The least square method (LSM) is a commonly used beamforming method. However, it limits the beamforming frequency bandwidth and is vulnerable to noise; therefore, diagonal loading is used to overcome these limitations. The diagonal loading proposed in this study can be used for broadband beamforming in cases in which noise does not exist, and it makes the loading factor adaptive to a singular value distribution. The simulation results show that the proposed method works stably above the beamforming frequency limit, even for an extended beamforming frequency. We expect that the proposed method can be used to form frequency-invariant beam patterns used in monopulse algorithms to detect signals of unknown frequencies.
This study proposes broadband direction (DOA) estimation through discrete Fourier transform (DFT) extrapolation. We used DFT extrapolation in the lower band and extended the sampled data to reduce the beam width in the spectral domain and improved the accuracy of the estimated DOA. The sampled data with a length of 12 were extrapolated to 36 by the addition of 12-element virtual arrays to 12 real arrays on both sides. The average RMSEs of the estimated DOAs were measured throughout the wide frequency band. To verify the validity of the proposed algorithm, we demonstrated that the RMSE obtained from the broadband DOA estimation for multiple signals of interest (SOIs) was reduced in the extrapolated array. It was demonstrated that the proposed algorithm can broaden the frequency band at which a fixed number of array can estimate the DOA accurately.
This paper presents a novel adjacent algorithm for the design of a beam-steerable passive transmitarray (TA) antenna. Even if the beam of a feed antenna is steering by varying the phase offset of the antenna array forming the feed antenna, the existing passive TA, which improves the gain only in the boresight direction, cannot improve the gain in all directions in which the beam is steering. To minimize the difference in the phase shift between different phase offsets by adjusting the reference phase instead of searching the entire space made up of the reference phase of each phase offset, an adjacent algorithm to change the reference phase with an adjacent phase that minimizes the objective function was adopted. This strategy improved the O(n k-1) algorithm to a linear algorithm of O(n). It was also experimentally shown that optimization using the adjacent algorithm did not change the final result regardless of the initial value. Weighing the magnitude of the electric field (E field), the average optimized phase shift was obtained to determine the phase shift of the passive TA unit cell. Simulation of a TA consisting of an effective simple medium with a thickness of 2.5 mm reflecting the previously determined phase shift showed that the gain was improved by less than 1 dB when the phase offset was 0° and by more than 1 dB when the phase offset was 75°.
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