Abstract-Superdirective beamforming can highly reduce the aperture size of high-frequency receive array. At the same time, the closely spaced elements of a small aperture array can make it low efficiency and sensitivity to the array uncertainty, which limit its application in practice. Using a parameter called sensitivity factor, we found that array efficiency and robustness against array error could be considered simultaneously. On that basis, we derive a novel superdirective beamforming criterion based on a constrained sensitivity factor for the HF circular receive array. New method is analytical and computationally inexpensive. Through making the directive gain with a given sensitivity factor maximum, we calculate the optimal weights of the array elements. To illustrate the proposed method can increase the acceptance of HF superdirective receive arrays in practice, several numerical results are provided.

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Abstract-The performance of high resolution subspace-based algorithms are particularly sensitive to the prior information of the source number, the Signal-to-Noise Ratio (SNR) and the snapshot. Although the existing direction-of-arrival (DOA) estimation methods without estimating the source number could eliminate the awful impact brought by incorrect source number estimation, yet its performance would get deteriorated by small snapshots and low SNR. Methods which exploit noise and signal subspaces information simultaneously, such as SSMUSIC, could provide a high resolution performance in such nonideal circumstances. However, its performance would degrade severely when the prior information of the source number is incorrect. To provide a DOA estimation method without estimating the number of source, which has a high resolution performance in small sample and low SNR scenario, using all information spreads in eigenvalues and eigenvectors, this paper reconstructs a new spatial spectrum which is very similar to the SSMUSIC algorithm. In order to enhance the robustness of the new method, we provide an empirical method to modify the eigenvalues to prohibit the spreading of noise eigenvalues caused by snapshot deficient and low SNR. To verify the validity of the new method, comparisons with other algorithms are made in computer simulations and the measured data test.

In this work, the collection of solar energy by a broad-band nanospiral antenna is investigated in order to solve the low efficiency of the solar rectenna based on conventional nanoantennas. The antenna impedance, radiation, polarization and effective area are all considered in the efficiency calculation using the finite integral technique. The wavelength range investigated is 300-3000 nm, which corresponds to more than 98% of the solar radiation energy. It's found that the nanospiral has stronger field enhancement in the gap than a nanodipole counterpart. And a maximum harvesting efficiency about 80% is possible in principle for the nanospiral coupled to a rectifier resistance of 200 Ω, while about 10% for the nanodipole under the same conditions. Moreover, the nanospiral could be coupled to a rectifier diode of high resistance more easily than the nanodipole. These results indicate that the efficient full-spectrum utilization, reception and conversion of solar energy can be achieved by the nanospiral antenna, which is expected to promote the solar rectenna to be a promising technology in the clean, renewable energy application.

Abstract:In this work, a novel digital beamformer applied in vehicle-mounted high frequency (HF) receiving device has been developed. The system adopts robust superdirective beamforming algorithm, which not only effectively reduces the receiving array aperture but also maintains a higher directive gain compared with conventional beamforming method (CBF). The system is designed based on the idea of radio-defined software (SDR), which is easy to update. It contains 16 receiving channels and can output 3 analog beam signals. Experiment shows that the system has fast response and is feasible in engineering.