Modification of transformer coupled permeameter for frequency extension

A broadband and high-sensitivity permeability measurement system that covers 10 MHz-20 GHz was previously developed and named the transformer coupled permeameter (TC-Perm). This paper describes the modifications of the TC-Perm system to further extend the operation frequency range on both the high and low frequency sides. In the previous system, the high frequency limit was set by a large notch appearing at around 22 GHz, which was considered to be caused by the excitation of two unwanted modes. In the new system, the jig design was modified to have a back ground plane and vias to suppress these unwanted modes, which resulted in a clean transmission characteristic over the entire frequency range up to 44 GHz. The low frequency limit is determined by the noise figure (NF) of the vector network analyzer input, which was measured to be ∼35 dB in the previous system configuration. The new system employed a low noise amplifier and analog switches to improve the NF to be 2.7 dB below 100 MHz. As a result of these modifications, the operation frequency range of the new TC-Perm system was extended to cover 1 MHz-44 GHz, which is sufficient for characterizing magnetic materials used in noise suppression sheets targeting fifth-generation millimeter-wave (5G mmWave) wireless communication.