Electronic Countermeasure (ECM) Antennas
The conventional horn antennas are linearly polarised operating over limited frequency bandwidth. DRDO has developed horns with linear, circular, slant
linear (45°) and dual polarisation. Suitably designed ridges have been incorporated for
achieving broad bandwidth. Dielectric phase shifters/metallic phase shifters have been
developed to achieve circular polarisation with minimal ellipticity ratios over large
bandwidth. Unique external dielectric decollimating lenses are used for achieving required
beam width aspect ratio. These antennas have high power handling capability.
DRDO has developed state-of-the-art broadband horn antennas for airborne and ship borne
jammer applications over the frequency range of 0.5Ä40 GHz in split bands. These antennas
also find application as feed to reflectors and as auto track horns. All these antennas
have been subjected to rigorous electrical and environmental qualification tests.
Production lines have been established for meeting the bulk requirement.
High Power ECM Reflector Antennas
The ECM system requires high
effective raDIATed power (ERP) for effective jamming. High ERP which is the product of
transmitter power and antenna gain can be obtained by increasing either the antenna gain
or the transmitter power. Power output of the transmitter is limited by many important
considerations, like size, weight, cooling, etc. principal contributor the antenna gain.
Increase in antenna gain is accompanied by narrow beam-width thereby decreasing the
coverage substantially. The narrow beam creates its own problem of missing the target or
ineffective jamming. The high gain is obtained by using prime focussed paraboloidal
reflector fed by high power ridged horn feed. To direct the narrow beam of this jammer
antenna accurately to the enemy radar, two pairs of amplitude matched auto-track horns are
integrated to the reflector. These auto-track horns work on amplitude comparison monopulse
technique with their crossover axis aligned accurately to main jammer antenna axis for
directing the jammer beam to enemy radar both in azimuth as well as elevation plane for
effective jamming. Such ECM antenna has been developed capable of working over L, S, C,
X-Ku and millimeter frequency bands for the Services.
Microwave Rotman Lens Fed Multiple Beam Array Antenna
Microwave Rotman lens fed multiple beam array antenna system providessimultaneous high gain multiple beams with each beam possessing
full gain of array aperture. The microwave Rotman lens is a power distribution-cum-phasing
network. It is considered as a microwave analogue of optical lens. It offers the
possibility of variable refractive index which provides many degrees of freedom to design
lenses with multiple foci as compared to optical lenses which are made of dielectric with
fixed refractive index and hence single on axis focal point.
The Rotman lens consists of TEM mode parallel plate transmission region with input and
output ports called beam and array ports, respectively. Coaxial transmission lines of
unequal lengths connect the array ports to the raDIATing elements of the array. These
variable length transmission lines which constitute a transmission delay provide variable
refractive index to achieve the path length compensation. The length of these transmission
lines and array port positions are designed to provide perfect focussing along the input
circular arc. The focussing is a consequence of providing equal electrical path length
from a given focal point out to the corresponding raDIATed wave front to each element of
the array. These lens-fed array systems provide optimum utilisation of system resources in
time, space and frequency. Microwave Rotman lens fed array system is cost-effective with
inertia-less scanning capability and finds extensive application in: (i) ECM against
simultaneous multiple threats, (ii) surveillance, (iii) point to multi-point
communication, (iv) remotely piloted vehicle system for multiple drone control and
broad-band data retrieval links, (v) integrated multipurpose system accomplishing the
functions of radar, ECM, surveillance and communication, (vi) satellite communication with
spot beam coverage capability, and (vii) low side lobe pattern generation.
A microwave Rotman lens fed array antenna system which is a state-of-the-art concept
has been designed and developed, covering the frequency band more than 2:1 capable of
generating 15 simultaneous beams with ERP 100 KW nominal.