Transcript
Presented by Ms.R.Krishnaveni
Assistant Professor Department of ECE KIT-Kalaignarkarunanidhi Institute of Technology
CONTENTCONTENT INDRODUCTIONINDRODUCTION PRINCIPLEPRINCIPLE CONSTRUCTION CONSTRUCTION WORKING.WORKING. PICTURE OF ANTENNA.PICTURE OF ANTENNA. ADVANTAGES ADVANTAGES DISADVANTAGES.DISADVANTAGES. INTRODUCTION.INTRODUCTION. APPLICATIONS.APPLICATIONS.
INTRODUCTIONINTRODUCTION The Yagi-Uda antenna or Yagi Antenna is one of the most brilliant antenna designs. It is simple to construct and has a high gain typically greater than 10 dB.
The Yagi-Uda antennas typically operate in the HF to UHF bands (about 3 MHz to 3 GHz) and Covers 40 to 60 Km.
A Directional Antenna System Consisting of an array of Coupled Parallel Dipoles. This is commonly known as Yagi-uda or Simply Yagi Antenna.
Yagi-uda Antenna is familiar as the Commonest kind Of Terrestrial TV Antenna to be found on the Roof tops of houses.
PRINCIPLEPRINCIPLE
Yagi-uda antenna is an electromagnetic device that collects radio waves.
An antenna tuned to a particular frequency will resonate to a radio signal of the same frequency
CONSTRUCTIONCONSTRUCTION
THERE ARE THREE TYPES OF ELEMENTS:
THE REFLECTOR (R) THE DRIVEN ELEMENT (D) THE DIRECTORS (DI)
CONSTRUCTIONCONSTRUCTIONDRIVEN ELEMENT :The driven element of a Yagi is the feed point where the feed line is attached from the transmitter to the Yagi to perform the transfer of power from the transmitter to the antenna.
A dipole driven element will be "resonant" when its electrical length is 1/2 of the wavelength of the frequency applied to its feed point.
The feed point in the picture above is on the center of the driven element.
CONSTRUCTIONCONSTRUCTIONDIRECTOR :The director is the shortest of the parasitic elements and this end of the Yagi is aimed at the receiving station. It is resonant slightly higher in frequency than the driven element, and its length will be about 5% shorter, progressively than the driven element.
The directors lengths can vary, depending upon the director spacing, the number of directors used in the antenna, the desired pattern, pattern bandwidth and element diameter.
The amount of gain is directly proportional to the length of the antenna array and not by the number of directors used.
CONSTRUCTIONCONSTRUCTIONREFLECTORThe reflector is the element that is placed at the rear of the driven element (The dipole).
It's resonant frequency is lower, and its length is approximately 5% longer than the driven element. It's length will vary depending on the spacing and the element diameter
The spacing of the reflector will be between .1 wavelength and .25 wavelength. It's spacing will depend upon the gain, bandwidth, F/B ratio, and side lobe pattern requirements of the final antenna design.
WorkingWorking Reflector here derives it’s main Power from a driver , it reduces the
signal strength in it’s own direction and thus reflectes the radiation towardes the driver and directors.
The driven element is where the signal is intercpeted by the receiving equipment and has the cable attached that takes the recevied signal to the receiver
The radiator and driver can be placed more closer to increase the radiation length towards the directors.
WAVELENGTH = 3*10^8WAVELENGTH = 3*10^8 FERQUENCY(MHz) FERQUENCY(MHz)
To Determine The Wave-length Of A Radio Station With A Frequency Of 92.1 Mhz , SIMPLY DIVIDE THE SPEED OF LIGHT ( 300,000,000 METERS PER SECOND) BY 92,100,000 CYCLES PER SECOND.
The Seconds Cancels Out In The Formula With The Wave-length Ending Up At 3.26 Meters. In Other Words The Waves Passing You Buy Right Now From A Radio Station Transmitting At 92.1 Mhz ARE 3.26 Meters Long.
FIVE ELEMENT YAGI-UDA FIVE ELEMENT YAGI-UDA
REFLECTOR
DRIVER
Radiation pattern formedbY the directional antenna
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Radiation pattern formedbY the directional antenna
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The antenna exhibits a directional pattern consisting of a main forward lobe and a number of spurious side lobes.
The main one of these is the reverse lobe caused by radiation in the direction of the reflector.
The antenna can be optimised to either reduce this or produce the maximum level of forward gain.
PICTURE OF ANTENNA
ELEVEN ELEMENT’S OF YAGI-UDA ANTENNA
FORWARD DIRECTION
PICTURE OF ANTENNA for TVPICTURE OF ANTENNA for TV SIGNAL RECEPTION
The Yagi antenna is a particularly useful form of RF antenna design. It is widely used in applications where an RF antenna design is required to provide gain and directivity. In this way the optimum transmission and reception conditions can be obtained.
PICTURE OF ANTENNA IN RADAR
Radar using group of Yagi-antenna with antenna gain G = 69
ADVANTAGES It has a Moderate Gain Of About 7 (dB).
It is a Directional Antenna.
Can be used at High Frequency.
Adjustable from to Back Ratio.
DISADVANTAGES The Gain is not Very High.
Needs a large number of Elements to be used.
APPLICATIONS Yagi-uda antenna is a unidirectional antenna. Used for
television recivers.They provide better tunning because of large bandwidth and has decent gain.
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