Question 3-47F4

M-derived filters are designed to improve upon the performance of constant-k filters, particularly near the cutoff frequency. Constant-k filters exhibit a gradual attenuation slope as frequencies approach and pass their cutoff. An m-derived filter, however, introduces a resonant "trap" circuit (either in series or shunt configuration) that creates a very sharp attenuation peak, or "pole of attenuation," at a specific frequency just outside the desired passband. This sharply attenuates undesired frequencies that are too close to the cutoff frequency to be effectively suppressed by a constant-k filter alone. The parameter 'm' determines the location of this attenuation pole relative to the cutoff frequency. * **A) Incorrect:** A good filter aims for a relatively constant input/output impedance within its passband for proper impedance matching, not widely varying impedance. * **B) Incorrect:** This characteristic, where the product of series and shunt *reactances* is constant, is a defining property of a constant-k filter's image impedance, from which m-derived filters are derived. * **C) Incorrect:** The name "m-derived" comes from a mathematical parameter 'm' used in its design equations, not its physical schematic shape.