Đặc điểm cơ bản của sóng vô tuyến
2026-03-11
I. Basic Characteristics of Radio Waves WWW.WHWIRELESS.COM Estimated reading time: 15 minutes 1.1 Definition of Radio Waves Radio waves serve as the carrier of signals and energy, generated by the mutual coupling of oscillating electric and magnetic fields, adhering to the alternating coupling law of "electricity generates magnetism and magnetism generates electricity". During propagation, the electric and magnetic fields are always perpendicular to each other and both perpendicular to the propagation direction of the wave, making them **Transverse Electromagnetic Waves (TEM waves)**. Their generation originates from high-frequency oscillating circuits: when the current in a circuit changes rapidly over time, an alternating electromagnetic field is excited in the surrounding space. Once this electromagnetic field detaches from the wave source, it propagates through space in the form of radio waves, without relying on any medium—they can even transmit in a vacuum. 1.2 Relationship between Wavelength, Frequency and Propagation Speed The core formula governing the relationship between the wavelength (λ), frequency (f) of radio waves and their propagation speed (speed of light \( C \) in a vacuum, approximately \( 3×10^8 \, \text{m/s} \)) is: \[ \lambda = \frac{C}{f} \] **Key Conclusion**: In the same medium, frequency and wavelength are strictly inversely proportional—the higher the frequency, the shorter the wavelength. This relationship directly dictates the design dimensions of antennas: for example, the wavelength of a 2.4GHz WiFi signal is approximately 12.5 cm, corresponding to a half-wave dipole antenna length of about 6.25 cm; for a 700MHz low-frequency communication signal, the wavelength is approximately 42.8 cm, requiring a half-wave dipole length of 21.4 cm. Additionally, the electrical performance of an antenna (such as radiation efficiency, gain, and impedance) is directly related to its **electrical length** (the ratio of physical length to wavelength). In practical engineering, the required electrical length must be converted to the specific physical length to ensure the antenna operates properly. 1.3 Polarization of Radio Waves Polarization refers to the variation law of the electric field direction as a radio wave propagates, determined by the spatial motion trajectory of the electric field vector, forming a complete spectrum: **Circular Polarization ← Elliptical Polarization → Linear Polarization**. The core characteristics and application scenarios of the three are as follows: - **Phân cực tuyến tính**: Hướng điện trường không đổi, đây là dạng phân cực được sử dụng phổ biến nhất. Sóng có điện trường vuông góc với mặt đất là **sóng phân cực dọc**, có khả năng chống nhiễu phản xạ từ mặt đất mạnh và phù hợp với truyền thông di động mặt đất (ví dụ: các trạm gốc 2G/3G truyền thống); sóng có điện trường song song với mặt đất là **sóng phân cực ngang**, thường được sử dụng trong truyền dẫn radio và truyền hình, truyền thông chuyển tiếp ...
xem thêm