Microwave Circulator Design
Answers to RF Cafe Quiz #59

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Microwave Circulator Design - RF CafeThis quiz is based on the information presented in Microwave Circulator Design, 2nd Edition, by Douglas K. Linkhart.

Note: Some of these books are available as prizes in the monthly RF Cafe Giveaway.


Circulator design has advanced significantly since the first edition of this book was published 25 years ago. The objective of this second edition is to present theory, information, and design procedures that will enable microwave engineers and technicians to design and build circulators successfully. This resource contains a discussion of the various units used in the circulator design computations, as well as covers the theory of operation. This book presents numerous applications, giving microwave engineers new ideas about how to solve problems using circulators.



1.  What is the primary characteristic of a circulator?

d)  Energy entering one port is coupled to an adjacent port, but to no other ports

A circulator is defined as a device with ports (coaxial connectors or waveguide flanges) arranged such that energy entering a port is coupled to an adjacent port, but not coupled to the other ports.
(see p36)




2.  What is a common mechanical analog of ferrimagnetic resonance?

c)  A gyroscope

The simple gyroscopic mechanical model of ferrimagnetic resonance has withstood the test of time and, together with other magnetics, provides reasonable results for circulator analysis and simulation.
(see p12)




3.  What explains nonreciprocal action in ferrites?

a)  Coupling of microwave energy with electron spins
(see p29)




4.  What explains nonreciprocal action in semiconductors?

b)  Coupling of microwave energy with electron orbital motion

The electron precession resonance in semiconductors is called the cyclotron resonance. 
(see p29)




5.  What are ferrites?

c)  Artificial ferrimagnetic materials

The first artificial ferrimagnetic materials were made in 1909 by Dr. S. Hilpert.
(see p4)




6.  In which resonance region do most waveguide circulators operate?

b)  Below resonance

Coaxial and microstrip circulators operate either above or below resonance, but the majority of waveguide circulators operate below resonance.
(see p55)




7.  Which type of circulator typically has the highest power handling capability?

a)  Differential phase shift

The differential phase shift, or transverse-field, circulator has the advantage of very high power handling capacity, even at high frequencies.
(see p58)




8.  What is the primary difference between a circulator and an isolator?

b)  The isolator has an internally terminated, inaccessible port

An isolator is a two-port device that transfers energy from input to output with little attenuation and from output to input with high attenuation.
(see page 36)




9.  How important is the microwave transmission medium (waveguide, stripline, coaxial line) in ferrite selection?

b)  Transmission medium type is not important

The selection of ferrite material is substantially independent of the microwave transmission medium (waveguide, stripline, coaxial line), so the medium need not be considered in design discussions.
(see p96)




10.  What can be the result of imperfect contact between the ferrite and the ground plane?

c)  Both a) and b)

Imperfect contact between the ferrites and the ground planes can cause undesired resonances and generally poor electrical performance.
(see page 242)