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A novel ultrathin slot-based transmitarray antenna is presented. The related unit cell consists of two thin dielectric layers placed on top of each other, with annular ring slots placed on the outer layers and a PBG element placed on the common interface. The combination of the two annular ring slots and the PBG element acts as a bandpass filter for the transmitted wave. The design of the elements can be carried out through a simple circuit-based analysis approach. The proposed two-layer structure, the unit cell, has a thickness of and provides the required 360 of phase shift. Furthermore, over the bandwidth, the unit cell can have up to 7 of phase error for incident angles of up to 50 . The unit cell and the full transmitarray prototype are fabricated, and the results were compared with simulation and discussed. The full transmitarray has 1 dB gain bandwidth of 5.7% and efficiency of 38% at the center frequency. The structure is simulated via HFSS and CST software package.

A metallic, dual‐band, dual polarised slot‐based transmitarray antenna is presented. The antenna consists of three thin metallic layers do not use any dielectric substrates, with air gaps in between the layers. The unit cell uses interleaved orthogonal slots, as well as crossed‐dipole slot and uniplanar compact photonic bandgap slot elements to provide the lower and upper frequency band resonators, respectively. The frequency separation between the two resonances can be adjusted from closely spaced to far from each other. The antenna provides dual linear polarisation and circular polarisation with the use of the appropriate feed. The fabricated transmitarray antenna provides two independent frequency bands with a band ratio of 1.13 and low mutual coupling. The measurement of a 14 × 14 element transmitarray antenna at 11 GHz shows a maximum gain of 23.74 dB with −1 dB gain bandwidth of 6.8% and aperture efficiency of 38%; at 12.5 GHz, a maximum gain of 24.45 dB is obtained with −1 dB gain bandwidth of 5.4% and aperture efficiency of 34.6%. The antenna is simulated by using the CST software; the ADS package is used for equivalent circuit simulation.

A novel metallic multi-band frequency selective surface (FSS) is presented. The proposed FSS structure has operation bands from closely spaced to far from each other (wide range of band ratio) and has high selectivity at each operation band. The unit cell comprises four small square slots, each loaded with multiple stub resonators. The stubs are placed in each slot in such a way that the unit cell response to both TE and TM polarizations are the same. To miniaturize the unit cell and cover the lower frequency range, each stub resonator is terminated with a U-shaped section. The length of each stubs within the slot determine the resonant frequency of each passbands. The band ratio can be set from 1.09 (close to each other) up to 2.35 (far from each other). Single, dual, triple and quad band FSS structures are designed and simulated through HFSS software package. The fabricated dual-band unit cell shows that the proposed FSS structure can provide two close to each other bands, 9.8 and 10.9 GHz. Also, the measured results of a fabricated dual-band 17 x 17 FSS array show a relatively stable response to variations of incidence angle and polarization state. Index Terms-Frequency Selective Surface, Multi-band, Slot Array0018-926X (c)

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