Study On Off-axis Relfective Broadband IR Simulator Based On The Theory Of Vector Aberrations

With the advent of dual-color and even multi-color IR guided weapons, IR targetsimulators of single waveband have become incompetent to meet the needs ofhardware-in-the loop (HWIL) simulations. How to overcome the restriction of IRmaterials on the operating waveband and thus realize broadband IR target simulatorsare of great importance and urgency. The primary objective of this thesis is to developa method to design an off-axis three-mirror IR target simulator whose waveband cancover all the IR bands based on the theory of vector aberration, for the use ofadvanced HWIL simulation on IR guided missiles. The specific research contentsinclude:1. Vector aberration characteristics of off-axis optical systems are summarized,and the nodal theory of third-order aberrations in nonsymmetrical systems isdiscussed. In off-axis optical systems, there are no new aberrations, but the fielddependence of an aberration often changes and the lower field-power dependentaberration items arise in nonsymmetric systems. The method to calculate theaberration field center is discussed.2. A new method is proposed to obtain the aberration field of a pupil-decenteredoptical system. By introducing the pupil decentration vector, the off-axis aberrationfield is deduced from the aberration coefficients of an axially rotational system, so that the nodal features of optical aberrations are insightfully revealed. The methodshows great convenience since parameters of individual surface such as radius ofcurvature, decenter as well as the shifted center of the aberration field are not used inthe analysis. The field characteristics of single-node coma, dual-node astigmatism,triple-node distortion are analyzed. If an axially rotational system has its aberrationswell corrected, then the aberrations in the pupil-decentered state does not exist either.The aberration theory can be applied in the design of off-axis projection systembecause decentering the aperture is a frequently-used method to obtain an unobscuredoff-axis system.3. The detailed method to design an off-axis target simulator is proposed. Withaberration theory the co-axis system structure is calculated at first, then the pupil isdecentered and the system parameters are optimized under the control of layoutstructure and nodal positions. Finally an off-axis reflective projection system with alarge field of view of±3°, large pupil diameter of100mm, large exit pupil distance of500mm and high image quality is obtained. The tolerance is loose compared to that ofan imaging system and the system can be easily manufactured and aligned.4. A broadband IR target simulator is designed, manufactured and tested. Thesimulator adopts a trussed framework and has a lightweight by reducing the weight ofits mirrors. The exit pupil of the illuminating system is kept unchanged for therequirement of pupils' match between the IR target simulator and the unit under test,by using the relay illuminating system. The reflectors of the system are manufacturedby diamond turning and coated with highly-reflective gold material. MWIR andLWIR thermal imagers are respectively used to obtain the images of the IR targetsgenerated by the simulator. The results show that the broadband IR target simulatorbased on reflective structure can provide a uniform IR target which has a widespectral range from MW to LW infrared.