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# Note for ANTENNA ENGINEERING - AE By s

• ANTENNA ENGINEERING - AE
• Note
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Due to the time varying electric and magnetic fields, electromagnetic waves are created and these travel between the conductors. As these waves approach open space, free space waves are formed by connecting the open ends of the electric lines. Since the sinusoidal source continuously creates the electric disturbance, electromagnetic waves are created continuously and these travel through the transmission line, through the antenna and are radiated into the free space. Inside the transmission line and the antenna, the electromagnetic waves are sustained due to the charges, but as soon as they enter the free space, they form closed loops and are radiated. Explain the following terms w.r.t an antenna. a) Radiation Pattern lobes b) Power theorem and Poynting vector c) Radiation intensity. Radiation Pattern lobes: 1. Main Lobe: This is the radiation lobe containing the direction of maximum radiation. 2. Minor Lobe: All the lobes other then the main lobe are called the minor lobes. Theselobes represent the radiation in undesired directions. The level of minor lobes is usually expressed as a ratio of the power density in the lobe in question to that of themajor lobe. This ratio is called as the side lobe level (expressed in decibels). • Back Lobe: This is the minor lobe diametrically opposite the main lobe. • Side Lobes: These are the minor lobes adjacent to the main lobe and are separated by various nulls. Side lobes are generally the largest among the minor lobes. In most wireless systems, minor lobes are undesired. Hence a good antenna design should minimize the minor lobes. 2.