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Looking back to the history of mobile communication, antenna technology has made progress along with progress in mobile communication systems, and many varieties of antenna systems have been developed and used for mobile systems. Inside rapid increase telephone systems originated on early 1990, where digital technology was introduced . In the mobile communication for the past few decades, the size of the antenna is changing. In the past, the antenna was build outside the mobile phone. Now, because of the technological progress, the antenna can be build inside the mobile phone. But, the space is limited for antenna inside the casing of a mobile. So, antenna with small size as possible are needed but their performance have to be maintained.
The objectives of this project are:
To develop a small size of mobile antenna.
To develop a low cost mobile antenna.
To learn about the antenna simulation.
2.1. What is an antenna?
AnÂ antennaÂ orÂ aerialÂ is an electronic device designed to send or receive signals that have specific frequency. Some electronic devices likeÂ radio,Â television,Â radar,Â wireless LANÂ need antennas to work. Antennas work properly in air orÂ outer space. Antenna's length is usually up to theÂ wavelengthÂ it uses.
The simple dictionary meaning of an antenna is that it is usually metallic device (as a rod or wire) for radiating or receiving radio waves. The IEEE Standard Definitions of Terms for Antennas (IEEE Std. 145-1983) defines the antenna as "a means for radiating or receiving radio waves" . In other words, the antenna is the transitional structure between free space and a guiding device. The antenna is also referred to as aerial. Combining all these definitions, we can extract an excellent definition of antenna as "a metallic (usually) device used for radiating or receiving electromagnetic waves which acts as the transition region between free spaces and guiding structure like a transmission line in order to communicate even in a longer distance."
2.2 History of mobile communication
The first mobile communication system was developed by Thomas Edison on 1885 with wireless telegraph between trains and stations . Telegraph signals were conveyed through the trolley wires, which were electrostatically coupled with a metal plate installed on the ceiling of the train. Edison also experimented with communication on a vehicle in 1901, using a thick cylindrical antenna placed on the roof of the vehicle.
Real mobile communication services developed in 1898 by Guglielmo Marconi started with wireless telegraph on ships, using long vertical wire antennas in various forms such as T, inverted L, and umbrella shapes. Portable equipment appeared in 1910 .
Advanced antenna design and the surge of technology progress was provided during World Wars I and II were firmly established in the 1920s, while present-day microwave antenna design and technology were commonplace in the 1950s . In the 1960s a new antenna era emerged because of the revolutionary progress in semiconductor integrated circuits, attributed initially to the Cold War defense industry but substantially carried forward into the commercial equipment sector. Quite simply, the demand opened up designers to the possibilities of redesign, recreation, and transformation of known antenna types into less bulky, lightweight, low-cost, easy-to-manufacture radiating structures, compatible with the newly conceived integrated electronic packages. Most notable has been the creation of the printed antenna technology, which lends itself to multifunction antenna devices.
2.3 Types of antenna
2.3.1 Isotropic antenna
An isotropic antenna is a hypothetical lossless antenna having equal radiation in all directions. It radiates its power equally in all the direction in space co-ordinate system.
Figure 2.1: An example of isotropic antenna
2.3.2 Directional antenna
AÂ directional antennaÂ orÂ beam antennaÂ is anÂ antennaÂ which radiates greater power in one or more directions allowing for increased performance on transmit and receive and reduced interference from unwanted sources. Directional antennas like Yagi antennas provide increased performance over dipole antennas when a greater concentration of radiation in a certain direction is desired.
All practical antennas are at least somewhat directional, although usually only the direction in the plane parallel to the earth is considered, and practical antennas can easily beÂ omni-directionalÂ in one plane.
For long and mediumÂ wavelengthÂ frequencies,Â tower arraysÂ are used in most cases as directional antennas.
Figure 2.2: An example of directional antenna
2.3.3 Omni-directional antenna
AnÂ omni-directional antennaÂ is anÂ antennaÂ system which radiates power uniformly in one plane with a directive pattern shape in a perpendicular plane. This pattern is often described as "donut shaped". Omni-directional antenna can be used to link multipleÂ directional antennasÂ in outdoor pointÂ systems including cellular phone connections and TV broadcasts.
Figure 2.3: An example of omni-directional antenna
Mobile systems are presently being advanced toward fourth generation (4G) systems.
There are five major trends in modern mobile systems:
1. Progress of personalization.
2. Advancement of globalization.
3. Increase of multimedia services.
4. Deployment of multidimensional network.
5. Sophistication of mobile systems by implementing software processing.
The typical trends in modern mobile systems are listed in Figure 2.4, in which related demands and antenna structure are illustrated, and these are discussed in the following sections.
Figure 2.4 Trend in mobile communication and antenna structure.
Remarkable personalization has been seen in recent mobile terminals. This has been spurred not only by equipment downsizing, but also by the enhancement of functions of mobile terminals, especially of mobile phone systems. Modern mobile phones are equipped with functions to obtain various content, including functions of personal entertainment such as games, movies, TV broadcasting, and music, in addition to personal telephone use. Some mobile phones have the capability of ticketing, banking, navigation with GPS, e-mailing, and connection to the Internet for receiving information services. These mobile phones should be recognized as being no longer merely ''telephones,'' but as sophisticated information terminals.
The downsizing of mobile terminals has also given impetus to the personalization of mobile systems because the smaller terminals are more convenient to carry and easier to operate. There was a time when mobile phone manufacturers were competing on downsizing dimensions and reducing weight and volume of mobile phones. Downsizing gave rise to severe problems for antenna designers: the requirement of smaller antennas for downsized terminals without degradation of the antenna performance, and conversely with enhancement of antenna functions, and realization of wideband and multiband operation.
On the contrary, mobile broadband systems such as WMAN and worldwide interoperability for microwave access (WiMAX), which deal with high data rate signals, employ generally functional antennas such as adaptive arrays and MIMO systems.
Globalization of communication systems, including mobile systems, has progressed with satellite systems, which are classified by their orbits: low Earth orbit (LEO), medium Earth orbit (MEO), and geostationary orbit (GEO). However, the global communication services do not depend on satellite systems alone, but also on wired systems like Internet Protocol (IP)-based networks, which have worldwide linkage and also connections to wireless mobile networks. In addition, there are also wireless systems in which mobile terminals can roam from country to country, where the same network services are available.
The typical systems are GSM systems, which have deployed their networks worldwide, and some 3G systems, including WCDMA and CDMA2000 systems. Dual and triple band antennas are mounted on mobile terminals for these systems. Some mobile phones install a pentaband antenna and can operate in areas where both 2G and 3G services in different frequency bands are available, in addition to receiving GPS information at the same time.
2.4.3 Multidimensional Networks
A typical example is the combination of communication systems and broadcasting systems; one is the TV broadcasting through communication satellite systems and another is the terrestrial digital TV broadcasting for mobile terminals, including mobile phone handsets. The latter is referred to as ''one segment broadcasting,'' because one segment of the 13 orthogonal frequency division multiplexing (OFDM) segments is exclusively designed for broadcasting to mobile terminals.
Furthermore, a system referred to as fixed mobile convergence (FMC) has been in practical use recently. The mobile network is combined with a wired network at a home or office environment; thus, users use a mobile phone just as a wire line subscriber's phone at home, while alternatively using it as an ordinary mobile phone in the outdoor environment.
2.5 Brief Historical Review of Design Concept
Progress of antenna technology had reached together with progress portable phones and various WMS. Essential factors to be considered in antenna design are as follows:
Integration with nearby materials.
Two of the last items, multiband and built-in, are included according to the recent trend.
2.6 System Design and Antennas
Antennas cannot be designed in isolation from their host equipment, and system design is an essential technological approach in the realization of high-performance radio equipment operating to a critical specification.
The factors that a system designer would list include the following:
Zone configurations: defining signal coverage and antenna patterns.
Base station antennas: downsizing, height, physical constraints, and requirements for beam shaping, adaptive control, and multiband.
Noise levels: thermal, interference, and environmental.
Interference: its level and nature and co-channel and adjacent channel effects.
Signal requirements: optimal frequency of operation, bandwidth, inter modulation effects, and effective utilization of frequency spectrum.
Mobile terminals: downsizing, planar structure, multiband, built-in structure, adaptive control.
Cost of development and subsequent manufacture.
Reliability: servicing required and ease of access, and costs.
Vulnerability to damage: exposure to weather, corrosion, and durability against environmental conditions, operator's rough handling.
Network operation requirements: connectivity to IP network WAS, and so forth.
2.7 Some fundamental issues of small terminal antennas
2.7.1 Downsizing techniques for terminal antenna
The small antenna types can be classified according to their geometry: dipoles, slots, and cavities. From these fundamental antenna types more complex geometries can be developed.
The simplest omni-directional type of antenna is the dipole. The external antenna on a mobile terminal can be considered as an unbalanced dipole. Usually we call it a monopole antenna, because the antenna element is much smaller than the actual handset chassis size. Slot antennas, also called magnetic dipoles, can be seen from a long, narrow opening on a metallic surface. Notch antennas and IFA antennas are type of slot antennas. The planar inverted-F antenna (PIFA) can be considered as a mixed dipole and slot antenna. The cavity antenna in its simplest cases can be a patch antenna or a DRA antenna.
Many size reduction techniques for small antenna have been proposed. The common techniques applied to reduce antenna size are folding configurations, surface etching, shorting walls or pins, or utilizing high dielectric material loading. However, there is always some performance degradation when reducing the size.
2.7.2 Physical Limits of a Mobile Terminal Antenna
The performance of an electromagnetic passive device is sensitive to its electrical size compared to the wavelength, that is, given an operating wavelength and certain performance requirements, a small antenna cannot be made arbitrarily small. The bandwidth, losses, and dimensions of the antenna are closely interrelated. When the antenna size is smaller than a half wave dipole, the performance (bandwidth and efficiency) will be reduced when size is reduced.
Another parameter for small antennas is the bandwidth, which is related to the quality factor (Q). The quality factor Q is defined as the ratio of the time-average, non propagating energy to the radiated power of an antenna. This parameter is a quantity of enormous interest when designing small antennas because of its lower bound, which provides knowledge of how small an antenna can be constructed for a given certain bandwidth.
2.7.3 Impact of the Ground Plane Size and Phone Form
When considering antennas for mobile communications terminals in the practical case, the whole terminals, and even the human body, have their contribution to the radiation and losses. The effective antenna size should be equivalent to the antenna element size plus a part of the ground plane (handset chassis). It is not a simple task to calculate the equivalent size of the antenna in a real case. It is important to determine the fact that integrating an antenna in a terminal will affect its actual behavior regarding both bandwidth and radiation characterizations. Figure 2.2 shows an example of current distributions at low and high bands of a PIFA antenna mounted on a 100 Ã- 40-mm PWB of a bar phone. The radiation patterns of the handset at 900 MHz and 1,800 MHz are shown in Figure 2.3 and Figure 2.4. It has a nearly omni-directional pattern at 900 MHz, and has an irregular directive pattern at 1,800 MHz.
The ground plane sizes have influence upon the matching characteristics, the impedance bandwidth, the radiation patterns and the interaction with the user. Different phone forms have different ground plane features, which will affect the antenna performance.
(a) (b) (c) (d)
Figure 2.5: The current distribution of a PIFA handset antenna on a finite ground plane: currents at the (a) back and (b) front sides of handset at 900 MHz; and currents at the (c) back and (d) front sides of handset at 1,800 MHz. The PWB contributes greatly to radiation from the whole handset. The current at the front side is less than at the back side. It has different distributions in low and high bands.
Figure 2.6: The radiation pattern of a handset at 900-MHz band of the antenna shown in figure 2.2. It has a uniform omni-directional and nearly linearly polarized pattern.
Figure 2.7: The radiation pattern of the handset at 1,800 MHz of the antenna in Figure 2.2 has some irregular shape, the pattern is more directional, it has more minimums, and the pattern usually has high cross-polarization.
2.7.4 Extendable Antenna
In all cases the near field is a concern when the human body is included. Less current on the chassis is desired in this case. To overcome the small antenna limitation and reduce the human body absorption and the near field effects, an extendable antenna was commonly used, especially on lower cellular frequency bands. In the retracted mode, the bottom antenna, such as a helix or a meander, acts as a stubby antenna. In the extended mode, the whip antenna can significantly reduce the induced current on the phone chassis; and it has higher radiation efficiency in the talking position. The user absorption can be significantly reduced. An example of an extendable antenna is shown in figure 2.5.
Figure 2.8: An example of an extended whip antenna for a mobile phone.
3.1 Design of Antenna
Planar Inverted-F Antenna (PIFA)
Compact size, light weight, conformity built in, omni-directional, multi-band operation and low fabrication cost are required for modern mobile phone antenna . Conventional antennas such as helical and monopole antennas do not meet such requirements. The ideal choice for mobile phone is PIFA antenna because of the property of operating at multi-band, and can be incorporated into mobile phone chassis with no extending parts .
The Inverted F Antenna (IFA) typically consists of a rectangular planar element located above a ground plane, a short circuiting plate or pin, and a feeding mechanism for the planar element . The Inverted F antenna is a variant of the monopole where the top section has been folded down so as to be parallel with the ground plane. This is done to reduce the height of the antenna, while maintaining a resonant trace length. This parallel section introduces capacitance to the input impedance of the antenna, which is compensated by implementing a short-circuit stub. The stub's end is connected to the ground plane.
PIFA is a combination of micro strip antenna (MSA) and Wired Inverted-F Antenna . It begins with the idea of loading the antenna with high dielectric layer. MSA is a type of low profile antenna with a high dielectric constant substrate. This configuration can make the resonant size of the antenna smaller.
Figure 3.1: Planar Inverted-F Antenna
Figure 3.2: Inverted-F Antenna
3.2 Advantages of PIFA.
The advantages of PIFA are:
It can be hiding into the housing of the mobile compare with whip/rod/helix antennas.
Having reduced backward radiation toward the user's head, minimizing the electromagnetic wave power absorption (SAR) and increase antenna performance.
PIFA it exhibits moderate to high gain in both vertical and horizontal states of polarization.
3.3 Antenna Simulation
This antenna simulation for this project will use AWR TV's Microwave Office. In this chapter, I will discuss about the simulation software.
3.3.2 AWR TV's Microwave Office
Microwave Office design suite is the industry's fastest growing microwave design platform and has completely revolutionized the communications design world by providing users with a superior choice. Built on the unique AWR high-frequency platform with its open design environment and unified data model, Microwave Office design suite offers unparalleled ease of use, powerful technologies, and unprecedented openness and interoperability, enabling integration with best-in-class tools for each part of the design process . Microwave Office software includes all of the essential technology: linear and non-linear circuit simulators, EM analysis tools, integrated schematic and layout, statistical design capabilities, and parametric cell libraries with built-in design rule checking (DRC). The 2006 product release continues to deliver key productivity improvements, such as faster EM simulation, faster and higher capacity layout, and a more integrated EM editor, that shorten design cycle time and speed time-to-market for RF/microwave products.