The paper discusses the possibility of generating a pseudo-Bessel beam, with a propagation distance of several hundreds of wavelengths in microwave and millimeter frequency band, by using a radial line slot array (RLSA). A specific application for non-contact microwave detection of buried mines has been considered as test case. The design benefits of a holographic approach to assure the required aperture field distribution and makes use of an ad hoc optimization tool to control the antenna slot layout. The predicted and measured antenna behaviors show that high efficiency and polarization purity can be obtained by such a compact and flat antenna, achieving at the same time both manufacturing and setup simplicity.

This paper reports for the first time the design of a 60-GHz planar antenna system for radiative near-field region line-of-sight (LOS) link, based on an orbital angular momentum (OAM) multiplexing. The antenna system is composed of a radial line slot array (RLSA) fed by a Butler network, made in post-wall waveguide technology, and located underneath the array. The network can launch different progressive phase states in the RLSA parallel plate waveguide (PPW) to radiate three different OAM beams. To focalize each beam in the radiative near-region the use of a modified Laguerre-Gaussian aperture distribution is proposed to extend the range where the link is guaranteed. The design concept has been verified by prototyping and testing a 20 free-space wavelengths radius antenna. The measurements show that the proposed antenna can generate simultaneously the three OAM-mode states n = 0, –1, and +1.

This letter shows that it is possible to simultaneously generate, in the microwave frequency band, several pseudo-Bessel beams having an azimuthal field variation, characteristic of vortex modes, by making use of a single flat antenna. Specifically, a radial line slot array has been designed to prove the concept. The design benefits of a Butler matrix network to provide the correct phase progression along the azimuthal coordinate, and it makes use of a holographic approach to assure the required aperture field distribution.

Passive imaging cameras at millimeter and sub-millimeter wavelengths are currently entering a new era with the development of large format arrays of direct detectors. Several of these arrays are being developed with bare absorbing meshes without any antenna coupling (lens or horn) structures. The design of such arrays is typically done resorting to geometrical considerations or basic broadside plane wave incidence analysis. This paper presents a spectral technique for the analysis of such focal plane arrays in reception using Fourier Optics, which is valid also for moderately skewed incident angles. The analysis constitutes a step improvement with respect to previously used methods by providing an accurate and efficient way to estimate the point-source angular response and the throughput from a distributed incoherent source of an absorbing mesh in the focal plane of a quasi-optical component (e.g., a parabolic reflector or lens). The proposed technique is validated with full-wave simulations. After presenting the analysis, this paper compares the performance of arrays of bare absorber in the focal plane of a quasi-optical component to those of corresponding antenna based arrays. It is found that absorbers lead to a comparable tradeoff, in terms of spill-over and focusing efficiency, only for very tight samplings. For larger samplings, the focusing efficiency of absorbers is significantly lower than the one for antennas.

A novel solution for the manufacturing of a reflectarray antenna with cosecant-squared radiation pattern is presented. The unit cell simply consists of a 3-D printed nylon grid inserted in between two thick metallic plates. To introduce the required phase delay, C and reverse C slots are laser cut into the plate illuminated by the feeder. This solution allows obtaining an efficient, robust, and compact antenna with low-cost manufacturing process, even for no mass production. Measurements confirm the feasibility of the proposed solution and show its performances.

Although slot antennas are usually modeled as perfectly electric conductors, for accurate antenna design and optimization, ohmic loss effects cannot be neglected. This is especially true in millimeter and submillimeter-wave applications, and in low-cost technology for mass production, where highly conductive surfaces are out of budget. This paper presents a rigorous but efficient method-of-moments (MoM) formulation for the analysis of radial line slot array (RLSA) antennas, which includes the finite conductivity of metals. First, by using equivalence and reciprocity theorems, effective magnetic currents are defined on each slot aperture, instead of standard electric and magnetic equivalent currents. This choice halves the number of unknowns of the MoM linear system, still preserving the rigor of the electromagnetic formulation. Next, proper Green's functions accounting for the finite conductivity of metals are derived analytically and used in the MoM admittance matrix expressions. A numerical check of self and mutual admittances for a couple of slots etched in a nonperfectly conducting structure is provided against results from a finite-element method. Finally, a few RLSA realizations are analyzed to investigate the effect of ohmic losses in a practical antenna design.