microstrip antenna gain and directivity

jiripolivka said:

With any antenna, gain equals directivity minus loss. Some antennas are resonant and should be tuned for the best matching at a specified frequency (s11 >10 dB). Wideband antennas are considered if their S11 is poorer over the band width.
Low S11 means less RF power supplied from a transmitter is radiated, also in a receiver, some incident power is re-radiated due to the mismatch.
No antenna is perfect, also close objects affect the matching.

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amntt said:

many thanks.
in the resonance frequancy my s11 is less than 10db and its gain is 5 db is it acceptable?
do you know after i design my antenna how i can plot e plane and h plane pattern for my antenna?

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e plane and h plane pattern in cst simulator

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jiripolivka said:

Your antenna may be good for your application. To plot the radiation pattern, you need a test range or an anechoic chamber, with a reference antenna, a signal transmitter and a calibrated receiver. A positioner will rotate the antenna under test in E and H plane and you will record the response.

National metrology laboratory or a university dealing with microwave antennas may offer you such service. In private companies you will have to pay for such test.

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