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The design, simulation, and measurement of a beam steerable slotted waveguide antenna operating in X band are presented. The proposed antenna consists of a standard rectangular waveguide (RWG) section with longitudinal slots in the broad wall. The beam steering in this configuration is achieved by rotating two dielectric slabs inside the waveguide and consequently changing the phase of the slots excitations. In order to confirm the usefulness of this concept, a nonresonant 20-slot waveguide array antenna with an element spacing of $d = 0.6\lambda _{0}$ has been designed, built, and measured. A 14° beam scanning from near broadside ($\theta = 4^{\circ }$) toward end-fire ($\theta = 18^{\circ }$) direction is observed. The gain varies from 18.33 to 19.11 dBi and the antenna efficiency from 95% to 79%. The sidelobe level is −14 dB at the design frequency of 9.35 GHz. The simulated and measured co-polarized realized gains are in good agreement. [ABSTRACT FROM AUTHOR]

A simple and low-cost single substrate layer Luneburg lens-based beamforming network (BFN) operating in $W$ -band is proposed. A multibeam antenna is then realized using the novel BFN and fabricated using a low-cost printed circuit board process. The Luneburg lens is realized by drilling holes in a substrate, and to extend the refractive index variation, a high dielectric constant substrate is embedded at the lens center. The lens is excited by radially placed open-ended substrate integrated waveguides (SIWs) at the lens circumference, feeding a subset of antenna ports placed on the opposite side of the lens. The proposed BFN thus provides half-power beamwidth (HPBW) and beam steering angle flexibility for multibeam antennas. An antenna generating seven beams was prototyped at 79.5 GHz to validate this BFN, providing measured beam steering of approximately ±41° with a broadside HPBW of 10°. The bandwidth of the proposed BFN is determined by the single-mode operation of the SIW. The fabricated multibeam antenna impedance bandwidth is, however, about 2% at 79.5 GHz because of the radiating elements. The radiating elements are series fed slot arrays placed on SIWs. [ABSTRACT FROM AUTHOR]

A beam-steering technique in narrow-wall slotted ridge waveguide at X-band is proposed. An array of inclined slots cut in the narrow wall of a rectangular ridge waveguide is employed. Beam steering is achieved by rotating a dielectric slab inside the waveguide. The change of wavelength at different rotation angles of the slab is used as the phase shifter. To confirm the usefulness of this method, a short nonresonant 20-slot waveguide array antenna with an element spacing of $d= {{0.44}}\lambda _{0}$ has been designed, built, and tested. It is shown that the main beam can be steered from near broadside $(\theta = {{6^\circ)}}$ toward end fire $(\theta = {{42^\circ)}}$ by rotating the dielectric slab by 90°. A directivity variation of 2.8 dB and a half-power beamwidth increase of 3° are observed over this scan at the design frequency. The gain varies from 11.17 to 12.47 dB over the scanning range. Due to the relatively short length of the prototype, losses in the terminating load have limited the radiation efficiency to values between 43% and 86%. The E-plane radiation patterns measured at the operation frequency of 9.35 GHz and compared very well with the simulated results. [ABSTRACT FROM AUTHOR]

A novel two-dimensional fan-beam lens is presented. The principle of operation of the lens is based on Gaussian optics. The focal point of the circular interface between the dielectric and air is coincident with a focal point of a hyperbolic reflector, while the feeding source is located in the other focal point. The ray tracing method along with physical optics and full wave finite element method (Ansys HFSS) are used to simulate the structure and study the effect of the feed blockage. The two-dimensional lens is implemented in a parallel-plates waveguide and a technique for matching the feeding structure is proposed. Measurement results are presented and confirm the predicted performance. [ABSTRACT FROM PUBLISHER]

A new design of two-dimensional cylindrical Luneberg lens is introduced based on TE10 mode propagation between parallel plates, with special focus on ease of manufacturing. The parallel plates ace partially filled with low cost polymer material (Rexolite ϵr =2.54) to match Luneberg's law. A planar linear tapered slot antenna (LTSA) is inserted into the air region between the parallel plates at the edge of the Luneberg lens as a feed antenna, with fine positioning to the focal point of the Luneberg lens to optimize the antenna system performance. A combined ray-optics/diffraction method is used to obtain the radiation pattern of the system and results are compared with predictions of a time domain numerical solver. Measurements done on a 10-cm Luneberg lens designed for operation at 30 GHz agree very well with predictions. For this prototype, 3-dB E- and H-plane beamwidths of 6.6° and 54° respectively were obtained, and the sidelobe level in the E-plane was -17.7-dB. Although the parallel plate configuration should lead to a narrow band design due to the dispersion characteristics of the TE10 mode, the measurement results demonstrate broadband characteristics with radiation efficiencies varying between 43% and 72% over the tested frequency hand of 26.5-37 GHz. The designed cylindrical Luneberg lens can be used to launch multiple beams by implementing an arc array of planar LTSA elements at the periphery of the lens, and can be easily extended to higher mm-wave frequencies. [ABSTRACT FROM AUTHOR]

This paper presents a new approach to handle the nonlinear microwave tomography equations for dielectric materials. The electromagnetic tomography equations are rewritten in the framework of an equivalent wire grid model loaded with resistors and capacitors to represent the permittivity and conductivity of the material. The validation of the model is performed using near-field measurements at a frequency of 2.45 GHz on devices under test made of dielectric plates of various shapes surrounded by an unbounded free-space medium. The reconstruction algorithm is based on the contrast source inversion (CSI) technique. Here, we introduce an enhanced version of the CSI cost function by adding extra regularization terms; in addition, minimization is carried out using a logarithmic barrier constraint in order to avoid nonphysical permittivity and conductivity values. The distributions of those physical properties retrieved with experimental data, for nonhomogeneous dielectric structures of known composition, are in good agreement with the expected ones. The imaging resolution is limited by the density of the wire grid meshing. [ABSTRACT FROM AUTHOR]

Discusses design considerations and experimental investigations of an integrated active antenna for space power combining that makes use of unidirectional dielectric radiators (UDR). Implementation of UDR feed circuit; Advantages of distributing the devices into an array; Factors that caused a non-negligible negative shift of antenna's resonance frequency.