External antenna selection indicators

　　The selection of an external antenna depends on the specific application scenario (such as Wi-Fi, cellular communications, TV reception, IoT, etc.), but the core selection criteria are common. The following is a detailed analysis of these key indicators to help you accurately match your needs:

　　1. Gain

　　Definition: A measure of an antenna's ability to "focus" the radiation/reception of a signal in a specific direction. The unit is dBi (relative to an isotropic antenna) or dBd (relative to a half-wave dipole antenna, 1dBd ≈ 2.15dBi).

　　Key Selection Points:

　　High gain (e.g., 10dBi or above): Suitable for long-distance transmission (such as rural Wi-Fi coverage and long-distance TV signal reception), with stronger signal directionality but a narrower coverage angle.

　　Low gain (e.g., 3-6dBi): Suitable for short-range, wide coverage (such as indoor home Wi-Fi and IoT devices in small spaces), with a wide coverage angle (omnidirectional antennas often have low gain) and a more uniform signal.

　　Misconception: Higher gain isn't always better—if 360° coverage is required, a high-gain directional antenna may actually result in signal loss in some directions.

　　2. Operating Frequency

　　Definition: The frequency range in which an antenna can effectively radiate/receive signals. This must perfectly match the operating frequency of the device (e.g., router, modem, TV), otherwise normal communication will not occur.

　　Common frequency bands and scenarios:

　　Wi-Fi: 2.4GHz (2.4-2.4835GHz), 5GHz (5.15-5.85GHz), select a "Single-band (2.4G only/5G only)" or "Dual-band compatible" antenna;

　　Cellular (4G/5G): Sub-6GHz (e.g., 700MHz, 1800MHz, 2600MHz, 3.5GHz), millimeter wave (24GHz and above, requiring a dedicated high-frequency antenna);

　　Digital TV: UHF (470-862MHz), VHF (174-230MHz), select a "Full-band compatible" antenna to receive more channels.

　　Key selection tips: Always confirm the frequency band indicated on the device, for example, "5G CPE requires an antenna that supports 3.5GHz" to avoid "no signal due to frequency band mismatch."

　　3. Polarization

　　Definition: The direction of the electric field of the signal radiated by the antenna must align with the polarization of the transmitting/receiving antennas. Otherwise, polarization loss will occur (severe signal attenuation of over 50%).

　　Common Types and Scenarios:

　　Vertical Polarization: This is the default setting for most consumer devices (routers, mobile phones, and TV antennas). During installation, the antenna must be kept perpendicular to the ground (e.g., a router with a pole antenna standing upright).

　　Horizontal Polarization: This is used by some outdoor TV antennas and base station antennas. During installation, the antenna must be kept parallel to the ground.

　　Circular Polarization (left-hand/right-hand): Used in scenarios such as satellite communications and drone image transmission. It can prevent signal attenuation caused by changes in the device's posture (no strict alignment is required).

　　Key Selection Points: Prioritize antennas with the same polarization as the device. For complex scenarios (such as mobile devices), consider circularly polarized antennas for improved compatibility.

　　4. Directivity

　　Definition: The ability of an antenna to radiate/receive signals in different directions. Antennas are categorized as omnidirectional and directional, which directly impacts signal coverage and transmission distance.

　　Features of the Two Antenna Types:

　　Omnidirectional antennas offer 360° coverage and a shorter transmission range, making them suitable for scenarios requiring wide coverage, such as home Wi-Fi and indoor IoT devices. Directional antennas offer coverage within a specific angle (e.g., 30°-120°) and offer a longer transmission range, making them suitable for scenarios requiring long-distance transmission, such as rural long-distance Wi-Fi, TV signal reception, and point-to-point communication (e.g., data transmission between factory rooms).

　　Key Selection Points: Choose omnidirectional for wide coverage and directional for long-range transmission. If signal interference exists (e.g., in a multi-base station environment), directional antennas can reduce interference by focusing the signal.

　　5. Impedance Matching

　　Definition: The antenna input impedance must match the device output impedance (or transmission line impedance). Otherwise, the signal will reflect at the antenna-device interface, resulting in signal loss and reduced efficiency.

　　Common Impedance Values:

　　Consumer devices (routers, mobile phones, TVs): Most are 50Ω (a few TV antennas are 75Ω, so be careful to distinguish them);

　　Transmission lines (such as coaxial cables): They must match the antenna impedance (e.g., a 50Ω antenna with a 50Ω RG58 cable).

　　Key Selection Tips: Prioritize antennas that match the device impedance. If the impedances do not match, an additional "impedance matcher" (such as a balun transformer) will be necessary, otherwise signal quality will be severely affected.

　　6. Environmental Adaptability

　　Core Indicators: For antennas used outdoors or in harsh environments, pay attention to the following parameters:

　　Waterproof Rating (IP Rating): For example, IP65 (dustproof and water jet-proof) or IP67 (dustproof and temporarily submerged in water). Outdoor antennas should be rated at least IP65 to prevent damage from rain.

　　Temperature Range: For example, -40°C to +85°C, the antenna should match the extreme temperatures of the environment (for example, cold northern regions require low-temperature-resistant antennas).

　　Wind Resistance: Outdoor high-gain directional antennas (such as parabolic antennas) should be rated at "Wind Resistance Class 12 or higher" to avoid damage from strong winds.

　　Corrosion Resistance: For use in coastal/industrial areas, select antennas with "salt spray protection" or "anti-corrosion coating" (such as stainless steel) to prevent rust.

　　Selection Key Points: For indoor antennas, waterproofing and wind resistance can be ignored, but size is important (e.g., for small apartments, choose a low-profile, thin antenna). Outdoor antennas must strictly monitor environmental parameters.

　　7. Power Handling

　　Definition: The maximum input power (in watts) an antenna can withstand. Exceeding this level can cause overheating, damage, and even compromise device safety.

　　Selection Key Points:

　　For low-power home devices (routers, TVs): Choose an antenna with a power handling rating of "under 5W."

　　For high-power devices (base stations, industrial-grade wireless transmission equipment): Choose an antenna with a power handling rating of "over 20W" to avoid overload.

　　8. Size & Installation

　　Size: Antenna size is related to the frequency band (lower-band antennas are larger, e.g., a 700MHz TV antenna is larger than a 5GHz Wi-Fi antenna). The antenna should be selected based on the installation space (e.g., a small wall-mount antenna for an apartment interior, or a large pole-mount antenna for an outdoor rooftop).

　　Mounting Method: Common options include wall-mount, ceiling-mount, pole-mount, and magnetic mount (for temporary installations, such as in RVs and mobile devices). The antenna should be tailored to the installation location (e.g., a wall-mount antenna, a pole-mount antenna for a rooftop).

　　Summary: Selection Logic

　　First, identify the application scenario (Wi-Fi/TV/5G) and core requirements (wide coverage/long transmission distance/interference resistance);

　　Match the three basic parameters: frequency band, impedance, and polarization (if they don't match, the device won't work);

　　Select gain and directionality based on your needs (long range → high-gain directional, wide coverage → low-gain omnidirectional);

　　Based on the usage environment, determine waterproofing, temperature resistance, and mounting method (high protection for outdoor use, compact size for indoor use).