Antenna | Directionality

Question 1

Dipoles (can/cannot) achieve a small level of directionality

Answer 1

can

Question 2

A rod slightly ___ than the antenna placed just less than a ___ wavelength away from it will strengthen the signal in that direction. This is known as a ____

Answer 2

shorter quarter director

Question 3

A slightly ___ rod placed just less than __ wavelength away will strengthen the wave in the opposite direction, this is a ____

Answer 3

longer, quarter, reflector

Question 4

Outline briefly how a reflector works.

Answer 4

• Acts like a resonant coupled circuit.
• The currents re-radiate and the quarter spacing causes it to be in such phasing that the original radiation is cancelled out

Question 5

The higher the number of dipoles in an array, the ___ and more ___ the beam of radiation will be

Answer 5

narrower, intense

Question 6

Directors and reflectors can create ___ as well as the main beam

Answer 6

side beams and lobes

Question 7

There must be a difference in ___ pressure between two points for electrons to flow

Answer 7

electrical

Question 8

The maximum signal is found when the loop is __ ___ with the transmission, when the points of contact are ___ __ ___, so a current is generated, driving an electric motor to continually seek the null position.

Answer 8

in line, out of phase

Question 9

The helical antenna is used with ___

Answer 9

GPS

Question 10

The maximum radiation is ___ to the axis of the helix

Answer 10

perpendicular

Question 11

For a helical antenna, the radiation is ___ polarised to the axis

Answer 11

linearly

Question 12

For a helical antenna in the axial mode, the radiation comes out of the ___, and works as a directional antenna, radiating ___ polarised waves.

Answer 12

end. circularly

Question 13

Parabolic antennas are used with ___

Answer 13

radar

Question 14

A slotted planar array is used with ___

Answer 14

modern weather radar systems

Question 15

The slotted planar array has ___ ___ which act as waveguides

Answer 15

flat slots

Question 16

Slotted planar array will ___ the sidelobes

Answer 16

reduce

Question 17

Gain is the ratio between the ___ in a particular direction, and that which would be propagated if the antenna were not directional

Answer 17

amount of energy propagated

Question 18

Gain can be thought of as making ___ of the energy available

Answer 18

best use

Question 19

With an omnidirectional antenna, the gain can come from spreading the RF energy ___ and ___ to the ground, creating stronger ___ ___

Answer 19

closer, flatter, ground waves

Question 20

Reciprocity is the ability of the antenna to be used for ____ ___ ___

Answer 20

transmitting and receiving