Active Probes for Creating H-Field Probes for Flat Frequency Response Surbhi Mital #l , Ji Zhang #2 , Dr. David Pommerenke #3 , Dr. James L. Drewniak #4 , Kuifeng HU * l , Xiaopeng Dong &l # EMC lab, Electrical and Coputer Engineering, issouri University ofScience and Technology Rolla, MO 65409 USA 3davidjp@mst.edu * gilent Technologies 1900 Garden ofGods Roa, Mail Stop 123 Colorado Springs, CO 80920, USA lKuifeng.Hu@agilent.com & 2111 E 2S h Ave, Intel Corporation, Hillsboro, OR 97124, USA lxiaopeng.dong@intel.com bsract- This paper presents an approach to obtain a lat requency response rom the irst order derivative behavior of an electrically small lop and electrically short electric ield probe by using them in combination with active oscilloscope probes. n H-ield probe made in flex circuit technology was desined to operate up to about 5 GHz. These probes have loop dimensions as small as 3x3 mil and trace widths in the order of 1.75 mils. The H-field probe terminals are connected to the differential amplifier of the active oscilloscope probe which unctions as an integrator to achieve a lat requency response. The interator behavior compensates for the irst order derivative response of the lex circuit probes. The E-ield probe utilizes the high input impedance of the browser attached to the active probe for achieving a lat requency response. eors-E-dot sensor, H-dot enso, nterato, deriaie, lat "quency resonse INTRODUCTION EM-field mapping has proved beneficial not only to optimize and adjust RF circuits but also to predict complicated EMIIEMC problems. Self interference within systems, digital ICs or switched power supplies disturbing RF receivers is clearly a problem of growing concen. Various kinds of 8-dot/H-dot sensors are commercially available and numerous articles have covered probes [1]-[8]. The 8-dot and D-dot sensors show a first order derivative frequency response. To recover the EM field waveform from data captured by these sensors analog or numerical integration is required. This is dificult to achieve over many decade bandwidth because of the limitations of the dynamic range of the data captured by the oscilloscope. To overcome this several non-differentiating sensors were developed based on TEM hom, resistively loaded dipoles or dipoles with curved arms [3] but they suffered rom large 978-1-4244-4267-6/09/$25.00 ©2009 IEEE 12 physical dimensions. A non-differentiating free space sensor was designed based on shielded loop antenna with a reasonably flat frequency response reported in [4]. This paper introduces a different approach to obtain a flat frequency response from B-dot and D-dot field probes by attaching them to active oscilloscope probes as those are available in most labs. Active probe amplifiers can be used as both E and H-field probes to achieve a reasonably wide band lat frequency response. This paper also introduces first order derivative H-f ield probes based on flex circuit technology which can operate upto a few GHz and have a high spatial resolution. This probe has a trace width as small as 1.75 mils and loop dimensions as small as 3x3 mil. The self resonance requency of these probes is of the order of ten's of GHz. Figure 1: Basic Design of Flex Circuit Probe The flex circuit probes are differential H-field probes. Figure 1 shows the basic design of the loop portion of the flex circuit probe. This probe has loop dimensions of