Antennas And Radio Wave Propagation:

HPBW stands for Half Power Beamwidth. It is the angular width of the main lobe of a radiation pattern in which the power is at least half of the maximum power. The term "3-dB" refers to the power level at which the HPBW is measured. It indicates that the beamwidth is measured at the -3 decibel (dB) point, which corresponds to half of the maximum power. Therefore, the correct answer is 3-dB.

A linear array is a system of equally spaced elements. This means that the elements in the array are arranged in a uniform manner, with the same distance between each element. This arrangement allows for efficient and consistent processing of data or signals in the array.

The correct answer is "Area". Antenna aperture refers to the effective area of the antenna that captures the electromagnetic waves. It is the measure of the antenna's ability to receive or transmit signals. The aperture is typically expressed in terms of area, as it represents the cross-sectional area of the antenna that interacts with the incoming or outgoing waves. Therefore, the antenna aperture is the same as the area.

The Yagi-Uda antenna consists of a folded dipole, a reflector, and one or more directors. The folded dipole is the driven element that receives and transmits the electromagnetic waves. The reflector is placed behind the driven element to improve the antenna's directivity by reflecting the waves back towards the driven element. The directors are positioned in front of the driven element to further enhance the antenna's gain by focusing the waves in a specific direction. Therefore, all of the mentioned components (folded dipole, reflector, and directors) are included in a Yagi-Uda antenna.

In an end-fire array, the radiation is directed along the X-direction. This means that the main beam of radiation is focused in a forward direction, with maximum radiation occurring in the X-direction. The other options, XY-direction and Y-direction, are not correct because they do not accurately describe the radiation pattern of an end-fire array.

The radiation resistance of a folded dipole with equal radii is 292 Ohms. The folded dipole antenna consists of two parallel conductors that are connected at both ends. This design increases the electrical length of the antenna, resulting in a higher radiation resistance compared to a regular dipole antenna. The radiation resistance represents the power radiated by the antenna and is an important parameter for antenna efficiency. In this case, the radiation resistance is determined to be 292 Ohms.

The gain of an antenna is a measure of how effectively it converts input power into radiated power in a specific direction. In this case, the radio station has a transmit power of 1.73 kW and an Effective Isotropic Radiated Power (EIRP) of 25 kW. The gain of the antenna can be calculated by dividing the EIRP by the transmit power. Therefore, the gain of the antenna is 25 kW / 1.73 kW = 14.45.

Directivity refers to the ability of an antenna to focus its radiation pattern in a particular direction. It is a measure of how well an antenna can transmit or receive signals in a specific direction. Gain, on the other hand, is a measure of the increase in signal power that an antenna can provide in a particular direction compared to an isotropic radiator. Since gain is a measure of the antenna's ability to concentrate power in a specific direction, it is always lesser than directivity.

The minimum value of the directivity of an antenna is unity. Directivity is a measure of how well an antenna focuses its energy in a particular direction. A directivity value of unity means that the antenna radiates equally in all directions, resulting in no preferential direction for energy transmission. In other words, the antenna has no gain or loss in any particular direction, and its radiation pattern is isotropic.

One steradian is equal to (180/π)2 square degrees. This is because a steradian is a unit of solid angle that represents the area of a sphere that is covered by a cone with a vertex at the center of the sphere. The total surface area of a sphere is 4π square units, and a complete sphere covers 4π steradians. Therefore, to convert steradians to square degrees, we divide the total surface area of a sphere (4π) by the total number of steradians (4π), giving us 1 square degree per steradian. Hence, (180/π)2 square degrees is the correct answer.

Multimode graded index fibers are manufactured from materials with higher purity than multimode step index fibers. This is because graded index fibers have a more complex structure, with a varying refractive index profile that allows for the dispersion of different light modes. To achieve this, the material used needs to have a higher purity to ensure consistent and precise control over the refractive index profile. In contrast, step index fibers have a simpler structure and do not require the same level of purity in the material.

The correct answer is "Curved region" because for large distances, the curvature of the Earth becomes more noticeable. This means that the Earth is not completely flat, but rather has a curved shape. This curvature is important to consider when dealing with long-distance measurements and calculations, such as in navigation or satellite communication.

The length of the driven element in a Yagi at 290 MHz is 0.517 m. This length is determined by the wavelength of the frequency being used. In this case, the wavelength at 290 MHz is approximately 1.034 m, and the driven element is typically a half-wavelength long. Therefore, the length of the driven element is calculated as half of the wavelength, which is 0.517 m.

A multimode step index fiber typically has a larger core diameter compared to single mode fibers. The range of 100 to 300 μm is a reasonable size for a multimode step index fiber as it allows multiple modes (light rays) to propagate through the fiber. This larger core diameter helps to accommodate different angles of light rays, allowing for efficient transmission of light signals over short distances.

The radiation resistance of an antenna refers to the equivalent resistance that an antenna presents to the flow of radio frequency energy. It is called virtual resistance because it does not represent an actual physical resistance in the antenna, but rather the resistance that would be required to dissipate the same amount of power as is radiated by the antenna. This virtual resistance is important in antenna design and analysis as it helps determine the efficiency and performance of the antenna.

Antennas are devices that can both transmit and receive electromagnetic waves. When transmitting, antennas convert electrons (current) into photons (electromagnetic waves), which are then propagated through space. When receiving, antennas convert the received photons (electromagnetic waves) back into electrons (current) that can be used by electronic devices. Therefore, antennas can convert photons to electrons (a) when receiving and electrons to photons (b) when transmitting.

The troposphere is the lowest layer of the Earth's atmosphere, extending from the surface up to about 15 km (9 miles) in height. This layer is where weather phenomena occur, and it contains most of the Earth's air mass. Above the troposphere, the temperature generally stops decreasing with altitude and remains constant or starts to increase, marking the boundary between the troposphere and the next atmospheric layer, the stratosphere.

In a Broad side array, the radiation is directed along the Y-direction. This means that the array is designed to emit or receive electromagnetic waves perpendicular to the plane of the array, in a direction parallel to the Y-axis. The Y-direction is commonly used in antenna arrays to achieve a more focused and efficient radiation pattern.

Multimode graded index fibers have better performance characteristics compared to multimode step index fibers. Graded index fibers have a refractive index profile that gradually decreases from the center to the outer edge of the fiber, allowing for better control of modal dispersion. This results in higher bandwidth and longer transmission distances. On the other hand, multimode step index fibers have a constant refractive index profile, which leads to higher modal dispersion and lower performance. Therefore, the performance characteristics of multimode graded index fibers are better than multimode step index fibers.

Graded index is the most beneficial index profile in single mode fibers. This is because it allows for the efficient propagation of light by reducing modal dispersion. In a graded index fiber, the refractive index gradually changes from the center of the core to the outer cladding, creating a smooth gradient. This gradient helps to minimize the difference in propagation speeds between different modes of light, resulting in improved signal quality and reduced signal loss. Therefore, the graded index profile is preferred over step index or multi-step index profiles in single mode fibers.