An antenna gives the wireless system three fundamental properties: gain, direction, and polarization. Gainis a measure of increase in power. Directionis the shape of the transmission pattern. A good analogy for an antenna is the reflector in a flashlight. The reflector concentrates and intensifies the light beam in a particular direction similar to what a parabolic dish antenna would do to an RF source in a radio system.
Antenna gain is measured in decibels, which is a ratio between two values. The gain of a specific antenna is compared to the gain of an isotropic antenna. An isotropic antenna is a theoretical antenna with a uniform three-dimensional radiation pattern (similar to a light bulb with no reflector). The decibels over an isotropic radiator (dBi) value is used to compare the power level of a given antenna to the theoretical isotropic antenna. The U.S. regulatory agency (the Federal Communications Commission, or FCC) uses dBi in its calculations. An isotropic antenna is said to have a power rating of 0 dB, meaning that it has zero gain/loss when compared to itself.
Unlike isotropic antennas, dipole antennas are real antennas. Dipole antennas have a different radiation pattern compared to isotropic antennas. The dipole radiation pattern is 360 degrees in the horizontal plane and 75 degrees in the vertical plane (assuming the dipole antenna is standing vertically) and resembles a doughnut in shape. Because the beam is “slightly” concentrated, dipole antennas have a gain over isotropic antennas of 2.14 dB in the horizontal plane. Dipole antennas are said to have a gain of 2.14 dBi (in comparison to an isotropic antenna).
Some antennas are rated in comparison to dipole antennas. This is denoted by the suffix dBd, short for decibels over a dipole antenna. Hence, dipole antennas have a gain of 0 dBd (= 2.14 dBi).
Note that the majority of documentation refers to dipole antennas as having a gain of 2.2 dBi. The actual figure is 2.14 dBi, but it is often rounded up.
クイックスペック
テーブル 1 クイックスペックを示します.
モデル | AIR-ANT2566P4W-R |
製品の種類 | アンテナ |
Enclosure Color | 白 |
Intended For | Wi-Fi |
Compatibility | 802.11n |
Frequency Range | 2.4 GHz, 5 GHz |
Gain | 2 dBi (for 2.4 GHz), 4 dBi (for 5 GHz) |
Designed For | Cisco Aironet 2802e Controller-based, 3802E, 1852E |
サポートされているプラットフォーム
テーブル 2 shows recommended supported platforms.
モデル | 説明 |
AIR-AP2802E-H-K9 | 802.11交流波 2 CleanAir 搭載 AP, 4×4:3, 外部アンテナ, -H 規制ドメイン |
AIR-AP2802E-H-K9C | 802.11交流波 2 CleanAir 搭載 AP, 4×4:3, 外部アンテナ, H 規制ドメイン, 設定可能 |
AIR-AP3802E-H-K9 | 802.11交流波 2 CleanAir 搭載 AP, 4×4:3, モッド, 外部アンテナ, ミリギグ, H 規制ドメイン |
AIR-AP3802E-H-K9C | 802.11交流波 2 CleanAir 搭載 AP, 4×4:3, モッド, 外部アンテナ, ミリギグ, H 規制ドメイン, 設定可能 |
AIR-AP1852E-C-K9 | Cisco AIR-AP1852E-C-K9, 外部アンテナ, 802.11a/b/n/ac 波 2, 1.733Gbpsのスループット, 4 バツ 4 ミューミモ, デュアルバンド |
AIR-AP1852E-H-K9 | Cisco AIR-AP1852E-H-K9, 外部アンテナ, 802.11a/b/n/ac 波 2, 1.733Gbpsのスループット, 4 バツ 4 ミューミモ, デュアルバンド |
AIR-AP1852E-C-K9C | 802.11交流波 2 アクセス・ポイント, 4×4:4, 外部アリ, C 規制ドメイン, 設定可能 |
AIR-AP1852E-H-K9C | 802.11交流波 2 アクセス・ポイント, 4×4:4, 外部アリ, H 規制ドメイン, 設定可能 |