Hi Mike, Yes, you can reduce the radiated emission of a microstrip by using ground guards. This method increases the mutual inductance between the signal conductor and its return current conductor(s). But I do not call this as "terminating the fields." Electric field start from a positive charge and terminates to a negative charge, but magnetic fields do not terminate to anything. Further, if you have a monopole above a ground plane, the charges and image current on the ground plane increases the radiation efficiency. I believe the phenomenon you are talking about is not "terminating the fields," but minimizing the current loops. George -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of MikonCons@xxxxxxx Sent: Sunday, June 16, 2002 12:23 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Copper Fill In a message dated 6/14/2002 7:57:23 PM Pacific Standard Time, gtang@xxxxxxxx writes: > 5. Some also mentioned that the copper fill can be used to terminate > electromagnetic waves to reduce emi emission. This idea rarely works. We > know that a signal on a transmissionline can be terminated by a matched > impedance load. A copper fill with vias tied to ground has an impedance > varying with frequency. This is a resonating structure at best. EMI > emissions from digital circuits occur at multiple frequencies, and these > frequencies can drift with temperature and / or change due to manufacturing > tolerances of discrete components (capacitors). Using a resonating > structure for impedance matching at multiple frequencies that may drift > with > temperature is a task that few have even attempted. And even fewer have > succeeded. > Hi, George: As you know, it is sometimes difficult to place all-inclusive comments in the difficult and complex SI domain. One would have to write a comprehensive technical article for each response to be complete. To eleborate on my earlier comments (in one area only), I offer the following. Your (item 5) comments are understood and appreciated as to their cautions. However, the nearby presence of a conducting structure that is connected to the reference of an emitting source indeed reduces emissions considerably. One must indeed take care to have sufficient ground vias, unevenly spaced to avoid resonant symmetries, on any grounded fill. The dimensions must consider the highest frequencies (harmonics) of interest. A good illustration of this suppressive effect can be observed by comparing a simple 50-Ohm microstrip (one inch long will do just fine) carrying a 66 MHz clock with 1 ns rise/fall times. Using any number of radiated emission computation methods, you can predict maximum radiated emissions (ignoring any enclosure) from this surface trace that exceed the CISPR Class A limit at 66 MHz by approximately 5 dB. Simply by having multiple adjacent circuits (as is common on normal PC boards, the emissions can be reduced by 8 to 15 dB. A similar (but directly related) demonstration is to measure an emissions reduction of 6 to 8 dB (typical) offered by the addition of grounded guard traces on each side of the emitting trace. The crosstalk between multiple signal traces with and without guard traces exhibit a 12 to 14 dB reduction because of the field termination effect. Mike Michael L. Conn Owner/Principal Consultant Mikon Consulting Cell: (408)821-9843 *** Serving Your Needs with Technical Excellence *** ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu