“They have a missile-lock on us!” is a phrase we’ve heard countless times in movies and is usually a sign that a radar-guided missile is incoming. Ever wonder how the aircraft’s systems detect this type of threat? In this post, we'll discuss how a radar warning receiver provides information on an adversary’s radar, as well as some general information on electronic support. Before we get into the details, I recommend reviewing the two previous posts for a brief background of the history of electronic warfare and an overview of radar.

What is Electronic Support?

Electronic support (ES) is the set of technologies and methods designed to receive and analyze an adversary’s transmissions of electromagnetic signals. This includes locating the sources of radar signals as well as identifying the adversary’s communication signals.

There is crossover between ES and signal intelligence (SIGINT), but the key difference is that ES is more tactical while SIGINT is more strategic. For example, while an ES system might identify an adversary’s communication signal so it can be jammed, a SIGINT system will intercept the transmission for longer-term strategic planning. Additionally, electronic support is less concerned with the content of the signal and instead is focused on the technical details of the transmission itself.

While both ES and SIGINT are critical, this article focuses on electronic support and its objective of improving situational awareness.

Radar Warning Receivers

The purpose of a radar warning receiver (RWR) is to detect and analyze radar signals in order to provide actionable information. For example, a radar detector in a car will detect police radar to notify the driver that if they don’t slow down, they might get pulled over.

However, the below discussion will focus on airborne RWR systems. These systems detect radar signals using wideband antennas placed in key locations on the aircraft. Amplifiers located near the antennas boost the signal before it's sent to either a downconverter or directly digitized. The system then analyzes the signals and compares them to a threat library to determine information such as the type of radar, the direction to the radar and an estimate of the distance.

Consider an aircraft flying through a hostile area. Suddenly, an alarm goes off indicating the detection of a ground-based search radar. The pilot adjusts course to avoid the radar site but then sees a second alarm indicating the detection of a targeting radar from a ground-to-air missile. Using this information, the pilot is able to take actions to evade the missiles.

The Battle for Best Noise Figure

Looking back at the above example, we find that by increasing the range of the RWR, we give the pilot the maximum amount of time to respond to the threat. In the case of a search radar, the RWR ideally detects that threat before the aircraft is discovered.

Detecting a radar signal requires the signal to be greater than the noise floor. Similarly to radar, one of the first approaches to increasing the range is to improve the noise figure. This is why the low noise amplifiers are placed near the antennas—by reducing the cable length before the amplifiers, the loss is reduced thereby improving the noise figure. This clearly illustrates the back-and-forth competition between radar and electronic warfare. The radar system designer tries to maximize the radar range, and the EW system designer works to optimize the RWR range. Since technology is continually improving, the most successful systems are the ones that can quickly be updated to incorporate the latest technological advancements.

In this competition between radar and radar warning receiver, the RWR designer is faced with an additional challenge. While the radar system designer knows the operational frequency of the radar, the RWR must have sufficient bandwidth to detect multiple types of radar. This is a key concept that differentiates electronic warfare systems from most other technologies and one that we will see in all types of EW system design. For example, as mentioned in the previous post, search radars operate at lower frequencies and targeting radars operate at higher frequencies. In order to accurately detect these different threats, the EW receiver must have a very broad bandwidth, which is why it's common to see multi-octave electronic warfare tuners and converters. In the next post, we will discuss another key element of electronic warfare—electronic attack.

Part 4: Electronic Attack