Abstract
In this paper, we present a general closed-form solution of trifocal Rotman lens beamforming network (TFRL-BFN) design to excite a conformal phased array of antennas for multibeam radiations. This TFRL-BFN is a two-dimensional (2-D) configuration and is realizable in a dielectric substrate sandwiched by a pair of metal parallel-plates. In the development, instead of employing the geometric optic (GO) ray paths external to the Rotman lens to form an equal-phase wavefront by equal path lengths for directional beam radiation, we consider the phase need of antenna array excitation as the design target of TFRL-BFN. As a result, the TFRL-BFN concept can be extended to treat conformal arrays of antennas with well-planned excitation schemes, ranging from conventional near- and far-field focus multibeam radiations, as well as multibeam with shaped patterns. Basic theoretical concepts and foundations are presented with simulation and measurement examples to demonstrate the phase production characteristics of this TFRL-BFN. When used to feed a conformal array of antennas, the resulting radiation characteristics validate this TFRL-BFN generalization concept's feasibility.
Highlights
Two-dimensional (2-D) trifocal Rotman lenses [1]–[26] and its extension as multi-focal bootlace lens have been widely used as an effective beamforming network to excite planar arrays of antennas for multibeam radiations [2]–[7]
The profile is determined by using geometric optic (GO) ray path lengths to obtain three sets of equal-path length equations via the antenna array to the directional beams pointing to three symmetric directions [1], [2], [5]–[7], [22]
The theoretical foundation of a general TFRL-BFN has been developed for the excitations of conformal arrays of antennas to radiate near-fields focused (NFF)/far-field shaped multi beams, ranging from NFF to far-field focus radiations
Summary
Two-dimensional (2-D) trifocal Rotman lenses [1]–[26] and its extension as multi-focal bootlace lens have been widely used as an effective beamforming network (referred to as a TFRL-BFN, hereafter) to excite planar arrays of antennas for multibeam radiations [2]–[7]. Tri-focal points are considered for their closed-form solutions to easy design Such TFRL-BFN applicable scope can be widely extended if the forming mechanism is alternatively interpreted and formatted from equal-path length equations to the buildup of desired phase compensation for equal-phase wavefronts. Multiple field points can be selected in the field region to build up the TFRL-BFN for a shaped beam, which is realized by VOLUME 9, 2021 incorporating the desired phase distribution in the design equations. Note that a mechanical structure may be used to implement the antenna elements, which may cause creeping waves from some antenna elements in the shadow region to the field points for wide-angle beams These shadowing effects can be included in the proposed conformal multibeam TFRL-BFN design by planning proper excitation schemes if necessary. The geometrical theory of diffraction (GTD) based ray-tracing method [31] can be used to incorporate the creeping/surface wave effects
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