Feeder for satellite TV receiving antenna
The role of the feeder
Speaking of satellite antenna, we have to mention the satellite feeder (satellite collector), in the satellite TV receiving antenna, the satellite feeder as the primary radiator of the antenna, is the heart of the antenna. Its role is to organize the electromagnetic wave reflected by the reflecting surface, so that its polarization direction is the same. And impedance transformation, so that the feed source by the round waveguide propagation of electromagnetic waves into the high frequency head by the rectangular waveguide propagation of electromagnetic waves, so as to improve the efficiency of the antenna.
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Classification of feeders
According to the different antenna structure, the feed source is also divided into two categories: one is the forward-feeding feed source, suitable for ordinary forward-feeding parabolic antenna, commonly used forward-feeding feed source has a circular slot feed source and single-loop slot feed source; the other is the back-feeding feed source, suitable for Cassegrain antenna supporting the use. Commonly used after the feed type feed source cone horn feed source, step horn feed source, variable angle horn feed source and cone medium loading horn feed source.
The structure of the ring-slot feed-forward feeder.
The circular slot feeder consists of a main waveguide with a circular slot, a dielectric phase shifter and a circular moment waveguide converter, as shown in the figure below. The main waveguide is a section of circular waveguide with a diameter of (0.6~11lA (A is the wavelength of the received wave), which is equipped with a hollow disk with 3~4 annular slots at its outer port, called the waveguide ring (or choke slot, which we call the feeder disk).
The dielectric phase shifter consists of a phase shifting dielectric sheet inserted in the circular waveguide in a certain direction. The antenna polarization electromagnetic wave propagation in space. The instantaneous orientation of the electric field vector is called the direction of polarization of electromagnetic waves. If the electromagnetic wave in the process of propagation by the electric field vector traced out the trajectory, along the direction of electromagnetic wave propagation can be line polarization wave, horizontal polarization wave, vertical polarization wave, oblique polarization wave, right circular polarization wave, left polarization wave.
The effect is that when the transmission wave through the dielectric sheet. The wave produces a certain amount of phase shift, so that the wave completes the transformation of polarization.Circular a moment waveguide converter is the transition waveguide section from circular waveguide to rectangular waveguide transition, through which the impedance transformation and mode conversion of the electric wave is completed.
The circular slot feeder is a large-tension horn. Different focal length aperture ratio (f / D) of the antenna, with different apertures of the annular slot feed source, to provide different irradiation angle. The advantage of this feed source is: simple structure, easy processing, small size, small blocking of the radio waves. Since most of the satellite programs nowadays work with line polarization. A dielectric phase shifter is only needed for circular polarization
The difference between Ku-band Prime focus and offset
The difference between Ku-band prime focus feed and offset feed lies in the different structure of the corrugated slot. a section of the rectangular waveguide tube of the C-band split structure feed source is on the HF head, and the antenna oscillator is built into the rectangular waveguide tube on the HF head, and its installation position is shown below. Its role is to focus the electromagnetic wave reflected from the parabolic antenna (in essence, it should be the reflective surface of the antenna) to the built-in antenna of the feed source, and coupled to the high discharge circuit of the LNBF