JF-17: KLJ-7 Radar Overview

Operating in X-band, it is capable of tracking up to 40 contacts, 10 when operating in Track-While-Scan, and can engage two at the same time in BVR scenarios. Moreover, it provides air-to-ground mapping, target searching, terrain avoidance and other capabilities, making it a good all-around system.
This article introduces the main characteristics of the FCR and the information presented to the pilot. Later articles will focus on radar modes and peculiarities, including jamming effects, speedgates, et cetera.

Characteristics

Contrary to the KLJ-7A, its more modern AESA relative, the -7 is a quite typical mechanically steered radar in line with most of what we have in DCS. In fact, if you have played any 3rd-Gen+ fighter jet, you can probably jump straight into the JF-17 and operate the radar fairly proficiently. The KLJ-7 supports, in fact, several familiar scan modes, such as Track-While-Scan, Range-While-Search, Velocity Search, and Single-Target-Track. Ad hoc modes are also available for ACM and tracking targets for single and multiple engagements and air-to-ground.

Air-to-air radar information is usually represented on a B-scope, which displays the range in nautical miles on the ordinate and the relative azimuth on the abscissa. The latter, when referring to contacts or talking about geometry, is also known as ATA or Antenna Train Angle.
Air-to-ground modes use the PPI format or Plan position indicator. In this configuration, the point of view is not distorted as in a b-scope display, making it more suitable for ground mapping and targeting.
Later articles will discuss specific display configurations pertinent to peculiar modes, such as Velocity Search.

Air-to-Air Overview

The scanned airspace volume in air-to-air mode spans from ±15°, 1 bar to ±60°, 4 bars. The latter mode requires circa 8.1 seconds to complete a full sweep. The bar settings cover circa:

• 4 bars: 36,000 ft, angle: 8.43°;
• 3 bars: 28,000 ft, angle: 6.57°;
• 2 bars: 20,000 ft, angle: 4.7°;
• 1 bar: 12,000 ft, angle: 2.83°.

Similarly to most other radars, the coverage angle and the number of bars are not proportional, as the bars overlap slightly. The display provides the two altitude boundaries directly on the cursor, updated in real-time.

The antenna pattern moves from left to right in odd bars and right to left in even bars. For instance, 4 bars follow this pattern:

1. L→R ⤵
2. R→L ⤵
3. L→R ⤵
4. R→L ⤴

The 3-bar setting is available only in Track-While-Scan and follows a different pattern.
The elevation at which the antenna looks can be identified using the Elevation strobe located on the left side of the display. As Tomcat RIOs know, this indicator comes in very handy on several occasions, albeit modern displays can show the altitude bracket illuminated by the radar. Ab initio pilots especially should keep well in mind that the radar volume resembles more a truncated pyramid than a parallelepiped. As these simplified sketches show, there are blind spots around the main illuminated area. Thus, the pilot must change the antenna elevation angle according to the expected threat, mission, terrain and so on. If a section flies together, they can stack their radars and increase the overall scanned area. These topics have already been discussed on this website.

Back to the KLJ-7, the azimuth can be set to different values:

• ±15°;
• ±30°;
• ±60°.

60° is also the widest setting. In the other cases, the scan volume is centred around the cursor rather than being a separate control. Note that the scale of the display does not change, and vertical dashed lines delimit the illuminated airspace.

Once again, Track-While-Scan has its own set of options:

• ±10°, 4 bars;
• ±25°, and the mentioned 3 bars;
• ±60°, 2 bars.

Track-While-Scan is a peculiar radar mode that requires a fixed refresh of the illuminated contacts, and this causes the unusual combinations of azimuth and bars. The details of TWS will be discussed in a dedicated article.

Range Settings

The available range settings are 10, 20, 40 and 80 nm. Certain radars use the defined range as a data processing parameter, but this should not be the case for the KLJ-7. Take this sentence with a grain of salt, though. If true, however, the range setting modifies the scale of visualised airspace information. The width of the three notches located on the right-end side of the scope changes accordingly. For instance, at an 80 nm scale, each mark represents 20 nm. At 20 nm, each represents 5 nm.

Pulse Repetition Frequency

Two Pulse Repetition Frequency (PRF) are available: Medium and High, plus a third option that combines the two labelled “AUTO”. An in-depth discussion about the differences between the two is beyond the scope of this article, but here is a very quick and dirty recap:

• High PRF is a high-energy mode, so to speak, that works best at a high V-sub-C, or closure rate. It takes full advantage of the Doppler effect to find contacts and separate them from the ground, but this also means that two blind zones exist. The first one is a notch in the waveform characteristic and the radar modus operandi itself causes it. This is where the “notching” term comes from. To provide look-down shoot-down capabilities, the radar tries to remove ground returns, de facto filtering anything moving at the same relative speed as the terrain, including other aircraft. This filter is called the MLC filter or Main Lobe Clutter filter.
  The second is the lack of speed difference, which limits the Doppler effect and may make it difficult to reliably track targets flying at a high Target Aspect (or low Aspect Angle).
  In reality, and with modern radars, both effects are not as significant a problem as they were in the past. However, the effectiveness of notching is particularly exaggerated in DCS, especially when missile seekers are involved.
• Medium PRF is a more recent and clever addition. Whereas in the past Low PRF was used as an “all-aspect” mode, MPRF required some technological advancements and the digital revolution of the 4th-gen fighters before becoming widespread. MPRF filters returned waves by range and Doppler, and therefore, it is vastly more reliable in situations where HPRF suffers the most. On the other hand, it has a reduced detection range, and its performance at low altitudes is mediocre.

The “AUTO” option allows automatic scan using both High and Medium PRF in an alternate fashion. For instance, a first 4-bar sweep is MED / HI / MED / HI. The second continues with HI / MED / HI / MED, and the cycle restarts.

In all modes, the bottom of the display shows additional information, such as the JF-17’s speed and altitude.

Air-to-Ground Overview

Similarly to Air-to-Air, Air-to-Ground offers several different modes and submodels, such as mapping, terrain avoidance, and targeting. Information is displayed using a PPI display rather than a b-scope, thus preventing the otherwise inevitable distortion.
Unfortunately, some radar modes are unavailable in DCS due to the sim’s limitations. For example, alike the F-4E’s Antenna Polarisation setting, Weather Avoidance does not interact with the in-game situation yet. Hopefully, in the future, these settings will have meaningful usage.

The display shows several controls and settings. Common controls include:

• Azimuth;
• Range;
• Gain adjustments.

Not all settings are available in every mode, and more details will be added in later dedicated article about the air-to-ground radar functions.

In fact, there is not a lot to say about the KLJ-7 in these modes of operation without entering their details and introducing aspects such as targeting pods and ordnance employment.

I hope you have found this article & video useful. Feel free to provide feedback!