Keywords: spiral antenna
The pocket communication machine is widely used in various departments of society due to the advantages of small size, light weight and convenient use, and this machine now uses a helical antenna. Generally, the finished spiral antenna is wound into and sealed with a metal wire having good electrical conductivity. it is good. Under the working principle: Schematic diagram of the general antenna structure shown in Figure 1. D is a spiral antenna diameter, and L is a spiral antenna length, ρ is a pitch, I, II is two points corresponding to the helix. It is generally conceivable that electromagnetic waves can be moved at a speed of light at the metal helix. A helix is performed from the I point to II, and the required time is: T = πd / c, and the axial electromagnetic wave is moved in the axial electromagnetic wave, and its axial equivalent rate: υ = ρ / t = ρ / c (πd) This relationship can also be explained in the form of Fig. 2. As can be seen from Fig. 2: = csin θ = cρ / (πd) ≤ C is seen from the above formula, υ always less than or equal to C. Therefore, the spiral antenna can slow the speed of electromagnetic wave movement, is a slow wave system, and its equivalent wavelength λ is equivalent to less than the working wavelength λ. For spiral antenna, the resonument is resonant to its 1/4 equivalent wavelength, thus shortening the geometric length of the spiral antenna. For a communication machine operated in a certain center frequency, the number N of the required coil can be approximately calculated by the following formula: pitch: = l / n Description of metal wire length: ι = Nπd to take L = 20 ~ 40CMD = 10 ~ 20mm The following table is a design example of some common frequency spiral antennas, and other frequencies can also be similar. f is the working center frequency; D is a spiral antenna diameter; L is a spiral antenna length; n is a spiral ring number; ι is the required metal wire length. The above N, ρ is taken from the actual production needs. When making a diameter of 0.5 to 1.5 mm enameled wire or a silver-plated copper wire or an aluminum wire in an organic glass or other insulating material having a diameter D. The small hole is hit on the two heads of the rod to facilitate the fixed metal line; at a rod The bottom-end welding is fixed on a rod or a plug to facilitate the connection with the machine; the entire helix antenna can be sealed with a rubber tube or other material, and cover the rubber cap on the top or other materials, so It is beautiful and rare, and the rain is corrupted, and it is durable. If there is no such wire, a multi-shaped fine instead of a multi-stranding guide is used instead, the effect is the same, but it is difficult to fix it. The above spiral antenna can also be used in a variety of small remote control devices and other similar machines. In order to relatively slow wave antennas and the conventional trolley antenna, the advantages of smaller sizes of slow wave antennas are given, and we can calculate the tie rod antenna. The setting parameters are as follows: Frequency f = 27MHz wave speed C = 3 × 108M (Note: 108 8 times) Antenna should be resonant to 1/4 working wavelength, then calculate the length of the tie rod antenna by formula: L = 1 / 4λ = 1/4 c / f = 1/4 (3 × 108/27 × 108) = 2.78m (Note: 108 8 times) followed by the above table, can be seen if the spiral antenna, the center frequency The 27MHz slow wave antenna, which is only 40cm in length, and the dimension is only for one of the tie rod antenna.
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