The Uttam is an advanced active phased array radar (APAR) system being developed by Electronics and Radar Development Establishment (LRDE) for the HAL Tejas and other combat aircraft of Indian Air Force. Development of Uttam started in 2008 and it was first unveiled at Aero India 2009. Uttam is slated to be a successor to hybrid passive electronically scanned array radar EL/M-2032 currently equipping LCA Tejas. Radar is currently being integrated with an LCA.
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| Uttam AESA radar at Aero India 2017 |
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| Uttam being integrated with a prototype/LSP Tejas |
Difference between AESA and PESA radar:
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LRDE 3D MMR (left) and Uttam AESA radar (right). Notice the difference in size of the antenna array
(Image credits: shiv@BRF, Trishul) |
Conventional passive phased array radars have a single high power RF source (usually Travelling Wave Tube) at ‘back-end’ and RF signals are fed into slotted array antenna via a waveguide or coaxial tube. Introduction of the phase difference between each transceiver element allows the radiation pattern to be steered electronically. In the reception cycle, a PESA antenna cannot transmit. PESA radar has a light antenna which can be mounted on a mechanical steering mechanism thereby giving it a wide frontal coverage area or FOV.
Active phased array antennas have transmitter-receiver modules or transceiver module (TRM) built right into the antenna. A single array may feature hundreds or thousands of TRMs depending upon antenna size and operational requirement. Each TRM can either operate independently or under a hierarchy. Each TRM can generate and radiate its own signal of different phase and frequency as required, thus the transmitted signal is wideband in nature. Unlike PESA radar, signals can be transmitted and received simultaneously in an AESA radar. Active phased array antennas are usually heavier than slotted planar array antenna so it is difficult to mount them on a steering mechanism, which limits their field of view (FOV). Electronic steering is faster compared to mechanical steering but at high steering angle (90-120 degree) it may also increase side lobe power which is undesirable. FOV limitation can be mitigated by using a swash-plate repositioner.
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| Euroradar CAPTOR mounted on a swash-plate repositioner for ultra wide FOV |
Various aspects of Uttam AESA radar:
- Uttam features an active phased array (APAR) which gives it superior scanning performance over legacy passive phased array radar. Unlike most contemporary radars, Uttam features Quad TRM i.e. a single plank consists of 4 TRMs. It allows the array to be more densely packed. Each TRM is equipped with low noise power amplifier, built-in test facility, digital phase-gain, and side lobe control elements. The inert model displayed at Aero India 2015 had ~184 QTRMs i.e. 736 TRMs. The array temperature is controlled by a liquid coolant circulation system. The QTRM configuration makes Uttam maintenance friendly. The radar can be scaled up or down depending on antenna size requirement.
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| Uttam's QTRM configuration |
- The radar is capable of tracking 100 targets simultaneously and engage 6 of them by SARH/ARH missiles in high priority tracking mode. For comparison, Elta EL/M-2052 is capable of tracking 64 targets in TWS mode.
- In 2015 Uttam was stated to be capable of tracking a target having RCS of 2m2 at a distance of 92 kilometers. According to the new reports, the range has been increased to 150 kilometers for the target of the same RCS. In GMTT mode 2 targets can be tracked.
- Uttam has over 16 different types of operational modes and the radar can operate in multiple modes simultaneously by changing modes pulse-to-pulse which gives the pilot exceptional situational awareness and mission flexibility.
- Air-To-Air
- TWS (Track While Scan): Combination of search and track, essentially a surveillance mode.
- HPT – High priority Target: Dedicated tracking mode, also referred to as “Hard Lock”.
- AACQ/ACM (Auto-Acquisition/Air Combat maneuvering): radar searches a certain area and detected targets are automatically locked on transferred to HPT allowing the pilot to fire missiles quickly- Rapid target engagement.
- AJ (Anti-Jam): Rapid frequency changes and other techniques to cut through heavy jamming.
- RA (radar altimeter): measures altitude of the aircraft.
- Weather: Weather observation
- Air-To-Sea
- Sea TWS: Search and tracks targets on the water surface, high processing requirement to cut through the clutter. It also includes SSS (sea surface search)
- RS (Range Signature): Generating 1D profile of sea target, essentially a ‘quick look’, assessing the area of interest in a target, such as its length, position of high reflectivity area
- ISAR (Inverse Synthetic Aperture Radar): Imaging the target for classification, RS and ISAR are usually coupled with an automatic classification library
- STCT (Sea Target Continuous Track): Similar to air-to-air HPT but for sea targets
- Air-To-Ground
- AGR (Air-To-Ground Ranging): Radar uses a continuous single beam for ranging, similar to a laser rangefinder. Range information is used to assist gunfire (strafing run) and visual bombing.
- RBM (Real Beam Mapping): Radar scans the terrain to generate a topographic map. Pilots can use this map for terrain avoidance. It allows the aircraft to fly low while avoiding collision with a feature or ground.
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| Terrain Avoidance- The valley in front of the aircraft is black indicating that there is no terrain at the current altitude |
- SAR/DBS/HRM (Doppler Beam Sharpening/ High-Resolution Mapping): Enhanced Imaging mode used for high-resolution imaging of ground. Since the actual aperture of radar is very small compared to wavelength and energy is spread in a wide area, DBS is used to enhance the resolution.
- GMTI/GMTT (Ground Moving Target Tracing/Indication): Detection of a moving target on the ground, other objects such as trees and buildings are filtered out. These modes can be interleaved with RBM/SAR to produce terrain map and track the target at same time.
- Navigation
- Weather
- Terrain Avoidance.
- Advanced Electronic Counter-Countermeasure capabilities of Uttam AESA radar:
- Wide bandwidth: Since each TRM can generate and transmit radiate its own signal of different phase and frequency, a large number of spectral components can be generated in a single pulse i.e. radar can spread its frequencies across a wide band in a single pulse.
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| Chirp pulse |
The ability to quickly switch the frequency and wide bandwidth make Uttam a Low-Probability-of-intercept (LPI) radar i.e. it is difficult for an RWR to intercept it.
- Frequency agility: The Radar can rapidly+randomly switch through a large number of frequencies spread across wide bandwidth to counter certain types of jamming.
- Sidelobe Cancellation (SLC): SLC is a technique used to removing interference in which the processor subtracts the interference from the antenna output. It is designed to operate against active jammers. It is assumed that the jamming signal is entering the radar antenna through one of the sidelobes. In SLC, auxiliary antennas are used to gather information about interfering signal, the resulting signal is sent to rest of radar receiver and processor via SLC channels and interference is neutralized. Having multiple SLC channels allows Uttam to neutralize multiple jammers simultaneously.
- Ultra-low sidelobe antenna: Uttam has an ultra-low sidelobe antenna which allows it to generate very sharp pencil beams. In AESA radars low sidelobe regions can be created with TRMs using independent phase control at each element. Having low sidelobe level not only improves steering/tracking performance but also increase immunity against jammers. It also helps the aircraft to avoid detection by passive RF tracking systems (Emitter locator systems).
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