Design of RF MEMS Based Tunable Cell for CRLH Transmission Line(2)
3.2.1 Design of Interdigital Capacitor 16
3.2.2 Design of Stub Inductor 18
3.3 Design of Balanced CRLH TL . 20
3.4 Design of RF MEMS Switches 24
3.5 Model of Tunable unit Cell of CRLH TL . 26
4 Design of Zero Order Resonator (ZOR) 27
5 Problems 30
6 Further work. 31
Conclusion . 32
Acknowledgement . 33
Reference . 34
Appendix 36
1.1 Background of the Project
Studies on left-handed materials (LHMs), which are characterized as exhibiting
simultaneously negative permittivity (ε) and permeability (μ), have receive substantial
attention in the scientific and engineering communities. They were first theoretically
analyzed by the Russian Physicist Veselago. Since then, the unique properties of LHMs
have allowed novel applications, concepts, and devices to be developed and started to
be integrated into many microwave and optical applications [1].
Composite Right/left-handed Transmission line based on metamaterials (MTMs)
has gain interest recent years [2]. MTMs are artificial effective structures with useful
electromagnetic properties not readily found in nature, which constitute a new
paradigm in science and engineering [2] [3]. Two categories of metamaterials have
been explored so far: resonant structures made of thin wires (TWs) and/or split-ring
resonators (SRRs), and nonresonant transmission line (TL) structures made of lumped
inductors and capacitors [3]. Both can in principle exhibit novel properties, such as
left-handedness in one, two or three dimensions. The experimental realization of LHM
with resonance structures was demonstrated by Smith et al. [4]. For those MTMs of the
first category which are based on resonant phenomenon, their inherent drawbacks such
as narrow bandwidth, high loss and fabrication difficulties limit the application to the
microwave engineering. To overcome these problems, the transmission-line (TL)
approach was later proposed to realize LHMs. A composite right/left-handed
transmission line is a transmission line based on metamaterials.
CRLH-TLs are more practical approach, which are made up with additional series
capacitance (CL) and shunt inductance (LL) other than unavoidable parasitic series
inductance (LR) and shunt capacitance (CR) of the line. CRLH TLs show both
left-handed and right-handed behavior in the lower and upper frequency range. Since
CRLH TL can be realized by planar circuits, it can be conveniently implemented in
microwave circuits and antennas [5].
One of the heated fields of study on CRLH TLs is to add tunablity of CRLH TLs
for the purpose of application in broader areas. Current approaches are mainly based on
changing the parameters of reactive loads, which suffer from high loss, poor yield,
narrow tuning range, low operating frequency and low temperature condition for
superconducting [6]. Radio Frequency Microelectromechanical Systems (RF MEMS) Switches are considered to be the best solution to get better performance on the
tunability of CRLH TLs in the current scientific world. RF MEMS technology has the
potential of replacing many of the mechanical and semiconductor switches used in
mobile and satellite communication systems. In many cases, such RF MEMS switches
would not only reduce substantially the size and power consumption, but also promise
superior performance [7].
1.2 Introduction of the Design
This article focuses on the design of a tunable CRLH TL cell utilizing RF MEMS
technology based on a microstrip. It includes the design of interdigital capacitor and