directive gain การใช้

• The theoretical gain ( directive gain ) of a dish increases as the frequency increases.
• The word " directivity " is also sometimes used as a synonym for directive gain.
• It is also possible to depict the directive gain of the antenna as a function of the direction.
• The directive gain of an antenna can be computed from the published gain divided by the antenna's efficiency.
• Directive gain or directivity is a different measure which does " not " take an antenna's electrical efficiency into account.
• The directivity is therefore the maximum directive gain when taken over all directions, and is always " at least " 1.
• Thus, if expressed as dimensionless ratios rather than in dB, the total directive gain is equal to the sum of the two partial directive gains.
• Thus, if expressed as dimensionless ratios rather than in dB, the total directive gain is equal to the sum of the two partial directive gains.
• "' Partial directivity "'is calculated in the same manner as the partial directive gain, but without consideration of antenna efficiency ( i . e . assuming a lossless antenna ).
• In this case, rather than quoting the antenna gain, one would be more concerned with the " directive gain " which does " not " include the effect of antenna ( in ) efficiency.
• "' Partial directive gain "'is the power density in a particular direction and " for a particular component of the polarization ", divided by the average power density for all directions and " all polarizations ".
• Directive gain is represented as D ( \ theta, \ phi ) and compares the radiant intensity ( power per unit solid angle ) U ( \ theta, \ phi ) that an antenna creates in a particular direction against the average value over all directions:
• In other words, directive gain is the radiation intensity of an antenna at a particular ( \ theta, \ phi ) coordinate combination divided by what the radiation intensity would have been had the antenna been an isotropic antenna radiating the same amount of total power into space.
• If only a certain portion of the electrical power received from the transmitter is actually radiated by the antenna ( i . e . less than 100 % efficiency ), then the directive gain compares the power radiated in a given direction to that reduced power ( instead of the total power received ), ignoring the inefficiency.