Compact multi-band bandpass filters based on parallel coupled
split structure multimode resonators
J.Luo, K.B. Shi, S. S. Gao
Abstract: In this letter,
a
novel sext-band bandpass filter (BPF) using two split-type multiple-mode
resonators is proposed.
The
filter is composed of two sets of resonators which are respectively
designed to realize
Filter
1 with two passbands and Filter 2 with quad passbands. Then the two
BPFs are combined by parallel
coupling feed lines for sext-band responses, and each of the six centre
frequencies in the proposed sext-band BPF is able to be controlled due
to the
design
freedom. To validate the design and analysis, a prototype filter has
been fabricated with six passbands centered at
1.88/2.59/3.48/5.26/5.82/6.75 GHz. The measured result of the fabricated
filter agrees well with the simulation, which shows that the proposed
structure is a good candidate for sext-band BPF designs and validates
the proposed design
flow
well.
Key Words: Sext-band, bandpass filter, split-type multiple-mode
resonator, parallel coupling feed lines.
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Introduction: In the recent years, developments in microwave
multi-band bandpass filters (BPFs) have been gaining much attention for
multi-service wireless communication systems, such as GPS, WLAN, WiMAX
and RFID applications. However, it is still a challenge to carry out
high-performance multi-band BPFs with compact size, closely spaced
passbands, low insertion loss, high return loss and sharp skirt to
satisfy the whole WLAN application demands.
Recently, many approaches to multi-band BPF design have been reported to
address that problem[1]–[6]. In [1], Yan T F used two sets
of short-stub-loaded E-Type resonators to
realize
a quad-band BPF.
In
[2], Bukuru D
investigated
quad-mode stepped impedance resonator (QMSIR) to achieve a compact
quad-band bandpass filter. In [3], Li X realized novel quad- and
sext-band bandpass filters on a basis of multimode resonator (MMR) using
SIRsloaded tapered-line (SIRTL). In [4],
Kamma
A used T-shaped stubs loaded with a modified ring resonator (MRR) to
realize a quad-band BPF.
In
[5],
Chen
F C used six pairs of semi-lumped resonators to achieve a sext-band BPF.
In [6], Hsu K W realized a quint-band BPF using five tri-mode
stub-loaded SIRs among the common input/output (I/O) ports. These papers
show good electrical performance, but because of the use of many pairs
of resonators, the size is relatively large.
In this letter, a novel sext-band bandpass filter (BPF) using two
split-type multiple-mode resonators is proposed. The filter is composed
of two sets of resonators which are respectively designed to realize
Filter 1 and Filter 2. Filter 1 generates two passbands, meanwhile,
Filter 2 generates other four passbands. The proposed filter has compact
size, low insertion loss. Moreover, there are multiple coupling paths
between different stubs, resulting in controllable bandwidths.
Filter design procedure: Fig.
1
shows the equivalent transmission line model for the proposed sext-band
BPF.
Fig.1. The equivalent transmission line model for the
proposed sext-band BPF
Fig.2 shows that Filter 2 generates four passbands. And Filter 1
generates two passbands obviously. The two BPFs are then combined by
parallel coupling feed lines for sext-band responses.
Fig.2. EM simulated frequency response of quad-band
Filter 2
Fig. 3 displays the equivalent transmission line model for the proposed
three-band BPF in Filter 2.The center frequencies of the three passbands
are f 1, f 2 andf 3, respectively.