Effect of antenna feed antenna lifting bracket
Antenna feed refers to the primary radiator of continuous aperture antenna
or antenna array. Although corrugated Horn has high cost, it is widely used because of its good symmetry, low side lobe and wide frequency band.
Antenna feed excitation plane the primary radiator of the main and secondary reflective surfaces of the antenna (source horn or vibrator), referred to as the feed. It is an important device that determines the electrical characteristics and frequency band of the antenna. Its function is to radiate the RF power from feeder to the reflecting surface or lens in the form of electromagnetic waves, so as to generate appropriate field distribution on the caliber, in order to form the required sharp beam or shaped beam; At the same time, the power leaking from the edge of the reflecting surface or lens to the outside is as small as possible, so as to achieve the highest gain as possible.
The feed type includes machine antenna and vibrator. There are many types of feed horn, such as rectangle, fan, cone, etc. Commonly used are pyramid speakers and conical speakers, which are suitable for linearly polarized waves and circularly polarized waves.
The radiation of the feed horn should be spherical wave, that is, the phase directivity diagram is spherical, and the spherical center is called the phase center of the horn, and the width of the amplitude directivity diagram should match the aperture of the main (secondary) reflector, make the electromagnetic wave energy irradiate to the corresponding reflecting surface as much as possible to improve the irradiation efficiency and reduce the overflow loss. The feed should have good polarization performance, matching performance and side lobe characteristics in the working band. The main types of feed speakers are as follows:
2.1 Main model speaker
The main model Speaker works on a single main model. The Direction Diagram of the E-plane and the H-plane are inconsistent. The phase center varies greatly with the frequency and is rarely used.
2.2 Dual-mode speaker and multi-mode speaker
In order to compensate for the disadvantage of the difference between the E-plane and the H-plane pattern, the structure of the horn angle and diameter should be changed appropriately, and the high-order mode should be introduced to make the E-plane and the H-plane of the horn radiation direction tend to be equal; if more secondary modes are introduced and their amplitude and phase are properly combined, the E-plane and H-plane of the loudspeaker directional diagram tend to be more equal, but the loudspeaker structure is more complex. Its main disadvantage is that the frequency band is limited to some extent and it is difficult to realize broadband, which is only applicable to narrow band surface antennas. The base mode is called a dual-mode speaker when one high-order mode is added, and the multi-mode speaker is called when more high-order modes are introduced.
2.3 Waveform speaker
Wave Horn is an ideal feed horn. The corrugated structure design can produce mixed mode HE11. In HE11 mode, TE and TM components have the same cut-off frequency and phase velocity, it is independent of the design frequency band and frequency. Therefore, the directional diagram of E-plane and H-plane is completely equalized within the working bandwidth of about 1:1.7, and the phase center is basically independent of frequency, and it has good cross polarization performance and side lobe characteristics. The ring-loaded corrugated horn widens the frequency band and has excellent electrical characteristics in the 1:2.4 frequency band. Corrugated Horn as antenna feed can reduce overflow loss, improve irradiation efficiency and improve polarization purity, and can be widely used in various surface antennas with linear polarization and circular polarization. In the small-caliber feed-forward antenna, the shielding surface of the feed horn is relatively large, and the plane corrugated Horn is a corrugated horn with a small aperture angle of 90 °. The directional diagram is good, which is suitable for feed-forward antenna, the dual-mode corrugated horn, which increases the secondary mode HE12 on the base mode HE11, improves the horn direction pattern from Gaussian distribution to flat top fan beam, is the most ideal feed source for the feed-forward antenna.
Generally, the corrugated Horn can only be conjugate matched with the main polarization component and is suitable for symmetric systems. However, for the offset reflector antenna, it will lead to poor polarization characteristics, if the HE11 + HE21 mode combination method is used to design the feed dedicated to the bias antenna, the electrical characteristics of the bias antenna can be optimized.
2.4 combination speaker
Due to the need of automatic tracking, there are usually two combinations of four speakers and five trumpets.
Set four identical speakers symmetrically with antenna collimation axis, and use both receiving and sending communication. The sum of the received signal amplitude of the four speakers is called sum signal (that is, antenna main beam), the difference between the amplitude values received by the left and right speakers is called azimuth difference signal, and the difference between the amplitude values received by the upper and lower speakers is called pitch difference signal. The difference signal can be used as the azimuth pitch control signal of the antenna driven by Dynamic Tracking. When the two difference signals are zero, it is the sign of alignment target (at this time, the letter number is the maximum value).
The five trumpets method is to add a special speaker for communication in the middle collimation axis of the four speakers. The four speakers around are dedicated for tracking. It only receives beacon signals, which solves the problem that the offset of the four speakers requires stability during communication, sensitive contradictions are required during tracking, which makes it easier to achieve the best design. This method is widely used in remote control, telemetry, automatic tracking and radar antenna.
Function of feed
Feed is an important component of reflector antenna or lens antenna. Its function is to radiate the RF power from feeder to the reflecting surface or lens in the form of electromagnetic waves, so as to generate appropriate field distribution on the caliber, in order to form the required sharp beam or shaped beam; At the same time, the power overflowing from the edge of the reflecting surface or lens is as small as possible, so as to achieve the highest gain as possible. Taking rotating parabolic antenna 1 (figure a) as an example, if high gain is required for paraboloid with half opening angle θ m, the power emitted by the feed should be reflected to form a uniform distribution on the paraboloid caliber, and only a small amount of power will leak out from the paraboloid edge. Therefore, the main lobe width of the direction chart of the feed is required to be appropriate, not too wide or too narrow, and the field strength in Theta m direction is generally axial (θ = 0) about 1/3 of the field strength (I .e. about-10 decibels), and the side lobe and back lobe of the feed should be as small as possible. At the same time, it is also required that the feed radiates spherical waves to transform them into plane waves after parabolic reflection. That is to say, the phase pattern of the feed should be a spherical surface. The center of this sphere is called the phase center. Many antennas radiate undesirable spherical waves. At this time, the Isophase surface in the parabola angle range should be as close as possible to the spherical surface, and the center of this spherical surface is its approximate phase center. In addition, the feed is required to radiate only the wave to be polarized, match with the feeder, maintain excellent performance in a given frequency band, etc., and have sufficient power capacity when used as the feed of the transmitting antenna.