. Some characteristics of complex designs cannot be investigated this way, but advanced measurement methods can improve the design process significantly. In this work, a THz microscope is used to characterize a microwave network consisting of a branchline coupler and multiple patch antennas in a frequency range of 20 to 40 GHz. The radiation intensity above the patch antennas is spectroscopically measured and compared to conventional S-parameter analyses. The near-field pattern of the circuit is spatially measured and compared to corresponding simulations. The THz microscope is a versatile tool that can be used to validate simulation results and improve the overall microwave circuit design process.