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38 The PCB Magazine • July 2016 Figure 11 displays the cross section of the SPDR system. The two dielectric resonators are seen on top and bottom with the feed loops at the left and right. The cavity is setup such that the dielectric does not fill the entire cavity re- quiring that the air gap height (h G ) is greater than the sample height (h). The cavities un- loaded resonant frequencies and quality factors are measured with an air gap of height h G, and the shifted resonant frequencies and quality factors are measured with the sample inserted within the fixture without adjusting this overall height. As with other resonant methods, the dielec- tric characteristics can only be measured at cer- tain fixed frequencies and the sample material must have all copper removed before testing. Ad- ditionally, the values of ɛ r and tan δ are in plane with the material and not orthogonal. SPDR measurements were taken on all 10 samples at resonant frequencies of 10 GHz and 20 GHz. Bereskin Clamped Embedded Stripline Resonator to Measure ɛ r and tan δ The Bereskin clamped imbedded stripline resonator test method operates from approxi- mately 1 GHz up to 22 GHz. This resonant method, with a setup shown in Figure 12, oper- ates through the use of aperture launched and received energy that excites the resonant modes in a copper strip clamped between two sheets of dielectric material under test. This method is similar to IPC-TM-650-2.5.5.5.1, Stripline Test for Complex Relative Permittivity of Cir- cuit Board Materials to 14 GHz [14] , but is more thoroughly explained in Dr. Bereskin's two pat- ents [15,16] . This method has several pros, inso- much as it measures normal permittivity and tan δ directly. However, a downside is that air entrapped between the two dielectric layers cre- ates measurement error due to localized varia- tions in dielectric properties. The copper is re- moved from the dielectric prior to testing and the same copper strip is used in all the tests. The copper strip is stand-alone instead of being de- fined by etching in alternate stripline resonant methods. The specific test bed utilizes a signal generator and power meters, but a VNA can also be used if desired. The output power from the resonator is re- ceived at the power meter connected opposite the signal source. Sweeping the signal source through all frequencies in the band and com- paring variation in amplitude over frequency yields the resonant frequencies (fs) and qual- ity factors (Qs) of the system. Unlike the oth- er resonators the clamped embedded stripline ROUND ROBIN OF HIGH-FREQUENCY TEST METHODS BY IPC-D24C TASK GROUP (PART 1) Figure 10: Split post dielectric resonator. Figure 11: Split post dielectric resonator cross section. Figure 12: Clamped embedded stripline resonator.