Reactangular

CHAPTER 1 INTRODUCTION

1.1 INTRODUCION TO DIELECTRIC RESONATOR ANTENNA

Dielectric resonator antenna is a radio antenna mostly used in microwave frequencies that consist of a ceramic material block of various shapes. The DRA, mounted on a conducting surface is a ground plane. DRAs offer the advantages of compact size, lightweight, low profile, and low cost. They have been demonstrated to be practical elements for antenna applications and have several merits including high radiation efficiency, flexible feed arrangement, simple geometry, and compactness. Their resonant frequencies are predominantly a function of size, shape, and material permittivity. From last few decades there is a deep interest in antenna systems which operate at higher frequencies. Conventional metallic antennas suffer problems with regard to power losses, radiated power capabilities and fabrication difficulties when reduced to the size necessary to operate in this frequency band. These obstacles can be over-come by replacing metallic structure by a dielectric material structure resulting dielectric resonator antenna. DRAs have attracted the antenna designers in microwave and millimeter wave band due to its features like high radiation efficiency, light weight, small size, lowprofile , low temperature coefficient of frequency, zero conductor losses and suitable scale in microwave band. DRAs of low loss dielectric material, having dielectric constant as 1< εr < 100 are ideally suitable for antenna applications, so that a compromise can be made between size, operating frequency and other antenna radiation characteristics .Dielectric constant also affects the bandwidth, as dielectric constant decreases bandwidth increases hence to have broader bandwidth, material with suitable dielectric constant is required. The radiation Q-factor of a DR antenna depends on its excitation modes as well as the dielectric constant of the ceramic material. The Q-factor increases and hence the bandwidth decreases with increasing dielectric constant and vice-versa. For this reason, DRs of relatively low dielectric constant are almost always used in antenna applications. A substantial amount of research effort has been devoted to the study of DR antennas in the last decade.

1.1.1 Different Shapes of DRA

Figure 1.1 shows various shapes of DRA as shown in figure 1.1 there are various shapes of DRA figure 1.1 shows cylindrical, rectangular, hemispherical, triangular.

Abbildung in dieser Leseprobe nicht enthalten

Figure1.1 Different shapes of DRA

1.1.2 Feeding Techniques

To Excite the DRA various feeding techniques are used such as microstrip, coaxial cable, coplanar waveguide these techniques are also define in chapter 3 in the section 3.2.3.

1.2 NEED AND MOTIVATION

Both the wideband and dual band antennas are in very high demand to support wireless communication applications to meet the needs of simultaneous transmission and reception of audio and video data of high quality. In the last few decades research has been done to increase the bandwidth and gain of antenna. Recently in the field of wireless communication wideband DRA antennas have more attention mainly in the field of mobile communication and wireless communication. . Main aim of this thesis is to increase the return loss, to enhance the bandwidth, to achieve wideband to achieve the dual band and to increase the gain and efficiency of DRA antenna. Rectangular DRA is used since it provides maximum design flexibility than other shapes. Through some experiments it is found that by introducing air gap in between ground plane and rectangular dielectric material bandwidth can be increased, this technique is used in this project to increase the matching bandwidth. In this project quarter wave microstrip line is used which are helpful to obtain dual band.

1.3 PROBLEM STATEMENT

1.3.1 IDEAL CONDITION

Ideally we have to design microwave antenna which serve like an isotropic antenna, whereas an isotropic antenna is a point source that radiates equally in all directions. They have no losses, 100% gain, 100% efficient, very high impedance bandwidth, no conduction losses, high flexibility and versatility more over perfect impedance matching meets the requirement of many wireless applications and data communications.

1.3.2 CONSEQUENCES

In spite of them we have chosen a dielectric resonator antenna (DRA). The main characteristics of DRA is that a wide range of dielectric constants can be used allowing the designers to control The physical size and the bandwidth of the DRA, by selecting a dielectric material with low loss Characteristics, high radiation efficiency can be maintained in DRAs, DRAs can be designed to operate over a wide range of frequencies from 1 GHz to 44 GHz.DRA has much wider impedance bandwidth compared to microstrip antennas ,Depending upon the resonator shape, various modes can be excited within the DRA producing either broad side or Omni-directional radiation patterns for different coverage requirements, DRAs have high dielectric strength and hence higher power handling capacity, It has high degree of flexibility and versatility, allowing for designers to suit a wide range of physical or electrical requirements of varied communication applications. And design a DRA antenna choosing a microstrip feed technique.

1.4 OBJECTIVE

Main objective to design this antenna to achieve dual and wideband for wi-fi ,wireless and WiMax. To achieve dual band quarter wave microstrip line is used and concept of ground plane is used. With reducing in the size of antenna directivity, gain and bandwidth is also increased. Designing ring shaped DRA increases the matching bandwidth by keeping suitable impedance matching.

1.5 CHAPTER OUTLINE

Chapter 1 contains the basic of dielectric resonator antenna that is Introduction part, need and motivation, problem statement referring what are the problems related with conventional metallic antenna and whether these antennas are practically feasible or not. This chapter also contains the objective of this thesis. Chapter 2 is the Literature survey part which contains the literature review related to this project, findings of literature review and about the research gap. Historical background, Antenna fundamentals, quick over view of DRA and theoretical parts are thoroughly discussed in the Chapter 3. This chapter gives the brief knowledge to understand what are antenna, what are DRAs and also conclude the details about the performance parameters of antenna. Chapter 4 introduces the CST STUDIO SUITE along with the basic steps involved how to interface with this software. This chapter also contain methodology and step by step designing procedure of proposed structure. Chapter 5 is all about the simulation results and the parametric discussion. Graphical approach of all the simulated results and required comparisons in the form of tables are presented in this chapter. Along with the future scope, thesis is concluded in Chapter 6

CHAPTER 2

LITERATURE SURVEY

2.1 INTRODUCTION

This thesis reviews the evaluation of dielectric resonator antenna technology SINCE 1997 from the theoretical and experimental investigations on rectangular dielectric resonator antennas. An account on existing design aspects to have various operation bands like dual band, multiband, wideband, for also different radiation patterns and different polarizations are presented in this chapter.

2.2 LITERATURE REVIEW

2.2.1 The Beginning of DRA

Dielectric resonator is a ceramic block which is characterized by a definite volume, shape, size and dielectric constants. Radiation from open dielectric is realized by Richtymer in 1939 . But the first theoretical and experimental analysis of rectangular DRA was done by Long et al. in 1997. This experiment attracted many designers and researchers to work further over it which transforms it into the new geometry of DRAs such as cylindrical, triangular, hemispherical, ring etc.

2.2.2 Recent Advances in Dielectric-Resonator Antenna Technology

This section features some of the latest developments in DRA technology achieved at the CRC. Research has been divided into two categories:

1. Novel DRA elements.
2. Array configurations. The research carried out on novel DRAs can be categorized in the following
1. Wideband.
2. Compact.
3. Circular polarized.
4. High gain.
5. Active.

Here we describe about the wideband DRAs wideband antenna operation is desirable to accommodate the increasing data required for services such as video- conferencing, direct digital broadcast, EHF portable satellite communications, local multi-point communications, and indoor wire- less. Some of these requirements may be met by existing printed- antenna technology, but with the added cost and complexity associated with multi-layer configurations required for achieving broad bandwidths. This section presents some novel DRAs of relatively simple design, which have demonstrated wide-band performance, and may serve as suitable antenna candidates for these various applications. Different wideband DRAs are listed here.

1. Notch DRA.
2. Multi segment DRA.
3. Parasitic DRA.

2.3 Research Gap:

DRAs have been an active research area for the last two decades due to several striking characteristics such as high radiation efficiency, low dissipation loss, small size, light weight, and low profile, since the use of dielectric resonator as an antenna was originally proposed in 1983 ¹. Moreover, DRAs, which possess a high degree of design flexibility, have emerged as an ideal candidate for wideband, high efficiency, and cost-effective applications. Significant efforts for DRAs have been reported to achieve wide bandwidth enhancements in the past. The research of the wideband DRA with broadside radiation was first experimentally carried out in 1989 by Kick et al. ², who stacked two different DRAs on top of one another to obtain a dual-resonance operation with 25% impedance bandwidth. Since then, different techniques were proposed to achieve bandwidth enhancement. Various geometries of DRAs such as conical, ³, elliptical ⁴, ⁵, tetrahedral ⁶, well ⁷, stair ⁸ and H-shaped ⁹ were proposed for bandwidth enhancement techniques for broadside radiation by using the advantage of DR structure flexibility. Also, the introduction of an air gap between the DRA and ground plane can further improve bandwidth ¹⁰. A DRA of multiple layers can be used to enhance the bandwidth ¹¹ as can be loaded dielectric resonators ¹². Since the coupling between the excitation mechanism and the DR significantly affects the resonant frequency and radiation Q-factor of a DRA, feeding Techniques including T-strip-feed DRA ¹³, L-probe feed DRA ¹⁴, and vertical strip-fed ¹⁵, ¹⁶ have been proposed. By using the above bandwidth enhancement techniques, operating DRA bandwidth ranges from 25% to 67% have been reported for broadside radiation patterns. Wide bandwidth for monopole type radiation patterns have been reported ¹⁷, ¹⁸, which are much easier to achieve than the broadside type, and even wider bandwidth was previously achieved by loading a monopole with suspended annular DRA¹⁹, ²⁰. Recently, several papers proposed DRAs with planar type vertical ground plane to obtain an Omni­directional pattern ²¹ –²³. Among them, however, there are no DRAs with broadside patterns and none of them achieved the bandwidth that is needed for the UWB. Today, dual-band systems are commonly found in modern wireless communications, motivating the study of the dual-band DRA. Some design techniques have been developed for the dual-band DRA with two different radiation characteristics for GPS applications and communications ²⁴, others by using two different materials such as the rod-ring DRA ²⁵ or by deforming the ground plane ²⁶. A hybrid use of the DRA resonance and other resonator such as the slot excitations ²⁷ or parasitic patch combined with the DRA ²⁸ or recently, a higher order mode of the rectangular DRA has been used to obtain a dual-band DRA [29, 30], which avoids the need of a second separated resonator element.

CHAPTER 3

THEORY AND OVERVIW OF DRA

3.1 ANTENNA FUNDAMENTALS

3.1.1 Introduction to Antenna:

An antenna is an electrical device which converts the electric wave in to the radio waves. It is used with a radio transmitter or radio receiver. Antennas are essential components of equipments that use radio. Radio waves are electromagnetic waves used to convey signal or information .Antenna is used as broadcasting, television, mobile telephones ,antennas are also used in point to point communication link (telephone, data network).Antennas are also used in satellite communication, radar technology, astronomy. Thus antennas are used as transmitter and receivers. Antennas can be hidden as used in laptop and radio as Wi-Fi.

Antennas are categorized in to two categories.

a) Omnidirectional Antenna: They are also named as weakly directional antenna omnidirectional antennas radiate and receive weakly in all direction.
b) Directional Antenna: Directional antennas are the antennas which radiate and receive in a particular direction. They are also called as high gain antenna.

3.1.2 Bandwidth:

Bandwidth of a signal is difference between the signals of high and low frequencies.

Abbildung in dieser Leseprobe nicht enthalten

Table 3.1 Frequency Ranges

3.1.3 Gain:

Antenna gain describes how much power is transmitted in the direction of peak radiation to that of an isotropic source. Antenna gain sometimes refers as function of angle .To obtain gain plotting of radiation pattern are necessary. Antenna gain can be defined as G = erD. Wi-Fi antennas are considered as a high gain antenna. Antenna gain depends on which direction it is radiating.

3.1.4 Directivity:

Directivity is a measure of how “directional” of antenna pattern radiation pattern is, an antenna which radiates equally well in all direction have zero directionally, and directivity of this type of antenna is (0 dB).Thus mobile antennas have low directivity because mobile antenna can receive signals from any directions.

3.1.5 Radiation Pattern:

Figure 3.1 shows the radiation pattern of an antenna, according to the figure 3.1 there are 3 lobes are present main lobe defines the principal axis , side lobes defines unwanted radiation.

Abbildung in dieser Leseprobe nicht enthalten

Figure 3.1 Radiation Pattern

3.1.6 Antenna Impedance:

Antenna impedance defines as the ratio of voltage to current at the input of antenna. Impedance is required for best matching.

3.1.7 Antenna Efficiency:

Antenna efficiency defines as the ratio of power delivered to the antenna to the power radiated from the antenna. High efficiency antenna refers as most of the power radiated from antenna and low efficiency antenna refers as most of the power absorbed as losses or reflected. Antenna efficiency is defines as the ratio of radiated power to the input power. Antenna efficiency remains same for transmitting and receiving antenna. Antenna efficiency losses.

1. Conduction losses.
2. Dielectric losses.
3. Impedance Mismatch losses.

3.1.8 VSWR:

VSWR refers as voltage standing wave ratio it is a function of reflection coefficient. VSWR defines about how much power is reflected from antenna .if ґ is reflection coefficient, than VSWR will be defined as:

Abbildung in dieser Leseprobe nicht enthalten

Reflection coefficient is also defines as return loss, value of vswr should be low as possible but the ideal value of vswr is 1.VSWR alone is not sufficient for that antenna is functioning properly.

3.2 DIELECTRIC REASONATOR ANTENNA

3.2.1 Introduction:

Dielectric resonators using high-permittivity materials were originally developed for microwave circuits, such as filters or oscillators as tuning element ³¹.Indeed, in the late nineteen sixties, the development of low-loss ceramic materials opened the way for their use as high-Q elements [32-34]. Then, making use of dielectric materials to create the dielectric resonator antenna (DRA) illustrates the ingenuity of Professor S. A. Long ³⁵, who was the first to propose such a procedure in the early nineteen eighties. Indeed, it introduced the use of a dielectric resonator as an antenna by exciting different modes using multiple feeding mechanisms. During the nineties, emphasis was placed on applying analytical or numerical techniques for determining input impedance, fields inside the resonator and Q-factor ³⁶. Kishk, Junker, Glisson, Luk, Leung, Mongia, Bhartia, Petosa and so on, have described a significant amount of DRAs’ analyses and characterizations [37-18]. Petosa and al. proposed both in literatures and book [36,42] many of the recent advances on DRAs. Current DRA literatures focus on compact designs to address portable wireless applications. Among them, new DRA shapes or hybrid antennas are developed to enhance the antenna impedance bandwidth [43-49] or for multiband antenna applications [50-52]. The first part will address a brief overview of the most common used DRA shapes and structures including both rectangular and cylindrical DRAs. The emphasis will be placed on better understanding what DRAs exactly are and how to develop such an antenna. This part will detail fundamental modes of DRAs, their resonant frequencies, fields inside the resonator and radiation patterns corresponding to these modes. A second part will focus on the relevant dielectric material properties having a significant contribution to achieve better antenna performances. It will detail the kind of materials DRAs can use, which is closely linked to the targeted application.

3.2.2 DRA Characteristics:

1. The main dimension of a DRA is proportional A,0/Vsrur where sr and ur are the dielectric and magnetic constant of the material. Where XOfree space wavelength in the case of dielectric material is ur is considered as 1.so DRA is proportional toA,0/Vsr.
2. Low-loss dielectric material offers better efficiency because they offer minimum conductor losses.
3. A number of modes can be excited within the DRA; many of them provide dipolar-like radiation characteristics.
4. Mostly targeted frequencies for researchers are 1 GHz-40GHz.
5. For a given DRA geometry radiation pattern can be made to change by exciting different Resonant modes.
6. Different kinds of excitation method are used such as microstrip line, coaxial cable, and coplanar waveguides.

3.2.3 DRA Feeding:

Various techniques are used to excite different resonant modes. Here various techniques are defined to excite a DRA.

a. Coaxial probe excitation: It can be located within the DRA or adjacent to it. There are two methods of probe excitation first is coupling the probe inside the DRA figure 3.2 shows the coaxial probe coupling the E field and figure 3.3 shows the coupling the H field using coaxial probe.

Abbildung in dieser Leseprobe nicht enthalten

Figure 3.2 Coaxial probes coupling the E Field.

Abbildung in dieser Leseprobe nicht enthalten

Figure 3.3 coaxial probes coupling the H field

b. Microstrip feeding line and coplanar waveguide: Figure 3.4 shows the microstrip and coplanar waveguide coupling as shown in figure 3.4 microstrip and coplanar waveguide are used for better coupling.

Abbildung in dieser Leseprobe nicht enthalten

Figure 3.4 Microstrip and Coplanar waveguide coupling

c. Aperture Coupling: According to the figure 3.5 aperture coupling is used to excite a DRA as shown in figure 3.5 aperture coupling is used to excite a DRA as shown in figure 3.5 a microstrip line is used to excite a DRA and a aperture is created in the substrate for feeding .

Abbildung in dieser Leseprobe nicht enthalten

Figure 3.5 Aperture Coupling

3.2.4 Rectangular DRA:

Rectangular DRA have one degree of freedom over other shaped DRAs. It has greater design flexibility because its dimensions. The modes in a isolated DRA is categorized as TE and TM mode but DRA mounted on a ground plane only TE mode is excited. The fundamental mode is TE111

3.2.5 Minimization Techniques of DRAs:

a. Addition of metallic plate on a DRA Face: Figure 3.6 shows that a metallic plate is inserted and DRA dimensions are decreased.

Abbildung in dieser Leseprobe nicht enthalten

Figure 3.6 Metallic Plates on A DRA Face

b. Multisegment DRA: Figure 3.7 shows the multisegment DRA as shown in figure 3.7 two DRA are combine.

Abbildung in dieser Leseprobe nicht enthalten

Figure 3.7 Multisegment DRA

3.2.6 Application of DRA

a. Satellite communication and direct broadcast services.
b. Doppler’s and other RADAR.
c. Telemetry and Missiles.
d. Mobile radios (pagers, telephone, man pack systems).
e. Biomedical radiators and intruder alarms.

3.2.7 Limitation of DRA

a. The fabrication price is more as compared to micro strip antenna.
b. Ceramic materials are typically used, which must either be machined from large blocks or cast from molds. Drilling may be required and the DRA has to be bonded to a ground plane or substrate.
c. Compared to the printed circuit antennas, the fabrication is generally more complex and more costly, especially for array applications.
d. Difficulty to choose dielectric material of desire dielectric constants.

[...]