Amateur Radio Quiz: Uda Thunk It?


By H. Ward Silver, N0AX

The Yagi-Uda array, best known as “the Yagi,” is in its ninth decade of wireless service. Arguably the most useful antenna design ever devised beyond the dipole, Yagis are found everywhere in Amateur Radio -- from the low HF bands to microwaves. Why not swing your beam in the direction of this quiz and see if it “peaks” your interest?

1) The most common feed point impedance for a Yagi’s driven element is _______________ 50 ohms.
a. lower than
b. equal to
c. higher than
d. the complex conjugate of

2) Which of the following balanced feed point matching systems was adapted to create the gamma match?
a. Hairpin
b. Delta
c. T
d. Link

3) In a multiband Yagi that uses traps, what function is performed by the traps?
a. Changing the element’s electrical length
b. Increasing gain
c. Decreasing SWR
d. Increasing front-to-back ratio

4) The Yagi antenna is what type of array?
a. Phased
b. Broadside
c. Curtain
d. Parasitic

5) Which of the following matching systems requires the driven element of a Yagi to be insulated from the boom?
a. Alpha
b. Gamma
c. Phi
d. Beta

6) The Yagi’s radiation pattern is best characterized as which of the following?
a. End fire
b. Omnidirectional
c. Isotropic
d. Cardioid

7) Which design parameter has the strongest effect on Yagi gain?
a. Driven element impedance
b. Number of reflectors
c. Boom length
d. Trap Q

8) In a 2 element Yagi design, which configuration offers the highest gain?
a. Driven element and a director
b. Driven element and a reflector
c. Both have the same maximum gain
d. Yagis need at least three elements to function properly

9) The impedance of a Yagi’s driven element is designed to be _______________.
a. Purely resistive
b. Slightly inductive
c. Slightly capacitive
d. Purely reactive

10) Mutual coupling between elements in a Yagi results in which of the following?
a. Pattern distortion
b. Ground gain
c. Re-radiation
d. Flat SWR

Bonus Question: Although Professor Uda did most of the research in developing the antenna, why is Professor Yagi most often associated with the design?



1) a -- usually less than 30 ohms
2) c -- The gamma match is essentially half the T match.
3) a -- The traps act as switches to isolate sections of the elements.
4) d -- Mutual coupling between elements creates directivity.
5) d – This is also known as the hairpin match.
6) a -- The maximum direction of radiation is along the axis of the antenna.
7) c
8) b -- The driven element/reflector combination can achieve about 1 dB more gain.
9) a
10) c -- Re-radiation with the proper phase is the basis of the Yagi design.

Bonus: Professor Yagi presented the initial technical papers in English outside Japan, so he became the public face of the new antenna.