Design Methodology of Resonant H-field Probe with a High Bandwidth in Near-Field Measurements

Resonant near-field probes can be used for localization and characterization of noise sources in electromagnetic compatibility (EMC) applications. However, the usability of a resonant probe is limited by its narrow bandwidth. This article presents a design and the corresponding optimization flow which improves the bandwidth of a resonant H-field probe by adapting the impedance variation ratio of the transmission line balun. Compared to the traditional design, the proposed one achieves triple bandwidth with only 2.7 dB sensitivity loss. The improved design enables a more efficient scanning in real applications.

I. Introduction

Near- field scanning technique is used to visualize, identify and characterize the noise sources present inside an electric device [1]. As the devices are becoming increasingly integrated, the size of a H - field probe is minimized to improve its spatial resolution. The sensitivity of the probes is then sacrificed [2]. Probes with structural resonance are then developed to increase the sensitivity of measurements. However, the operation bandwidth of resonant probes is typically limited to dozens of MHz [3]. Multiple probes are required to cover the bandwidth of communication networks, e.g., the 900MHz-band GSM [4]. Active-tuning method is deployed in probes so that the center-frequency and bandwidth of the probes are configurable. However, the circuits are complicated and can introduce extra noise in the measurement [5]. A resonant probe with a wider bandwidth is desired to simplify and accelerate the near-field measurement.