12 Radar Systems of Maritime Transport
211
The wavelength of the shipboard navigation radar is selected based on the task:
to ensure the detection of both large and small surface and ground objects within a
given radius of radar range; ensure the radar operation with short pulses; to obtain
high directivity of antenna in horizontal plane without excessively increasing the
antenna size.
Effective reflection of energy from objects is possible only when objects dimensions and the radii of curvature of individual sections are at many times greater
than the wavelength. In this case, the reflection intensity reaches a noticeable value,
depends little on the wavelength and is mainly determined by the reflecting properties and object dimensions. Taking into account the size of surface objects (buoys,
milestones, boats, etc.), only the ultrashort-wave (VHF) range, more precisely, the
short-wave section of the VHF range, is suitable for their successful detection using
the shipboard radar.
The radar wavelength affects the detection range of low-lying (low-set) surface
objects and the maximum range of radar detection. With a decrease in the wavelength,
the detection range of low-lying surface objects increases, but at the same time the
maximum operational range of the radar decreases due to attenuation associated with
an increase in the absorption of electromagnetic energy in the troposphere.
Based on the abovementioned, the shipboard navigation radar uses the centimeter
range of radio waves (S-band). Moreover, the standard wavelengths in this range are
3.2 and 10 cm.
To ensure a high potential azimuth resolution and increase the potential accuracy
of determining directions, the beam width of shipboard navigation radars should be
1–0.25°.
The pulse-recurrence rate or pulse repetition rate is selected based on the problem
of unambiguously determining of range and object detection efficiency in conditions of circular scan. Shipboard navigation radars usually operate on different range
scales, the operating frequency F p pulse repetition may vary. For example, on shortrange scales, frequencies of 1000 ÷ 3200 pulses/s are used, on long-range scales,
400 ÷ 800 pulses/s.
The transmitter power has an effect on the radar operational range. The distinction
is made between pulsed and average powers. Pulse is the average value of power over
the time τ p of pulse duration. The average is the power over the period T p of pulse
repetition.
Since an increase in the average power is connected with an increase in the repetition rate or pulse duration, then in order to maintain the constancy of thermal regime
of magnetron generator, it is recommended to leave the average radar power as
unchanged as possible at different pulse-recurrence rate or different pulse durations.
This is achieved by the fact that when the radar switches a mode to operate with
shorter pulses, the repetition rate or pulse sending (pulsing) increases and vice versa.
To ensure a normal operation of the shipboard radar, the side-lobe level should
be at 20–30 dB below the main lobe level.
The behavior of electromagnetic field polarization is usually the shipboard radar
antenna used the linear horizontal or vertical polarization of the field, at which the
direction of E vector is vertical or horizontal.
211
The wavelength of the shipboard navigation radar is selected based on the task:
to ensure the detection of both large and small surface and ground objects within a
given radius of radar range; ensure the radar operation with short pulses; to obtain
high directivity of antenna in horizontal plane without excessively increasing the
antenna size.
Effective reflection of energy from objects is possible only when objects dimensions and the radii of curvature of individual sections are at many times greater
than the wavelength. In this case, the reflection intensity reaches a noticeable value,
depends little on the wavelength and is mainly determined by the reflecting properties and object dimensions. Taking into account the size of surface objects (buoys,
milestones, boats, etc.), only the ultrashort-wave (VHF) range, more precisely, the
short-wave section of the VHF range, is suitable for their successful detection using
the shipboard radar.
The radar wavelength affects the detection range of low-lying (low-set) surface
objects and the maximum range of radar detection. With a decrease in the wavelength,
the detection range of low-lying surface objects increases, but at the same time the
maximum operational range of the radar decreases due to attenuation associated with
an increase in the absorption of electromagnetic energy in the troposphere.
Based on the abovementioned, the shipboard navigation radar uses the centimeter
range of radio waves (S-band). Moreover, the standard wavelengths in this range are
3.2 and 10 cm.
To ensure a high potential azimuth resolution and increase the potential accuracy
of determining directions, the beam width of shipboard navigation radars should be
1–0.25°.
The pulse-recurrence rate or pulse repetition rate is selected based on the problem
of unambiguously determining of range and object detection efficiency in conditions of circular scan. Shipboard navigation radars usually operate on different range
scales, the operating frequency F p pulse repetition may vary. For example, on shortrange scales, frequencies of 1000 ÷ 3200 pulses/s are used, on long-range scales,
400 ÷ 800 pulses/s.
The transmitter power has an effect on the radar operational range. The distinction
is made between pulsed and average powers. Pulse is the average value of power over
the time τ p of pulse duration. The average is the power over the period T p of pulse
repetition.
Since an increase in the average power is connected with an increase in the repetition rate or pulse duration, then in order to maintain the constancy of thermal regime
of magnetron generator, it is recommended to leave the average radar power as
unchanged as possible at different pulse-recurrence rate or different pulse durations.
This is achieved by the fact that when the radar switches a mode to operate with
shorter pulses, the repetition rate or pulse sending (pulsing) increases and vice versa.
To ensure a normal operation of the shipboard radar, the side-lobe level should
be at 20–30 dB below the main lobe level.
The behavior of electromagnetic field polarization is usually the shipboard radar
antenna used the linear horizontal or vertical polarization of the field, at which the
direction of E vector is vertical or horizontal.