Vol 1. Introduction To Radar Systems, Unit 1. Radar Fundamentals

A duplexer is a radar component that allows the use of a single antenna for both transmitting and receiving signals. It is responsible for separating the incoming and outgoing signals, allowing the radar system to alternate between transmitting and receiving without any interference. This helps to optimize the use of the antenna and conserve space in the radar system.

A paraboloid is the most common reflector shape because it has the ability to focus incoming light or sound waves to a single point known as the focal point. This makes it ideal for applications such as satellite dishes, telescopes, and headlights, where a concentrated beam of light or sound is required. The paraboloid shape allows for efficient reflection and minimal distortion, making it a popular choice in various industries.

The propagation of a wave from one point to another by more than one path is known as multipath. This occurs when the wave reflects, refracts, or diffracts off of various surfaces or obstacles, resulting in multiple paths for the wave to travel.

Reflected energy is used, with proper receiving equipment, to detect the presence of a distant object. When an object reflects energy, such as light or sound waves, it can be detected by specialized equipment. This detection allows us to sense the presence of objects that are not within our direct line of sight. Light and sound waves are forms of energy that can be reflected off objects and detected, but a mirror is simply a surface that can reflect light and does not have the capability to detect distant objects.

Polarization refers to the orientation of the electromagnetic wave as it travels through space. It describes the direction of the electric field vector of the wave. The electric field vector can oscillate in any direction perpendicular to the direction of propagation, and the specific orientation of this vector is what determines the polarization of the wave. Different polarizations have different characteristics and can interact differently with various materials and devices.

Radio waves are a type of electromagnetic wave, and all electromagnetic waves, including light, travel at the same speed in a vacuum, which is the speed of light. Therefore, radio waves also travel at the speed of light.

The radar assembly that supplies timing signals to coordinate the operation of the complete system is called a synchronizer. A synchronizer ensures that all components of the radar system are working in sync and at the correct timing intervals. It plays a crucial role in ensuring accurate and coordinated operation of the radar system.

The gain of the individual pencil beams is higher compared to the fan-beam antenna. This means that the individual pencil beams have a stronger signal strength and can provide better coverage and reception compared to the fan-beam antenna.

The correct answer is the scanning method used by the system. When the radar looks for an aircraft, it uses a scanning method to move the antenna axis (of the beam) in order to cover a specific area and detect any incoming signals. This scanning motion allows the radar to search for and track targets within its range. The other options, such as receiving, transmitting, and filtering methods, are not directly related to the motion of the antenna axis during the search process.

A parabolic reflector is used to shape the beam. A parabolic reflector is a curved surface that reflects light or radio waves and focuses them into a single point or line. The shape of the parabolic reflector allows it to gather and concentrate the beam of light or waves, resulting in a focused and directed beam. This makes it an effective tool for shaping the beam in a desired manner.

To reduce multipath effects on radar tracking accuracy, several attempts are made. These include the use of frequency agility, which allows the radar system to change its operating frequency to avoid interference from multipath signals. Polarization agility is another technique that involves changing the polarization of the radar signal to minimize multipath effects. High-resolution antennas are used to improve the spatial resolution of the radar system, reducing the impact of multipath reflections. Clutter fences are physical barriers or structures that are placed around the radar antenna to block or minimize the reflection of unwanted signals. Finally, complex indicated angle processing techniques are employed to extract accurate target information from the received signals, compensating for multipath distortions.

The shape of the pattern can be modified by altering the distribution of energy over the aperture. The aperture refers to the opening through which the energy passes. By changing how the energy is distributed across this opening, the antenna designer can change the shape of the pattern that is emitted or received by the antenna. This can be done by adjusting the size, shape, or arrangement of the elements within the aperture, or by using techniques such as beamforming to control the directionality of the energy distribution.

The antenna on transmit functions to concentrate energy in a predetermined beam shape and to point the beam in a predetermined direction. This allows for the selective gathering and transmission of energy in a specific direction, rather than dispersing it randomly.

The active feedhorn is the normal feedhorn that is used for both transmitting and receiving signals. It is the primary component responsible for capturing and focusing signals in a communication system. By using the active feedhorn, signals can be transmitted from the antenna to the receiver and vice versa. This allows for bidirectional communication and ensures efficient signal transmission and reception.

In a stacked beam radar, each pencil beam is directed towards a specific target or area of interest. To receive the reflected signals from these pencil beams, only one receiver is used. This receiver collects the signals from all the pencil beams and processes them to extract relevant information about the targets. Therefore, the correct answer is 1.

A two-dimensional planar array is particularly useful in radar applications because it allows for both azimuth and elevation scanning. This means that it can detect and track targets in both horizontal and vertical directions, providing a comprehensive view of the radar coverage area. This is important in radar applications where accurate target detection and tracking is crucial, such as in military surveillance or air traffic control systems. The two-dimensional planar array offers enhanced situational awareness and improves the overall effectiveness of the radar system.

The fictitious surface located on or near an antenna is called the antenna aperture. The antenna aperture refers to the opening or area through which the electromagnetic waves pass. It is an important component of the antenna system as it determines the amount of energy that can be received or transmitted. By controlling the size and shape of the aperture, the antenna's performance can be optimized for specific frequencies and applications.

The correct answer is 12.36 microseconds. This is because a radar mile is defined as the distance that a radar pulse travels in one microsecond. Therefore, to travel one radar mile, it would take 12.36 microseconds.

The dipole, the open-ended waveguide, and the slotted waveguide have been used more than other kinds of radiators in phased arrays.

The correct answer is "Its inherent ability to steer a beam without the necessity of moving a large mechanical structure." This means that the phrase-array ability allows the beam to be directed without the need for physically moving a large antenna. This is advantageous because it reduces the complexity and cost of the system, as well as the potential for mechanical failures.

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The purpose of Aircraft control and warning (AC&W) radar is to control friendly aircraft, detect hostile aircraft, and control interceptors. This radar system is designed to provide situational awareness and enhance air defense capabilities by monitoring and managing the airspace. It helps in identifying and tracking both friendly and hostile aircraft, allowing for effective control and coordination of friendly forces. Additionally, it enables the detection of hostile aircraft, providing early warning and enabling timely response to potential threats. The ability to control interceptors is crucial for effective air defense operations, as it allows for the interception and neutralization of hostile aircraft.

The pattern of the antenna is determined by the distribution of electromagnetic energy from the antenna over the aperture. The aperture is the opening through which the electromagnetic waves pass, and the distribution of energy across this aperture affects how the waves propagate and interact with the environment. Therefore, the distribution of energy over the aperture directly influences the pattern of the antenna.

The three primary performance parameters for an antenna are gain, beamwidth, and sidelobe level. Gain refers to the ability of the antenna to direct or focus its energy in a particular direction. Beamwidth is the angular width of the main lobe of the antenna's radiation pattern, indicating the coverage area. Sidelobe level refers to the level of radiation outside the main lobe, which should ideally be minimized to avoid interference. Therefore, the correct answer is gain, beamwidth, and sidelobe level.

When a low-altitude target is illuminated by a radar system or higher-angle situations involving appreciable antenna sidelobes, energy can enter the tracking antenna through two paths. The first path is a direct path from the target, where the radar energy is transmitted directly towards the target and then received by the tracking antenna. The second path involves energy reflected from the surface of the earth. In this case, the radar energy is transmitted towards the target, but instead of reaching the target directly, it is reflected off the surface of the earth and then received by the tracking antenna.

The correct answer is Modulator high-voltage pulse. In a transmitter, the high-power oscillator is switched on and off by the modulator high-voltage pulse. This pulse controls the operation of the oscillator, allowing it to produce the desired output pulses.

Using two feedhorns provides an amount of control over the received beam pattern. By using two feedhorns, the signals can be combined or adjusted in a way that allows for control over the pattern of the received beam. This can be done by adjusting the position, orientation, or phase of the signals from the two feedhorns. By manipulating these factors, the beam pattern can be shaped and controlled to meet specific requirements or objectives.

Using the clutter-reducing aspect of the dual-feedhorn system on a mountain range reaching 3 degrees above the horizon would result in a significant reduction in the returns from ground targets. This is because the clutter-reducing aspect of the system helps to filter out unwanted signals and noise from the ground, thereby reducing the returns from ground targets.

Using a 12-feedhorn antenna can eliminate the problem of multipath reflections. Multipath reflections occur when signals bounce off objects and create multiple paths for the signal to reach the antenna. This can cause interference and signal degradation. By using a 12-feedhorn antenna, the signals can be received from multiple directions simultaneously, reducing the chances of multipath reflections and improving the overall signal quality.

A stacked-beam radar refers to the use of contiguous beams stacked in elevation. This technique allows for improved target detection and tracking capabilities by providing a more detailed and accurate picture of the radar environment. By stacking the beams, the radar can cover a larger area and gather more information about the targets within that area. This type of radar is commonly used in applications where high resolution and accuracy are required, such as air traffic control or military surveillance.

The attractive features of the phased-array antenna include the capability to generate more than one beam with the same array and flexibility in the control of the aperture illumination. This means that the antenna can produce multiple beams simultaneously, allowing for increased coverage and the ability to track multiple targets. Additionally, the control of the aperture illumination provides flexibility in adjusting the antenna's performance, such as adjusting the beam shape or focusing the beam on a specific target.

The antenna on receive functions by forming a beam in a specific direction. This allows it to selectively gather transmitted energy that has been reflected from different targets. The received energy is then sent to the receiver through transmission lines.

The purpose of the passive feedhorn is to receive signals. It is only connected to the receiver when the signal received by that horn is preferred over the signal from the normal horn. This means that the passive feedhorn is used to selectively receive specific signals when needed, allowing for better control and optimization of the received signals.

The paraboloid shape is useful because it ensures that all rays leaving the focal point and striking the reflector are reflected along a path parallel to the focal axis. This property allows for the concentration of the reflected rays at a single point, resulting in a focused beam of light or sound. The paraboloid shape is commonly used in applications such as satellite dishes, telescopes, and parabolic microphones, where precise focusing is required.

The advantage of individual pencil beams when handling rain clutter or chaff is that they limit the volume of space observed. This means that the radar system can focus on specific areas and filter out unwanted signals from rain or chaff, allowing for more accurate detection and tracking of targets.

Reflector antennas are extremely important and practical devices for use in radar systems because they offer an economical method of distributing energy over a large aperture area. This means that they can cover a wide area without requiring excessive energy consumption. Additionally, reflector antennas can produce shaped or pencil beams with high gain, allowing for more precise and focused radar detection. This makes them highly effective in radar systems where accuracy and efficiency are crucial.

MTI stands for Moving Target Indicator, which is a radar technique used to filter out unwanted clutter caused by stationary objects or environmental factors. By using MTI, the clutter is reduced, allowing for a clearer detection of moving targets. This is advantageous as it improves the accuracy and effectiveness of radar systems by eliminating unnecessary information and focusing on relevant moving targets.

The radar antenna has two basic functions. The first function is to efficiently launch and receive electromagnetic energy into the atmosphere or space. This means that the antenna is responsible for transmitting and receiving the radar signals. The second function is to direct the energy into an appropriately shaped beam. This means that the antenna is responsible for shaping the radar beam so that it can accurately detect and track targets.

The helical scan is the correct answer because it describes a radar antenna rotation pattern in which the azimuth sweep occurs while the elevation angle gradually increases from 0° to 90°. In a helical scan, the antenna rotates in a spiral or helix pattern, allowing for simultaneous azimuth and elevation scanning. This scanning technique is commonly used in radar systems to provide a comprehensive coverage of the surrounding airspace.

At frequencies below about 40 MHz, a multipath may include more than one path through the ionosphere. This is because at lower frequencies, the ionosphere is less dense and less reflective, allowing radio waves to penetrate it and take multiple paths. As the frequency increases, the ionosphere becomes more reflective, causing radio waves to be refracted and reflected in a single path.

Using automatic detection, sidelobe cancellation, or MTI in radar systems can result in increased cost and complexity. These techniques require additional hardware, software, and processing capabilities, which can add to the overall cost of the radar system. Additionally, implementing these features may require more advanced algorithms and signal processing techniques, leading to increased complexity in the design and operation of the radar system. Therefore, the use of automatic detection, sidelobe cancellation, or MTI can have a negative impact on both the cost and complexity of radar systems.

Reciprocity in the context of antennas refers to the property where the transmit and receive patterns of the antenna are usually identical. This means that the antenna behaves the same way when transmitting a signal as it does when receiving a signal. In other words, the antenna exhibits the same characteristics and performance regardless of whether it is used for transmitting or receiving signals. This property is important in many applications, such as wireless communication systems, where the antenna needs to be efficient and reliable in both transmitting and receiving signals.

The circular scan is identified at the ECM receiver by its regular intervals between illuminations. This means that the circular scan follows a consistent pattern of illuminating targets at regular intervals as it rotates, allowing the ECM receiver to detect and identify this scanning method. The other options, conical scan, raster scan, and helical scan, do not exhibit the same regular intervals between illuminations as the circular scan.

The paraboloid is formed by rotating a two-dimensional parabola about its focal axis. When a parabola is rotated around its focal axis, it creates a three-dimensional shape known as a paraboloid. This rotation expands the parabola in the third dimension, creating a curved surface that resembles a bowl or a satellite dish. The focal axis is the line passing through the focus of the parabola and perpendicular to its directrix.

The range gating in the 12-feedhorn system is adjusted individually in each of the four azimuth quadrants, relative to the north reference. This means that the range gating is customized and fine-tuned separately for each quadrant, taking into account the north reference as a point of comparison. This allows for precise and accurate range gating adjustments in each quadrant, optimizing the performance and functionality of the system.

Stacked-beam is a good technique because it utilizes simultaneous pencil-beam radiation patterns from a single aperture to cover the elevation angles of interest. This means that multiple beams are transmitted simultaneously, allowing for efficient coverage of the desired elevation angles without the need for multiple apertures or consecutive beam transmissions. This technique offers improved performance and flexibility in beamforming for various applications.

It is important for the minor lobes of radar antennas to be small compared to the main lobe for several reasons. Firstly, having an antenna with high directivity allows for more accurate and focused signal transmission and reception. Secondly, reducing the susceptibility of the antenna to interfering signals improves the overall performance and reliability of the radar system. Thirdly, by reducing the possibility of detecting a target in a minor lobe, false alarms and unnecessary data processing can be minimized. Lastly, minimizing the probability of interference with other nearby systems ensures that the radar system operates efficiently without causing disruptions to other communication systems.

Multipath in radar usually consists of a direct path and one or more indirect paths by reflection from the surface of the earth or sea or from large man-made structures.

Ducting refers to the atmospheric condition where a layer of warm air is trapped between two layers of cooler air, causing the radar waves to be guided along the layer of warm air. This can result in extended radar coverage as the waves travel farther than usual. However, ducting can also create holes in radar coverage as the waves may be blocked or absorbed by the layers of cooler air. Therefore, ducting can have the effect of both extending radar coverage and creating holes in it.

Each beam in an array antenna is considered as a separate radar because an array antenna consists of multiple individual radiating elements that can be electronically steered to create multiple beams. Each beam can be directed towards a specific target or area of interest, allowing the array antenna to function as multiple radars simultaneously. This enables the array antenna to track multiple targets or gather information from different directions at the same time.