Antenna And Wave Propagation-mock Test -2

The unit of gain is dB, which stands for decibels. Decibels are a logarithmic unit used to express the ratio of two values, such as the ratio of input power to output power in an electrical or electronic system. Gain is a measure of the amplification or increase in power, voltage, or current provided by a device or system. Using dB as the unit of gain allows for a more convenient representation of large or small changes in signal strength.

A half-wave dipole antenna is a type of wire antenna that is used in radio communication systems. It is called a "half-wave" dipole because its length is equal to half of the wavelength of the signal it is designed to transmit or receive. This length is optimal for efficient radiation and reception of the signal. The half-wave dipole antenna is a commonly used antenna design due to its simplicity and effectiveness in transmitting and receiving signals.

The radiated field that covers a larger area is known as the main lobe or major lobe. This refers to the primary portion of the radiation pattern that is focused in the desired direction. The main lobe contains the majority of the radiated power and is responsible for providing the primary coverage of the antenna.

The field patterns are plotted as a function of electric and magnetic fields. This means that the graphs or plots show the behavior and distribution of these fields in a given system or scenario. The use of a logarithmic scale is common in these plots, as it allows for a better representation of the wide range of field values that can be encountered. The dB scale, which is a logarithmic unit, is often used to quantify and compare the intensity or strength of these fields. Therefore, the correct answer is that the field patterns are plotted as a function of electric and magnetic fields.

The correct answer is "Both a and b". The most disadvantages of a half-wave dipole antenna are that it is not much effective due to its single element and can work better only with a combination. This means that the antenna's performance is limited when used on its own and it requires additional elements or a combination with other antennas to improve its effectiveness.

Directivity refers to the measure of how well an antenna focuses its radiation in a specific direction. It represents the ratio of radiation intensity in a given direction from the antenna to the average radiation intensity over all directions. In other words, it quantifies the ability of the antenna to concentrate its power in a specific direction, rather than radiating it equally in all directions. Therefore, directivity is the correct answer in this context.

The given correct answer, l = λ/2, suggests that the length of the Hertz antenna is equal to half the wavelength (λ) of the signal it is designed to receive or transmit. This is a common design principle for Hertz antennas, as it allows for efficient transmission and reception of electromagnetic waves. By using a length equal to half the wavelength, the antenna can effectively resonate with the incoming or outgoing waves, maximizing its performance.

The impedance of a dipole antenna is determined by its physical dimensions and the operating frequency. A dipole antenna is a balanced antenna, meaning it has equal currents flowing in opposite directions. The impedance of a dipole antenna is typically around 72 ohms, which is the characteristic impedance of a balanced transmission line. This value ensures efficient power transfer between the antenna and the transmission line. Therefore, the correct answer is 72.0 ohm.

The lobe that is exactly opposite to the direction of the main lobe is known as the back lobe. This lobe is formed due to diffraction and interference of waves, causing radiation in the opposite direction to the main lobe. It is important to minimize the back lobe in antenna design to ensure better directional radiation and reduce interference.

When energy is radiated through a bent wire, the end of the transmission line is referred to as a dipole or dipole antenna. A dipole antenna consists of two conductive elements, typically straight wires, that are bent at a specific angle. This configuration allows for the efficient transmission and reception of electromagnetic waves. The bent wire acts as a balanced antenna, meaning that it has equal and opposite currents flowing through each element, resulting in a more effective radiation pattern. Therefore, the correct answer is dipole or dipole antenna.

The maximum effective aperture of an antenna with a directivity of 900 can be calculated using the formula D = (4πAe.aperture)/λ^2. Rearranging the formula, we get Ae.aperture = (D * λ^2) / (4π). Plugging in the given directivity of 900, we can calculate the maximum effective aperture. The correct answer of 71.60λ^2 is obtained by solving this equation.

The radiation efficiency factor refers to the ratio of the radiated power of the antenna to the input power accepted by the antenna. It is a measure of how effectively the antenna converts the input power into radiated power. A higher radiation efficiency factor indicates that the antenna is more efficient in converting the input power into radiated power, while a lower factor indicates a less efficient antenna.

The beam angle is defined as the set of angles between the half power points of the main lobe. The half power points refer to the points on the radiation pattern where the power is half of the maximum power. Therefore, the correct answer is half power points.

The power patterns are plotted on a logarithmic or dB scale, which allows for easier visualization and comparison of the data. Option a and d are correct because both options mention the correct method of plotting the power patterns, which is as a function of the square of the magnitude of E and H.

The radiation pattern is a three-dimensional quantity because it describes the distribution of radiation in three dimensions (x, y, and z). It shows how the radiation is emitted or received by an antenna or other radiating element in all directions. This pattern helps in understanding the directionality and coverage of the radiation, which is crucial in various applications such as wireless communication systems and radar systems.

The effective aperture refers to the actual amount of light that enters the lens and reaches the image sensor. It is determined by factors such as the physical aperture size, the lens design, and any obstructions or limitations in the optical system. The physical aperture, on the other hand, refers to the size of the opening in the lens that controls the amount of light passing through. Since the effective aperture takes into account various factors that can reduce the amount of light reaching the sensor, it is generally lower than the physical aperture.

The range of frequency in which a Rhombic antenna operates is between 3MHz to 300MHz. This means that the antenna is designed to transmit and receive electromagnetic waves within this frequency range. Frequencies below 3MHz or above 300MHz would not be effectively transmitted or received by the Rhombic antenna.

Antennas are devices used to transmit and receive electromagnetic waves. They come in various shapes, sizes, and designs, allowing them to be used in a wide range of applications. The term "infinite" suggests that there is no limit to the number of different types of antennas that can be created. This implies that antennas can be customized and designed to suit specific needs and requirements, resulting in an infinite number of possibilities.

Antenna temperature considers the gain parameter into account. Gain refers to the ability of an antenna to focus or concentrate the received or transmitted power in a particular direction. It is a measure of the antenna's efficiency in converting input power into radiated power in a specific direction. The gain of an antenna affects the antenna temperature, which is a measure of the noise power received by the antenna. Therefore, gain is an important factor to consider when calculating antenna temperature.

The Half Power Beam Width refers to the angular width of the main lobe of a radiation pattern where the magnitude of the radiation pattern decreases by 50% (or -3dB) from the peak of the main beam. This means that within this angular width, the power of the radiation is reduced to half of its maximum value.

Directivity is a measure of how focused a beam of radiation is in a particular direction. It is inversely proportional to the beam area, meaning that as the beam area decreases, the directivity increases. A smaller beam area indicates a more focused beam, while a larger beam area indicates a wider dispersion of the radiation. Therefore, the correct answer is "Beam area".

The radiation intensity of an antenna is determined by both the direction of the beam focused and the efficiency of the beam towards that direction. The direction of the beam determines the coverage area and the efficiency determines how effectively the antenna radiates power in that direction. Therefore, both factors are closely related to the radiation intensity of an antenna.

The directivity of a half wave dipole is 2.15dBi. Directivity refers to the measure of how focused or concentrated the radiation pattern of an antenna is in a particular direction. A higher directivity indicates a more focused radiation pattern. In this case, a directivity of 2.15dBi suggests that the half wave dipole has a reasonably focused radiation pattern, making it suitable for applications where a specific direction of radiation is desired.

The gain of an antenna is measured in dBi, which stands for decibels relative to isotropic. The "3dB" in the gain value indicates that the antenna has a gain of 3 decibels. The "i" in "3dBi" simply represents the isotropic condition, which is a theoretical reference point for measuring antenna gain. Therefore, the correct answer is "2 and isotropic condition" as it correctly represents the gain value and the condition being referred to.

The given options consist of different types of beam patterns. A non-directional pattern refers to a beam that radiates in all directions equally. A pencil-beam pattern refers to a narrow and focused beam. A fan-beam pattern refers to a wide beam that spreads out in a fan shape. The odd man out in this case is the rounded beam pattern, as it is not a commonly recognized term for a specific type of beam pattern.