4.2 Angular Coordinates Measurement Methods
69
Now then, according to picked out in comparison circuit phases shift in two spaced
antennas, an angular target coordinate can be determined:
α = arcsin
λ
2πl
ϕ
.
(4.18)
Phase difference ϕ, usually picked out in a form of voltage at the phase detector
output of comparison circuit, acquires a zero value when α = 0.
A curvature of direction-finding characteristic will be defined via differentiation
of ϕ in α that leads to the next equitation:
S =
d(ϕ)
dα
=
2πl
λ
cosα,
(4.19)
which at small angles α becomes:
S =
2πl
λ
.
(4.20)
As we can see, a curvature of direction-finding characteristic of phase direction
finder, and, consequently, accuracy of direction-finding in real conditions depend on
base relation to wavelength l/λ.
As at range measurement, a clear phase method of angular coordinates measuring
features a readout ambiguity. The indistinguishable readouts values (ϕ i ϕ+2π n)
can correspond to different angular coordinates. Condition of measurement single
valuedness of angular coordinate at phase direction-finding consists in ϕ < 2π .
This condition of ambiguity requires a relation reducing between base value and
operating wavelength.
l
λ
<
1
sinα max
.
(4.21)
For instance, for intention of angular target position within ±30°, the relation l/λ
should be less than 2.
Formulas comparison shows that requirements to accuracy and ambiguity of
phase direction-finding are inconsistent. Thus, in radar engineering in some cases,
the combination of amplitude and phase methods is used for angular coordinates
measuring.
Temporal angular coordinates measurement method. Temporal measurement
method of object angular coordinates found a use in goniometric radio navigation systems (RNS). Azimuth determination of an object relatively to groundbased beacon in such systems is based on measuring of time interval between
receiving moment of reference signal (i.e., readout moment) and receiving moment of
azimuthal signal. The sense of this method of measuring angular parameter consists
in the following.
69
Now then, according to picked out in comparison circuit phases shift in two spaced
antennas, an angular target coordinate can be determined:
α = arcsin
λ
2πl
ϕ
.
(4.18)
Phase difference ϕ, usually picked out in a form of voltage at the phase detector
output of comparison circuit, acquires a zero value when α = 0.
A curvature of direction-finding characteristic will be defined via differentiation
of ϕ in α that leads to the next equitation:
S =
d(ϕ)
dα
=
2πl
λ
cosα,
(4.19)
which at small angles α becomes:
S =
2πl
λ
.
(4.20)
As we can see, a curvature of direction-finding characteristic of phase direction
finder, and, consequently, accuracy of direction-finding in real conditions depend on
base relation to wavelength l/λ.
As at range measurement, a clear phase method of angular coordinates measuring
features a readout ambiguity. The indistinguishable readouts values (ϕ i ϕ+2π n)
can correspond to different angular coordinates. Condition of measurement single
valuedness of angular coordinate at phase direction-finding consists in ϕ < 2π .
This condition of ambiguity requires a relation reducing between base value and
operating wavelength.
l
λ
<
1
sinα max
.
(4.21)
For instance, for intention of angular target position within ±30°, the relation l/λ
should be less than 2.
Formulas comparison shows that requirements to accuracy and ambiguity of
phase direction-finding are inconsistent. Thus, in radar engineering in some cases,
the combination of amplitude and phase methods is used for angular coordinates
measuring.
Temporal angular coordinates measurement method. Temporal measurement
method of object angular coordinates found a use in goniometric radio navigation systems (RNS). Azimuth determination of an object relatively to groundbased beacon in such systems is based on measuring of time interval between
receiving moment of reference signal (i.e., readout moment) and receiving moment of
azimuthal signal. The sense of this method of measuring angular parameter consists
in the following.