An optimisation framework for near field multifocusing on antenna arrays is proposed. Its aim is to obtain the feeding weights that must be applied to the elements of the array so that the antenna focuses on two or more targets simultaneously. The method is based on the definition of a proper cost function, which is minimised using an optimisation algorithm over an equivalent least squares problem. The success of the technique is noted in the fact that different array parameters can be obtained: magnitude and phase of the array elements or only phase synthesis. In order to show the efficiency of the method, several tests are carried out using different arrays and optimisation parameters. The simulation, manufacture and measurement of an 8 × 8 planar array able to focus on two different targets is also performed. Results show how the framework can be applied to general arrays and demanding requirements, so it may be easily extended to different synthesis problems besides multifocusing.

Traditional synthesis methods usually deal with the Array Factor information or with approaches based on considering ideal radiating elements without interaction between them. Taking into account the coupling between elements increases the complexity of the synthesis tasks, so it is usually disregarded assuming a certain error in the solution. As shown in the paper, this error can be unacceptable in some antenna array designs. A neural network-based solution can exploit the "a priori" knowledge of the radiating system to relate a given radiated field distribution with the voltages that must be applied to each radiating element taking into account mutual coupling effects without increase of complexity from the designer's point of view. A set of techniques based on the use of neural networks for synthesis purposes are presented in this paper. Results of a prototype of antenna array with feeding values designed using the proposed techniques are also presented

In this letter, we demonstrate that the dispersion properties of printed double-sided parallel-strip lines can be controlled by using glide symmetry. Glide symmetry is introduced in with corrugations in both strips of a double-sided line. We demonstrate that glide symmetry eliminates the stopband between first and second propagating modes and yields to a higher propagation constant, preserving its linearity, and the broadband nature of the underlying guiding technology. Thus, the glide-symmetric double-sided line can be designed to possess a high equivalent refractive index in an ultrawide range of frequencies. These exceptional properties have been numerically and experimentally validated. Finally, we demonstrate the possibilities of this technology with a specific design, a glide-symmetric double-sided parallel-strip line with filtering properties. Potential applications are low-dispersive leaky-wave antennas and electromechanical tunable phase shifters and filters.

This letter demonstrates that glide symmetry can be used to match the impedance of highly dense dielectric profiles in wide angle and broad bandwidth. Using glide-symmetric metasurfaces permits tuning the magnetic properties of materials, so high values of permittivity can be matched to free space in wideband. This matching is achieved without disturbing the performance of the device, since the refractive index remains fixed. The performance of the proposed matching method is validated through measurements for normal incidence. For oblique incidence, a hyperbolic dielectric lens is matched with glide-symmetric structures in simulations. These simulations demonstrate a smooth transmission of the fields, manifesting a well-matched profile of the lens.

A new optimization method is presented for the design of microwave high-conversion gain harmonic self-oscillating mixers (SOMs). It is based on the control of the harmonic content of the transistor input-voltage waveform of the self-oscillation, through the use of a nonperturbing auxiliary generator and a substitution generator. The combination of the two generators allows obtaining the optimum harmonic content of the transistor-gate voltage waveform for a maximum conversion gain. Two different downconverter circuits have been designed using this method, a second harmonic SOM and a third harmonic SOM, obtaining a high conversion gain. A good agreement between the simulated and experimental results has been found

In this letter, a new microwave variable phase-shifter based on an injection-locked harmonic self-oscillating mixer, is presented for its application in an active microstrip phased antenna array. The circuit provides the double functionality of variable phase-shifter and down-converter. Maximum conversion gain is obtained, through the optimization of a new multi-harmonic load at the input-port of the circuit. The ranges of synchronized operation are analyzed versus the circuit parameters and the corresponding phase-shifts are calculated. The stability of the synchronized solutions is analyzed using the envelope transient simulation method. An 11.25-1.5-GHz down-converter with a 3.25-GHz free-running frequency has been designed, providing a phase-shift variation at intermediate frequency up to 540/spl deg/, with a 4.5-dB conversion gain. A good agreement between the simulated and experimental results has been found.