National Digital Library

Govt. Of India has created #National_Digital_Libray for students for all subjects. Below is the link

It contains 4 crore 60 lakhs books.

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Antenna Theory - Beam Width

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In this chapter, we shall discuss about another important factor in the radiation pattern of an antenna, known as  beam width . In the radiation pattern of an antenna, the main lobe is the main beam of the antenna where maximum and constant energy radiated by the antenna flows. Beam width  is the aperture angle from where most of the power is radiated. The two main considerations of this beam width are Half Power Beam Width  (HPBW)  and First Null Beam Width  (FNBW) . Half-Power Beam Width According to the standard definition, “The angular separation, in which the magnitude of the radiation pattern decreases by 50% (or -3dB) from the peak of the main beam, is the  Half Power Beam Width .” In other words, Beam width is the area where most of the power is radiated, which is the peak power.  Half power beam width  is the angle in which relative power is more than 50% of the peak power, in the effective radiated field of the antenna. Indication of HPB...
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Antenna Theory - Half-Wave Folded Dipole

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A folded dipole is an antenna, with two conductors connected on both sides, and folded to form a cylindrical closed shape, to which feed is given at the center. The length of the dipole is half of the wavelength. Hence, it is called as  half wave folded dipole antenna . Frequency range The range of frequency in which half wave folded dipole operates is around 3KHz to 300GHz. This is mostly used in television receivers. Construction & Working of Half-wave Folded Dipole This antenna is commonly used with the array type antennas to increase the feed resistance. The most commonly used one is with Yagi-Uda antenna. The following figure shows a half-wave folded dipole antenna. This antenna uses an extra conducting element (a wire or a rod) when compared with previous dipole antenna. This is continued by placing few conducting elements in parallel, with insulation in-between, in array type of antennas. The following figure explains the working of a half-wave folded dipole antenna, whe...
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Antenna Theory - Near and for fields

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After the antenna parameters discussed in the previous chapter, another important topic of consideration is the near field and the far field regions of the antenna. The radiation intensity when measured nearer to the antenna, differs from what is away from the antenna. Though the area is away from the antenna, it is considered effective, as the radiation intensity is still high there. Near Field The field, which is nearer to the antenna, is called as  near-field . It has an inductive effect and hence it is also known as  inductive field , though it has some radiation components. Far field The field, which is far from the antenna, is called as  far-field . It is also called as  radiation field , as the radiation effect is high in this area. Many of the antenna parameters along with the antenna directivity and the radiation pattern of the antenna are considered in this region only. Field Pattern The field distribution can be quantifying in terms of field intensity is r...
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