A new iterative adaptive beamforming (ABF) algorithm based on conventional beamformers is proposed in order not only to steer the main lobe toward the desired signal and place radiation pattern nulls toward respective interference signals but also to achieve the desired sidelobe level (SLL). Thus, the algorithm becomes less susceptible to unpredicted interference signals than conventional beamformers. In each iteration, the algorithm finds the direction of the peak of the greatest sidelobe, which is considered as direction of arrival (DoA) of a hypothetical interference signal, and the conventional beamformer is then employed to find proper antenna array weights that produce an extra null toward this direction. The iterative procedure stops when the desired SLL is obtained. The algorithm is applied on three conventional beamformers and is tested for various signal DoA, while the direction deviation of the main lobe and the nulls is recorded, to evaluate the algorithm in terms of robustness. The proposed algorithm needs a few iterations to achieve the desired SLL and thus is much faster than any evolutionary iterative method employed for sidelobe suppression. Finally, unlike methods that employ neural networks (NNs), the proposed algorithm does not need any training to become functional.

An improved particle swarm optimization (PSO) method applied to the design of a new wideband log-periodic antenna (LPA) geometry is introduced. This new PSO variant, called PSO with velocity mutation (PSOvm), induces mutation on the velocities of those particles that cannot improve their position. The proposed LPA consists of wire dipoles with lengths and distances varied according to an exponential rule, which is defined by two specific parameters called length factor and spacing factor. The LPA is optimized for operation in 790-6000MHz frequency range, in order to cover the most usual wireless services in practice, and also to provide in this range the highest possible forward gain, gain flatness below 2dB, secondary lobe level below –20dB with respect to the main lobe peak, and standing wave ratio below 2. To demonstrate its superiority in terms of performance, PSOvm is compared to well-known optimization methods. The comparison is performed by applying all the methods on several test functions and also on the LPA optimization problem defined by the above-mentioned requirements. Furthermore, the radiation characteristics of the PSOvm-based LPA give prominence to the effectiveness of the proposed exponential geometry compared to the traditional Carrel’s geometry.

Antenna array beamforming (BF) refers to a realtime procedure that aims at calculating proper feeding weights applied to the array elements in order to create a main lobe and a number of nulls towards respective preassigned directions. Most of the research performed on BF has been based on a simplified mathematical model, which ignores the non-isotropic radiation pattern of the array elements and the element mutual coupling. This paper introduces an innovative way to incorporate the actual radiation pattern of the array elements and the element coupling into two popular deterministic BF methods, thus making these methods applicable to realistic antenna arrays. The two modified methods are applied in several scenarios, where a desired signal and several interference signals with various directions of arrival are received by a realistic microstrip linear antenna array. The statistical analysis performed in every scenario demonstrates the validity and effectiveness of the proposed modification.

Most of beamforming methods rely on the proper estimation of the steering vectors of the incoming signals in order to calculate appropriate array feeding weights. However, this estimation is often performed on a theoretical basis, since most methods assume that the array elements radiate like isotropic sources and consider only the phase differences between them due to their different spatial positions. This is a rough estimation as it ignores both the non-isotropic radiation pattern of the array elements and the mutual coupling between them. To overcome these limitations, we use a different approach for the construction of steering vectors based on the embedded patterns of the array elements, extracted through full-wave analysis. This approach is used in this paper to modify two well-known beamforming methods, namely the null steering beamforming and the minimum variance distortionless response method. Both modified methods are applied to a realistic model of a microstrip planar antenna array, and thus, both the azimuth and polar angles of the main lobe and nulls directions are controlled (beamforming in 3D space). Extensive statistical analyses are performed by implementing several scenarios of escalating difficulty, in order to examine the performance and temporal response of the modified beamforming methods in comparison to the respective conventional methods and also in comparison to beamforming methods based on evolutionary techniques.

A near-optimal design of a log-periodic dipole array (LPDA), suitable for DVB-T reception (470-790 MHz), is presented. The LPDA is required to provide low standing wave ratio as well as high-gain radiation pattern with sufficient gain flatness over the entire passband, and concurrently achieve low gain for frequencies above 800 MHz to reject LTE800 signals and thus improve the reception quality in the DVB-T band. All the above requirements are better satisfied by applying a novel particle swarm optimization (PSO) variant, called PSO with velocity mutation (PSOvm). PSOvm induces mutation on the velocities of those particles, which are unable to improve their fitness. As shown in this paper, PSOvm comes closer to the above requirements compared to four well-known optimization methods and outperforms the traditional LPDA design method proposed by Carrel. The LPDA geometry chosen for optimization is not the conventional one and therefore the dipoles are not considered to be included inside a specified angle as proposed by Carrel. Thus, the dipole lengths and distances as well as the boom dimensions are independently optimized. The PSOvm-based LPDA sufficiently meets all the above requirements and thus is suitable for DVB-T reception without the use of an external LTE-band rejection filter.

A microstrip feeding network (MFN) that implements a Dolph-Chebyshev current distribution is designed to feed a microstrip antenna array (MAA) operating in B2 LTE band. The study consists of three phases. In the first one, the elements of MAA are directly excited by equi-phase current sources complying with a Dolph-Chebyshev amplitude distribution to ensure a side lobe level (SLL) of −20 dB. Then, MAA is optimized for maximum forward gain. Finally, the input impedances of the elements of the optimized MAA and the element spacing are recorded. In the second phase, the MFN is considered to terminate at lumped loads with values equal to the input impedances of the respective elements of the optimized MAA, and is then optimized to achieve low standing wave ratio, high power efficiency, and output currents equal to those applied in the first phase by the current sources. All optimizations are performed with an improved particle swarm optimization variant in conjunction with CST. In the third phase, the optimized MFN is attached to MAA and is evaluated with CST. The purpose of this study is to show that it is possible to design an MFN that satisfies multiple requirements, without the knowledge of MAA geometry.