DESIGN AND DEVELOPMENT OF METAMATERIAL BASED MICROWAVE COMPONENTS

Abstract

Planar technology has gained a lot of popularity since its inception due to various advantages it offered to the scientific world such as, light weight, compact size, ease of fabrication and integration, suitability of mass production and compatibility with planar solid state devices. However they also have certain drawbacks in terms of bandwidth, further miniaturization, gain, efficiency, etc. Metamataterials are introduced in the late 60s by a Russian physicist Victor Veselago [1], which were further investigated by Pendry et. al. [2] and are an active area of research these days. Metamaterials are the artificially engineered structures that offer extraordinary electromagnetic properties not found in nature such as epsilon negative media (ENG), mu negative media (MNG), double negative media (DNG), photonic band gap structures etc. They consist of multiple unit cells whose dimensions are much smaller than l0/4, where l0 is the wavelength corresponding to the highest frequency of operation, to achieve homogenization. It was discovered that these materials alter the behaviour of electromagnetic waves in an unconventional way leading to important phenomenon such as, reversal of Snells Law, Doppler effect and Vavilov-Cerenkov radiation. Due to the extraordinary behaviour of metamaterials they are used to improve the properties of various planar devices and components which are discussed earlier. They can be used to improve antenna’s gain, directivity, bandwidth and size, filter’s size, roll off, out of band rejection levels and bandwidth. They are used for multiple frequency operation. They are also being used for the development of super lenses, ultrathin perfect absorbers, cloaks, high sensitivity and high resolution sensors, phase compensator etc. The main focus of this thesis is on metamaterial based antennas, filters and absorbers. Chapter 3 presents the design of a compact, low-profile, coplanar waveguide (CPW)-fed metamaterial inspired dual band microstrip antenna for WLAN application. To achieve the goal a triangular split ring resonator (TSRR) is used along with an open ended stub. The proposed antenna has a compact size of 20×24 mm2 fabricated on an FR-4 epoxy substrate with dielectric constant (er=4.4). The antenna provides two distinct bands I from 2.40-2.48 GHz and II from 4.7-6.04 GHz with reflection coefficient better than -10 dB, covering the entire WLAN (2.4/5.2/5.8 GHz) band spectrum. The performance of this metamaterial inspired antenna is also studied in terms of the radiation pattern, efficiency, and realized gain. The antenna is practically fabricated and tested to show good agreement with the simulated results. Chapter 4 is divided into four sections. The first section presents a compact, low-profile Band Stop Filter (BSF) designed using Complimentary Split Ring Resonator (CSRR). An equivalent circuit model is also presented along with the simplified mathematical approach to extract the parameters of the circuit model. This paper also presents the effect of variation in the dimensions of split rings on characteristics of BSF. The proposed BSF has a compact size of 27×20 mm2 designed on FR-4 substrate with dielectric constant (er)=4.3. The filter provides complete suppression of the band at 2.4 GHz. The design and circuit analysis of this metamaterial based filter is presented in terms of reflection coefficient, transmission coefficient and impedance curve. The second section presents the design and analysis of a metamaterial inspired Bandstop Filter (BSF) providing suppression of frequency at 3 GHz. The overall size of proposed BSF is 20mm×20mm×1.6mm. Further,the extraction of lumped parameters of the designed BSF using simulated results is presented and validation of the results using equivalent circuit simulation is also presented. The third section presents a comparison based study of microstrip transmission line based bandstop filters taking different complementary resonators on the ground plane. Six metamaterial resonators unit cells have been investigated from the literature. The dimensions are optimized to operate at 3 GHz and then their comparative analysis is performed based on various properties of filters such as insertion loss, 3 dB v bandwidth, quality factor (Q), shape factor, overall size, unit cell size and group delay. There are a number of metamaterial based resonators available in literature, so the objective of this section of the chapter is to provide a comparative analysis so that the user can point out the best configuration required while designing the bandstop filter that suits the desired specification and also helps in developing the future ideas by taking into account the advantages of the available structures. The forth section presents a compact, low-profile, Band Pass Filter (BPF) based on balanced Dual Composite Right/Left Handed (D-CRLH) Transmission Line (TL) is presented in this chapter. A balanced D-CRLH TL can be used to provide wideband filter characteristics due to no frequency separation between the RH and LH frequency bands. The proposed D-CRLH TL is designed using U-shaped complementary split ring resonator (UCSRR). The extraction of equivalent circuit model of proposed UCSRR unit cell is also performed. Further, the bandwidth of the proposed filter is enhanced by using the concept of electric and magnetic coupling between the slot lines. The proposed via less BPF has a compact size of 15×15 mm2 designed on an FR-4 substrate with dielectric constant(er)=4.3. The design analysis of proposed bandpass filter is presented in terms of reflection coefficient, transmission coefficient, impedance curve, propagation constant and group delay. Chapter 5 presents a novel resonant metamaterial absorber exhibiting five resonant peaks with absorptivity more than 90% in the range from S band to Ku band for radar cross-section reduction and other FCC-airborne applications. The structure is designed on a low cost FR-4 substrate with 1 mm thickness which is equivalent to l /17.75 where l is the wavelength corresponding to maximum resonant frequency of absorption, showing its ultrathin nature. The fourfold symmetry of the design results in polarization insensitivity and provides an angular stability up to 60◦ of incident angle. The multiband characteristics are obtained by combining three different geometries in a single structure. Performance of the absorber is studied in terms of absorptivity, material parameters, normalized impedance, polarization insensitivity and oblique incidence. Finally, the design is fabricated on a 200×200mm2 FR-4 substrate and measurements are performed. Further, the chapter also presents a closed meander line shaped vi metamaterial absorber operating at 3.5 GHz WiMAX band. The proposed metamaterial absorber unit cell has a compact size of 0.11l0×0.11l0 design on an ultrathin FR-4 substrate with thickness 0.018l0, where l0 is the wavelength corresponding to operating frequency. The proposed absorber shows an absorptivity of 98.5 % at the intended frequency. The design is evolved from a simple square loop to a symmetrical meander line structure whose dimensions are optimized to operate at 3.5 GHz WiMAX band. An equivalent circuit model is also defined to depict the electrical properties of the structure. The proposed design also shows insensitivity to polarization as well as change in incident angle of the wave over a wide-angle (upto 60◦) for both TE and TM polarization. The proposed structure is a good candidate for radar cross section reduction of an antenna. Chapter 6 demonstrates the use of metamaterial absorber (MA) to achieve high isolation between two patch antennas in a 2-element MIMO system operating at 5.5 GHz resonant frequency useful for WiMAX application. The proposed flower shaped MA, designed on a 9×9mm2 FR-4 substrate with 1 mm thickness, exhibits near unity normalized impedance at 5.5 GHz with an absorptivity of 98.7 %. A 4 element array of the MA is arranged in the form of a line in the middle of the two radiating patches in order to suppress the propagation of surface current between them at the operating frequency. Using the proposed flower shaped MA, an isolation of nearly 35 dB is achieved. The MIMO structure is studied in terms of return loss, isolation, overall gain, radiation pattern, Envelope Correlation Coefficient (ECC), Diversity Gain (DG), and Total Active Reflection Co-efficient (TARC) etc. The structure is finally fabricated and measured to show good agreement with the simulated results.