NON-REFLECTING BRANCBING FILTER 



^ 



line C. Similarly, power in line D flowing towards the junction, will appear 

 equally in A and B but not in C or back in D. If these characteristics hold, 

 then by the principle of reciprocity similar characteristics must hold for lines 

 A and B. If proper planes of reference are chosen this behavior can be 

 described in a slightly different, but equivalent, manner. If waves in both 

 A and B flow towards the junction the vector sum of the voltages of these 

 times a constant (0.707) appears in C and the vector difiference times the 

 same constant appears in D, but nothing is reflected back into A or B. An 

 equivalent statement can be made if the waves start in C and D. 



With the properties of the hybrid in mind, and if it is assumed that the 

 hybrids, the identical reflection filters and the quarter wave lines are perfect 

 and free of ohmic loss, the operation of the circuit of Fig. 3 is easy to under- 

 stand, and is as follows: A wave entering from arm C of the input hybrid is 

 divided equally into the two arms A and B. None of the power in this wave 



r(5HVW| 



A 



^> 



B 



^ 



(a) CLASSICAL HYBRID COIL 



HYBRID 

 JUNCTION 



>D VNA TERMINATING 



^ IMPEDANCE 



(b) HYBRID WAVEGUIDE JUNCTION 

 SCHEMATIC DIAGRAM 



Fig. 4 — a. Classical hybrid coil, 

 b. Hybrid junction schematic diagram. 



is reflected back into the arm C or appears initially in arm D. The two equal 

 components of the wave now travel along the lines which are connected to the 

 arms A and B of the input hybrid. If the frequency lies outside the band of 

 the reflection filters the waves travel through these filters and appear in phase 

 in the arms A and B of the output hybrid. The vector sum of these two 

 waves appears in the arm C of the output hybrid and has an amplitude equal 

 to that of the original input wave. Consequently all energy in the input line 

 incident on this network, except that lying in the band of the reflection filters, 

 will pass through it to the output fine. 



If now the frequency of the input wave lies within the band of the reflection 

 filters, the two equal components of the wave traveling away from the input 

 hybrid will be reflected at the filters and will travel back towards the input 

 hybrid. One of these components must, however, travel twice through an 

 extra quarter wavelength of line, and will therefore be reversed in phase; with 



