What are the types of antennas

1. What types of antennas are there

An antenna is a device that radiates radio frequency signals from a transmission line to the air or receives them from the air to the transmission line. It can also be seen as an impedance converter or an energy converter, which transforms the guided waves propagating on the transmission line into electromagnetic waves propagating in an unbounded medium, or performs the opposite transformation. The design and selection of antennas are important parts of designing a wireless transceiver device for RF systems. A good antenna system can achieve optimal communication distance. The size of the same type of antenna is proportional to the wavelength of the RF signal, and the lower the frequency of the signal, the larger the required antenna.

Antennas can be divided into external antennas and internal antennas based on their installation location. Antennas installed inside the device are called internal antennas, while antennas installed outside the device are called external antennas. For small-sized products such as handheld devices, wearable designs, and smart homes, built-in antennas are commonly used, which have high integration and beautiful appearance. The Internet of Things and intelligent hardware products require the use of antennas to transmit data through the internet. The smaller the space and the more frequency bands, the more complex the antenna design. External antennas are generally standard products, and can be used by selecting the required frequency band antenna without debugging, plug and play. For example, express delivery cabinets, vending machines, etc. commonly use external antennas with magnetic suction, which can be attached to the iron shell. These antennas cannot be placed inside metal cabinets as metal can shield antenna signals, so they can only be placed outside. This article focuses on the classification and selection methods of antennas, and introduces relevant information about antennas.

1.1 External antenna

External antennas can be divided into omnidirectional antennas and directional antennas based on the different radiation angles and directions of the radiation field.

1.1.1 Omnidirectional antenna

Omnidirectional antenna, which exhibits uniform radiation at 360 ° in the horizontal direction, also known as directionless, and a beam with a certain width in the vertical direction. Generally, the smaller the lobe width, the greater the gain. External omnidirectional antennas mainly include suction cup antennas, fiberglass antennas, and rubber rod antennas.

1.1.2 Directional antenna

Directional antenna refers to an antenna that emits and receives electromagnetic waves with strong characteristics in one or several specific directions, while transmitting and receiving electromagnetic waves in other directions are zero or extremely small. The purpose of using directional transmission antennas is to increase the effective utilization of radiation power and enhance confidentiality; The main purpose of using directional receiving antennas is to enhance signal strength and increase anti-interference ability. External directional antennas mainly include flat panel antennas, Yagi antennas, and logarithmic periodic antennas.

1.2. Built in antenna

Built in antennas mainly refer to antennas that can be placed inside devices. Built in antennas mainly include FPC antennas, PCB antennas, spring antennas, ceramic patch antennas, laser direct forming technology (LDS), and hardware patch antennas.

2. Selection Guide

When selecting a suitable antenna for the device, the first step is to determine whether to use an internal or external antenna based on the product structure. An external antenna is to install the antenna outside the device;

2.1 External antenna selection

Firstly, it is necessary to determine the coverage area of the device signal. The direction of signal coverage is determined by the radiation pattern of the antenna. According to the radiation direction of the antenna, the antenna is divided into omnidirectional antenna and directional antenna.

Omnidirectional antenna, which exhibits uniform radiation at 360 ° on a horizontal pattern, is commonly known as directionless.

2.1.1 Suction cup antenna

The gain is relatively high, and the biggest feature is the strong magnetic suction cup, which is very convenient to install and fix. However, the suction cup must be adsorbed on the metal surface. In the wireless module industry, the suction cup antenna is often used in conjunction with wireless modules to increase the communication distance of wireless modules, such as intelligent meter reading, vending machines, express cabinets, car radios, etc.

2.1.2 Copper rod suction cup antenna

Similar to a regular whip shaped suction cup antenna, but with the advantage of using a larger diameter pure copper radiator, its ohmic loss is small, the antenna efficiency is high, and the bandwidth coverage is wide. Suitable for data transmission radios with relatively high performance requirements, medium distance image transmission, etc.

2.1.3 Rubber rod antenna

The most common external antenna, with moderate gain and relatively low price, is commonly used in wireless communication modules, wireless routing, data transmission radios, etc. An antenna of appropriate size can be selected according to the installation space requirements. The selection of antenna size is related to the gain. Generally, the longer the length of the same frequency band, the higher the gain.

2.1.4 Fiberglass Antenna

Among omnidirectional antennas, fiberglass antennas have the best performance, with a pure copper core, balanced feeding, and minimal environmental impact; The shell is made of high-quality fiberglass, which has excellent three protection characteristics and is well adapted to harsh natural environments. Especially suitable for ultra long distance gateway signal coverage, image transmission, etc.

Generally used in environments with long communication distances, small signal coverage, and high target density, with extreme examples being point-to-point long-distance communication.

2.1.5 Flat panel antenna

High efficiency, small size, easy installation, and can balance gain and radiation areas. Suitable for indoor and tunnel wireless signal coverage; Medium distance signal transmission, image transmission, and signal passing through walls.

2.1.6 Yagi antenna

The gain is very high, the volume is slightly large, the directionality is strong, and attention should be paid to the direction of the antenna when using it. It can be used for ultra long distance signal transmission, image transmission, and direction finding.

2.1.7 Logarithmic periodic antenna

Ultra wideband antenna, with a very wide bandwidth coverage and a bandwidth of up to 10:1, is commonly used for signal amplification, indoor distribution, and elevator signal coverage.

2.2 Selection of built-in antenna

The forms of built-in antennas can be divided into FPC/PCB/spring/ceramic/hardware shrapnel/laser direct forming technology (LDS) and other types. Currently, FPC and PCB antennas are commonly chosen; In situations where cost control is high and performance requirements are average, there are more options for choosing springs and hardware springs; Special application scenarios may choose ceramic patches or LDS antennas. Generally, built-in antennas are affected by the environment and require customized design or impedance matching.

2.2.1 FPC (Flexible Printed Circuit Board)

Has good cost-effectiveness and can match various exterior colors after fuel injection; The product has good flexibility and can perfectly fit on regular circular surfaces; Mature and stable technology, fast production cycle, and good batch delivery performance; Suitable for broadband smart device antenna design with high performance requirements.

2.2.2 PCB antenna (printed circuit board)

The biggest difference between PCB antenna and FPC antenna is that FPC has good flexibility. PCB antenna is a hard board, and in structural installation, if bending and curved surface are required, FPC antenna can be selected. If it is a flat surface, PCB antenna can be selected, which is easier to install than FPC.

2.2.3 Spring antenna

Its biggest feature is its cheap price, but low gain and narrow bandwidth; When embedded inside a product, it is often necessary to debug antenna matching.

2.2.4 Ceramic patch antenna

Small footprint and good performance; Narrow bandwidth makes it difficult to achieve multi frequency bands; Effectively improving the integration of the motherboard and reducing the limitation of antennas on IDs; Design needs to be imported at the beginning of defining the motherboard.

2.2.5 LDS antenna

Suitable for antennas with special appearance surfaces, fully utilizing antenna space; The implementation of antenna performance is closer to the physical limits of the environment; There are special material requirements for the shell or bracket attached to the antenna; The process is mature and can be color matched through spraying, with a certain defect rate during the process.

2.2.6 Hardware spring antenna

Has a high cost performance ratio, effectively reducing costs; The product has high strength and is not easily damaged; Mature and stable technology, fast production cycle, and good batch delivery performance; There are certain limitations in the application of antenna areas and circular arc appearance surfaces.