23-05-2014, 02:06 PM
COMPACT DUAL-MODE DOUBLE SQUARE-LOOP RES- ONATORS FOR WLAN AND WIMAX TRI-BAND FILTER DESIGN
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Abstract
The improved configurations with dual-mode double-
square-loop resonators (DMDSLR) for tri-band application are
proposed in this paper. Two sets of loops including double-square-
loop and G-shaped loop are involved in the resonators. The resonant
frequency equations related to DMDSLR geometries are introduced for
simply designing tri-band bandpass filter (BPF). Resonant frequencies
and transmission zeroes can be controlled by tuning the perimeter
ratio of the square rings and the couples. To obtain lower insertion
loss, higher out-of-band rejection level, wider bandwidth of tri-band,
and compact applications, the miniaturized DMDSLR structure is
designed. The effective design procedure is provided. The proposed
filter is successfully simulated and measured. It can be applied to
WLAN (2.45, 5.20 and 5.80 GHz) and WiMAX (3.50 GHz) systems.
INTRODUCTION
The increasing demand for multi-band applications has required a
single wireless transceiver to support multi-band operations. The
multi-band BPFs play an important role in a multi-band transceiver,
such as dual-band [1, 2], tri-band [3–21] and quad-band [22–29] filters.
Recently, a new excitation for DMDSLR with CPW was proposed
for dual-band applications [1]. The square ring resonators with back-
to-back and concentric configurations were presented.
DESIGN OF IMPROVED DMDSLR TRI-BAND
FILTER
The perimeters of the square loops are related to the guided
wavelength at corresponding resonant frequencies basically. The
modified DMDSLR filter employs two sets of the loops to present the
dual-band in Figure 1 at first. Then the square loop is designed to
operate at the first and third resonated frequencies and the G-shaped
loop is employed at the second and fourth resonated frequencies. By
using the third and fourth resonated frequencies to form an operating
band, a wide pass-band is obtained.
Current Distributions
Figures 4(a), (b) and © present the surface current distributions
of DMDSLR filter in each band of the tri-band. In the central
configurations of Figures 4(a) and ©, the distributions are presented
with even and odd modes in band I (2.35 and 2.52 GHz) around the
two square loops respectively. In the central parts of Figures 4(b)
and (d) are the distributions of even and odd modes in band II (3.39
and 3.6 GHz) around the G-shaped loops respectively. There are three
resonances in band III (5.39, 6.31 and 6.82 GHz) exist in the DMDSLR.
In both sides of Figures 4(a) to ©, these are distributions of two
transmissions.
Design Procedure
For simply and accuracy design, this paper proposes a systematic
design procedure by using the variations of side-length ratio of the
tri-band filter. Since the perimeters of the square loops determine
the first resonated frequency, and the perimeters of the G-shaped
loops determine the second resonated frequency mainly, thus, the
Equations (1) and (2) show two frequencies can be obtained by
adjusting the side-length ratio L1 /L2 and the couple L3 at first. Then
the BW of each band related to the couple (L3 ) and perturbation
(P1 ) can be obtained by tuning. Both resonated frequencies and
bandwidth in each band are controllable. Second, the third band is the
periodicity of the first and second resonated frequencies basically. The
Equations (3) and (4) show that the lower/higher frequencies of the
third band. The lower/higher frequencies can be obtained by adjusting
the side-length ratio and the couple. The BW of the third band also
related to the couple and perturbation can be obtained by tuning.
Finally, the response is obtained by tuning the improved T-couple
line.In practical design procedure, we can choose appropriate values
for those parameters and by tuning to obtain the desired responses.
Current Distributions
Figures 7(a) to © present the surface current distributions. All
the square loops exhibit the identical surface current distributions
according to multiple resonance (2.37 and 2.47 GHz), (3.49 and
3.66 GHz), (5.45, 6.26 and 6.51 GHz) respectively. The transmission
zero (1.96 and 2.8 GHz), (3.21 and 4.1 GHz), (4.1 and 7.53 GHz) are
represented with attenuation (blue) in output port. The photograph
is presented in Figure 8. The size reduction with 13% is obtained.
CONCLUSIONS
The DMDSLR structure and resonant frequency equations for tri-
band BPF provide a viable alternative to current multi-band filter
design techniques. Based on the inherent high-Q characteristics of the
ring resonators, it is found that the miniaturized DMDSLR filter can
successfully present good tri-band pass-band performance, high stop-
band rejection and deep transmission zeros between pass-bands. The
resonant frequency equations and design procedure are available and
useful for simply designing tri-band BPF. Tuning the perimeter ratios
of the loops and couples provides four controllable resonant frequencies.
The BW of each band can be obtained by tuning the couple and
perturbation. Transmission zeros can be obtained by tuning the T-
couples.