452 



THE BELL SYSTExM TECHNICAL JOURNAL, MARCH 1957 



A. Reflection Cavity 



Fig. 1 shows a magic (liybrid) T which serves to observe the reflected 

 power from the cavity. Arm 3 has a shde screw tuner which serves to 

 balance out some of the power coming from arm 2. This does not affect 

 the present analj^sis and will be considered later in connection with 

 detector noise. It should be mentioned, however, that a certain ampU- 

 tude or phase unbalance has to be left. This insures that the signal in 

 arm 4 will be a function of either x' oi' x"-^ In the case that the magic T 

 is completely balanced out the signal in arm 4 will be a function of both 

 x' and x" and the experimental results become difficult to analyze. 



Fig. 2 shows the equivalent circuit for a reflection cavity.^ The \/2 

 in the source voltage arises from the fact that half the power is lost in 

 arm 3. From this equivalent circuit we can define the following relations: 



Unloaded Q = Qo = — (Losses due to cavity alone) 



r 



External Q = Qx = 

 Loaded Q = Ql = 



coL (Losses arising from power 

 Ron^ leaking out of the cavity) 



coL (Losses due to both cavity 

 Rou^ + r and leakage out) 



(6) 

 (7) 

 (8) 



MAGIC 



_ SLIDE 



T^r- SCREW 



TUNER 



SIGNAL 

 SOURCE 





AP, 



^>^ DETECTOR 



— CAVITY C 



Fig. 1 — A simple arrangement to observe the reflected power from cavity C. 



Ron^ r C 



■^TT 



nm^ — 



2 i:n L L 



Fig. 2 — Equivalent circuit for a reflection cavity. 



