430 



REGULATORY CIRCUITS 



Space Pointing 

 Direction 



At, 



Fig. 8-23 Basic Relationships in the Airborne Antenna Drive System. 



This technique is generally applicable to fan-beam AEW systems and 

 other similar applications where platform motions cause measurement 

 errors but do not cause loss of the target. Data stabilization finds particular 

 favor where the antenna structure is so bulky as to preclude any other 

 approach. 



Antenna Stabilization. For the vast majority of airborne radar 

 applications — missile seekers, AI radars, side-looking radars, infrared 

 systems — stabilization of the antenna itself usually is required. 



The basic objectives of such a stabilization system may be derived as 

 follows. 



From Fig. 8-23, the space pointing direction of the antenna may be 

 expressed : 



^TL = Ga X (antenna command) -\- Gd X (aircraft disturbance inputs) 

 + Gm X (maneuver commands) (8-21) 



where Ga, Gd, and Gm are the transfer functions of the antenna drive and 

 the aircraft. 



From a tactical standpoint, the desired relationship is 



^TL = Ga X (antenna command) = j^tl desired. (8-22) 



Thus, the stabilization system must have two primary objectives: 



1. It must provide control loops which reduce the effective couplings 

 (Gd and Gm) between aircraft and antenna motion. (The required amount 

 of reduction is a function of the expected tactical use requirements). 



2. It must provide control means for driving the antenna to the desired 

 space pointing direction. 



Antenna Stabilization During Search. During the search phase of 

 radar operation, the problem is to maintain surveillance of a predetermined 

 volume of space despite the perturbations caused by platform motion. 

 During this phase, target data are not used for control of the antenna; 

 rather the antenna is driven by open-loop command data to sweep out the 



