MICROWAVE RADAR TESTING 



459 



frequency range. An untuned echo box is a fixed cavity of a size sufficient 

 to support a very large number of modes within the working range. Tuned 

 echo boxes are more versatile and more widely used than untuned boxes. 

 The most common type of tuned echo box is designed for hand tuning. 

 While other shapes are possible, the most convenient one is a right cylinder 

 whose length is adjusted by a movable piston. The TEo.i.n mode gives 



•BACKGROUND 

 NOISE 



-RING TIME 



RANGE 

 CLASS A 



AZIMUTH 



CLASS B 



(INTENSITY MODULATION) 



•AZIMUTH — 



PPI 



(INTENSITY MODULATION) 



Fig. 12 — ^.Tj-pical ringtimc patterns on radar indicators. 



maximum Q for a given volume and minimizes the number of unwanted 

 modes present within the desired band. The value of n is determined by 

 the desired value of Q (see formula 5). Unwanted modes can be partially 

 avoided by choice of design parameters. However, for high values of Q, 

 and especially for broad frequency bands, the suppression of unwanted 

 modes involves design problems of the highest order. 



