The main points of making parabolic antennas by amateur--the relationship between the F / D of the parabolic antenna and the radiation direction angle Q of the feed F / D (F is the focus of the parabola, D is the diameter of the parabola) and the directional angle Q of the feed is a subordinate relationship, which means that the diameter and focal length of the parabolic antenna you want to make can only be determined after the directional angle of the feed is determined . As an amateur, it is not enough to know that F / D = 0.3--0.5. How to make a suitable F / D for an antenna and a feeder is an important issue. It directly affects the efficiency and efficiency of the antenna system. S / N ratio, etc. The Q shown in Figure 1-1 is inherent in the feed. When the feed is determined, Q is also determined.
To make an antenna, we must first determine the feed source. Only when the direction angle of the feed source is known, can we make antennas with different diameters according to different F / Ds. To achieve the desired effect, the situation shown in Figure 1-2 or Figure 1-3 must be produced. The situation in Figure 1-2 will cause clutter reflected from the ground to enter the feed, and microwaves and diffracted waves at the edge of the antenna will also enter the feed, reducing the signal-to-noise ratio of the antenna receiving system. The situation in Figure 1-3 will reduce the utilization of the antenna and cause artificial waste and the side lobes 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, and then draw the mold according to the parabolic equation: X = Y * Y / 4F.
The caliber of the parabolic antenna can be calculated by the following formula:
Direction angle of feed (Q) | 100 degree | 120 degrees | 160 degrees | 180 degree |
Antenna efficiency (K) | 70% | 60% | 55% | 50% |
The direction angle of the general half-wave oscillator feed (with back reflector) and the spiral feed is about 100 degrees.
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Source: Newsletter