What is a Parabolic Antenna?

A parabolic antenna is a planar antenna composed of a parabolic reflector and an illuminator (feed source) located at its focal point. Generally, a metal rotating paraboloid, a cut rotating paraboloid or a cylindrical paraboloid is used as a reflector, and a horn or a symmetrical oscillator with a reflector is used as a feed source.

A parabolic antenna is a single-reflection antenna. It uses an axisymmetric rotating paraboloid as the main reflection surface, and places the feed on the focal point F of the parabola. The feed usually uses a horn antenna or horn antenna array, as shown in the figure.

When a high-frequency current flows through a conductor, an electric field and a magnetic field are generated in the surrounding space. press

The main types of parabolic antennas are (a) feedforward parabolic antennas; (b)

The parabolic antenna was invented by the German physicist Heinrich Hertz when he discovered radio waves in 1887. In his historic experiments, he used a cylindrical parabolic reflector and a spark-excited dipole antenna to transmit and receive at the focal point.

The main advantage of a parabolic antenna is its high directivity. It functions like a searchlight or flashlight reflector, converging radio waves in a specific direction to a narrow beam, or receiving radio waves from a specific direction. Parabolic antennas have some of the highest benefits, that is, they can produce the narrowest beam widths, regardless of the type of antenna. In order to achieve a narrow beam width, the parabolic reflector must be much larger than the wavelength of the radio wave used, so parabolic antennas are part of the high-frequency radio spectrum (

Relationship between F / D of parabolic antenna and radiation direction angle Q of feed source

F / D (referred to as the focal diameter ratio, where F is the focal length of the parabola and D is the diameter of the paraboloid projected on a plane perpendicular to the axis) and the direction angle Q of the feed is dependent, that is, only the feed After the direction angle is determined, the diameter and focal length of the parabolic antenna you want to make can be determined. As an amateur, only knowing that F / D = 0.3--0.5 is not enough. How to make a matching F / D with an antenna and the feed is a very important issue. It directly affects the efficiency of the antenna system and S / N ratio, etc. The Q shown in Figure 1-1 is inherent to the feed. Once the feed is determined, Q is also determined.

To make an antenna, you must first determine the feed source. Only when the direction angle of the feed source is known, can you make antennas with different diameters according to different F / D. To achieve the desired effect, the situation shown in Figure 1-2 or Figure 1-3 is bound to occur. The situation in Figure 1-2 causes the clutter reflected on the ground to enter the feed, and the microwave and diffraction waves at the edge of the antenna will also enter the feed, which reduces the signal-to-noise ratio of the antenna receiving system. In the case of the graph, the utilization of the antenna will be reduced, causing artificial waste and the sidelobes of the signal will also enter the feed. The relationship between F / D and Q is: F / D = 1/4 * Ctg Q / 2.

So first have the feed direction angle, and then determine F = D * (1/4 * Ctg Q / 2) according to how many diameter antennas you want to make, then draw the model according to the parabolic equation: X = Y * Y / 4F. The caliber of a parabolic antenna can be calculated using the following formula:

The orientation angle of the general half-wave oscillator feed (with rear reflector) and the spiral feed is about 100 degrees