FILTER-TYPE CIRCUITS 



201 



tion, showing regularly spaced slots S cut in the ridge R. The slots S may be 

 thought of as resonators. 



Figure 4.11 shows in cross section a circuit made of a number of axially 

 symmetrical reentrant resonators R, coupled by small holes H which act as 

 inductive irises. 



It would be very difficult to apply Maxwell's equations directly in de- 

 ducing the performance of the structures shown in Figs. 4.10 and 4.11. 

 Moreover, it is apparent that we can radically change the performance of 



Fig. 4.11 — A circuit consisting of a number of resonators inductively coupled by means 

 holes. 



JBs 



JB, 



JB2 



JB, 



JBj 



JB, 



J B2 



2JB, 



JBa 



JB, 



JB, 



JB, 



JB, 



JB, -- 



:b) 



Fig. 4.12 — Ladder networks terminated in -w (above) and T (below) half sections. Such 

 networks can be used in analvzing the behavior of circuits such as those of Figs. 4.10 

 ;ind 4.11. 



such structures by minor physical alterations as, by changing the iris size, 

 or by using resonant irises in the circuit of Fig. 4.11, for instance. 



As a matter of fact, it is not necessary to solve Maxwell's equations afresh 

 each time in order to understand the general properties of these and other 

 circuits. 



4.3 Lu.MPED ITER.A.TED An.ALOGUES 



Consider the ladders of lossless admittances or susceptances shown in 

 Fig. 4.12. Susceptances rather than reactances have been chosen because the 



