Even though ghost imaging (GI), an unconventional imaging method, has received increased attention by researchers during the last decades, imaging speed is still not satisfactory. Once the data-acquisition method and the system parameters are determined, only the processing method has the potential to accelerate image-processing significantly. However, both the basic correlation method and the compressed sensing algorithm, which are often used for ghost imaging, have their own problems. To overcome these challenges, a novel deep learning ghost imaging method is proposed in this paper. We modified the convolutional neural network that is commonly used in deep learning to fit the characteristics of ghost imaging. This modified network can be referred to as ghost imaging convolutional neural network. Our simulations and experiments confirm that, using this new method, a target image can be obtained faster and more accurate at low sampling rate compared with conventional GI method.

In this letter, an active metasurface for vortex beam generation is proposed. This metasurface can transform the incident plane wave into beams carrying orbital angular momentum (OAM) of three different orders. This active metasurface is composed of an array of varactor diodes loaded unit cells. The transmission phase of each metasurface unit cell can be fully controlled by the capacitance of the varactor diodes. Different modes of vortex beams can be separately generated by simply changing the transmission phase distribution on the metasurface aperture. The properties of the proposed active metasurface are demonstrated by simulation and measurement results, which have a good agreement with each other.

The reverberation chamber (RC) has traditionally been used for electromagnetic compatibility tests. About two decade ago, it found application in various over-the-air (OTA) tests of antennas and wireless devices. This paper gives an overview of nearly two decades of research on the RC-based OTA tests, ranging from antenna measurements and characterizations to OTA tests of both terminals and base stations. Apart from the advantages of the RC-based OTA tests, some important issues are identified.

This article reports on a new class of broadband and fully 3-D printed E-plane coax-to-waveguide transition and a monolithically 3-D printed waveguide magic-T based on the transition. The transition is constructed by a section of air-filled rectangular coaxial transmission line (TL) that is placed between two broadband coax-to-waveguide probe transitions. It is used to interconnect the magic-T's sum port and the waveguide T-junction. The incorporation of the transition reorients all the waveguide arms of the magic-T into the E-plane. Some X-band prototypes of the proposed transition and the magic-T are designed and implemented. Polymer-based additive manufacturing and copper electroplating techniques are employed to monolithically fabricate each prototype. The transition and the magic-T exhibit broadband and low-loss characteristics from 8.2 to 12.4 GHz with the measured performance well matched with the simulations. In addition, the power handling capability (PHC), including the peak PHC (PPHC) and the average PHC (APHC), of the magic-T is evaluated by simulations, showing that the proposed magic-T could handle 100 W of APHC.

Correlations and mutual couplings in antenna arrays lead to performance deterioration of multiple-input-multiple-output (MIMO) systems. The relation between mutual coupling and correlation is complex, especially in non-isotropic multipath environments. Reducing mutual coupling does not guarantee an eventual reduction of the overall correlation and vice versa. In general, it is not a trivial task to reduce mutual coupling and correlation simultaneously in arbitrary multipath environments. In this correspondence, a planar metamaterial structure (PMS) and an array-antenna decoupling surface (ADS) are applied to the antenna array for simultaneous reductions of correlations and mutual couplings. The PMS comprises regularly arranged metamaterial elements holding certain transmission features. The ADS placed between the PMS and array is a substrate with printed rectangular metal strips. A 1 × 4 patch array is taken as an example to demonstrate the effectiveness of the proposed scheme. According to the simulated and measured results, the combination of PMS and ADS can work together without interfering or affecting the matching condition of the antennas. As a result, the mutual coupling and overall correlation between the antenna elements are reduced in a general multipath environment.

A frequency-diverse bunching metasurface antenna (FDBMA) that can be used for microwave computational imaging (MCI) systems is proposed in this paper. The proposed FDBMA can generate low-correlated radiation patterns with a reduced frequency interval of 20 MHz and a bunching angle of 45° from 32 to 36 GHz. The frequency interval is reduced by combining a disordered cavity and an optimized frequency-diverse random metasurface. The directivity of the radiation patterns is improved by leveraging the joint-bunching method that combines the metal baffle, the Fresnel dielectric lens, the quasi-gradient random metasurface, and the random-coherent superposition comprehensively. The performance of the proposed FDBMA is evaluated in terms of the reflection coefficient, singular values and correlation coefficients of measurement modes. The reduced frequency interval and the bunching characteristic are also demonstrated. Finally, MCI experiments are implemented using the proposed FDBMA. Comparative experiments are also carried out to validate the advantage of reducing the frequency interval and improving the directivity.