The Full Form of ABF is Agile Bandpass Filter.

Frequency-agile bandpass diplexer (FA-BPD) applying to
the reconfigurable and multiband wireless communication
systems have been researched for many years (e.g. [1]–[9]).
Some frequency-duplex-division (FDD) transceivers using
the same transmitting and receiving bandwidth [1], [2]
require the employed FA-BPDs with identical and constant
absolute bandwidth (IC.ABW).
To develop such a high-performance FA-BPD, a lot of
efforts have been made e.g. in [3]–[9]. A three-pole tunable diplexer with the frequency tuning ranges (FTRs)
of 1.43-2.07 GHz (37.3%) and 1.53-2.07 GHz (39%) was
demonstrated in [3]. But its insertion loss (IL) was 7.7 dB
because of the extra T-junction. In [4], a three-pole tunable
diplexer with FTRs of 1.28-1.78 GHz (32.7%) and 2-2.3 GHz
(13%) was presented. Its IL was 8.2 dB. In [5], a fourthorder tunable diplexer with the FTRs of 1.2-1.8 GHz (35%)
and 2.0-2.6 GHz (26.1%) was proposed. However, the IL

was 8.5 dB. A three-pole tunable diplexer with the reconfigurable bandwidth was presented in [6]. It is found that
although its IL was very good (2.9 dB), its FTRs were only
25.1% (0.94-1.21 GHz) and 23.5% (1.51-1.91 GHz). A threepole diplexer with around 50% FTR was presented in [7].
Due to too many varactors used there, the IL was 7.7 dB. The
higher-order tunable diplexers employing the classical cascaded trisection (CT) and cascaded quadruplet (CQ) topology
were developed in [8] and [9]. However, the IL was 4.9 dB for
the tunable diplexer in [8], and the FTR was only 25% for the
diplexer in [9].