1. Function of antenna
In any radio communication equipment, there is always a device that radiates electromagnetic energy into and receives electromagnetic energy from space. This device is called antenna.
The function of the antenna is to transmit the digital signal or analog signal modulated to the RF frequency to the space wireless channel, or receive the digital or analog signal modulated on the RF frequency from the space wireless channel.
2. The essence of the antenna problem
From the electromagnetic field theory, the essence of antenna problem is to study the spatial electromagnetic field distribution generated by the antenna and the electrical characteristics determined by the spatial electromagnetic field distribution. The electromagnetic field at any point in space meets the electromagnetic field equation – Maxwell equation and its boundary conditions. Therefore, antenna problem is a special form of time-varying electromagnetic field problem.
From the perspective of signal system, the antenna problem can be understood as investigating the electromagnetic response characteristics generated by an electromagnetic wave excitation source. From the perspective of communication system, antenna can be understood as signal transmitter and receiver. The radio signal strength between the receiving and receiving antennas meets the channel transmission equation and multipath fading characteristics.
- Common antenna shapes
- Evolution of Japanese Wi-Fi AP antenna
4.1. Indoor AP
The earliest AP is to use external antenna. Considering the coverage performance, the pole antenna is commonly used.
With the user’s requirements for beauty, it gradually began to change to the form of built-in antenna, as shown in the figure below.
After the antenna is converted to built-in, and due to the increasing performance requirements of users, AP products with smart antenna technology begin to appear.
4.2. Outdoor AP
The earliest AP form is the use of external antenna, which must be covered by external antenna.
Then it began to produce outdoor AP products with internal and external switchable to meet the requirements of high performance and beauty.
Finally, AP products with smart antennas also began to appear outdoors.