This article presents the design and fabrication of low-loss, -weight, and -cost, modified Butler matrix in groove gap waveguide technology at W-band, implemented by additive manufacturing. The design, simulations, and measurements of each of the elements that conform to the modified Butler matrix are presented. The proposed modified Butler matrix is asymmetric and oriented to an easy assembly with a radial antenna in order to obtain simultaneous sum and difference patterns for a narrowband radar application. The measured individual components of the modified Butler matrix fit very well with the simulations. As for the full modified Butler matrix, measurements provide a 0.7% bandwidth below -20 dB for sum and difference ports centered at 94 GHz. The amplitude and phase imbalance are below 1.5 dB and 20°, respectively. This narrow bandwidth is due to the difference in length between input and output ports due to the asymmetry of the design. The total losses of the modified Butler matrix are below 1 dB.

In this letter, a dual circular polarized steering antenna for satellite communications in X-band is presented. This antenna consists of printed elements grouped in an array, able to work from 7.25 up to 8.4 GHz in both polarizations: left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP). The module antenna is compact, with narrow beamwidth, and reaches a gain of 16 dBi. It has the capability to steer in elevation to ±10^° and ±40^° electronically with a Butler matrix. In order to reduce the mutual coupling between adjacent patches, electromagnetic band-gap (EBG) structures are introduced. These EBGs combine double-layer and edge location via in order to reduce the size, without changing the low-permittivity substrate, and therefore maintaining the high radiation efficiency of the antenna.

In this communication, the design of a circularly polarized perforated gradient index flat lens antenna with directive beam-steering properties is presented for millimeter-wave applications at W- band (75 – 95 GHz). The dielectric lens, fed by an open-ended square waveguide located in the lens focal plane, enhances the radiation in a particular direction, generating a high-directivity beam with planar wavefront. The integration of a dielectric polarizer with the lens allows the conversion from a linearly polarized incident wave to a circularly polarized emitted wave over the whole bandwidth. Horizontally and vertically polarized waves, achieved by the excitation of the fundamental square waveguide TE01 and TE10 modes are transformed to left-hand circularly polarized and right-hand circularly polarized waves, respectively. A ±30° scan range in both azimuth and elevation planes is demonstrated for the whole frequency range, attained by displacing the feed along the focal plane of the lens. Lens and polarizer are manufactured as a single piece by stereolithography 3D printing technology with Form 3 Formlabs 3D-printer. Measured results show maximum measured directivity values that range from 23.5 to 23.8 dB, a remarkable circular polarization purity as a wide axial ratio bandwidth of 20.58% (< 3 dB), from 77.5 GHz to 95 GHz, is achieved for the principal beam steers and an aperture efficiency for broadside beam direction between 90.32% and 57.34% in the frequency band of interest.

This paper presents the design and fabrication of low loss, weight, and cost prototypes in groove gap waveguide technology at Ka-band, manufactured with a metallized 3-D printing technique. A wide analysis of loss mechanisms and printing imperfections has been conducted, as well as the effect of temperature on structural deformations. Metallized 3-D printed and CNC machined prototypes have been compared and characterized with simulations and measurements at a band from 28 to 30 GHz. The average measured losses for metallized plastic prototypes are 1.4 dB/m.

An embedded folded, printed, quadrifilar helix antenna (FPQHA) with a wide-angle coverage for unmanned aerial vehicles (UAVs) telemetry and remote control systems is presented in this article. The novelty of this design is that the FPQHA needs to be designed carefully due to UAV tail dimensions and weight constraints while maintaining a high performance to be integrated in the inner part of the UAV tail fuselage to reduce aerodynamic drag. The radiating terminal, formed by a folded, printed, four-helix, radiating section and a compact feeding network, is designed to provide left-handed, circular polarization (LHCP). The complete design offers a very homogeneous pattern in azimuth with a very good axial-ratio (AR) level over a wide range of elevation angles. The use of low-loss and lightweight materials is also an advantage of this design. The wide radiation pattern favors its use for multielement communication systems. Finally, the antenna performance results are obtained mounted inside a UAV tail platform.

A lightweight portable planar slot array antenna at X-band for fixed satellite communications is presented in this letter. The terminal is composed of two radial-line slot antennas (RLSAs) with the slots placed on the upper layer in spiral: one for reception (RX) band with left-handed circular polarization (LHCP), and the other one for transmission (TX) band with right-handed circular polarization (RHCP). A lightweight two-layer dielectric structure is used to achieve and optimize the RLSA weight. The radiating element is a slot pair, designed to provide circular polarization. The feeding network consists of a 50-Ω SMA connector for each RLSA. A radiation efficiency of more than 70% is achieved due to the low dielectric constant substrate. Finally, measurements of the lightweight portable planar RX/TX antenna prototypes are presented and compared to simulations, where very good agreement is observed.