226 BELL SYSTEM TECHNICAL JOURNAL 



diameter is increased for higher voltage operation or to accommodate a 

 greater number of resonators around the anode periphery. 



Finally, it should be pointed out that the location of the straps at the ends 

 of the anode structure causes their effectiveness to reduce with increasing 

 anode length. As anode length is increased, the mode frequency distribu- 

 tion approaches that of the unstrapped resonator system of infinite length. 



7.3 Asymmetries in Strapping — Strap Breaks: Of very great importance 

 to the operation of a strapped resonator system is the degree of symmetry 

 in the strapping system. The early British strapping is not symmetrical 

 around the anode. The other three types shown in Fig. 24 are symmetrical 

 except for breaks which are usually incorporated at least on one end of the 

 anode. These asymmetries in the strapping provide the most convenient 

 method of incorporating in the resonator system the additional asymmetry 

 needed to orient the standing wave patterns of doublet modes with re- 

 spect to the output circuit of the magnetron so as to equalize their loading. 

 In addition, the strap asymmetries are arranged so as not to affect the sym- 

 metrical distributions of voltage and current in the resonator system for the 

 TT mode but to destroy such symmetry to an appreciable extent for other 

 modes. For example, the destruction of the symmetry of the w = 3 mode 

 pattern in a system of eight resonators by a single asymmetry in the strap- 

 ping amounts to its contamination with a field component of periodicity 

 corresponding io n = 1. Since the voltage and magnetic field values at 

 which this contaminating component may be driven by the electrons are 

 considerably farther removed from the tt mode values than are those of the 

 w = 3 mode, one has effectively converted the « = 3 mode into another 

 mode less troublesome electronically. 



In the echelon strapping of Fig. 24 (c) the asymmetry is produced by 

 removal of two of the connecting links. The breaks in the strip or ring 

 straps of Fig. 24 (d) are located as shown in the center of a hnk between two 

 strap "feet". The break is thus at a current node in the strap for the it 

 mode and has no effect on the pattern symmetry of this mode. For the 

 other modes, however, the breaks appear at points where currents would 

 normally flow and so represent sharp discontinuities in the structure for 

 these modes. 



In connection with strapped resonator systems there are two further points 

 which should be mentioned. The first of these is the necessity in some cases 

 of shielding the straps from the interaction space. The inner ring straps, 

 mounted on the ends of the anode structure, present potentials to the inter- 

 action space which are independent of angle. This amounts to a perturb- 

 ing n = like component in the field pattern which is particularly strong 

 near the ends of the anode and which affects magnetron operation adversely 



