We analize the performance of a microstrip antenna array considering mutual coupling (MC) and diffraction phenomenon (DF). These effects are the reason of distortions on the individual radiation patterns of each antenna when they are placed together. A four element plane array capable of receiving GPS signals at L1 band is analized. The effects of MC and DF are quantified through numerical simulations to compare the advantages of knowing the implemented beamforming based on the characterized distorted patterns. Results prove that, for a few elements array, precise knowledge of each individual radiation pattern in the array is essential for achieving good performance on interferences mitigation. Finally, first measures of a built prototype are shown and they fit properly with simulations.

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The performance of an isolated antenna compared with itself but embedded (in-situ) in an array is not the same mostly due to the influence of mutual coupling and electromagnetic diffraction. Although signal processing techniques have been widely spread in literature for antenna arrays of elements with same physical properties and same performance, there is not enough mention regarding antennas with dissimilar behaviors. The usual way of avoiding this problem is by means of some kind of compensation that can reduce the differences but not always eliminate them, unless the information of the active radiation pattern of the antennas in array and wideband compensation techniques are used. A great advantage of employing adaptive methods for processing with antenna arrays is that it ensures good performance even without requiring this complete information.

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Abstract-In this letter, we present a new variable impedance termination consisting of two polarized diodes. To generate a complex-valued impedance, two controlled current sources polarize the diodes, which are interconnected with a Wilkinson power divider through transmission lines of different electric lengths. Because of the reduced number of diodes, this structure presents low power consumption and simple control. We validated the proposed design by implementing a prototype at the operating frequency of 1575.42 MHz. Mapping the measured results in the Smith chart, the impedance can produce reflection coefficients with full-phase coverage within the circle of magnitude 0.35 over a frequency range of 1.5-1.6 GHz.Index Terms-One-port impedance termination, p-i-n diode, programmable load, variable impedance.