THE MICROWAVE GYRATOR 3 



direction of propagation is the negative of that for the other direction of 

 propagation. Essentially this means that a 180° phase difference exists 

 between the two directions of propagation. For this reason it has been 

 suggested that the element could be more aptly called a directional 

 inverter.- 



Network synthesis today is based upon the existence of four basic 

 circuit elements: the capacitor, the resistor, the inductor, and the 

 ideal transformer. It is apparent that the introduction of a fifth circuit 

 element, the g3'rator, would lead to considerably improved solutions for 

 many network problems. In fact, Tellegen has shown that the synthesis 

 of resistanceless four-pole networks would be much simplified by its 

 introduction. In addition, McMillan has shown that it would be possible 

 to construct a one-Avay transmission system if a gyrator were available, 

 and Miles has shown that it would be possible by use of a gyrator to 

 construct a network which is equivalent to a Class A vacuum tube 

 amplifier circuit. While the realizable power gain of these gyrator circuits 

 is necessarily always not greater than unity, many other networks in- 

 cluding gyrators are possible which have properties analogous to vacuum 

 tube circuits and some of these may be of practical importance. Since 

 this new element offers such interesting possibilities in network synthesis, 

 a study has recently been made in these Laboratories of possible methods 

 for realizing the gyrator. 



A gyrator was employed by Bloch^ in his measurement of the mag- 

 netic moment of the proton. Bloch made use of the phenomenon that 

 if two crossed coils with a mutual core are adjusted so that there is zero 

 mutual inductance between them and if a steady magnetic field is 

 appHed perpendicular to the axes of both coils, then an ac voltage ap- 

 plied to one of the coils will induce a voltage in the second due to the 

 gyromagnetic resonance phenomenon. This induction is ordinarily 

 extremely small unless the magnetic field is adjusted so that the exciting 

 frequency coincides with a gyromagnetic resonance frequency of the 

 material which forms the mutual core of the two coils. In Bloch 's ex- 

 periment, the magnetic field was held constant and the exciting fre- 

 quency was adjusted until it coincided with the gyromagnetic resonance 

 frequency of the proton. If they were wound over a paramagnetic or 

 ferromagnetic material, the two crossed coils would form a gyrator 

 when the magnetic field was adjusted so that the frequency of the 

 exciting field coincided with the gyromagnetic resonance of the unpaired 

 electrons. The fact that this structure constituted a gja-ator was first 

 recognized by Tellegen^ and has been discussed by Beljers and Snoek 



