In this paper, a modular technique is described for the analysis of dual-reflector antennas using a reflectarray as a subreflector. An antenna configuration based on a sub-reflectarray and a parabolic main reflector provides better bandwidth than a single reflectarray, and has a number of advantages compared with a conventional dual-reflector antenna. Examples include the possibility of beam shaping by adjusting the phase on the sub-reflectarray, and potential capabilities to scan or reconfigure the beam. The modular technique implemented for the antenna analysis combines different methods for the analysis of each part of the antenna. First, the real field generated by the horn is considered as the incident field on each reflectarray element. Second, the reflectarray is analyzed with the same technique as for a single reflectarray, i.e., considering local periodicity and the real angle of incidence of the wave coming from the feed for each periodic cell. Third, the main reflector is analyzed using the Physical Optics (P0) technique, where the current on the reflector surface is calculated by summing the radiation from all the reflectarray elements. Finally, the field is calculated on a rectangular periodic mesh at a projected aperture, and then a time-efficient fast Fourier transform (FFT) algorithm is used to compute the radiation pattern of the antenna. The last step significantly improves the computational efficiency. However, it introduces a phase error, which reduces the accuracy of the radiation patterns for radiation angles far away from the antenna's axis. The phase errors have been evaluated for two integration apertures. It has been demonstrated that accurate patterns are obtained in an angular range of ?6', which is sufficient for large reflectors. The method of analysis has been validated by comparing the results with simulations obtained from GRASP8. Finally, the theoretical beam-scanning performance of the antenna is analyzed.
The performance of downlink power control model, based on a n-th power distance law, is evaluated for LEO satellite W-CDMA systems. The downlink pole capacity using this model is given for voice and data services.
Multiple-Input Multiple-Output (MIMO) systems have been considered as a solution to increase the data rate and quality of signals in the next generation wireless communication systems. The performances of these systems depend on three main aspects: channel propagation characteristics, processing algorithms and antenna array configurations. In order to obtain MIMO channel measurements at ISM band (2.45 GHz) taken into account the use of different antennas such as reconfi- gurables, a MIMO-testbed which uses OFDM technique has been designed and implemented in order to carry out the measurements in indoor scenarios. In this paper, the signal processing module is described which is based on Software-Radio platform
We compute the uplink capacity of a W-CDMA 3-D air-to-ground (AG) "cellular like" network. The capacity of the system depends on both the cell height and the cell radius.
In the near future, an enormous increase in traffic will be experienced in mobile communication networks due to the introduction of new high bit rate data and multimedia services. Smart antenna systems are recognized as one of the most promising technologies for allocating the capacity demand when employed instead of conventional sector antennas. Network operators need to estimate the actual performance gain that can be achieved with a smart antenna system. This paper presents a technique to introduce smart adaptive antenna schemes in system level simulations based on the statistical performance gain computed in link-level simulations. Results in a typical deployment scenario quantify throughput increases with smart antennas of up to 87 % over conventional sector antennas.
In this paper, the performance of HAPs (High Altitudes Platforms) UMTS HSDPA (High Speed Downlink Packet Access) is studied for different scenarios and two directions (0° and 30°) within the cell. The studied network is assumed to have 61 ground cells. It is conclude that, for urban zone users, the effective range is lower than the effective range for users in rural zones. It is noticed that in rural zones, the HSDPA mode can support the modulation 16QAM when cells are not fully loaded. For fully loaded rural cells, the 16QAM modulation scheme with code rate of ⅞ can not be supported. Also, it is noticed that, in urban zones, HSDPA mode can support 16QAM with code rate of frac12 and QPSK modulation schemes when cells are not fully loaded. For fully loaded urban cells, only QPSK with code rate of ½ can be supported. It is noticed that, HSDPA multi users with 16QAM modulation scheme can be supported when cells exist in rural zones and are not fully loaded.
A compact array of monopoles with a slotted ground plane is analyzed for being used in MIMO systems. Compact arrays suffer usually from high coupling which degrades significantly MIMO benefits. Through a matching network, main drawbacks can be solved, although it tends to provide a low bandwidth. The studied design is an array of monopoles with a slot in the ground plane. The slot shape is optimized with a Genetic Algorithm and an own electromagnetic software based on MoM in order to fulfill main figures of merit within a significant bandwidth
This paper presents an improved test-bed designed for analyzing the spatial behaviour of wideband indoor channels using MIMO-OFDM systems. A 3D antenna positioning system (3-DAPS) is specifically designed for obtaining 3D spatial data. Also, it allows carrying out some measurements in the range of correlation distance where fading of the radio channel link is significant for indoor scenarios. Special emphasize is made on the RF calibration module, which is designed to track the frequency response of all RF chain of transmitter and receiver and apply those responses to the channel measurements. The average of the pseudo-spectrum MUSIC over all frequencies improves the resolution of the spatial spectrum giving clear peaks where a signal source is and smoothing fake peaks coming from scatters.
In this paper is presented a solution for the focalisation of the new 40 m radiotelescope of the Centro Astronomico de Yebes (CAY) in Guadalajara, Spain. Quasi-optics theory is used in this paper for the propagation analysis of the beams through the different optics elements. The goal of this paper is to design the optical system that can focalize several bands reducing to the minimum number of possible optic elements, and sharing the maximum number of them. Hyperbolic lenses and ellipsoidal mirrors parameters, focal distances, and the feeder dimensions necessary for the focalization in each band are calculated.