Understanding Radar Part 3: Phased Array Radar
2020-11-24 | 6 min read
In part 1 of “Understanding Radar”, we provided the fundamentals of radar, and in part 2, we learned more about synthetic aperture radar. Now we’re going to discuss the uses of phased array radar’s (PAR) military and civilian applications. But to understand what PARs are, we need to start with phased array antennas.
What is a phased array?
A phased array antenna is typically a computer-controlled array of antennas. Normally, when a signal is broadcast from multiple antennas there is a risk of an interference pattern that can cause a reduction in signal strength. For radars, this can lead to a misrepresentation of the radar target’s size, as well as false positives or negatives. However, an interference pattern can be used to improve a radar’s accuracy. By carefully controlling several beams of radio waves, a constructive interference pattern can be created which boosts the signal strength. By adjusting the phase relationship between the antennas, the signal can be electronically ‘steered’ to point in different directions without moving the antennas, this is known as beamforming.
Beamforming can be achieved with as few as two antennas, but phased array antennas number in the hundreds or thousands of individual antennas. Beamforming is especially beneficial for radar as it can reduce signal radiation in some directions while boosting the signal radiation in the desired direction. As a result, the accuracy of the radar reflection signal is substantially improved. The large number of antennas in the system also add redundancy, which can be invaluable in mission-critical applications, such as aerospace and defense.
Why use a phased array antenna for radar applications?
As mentioned above, PARs do not have moving parts, which is enormously beneficial for radar applications. First and foremost, the field of view can be changed in a few microseconds. This is significantly faster than a conventional rotating radar dish, which can take longer to complete a revolution. The dwell time, or the time that a radar can spend sending signals to a target, is freely selectable, increasing the hits per scan on the target. More hits per scan means a richer image quality of the target. For conventional radars the dwell time is limited by the speed of rotation of the antenna.
This beam agility and increased signal quality means that PARs can be used for several applications simultaneously. However, PARs have a low frequency agility and a limited scanning range, typically only 120° in azimuth and elevation. Due to their complexity in development and construction, as well as the computing requirements to process the high volume of data in real-time, PARs are very expensive, and therefore have limited applications.
Where are PARs used?
PARs are commonly used in the aerospace and defense industry. One example is contemporary warships, where a single PAR can track over 100 targets simultaneously. In fast paced modern naval warfare detecting and tracking enemy vessels, aircraft and missiles, and augmenting target data for missiles and close-in weapons systems (CIWS) are all vital tasks in which PARs excel. For naval applications, PARs typically operate at the S and X bands.
However, PARs are not just found attached to the side of a warship. Some ground-based PARs scan the skies for incoming projectiles like ICBMs, while others search for fast-moving objects in space. They are also found in military aircraft, performing similar tasks to their ship-based siblings: detecting enemy targets and incoming missiles.
Due to the recent rise of commercial and recreational drones, PARs are even more useful. Attaching a PAR to a drone enables it to see potential obstacles and threats such as powerlines and other aircraft, an important step on the road to autonomous drone delivery services. K-band PARs are increasingly used for detecting drones entering restricted areas, such as airports. While a drone’s radar signature isn’t readily distinguishable from that of a bird, when paired with a camera it can easily detect drones.
Due to the complexity and use cases of PARs, the development process can be costly and challenging. Keysight’s PathWave system design software helps to overcome these challenges and reduce development costs by accurately simulating the entire system. Keysight’s W1720 Phased Array Beamforming Kit for PathWave helps radio frequency (RF) systems and system-level PHY architects validate designs for 5G and PAR applications.