Air Defence, Weapon Locat - ing and Battle Field Surveillance Radars are employed by the land forces. This article will focus only on Weapon Locating Radars (WLR) and Battle Field Surveillance Radars (BFSR).

WLR

WLR is employed to locate the hostile artillery guns, mortars and rockets so that rapid counter bombardment can be resorted to in order to neutralise them. Time is of essence as hostile artillery can resort to shoot and scoot tactics. During an insurgency scenario it greatly helps in locating them if the insurgents are resorting to artillery fire. The technology employed for WLR is radar based arrays which detects and tracks the trajectory of round/mortar/rocket in various stages of the flight and then extrapolates the origin of the fire with the help of a computer. Earlier acoustic technology called ‘Sound Ranging’ was employed for WL but had limited range and was termed sound ranging however both the technologies can be used in tandem.

BFSR

The early technology for BFSR was developed to provide detection of both fixed and moving targets, along with detection and tracking of ground targets. The system operational requirements varied from a long range to a small range of a tactical UAV. These diverse applications resulted in significant development of lightweight electronically scanned antennas, adaptive detection of targets in severe clutter, and transmission of critical target information over modest bandwidth data links. Another recent trend is microwave photonic technologies. Due to the broad bandwidth, flat response, low loss transmission, multidimensional multiplexing, ultrafast analogue signal processing and electromagnetic interference protection provided by modern photonics, implementation of the radar in the optical domain can achieve better performance in terms of resolution, coverage and speed as compared to current technology. There is a growing market for manportable BFSR. As per Market Research and Market Future 10 per cent growth is expected from 2018-23 due to insurgency and terrorism threat, amounting to a figure of $4,700 million.

India

Swathi. Swathi WLR is a mobile phased array radar developed jointly by Electronics and Radar Development Establishment (LRDE) of Defence Research and Development Organisation (DRDO) and Bharat Electronics Limited (BEL). The WLR is similar to the AN/TPQ-37 radar in design with a passive electronically scanned array radar. In 2008, the Ministry of Defence ordered 30 Swathi and some have been exported to Armenia. Large calibre artillery rounds (105mm and 155mm) can be tracked from a distance of 30 km. The WLR utilises a C-Band radar, an azimuth range of -45 to +45 degrees, and an up-down slew-able range of -135 to +135 degrees. Swathi is a great achievement of India.

PJT-531 BFSR. BFSR Short Range (BFSR-SR) is a man portable 2D shortrange battlefield and perimeter surveillance radar developed by the LRDE of DRDO and is being manufactured by BEL. PJT-531 has been extensively deployed on the Indian border and LOC in Jammu and Kashmir. It is reported that about 1,400 units are in use by the Indian Army. Foreign countries have also placed orders for the BFSR. It can detect a crawling man at 700 m, walking man at 3 km, group of people at 7 km, light vehicles at 10 km and heavy vehicles at 14 km.

A BFSR that can penetrate foliage is under development. This will be very useful in carrying out operations against Left Wing Extremism.

Latest Trends

The latest trends in both type of radars are:

Phased Array. In older radars there was one point of transmission and the antenna had to move in two D (range and bearing) to cover a larger area for surveillance which was a major limitation. If height was required then another antenna or radar was required. This problem was solved with the development of phased array which produced a beam of radio waves through computer controlled multiple emitting arrays.

Active Electronically Scanned Array (AESA). This is a further development of phased array system in which the beam of signals can be steered electronically in any direction without physically moving the antenna. Electronic steering is carried out by controlling the phase of the radio waves whereas the digitally controlled scanning enables rapid scan in any direction. AESAs are mainly used in radars providing detection, targeting, tracking, and self-protection capabilities. In AESA, every element has its own transmit/receive module (TRM), which makes this system more reliable as the failure of a single element won’t hinder the functioning of the system.

Dual role WLRs. The latest trend is to combine air defence and WLR function in a single radar platform with 3D AESA technology which can detect long range missiles as well UAVs. Lockheed Martin’s Q-53 has the capability to identify and track UAVs thus combining air surveillance simultaneously with counter target acquisition in a single sensor.

BFSR. Employment of BFSRs has been for shorter ranges and man portable versions with the use of narrow band with high PRF for accuracy, use of electronic scan for rapid detection and also systems being developed to detect through the foliage which could be particularly useful in jungle and dense forest terrain where India’s Left Wing Extremists operate. Another trend is to detect movement through doppler effect with aural detection.