S4 



BELL SYSTEM TECHNICAL JOURNAL 



signals entering the receiver except those in the vicinity of the receiver image 

 bands. Because of this, suppression requirements on the branching filters, 

 except possibly in the vicinity of receiver image bands, are not severe. 



Problems connected with the design of suitable microwave branching 

 filters naturally differ considerably from previous filter problems. The dis- 

 crimination and band utilization requirements are readily met, but the 



ANTENNAS 



SEPARATE OR COMBINE CHANNELS 

 WITH MINIMUM POWER LOSS. 



PROVIDE EXCELLENT IMPEDANCE 

 MATCH TO ANTENNA LINES 



LESS IMPORTANT AT PRESENT 

 BECAUSE OF: 



ANTENNA DIRECTIVITY, 



l.F. DISCRIMINATION 



Fig. 1— Possible five-channel radio repeater station schematic diagram. 



impedance control required is not easy to obtain by familiar filter techniques. 

 Not more than about 5% variation in impedance or about 0.5 db standing 

 wave ratio in the channels could be tolerated. At lower frequencies channel 

 passing networks which can be connected in series or parallel to form a 

 channel branching filter can be designed on the basis of lumped circuit theory 

 and built of coils, condensers and resistances, but in the microwave region 



