CHAPTER -1INTRODUCTION Antennas are required every where ,any wireless communication requires antenna.The changes in the wireless communication taking different steps so as the antenna requirements. Eventhough the history of antenna is 100 years old , we are unable to design an antenna which can meet all the requirements of todays wireless commuication.The pioneer of the term antenna is Marconi in 19th century.MARCON’S 1st monoppole transmitting antenna Basically antenna is a wireless device which can transmit or receive tinformation through electro magnetic waves.They radiate the energy in to space from source to destination and also which converts electrical power into radio waves and vice versa.Antennas are used in many application in satellite communication.
In order to use the antenna for different applications the size of an antenna should be taken as major consideration and many modern techiniques are applied to reduce the size of an antenna .present day technology and developing technology depends upon the change in different parameters of antenna.1.
1Antenna Parameters:By knowing the parameters of an antenna such as beam width,radiation pattern,gain,directivity,Polarization,radiation intensity,radiation,power density,efficiency we can determine the characteristics of an antenna.1.1.1Radiation Pattern:Radiation pattern is the graphical representation of radiation properties of an antenna in spatial coordinates.It is of two types filed pattern and power pattern.Field pattern is the plot magnitude of electric or magnetic field with respect to the space co-ordinates.power pattern is the plot square of the magnitude of electric or magnetic field as a functionof space coordinates.we can describe the behaviour of an antenna in the far field region.
1.1.2 Beam Width:Beam width is the gap angle where the maximum power of an antenna is radiated .There are two considerations in beam width they are First null beam width and Half power beam width. 1.1.
3 Efficiency:It is the ratio of power radiated by antenna to the input power of an antenna .In other words we can say that how much amount of power will be radiated without return loss. Efficiency=power radiated/ input power1.1.4 Directivity:Directivity is defined as the ratio of radiation intensity in a given direction of an antenna to the radiation intensity averaged in all directions.For an antenna there is no specific direction.It can be determined by in which direction it has the maximum radiation intensity.
1.1.5 Gain:The term gain can be described as the how much amount power is transmitted in the direction of maximum radiation intensity to that of isotropic source. Gain=efficency *directivity1.1.
6 Radiation intensity:It is the measure of how far the maximum radiation occurs is nothing but radiation intensity.It is defined as power per unit solid angle.Radiation intensity (U)=R^2*W_radWhere U=radiation intensity R=radial distance W_rad=power radiated1.1.7 Voltage standing wave ratio (vswr):It is defined as the ratio of maximum voltage to the minimum voltage in standing wave. vswr Occurs whenever there is a impedence mismatch due to impedence mismatch power will not be effictively radiated and some amount of power is reflected back .
1.1.8 Polarization:Polarization gives the instantaneous direction of electric field .If the polarization occurs in straight line then it is called as the linear polarization. If it occurs in elliptical it is called as elliptical and if electric field in circular then it is called circular polarization. 1.1.9 Return loss:Return loss can be claculated by using S11 and S22 parameters,whenver there is a impedence mis match the power is not effictively radiated the power is not received by load and this occurs loss and if it returns then it is return loss.
RL=10log(Pr/Pi)Where Pr= power reflecte Pi=power from source1.2Antenna working: Antenna is a metal which is having the radiation as basic property. It radiates when it is Fed with some voltage as input the electrons in the metal produces electromagnetic radiation which is invisible they travel with a velocity of light and at receiver side these waves causes the electrons to move back and froth which is converted into original transmitted signal. An antenna transmits Signal from source to destination using electro magnetic waves propagated infree space.1.3 Fractal antenna: Fractal antenna is different from regular antennas which antennas which are having fixed band width whereas fractal antenna has wideband and dual bands.It uses self similar size or fractal shapes to form resonant frequiencies.
Fractal shapes they are very compact in size due to this they are used in applications like cellular telephone and microwave communications it can operate at different frequencies simultaneously. By using fractal shape the size of antenna is reduced. For example if we look at our mobile phone which has bluetooth,gps,wifi etc they work at diiferent frequency bands for all these we require diffferent antennas but we can replace those antenna by single fractal antenna which works at at higher frequencies and it is having wider band width we can use one antenna instead of many antennas. They undergo different iterations by using fractal geometry. Fractal shapes can be observed in nature also like mountains and trees etc.some of the fractal shapes are given below figure.
1.4 Monopole antenna: It is a radio antenna in which a conductor of rod shape is mounted perpendicularly on a conducting surface called as called ground plane. Basically monopole antenna isknown as resonating antenna as its characteristics are depending on the length. The fundamental form of monopole antenna is quarter-wavemonopole in which its length is ¼ of the radio waves wavelength it has been using A monopole antenna can be viewed as unlike the dipole antenna here the bottom half overtical dipole is replaced by conducting plane i.e ground plane at right angles to the remaining half. There are many types of monopole antennas in which ground plane usedmay be actual earth or any other.1.5 Feeding techniques:There are different types of feeding techniques used to design an antenna co-axialcable feed coupled feed ,aperture feed ,micro strip feed etc.
We can analyze the results of the antenna depending on the feeding technique.1.5.1 Co-Axial feed technique One of the most common techniques used for the design of any antenna is co-axial feed technique. patch is placed at the top of the substrate and at the bottom of the substrate ground plane is attached.
Its bandwidth ranges in between 2-5%. 1.5.2 Aperture feedIn this type of feeding technique the patch antenna which is radiating and the feed that is used is separated by the ground plane and by using a slot coupling between them takes place. It is having bandwidth in the order of 2-5%. 1.5.3 Micro-strip feed line In this type of feeding technique a strip which is conducting is placed at one of the edges of the patch antenna.
1.5.3 Proximity Coupled Feed Two dielectric substrates are used and a feed line is in between substrates and a radiating patch is on the upper substrate. The advantage of proximity coupled feed is it eliminates spurious oscillations, provides high bandwidth and helps in the optimization of individual performances 1.5.4 Coupled Feed: This is considered as indirect feed technique as it will not touch the antenna directly. It also offers some advantages like as it is not directly touching the antenna there should be some gap between the feed and the patch and this gap will produces some capacitance which will not allow the inductance to be entered into the feed.
Its bandwidth ranges in between 2-5%.CHAPTER -2LITERATURE REVIEW2.1Statement of purpose: The design of particular antenna gives description for the use of UWB applications by using fractal shapes for fabrication under required cut off frequencies. The overview of this paper describes the use of FRACTAL antenna for UWB applications using fractal shapes under different iterations and unit layout techniques.2.2 Literature Survey: Now a day’s wide band antenna are getting more useful in wireless communications. Conventional patch antennas do not provide wide band and ultra wide band. This can be achieved by using fractal antennas these are designed by using fractal geometry.
A better gain improvement was observed. A monopole antenna is attached with different fractal shapes and observed good return loss and gain value.
