In this paper, we propose an efficient method that specifies the minimum number of samples and their locations to measure the spherical near-field (SNF) of antennas utilizing information theoretic tools. To this end, spherical harmonics are investigated from the information theoretic point of view. Our study determines the minimum required samples and provides a validation tool to assess the ability of a sampling scheme to recover the antenna characteristics by the measured data. Further, an optimum sampling scheme is proposed by clustering the energy of vector spherical harmonics using the frame theory without any time-consuming iterative which leads to a highly efficient SNF measurement procedure. The number of samples determined by the proposed method is only 50% of the Nyquist method which provides significant advantages for storage and processing time. Our method additionally shows a great promise for recovery of far-field radiation pattern from near-field samples with the same performance as the Nyquist sampling on a sphere. To derive the proposed sampling scheme with the minimum redundancy, no prior information on the antenna is assumed. Finally, the proposed sampling scheme is validated on measurement data.

This study presents an accurate method to synthesise a shaped‐beam flat reflectarray (RA) antenna based on the phase synthesis of its equivalent aperture. For this purpose particle swarm optimisation is used to determine the optimal phase distribution on the reflective surface of the antenna. Furthermore, by dividing the equivalent aperture of the antenna into small parts and by appropriate approximation of the induced current in each part, the radiation fields have been evaluated via the sum of the simple integrals. In this approach the relation of the amplitude and phase of the reflection co‐efficient of the RA elements with the radiation fields of the antenna can be obtained. Therefore the effect of the RA elements can directly be considered in the optimisation process. Also, in the proposed method the effects of the feed antenna including the angle, polarisation, amplitude and phase of the radiated fields from the feed are fully considered in the synthesis procedure. To verify the synthesis method a RA with flat reflective surface has been designed and manufactured that shows a good agreement with the simulation results obtained from commercial full‐wave electromagnetic software, CST Microwave Studio.

This paper presents an accurate method for synthesis of True Time Delay (TTD) reflecting elements to design wideband reflectarray (RA) antennas. In doing so, primarily the conventional phase distribution formulation of RA is modified to accommodate the design of resonant reflecting elements based on TTD technique. An accurate circuit model is then presented to realize the linear reflection coefficient phase of the reflecting elements of the RA antenna using the continued fraction theory. Finally, the equivalent circuit models of reflecting elements are implemented via multilayer Frequency Selective Surface (FSS) structures. The RA antenna is designed and fabricated to operate in the X band frequency. Stable aperture phase efficiency of about 80 % and stable radiation patterns throughout the operating frequency band, confirm the accuracy of the proposed method.

In this letter, high-selective bandpass filters, in the printed ridge gap waveguide technology, are presented. The filters are designed to perform 4.68% fractional bandwidth at center frequency f₀ = 24.78 GHz. In the proposed filters, to obtain high selectivity, a cross-coupling between the nonadjacent resonators and also a coupling between the input and output ports to create an extra pair of transmission zeros in the transfer function of the filters are used. Finally, the filters are fabricated, and their scattering parameters are measured to verify the simulation results.

Spherical near‐field antenna measurement requires the acquisition of many points, which makes the measurement process time‐consuming. Since the antenna radiation pattern has a sparse representation on the basis of vector spherical harmonics, compressive sensing (CS) can be used to reduce the number of sampling points in the near‐field antenna measurement. CS requires knowledge of sparsity in advance to determine the number of sampling points. The phase transition diagram is usually used to determine the number of measurements, which is again time‐consuming and requires a large number of computing data. In this study, the method for sparsity level estimation is used to estimate the sparsity level of an arbitrary antenna's near field. Using this sparsity estimation method is a novel antenna measurement which has many applied advantages. As a case in point, it estimates the sparsity level of a radiation pattern with a few numbers of measurements, which makes the CS method efficient and affordable in the near‐field measurement technique. To confirm the effectiveness of the proposed method, a standard horn antenna is investigated.