What is Gyrator in Microwave ?

It is a two port microwave device which has relative phase difference of 180 degrees for transmission from port-1 to port-2 and no phase shift for transmission from port-2 to port-1.

Let us understand construction of gyrator. As shown in the figure-1 below, it houses thin circular ferrite rod tapered at both ends. This ferrite rod is located inside circular waveguide supported by polyfoam. The waveguide is surrounded by permanent magnet which generates DC magnetic field for proper operation of the ferrite.

At the input end, a 90 degree twisted rectangular waveguide is installed. The ferrite rod is tapered at both the ends which reduces the attenuation. Moreover these tapered ends offer smooth rotation of the polarized wave.

Gyrator working principle

gyrator working principle and gyrator construction

Let us understand how gyrator works when Electro-Magnetic (EM) wave enters through either of its ports.

Case-1 :
When a wave enters through port-1, its plane of polarisation gets rotated by 90 degrees because of twist in the waveguide . It again undergoes Faraday rotation of 90 degrees due of ferrite rod. Due to above two phase shifts, the total phase shift of 180 degrees have been applied to the wave when it comes out of the port-2.

Case-2 :
When wave enters through port-2 , it undergoes faraday rotation of phase shift equals 90 degrees in the anti-clockwise direction. Again, this 90 degree shifted wave passes through the twist , and it gets rotated back by 90 degree in the opposite direction and cancels out previous phase shift. As a result, the wave arrives at port-1 with 0 degree phase shift. Hence an EM wave which is fed at port-2 does not have any phase change when it passes through the gyrator.

Gyrator S-matrix

In the context of the microwave domain, a gyrator is a passive, two-port electrical network element that exhibits gyration. Gyration is a property in which the phase relationship between the voltage and current at the ports is rotated in a specific direction. This rotation of phase is a fundamental characteristic of a gyrator.


The S-matrix (scattering matrix) for a gyrator is typically represented as a 2x2 matrix. The S-matrix describes the relationship between the incident and reflected waves at the ports of the gyrator. The S-matrix of the gyrator device is shown above. Gyrators are often realized using passive components like resistors, capacitors, and sometimes operational amplifiers.

Applications of Gyrator

Gyrators find various applications in the RF (radio frequency) and microwave fields.
➨Gyrators are often used in the design of microwave filters, especially in situations where the physical size of an inductor becomes a limiting factor.
➨Gyrators can be employed in impedance matching networks.
➨Gyrators can be used in frequency synthesizers to provide tunable inductance. Frequency synthesizers are widely used in communication systems for generating stable and precise output frequencies.
➨In some RF systems, antennas may need to be tuned for optimal performance. Gyrators can be utilized to provide tunable inductance in the matching networks associated with antennas.
➨Gyrators are employed in certain configurations of RF amplifiers to replace inductors.
➨Gyrators are used in the design of circulators and isolators.
➨Gyrators can be integrated into phase shifters, which are devices used to vary the phase of a signal in RF and microwave systems. This is useful in applications such as phased-array antennas and beamforming.

Conclusion: In summary, microwave gyrators contribute significantly to advancing the capabilities of RF and microwave systems by providing compact, tunable, and efficient solutions for inductance simulation, ultimately enhancing the performance and functionality of these systems.

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