A Compact High-sensitivity Tangential E-Probe With Resonator and Coupled Balun

Shang Zhang^1,2, Zhenguo Liu^{1, 2, 3}, Zhipeng Chen^{1, 2}, Mengzi Li^{1, 2}, Weibing Lu^{1, 2, 3}

¹ State Key Laboratory of Millimeter Waves, Southeast University, Nanjing China.

² School of Information Science and Engineering, Southeast University, Nanjing, China.

³ Purple Mountain Lab., Nanjing, China.

Email: liuzhenguo@seu.edu.cn

Introduction: With the increase of operating frequency modern radio frequency (RF) integrated circuits have become more and more miniaturized, which results printed circuit board (PCB) has become more dense. Thus, unexpected electromagnetic radiation coupling between some sensitive components will affect the normal operation of RF integrated circuits, resulting in very serious electromagnetic compatibility (EMC) issues [1]. To improve the performance of RF integrated circuits, a proper electromagnetic analysis model is needed to determine the location of interference source in the RF integrated circuits, which is the key to solve EMC issues.

In recent year, the near-field scanning technology for detection location of interference sources has been developed rapidly [2-3], which play significant role in EMC problems. The probe used to sample E-field component is the key part of the near-field scanning measurements. Much effort has been devoted to studying the normal E-field probe [4-6], such as how to design the miniaturized probe and improve the working frequency band of probe for wideband measurements, but less attention has been paid to the probe detected the tangential component of E-field. Yan proposed a broadband tangential E-probe loaded with electric dipole and integrated balun for the near-field measurement covering the GPS band [7]. However, for integrated circuits working in narrowband, the high-sensitivity probe detected tangential E-field can convey more power to the instruments, therefore, a weaker electric field can be detected. A resonant tangential E-probe [10] has high sensitivity for sensing up the weak electric field, compared with it, the structure of the resonator in the probe proposed in this work is simpler and the coupled balun without via fence has more concise structure. Moreover, the performance of this probe is better.

In this paper, a compact high-sensitivity probe for capturing tangential E-field with resonator and coupled balun is suitable for locating the noisy sources or the electromagnetic interference sources of circuits working in narrow band. The proposed probe has been fabricated and measured.

Probe structure: Fig. 1 shows the overall structure of the probe with resonator and coupled balun based on 4-layer PCB. Fig. 2(a) exhibits the layout of the probe with physical dimensions. The structure from top to bottom is the top layer, the middle layer 1, the middle layer 2 and the bottom layer. Both the top and bottom layers are copper planes, which can provide the currents return paths and shield the external field. The middle 1 layer is the metal grounding plane of coplanar waveguide. In the middle 2 layer, the folded electric dipole and the resonator composed of open- and short-circuit stubs as well as the coupled balun are cascaded in turn. Fig. 2(b) shows the stack-up of the resonator probe, which is made up of three layers of 0.254-mm thick Rogers4350B and two layers of 0.2 mm thick Rogers4450F.