RF Antenna introduction

The antenna is a key element used to transmit or receive radio waves. It can also be said that the antenna is used to generate electromagnetic wave radiation. However, there are many factors that can affect the antenna, including the application environment, the material used by the antenna, and the performance of the antenna itself.

Antenna parameters: There are many critical parameters that affect antenna performance, which can usually be adjusted during the antenna design process, such as resonance frequency, impedance, gain, aperture or radiation pattern, polarization, efficiency, and bandwidth. In addition, the transmitting antenna has a maximum rated power, and the receiving antenna has noise suppression parameters.

Antenna types: There are many types of antennas; all are evolved from dipole antennas. Common antenna types are: Dipole Antenna, Monopole Antenna, Loop Antenna, Inverted F antenna (PIFA), patch antenna (Patch Antenna), microstrip antenna, array antenna (series, parallel)... etc.

Antenna resonant frequency and bandwidth: The antenna frequency must be used in accordance with the standard frequency determined by each country, such as: LTE, WI-FI, GPS and even the fifth generation communication (5G), and in general, the bandwidth impedance is proportional to the frequency For example, the lower the frequency, the narrower the bandwidth, the more difficult it is to adjust the impedance, and the higher the frequency, the opposite.

Antenna Impedance: Why is it 50 ohms? In fact, 50 ohms is a result of many experiments done by Bell Laboratories, only to find that the characteristic impedance of coaxial cables that meet this high-power transmission and low loss are 30 ohms and 77 ohms. Among them, the 30-ohm coaxial cable can transmit the largest power, and the 77-ohm coaxial cable has the smallest signal loss.

The arithmetic average of 30 ohms and 77 ohms is 53.5 ohms, the geometric average of 30 ohms and 77 ohms is 48 ohms, 50 ohms is an engineering compromise between 53.5 ohms and 48 ohms, considering maximum power transmission and minimum loss At the same time as possible, the port impedance of the half-wavelength dipole antenna and the quarter-wavelength monopole antenna are also matched, and the reflection loss caused is the smallest.

Antenna radiation efficiency: Antenna efficiency refers to the ratio of the power radiated by the antenna (that is, the power that effectively converts the electromagnetic wave part) to the active power input to the antenna. Theoretically, the larger the better, but the value is always less than 1, and needs to be considered Factors such as use environment, material and design.

Antenna gain: The antenna gain is passive. In the antenna design, "gain" refers to the ratio of the intensity of the antenna radiation pattern in the strongest radiation direction of the antenna to the intensity of the reference antenna. If the reference antenna is an omnidirectional antenna, the unit of gain is dBi. For example, the gain of the dipole antenna is 2.15dBi. Dipole antennas are also often used as reference antennas. The higher the antenna gain, the smaller the effective angle used. This is the part that people will forget, that is, their power adjusted from other directions is then superimposed on the radiation in the desired direction.

Antenna polarization: When electromagnetic waves propagate in space, if the direction of the electric field vector remains fixed or rotates according to a certain rule, this electromagnetic wave is called polarization, which can be divided into horizontal polarization, vertical polarization, and 45 degree polarization.
Array antenna: If you want to increase anenna gain . You must use an array antenna. This type of antenna has directivity (mainly in parallel) and omni-directional (mainly in series). Of course. You can also start from the material in antenna.