In some papers antennas are observed with gain of -7.5 dBd. What is the significance of negative gain and how is it produced?
A negative dBd gain means that the antenna is not radiating very well at all in that direction in comparison to a dipole. Remember that gain, and directivity, are 3-D functions depending on azimuth and elevation. A directional antenna may have good gain in one direction and poor gain in others. The poor gain may come from the pattern shape, poor match, internal losses or external loading. This depends on the antenna and the application,
A negative dBd gain means that the antenna is not radiating very well at all in that direction in comparison to a dipole. Remember that gain, and directivity, are 3-D functions depending on azimuth and elevation. A directional antenna may have good gain in one direction and poor gain in others. The poor gain may come from the pattern shape, poor match, internal losses or external loading. This depends on the antenna and the application,
Negative gain in dB means that the nominal gain is less than 1 (i.e., it is a loss).
Actually, gain of antenna is relative parameter. There are several gains ie realized gain, IEEE gain. Gain is function of frequency and direction. If it has no specific direction, it usually means the maximum direction. That means one antenna can has both positive and/or negative gains which depend on direction. However, if maximum gain (realized gain) is negative, it has two or three factors. Realized gain = efficiency x directivity that efficiency is composed of radiation eff and reflected eff (Matched).
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