 myself Rohini Merugu from Walshian Institute of Technology talking about the log periodic antenna. Learning outcomes, at the end of this video you will be able to explain the log periodic antenna and its feed types. You will be able to plot the radiation pattern of log periodic antenna. You will be able to list the applications of log periodic antenna. So, in history the log periodic antenna was invented by John Dunleavy in 1952 while working for the United States Air Force but was not credited to it due to the secret classification. So, this is the log periodic antenna which is shown here. What is a log periodic antenna? A log periodic antenna is a broadband multi element directional narrow beam antenna. It is a broadband multi element directional narrow beam antenna which has impedance and that has impedance in radiation characteristics which are regularly repetitive as a logarithmic function of excitation frequency. The individual components are often dipoles. The length and spacings of elements of the log periodic antenna increase logarithmically from one end to another. It is high bandwidth and moderate directivity. Log periodic antenna is a frequency independent antenna. When I say frequency independent antenna, can we talk about what is frequency independent antenna means? So, here is the answer. Frequency independent antenna which is called FI antenna, is it really completely frequency independent? No, it is not so, but frequency range is wide enough. So, frequency independent FI antennas are radiating structures capable of maintaining consistent impedance and pattern characteristic over multiple decade of bandwidths or multiple decade of bandwidths. Antennas theoretically have no limitation on bandwidth are called frequency independent. The lower frequency limit is determined by the size of the antenna and upper frequency limit is determined by the precision of construction. The electrical performance is not strictly independent of frequency rather it is periodic with the logarithm of the frequency. Hence, these antennas are named as logarithmic periodic or log periodic or simply LP antenna. LP stands for log periodic. Here is a structure of log periodic antenna. The log periodic LPDA means log periodic dipole array normally consists of series of half wave dipole elements. So, series of half wave dipole elements. A pair of metal rods positioned along the support beam lying along the antenna axis. So, metal rods which are positioned along the support beam, this is support beam lying along the antenna axis. The elements are spaced at the intervals following a logarithmic function of frequency. So, this spacing is following the logarithmic function of frequency and this is called as sigma or D. The successive elements gradually decrease in length along the boom. So, the lengths are successfully decreasing along the boom as you can see the lengths are decreasing. The relationship between the length is the function of tau. It is a function tau sigma and tau. These are the key design elements for log periodic dipole array. Point of excitation. The single element is provided excitation via these crisscross connection line. Here you can see this is the source of excitation and which is provided to the single element. So, to this element the excitation is provided. Then using the crisscross connection, this crisscross connection you can see the strangler parts. So, this crisscross connections are providing excitation to the next elements, but actual excitation is provided to the single element. So, by varying this point of excitation, the radiation pattern here we have shown the radiation pattern. The radiation pattern of the antenna also varies as the way that we are providing the excitation. What are the different ways that we can provide the excitation that is shown here? So, log periodic dipole array with various connections is shown. This is the log periodic dipole array where you can see this is the length, the length is then increasing. And here you can see the how the elements, these different elements are excited is the first connection is a straight connection. So, using the straight conductor we can excite these different elements. So, these straight conductors are there you can see. Second is a crisscross connection. That means the excitation is provided to this, then goes to this, then goes to this, likewise this is a crisscross connection. Or the excitation can be provided using coaxial connection. So, here is a coaxial line, this side is also coaxial line and these coaxial lines are exciting this elements. So, log periodic dipole array with the coaxial feed is shown here, which is providing the impedance around 50 to 75 ohm. And the log periodic array with the crisscross connection is shown here. See crisscrossed open wire line twin lead feed is shown. So, this array is providing the impedance around 300 ohm. So, here you can see the log periodic dipole array where you can see this distance is r 1 from this point from the boom starting point from here to the any particular element the distance is named as r n, then it goes to r n plus 1. Then this is the diameter, diameter is d n and then this diameter is d n plus 1 for the next. Then the length, length of the dipole individual, this length if it is l n, the next one is named as l n plus 1. So, why I am explaining this because the design factor tau can be given like this 1 upon tau equal to l n plus 1 upon l n which is equal to r n plus 1 upon r n which is equal to d n plus 1 upon d n which is also equal to s n plus 1 upon s n. s n is the spacing between the dipoles. You can see here spacing s n is also shown. The length l n locations r n from apex, from apex the location is r n, diameter d n the gap spacing s n, the gap spacing s n of the dipole elements increase the logarithmically as 1 upon tau. These are increasing as 1 upon tau and tau is log periodic dipole array design parameter which is also called as scale factor. What is the radiation pattern of log periodic dipole array? The radiation pattern of antenna is unidirectional. As you can see here log periodic dipole array is shown. You can see the radiation is in the forward direction like this and these are the minor loops on the opposite side. But the pattern if you see you can understand it is a unidirectional. With the main loop along the axis of the boom, this main loop is along the axis of the boom of the ends with the shortest elements. So, towards the shortest element the main beam is along the shortest elements. Each dipole element is resonant at wavelength approximately equal to twice of its length. So, each dipole element every element individual element is resonant at a wavelength which is approximately equal to twice of its length. The bandwidth of the antenna is approximately between the resonant frequencies of longest and shortest element. So, resonant frequency of shortest element, resonant frequency of longest element. So, the difference between that will be giving us the bandwidth of this particular antenna. Applications, this antenna design is used where the wide range of frequencies are needed still having the moderate gain and directionality. So, the applications are UHF terrestrial television. The television spectrum extends over a wide bandwidth more than normal ag antennas. High frequency communications, log periodic antenna arrays are often used in the applications where high frequency communications for diplomatic traffic is needed. Then EMC measurements, electromagnetic compatibility measurements require scans over a wide band of frequencies. Log periodic antennas can be used in these applications. Any other applications where directivity and wide bandwidth is needed there also log periodic antenna can be used. These are the references used for preparing this video. Thank you.