1438 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1957 



Fig. 6 — J-6S333C directional coupler with cover plate removed to show cou- 

 pling elements. Optimum spacing for maximum directivitj'can be obtained b}' ad- 

 justing screws. 



matches the impedance seen looking into Port 4, all of the small signal 

 will be absorbed in Z. If Z is an adjustable resistance, then a controllable 

 portion of the small signal can be reflected back into Port 4, whence most 

 of it will come out Port 3. A small portion of the reflected signal will 

 emerge at Port 1, headed toward the input. This portion will be attenu- 

 ated b}' twice the coupling loss between the main and the branch line 

 plus the return loss of the reflection at Z, and can be made negligible. 

 The interactions caused by the reflected signal on the main delay line 

 entering previous couplers are also reduced by twice the coupler loss. 



ii 



