Abstract
A novel concept of four-beam antenna arrays operating in a one-octave frequency range that allows stable beam directions and beamwidths to be achieved is proposed. As shown, such radiation patterns can be obtained when radiating elements are appropriately spaced and fed by a broadband 4 × 4 Butler matrix with directional filters connected to its outputs. In this solution, broadband radiating elements are arranged in such a way that, for the lower and upper frequencies, two separate subarrays can be distinguished, each one consisting of identically arranged radiating elements. The subarrays are fed by a broadband Butler matrix at the output to which an appropriate feeding network based on directional filters is connected. These filters ensure smooth signal switching across the operational bandwidth between elements utilized at lower and higher frequency bands. Therefore, as shown, it is possible to control both beamwidths and beam directions of the resulting multi-beam antenna arrays. Moreover, two different concepts of the feeding network connected in between the Butler matrix and radiating elements for lowering the sidelobes are discussed. The theoretical analyses of the proposed antenna arrays are shown and confirmed by measurements of the developed two-antenna arrays consisting of eight and twelve radiating elements, operating in a 2–4 GHz frequency range.
Highlights
In recent years, the development of modern wireless systems caused interest in advanced antenna technology, among which multibeam antennas that offer multiple independent beams can be distinguished
Multibeam antenna arrays can be realized with the use of beamforming networks, such as Butler matrices, which ensure an appropriate signal distribution across the array [5]
Some concepts of scalable antenna arrays with constant broadside beam can be found [13,17,18] which are realized with the use of frequency-dependent feeding networks, whereas multi-beam antenna arrays with almost constant multiple beam patterns are rarely reported
Summary
The development of modern wireless systems caused interest in advanced antenna technology, among which multibeam antennas that offer multiple independent beams can be distinguished. Some concepts of scalable antenna arrays with constant broadside beam can be found [13,17,18] which are realized with the use of frequency-dependent feeding networks, whereas multi-beam antenna arrays with almost constant multiple beam patterns are rarely reported This is due to the required distance between radiating elements which has to be kept around 0.5 λ and appropriate signal distribution, which has to be ensured across the array in a broad bandwidth. A simpler approach to the realization of scalable multibeam antennas is presented in [25], where the feeding network consists of a broadband quadrature directional coupler and frequency-dependent power dividers As shown, this allows an attractive two-beam radiation pattern to be achieved over the frequency range reaching fH/fL = 3. The proposed concept was verified by the design and measurements of two four-beam antenna arrays operating in a 2–4 GHz frequency range and consisting of eight and twelve radiating elements, respectively
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