Types of Antenna

Question 1

Effective area can be increased by using

Answer 1

Yagi antenna

Question 2

For v < 1GHz use

Answer 2

simple elements, i.e. dipoles

Question 3

For v > 1GHz use

Answer 3

horns

Question 4

Horn diagram

Answer 4

see notes

Question 5

A large feed aperture (w) does what to the signal

Answer 5

it blocks it, so choose a small focal ratio (f/D)

Question 6

Cassegrain Telescope diagram

Answer 6

see notes

longer effective focal length
easy access to feed
can modify secondary to improve performance
usual choice for ~ 30m dishes

Question 7

Spherical mirrors diagram

Answer 7

see notes

Line-focus overcomes spherical aberration
Observations can be made up to ~20 degrees from the zenith

Question 8

Spherical Irregularities diagram

Answer 8

see notes

rms surface error ε => phase error Φ = 2π/λ*2ε

Question 9

Antenna arrays

Answer 9

Single antennas can be combined to make an antenna array with a larger collecting area Ae

Question 10

If the antenna array is equally spaced it acts like a

Answer 10

diffraction grating

Question 11

phase difference between adjacent antennas

Answer 11

Φ = 2π/λ*asinθ

A geometric progression

E = Eo exp( (iΦ/2)^(n-1)) * sin(nΦ/2)/sin(Φ/2)

Question 12

There is a Fourier transform relationship between the distribution of apertures

The power pattern

Answer 12

P(θ) ∝ |+∞ ∫-∞ A(x) exp(iksinθx)dx |²

Question 13

convolution theorem

Answer 13

f*g = f.g

Question 14

the Fourier transform of a convolution is

Answer 14

the product of the individual Fourier transforms