Each of the two methods described has advantages and disadvantages which 

 depend on the application desired. A distinct advantage of the true-time-delay 

 technique is that the beam position does not shift as the frequency is changed, as 

 is the case for the matrix approach. The beam-position shift is dramatically illus- 

 trated in figure 5 which gives the experimental radiation patterns of the SAMB 

 matrix antenna for different beam positions. Beams 1L and 1R are near the broad- 

 side position, beams 7L and 7R are about 22° off broadside, and beams 14L and 

 14R are about 50° off broadside. As is evident, the effect is more pronounced as 

 the beam is scanned to larger angles. Over a wide-frequency spectrum, this con- 

 dition would give large angular differences between the transmitted and received 

 signals when they are separated in frequency. This effect is also present when 

 phase-increment scanning is used and will be discussed later. If many beam posi- 

 tions are desired simultaneously, then the matrix-feed technique has a definite 

 advantage over other feed systems. Measured radiation patterns for the SAMB 

 true-time-delay antenna are shown in figures 6, 7, and 8 for two frequencies sepa- 

 rated by about 3 percent. Beams 1L, 6L, and 16L are shown and no beam-position 

 shift is observed for any beam. 





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AZIMUTH ANGLE (°) 

 Figure 5. SAMB beam-position shift with frequency using matrix. 



