1016

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 15, NO. 2, JUNE 2005

Design and Performance of Miniaturized
Quarter-Wavelength Resonator BandpassFilters With Attenuation Poles
H. Kanaya, Member, IEEE, K. Kawakami, F. Koga, Y. Kanda, and K. Yoshida

Abstract—For more size reduction of the high temperature superconducting coplanar waveguide (CPW) bandpass filter (BPF),
we introduce the design method of the meanderline quarter-wavelength resonator BPF. The admittance and impedance inverters( - and -inverters) are realized by using interdigital gaps andmeanderline short stubs. Also, we estimate the slope parameterof the meanderline resonator by using EM-simulator. In order tocontrol the attenuation poles, we adjust the meanderline intervals
and shapes of the cross-coupling section, so that we can design thefrequency and number of the attenuation poles. The size of the6-pole CPW quarter-wavelength resonator with two attenuation
poles (center frequency = 2 GHz) was 3.5 8 mm.

Fig. 1. Equivalent circuit model of the typical BPF with =4 resonators.

Index Terms—Attenuation pole, bandpass filter, coplanar waveguide, meanderline, quarter-wavelength resonator.

I. INTRODUCTIONI

N the wireless base station systems, which are used in themobile and satellite telecommunication, high temperature
superconducting (HTS) passive devices have an extremely highpotential because of significant low insertion loss and high sensitivity. There are many reports on microstrip bandpass filter(BPF) [1]–[3], and HTS BPF based cryogenic receiver frontends [4]. In order to reduce the cooling cost of the HTS filter subsystem, it is very important to miniaturize the HTS devices. The
coplanar waveguide (CPW) structure is more advantageous thanthe microstrip structure because of only one side HTS coatingand ease for size reduction.
In our previous studies [5]–[7], we designed the miniaturizedcross-coupled CPW BPF by using highly packed meanderline
resonators and interdigital gaps. In
half-wavelength
this paper, for further miniaturization, we designed and tested
resonator BPF by using interdigitalquarter wavelength
gaps and meander-shape short stubs. Moreover, elliptic andquasielliptic filters using cross-coupled resonators have sharper
skirt property than that of Chebyshev BPF in the same poleFig. 2. Transmission-line based circuit model around the J -inverter (a-1) andequivalent circuit model (a-2), and those of the K -inverter (b-1) and equivalentcircuit model (b-2).

numbers [8]. So, we can design thecross-coupled BPF
with attenuation poles by controlling the meander shape of- and impedance
the resonators. The exact admittance-inverters, and slope parameters of theresonators
are calculated by using the 2.5-dimensional electromagnetic
field simulator (EM-simulator) (ADS; Agilent). The prototype,
YBCO miniaturized BPF () was also tested in the cryogenic
2-pole,temperature.
II. DESIGN OF CHEBYSHEV QUARTER-WAVELENGTHRESONATOR CPW BANDPASS FILTER
A. Measurement of the Slope Parameter

Manuscript received October 4, 2004. This work was supported in part by
the Grant-in-Aid for Encouragement of Young Scientists (B) from the Japan
Society for the Promotion of Science (JSPS) and in part by a grant of Fukuoka
project in the Cooperative Link of Unique Science and Technology for Economy
Revitalization (CLUSTER) of Ministry of Education, Culture, Sports, Scienceand Technology (MEXT).
H. Kanaya, K. Kawakami, F. Koga, and K. Yoshida are with the Department of Electronics, Graduate School of Information Science and ElectricalEngineering, Kyushu University, Fukuoka 812-8581, Japan (e-mail: kanaya@ed.kyushu-u.ac.jp).
Y. Kanda is with Department of Electronics, Faculty of Engineering, Fukuoka
Institute of Technology, Fukuoka 811-0295, Japan.
Digital Object Identifier 10.1109/TASC.2005.850186

Fig. 1 shows the equivalent circuit model of the BPF withresonators. The resonator is connected with the - and-inverters [9]. In order to realize the miniaturized BPF, theseresonators are modified to the meanderline structures. So that,bending the resonators changes the slope parameters.
In order to design the -inverter, the exact reactance slope
parameter of theresonator is measured and calculated.
Fig. 2(a-1) shows the transmission-line based circuit model. In the figure,andaround the -inverter
are the electrical length of the transmission lines.
and1051-8223/$20.00 © 2005 IEEE

KANAYA et al.: DESIGN OF MINIATURIZED QUARTER-WAVELENGTH RESONATOR BPF

Fig. 3. Layout of the interdigital gap and meanderline short stub (n = 6, 12and 18), respectively.

Fig. 4. EM-simulation results of the d and d1017

dependences on inverters.

are the characteristic admittance of the transmission lines. Theis given bycascade matrix(1)
Nearand(in case of week cou,pling), by substitutingand(where,isthe reactance of the resonator) in to (1), we obtain,Fig. 5. Circuit model and layout of the J -inverter (a) and K -inverter,
respectively.

(2)
Equation (2) is equal to that derived from the equivalent circuit model given in Fig. 2(a-2). We can replace the transmission-line based circuit model with equivalent circuit model. The
can be calculated as,reactance slope parameter(3)
In Fig. 2(b-1),
andare the characteristic impedis the suscepances of the transmission lines. In the figure,istance of the resonator. The susceptance slope parametermeasured in the same way as that of the , and.
B. Realization of the - and-Inverter

Fig. 3 shows the layout of the -inverter and -inverter, respectively. They are realized by using interdigital gaps and meanderline short stubs. In the figure, is the finger number andbending number of the inverters. Fig. 4 shows the EM-simuand
dependence on both inverters.
lation results of theandare both saturated in large andregions.
Fig. 5(a) and (5b) show the circuit model and layout of the -inverter and -inverter, respectively. In the figure, and are
the electrical length and phase constant of the transmission line,respectively. The exact values and are calculated from thecascade matrix around the -inverter section given in Fig. 5(a),Fig. 6. Simulation results of the d dependence on B , B and J values,respectively (n = 18).

by using the EM simulator. The value and are represented
by the parameter
and, and are given by,(4)(5)
Fig. 6 shows the EM-simulation results of the dependence
and values, respectively, those are normalized byon ,.
has a linear dependence on . On the other hand,is saturated in large region, and value is also saturated. In
is also saturated in large
region.
the case of -inverter,

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IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 15, NO. 2, JUNE 2005

Fig. 9.

Circuit model of the 6-pole =4 BPF with attenuation poles.

Fig. 10.

Simulation layout of the 6-pole =4 BPF with attenuation poles.

Fig. 11.

Simulation results of the 6-pole =4 BPF with attenuation poles.

Fig. 7. Simulation layout of the 10-pole =4 CPW BPF.

Fig. 8. Simulation results of the n = 10=4 CPW BPF.

When we design the BPF, which has wide bandwidth, it is exvalue are saturated even if andbepected that andcomes longer.
III. DESIGN OF CPW QUARTER-WAVELENGTH BPF
A. 5 GHz 10-Pole CPW Meanderline

BPF

andof the meanderline resonators,Considering thewe design the standard Chebyshev CPW BPF by using theEM-simulator. The YBCO film is approximated as the perfect
substrate isconductor and the thickness of the MgO. The width of the signal line and gap interval is 60500
and 26, respectively.
BPFFig. 7 shows the simulation layout of the 10-pole(,, ripple, meander ra. Where, the angular resolution dependence
diusof the frequency response of the BPF is also discussed in theprevious paper, so that this bending angle has almost the same[5]. In order to saveproperties as that of the smooth arc
the memory and CPU time during the simulation, we chose
this bending angle. The filter size is 2.5 mm 9 mm. Fig. 8shows the simulation results of the 10-pole BPF. Simulated
performance such as return loss in the passband and bandwidth
are in good agreement with the circuit model.
B. 2 GHz 6-Pole CPW MeanderlinePoles

BPF With Attenuation

In the previous paper, we introduced the design method of theCPW half wavelength meanderline BPF with attenuation poles[7]. In this paper, we apply that method toresonator BPF.
resonator, we can expect that the filter size is
By using thereduced to half size. Figs. 9 and 10 show the equivalent circuit
BPF with twomodel and simulation layout of the 6-pole. The deattenuation poles. The width of the signal line is 60,, and,sign parameters arerespectively. In order to fabricate the two attenuation poles at
50 MHz from center frequency, we decided the meander raand) in the resonator. The filter
dius (size is 3.5 mm 8 mm. Fig. 11 shows the simulation results andcircuit model of the 6-pole
BPF with two attenuation poles.
In the figure, the responses of the 8-pole Chebyshev BPF (noattenuation pole) are also plotted. This BPF has the same skirt
characteristic of 8-pole standard Chebyshev BPF.

KANAYA et al.: DESIGN OF MINIATURIZED QUARTER-WAVELENGTH RESONATOR BPF

1019(GSG-150; Cascade Microtech). Fig. 13 shows the frequency reBPF at 20 K. In the figure,sponses of the 2-pole YBCO CPW
broken lines show the parameters of the EM simulation results.
The bandwidth is similar to that of the circuit model. Because ofthe over etching portions, design ripple is not in full agreementwith the simulation result in the pass band.
V. CONCLUSION

Fig. 12. Photograph of the prototype YBCO CPW =4 BPF for 10 GHz
application.

By measuring the exact - and -inverters, and slope paresonators, we design the miniaturized
rameter of thequarter-wavelength resonator BPF. We can apply this design
method to various pole number, center frequency and controlof the attenuation poles. These design method is effective for
reducing the cooling cost of the HTS filter subsystem. Moreover, in order to realize the RF-system LSI (System On aChip), we will design and fabricate this miniaturized BPF on
the CMOS chip.
REFERENCES

Fig. 13.

Frequency responses of the 2-pole YBCO CPW =4 BPF at 20 K.

IV. EXPERIMENTAL RESULTS OF PROTOTYPE YBCO BPF
Fig. 12 shows the photograph of the prototype YBCO CPW
BPF for 10 GHz application. In the figure, the meander structure and interdigital gap are also printed. YBCO film used inthis experiment was prepared on MgO single crystal, which hasand. The YBCO film thickness
is 0.8. This YBCO BPF has 2-pole and,and filter size is 1.4 1.8 mm. The BPF was fabricated by thewet etching process. In the figure, we can see the over etchingportion in the interdigital gap ( -inverter) and short stub ( -inverter). This BPF was placed in a vacuum chamber with refrigerator cooling system. We measured the parameters by a vector
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