Basic Types Of Smart Antennas Computer Science Essay

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There are two basic types of smart antennas. As shown in Fig. 6.1, the first type is the phased array or multibeam antenna, which consists of either a number of fixed beams with one beam turned on towards the desired signal or a single beam (formed by phase adjustment only) that is steered toward the desired signal. The other type is the adaptive antenna array as shown in Fig. 6.2, which is an array of multiple antenna elements, with the received signals weighted and combined to maximize the desired signal to interference plus noise power ratio. This essentially puts a main beam in the direction of the desired signal and nulls in the direction of the interference.

A smart antenna is therefore a phased or adaptive array that adjusts to the environment. That is, for the adaptive array, the beam pattern changes as the desired user and the interference move; and for the phased array the beam is steered or different beams are selected as the desired user moves.

Nearly every company the WTEC panel visited is doing significant work in smart antennas. Indeed, some companies placed strong emphasis on this research. In particular, researchers at NEC and NTT stated that they felt that smart antenna technology was the most important technology for fourth generation cellular systems. Researchers at Filtronics and other companies agreed that smart antenna technology was one of the key technologies for fourth generation systems. The reasons appear below.

Fig. 6.1. Phased array.

Fig. 6.2. Adaptive array.

Published: July 2000; WTEC Hyper-Librarian

Actually it is converted to EM radiation over a very wide band, from low frequency radio to very high frequency UV. Only a fraction is converted to light.

wikipedia:

EMR carries energy-sometimes called radiant energy-through space continuously away from the source (this is not true of the near-field part of the EM field). EMR also carries both momentum and angular momentum. These properties may all be imparted to matter with which it interacts. EMR is produced from other types of energy when created, and it is converted to other types of energy when it is destroyed. The photon is the quantum of the electromagnetic interaction, and is the basic "unit" or constituent of all forms of EMR. The quantum nature of light becomes more apparent at high frequencies (or high photon energy). Such photons behave more like particles than lower-frequency photons do.

In classical physics, EMR is considered to be produced when charged particles are accelerated by forces acting on them. Electrons are responsible for emission of most EMR because they have low mass, and therefore are easily accelerated by a variety of mechanisms. Rapidly moving electrons are most sharply accelerated when they encounter a region of force, so they are responsible for producing much of the highest frequency electromagnetic radiation observed in nature. Quantum processes can also produce EMR, such as when atomic nuclei undergo gamma decay, and processes such as neutral pion decay.

EMR is classified according to the frequency of its wave. The electromagnetic spectrum, in order of increasing frequency and decreasing wavelength, consists of radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. The eyes of various organisms sense a small and somewhat variable but relatively small range of frequencies

CHAPTER 1

Due to the rapid advancement in mobile and wireless communication system the need for efficient antenna design with good radiation capability

multiple simultaneous steerable beams and small size is becoming imperative. Research work to improve the antenna design for obtaining desired goals

has been carried out by various researchers in the last few decades. Smart antennas with wide scanning angle capabilities have emerged as a result of

continuous effort in making efficient antenna design. Modern day cutting edge applications like Radar and satellite communication require antennas

with wide scanning angle capabilities and good performance over broad frequency range. The spectrum is limited and the frequency of operation for a

device keeps on increasing. At higher frequencies, only direct waves are useful and the effective range is greatly reduced. Hence as the frequency

increases, the signal carrying large bandwidth information becomes more and more directional. At higher frequencies the absorption decreases and

maximum use of sky waves can be done to reliably transmit and receive the information from certain direction. A beam-forming device that produces

true-time delay, wideband, wide-angle and steerable beam is desirable. These antennas are efficient, and can be made sharply directive, thus greatly

increasing the strength of the signal transmitted in a desired direction. The power received is inversely proportional to the square of the distance

from the transmitter, assuming there is no attenuation due to absorption or scattering. The narrow beam produces good isolation between adjacent

radiation elements using space diversity; hence multiple beams are possible to be simultaneously obtained by reusing the antenna structure

A phased array is the essential device that utilizes the beam-forming network to radiate

energy into free space. Since decades, it has been widely adopted in many radar and

satellite systems to produce electronically-controlled beam scanning. Earlier, array

systems have been restricted for military applications due to high cost and complexity. In

recent years, low cost high performance array and its supporting devices have been

realized using printed circuit technology. Array-based commercial applications such

as wireless point-to-point communications and auto-collision avoidance radar have

emerged. Due to allocation of new bands for commercial ultra-wideband (UWB) [1] and Extremely High Frequency (EHF) applications [2], low-profile high

performance arrays have been under investigation. The low-cost high-performance beam-forming networks would facilitate new application development

The aim of this research work is to optimize the performance of Rotman lens in terms of minimizing the phase error and improving the scanning

capabilities with low loss using GA optimizing techniques. The antenna should be capable of producing multiple beams which can be steered without

changing the antenna orientation. The lens feeds a linear antenna array of Microstrip patch antennas which acts as radiating elements. Existing

design theory will be improved in terms of minimized phase errors and scanning capabilities. Prototype of the Microwave lens has been implemented

Optimization technique has been proposed to improve the scanning capabilities of the lens. A Rotman lens and Microstrip patch antenna have been

designed, fabricated and tested, and they are covered throughout these topics. The simulation and measurement data of the fabricated PCB's are used

to support the proposals in this dissertation

Before we begin, it is important to familiarize with the basic concepts of microwave, electromagnetic wave theory, antenna fundamentals, phased array

and beam-forming network because it forms the basis of this dissertation work

Basics of Microwave and Electromagnetic Wave theory

One can understand Microwaves as those waves whose wavelengths range from one mm to one metre, with frequencies between 0.3 GHz

GHz

Depending on the range they are classified as various bands

L-band: 1-2 GHz (1,000-2,000

S-band: 2-4 GHz (2,000-4,000

C-band: 4-8 GHz (4,000-8,000

X-band: 8-12.5 GHz (8,000-12,500

Lower K-band: 12.5-18 GHz (12,500-18,000

Upper K-band: 26.5-40 GHz (26,500-40,000

Marine radar systems commonly operate in the S and X bands, while satellite navigation system signals are found in the L-band. The break of the K band into lower and upper ranges is necessary because the resonant frequency of water vapor occurs in the middle region of this band, and severe absorption of radio waves occurs in this part of the spectrum. Electromagnetic wave can combine with each other and with the matter the effects like reflection,diffraction, polarization, scattering, diffraction, and few more. Absorption ,generally associated with the visible light is of much importance in the context of microwave propogation..Micro as the name suggests in Microwaves means small waves as compared to waves used in typical radio broadcasting.Generally microwave technology is used for point-to point communications (i.e., non broadcast uses) as they have more narrow and directional beams . They work in higher frequency range and thus allows high data rate on a broad bandwidth system. As the frequency range is high, the size of antenna is generally smaller because of the fact that the size and the frequency of the antenna are inversely proportional to each other. The broad area of applications are transmission of data in, TV, and telecommunications and can be used in transmissions between ground stations and to and from satellites. They are also majorly used in radar technology.

Electromagnetic energy can be described as different kinds of energies released or absorbed by the charged particles into the space where they show some properties like a wave. It is with the help of Maxwell's equations that many fundamental theories for complicated designs could be explained

Maxwell equations

1.1 Maxwell's Equations

Maxwell's equations are used to describe all the electromagnetic phenomena. There are four laws to explain the phenomena. The first is Faraday's law of induction, the second is Ampere's law which was modified by Maxwell to include the displacement current ∂D/∂t, the third and fourth are the Gauss' laws for the electric and magnetic. Maxwell's equations describe how electric and magnetic fields are generated and altered by each other and by charges and currents.

Maxwell's equations are

The quantities E (V/m) and H(Amp/m) are the electric and magnetic field intensities.The quantities D(coulomb/m2) and B (weber/m2)are the electric and magnetic flux densities .D is also called the electric displacement, and B, the magnetic induction.The quantities ρ[coulomb/m3)and J (ampere/m2)are the volume charge density and electric current density (charge flux) of any external charges (that is, not including any induced polarization charges and currents.) The charge and current densities ρ, J may be thought of as the sources of the electromagnetic

fields. For wave propagation problems, these densities are localized in space;

for example, they are restricted to flow on an antenna. The generated electric and magnetic fields are radiated away from these sources and can propagate to large distances

Antenna and its array: An antenna in a telecommunications system which is used to couple the radio frequency energy from the transmitter to the outside world and from the outside world to the receiver .The radio frequency energy distributed in the space and collected from the space has a deep influence on efficiently using the spectrum. Besides observing the main role of an antenna as a transmitting and receiving element the main aim is to see the focus shifting from omni directional antenna (equal radiation in all directions and no preferable direction) to Directional antenna (one direction)and beyond that from the use of single element to array of elements working as radiators to have efficient and better performance of the system.

Omnidirectional Antennas:The antennas those have been read about are the simple dipole antenna, which radiates and receives equally well in all directions[]Azhar:smart antenna systems presentation].

Figure 1: Omnidirectional

This was quiet adequate for simple RF environments where there was no knowledge of the users' whereabouts .Due to this unfocused approach, the signal was scattered in all directions trying to reach to the desired users. The energy which was always in limited amount was wasted by sending the signals in all directions to trace out for user. The only way to overcome the above mentioned drawback was to increase the power level of the broadcasting transmitters. The increase in the power increases the level of interference in the same or adjoining cells. In uplink applications i.e. from the user to base station omnidirectional antennas offers no preferential gain for the signals of served users. The single-element approach cannot selectively reject signals interfering with those of served users and has no spatial multipath mitigation or equalization capabilities. Therefore,omnidirectional strategies directly and adversely impact spectral efficiency, limiting frequency reuse

Directional Antennas and Sectorized Systems

A single antenna which are very directive in nature and it radiates and receives power in particular direction than in a all directions at same time.Sectorized antenna system can be very good example of directive antenna in which a given cellular area can be divided into large no. of sectors depending upon the type of sectoring ,that are covered using same base station .Each sector is treated as a different cell in the system, the range of which can be greater than in the omni directional case, since power can be focused efficiently to a smaller area. This is called as antenna element gain. Additionally, sectorized antenna systems increase the possible reuse of a frequency channel in such cellular systems by reducing potential interference across the original cell. However, since each sector uses a different frequency to reduce co channel interference, handoffs (handovers) between sectors are required. Narrower sectors give better performance of the system, but this would result in to many handoffs. While sectorized antenna systems multiply the use of channels, they do not overcome the major disadvantages of standard omnidirectional antennas such as filtering of unwanted interference signals from adjacent cells

1.Sheikh.k.; Gesbert D; Gore.D; Paulraj.A "Smart antennas for broadband wirelessacess networks" "IEEEcommunications Magazine" volume 37,issue 11,nov 1999. Page 100-105.

2. www.iec.org.

3. www.google.co.in

Figure 2: Sectorized antenna

Smart Antenna Systems [www.scribid.com]: A smart antenna is a phased ,multiple or adaptive array that adjusts to the environment. The Adaptive antenna system uses antenna of various types and configurations, which can be classified as phase array, multiple antennas or combination of both. Most desired antenna is MIMO which is multiple input multiple output, which use antenna array and smart signal processing and is used to identify the direction of arrival of the signal (DOA) using smart signal processing algorithm. They are generally used to calculate beamforming vectors which are used to track and locate the antenna beam on the target or the mobile. The antenna could optionally be any sensor. Smart antenna techniques are used notably in acoustic signal processing, track and scan RADAR, radio astronomy and radio telescopes, and mostly in cellular systems like W-CDMA and UMTS.Smart antennas have two main functions of DOA estimation and Beamforming .Earlier adaptive antennas were used as RADAR antenna with the side lobe elimination characteristics. The side lobe eliminator antenna consists of a conventional Radar antenna where output is coupled with that of much lower gain auxiliary antennas. The gain of auxiliary antenna is slightly greater than the gain of maximum side lobe of radar antenna. The smart antenna system has to estimate the direction of arrival of the signal for that it uses a technique such as MUSIC (Multiple Signal Classification) estimation of signal parameters via rotational invariance techniques (ESPRIT) algorithms. Each of these antenna configurations have several ports where received signals Pr appears in response to sources located in the antennas field of view [AWP by R.L.Yadava]. By characteristics, phased arrays have identical elements each of which has port where the output signal is represented as

Where

Where

Pm- Power radiated by mth source

Gm- Gain of antenna used by mth source

Rm - Distance between mth source and adaptive antenna

f- Operating frequency

Fn-Amplitude that relates to a signal at the antenna port

Hn-Phase that relates to a signal at the antenna port

-It represents the angular position of the mth source and measured in a suitable spherical co-ordinate system.

In most of the adaptive phased arrays, Fn is identical whereas Hn is generally different for all elements of array. For signals at the output port of multiple beam antenna the Hn is nearly equal and Fn is generally different .This fundamental difference phased array and

multiple beam antenna results in the inherently larger bandwidth .

Figure 3: Smart antenna

Beamforming [scribid.com]: Beam forming is the method in which all the phases of the signals are added constructively to create a radiation pattern in the direction of the targets desired, and nulling the pattern of the targets that are undesired or interfering targets. This can be done with a simple FIR tapped delay line filter. The weights of the FIR filter may also be changed adaptively, and used to provide optimal beam forming [en.wikipedia.org] antennas. It is the process in which amongst the generated number of fixed beams only one beam is turned towards the desired signal or a single beam formed by phase adjustment is steered towards the desired signal .Adaptive antenna array is an array of multiple antenna elements with the received signals weighted and combined to maximize the desired signal to interference and noise (SINR) ratio. This means that the main beam is put in the direction of the desired signal while nulls are in the direction of the interference.

A smart antenna system combines large number of antenna elements with a signal processing capability to optimize its radiation as well as reception pattern automatically in response to the signal environment[scribid.com].Smart antenna systems are customarily categorized as either switched beam or adaptive array systems. Switched beam antenna system forms multiple fixed beams with high sensitivity in particular directions. These antenna systems detect signal strength, chosen from one of several predetermined, fixed beams, and switch from one beam to another as demand changes throughout the sector instead of shaping the directional antenna pattern with the metallic properties and physical design of a single element (like a sectorized antenna), switched

beam systems combine the outputs of multiple antennas in such a way as to form finely sectorized (directional) beams with more spatial selectivity than it approach. Smart Antennas are arrays of antenna elements that change their antenna pattern dynamically to adjust to the noise, interference in the channel and mitigate multipath fading effects on the signal of interest. The difference between a smart (adaptive) antenna and "dumb" (fixed) antenna is the property of having an adaptive and fixed lobe-pattern, respectively. The secret to the smart antennas' ability to transmit and receive signals in an

adaptive, spatially sensitive manner is the digital signal processing capability present. An antenna element is not smart by itself; it is a

combination of antenna elements to form an array and the signal processing software used that make smart antennas effective. This shows that smart

antennas are more than just the "antenna", but rather a complete transceiver concept

Adaptive Antenna Arrays

Adaptive antenna arrays can be considered the smartest of the lot. An Adaptive Antenna Array is a set of antenna elements that can adapt their

antenna pattern to changes in their environment.Each antenna of the array is associated with a weight that is adaptively updated so that its gain in

a particular look-direction is maximized, while that in a direction corresponding to interfering signals is minimized. In other words, they change

their antenna radiation or reception pattern dynamically to adjust to variations in channel noise and interference, in order to improve the SNR

signal to noise ratio) of a desired signal. This procedure is also known as 'adaptive beamforming' or 'digital beamforming'.Conventional mobile

systems usually employ some sort of antenna diversity (e.g. space, polarization or angle diversity). Adaptive antennas can be regarded as an extended

diversity scheme, having more than two diversity branches. In this context, phased arrays will have a greater gain potential than switched lobe

antennas because all elements can be used for diversity combining

In antenna theory, a phased array is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in

such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.An antenna

array is a group of multiple active antennas coupled to a common source or load to produce a directive radiation pattern. Usually, the spatial

relationship of the individual antennas also contributes to the directivity of the antenna array. Use of the term "active antennas" is intended to

describe elements whose energy output is modified due to the presence of a source of energy in the element (other than the mere signal energy which

passes through the circuit) or an element in which the energy output from a source of energy is controlled by the signal input. One common

application of this is with a The relative amplitudes of - and constructive and destructive interference effects among - the signals radiated

individual antennas determine the effective radiation pattern of the array. A phased array may be used to point a fixed radiation pattern, or to scan

rapidly in azimuth or elevation. Simultaneous electrical scanning in both azimuth and elevation was first demonstrated in a phased array antenna at

Hughes Aircraft Company, Culver City, CA, in 1957 (see Joseph Spradley, "A Volumetric Electrically Scanned Two-Dimensional Microwave Antenna Array

IRE National Convention Record, Part I - Antennas and Propagation; Microwaves, New York: The Institute of Radio Engineers,

phased arrays are used in sonar, it is called beamforming

ESA:Functioning of a Radar system is generally by connecting an antenna to a powerful radio transmitter to emit a short pulse of signal. The

transmitter is then disconnected and the antenna is connected to a sensitive receiver which amplifies any echos from target objects. By measuring the

time it takes for the signal to return, the radar receiver can determine the distance to the object.To scan a portion of the sky, the radar antenna

must be physically moved to point in different directions. An active electronically scanned array (AESA), also known as active phased array radar is

a type of phased array radar whose transmitter and receiver functions are composed of numerous small solid-state transmit or receive modules .AESA

radars aim their "beam" by emitting separate radio waves from each module that interfere constructively at certain angles in front of the antenna

They improve on the older passive electronically scanned radars by spreading their signal emissions out across a band of frequencies, which makes it

very difficult to detect over background noise. AESAs allow ships and aircraft to broadcast powerful radar signals while still remaining stealthy

Modern antenna applications such as MIMO Systems,Smart Antennas, Phased Antenna Arrays, etc, require the capability to handle several beams

independently

Beamforming or spatial filtering is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is

achieved by combining elements in a phased array in such a way that signals at particular angles experience constructive interference while others

experience destructive interference. Beamforming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity. The

improvement compared with omnidirectional reception/transmission is known as the receive/transmit gain (or loss

Beamforming can be used for radio or sound waves. It has found numerous applications in radar, sonar, seismology, wireless communications, radio

astronomy, acoustics, and biomedicine. Adaptive beamforming is used to detect and estimate the signal-of-interest at the output of a sensor array by

means of optimal (e.g., least-squares) spatial filtering and interference rejection. To change the directionality of the array. When transmitting, a

beamformer controls the phase and relative amplitude of the signal at each transmitter, in order to create a pattern of constructive and destructive

interference in the wavefront. When receiving, information from different sensors is combined in a way where the expected pattern of radiation is

preferentially observed. Conventional beamformers use a fixed set of weightings and time-delays (or phasings) to combine the signals from the sensors

in the array, primarily using only information about the location of the sensors in space and the wave directions of interest. In contrast, adaptive

beamforming techniques generally combine this information with properties of the signals actually received by the array, typically to improve

rejection of unwanted signals from other directions. This process may be carried out in either the time or the frequency domain

Applications

Beamformers have much higher Gain than omnidirectional antennas: Increase coverage and reduce number of antennas

Beamformers can reject interference while omnidirectional antennas cat improve SNR and system capacity

Beamformers provide N-fold diversity Gain of omnidirectional antennas: increase

system capacity(SDMA

Beamformers suppress delay spread:improve signal quality

Beamforming can be used for radio or sound waves. It has found numerous applications in radar, sonar, seismology, wireless communications, radio

astronomy, acoustics, and biomedicine. Adaptive beamforming is used to detect and estimate the signal-of-interest at the output of a sensor array by

means of optimal (e.g., least-squares) spatial filtering and interference rejection

Scope

In this dissertation, optimized design of Rotman lens with linear array of microstrip patch antenna as radiating elements is

important electrical parameters deduced are phase error, maximum scanning angle, array factor, side lobe level, spill over losses, return loss

bandwidth, antenna efficiency.Research work on Rotman lens antenna started way back in 1963 when W.Rotman and R.F.Turner published their research

work.In this work basic design equations of Rotman lens were derived for improving scanning capability of the lens along with the reduction in beam

to array port phase error. This work still remains the bench mark for researchers in this area. In this dissertation, new design equations are

explored by applying Genetic algorithm so as to reduce the phase error and improve the scanning angle. By improving these parameters effort has been

made to reduce the insertion loss,side lobe level, grating lobes and spill over losses for the designed Rotman lens. Various design parameters of

radiating elements are also kept in view like improvement in return loss,VSWR,antenna efficiency,gain and bandwidth. Ultimate aim is integration of

Microwave lens and patch radiating elements to generate a beam forming network and achive the desired goal. The classical lens design theories are

all based on focal lens schemes, which presumably achieve zero phase errors for limited number of given focal beam ports, thus the non-focal ports

have relatively high phase errors. The exploration of microstrip lenses and non-focal lenses leads to a method for improving scanning angle of

microwave lenses. Because of the constraints on focal equations, the existing lens theory can only design an asymmetric contour lens, which results

of a maximum scanning angle of 60 or 90 degrees. The concept of non focal lens design is chosen in this dissertation

beam and receiving ports to reoccupy a symmetric lens contour, scanning an azimuth region of 360 degree. It possesses most of the classical

Both simulation and measurement of the prototype lens have demonstrated very good results

The following chapters of the dissertation enumerate the design , analysis and optimization of microwave lens and linear array of microstrip

antenna which acts as the radiating elements. Chapter 2 gives the details of soft computing techniques used,.Chapter 3 reviews the

applications and design of microstrip patch antenna.Chapter 4 covers the detailed analysis of Rotman lens antenna and the improved

non-focal lens design scheme. The comparison with existing design methods are

Investigated by numerical simulations. Both simulation and measurement data are used in the analysis of Chapter 4. Chapter 5

integration of Rotman lens and MPA. Chapter 6 describes the prototype designed, fabricated, and tested, and both the simulation and the

used to prove the concepts. Finally, the dissertation is closed by conclusions and future perspectives in Chapter

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