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.
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.
Antenna array beamforming (BF) refers to a real-time procedure that aims at calculating the proper feeding weights applied to the array elements in order to create a main lobe and a number of nulls toward respective preassigned directions. Most of the research performed on BF has been based on a simplified mathematical model, which ignores the nonisotropic radiation pattern of the array elements and the element mutual coupling. This article 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. These 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. Index Terms-Antenna array beamforming (BF), direction of arrival (DoA), microstrip arrays, minimum variance distortionless response (MVDR), mutual coupling, null steering beamforming (NSB). I. INTRODUCTION A NTENNA array beamforming (BF) is related to a particular problem that has to be solved in real time. It concerns the calculation of feeding weights applied by a proper feeding network to the elements of the antenna array in order to make the array create a main lobe and a number of radiation nulls toward respective preassigned directions [1]-[19]. In fact, the main lobe direction must coincide with the direction of Manuscript
A new iterative adaptive beamforming (ABF) algorithm based on conventional beamformers is proposed, in order not only to steer the main lobe towards a desired signal and place radiation pattern nulls towards respective interference signals, but also to achieve a desired side lobe 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 side lobe, 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 towards 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 side lobe suppression. Finally, unlike methods that employ neural networks, the proposed algorithm does not need any training to become functional.
The coexistence of TV broadcasting and mobile services causes interference that leads to poor quality-of-service for TV consumers. Solutions usually found in the market involve external band-stop filters along with TV reception log-periodic and Yagi-Uda antennas. This paper presents a log-periodic antenna design without additional filtering that serves as a lower cost alternative to avoid interference from mobile services into the UHF TV. The proposed antenna operates in the UHF TV band (470–790 MHz-passband) and rejects the 800 MHz and 900 MHz bands (stopband) of 4G/LTE-800 and GSM900 services, respectively. Matching to 50 Ohms is very satisfactory in the passband with values of S11 below −12 dB. Furthermore, the antenna is highly directive with a realized gain of approximately 8 dBi and a front-to-back ratio greater than 20 dB.
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