Abstract-Circularly-polarized arrays of cavity backed slot (CBS) antennas are proposed for X-band satellite-earth communications. Two configurations of such circularly polarized arrays are investigated: cross-shaped and square-shaped arrays. Both configurations can produce right-hand circular polarization (RHCP) as well as lefthand circular polarization (LHCP) by proper setting of excitation phase for each element in the array. The finite-difference timedomain (FDTD) method is used to analyze the characteristics of the proposed arrays including the input impedance, S-parameters, radiation pattern, gain and axial ratio. The results show that the proposed array configurations seem very promising and useful for geostationary satellite applications.

This paper presents the design and analysis of a diplexer for satellite communication system based on hybrid spoof surface plasmon polariton (SSPP) and substrate integrated waveguide (SIW) transmission lines. The proposed diplexer consists of a SSPP printed line composed of H-shaped periodical grooved strips to operate as a low pass filter and a SIW to operate as a high pass filter. The operating frequency bands of the proposed diplexer are from 11.7 to 12.75 GHz for the downlink (DL) band, and from 17.3 to 18.35 GHz for the uplink (UL) band. These frequency bands correspond to the operating frequencies in Nile Sat 201 system. The frequencies of the DL and UL bands are adjusted independently by tuning the structure parameters of SSPP and SIW sections, respectively. The proposed hybrid SSPP-SIW diplexer is fabricated and measured. Simulated and measured results show good channel isolation, low return loss and low insertion loss in the required frequency bands.

This paper presents the analysis and design of an X-band reflectarray. The proposed antenna can be used for a medium Earth orbit (MEO) remote sensing satellite system in the 8.5 GHz band. To obtain a nearly constant response along the coverage area of this satellite system, the proposed antenna was designed with a flat-top radiation pattern with a beam width of around 29° for the required MEO system. In addition, broadside pencil beam and tilted pencil beam reflectarrays were also investigated. The feeding element of the proposed reflectarray antennas is a Yagi–Uda array. The amplitude and phase distribution of the fields due to the feeding element on the aperture of the reflectarray antenna are obtained directly by numerical simulation without introducing any approximation. The required phase distribution along the aperture of the reflectarray to obtain the required flat-top radiation pattern is obtained using the genetic algorithm (GA) optimization method. The reflecting elements of the reflectarray are composed of stacked circular patches. This stacked configuration was found to be appropriate for obtaining a wide range of reflection phase shift, which is required to implement the required phase distribution on the reflectarray aperture. The antenna was fabricated and measured for verification.

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