Thesis - Leigh Moody.pdf - Bad Request - Cranfield University

Chapter 3 / Sensors / Seeker
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3.9 Missile Seeker
3.9.1 Review
The development of RF and IR seekers, from the continuous wave devices
of the 60s to the phased and staring arrays of today is an immense subject.
The 60s single element detectors were capable of lock-before-launch against
short-range targets with a tail-on aspect. During the 70s multiple element
devices provided improved counter-measure performance. Dual frequency
sensors were introduced in the 80s improving range with an all aspect
attack. The single frequency imaging seekers of the 90s provide aim-point
refinement with increasing FoR to 50°-60° off-boresight with clutter and
counter-measure rejection. The next decade will bring all-weather Multi-
Spectral Seekers (MSS) combining RF/IR and Laser/IR for stealth, 3D
imaging to obtain range data, increased acquisition ranges, and
improvement in clutter and countermeasure rejection.
The phased array radar, once restricted to large facilities such as Pave-Paws
for ICBM launch detection and Aegis class missile frigates, is now used in
aircraft, and even missiles. Future RF improvements are expected in the
Pulse Repetition Frequencies (PRF) used, and in frequency agility to
improve jamming resistance, reducing glint errors, and avoiding range and
range-rate ambiguities.
Passive IR seekers with staring arrays are an important alternative to active
RF devices with a number of modern short-range missiles using IR staring
arrays. These impose exacting demands on the gimbal controllers to
provide inertial stabilisation thereby preventing image smearing that reduces
acquisition range. This requires smaller integration times commensurate
with the high frame rates needed for agile missiles. The cost of ensuring
that array elements remain in their response range with uniform random
noise, spectral response and photon conversion is inevitably increasing. The
presence of dead-elements and fixed pattern noise requires calibration,
element acceptance criteria, and complex signal processing.
The MSS warrants special attention since it will be a catalyst for air-defence
sensor data fusion. Conceptually the MSS contains two sensors operating
on different wavelengths providing resistance to countermeasures, clutter,
false alarms etc. The IR staring array provides accurate bearing and
elevation measurements whilst the RF phased array adds range, range rate,
and a second source of less accurate angular data. If radome transmittance
at high off-boresight angles permits, the two sensors may use a common
gimbal arrangement, and hence a single aperture. Alternatively, and more
likely, two sets of gimbals and separate apertures will be required, each
system being developed separately. Although ideal for modular design, the
state observers and more complex autopilot will be required to point each
sensor at the target, the acquiring sensor steering the other onto the target.
3.9-1