New Differential Probes With Grounded and Nongrounded Parasitic Units for Near-Field Measurement

Herein, two new differential magnetic and composite probes (Probes A and B) with high sensitivity are presented. These Probes A and B consist of a pair of differential loops as a driven element, an inner U-shaped loop with two connected vias, a pair of outer grounded and non-grounded U-shaped loops as parasitic units, and two striplines terminated with two 2.92 mm radio-frequency Subminiature Version A (SMAs) with 50 Ω. Firstly, these differential loops and inner U-shaped loop are connected in series to obtain high detection sensitivity in Probes A and B. Secondly, in order to further enhance detection sensitivity, the grounded and non-grounded U-shaped loops are placed at the outer layers in Probes A and B, respectively. The function of the grounded U-shaped loops in Probe A is to receive more magnetic fields, while that of non-grounded U-shaped loops in Probe B is to sense more electromagnetic fields. Finally, in order to prove the design effectiveness, these probe prototypes are simulated by electromagnetic simulation software, etched on a five-layer PCB, and characterized by a near-field test system with a standard microstrip line. The measured results reveal that the sensitivity of the magnetic Probe A exceeds -40 dB at 1.3–6 GHz, while the sensitivities of the composite Probe B are over −40 dB at 2.8–6 GHz and 1.5–6 GHz in the electric and magnetic field measurements, respectively.