 |
5. Efficiency and Temperatures |
| |
5. Efficiency and Temperatures |
The antenna gain is defined as :
m = 0.5 (non polarized radiation)
Ag = geometric area
kB = Boltzmann's constant
ηA = antenna efficiency
For the Noto antenna, the constants are :
ηA is the overall efficiency, estimated assembling all the signal degradation factors.
The antenna gain varies according to the elevation and it reaches a maximum at 45°. A good interpolation is obtained with a second degree polynomial, such as :
The coefficients of the normalized polynomials, at each frequency, are listed in the following :
|
Frequency (GHz) |
a |
b |
c |
|
5 |
-1.4396956∙10-5 |
1.9594323∙10-3 |
9.3333009∙10-1 |
|
8.3 |
-6.2013643∙10-5 |
6.9932510∙10-3 |
8.0284355∙10-1 |
|
22 |
-1.1407653∙10-4 |
1.1413276∙10-2 |
7.1452747∙10-1 |
|
43 |
-2.0746800∙10-5
|
1.7584500∙10-3
|
2.0928100∙10-2 |
Tab. 5.1 : Normalized gain curves, coefficients
The sensitivity can be estimated as follows :
= receiver constant (=1)
Tsys = system temperature
G = gain (K/Jy)
Δν = bandwidth
τ = integration time
n = integration number
NIF = available channels (= 1,2)
In the following table the system temperatures and the sensitivities of the Medicina antenna are listed :
|
ν0 (GHz) |
T receiver (K) |
Tsys (K) |
ηA (%) |
G (K/Jy) |
SEFD (Jy) |
Bandwidth (MHz) |
|
|
5 |
30 |
48 |
51 |
0.15 |
320 |
2x350 |
12 |
|
8.3 |
110 |
130 |
51 |
0.15 |
867 |
2x400 |
31 |
|
22 |
90 |
110 |
44 |
0.13 |
846 |
2x400 |
30 |
|
43 |
70 |
80 |
28 |
0.1 |
800 |
2x400 |
21 |
Tab. 5.2 : Sensitivity of the antenna, assuming τ = 1 sec, n=1, NIF = 2
| Primary Focus |
| Cassegrain Focus |
Notice: in some cases, the presence of RFI does not allow to use the full bandwidth of the receivers.
