Complex Near-field Measurement using On-The-Fly Scan with In-phase and Quadrature Demodulation

Recently, a new near-field measurement technique based on on-the-fly (OTF) scanning and a Hilbert transform (HT) was proposed, allowing for rapid phase retrieval using a single probe. However, because of the required Nyquist rate sampling, this method encounters challenges related to costly data acquisition, storage, and processing demands, thereby restricting its use at MHz and GHz frequencies. In this paper a novel method is proposed, which addresses these issues by introducing in-phase and quadrature (IQ) demodulation in place of the HT. Its inherent frequency down conversion of the measured signal enables sampling at a significantly lower rate. To demonstrate the effectiveness of the proposed method, it is employed in a near-field scanner to measure the magnetic fields of two distinct devices under test: a wireless power transmitter and a microstrip line, operating at 125 kHz and 1 GHz, respectively. Measurement results, compared to conventional field measurement approaches, show a good correlation, affirming the suitability of this fast and cost-effective solution for antennas, and RF systems.