46
2 Observations of Radio and X-ray Pulsars
Fig. 2.3 Antenna’s
receiving power pattern
HKF are equal. In other words, there is same phase of the reflected signals of each
light path at focal point F, and thus the reflected signals from the parabolic surface
are overlain one other and strengthened at the focal point. If there is a big deviation
between the direction of the radio radiation signals and that of the major axis, the
reflected signals will not be focused on the feed source at the focal point. Therefore,
the radio telescope can only receive the radio waves within smaller angle deviated
from the major axis. This angle is usually called angular resolution, whose size is
decided by the antenna receiving power pattern. The antenna pattern is composed of
major lobe, side lobe and back lobe, which is shown in Fig. 2.3.
The resolution is a capability with which the radio telescope can distinguish the
smallest angular separation between two point objects on the celestial sphere, which
is usually denoted by the angular resolution, and also expressed as two times the
angle at the half maximum power point of the major lobe, that is,
2ϕ = 1.22
λ
D
,
(2.2)
where 2ϕ is the angular resolution (at a unit of radian), λ is the wavelength of the
radio telescope (at a unit of meter) and D is the antenna aperture (at a unit of meter).
It is known from formula (2.2) that the resolution is proportional to the wavelength
of the radio telescope and inversely proportional to the antenna aperture. The smaller
is the angular resolution, the stronger the capability with which the radio telescope
can clearly distinguish the details of the celestial bodies. Of course, the resolution is
also the higher.
2 Observations of Radio and X-ray Pulsars
Fig. 2.3 Antenna’s
receiving power pattern
HKF are equal. In other words, there is same phase of the reflected signals of each
light path at focal point F, and thus the reflected signals from the parabolic surface
are overlain one other and strengthened at the focal point. If there is a big deviation
between the direction of the radio radiation signals and that of the major axis, the
reflected signals will not be focused on the feed source at the focal point. Therefore,
the radio telescope can only receive the radio waves within smaller angle deviated
from the major axis. This angle is usually called angular resolution, whose size is
decided by the antenna receiving power pattern. The antenna pattern is composed of
major lobe, side lobe and back lobe, which is shown in Fig. 2.3.
The resolution is a capability with which the radio telescope can distinguish the
smallest angular separation between two point objects on the celestial sphere, which
is usually denoted by the angular resolution, and also expressed as two times the
angle at the half maximum power point of the major lobe, that is,
2ϕ = 1.22
λ
D
,
(2.2)
where 2ϕ is the angular resolution (at a unit of radian), λ is the wavelength of the
radio telescope (at a unit of meter) and D is the antenna aperture (at a unit of meter).
It is known from formula (2.2) that the resolution is proportional to the wavelength
of the radio telescope and inversely proportional to the antenna aperture. The smaller
is the angular resolution, the stronger the capability with which the radio telescope
can clearly distinguish the details of the celestial bodies. Of course, the resolution is
also the higher.