| 摘要 |
In a filter assembly having a bandpass filter and a group-delay equalizer coupled thereto by a circulator, there is disposed in the filter and/or the equalizer an electromagnetic wave propagation structure having a cavity with a plurality of tuning elements extending therein. The wave-propagation structure supports a first wave propagating in a first mode and a second wave propagating in a second mode. A first of the tuning elements is positioned to interact with the first wave, a second of the tuning elements is positioned to interact with the second wave, and a third of the tuning elements is positioned for coupling electromagnetic energy between the first wave and the second wave. A fourth of the tuning elements has an orientation perpendicular to an orientation of the third tuning element. Each of the first, the second and the third tuning elements is essentially non-lossy while the fourth tuning element is lossy for obtaining improved flatness of a spectral characteristic of amplitude versus frequency to electromagnetic waves propagating through the filter assembly. A ceramic resonator is located on a central axis of the cavity, and each of the tuning elements is directed toward the central axis. Each of the tuning elements may be constructed as screws for adjustment of depths of penetration of the screws into the cavity for interaction with the electromagnetic waves.
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