Antennas are the cornerstone of wireless communication, responsible for effectively radiating electromagnetic waves into or receiving them from the air. The following is a detailed introduction to the basic knowledge of antennas, including their principles, definitions, and classifications.
1.1 Basic Concepts of Antennas
An antenna is a special device that can convert electronic signals into electromagnetic waves and radiate them in a specific direction, or receive electromagnetic waves from a specific direction and convert them back into electronic signals. In a radio transmitter, an antenna receives radio frequency signals and radiates these signals by converting them into electromagnetic waves. At the receiving end, the antenna is responsible for capturing electromagnetic waves and converting them back into RF signals for processing by the receiver.
The function of an antenna is based on the reciprocity theorem, which means that the same antenna can be used as both a transmitting antenna and a receiving antenna. In both cases, the basic characteristic parameters of the antenna remain consistent.
1.2 Working principle of antenna
The working principle of an antenna is mainly based on the principles of electromagnetic induction and electromagnetic radiation. When an antenna receives a radio frequency signal, it generates a changing electromagnetic field around it. This electromagnetic field will then radiate into the surrounding space in the form of electromagnetic waves. Similarly, when there are electromagnetic waves in space, the antenna can sense these waves and convert them into electrical signals.
In addition, the antenna also uses an LC circuit as a resonant circuit to improve the quality of the signal. The quality factor of LC circuit is much higher than that of RC circuit, which enables the antenna to induce strong oscillation signals under weak external electric field conditions. According to Maxwell's electromagnetic field theory, the changing electric and magnetic fields are interdependent and alternate, forming electromagnetic waves in space.
Symmetrical oscillator antenna is a common type of antenna, which consists of two equally long wires forming an open transmission line. When a signal is transmitted over a wire, the current exhibits a standing wave distribution on the wire. By gradually opening the end of the wire, the radiation capability of the antenna gradually increases. When the wires are fully unfolded, they form a radiating symmetric oscillator.
The basic radiating element of an antenna is a half wave symmetrical oscillator, whose length is half the wavelength of an electrical signal. This type of oscillator is widely used in the short wave, ultra short wave, and microwave bands. The actual length of a conductor is related to the wavelength of the electrical signal, and the signal generator provides electrical energy to the antenna through the antenna feeder. Forming standing waves of voltage and current throughout the entire conductor, thereby converting electrical energy into electromagnetic radiation.
For microstrip antennas, actual simulations show that their resonant frequency point is not a quarter of the conductor length, but slightly smaller than this value. Therefore, when designing microstrip antennas, simulations are usually conducted using lengths slightly less than a quarter wavelength.
Antennas can be classified according to different classification criteria, including working nature, purpose, antenna characteristics, current distribution, frequency band, carrier, and shape. Different types of antennas play different roles in wireless communication, meeting various specific needs.
Diversified classification of antennas
Antennas can be classified based on various factors to meet different communication needs and application scenarios. According to the nature of work, antennas can be divided into transmitting antennas, receiving antennas, and shared transmitting and receiving antennas. By purpose, antennas can be used in fields such as communication, broadcasting, television, radar, navigation, and direction finding. The characteristics of antennas, such as directionality, polarization, and frequency band, are also important criteria for classification. In addition, the current distribution, frequency band, carrier, and shape of the antenna are also common classification criteria.
By understanding the different types and characteristics of antennas, we can better understand the important role of antennas in wireless communication and choose the appropriate antenna type based on actual needs.
