Antenna
From the perspective of energy conversion, unlocking the evolution code of antennas
Estimated 15minutes to finish reading
In the vast system of wireless communication, antennas play a key role. Essentially, they are a very special type of energy converter that can achieve energy conversion between guided waves and free space waves. This conversion process is of paramount importance in the transmission and reception stages of communication signals.
When in the signal transmission state, the high-frequency current from the transmitter is transmitted along the transmission line to the antenna. At this moment, the antenna acts like a magical wizard, skillfully converting the energy in the form of guided waves (high-frequency current) into free space waves, which we commonly refer to as electromagnetic waves, and then radiating them into the surrounding space. For example, in common mobile phone communication, the internal circuits of the phone generate high-frequency current signals, which are transmitted to the phone's antenna. The antenna then converts these signals into electromagnetic waves and emits them, establishing a communication connection with the base station to achieve information transmission.
In the signal reception phase, the antenna's work is the reverse of the above process. When electromagnetic waves propagating in space reach the antenna, it sensitively captures these electromagnetic waves and converts the energy they contain into high-frequency current, which is the conversion from free space waves to guided waves. This high-frequency current is then transmitted through the transmission line to the receiver for subsequent signal processing and information extraction. For example, the television antenna in our home can receive electromagnetic waves emitted by television stations and convert them into electrical signals, which are transmitted to the television, allowing us to watch a variety of television programs.
Early Exploration: The Prototype of Antennas and Initial Energy Conversion
In the 19th century, the field of electromagnetism witnessed significant theoretical breakthroughs. James Clerk Maxwell proposed the famous Maxwell equations, theoretically predicting the existence of electromagnetic waves and laying a solid theoretical foundation for the birth of antennas. In 1887, German physicist Heinrich Hertz conducted a series of pioneering experiments to verify Maxwell's predictions. He designed and manufactured the world's first antenna system, consisting of two metal rods about 30 centimeters long, with the ends connected to two metal plates of 40 square centimeters. Electromagnetic waves were excited through spark discharges between the metal balls; the receiving antenna was a single-loop metal square ring antenna, which indicated that a signal was received when sparks appeared between the endpoints of the ring. Hertz's experiment not only successfully confirmed the existence of electromagnetic waves but also marked the official birth of antennas, opening a new era for human exploration of wireless communication. Although Hertz's antenna structure was very simple and the energy conversion efficiency was relatively low, it achieved the initial energy conversion from guided waves to free space waves, allowing people to intuitively experience the wonders of electromagnetic waves for the first time and accumulating valuable experience for the subsequent development of antenna technology.
After Hertz, Italian inventor Guglielmo Marconi made significant progress in the application of antennas. In 1901, Marconi successfully achieved transoceanic communication using a large antenna. His transmitting antenna consisted of 50 downward copper wires arranged in a fan shape, with the top connected by a horizontal line suspended between two towers 150 feet high and 200 feet apart. The electric spark discharge transmitter connected between the antenna and the ground can be regarded as the first practical monopole antenna. This milestone communication experiment crossed the Atlantic Ocean, achieving long-distance signal transmission of about 2500 kilometers, demonstrating the enormous potential of antennas in long-distance communication and moving wireless communication from the laboratory to the broad stage of practical application. Marconi's success ignited global enthusiasm for research in antenna technology and wireless communication, prompting many scientists and engineers to engage in this field and continuously advance antenna technology.
Development History: Technological Innovations Driving Energy Conversion Upgrades
After the pioneering work of Hertz and Marconi, antenna technology entered a rapid development track. In the first half of the 20th century, there was a boom in the development of wire antennas. With the continuous expansion of applications such as radio broadcasting and communication, various types of wire antennas emerged, such as dipole antennas, loop antennas, and long wire antennas. These antennas were structurally more complex than the early simple antennas, significantly improving energy conversion efficiency and signal radiation directionality through careful design of antenna shapes, sizes, and arrangements. For example, the Yagi-Uda antenna consists of an active element, a reflector, and multiple directors, allowing it to concentrate energy in one direction, greatly enhancing the antenna's gain. Compared to early simple antennas, the Yagi-Uda antenna is more efficient in energy conversion and signal transmission, enabling longer distances and more stable communication, and has been widely used in broadcasting and television.
From the early 1930s to the late 1950s, with the invention of microwave traveling wave tubes and magnetrons, microwave technology rapidly emerged, and antenna technology entered the era of aperture antennas. During this period, parabolic antennas and reflector antennas were widely used. Parabolic antennas utilize the reflective properties of parabolas to convert spherical waves radiated from the feed into plane waves, achieving high gain and narrow beam signal radiation, allowing energy to be emitted more concentratedly, greatly improving communication distance and quality, playing a key role in radar and satellite communication. Meanwhile, new types of antennas such as waveguide slot antennas, dielectric rod antennas, and helical antennas continued to emerge, each with unique performance advantages, adapting to the diverse needs of different application scenarios.
After the mid-20th century, with the rapid development of communication technology, higher demands were placed on antenna performance, driving antenna technology towards diversification and intelligence. Array antennas achieve beamforming and spatial diversity by arranging multiple antenna elements in a certain pattern, allowing flexible adjustment of signal radiation direction and gain according to communication needs, effectively improving the capacity and anti-interference ability of communication systems. Phased array antennas, through electronic control, can quickly and accurately change the direction of the antenna beam, enabling simultaneous tracking and communication with multiple targets, showcasing significant advantages in military radar and mobile communication base stations. Smart antennas combine advanced signal processing technology and adaptive algorithms to automatically adjust antenna parameters such as beam direction and gain according to changes in the surrounding environment and communication signals, achieving optimal communication effects and greatly enhancing the intelligence level and spectrum utilization of communication systems.
Modern Diversity: Intelligent Energy Conversion in Various Scenarios
Entering modern society, communication technology has developed exponentially, and the application scenarios of wireless communication have become increasingly rich and diverse, prompting continuous evolution of antenna technology to meet the special needs of different scenarios, demonstrating outstanding wisdom and innovation in energy conversion.
In the 5G communication era, the demand for high speed, low latency, and large capacity communication is extremely urgent, posing unprecedented challenges to antenna performance. 5G base stations widely adopt Massive MIMO (Massive Multiple Input Multiple Output) antenna technology, deploying a large number of antenna elements at the base station to form large-scale antenna arrays, achieving spatial multiplexing and beamforming. This technology can precisely adjust the radiation direction and gain of signals according to the user's location and communication needs, concentrating energy towards target users, thereby improving signal transmission efficiency and coverage, significantly enhancing the capacity and performance of communication systems. For example, in densely populated urban areas, 5G base station's Massive MIMO antennas can use beamforming technology to concentrate coverage on various users within high-rise buildings, effectively solving signal blockage and interference issues, ensuring users can enjoy high-speed and stable 5G network services.
In the field of satellite communication, antennas also have stringent performance requirements. Satellite antennas need to possess high gain, high pointing accuracy, and good anti-interference capabilities to achieve reliable communication with satellites. Phased array antennas are widely used in satellite communication, as they can quickly and flexibly change the direction of the beam by controlling the phase and amplitude of each element in the antenna array, achieving precise tracking and communication with satellites. Multi-beam antennas are also a key technology in satellite communication, capable of concentrating electromagnetic wave energy in multiple directions, forming multiple beams, and covering users in different areas, greatly improving the efficiency and capacity of satellite communication. For instance, multi-beam antennas in low Earth orbit satellite communication systems can dynamically allocate electromagnetic wave energy according to the communication needs of different regions, providing high-quality communication services to users on the ground.
Radar systems, as important detection devices, play an indispensable role in military, meteorology, aerospace, and other fields. The performance of radar antennas directly affects the detection capability and accuracy of radar systems. Modern radar antennas typically use phased array technology and digital beamforming technology. Phased array antennas achieve rapid scanning and flexible control of beams through electronic scanning, enabling detection and tracking of multiple targets in a short time. Digital beamforming technology allows for more precise beam formation and control by digitally processing the signals from antenna elements, improving radar resolution and anti-interference capabilities. For example, in military radar, phased array radar antennas can quickly scan the airspace, timely detecting and tracking aerial targets, providing strong support for air defense operations. In meteorological radar, digital beamforming technology can more accurately detect meteorological information in cloud layers, improving the accuracy of weather forecasts.
