Antennas are essential passive components in all wireless communication, radar, navigation, and other wireless systems. Essentially, they are electromagnetic energy converters that achieve bidirectional conversion between guided electromagnetic waves in transmission lines and free electromagnetic waves in free space, while also undertaking the tasks of electromagnetic wave radiation and reception. From the perspective of system architecture, the antenna connects the RF transceiver equipment with the spatial propagation medium, and is the only interactive interface between electrical signals and spatial electromagnetic signals. Without an antenna, all wireless devices cannot achieve long-distance signal transmission and can only complete the signal flow inside the circuit. The working principle of an antenna relies entirely on the electromagnetic induction and radiation laws of Maxwell's electromagnetic field equations, which run through the bidirectional working process of transmission and reception.

In the transmitting working state, the RF transmitter transmits a guided wave composed of high-frequency alternating current and voltage to the antenna body through a feeder line. When ordinary wires transmit high-frequency signals, the electromagnetic field is confined around the wire and cannot diffuse and radiate outward. However, antennas are designed with special structures to break the electromagnetic field confinement conditions. When the physical size of the antenna matches the operating wavelength, the alternating charges on the antenna conductor will produce periodic oscillations, thereby exciting alternating electric and magnetic fields. According to the principle of electromagnetic radiation, an alternating electric field excites an alternating magnetic field, which in turn generates an alternating electric field. The two are coupled and alternately generated, forming electromagnetic waves that break away from conductors and continue to propagate into free space, completing the conversion from electrical energy in circuits to electromagnetic energy in space.

In the receiving working state, the process and transmission are completely reversible. When electromagnetic waves propagating in space are incident on the antenna structure, the alternating electromagnetic field will cut the antenna conductor, inducing periodic alternating electromotive force and induced current inside the antenna. These weak electrical signals are transmitted to the receiver through a feeder line, and after amplification, filtering, demodulation, and other subsequent processing, the original speech, data, images, and other effective information are restored, completing the conversion of spatial electromagnetic energy to circuit electrical energy. The vast majority of antennas have reciprocity in transmission and reception, meaning that the same antenna can simultaneously meet both transmission and reception requirements, and the transmission and reception performance parameters are basically the same. Only some dedicated transmission or reception antennas will be optimized accordingly.

The radiation efficiency and working performance of an antenna are not fixed and unchanging, and their core depends on the structural size, shape, material, impedance matching status, and working frequency. Low frequency antennas have longer wavelengths, so their physical dimensions are generally larger, and they are often used for broadcasting, television, and shortwave communication; High frequency antennas have shorter wavelengths, compact and compact structures, and are widely used in 5G communication WiFi、 Satellite navigation and other scenarios. At the same time, the design of the antenna must meet the resonance condition. Only in the resonance state, the electromagnetic conversion efficiency of the antenna is the highest and the signal loss is the smallest. This is also the core basis for antenna selection and debugging. In short, the core value of an antenna is to build an electromagnetic transmission bridge between the circuit system and free space, enabling long-distance transmission and interaction of wireless signals.