A Dual-Layer Printed Antenna System for DCS/PCS/UMTS A. Rennings, M. Rauf, P. Waldow and I. Wolff

Department of Engineering, Duisburg-Essen University, Bismarckstr. 81, 47048 Duisburg, Germany, Tel: +49-203-379-3183, Fax: +49-203-379-3499, E-Mail: renny@ate.uni-duisburg.de

Abstract — For CDMA systems usually a duplexer for Rx/Tx separation is required. The separation can also be done by two antennas – one receive antenna and one transmit antenna. A high isolation of these antennas is a key issue. Here we present a Rx/Tx printed antenna system for the UMTS/DCS combination. The performance was simulated using a commerical FDTD software, and validated with measurements on fabricated prototypes.

I. INTRODUCTION

The mobile phone industries integrates more and more standards into their products - GSM850, EGSM900, DCS, PCS, UMTS, BT and soon WLAN. A suitable antenna concept might be to use a conventional PIFA for GSM850 and EGSM900 - where the PIFA acts more as a coupling element to the PCB, which mainly radiates [1]. The radiation for the higher bands can be done by printed multi-band antennas at the edges of the PCB. In [2] we presented a printed antenna for all WLAN standards. The novel structure shown in Fig. 1 enables two usable λ/4 resonances (Fig. 4). Between the two passbands the proposed structure has a stopband (Fig. 3). Two of these antennas might be used for Rx/Tx separation in systems where CDMA is involved. Their frequence selectivity, together with an optimized position of the two antennas, is used to achieve a high isolation between Rx and Tx antenna. By so doing, the use of a duplexer is no longer nec essary. Here a FR-4 printed circuit board (PCB: 75 x 36 x 1 mm3) is used as a simple phone mockup.

Fig. 1: 3D-view of antenna structure on top & bottom layer

Fig. 2: λ/4 current distribution in radiator on bottom layer

II. SINGLE ANTENNAS FOR DCS/PCS

Firstly, single antennas for the DCS/PCS Rx and Tx bands have been designed. A photo of the Rx antenna is shown in Fig. 3. The return loss results for the Rx antenna are shown in Fig. 4. The difference between the EMPIRE™ [3] result and the measurement is due to the lossless FDTD simulation. Since the DCS Rx and PCS Tx band overlap from 1850 up to 1880 MHz a high isolation which is based on frequency selectivity is not possible. Therefore the DCS/UMTS combination has been chosen for the two-antenna-system in the next section.

Fig. 3: Prototype of dualband antenna for Rx bands of DCS/PCS

Fig. 4: Comparison between FDTD simulation and measurement

III. ANTENNA SYSTEM FOR DCS/UMTS (PROTOTYPE I)

The second design of this paper comprises two antennas, Rx- and Tx-antenna for the two standards DCS and UMTS. With this combination voice communication over DCS and data transfer over UMTS is possible simultaneously. The objective was a compact design together with a high isolation of the Rx- and Tx- antennas. The area on the PCB for one antenna measures 4 by 28 mm2. In Fig. 5 the FDTD model of a first two-antenna-setup together with the λ/2 current distribution which is excited in the PCB ground plane is depicted. Here the two antennas are located in the upper left and right corner of the PCB.

Fig. 5: Two-antenna-system for DCS/UMTS combination

The next figure shows a prototype (I) that we have

built. The two antennas are feeded by semi-rigid cables.

Fig. 6: Prototype I of antenna system feeded by semi-rigid cables

FDTD simulations with EMPIRE™ [3] and measurements with the HP NWA 8722C have been done. The two-port scattering parameters are presented in Fig. 7 (simulation) and Fig. 8 (measurement). The measurement indicates an isolation better than 14 dB.

Fig. 7: Simulated S-parameters of antenna system in Fig. 5

Fig. 8: Measured S-parameters of prototype in Fig. 6

FDTD Simulation II w ith EMPIRE

-35-30-25-20-15-10-50

1,6 1,7 1,8 1,9 2,0 2,1 2,2 2,3

f [GHz]

S11

[dB

]

S11 (Rx bands) S21 S22 (Tx bands)

Measurement II

-35-30-25-20-15-10-50

1,6 1,7 1,8 1,9 2,0 2,1 2,2 2,3

f [GHz]

S11

[dB

]

S11 (Rx bands) S21 S22 (Tx bands)

Rx-Antenna for DCS / PCS

-30

-25

-20

-15

-10

-5

0

1,6 1,7 1,8 1,9 2,0 2,1 2,2 2,3

f [GHz]

S11

[dB

]

EMPIRE (FDTD) Measurement

The simulated 3D radiation patterns are presented in Fig. 9. The patterns on the left hand side belong to the Rx bands of DCS and UMTS. On the right hand side the Tx versions are shown. All of the four patterns are dipole-like. The slightly unsymmetry is caused by the ground plane of the PCB, which acts like a reflector.

Fig. 9: 3D radiation patterns for Rx (left) and Tx bands (right)

IV. ANTENNA SYSTEM FOR DCS/UMTS (PROTOTYPE II)

The FDTD model of the second prototype (prototype II) for the two-antenna-system is shown in Fig. 10. In the same figure the 3D radiation patterns are depicted. All of them are quasi dipole-like. A photo of the prototype that we have built is shown in fig. 11. Again, the scattering parameters of the two port have been simulated with the FDTD software EMPIRE™ and also measured with our NWA. The results are presented in Fig 12 (FDTD simulation) and Fig. 13 (measurement).

Fig.10: 3D radiation patterns for Rx (top) and Tx bands (bottom)

Fig. 11: Prototype II feeded by semi-rigid cables

Fig. 12: Simulated S-parameters of antenna system in Fig. 10

Fig. 13: Measured S-parameters of prototype II in Fig. 11

FDTD Simulation III w ith EMPIRE

-35-30-25-20-15-10-50

1,6 1,7 1,8 1,9 2,0 2,1 2,2 2,3f [GHz]

S11

[dB

]

S11 (Rx bands) S21 S22 (Tx bands)

Measurement III

-35-30-25-20-15-10-50

1,6 1,7 1,8 1,9 2,0 2,1 2,2 2,3f [GHz]

S11

[dB

]

S11 (Rx band) S21 S22 (Tx band)

The measurement of prototype II indicates an isolation better than 12 dB. The performance in terms of isolation and radiation pattern (quasi-dipole for the four bands) is nearly the same for the two presented approaches (prototype I and II). However, since one of the antennas of the system in Fig. 10/11 will be closer to the user’s hand compared to the ones in Fig. 5/6, the overall efficiency for prototype II will be lower than for prototype I. Therefore we prefer the first approach in Fig. 5/6.

V. CONCLUSION

We introduced shortly a compact dual-band antenna based on a dual-layer approach. Two of these printed antennas might be used for Rx/Tx separation in CDMA systems. Here we choose a

DCS/UMTS combination. Two setups have been designed. The measured isolation for prototype I and II are 14 dB and 12 dB, respectively.

REFERENCES

[1] P. Vainikainen, J. Ollikainen, O. Kivekas, K. Kelander, "Resonator-based analysis of the combination of mobile handset antenna and chassis," IEEE Trans. Antennas and Propagation, vol. 50, no. 10, pp. 1433-1444, 2002.

[2] A. Rennings, R. Müller, S. Otto, P. Waldow, I. Wolff, "A novel integrated dual-band antenna for all relevant WLAN standards (IEEE 802.11 a, b and g)," Proceedings of 2003 European Microwave Conference, Munich, Germany, Vol. 3, pages 1263 - 1266, October 7 - 9, 2003.

[3] IMST GmbH, “User and Reference Manual for the 3D EM Time Domain Simulator Empire”, www.empire.de, Jan. 2004.