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Novel Microwave Diplexer System Based on Planar Waveguide and Metamaterial Technologies

Kuan Deng 1, Wenquan Che 1, 2, Chao Li 1 and Peter Russer 2

1JGMT of Ministerial Key Laboratory, Nanjing University of Science &Technology, China 2The Institute for High Frequency Engineering, Technische Universitat Munchen, Germany 1yeeren_che@http://www.wendangxiazai.com

Introduction

Microwave diplexer is an important integral part in a radar or communication transceiver system, which makes it possible for both transmit and receive channels to share the same antenna. During the transmission state, the diplexer must provide reliable path for the microwave signal from the transmitter to the antenna while providing sufficient isolation for the receiver to prevent damage by power leakage through the diplexer. During the receiving state, the diplexer is required to provide a low-loss path from the antenna to the receiver.

The waveguide diplexers/multiplexers are well studied and widely used in wireless communication systems, due to their excellent performance [1, 2]. However, they are very difficult to integrate with planar circuitry due to its 3D geometry. In recent years substrate-integrated waveguide (SIW)[3, 4] was proposed to solve the problems, which largely preserves the advantages of conventional rectangular waveguides and microstrip lines. The most highlight of SIW structure is its easy connection with other planar transmission lines.

The split-ring resonators (SRRs), originally proposed by Pendry [5], have attracted a great deal of interest for the design of negative permeability and left-handed (LH) effective media. The complementary split resonance ring (CSRR) [6, 7] is the negative image of the SRR, which can provide a negative effective permittivity in the vicinity of its resonant frequency and produces sharp rejection band. In this work, one novel bandpass filter based on SIW and CSRR is proposed, a simple SIW highpass filter is designed also. The simple combination of these two filters thus leads to one novel frequency diplexers. Good performances especially high isolation between transmit and receive paths can be observed from the simulations and the experiments of a prototype, demonstrating the validity of the proposed strategies.

Design of SIW-CSRR bandpass filter and SIW highpass filter

a. SIW-CSRR bandpass filter

As we know, the electric field of TE10 mode within SIW is orthogonal to the top and bottom surfaces of SIW, it is thus appropriate to etch the CSRR cells either on top surface of SIW or bottom plane, which can guarantee that CSRR are properly excited. The behavior of the complementary structure excited by an axial electric field will be similar to that of the original SRR excited by an axial magnetic field. However, it is better to etch the CSRR cells on the top surface to preserve the integrity of the bottom plane, which is usually required in practical engineering. The resultant SIW-CSRR bandpass filter is illustrated in Fig. 1, which is implemented in a substrate with height 0.508mm and dielectric constant 2.65.

We may note that, the proposed SIW-CSRR filter in Fig. 1 is the combination of SIW and 10 CSRR cells, a microstrip taper is employed to carry out the transition from SIW to microstrip. The parameters are listed below: W50 = 1.4mm, L1 = 9mm, D1 = 3.8mm, a1 = 18mm, W =

1.8mm, R = 0.5mm, R1 = 1.2mm, g1 = 0.3mm, g10 = 4.75mm, g11 = 10.25mm, g12 = 9mm, Lcsrr =52mm. It must be mentioned that, the higher stopband is quite related to R1 and g1, 978-1-4244-2642-3/08/$25.00 ©2008 IEEE Novel Microwave Diplexer System Based on Planar Waveguide and Metamaterial Technologies

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