5.1 Operational Range of Radar Location and Radio Navigation Systems
81
fixed minimum level E rcv , serving as a boundary of dilemma: “Signal exists–no
signal,” is principally impossible. One can speak about conditional concept of a
minimum value E rcv min , designated as sensitivity of receiving unit, in which a signal
reflected from a target can be detected with a probability accepted by an information
recipient.
An obtained in such way value E rcv min , determines a maximum detection range
D max , the values of which, for the case when transmitting and receiving is conducted
by the same antenna, i.e., for the case when G 1 = G 2 i S eff1 = S eff2 , are of the form
of:
D =
4
E G 2 λ 2 A
E(4π )
3
rcv min
=
4
E S
2
eff A
E2 rcv min
.
(5.6)
Correlation (5.6) bears a name of range equation in free space.
As we can see, radar detection—is a reciprocal process depending both on RCS of
A target and on parameters of the radar itself. For pulse radar, we can obtain a more
convenient form of range equation by introducing a frequently used power value in
pulse P. This is simple to do, if we consider that intervals of radiation and receiving
time are equal between each other. By dividing a transmitting and receiving energy
in (5.4) and (5.5) formulas into the same time, i.e., radiation time of one target, we
obtain:
D =
4
E G 2 λ 2 A
E(4π )
3
rcv min
=
4
P S
2
eff A
P P2 min
.
(5.7)
From Eq. (5.7), we can make a false conclusion that a range of radar detection
depends not on sounding and reflected energy, but on corresponding powers. Here
we should pay attention that correlation (5.5), basing on which a second Eq. (5.7)
was obtained, guided by energy relations, thus in general case it is necessary to use
equation E =
T
0 P(t)dt, which only at constant in time power P(t) = const
derives to a second equation in (5.7) formula. Local power increase, without time
considering of this period, can set forth nothing.
Let us assume the written above equation in the following form: E =
T
0 P(t)dt = P avr T , where P avr —is an average radiation power in T time period.
Increase of an average power will provide an increase in range.
As we can see, at radar detection, as in the most physical phenomena, for achievement of desirable result it is necessary to consume some certain energy. Specific
processing technique of receiving signal in radar terminal unit requires an energy
presence, larger than its some lowest value.
Receiver sensitivity E rcv min finally plays a crucial role in determining of radar
operational range. Value of lowest required threshold signal energy E rcv min depends,
from one side, on the presence and intensity of different random processes following
a radar detection, and from another side—on effectiveness of signals processing
applied in radar intended for filtration of random processes.
81
fixed minimum level E rcv , serving as a boundary of dilemma: “Signal exists–no
signal,” is principally impossible. One can speak about conditional concept of a
minimum value E rcv min , designated as sensitivity of receiving unit, in which a signal
reflected from a target can be detected with a probability accepted by an information
recipient.
An obtained in such way value E rcv min , determines a maximum detection range
D max , the values of which, for the case when transmitting and receiving is conducted
by the same antenna, i.e., for the case when G 1 = G 2 i S eff1 = S eff2 , are of the form
of:
D =
4
E G 2 λ 2 A
E(4π )
3
rcv min
=
4
E S
2
eff A
E2 rcv min
.
(5.6)
Correlation (5.6) bears a name of range equation in free space.
As we can see, radar detection—is a reciprocal process depending both on RCS of
A target and on parameters of the radar itself. For pulse radar, we can obtain a more
convenient form of range equation by introducing a frequently used power value in
pulse P. This is simple to do, if we consider that intervals of radiation and receiving
time are equal between each other. By dividing a transmitting and receiving energy
in (5.4) and (5.5) formulas into the same time, i.e., radiation time of one target, we
obtain:
D =
4
E G 2 λ 2 A
E(4π )
3
rcv min
=
4
P S
2
eff A
P P2 min
.
(5.7)
From Eq. (5.7), we can make a false conclusion that a range of radar detection
depends not on sounding and reflected energy, but on corresponding powers. Here
we should pay attention that correlation (5.5), basing on which a second Eq. (5.7)
was obtained, guided by energy relations, thus in general case it is necessary to use
equation E =
T
0 P(t)dt, which only at constant in time power P(t) = const
derives to a second equation in (5.7) formula. Local power increase, without time
considering of this period, can set forth nothing.
Let us assume the written above equation in the following form: E =
T
0 P(t)dt = P avr T , where P avr —is an average radiation power in T time period.
Increase of an average power will provide an increase in range.
As we can see, at radar detection, as in the most physical phenomena, for achievement of desirable result it is necessary to consume some certain energy. Specific
processing technique of receiving signal in radar terminal unit requires an energy
presence, larger than its some lowest value.
Receiver sensitivity E rcv min finally plays a crucial role in determining of radar
operational range. Value of lowest required threshold signal energy E rcv min depends,
from one side, on the presence and intensity of different random processes following
a radar detection, and from another side—on effectiveness of signals processing
applied in radar intended for filtration of random processes.