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.

A substrate integrated waveguide (SIW) linear array is presented with a new circularly polarized (CP) element. The single radiator consists of four cross tilted slots. In addition, a pair of tuning metallic vias is included to improve the reflection of longest slots. A 16-element antenna prototype with -26-dB Taylor distribution and 1.5% residual power was designed, manufactured and measured to verify the new slot performance in an array configuration. A 17-dB peak gain, 1.86-dB axial ratio and 80% radiation efficiency were experimentally achieved at 17 GHz. A 3% usable bandwidth was obtained owing to frequency main beam tilt dispersion.

A circular conformal array antenna (CAA) with beamsteering capabilities as well as omnidirectional performance at 3.5 GHz (S-band) is presented. The single radiating elements are formed by double-stacked microstrip patches placed on the planar faces of an octagonal holding structure fabricated with a 3D printer. An eight-way tunable feeding network (TFN) is designed, manufactured, and integrated into the conformal structure to excite the array elements. Novel tunable T-junctions (TTs) based on p-i-n diodes are proposed to form the TFN in microstrip technology. This novel T-junction allows a splitting configuration with uniform distribution to the two output ports or a switching mode to deliver the signal to either output port. In all T-junction operation modes, good input matching performance is achieved. The TFN network is integrated into the conformal antenna and digitally controlled by a microcontroller Arduino MEGA. A total of 29 states grouped in six modes with a global matching bandwidth of 17.2% can be selected. The omnidirectional radiation and beamsteered directional patterns (covering 360°) can be electronically tuned. The proposed antenna is suitable for future 5G terrestrial communications in the 3.5-GHz International Mobile Telecommunication (IMT) range, the primary candidate band for the first 5G networks.

A conformal array antenna with a reconfigurable radiation pattern in the azimuth plane at Ku band is presented. An eight-faced prism has been set as 3-D antenna structure. The radiating element consists of a rectangular waveguide ended on a slotted cavity. A radial waveguide network (RWGN) fed by a symmetrically placed coaxial probe has been implemented to equally feed each radiating element obtaining an omnidirectional behavior in the azimuth plane. The insertion of several metallic tuning screws (TSs) provides a reconfiguration mechanism of the electric field distribution in the RWGN and modifies the conformal array antenna amplitude feeding. Eight different configurations generating directional radiation patterns can be tuned by means of the insertion of certain TSs. In addition, the symmetrical positioning of them allows performing a main beam scanning every 45° in the azimuth plane. Several prototypes have been manufactured and measured to experimentally validate the antenna performance. A total of 65 different radiation patterns have been experimentally obtained using the proposed TSs, which provides a simple, low-loss, and low-cost reconfigurability mechanism to the presented conformal array antenna.

In this letter, additive manufacturing technologies have been evaluated for waveguide antenna array prototyping at Ku band. Direct metal laser sintering (DMLS) and stereolithography have been assessed in terms of manufacturing limitations, electrical performance, accuracy, cost and weight, compared with traditional manufacturing methods. This assessment is performed on a corporate-fed waveguide array antenna for end-user digital broadcast satellite communications at Ku band. The objective is to manufacture this intricate multilayer structure as a single block, in order to prevent contact and leakage issues in the interface between antenna layers. This monolithic implementation is unfeasible with conventional milling in aluminum, renowned in the literature for its reliability in waveguide antenna implementation. A prototype has been machined with such technique as a reference for experimental results. A single block fabrication has been possible by DMLS, presenting a similar performance to the reference prototype. Experimental results, including impedance matching, realized the gain and axial ratio have been performed on the antenna prototypes. A 14.7% effective bandwidth has been obtained for the DMLS antenna.