Technical analysis of 2.4GHz antenna gain: range, principle and performance correlation

　　In wireless communication, antenna gain is the core indicator to measure the signal focusing ability, which directly affects the transmission distance and coverage. The gain of 2.4GHz antennas (widely used in Wi-Fi, Bluetooth, ZigBee and other scenarios) ranges from 0dBi to more than 20dBi, and the difference comes from the technical trade-offs of antenna structure, radiation pattern and application scenario. From the technical bottom, the essence of gain is the concentration of directional energy radiation, not "signal amplification" - it sacrifices the radiation energy in some directions and focuses it in a specific direction, thereby improving the effective signal strength in that direction.

　　1. The technical essence and quantitative standard of gain

　　The unit of gain "dBi" represents the gain relative to an ideal omnidirectional point source antenna (an ideal point source radiates energy evenly in all directions). For example:

　　3dBi means that in the direction of the strongest radiation, the signal strength is twice that of the ideal point source (10^(3/10)≈2);

　　10dBi means 10 times (10^(10/10)=10), and 20dBi can reach 100 times.

　　This energy focusing is inevitably accompanied by changes in the radiation pattern: the higher the gain, the stronger the directivity of the antenna (the narrower the beam), and the more obvious the signal attenuation in the non-main lobe direction. This is also the core reason why high-gain antennas need to be accurately aligned - if they deviate from the main lobe direction by 5°-10°, the signal strength may drop by 30%-50%.

　　2. Gain range and technical design of different types of 2.4GHz antennas

　　1. Omnidirectional antenna (0dBi - 8dBi): balance coverage and convenience

　　Omnidirectional antennas (such as rod antennas, PCB built-in antennas) radiate uniformly 360° in the horizontal direction and have a certain beam width in the vertical direction. They are suitable for scenarios that require all-round coverage (such as home routers and smart home devices).

　　Ultra-low gain (0-2dBi):

　　Typical design: PCB patch antenna, FPC flexible antenna, ceramic antenna (size <10mm×10mm).

　　Technical features: Adopt miniaturized dipole structure, low radiation resistance (30-50Ω), and sacrifice gain for miniaturization. For example, the built-in antenna of Bluetooth headset needs to achieve basic communication in a 5mm×3mm space, with a vertical beam width of >120°, but the transmission distance is only 5-10m.

　　Application scenarios: wearable devices, IoT sensors (such as temperature and humidity probes), TWS headsets.

　　Low gain (2-5dBi):

　　Typical design: built-in PCB antenna of router (length 8-15cm), laptop Wi-Fi antenna.

　　Technical features: Adopt half-wave dipole or folded dipole structure, impedance matching optimized to 50Ω, vertical beam width 80°-100°, horizontal coverage without dead angle. For example, the built-in antenna of a home router can achieve 50-100m coverage by using multi-antenna MIMO (2×2) to make up for the lack of single antenna gain.

　　Application scenarios: smartphones, tablets, smart speakers, mainstream Wi-Fi routers.

　　Medium gain (5-8dBi):

　　Typical design: external omnidirectional rod antenna (length 20-30cm), high-gain rubber stick antenna.

　　Technical features: The loading coil is used to extend the electrical length (equivalent half-wavelength 12.5cm), the vertical beam width is compressed to 40°-60° ("flattened" radiation pattern), and the horizontal direction remains omnidirectional. The cost of the gain increase is the narrowing of the vertical coverage range. For example, in a multi-story building, the inter-floor signal attenuation of a 5dBi antenna is 10-15dB higher than that of a 2dBi antenna.

　　Application scenarios: enterprise-level AP, Mesh network node, outdoor coverage base station.

　　2. Directional antenna (8dBi and above): Focusing energy to extend distance

　　Directional antennas focus energy to a specific direction (narrowing horizontal/vertical beam width) through reflectors and array structures, and are suitable for point-to-point transmission (such as wireless bridges) or long-distance coverage (such as surveillance cameras).

　　Higher gain (8-12dBi):

　　Typical design: flat directional antenna (15cm×15cm), Yagi antenna (3-5 units).

　　Technical features: Use a reflector (metal backplane) to reflect the energy radiated backward to the front to form a directional main lobe (horizontal beam width 30°-60°). For example, the transmission distance of an 8dBi flat antenna in the aligned direction is 2-3 times that of a 5dBi omnidirectional antenna (at the same transmission power), but the signal attenuation is >20dB after deviating from 15°.

　　Application scenarios: outdoor surveillance camera backhaul, wireless bridging between buildings (100-500m).

　　High gain (12-20dBi):

　　Typical design: grid parabolic antenna, high-gain array antenna (8-16 units).

　　Technical features: Through parabolic reflection focusing (grid antenna) or multi-unit array (Yagi antenna extension), the horizontal beam width is compressed to 5°-20°, and the energy is highly concentrated. The transmission distance in the main lobe direction of the 18dBi grid antenna can reach 1-3km, but it needs to be accurately aligned (deviation <1°), otherwise the signal will drop sharply.

　　Application scenarios: long-distance point-to-point communication (such as equipment networking in mining areas and oil fields), Wi-Fi coverage in rural areas.

　　III. Technical trade-offs between gain and performance

　　Gain and coverage:

　　Omnidirectional antenna: For every 3dBi increase in gain, the theoretical coverage radius increases by about 40% (free space), but the vertical coverage is reduced by 30%-50%. For example, the signal strength of a 5dBi antenna at 100m is 4dB higher (about 2.5 times) than that of a 2dBi antenna, but in vertical coverage of three floors, the signal on the ground floor may be weaker than that of a 2dBi antenna.

　　Directional antenna: For every 6dBi increase in gain, the transmission distance can be doubled (under the same receiving sensitivity), but the beam width is halved, and the difficulty of alignment is significantly increased.

　　Gain and bandwidth/efficiency:

　　High-gain antennas (especially directional ones) have narrower operating bandwidths. For example, the 3dB bandwidth of an 18dBi grid antenna may be only ±50MHz, while a 2dBi omnidirectional antenna can reach more than ±100MHz, which is more suitable for 2.4GHz full-band (2400-2483.5MHz) applications.

　　When the gain exceeds 12dBi, the antenna efficiency (actual radiated power/input power) may drop from 80% to below 60%, and the loss caused by the complex structure increases.

　　Gain and multipath interference:

　　High-gain directional antennas can reduce multipath reflections in non-main lobe directions (such as interference signals reflected by walls), improve the signal-to-noise ratio (SNR) by 2-5dB, and are suitable for high-speed transmission (such as 300Mbps for 802.11n).

　　Although omnidirectional antennas are susceptible to multipath, 360° coverage can avoid "blind spots" in complex indoor environments and is more suitable for random deployment of IoT sensors.

　　IV. Selection Technical Guide

　　Consumer electronics: Prioritize 2-5dBi omnidirectional antennas, balance size (<10cm) and coverage. For example, the built-in antenna of a router needs to achieve 5dBi gain within a length of 5cm, and often uses an FPC bending structure to reduce space occupation.

　　Enterprise-level coverage: 5-8dBi external omnidirectional antenna (with MIMO), or 8-12dBi directional antenna (sector coverage), and the link budget needs to be calculated in combination with the environment (wall material, interference intensity).

　　Long-distance communication: Select a 12-20dBi directional antenna according to the distance, match a high-power module (≤1W, in compliance with FCC/CE specifications), and use GPS positioning to assist in alignment.

　　In short, the gain selection of the 2.4GHz antenna needs to be combined with the scene requirements, installation conditions, and cost budget. There is no "higher is better". For example, in a home environment, the comprehensive experience of a 5dBi omnidirectional antenna is better than that of an 8dBi antenna (to avoid insufficient vertical coverage); and in point-to-point transmission, a 12dBi directional antenna is the optimal solution to balance distance and alignment difficulty. Only by understanding the radiation pattern and technical limitations behind the gain can efficient deployment of wireless communications be achieved.