4.1 Range Measurement Techniques
61
In naval FM radars, the same principle permits to suppress clutter reflections from
sea disturbance for detection of a shore and target ships.
Phase range measurement method. Phase method of range detection is based
on measurement of phase difference of radiated and received oscillations.
Radiating oscillations of constant frequency are having a phase:
ϕ rad = ϕ 0 + 2π f 0 t.
(4.5)
Phase of receiving in t moment reflected from stationary target oscillations should
be equal to a phase of earlier radiated oscillations, i.e., phase of oscillations radiated
in a time moment (t − t D ):
ϕ
∗
rcv = ϕ 0 + 2π f 0 (t − t D ).
(4.6)
Since a process itself of radio waves reflection is connected with additional change
of reflected wave phase φ rfl , a relation (4.6) is due to be corrected:
ϕ rcv = ϕ 0 + ϕ rfl + 2π f 0 (t − t D ).
(4.7)
Difference of phases of radiated and received oscillations will comprise:
ϕ = ϕ rad − ϕ rcv = −ϕ rfl + 2π f 0 t D = −ϕ rfl + 2π f 0
2D
c
.
(4.8)
Range to a target:
D = ϕ rfl
c
4π f 0
(ϕ rfl + ϕ).
(4.9)
At condition of phase change consistency arising due to reflection ϕ rfl , we have
linear relationship between target range and phases equality of radiating and receiving
oscillations:
D = const +
c
4π f 0
ϕ = const +
λ 0
4π
(4.10)
As we can see from formula (4.10), phase meter can be graduated directly in range
units.
Considerable disadvantage of phase method is non-single-valued range measurement. In fact, phase meter will give out the same range readout both as at measuring
of phase ϕ, and phase ϕ + 2π n, (n—is any whole (integral) number), despite
that these are oscillations phases received from different ranges.
It is known that condition of single-valued range measurement via phase method
will consist in ϕ max < 2π . By substituting it into equality, a shift of phases for the
most remote target based on relation (4.9), we have: −ϕ r f l + 4π
D max
λ 0
, from which
we obtain a condition of the largest single-valued range measurement:
61
In naval FM radars, the same principle permits to suppress clutter reflections from
sea disturbance for detection of a shore and target ships.
Phase range measurement method. Phase method of range detection is based
on measurement of phase difference of radiated and received oscillations.
Radiating oscillations of constant frequency are having a phase:
ϕ rad = ϕ 0 + 2π f 0 t.
(4.5)
Phase of receiving in t moment reflected from stationary target oscillations should
be equal to a phase of earlier radiated oscillations, i.e., phase of oscillations radiated
in a time moment (t − t D ):
ϕ
∗
rcv = ϕ 0 + 2π f 0 (t − t D ).
(4.6)
Since a process itself of radio waves reflection is connected with additional change
of reflected wave phase φ rfl , a relation (4.6) is due to be corrected:
ϕ rcv = ϕ 0 + ϕ rfl + 2π f 0 (t − t D ).
(4.7)
Difference of phases of radiated and received oscillations will comprise:
ϕ = ϕ rad − ϕ rcv = −ϕ rfl + 2π f 0 t D = −ϕ rfl + 2π f 0
2D
c
.
(4.8)
Range to a target:
D = ϕ rfl
c
4π f 0
(ϕ rfl + ϕ).
(4.9)
At condition of phase change consistency arising due to reflection ϕ rfl , we have
linear relationship between target range and phases equality of radiating and receiving
oscillations:
D = const +
c
4π f 0
ϕ = const +
λ 0
4π
(4.10)
As we can see from formula (4.10), phase meter can be graduated directly in range
units.
Considerable disadvantage of phase method is non-single-valued range measurement. In fact, phase meter will give out the same range readout both as at measuring
of phase ϕ, and phase ϕ + 2π n, (n—is any whole (integral) number), despite
that these are oscillations phases received from different ranges.
It is known that condition of single-valued range measurement via phase method
will consist in ϕ max < 2π . By substituting it into equality, a shift of phases for the
most remote target based on relation (4.9), we have: −ϕ r f l + 4π
D max
λ 0
, from which
we obtain a condition of the largest single-valued range measurement: