What is a log-periodic antenna and how does it work?

　　What is a log-periodic antenna and how does it work?

　　The log-periodic antenna (sometimes also called a log-periodic array) is an antenna designed to operate over a wide frequency range, with a particular focus on low-frequency radio waves. Invented and patented in 1952 by John Dunlavey of Colorado, it is now used in a variety of fields, such as fire departments that use specific models of log-periodic antennas to scan for dangers and sound alarms.

　　Components of a log-periodic antenna

　　Similar to other antenna devices, a log-periodic antenna consists of three core components:

　　Tuning circuit: As a key part of signal processing, it participates in signal tuning and optimization.

　　Transmitter: Responsible for signal transmission and is the signal output end of the antenna.

　　Loop: As a receiving element, it is usually made of metal alloy and has many loops of metal wire on the surface to capture external signals; its matching tuning assembly contains a series of diamond-shaped teeth surrounded by rubber beads, which act as tuning elements to help optimize signal reception.

　　Working principle of log-periodic antenna

　　The working process of log-periodic antenna revolves around signal reception, processing and matching, and the core mechanism is as follows:

　　The basis of signal reception: To receive the transmitted signal, the antenna's receiver needs to be equipped with a resonator that can receive the shortest waveform within its bandwidth (for example, a waveform with a frequency of about 3000 MHz).

　　Energy calculation and wavelength matching: By analyzing the reflection and emission methods of radio waves in the transmitter and antenna, the maximum energy that the medium can absorb can be calculated using mathematical formulas. After that, the "activation zone" of the log-periodic antenna is used to match the emission wavelength to ensure effective signal transmission.

　　The role of the activation zone and the zero interference zone: The activation zone refers to the part where the length of the wave remains unchanged when the transmitter and antenna transmit the wave along a straight line; when there is no component on the propagation path of the wave, it is in the "zero interference zone". When the output signal level is higher than a certain critical level, the antenna enters the activation zone (the critical level of different components may be different), and the total harmonic distortion of the system is less than the minimum value. Since the total harmonic distortion is equal to the difference between the input and output levels of the system, the critical level is zero.

　　Features and application advantages of log-periodic antennas

　　Wide signal reception capability: Mobile phone calls, cell phone signals and even TV broadcasts can be received without relying on directional couplers or dipoles. With modern technology, most analog signals can be transmitted with only a single dipole or a single cellular signal booster.

　　Performance advantages: Compared with traditional systems, its mobile communication system has low power consumption and high signal-to-noise ratio. Low power consumption comes from using only one unit for each transmitted cellular signal; high signal-to-noise ratio ensures signal quality and reduces noise interference.

　　Receiving distance and limitations: The maximum receiving distance is about three times the receiving antenna frequency (for example, 3.5 mm wireless devices with the same frequency have a maximum receiving range of up to 30 miles). But it does not work well in dual-motor transmission systems because the receiving range is short. In addition, the maximum signal-to-noise ratio is an important consideration when purchasing.