Tunable 5.8–6.2 GHz Six-Pole Ceramic-Monoblock Filters With Constant Selectivity

This article proposes a new class of tunable ceramic-monoblock bandpass filters (BPFs) with constant selectivity for 5G applications. We develop the new mechanical-tunable ceramic-monoblock resonator (MTCR), which provides the filter with compact size and good
$Q_{u}$
performance. The coupling and feeding structures are investigated to allow the ceramic-monoblock realization of the tunable cascade triplet (CT) with a constant response shape. As a result, the proposed BPF not only offers the near-band transmission zeros (TZs) that readily steepen the roll-off, but can also keep the response shape unchanged when the frequency changes. We present the designs and measurements of two wideband six-pole tunable BPFs for 5G applications. One is the 5.8–6.2 GHz quasi-elliptic filter with constant 430 MHz bandwidth. Another is the tunable BPF with two upper-skirt TZs. These two TZs constantly steepen the upper skirt as the skirt is tuned from 6 to 6.4 GHz. The measured unloaded
$Q_{u}$
of two filters is better than 560 for all the tuning states.