Радиофизика и электроника (Jun 2018)
BROADBAND ANTENNAS AND ANTENNA ARRAYS WITH REACTIVE LOADS
Abstract
Subject and Purpose. The results of studies of actual methods for expanding the frequency range of vibrational curved whip and loop antennas, and antenna arrays based on them are presented. Optimal designs of broadband antennas with the concentrated reactive loads included in the shoulders are considered. Methods and methodology. Calculations of the electrical parameters of the antennas were performed by the integral equation method, which allowed us to investigate new variants of broadband pin and loop antennas and antenna arrays more deeply. Two types of antennas are investigated, which are promising for the use in the microstrip implementation in the form of single antennas and as part of antenna arrays. The first variant is a Z-shaped antenna of orthogonal linear polarization, supplemented by concentrated capacitive loads; the second one is a loop in the form of a frame also with capacitive loads. To approximate the actual application conditions, the antenna parameters were determined when they were placed at a small height above the conductive screen (plane). Results. As a result of calculations of the electrical parameters of Z-shaped antennas with capacitive loads and antenna arrays based on them in the wide frequency range of 0.9...1.2...2.7 GHz, we obtained a significant improvement (decrease) in the standing wave voltage coefficient up to values not exceeding five in comparison with similar antennas without loads, for which the values of this parameter reach thirty or more. Compared with conventional rectilinear antennas of the same length and thickness of the rod, the antenna gain factor with loads increased from 7.8 to 9.8 dB at a decrease in the standing wave voltage coefficient from 3.5 to 3.1 at the middle frequency of the investigated range. For loop antennas with capacitive loads, the values of the standing wave voltage coefficient were not more than five in the same range, and at the middle frequency of the range these values did not exceed 1.9, while in antennas without loads this parameter is much higher (up to thirty) and at the middle frequency of the band has a relatively high value up to 15. Coplanar linear in-phase antenna arrays of three Z-shaped and three loop antennas with capacitive loads have been investigated. It is shown that due to the difference in the conditions for the mutual arrangement of the antennas in the gratings, the standing wave voltage coefficient of the terminal array antennas differs from this parameter of the average antenna. Conclusions. To obtain the operating mode of a current close to the traveling wave mode in Z-shaped and loop antennas and antenna arrays based on them, and, as a consequence, to reduce the frequency dependence of the input parameters and radiation patterns of these antennas, it is sufficient to include no more than four capacitive loads in the symmetric antenna arm. This makes it possible to simplify broadband antennas and save the expenses of time and resources for their development and fabrication in comparison with the known works, where it was proposed to include several tens of capacitive loads in the antenna arm.
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