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In this paper, a new frequency selective surface (FSS) for antenna gain enhancement is proposed. The antenna and FSS have an isosceles trapezium geometry. Three different versions of an antenna are created. For each version, the S-parameters S11 and S21 were simulated with the software CST Microwave Studio®. Then, one of the three trapezoid antennas is simulated with an FSS. These two devices, antenna and FSS, were manufactured and had the S11 and S21 parameters measured at the laboratory. The resonance frequency obtained for the trapezium FSS was equal to 2.27 GHz for $\alpha$ equal to 0 °, 2.70 GHz for $\alpha$ equal to 15 ° and 3.12 GHz for $\alpha$ equal to 30 °. The simulated antenna gain increased when the FSS is used as superstrate. Without the presence of the FSS, a maximum gain of approximately 1.50 db occurs at 2.20 GHz, when using the FSS as superstrate, the gain increases to approximately 5.25 db. The measured results agree with the simulated results.

This paper presents a microstrip antenna with controlled gain and directivity. The gain control of antenna is achieved by employing a Reconfigurable Frequency Selective Surface (RFSS) as superstrate which is formed by 2 × 2 array of square loops. The RFSS resonance is variable and depends on the PIN diodes biasing. When all diodes are in the ON-state, the RFSS resonates at 1.89 GHz, and at 3.00 GHz when the diodes are in the OFF-state. The RFSS resonance influences the antenna behavior which operates at 2.40 GHz. Analyses of the simulated antenna gain, radiation pattern and return loss are shown. The gain improvement depends on the PIN diodes biasing. The improvement is 2.95 dB and reduction is 6.95 dB at 2.40 GHz for reverse and forward bias, respectively. At reverse bias, the main lobe is in the opposite direction comparing to the forward bias.

This paper presents a high gain dual-band microstrip antenna. The antenna operates in 9.25 and 11 GHz (X-band). High gain of antenna is achieved by employing a FSS as superstrate which is formed by the 5 × 5 array of square loops. The square loop FSS resonance is varied and its influence on the antenna behavior is analyzed. Analyze of the simulated antenna gain and return loss are shown. The gain improvement depends on the resonance of the FSS superstrate. The higher gain obtained is 6 dB at 11 GHz while maintaining a good matching level for the first resonance.