Design of an Input Multiplexer using Dual-Band Planar Filters. Gaëtan Prigent 1,2, Thanh-Mai Vu 1,2

1 Université de Toulouse ; INPT, UPS ; LAPLACE (Laboratoire Plasma et Conversion d’Energie) 2 CNRS ; LAPLACE ; F-31071 Toulouse, France.

Abstract — The design of an input quadriplexer is presented. It is based on a novel topology of ring-based dual-band filters. Two 2nd-order dual-band filters are implemented in microstrip technology and measured. These filters are then set in parallel to form the final IMUX dedicated to telecommunications standards: GSM (1.8 GHz), UMTS (2.1 GHz), Wi-Fi (2.45 GHz) and Wi-Max (2.9 GHz). The proposed concepts are validated by measurement results.

Index Terms — Dual Band, Bandpass filter, Quadriplexer.

I. INTRODUCTION

As wireless systems become more multifunctional, it increases the importance of having multiband operations. Multi-band filters appear thereby as one of the solutions to optimize the size and cost of such multifunctional system. These filters are located at the front ends of the wireless system enabling pre-selection of more than one band at the same time as well as rejection of interferers. There are numerous methods in producing a multi-band bandpass filter. It can be observed that by directly cascading several individual filters with specified single pass-bands will produce the multi-band effect [1]-[2]. However, this approach needs large overall size.

The most efficient method consists in determining filter topologies that are naturally multi-band. Previous work was developed using ring-based resonators. The topology proposed in [3] was based on the use of side coupled ring resonators. Such resonators are characterized by two poles and two transmission zeros ensued from destructive and constructive interaction between the two modes that are propagated. However, this topology was difficult to design since it uses three coupled lines and important corrections had to be brought so as to compensate the phase velocity that occurred for each propagating mode.

The approach that is developed in this paper consists in modifying the ring-based topology so as to make the design easier. Thereby, contrary to the Side – Coupled Ring resonator design [4], direct access were used that limit difficulties due to coupled-lines. The filter topology is described in Figure 1. In such a simple structure, each transmission lines are quarter wavelength at the center frequency. The electrical response is symmetric and frequency-ratio between center frequency and transmission zero is controlled by the impedance-ratio (Z2/Z1).

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Z1=22 ΩZ1=24 ΩZ1=26 ΩZ1=28 Ω

Fig. 1 Direct access Ring resonator topology and electrical response. Dependence with impedance ration (Rz) and Z1 values

II. DUAL-BAND FILTERS

So as to develop a higher-order filter, one of the possible uses of the ring-resonator consists in cascading n rings. This leads to either a 2n-order single-bandpass filter or a n-order dual-bandpass filter, depending on the value of n.

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Z 1,λ

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Z2, λ/4 @ fc

INZ2, λ/4 @ fc

Zoe,

Zoo

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Zoo

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Fig. 2 Electrical response of cascaded ring rnumber n of ring: (a) n even, n-order dual-bandpa2n-order single-bandpass filter.

Indeed, as depicted in Figure 2, if n is enaturally dual-band. Based on this concept, twfilters were developed. So as to limit the glfilter a 2nd-order filter was chosen, i.e. cocascaded rings. The first filter is dedicated to

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The electrical responses are depicslight frequency shift due to the dielectric constant of the substrateagreement with the simulations (Mo

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MeasurementsSimulations

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Fig. 3 Photograph of a dual-banComparison between measurements andband filters: (a) GSM, Wi-FI & (b) UM

addresses UMTS and Wi-plemented in microstrip bstrate (�r=10.7, h=59mils,

cted in Figures 3. Despite a substrate tolerance on the , the results are in a good

omentum).

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d bandpass filter cell (a). d simulations for the two dual-TS, Wi-Max.

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III. IMUX DESIGN

Once the concept was validated for dual-band filters, the IMUX is formed by setting these filters in parallel. Performances obtained by such a topology are described in Figure 4. One can observe that the performances of each dual-band filters are maintained. Moreover, even though the filter order is low, the isolation performances are quite good (higher than -20 dB in the frequency range). This is due to the presence of transmission zeros in the electrical response of the nominal dual-band filters. However, an improvement of this electrical parameter consists in the use of higher order filter, a fourth order filter for instance, i.e. formed by four coupled rings. Insertion losses obtained in the three pass bands are lower than 1.3 dB.

IV. CONCLUSION

This paper was aimed at demonstrating the feasibility IMUX using dual-bandpass filters. The standards to be addressed by such a topology are: one GSM band at 1.8 GHz, UMTS at 2.1 GHz and WiFi at 2.45 GHz and Wi-Max at 2.9 GHz. The IMUX was based on the use of a direct access ring resonator. Such a resonator, which is of 2nd-order by nature, allows achieving either single- or dual-bandpass filter, depending on the number of cascaded ring. Two filters were developed in microstrip technology whose measurement results allowed validating the concept used. The final IMUX was formed by these filters. The experimental electrical performances have proved the interest of the use of ring based dual-band filter for design of multiplexer. Therefore, synthesis of a n-order filter is being developed to further improve the design control while providing a better isolation characteristic for multiplexer.

REFERENCES

[1] C. P. Wang, W.T. Liu, M.G. Chen and Y.C. Lin, "Desing of dual-band bandpass filters whith short-end coupled lines", European Microwave Conference Digset, 2009.

[2] K. Kim, H.S. Pyo, J.M. An and Y. Lim, “Dual-Band filter using half wavelength resonators an dual-mode resonators”, International conference on Electrical Engineering/Electronics, Computer, Telecommunications and Information Technology,2009.

[3] M.K. Mohd Salleh, M.T. Ali, M.K. Hamza, G. Prigent, "Series coupled microwave ring resonators", IEEE International Conference on System Engineering and Technology Digest,2011.

[4] M.K. Mohd Salleh, G. Prigent, O. Pigaglio, R. Crampagne, "Quarter Wavelength Side-Coupled Ring resonator for Band pass Filter", IEEE Transactions on Microwave Theory and Techniques, vo 56, no 1, pp 156-162, January 2008.

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Fig. 4 Electrical performances for the IMUX (GSM, Wi-FI) & (UMTS, Wi-Max) : Transmission, return losses and Isolation.

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978-1-4673-2141-9/13/$31.00 ©2013 IEEE