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The design of a 1 × 0.33 m dual-polarized reflectarray antenna (RA) operating in Ku-Band (17.2 GHz) for a synthetic aperture radar (SAR) mission using a 12 U CubeSat is presented. The SAR RA has larger electrical size, larger aspect ratio, and smaller focal to aperture length ratio (F/L) compared to existing CubeSat RAs designed for communication payloads. Electrically small unit cells accounting for large incidence angle variations, improving phase resolution, and preventing grating lobes are designed. To illuminate the RA with the desired elliptical beam, a compact aperture-coupled microstrip patch array antenna was designed. Tests done on a CubeSat mockup integrating the dual-polarization feed source and a five-panel reflectarray showed good agreement between the simulated and the measured beamwidths, with low sidelobe and cross polarizations levels. [ABSTRACT FROM AUTHOR]

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 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]

In this paper, an adaptation of Hurst's method to take into account the presence of array guided surface waves in the calculation of the scattered field of finite frequency selective surfaces in free space is presented. Numerical approaches to determine the guided wave's wavenumber needed in this calculation, namely Prony's method and the discrete Fourier transform (DFT), are examined and compared. The results show that the scattered fields obtained with the proposed method, which is based on numerically extracted diffraction coefficients, are in very good agreement with those obtained with the method of moments. [ABSTRACT FROM PUBLISHER]

A system to measure the direction of arrival (DOA) of a signal within a 45-degree conical sector is demonstrated. The system is compact and uses only four circularly polarized patch elements. A printed beamforming network is used to create a set of partially overlapping beams allowing DOA estimation without ambiguity. Neural networks are used to first classify the antenna signals and then estimate the DOA. The proposed system was validated experimentally in C band and, in spite of the highly disturbed beams caused by the finite size of the antenna platform, it was shown that DOA estimation errors in the order of one degree were achievable under signal-to-noise ratios of 10 dB. [ABSTRACT FROM AUTHOR]

The design of a C-band electronically beam scanning reflectarray is presented. The reconfigurable reflectarray element consists of a microstrip patch, printed on a flexible membrane substrate, aperture-coupled to a transmission line loaded with two varactor diodes. The designed element allows continuous tuning of the reflected signal's phase over a 360° range with a maximum loss of 2.4 dB at 5.4 GHz. The measured results on a 30-element reflectarray breadboard show that by varying the bias voltages on each element the main beam can be steered to large angles, up to 40° from broadside in the H-plane. A loss analysis of the proposed reflectarray is also presented. [ABSTRACT FROM AUTHOR]

The equivalent magnetic currents method can be used to characterize radiating structures and to obtain information about the current distribution on the radiating device under test (DUT). In order to do so, the system is assumed to be linear and inversion from near-field measurements can be carried out using numerical techniques such as the singular value decomposition. However this approach is very sensitive to modeling and measurement errors, which is a consequence of the ill-conditioned nature of the inversion process. Here, we propose to account for the ill-conditioning by using a Tikhonov regularization technique to perform the inversion. This technique requires a regularization parameter to be set to an appropriate value, and we show that a generalized cross-validation approach yields adequate determination of the regularization parameter directly from the measured data. The proposed method can be tailored to account for specific characteristics of the DUT. This point is illustrated by the estimation of the current distribution of a bidimensional radiating structure for which prior information about the orientation of radiating edges is incorporated into the inversion method. [ABSTRACT FROM AUTHOR]

Focuses on a study which investigated the performance of a neural network-based direction-finding system. Antenna array and radio frequency combining network; Information on beamforming network; Experimental results; Conclusions.

Presents a concept for exciting slots with a coplanar waveguide line based on inductive coupling. Antenna impedance tuning; Description of single elements and arrays designed for 5- and 25-GHz operation; Simulation and measurement of characteristics.