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Note: Many answers contain passages quoted in whole or in part from the text.
This 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
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
3. What explains nonreciprocal action in ferrites?
a) Coupling of microwave energy with electron spins
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.
5. What are ferrites?
c) Artificial ferrimagnetic materials
The first artificial ferrimagnetic materials were made in 1909 by Dr. S. Hilpert.
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.
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.
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.
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)