## Monday, December 30, 2013

### Calculating vibrator logoperiodic antenna

Broadband log-periodic antenna aimed work without rebuilding ten - twenty fold and the broader range of wavelengths . Log-periodic antenna can be used as antennas connected to the HF and VHF bands , as well as for receiving TV channels . The figure shows the log-periodic antenna, it consists of a series of vibrators connected with consistent variable phase to two-wire line . Dimensions vibrators and the distance between them decreases exponentially towards the connection point of the feeder or coaxial cable. Behind the longest dipole antenna located logoperiodic jumper that improves coordination with feeder . The distance between the jumper and the vibrator is chosen experimentally in the antenna settings. Feeder (coaxial cable with an impedance of 50-75 ohms) goes inside one of the tubes of a double line (no matter through what) . Parameters and log-periodic antennas determine the size structure of the period "t", equal to the ratio of the length to the length of follow- vibrator and the previous angle "a" at the apex of the triangle , which are inscribed vibrators . The closer the structure period "t" by one and the smaller the angle "a", the higher the gain the log-periodic antenna. But this increases the size of the antenna , often choose "t" = 0.8-0.9 and the angle "a" = 30-45 degrees. At each frequency waves in the operating range of the work involved those vibrators, resonant frequencies that are closer to this frequency (3-4 vibrator ) . Strengthening logoperiodic antenna are obtained with approximately 5-7 dB. In order to calculate the size of the log-periodic antenna vibrators need to know the length of the extreme waves Lmax and Lmin operating range. To determine the length of the longest start vibrator l1 it should be 0.55Lmax, built on an isosceles triangle with an angle "a" at the top equal to 30-45 degrees, the base of the triangle will vibrator l1. Second vibrator logoperiodic antenna located at a distance d1 = (0.15-0.18) Lmax from the first. The dimensions of the vibrator are uniquely determined size of the triangle. Likewise, the following dimensions are determined antenna dipoles . Distance d2 = d1 * t, d3 = d1 * t and so on. This arrangement continues until the next length is not equal to oscillator 0.45Lmin, this vibrator will last