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RF Electronics Chapter 7: RF Filters Page 269 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. Figure 7.94 shows a very good agreement in the passband for the 4 different EM filter simulations. That also shows that the screening ring or the top boundary conductor does not affect the passband response. Figure 7.95 shows the harmonic response of the 5 filter simulations. The EM simulation of circuits 3, 4 and 5, those with the boundary ring, show a lower attenuation in the 500 MHz to 750 MHz frequency regions. The second harmonic response of the filter is shifted in the EM simulation compared to the circuit simulation. The measured frequency of the second harmonic response on figure 7.87 exactly matches the second harmonic response from the EM simulation in figure 7.95. This shows that EM simulation is required, to determine the frequency response of a filter accurately. As expected figure 7.87, shows less stopband attenuation, due to leakage between cables used in the measurement setup Since Cadence AWR DE V10, the ability to use the Extraction control block with AXIEM has made it feasible to obtain accurate EM simulations of RF designs, including the effect of any screening ground-planes on the top layer. Prior to the Extraction being available, EM simulation required a significant effort without a guaranteed useful result. Coaxial Filters Figure 7.96. Coaxial cavity dimensions. Figure 7.97. Coaxial cavity diplexer for 80 MHz (UM). Coaxial filters are similar in principle to helical filters, except that the resonator is a straight rod, rather than a wound helix as shown in figure 7.96. The length of the centre rod is a quarter wavelength. For the highest Q values, the ratio of the centre rod diameter to the inner diameter of the cavity is such that the characteristic impedance of the coaxial line forming the resonator is 77 Ω. The equation for the characteristic impedance of a coaxial transmission line is: ) ln( 60 ) ln( ) ( 2 1 0 0 A B A B Z r c Eqn. 7.30 RF Electronics: Design and Simulation 269 www.cadence.com/go/awr