882

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 17, NO. 2, JUNE 2007

Development of a HTS Slot Antenna With
Multi-Bandpass Filters
H. Kanaya, Member, IEEE, T. Hashiguchi, R. K. Pokharel, Member, IEEE, and K. Yoshida, Member, IEEE

Abstract—We developed a single-chip receiver antenna combined with coplanar waveguide (CPW) impedance matchingcircuits and multi-bandpass filters (multiplex receiver). Firstly,
we designed a HTS slot antenna with 10.5 GHz center frequency.
Next, in order to compensate the reactance of the antenna at different center frequencies of the BPFs, we attached the reactancecompensation transmission lines behind the -junctions. Finally,
we design the channel #1 BPF and channel #2 BPF matched tothe input impedance of the antenna and reactance compensation
line. The channel #1 BPF has center frequency = 10 3 GHz
and channel #2 BPF has center frequency = 10 7 GHz. The
prototype YBCO 2-channel BPFs was fabricated and verified thedesign theory.
Index Terms—Coplanar waveguide, impedance matching circuit, multiplexer, slot antenna.
Fig. 1. Block diagram of a multi-channel receiver with slot antenna.

I. INTRODUCTIONIN RECENT years, many RF passive devices made of highsuperconducting (HTS) thin films, such as bandpass filter(BPF), have been studied, which have extremely low surface
impedance at microwave frequencies.
It is widely known, however, that in order to realize HTS antenna we must simultaneously realize an impedance matchingcircuit, which compensates the narrow bandwidth (or highquality factor) peculiar to the superconducting small antenna[1]. Moreover, it will be necessary to combine some RF
front-end devices for multi channel applications.
So, we will fabricate the HTS single-chip receiver antenna
combined with broadband impedance matching circuits and duplexer or multiplexer with BPFs.
There are many reports of surface acoustic wave (SAW) duplexers, and SAW duplexers are already used commercially [2].
However, because SAW duplexer has thee dimensional structure, it is difficult to realize single chip RF front-end. On theother hand, duplexer composed of planar type passive devices
such as coplanar waveguide (CPW) bandpass filter (BPF) iseasy to fabricate on the single chip, because the signal line andground plane exist only on the same side, and also easy to realize
desired characteristic impedance. There are some reports aboutplanar type duplexer which has 50 input and output ports [3].
Additionally, in the RF section, impedance matching circuit isnecessary for interconnecting antenna, duplexer low noise amplifier (LNA) and power amplifier (PA). It is particularly effective to fabricate the matching circuit by using distributed elements made of transmission lines because their size becomes
smaller, as the frequency is higher.
In our previous papers [4], [5], we proposed a design methodof the broadband impedance matching circuit for interconnecting the single-chip devices such as small antenna, CMOS
LNA and PA.
In this paper, we designed the planar antenna combined withcoplanar waveguide (CPW) impedance matching circuits andduplexer for HTS single chip multi-channel receiver. Fig. 1
shows the block diagram of a multi-channel receiver withantenna.
II. DESIGN OF ANTENNA COMBINED WITH CPW IMPEDANCEMATCHING CIRCUITS AND DUPLEXER
A. Design of a Slot Antenna

Manuscript received August 29, 2006. This work was supported in part by
the Grant-in-Aid for Scientific Research (C) from the Japan Society for thePromotion of Science (JSPS) and 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, Science and Technology(MEXT).
The authors are with Department of Electronics, Graduate School of Information Science and Electrical Engineering, Kyushu University, 744 Motooka,
Nishi-ku, Fukuoka 819-0395, Japan (e-mail: kanaya@ed.kyushu-u.ac.jp).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TASC.2007.898275

We adopted the slot dipole antenna as shown in Fig. 2(a),which is fed by CPW transmission line. The size of the antenna
section is 12 mm 8 mm. The widths of the signal line and between the ground conductors in the CPW feed line are 35
and 66, respectively, and of the substrate is 9.6, which has
50 characteristic impedance. We assumed the loss-less conductor is placed on the MgO substrate with thickness on 500 .
Fig. 2(b) shows the circuit model of the antenna section. Our slot
antenna has a series resonance. Fig. 3 shows the S parameter ofthe slot antenna. The geometry of the slot antenna was adjusted

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KANAYA et al.: DEVELOPMENT OF A HTS SLOT ANTENNA WITH MULTI-BANDPASS FILTERS

883

Fig. 5. Circuit model of the reactance compensation transmission line.

Fig. 2. EM simulation layout of slot antenna 2(a) and circuit model of antenna
section 2(b).

Fig. 6. Frequency dependence ofFig. 3. EM simulation result of the return loss of the slot antenna.

XandX.

be 10.7 GHz, respectively. In order to separate the RF signal ofchannel #1 (port #1) and #2 (port #2), -junction is attached on
the CPW feed line.
atAs shown in Fig. 4,andareand, respectively, where, “P1” and “P2” is the port number. In order
to compensate the imaginary part, CPW transmission linesand ) are attached on the -junction,(as shown in Fig. 5. Fig. 6 shows the frequency dependence ofandof, and.
As shown in Fig. 6, the reactance is zero at 10.3 GHz and10.7 GHz, respectively.
,) is inThe real part of the input impedances (verted into 50 by using admittance inverter as shown in thenext subsection.
B. Design of Matching Circuit and Duplexer

Fig. 4. Frequency dependence of the antenna impedance.

so that the center frequency is 10.5 GHz. Fig. 4 shows the fre,quency dependence of the antenna impedance
which is calculated by using electro magnetic (EM) simulator(ADS, Agilent technologies).
For multi-channel receiver, the center frequency of a channel#1 is assumed to be 10.3 GHz and a channel #2 is assumed toFig. 7 shows the circuit model of the antenna with matchingcircuit and duplexer. The n-pole Chebyshev BPFs withmatching circuit are attached on the reactance compensation lines, which have different resonant frequency, namely,and, respectively.
,,,
In the figure,,andare admittance inverters( inverters) composed of the matching circuit in the BPF.
,,andare susceptance slope parameters,,and) of theof the susceptance (parallel resonance.

884IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 17, NO. 2, JUNE 2007

Fig. 7. Circuit model of the antenna with n-pole matching circuit and duplexer.
S is S -parameter.

Fig. 9. Layout of the slot antenna with n = 2 duplexer.

Fig. 8. Frequency responses of the circuit model of the n = 2 duplexer.

inverters of the antenna section are described in our previous paper [6], and are written for port #1 by,

(1)
(2)
(3)
(4)
(5)
is the fractional bandwidth andis the filter
Where,
resonator BPF [7].
parameters of the Chebyshev type
is the reactance slope parameter of the reactanceWe can obtain the design parameters for port #2 in the replacement of subscript “ ” with “ ”.
III. SIMULATION RESULTS OF SINGLE-CHIP ANTENNACOMBINED WITH CPW DUPLEXER
Fig. 8 shows the frequency responses of the circuit model
duplexer. The 16 dB bandwidthof the two-poleFig. 10. EM simulation results of the duplexer.

and isolation between the ports ofthe duplexer are 100 MHz and 28 dB, respectively.
duFig. 9 shows the layout of the slot antenna withplexer for EM simulation. inverters are realized by the interdigital gaps. The line and space width of the interdigital gap are, respectively. For size reduction, theresonator com5
posed of CPW transmission line was bent into meander structure. (See Fig. 9). The widths of the signal line and between theground conductors in the CPW duplexer are the same configurations in the antenna section. [See Fig. 2(a)]. The total sizeof the single-chip antenna with impedance matching circuit andduplexer is 10 mm 12 mm. Fig. 10 shows the EM simulation results of the duplexer. The EM simulation results of theboth center frequencies and bandwidths are similar to those thecircuit model. However, because of the unexpected electromagnetic couplings between the resonators, off-band responses anddesign ripple are different from those of the circuit model.
IV. EXPERIMENTAL RESULTS AND DISCUSSION OF
PROTOTYPE YBCO DUPLEXER
Fig. 11 shows the layout and photograph of the prototype
YBCO CPW duplexer. In order to confirm our design theory,the 50 port is attached instead of the slot antenna. (See port

KANAYA et al.: DEVELOPMENT OF A HTS SLOT ANTENNA WITH MULTI-BANDPASS FILTERS885shifted to the lower frequency because of the kinetic inductanceof the YBCO, the effect of errors in the dielectric constant andthickness of the substrate, so that simulation data is shifted to
the lower frequency. The shifted channel center frequencies andbandwidth are similar to that of the circuit model. Because of
the contact loss and over etching, design ripple is not in fullagreement with the simulation result. However, we can verify
our new design theory by cryogenic experiment. In order to reduce the over etching portion, it will be necessary to fabricate
the YBCO duplexer by the dry etching process like an electron
beam etching.
V. CONCLUSION

Fig. 11. Layout and photograph of the prototype YBCO CPW duplexer.

For realizing the HTS receiver, we developed the singe-chipreceiver antenna combined with -junction, reactance compensation CPW line, impedance matching circuits and duplexer. We designed the 2-pole BPFs which have centerand 10.7 GHz, respectively. Finally, aprototype YBCO duplexer was fabricated and tested at cryogenic temperature.
By using the CPW BPF with attenuation poles, which wasintroduced in our previous paper [8], [9], we can realize thehighly selective duplexer.
Moreover, we can design the HTS multiplexer by adding thereactance compensation CPWs, matching circuit with BPFs.
REFERENCES

Fig. 12. Frequency responses of the YBCO CPW duplexer at 20 K.

#3 in Fig. 11). In the figure, the meander structure and interdigital gap are also printed. YBCO film used in this experimentandwas prepared on MgO single crystal, which has. The YBCO film thickness is 0.8.
The duplexer was fabricated by the wet etching process. In thefigure, we can see the over etching portion in the interdigital
gap. This duplexer was placed in a vacuum chamber with refrigerator cooling system. A vector network analyzer (HP8722C;HP) measured the S parameters though the air coplanar probes(GSG-150; Cascade Microtech).
Fig. 12 shows the frequency responses of the YBCO CPW
duplexer at 20 K. These characteristics include the residual loss
due to the contact between the YBCO film and air coplanar
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