Keep in mind that impedance bandwidth can be defined in a couple of ways and that these do not forcibly mean the same thing: VSWR = 2:1, S11 <–10 dB or the maximum real impedance divided by the square root of two [Z(Re)/√2] bandwidth.Directivity/gain bandwidth:This is the frequency range where the antenna meets a certain directivity/gain requirement (like a 1 dB gain flatness).Efficiency bandwidth:This is the frequency range where the antenna has a defined efficiency. Polarization bandwidth:This is the frequency range where the antenna maintains a suitable co/cross ratio.Axial ratio bandwidth:This bandwidth is related to the polarization bandwidth and this number expresses the quality of the circular polarization of an antenna.Alternative Feed TypesA classic way to feed a patch antenna is by using a coaxial probe or connector mounted at the appropriate impedance point and we will look at a couple of alternate ways to connect to a patch. Since in most patch antennas, the impedance bandwidth is much smaller than the radiation bandwidth, we will also look at some techniques to increase the bandwidth.While the probe feed discussed so far has a bandwidth of only a couple %, it is still very useful for a lot of applications like GPS and WLAN.
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