Vol. 52

An L/C dual-band dual-polarized (DBDP) shared aperture microstrip array is proposed in the paper. In the array, the sandwiched stacked patch is employed for the L-band element to exploit the bandwidth for given element thickness. Several key issues regarding the proposed structure are discussed, including: 1) benefit of proposed L band sandwiched stacked patch; 2) C-band feeding method; 3) radiation performance in both bands. A prototype array of L/C DBDP sandwiched stacked patch is designed and fabricated to verify the feasibility of the proposed structure, where the measured data are presented in the paper.

This article presents the Wave Concept Iterative Procedure, an efficient method for characterization of substrate integrated Non-Radiative Dielectric passive circuits based on wave concept formulation and its iterative solution. WCIP simulations are compared to measurements and Finite Element Method simulations. A good agreement is achieved with computation time saving.

The existing robust narrowband beamformers based on probability-constrained optimization have an excellent performance as compared to several state-of-the-art robust beamforming algorithms. However, they always assume that the steering vector errors are small enough. Without this assumption, we extend the probability-constrained approach to a wideband beamformer. In addition, a novel robust wideband beamformer with frequency invariance constraints is proposed by introducing the response variation (RV) element. Our problems can be reformulated in a convex form as the iterative second order cone programming (SOCP) problem and solved effectively using well-established interior point method. Compared with existing robust wideband beamformers, a more efficient control over the beamformer's response against the steering vector errors is achieved with an improved output signal-to-interference-plus-noise ratio (SINR).

A new compact antenna with the capability of covering Ultra Wide Band (UWB) Communication is presented. The size of the antenna is 22×24 mm². Moreover, the proposed antenna has been successfully fabricated and measured, showing broadband matched impedance (~149%, 2.1 up to more than 14.3 GHz, VSWR ≤ 2). Also the antenna has dual band rejected characteristic on WLAN and WiMAX bands. Frequency and time domain performances of the antenna such as fidelity factor are examined at the end of the paper.

In this paper, we present the design of a metamaterial based microstrip patch antenna, optimized for bandwidth and multiple frequency operations. A Criss-Cross structure has been proposed. This shape is inspired by the famous Jerusalem Cross. The theory and design formulas to calculate various parameters of the proposed antenna have been presented. The software analysis of the proposed unit cell structure has been validated experimentally thus giving negative response of ε and μ. Following this, a metamaterial-based-microstrip-patch-antenna is designed. A detailed comparative study is conducted exploring the response of the designed patch made of metamaterial and that of the conventional patch. Finally, antenna parameters such as gain, bandwidth, radiation pattern and multiple frequency responses are investigated and optimised and presented in tables and response-graphs. It is also observed that the physical dimension of the metamaterial based patch antenna is smaller than its conventional counterpart operating at the same fundamental frequency. The response of the patch antenna has also been verified experimentally. The challenging part was to develop metamaterial based on some signature structures and techniques that would offer advantage in terms of bandwidth and multiple frequency operation, which is demonstrated in this paper. The unique shape proposed in this paper gives improvement in bandwidth without reducing the gain of the antenna.

An extremely simple design of a planar Fabry-Pérot cavity antenna is proposed as a very promising candidate for millimeter-wave wireless systems. The simplicity of this design is obtained by using a dielectric slab, here quartz, to form a single-layer cavity with thin layers of copper etched/printed on both sides, to form the ground plane on one side and the frequency-selective surface (FSS) on the opposite side of the slab. By keeping the planarity of the structure and not-requiring an additional supporting layer, the cavity is excited using an integrated feeding-slot antenna etched on its ground plane. The variations in the radiation properties of the proposed antenna, linked to its leaky-wave behavioral explanation, are studied by designing three prototypes with different maximum gain values. The prototype FPCs are designed to operate for Q-band wireless communication systems (here, resonating at three different frequencies in the range of 42-46 GHz). The performance of the designed antennas, backed by initial analytical and numerical simulations, is verified with a full set of measurement results.

Feed-forward artificial neural networks (ANNs) can provide the adequate model required for the linearization of power amplifiers (PAs) used in wireless communication systems. A common characteristic of previously available ANN-based models for linearization purposes is the use of a single real-valued ANN having two outputs. The contribution of this work is to report the benefits of performing such behavioral modeling based on two independent real-valued ANNs, where each network has a unique output. The proposed ANN-based model is applied to the behavioral modeling of a GaN HEMT class AB PA, and its accuracy is compared to previous approaches in two different scenarios. First, in case of similar number of network parameters, it is observed that the proposed ANN-based model can reduce the normalized mean-square error (NMSE) by up to 1.3 dB. Second, in a situation of comparable modeling accuracy (NMSE = -40 dB), it is observed that the proposed ANN-based model can reduce the number of network parameters by up to 40% (from 62 to 38 real-valued parameters).

A novel compact wideband inphase multilayer power divider based on slotline-to-microstrip coupling structure is presented in this paper. To improve the isolation between output ports, this power divider breaks the conventional half-wavelength slotline configuration and introduces a lumped resistor. A wideband bandpass filter integrated with the power divider is designed to allow the power divider to reject the undesired signals located in adjacent frequency channels. This filter consists of two E-shape units. In order to improve its performance at low frequency band, a lumped capacitor is bridged between the two E-shape units. As an example, a wideband power divider combining with a filter is designed and fabricated. The experimental results show that the proposed power divider has a low insertion loss, high isolation, good return losses at all ports, good amplitude and phase balance, as well as flat group delay over the wide frequency band from 3.5 GHz to 10 GHz. In addition, the width of upper stopband reaches up to 3.8 GHz (12.9 GHz-16.7 GHz) corresponding to attenuation more than 20 dB.

In this work, a planar monopole ultra-wideband (UWB) antenna with an L-shaped stub on the ground plane is proposed. The novel extended L-stub in conjunction with the UWB radiator achieves an ultra wideband impedance matching with a compact size. The proposed antenna is fabricated and measured showing an ultra wide operating frequency range from 2.3 to over 14 GHz (VSWR < 2) with a unidirectional gain from 3-6.5 dBi and efficiency from 70-85% within the UWB band from 3.1-10.6 GHz. The proposed antenna provides a new way to improve ultra wideband impedance matching other than the frequently used tapered microstrip feed line. It also provides a way to improve the lower frequency bandwidth of the antenna without increasing the antenna's physical size, which is the most common method to use.

A simple microstrip circular disc antenna to excite circularly polarized radiation is presented. In a single-probe fed circular disc sector patch, the corners are further truncated to obtain circular polarization characteristics. The truncation helps to reduce the ground plane dimensions making the antenna more compact with overall dimensions of 50 mm x 50 mm x 1.6 mm. The lengths of truncation necessary to achieve circular polarization are mathematically expressed. The simulated and experimental results are compared and are found to be in good agreement. Axial ratio bandwidth of 1.3% is obtained. The overall size reduction is 55% in comparison with the original disc sector antenna. The antenna resonates in the UMTS 1900-2170 MHz band and can be employed for Mobile Communication applications.

A dual-band capacitive coupled planar inverted F antenna is presented. The antenna operates in two bands centered around 1.5 GHz and 2.4 GHz with nearly omnidirectional radiation pattern in the entire operating band. It offers a peak gain of 2.4 dBi at 1.5 GHz and 7 dBi at 2.4 GHz with an average efficiency of 82%, 97% respectively. Effects of key design parameters such as the distance between feed strip and radiator patch, the dimensions of the feed strip on the input characteristics of the antenna and length of slot have been investigated and discussed. The antenna is compact and simple to fabricate. The antenna posses an overall dimension of 10×40×6 mm³ when fabricated on substrate of dielectric constant 4.4 and thickness 1.6 mm.

A compact ultra wide band (UWB) antenna with dual band notch characteristics is proposed. The antenna consists of a coplanar waveguide (CPW) fed bevelled rectangular patch and a modified rectangular ground plane. A Z-shaped meander line parasitic element and a pair of symmetrical L-shaped quarter-wavelength stubs are employed to realize band-notched functions at WiMAX and WLAN bands respectively. By optimizing the dimensions and positions of these notch structures, the desired notch-bands of WLAN and WiMAX are achieved. Unlike other dual band-notched antennas reported in literature this antenna has a merit of regulating the centre frequency as well as the bandwidth of both the notched bands easily and independently. The measured -10 dB S₁₁ covers the bandwidth from 2.5 to 11.5 GHz, with two notched bands from 3.3 to 3.6 GHz and 5.2 to 5.75 GHz. The proposed antenna exhibits nearly omni-directional radiation patterns with moderate gain and small group delay variations less than 0.5 ns over the entire operating bandwidth except at the notched bands. Moreover, by using antenna transfer function, the time domain characteristic of the antenna is also studied to confirm its suitability for UWB pulse communication.

Fragment structure should find its application in acquiring high isolation between multiple-input multiple-output (MIMO) antennas. By gridding a design space into fragment cells, a fragment-type isolation structure can be constructed by metalizing some of the fragment cells. For MIMO isolation design, cells to be metalized can be selected by optimization searching scheme with objectives such as isolation, return losses, and even radiation patterns of MIMO antennas. Due to the exibility of fragment-type isolation structure, fragment-type structure has potentials to yield isolation higher than canonical isolation structures. In this paper, multi-objective evolutionary algorithm based on decomposition combined with genetic operators (MOEA/D-GO) is applied to design fragment-type isolation structures for MIMO patch antennas and MIMO PIFAs. It is demonstrated that isolation can be improved to different extents by using fragment-type isolation design. Some technique aspects related to the fragment-type isolation design, such as effects of fragment cell size, design space, density of metal cells, and efficiency consideration, are further discussed.

This article proposes a new design of wideband wide beam microstrip like antenna (MLA) in X-band (8-12 GHz) overcoming the limitations of conventional MLA design. The waveguide is filled with a dielectric material, which is shaped beyond the waveguide aperture as a pyramidal structure. This helps in achieving the size reduction of the waveguide and matching of aperture admittance over the complete operational band. Also a vertical electric dipole feed design is proposed to excite MLA and match the source and load admittances. The input reflection coefficient observed over the complete band is better than -10 dB. The measured gain and cross polarized levels of antenna achieved are better than 3 dBi and -18 dB across the bandwidth, respectively. The measured and simulated results are in good agreement.

A Multiple Input Multiple Output (MIMO) antenna consisting of two 90° angularly separated semicircular monopoles with steps for Bluetooth, Wi-Fi, Wi-MAX and UWB applications is proposed. Initially, an array of two coplanar circular monopoles with element separation of 25 mm is investigated. In this configuration, mutual coupling is < -5 dB and < -10 dB over 2 GHz-3 GHz and 3 GHz-10.6 GHz, respectively. Mutual coupling is reduced by using 90° angularly separated semicircular monopoles. With semicircular configuration, though the mutual coupling is improved, impedance bandwidth is reduced due to reduction in electrical length. A step like structure is introduced in the semicircular monopoles, and ground plane is modified and extended between the two elements to improve the impedance bandwidth and mutual coupling. Impedance bandwidth from 2.0 GHz-10.6 GHz with S₂₁ < -20 dB and -14 dB is achieved over 3.1 GHz-10.6 GHz and 2.0-3.1 GHz, respectively. The antenna is fabricated using 46 mm × 37 mm RT Duroid substrate. Measurement results agree with the simulation os. Radiation patterns are stable, and correlation coefficient is < 0.02 over 2.0-10.6 GHz.

The visibility distribution, which is related to the configuration of stations, can be categorized into different features, each having different levels of data number density. A computationally efficient multi-feature image reconstruction algorithm, well adapted for next-generation telescopes, is proposed based on this observation, which is more flexible to handle massive amount of visibility data expected in the future. In reconstructing the M87 image with the visibility data simulated on the Low-Frequency Array (LOFAR), this algorithm turns out to be a few hundreds to one thousand times faster and is more resilient to noises than the conventional algorithms.

Decoupling networks (DNs) have frequently been used to obtain high isolation performance between coupled antennas in multiple-input multiple-output (MIMO) systems due to their advantage of spatial efficiency, which is particularly important for mobile devices. However, conventional DNs suffer from narrowband limitations. In this paper, a broadband decoupling technique is proposed that broadens the isolation bandwidth using a parallel resonant point. A 1.95 GHz MIMO antenna system with 460 MHz of bandwidth (fractional bandwidth, FBW = 23.6%) is designed and measured using the scattering parameters. The isolation is found to be better than -15 dB, while the reflection coefficient is better than -6 dB. Furthermore, the antenna efficiency and envelope correlation coefficient (ECC) are evaluated in a reverberation chamber.

A real time, low complexity algorithm is developed to steer a planar patch antenna array beam to the maximum received signal strength (RSS) direction for communication link enhancement. The beam steering towards the maximum incoming signal direction is based on an iterative technique utilizing a set of RSS measurements taken from specific locations in the search space, these locations collectively form an ellipse. The algorithm is denoted as ``elliptical peeking''. It was simulated for a flying unmanned aerial vehicle (UAV) as the vehicle tries to identify the maximum signal strength incoming direction of a stationary ground signal and it was tested on an embedded platform to validate its low demand for computational power. Such an algorithm is suitable for autonomous platforms due to its simplicity and low cost.

A novel feed network based on the microstrip/slotline transition is proposed in this paper. This feed network not only has ultra-wide impedance bandwidth but also can improve space utilization and make the design of antenna array easier. Then an ultra-wideband (UWB) antenna array with four elements fed by the network is designed. The antenna array is simulated, manufactured and measured. The results show that: the impedance bandwidth with return loss under -10 dB is 88.76%, from 2.35 GHz to 6.1 GHz. Within the impedance bandwidth, the radiation performance is satisfactory, and the gain of the array is 2.1-7.1 dB, higher than that of the element. The cross-polarization level of the array is lower than -20 dB, just as the element. A reasonable agreement of results is achieved between simulation and measurement.

A novel wideband sleeve antenna with capacitive annulus for wireless communication applications is presented in this paper. A sleeve structure is introduced to improve the impedance bandwidth through exciting a new resonate point. By loading capacitive annulus at the center of sleeve, an impedance bandwidth enhancement is achieved at the upper frequency band. The measured impedance bandwidth for VSWR≤2 about 142.8% ranging from 1.01 to 6.06 GHz is achieved, and monopole-like radiation patterns are presented. A prototype has been fabricated and tested, and the experimental results validate the design procedure. It is sufficient for accommodating recent wireless communication services such as DCS1800, PCS1900, IMT2000, WLAN, WiMAX2350/3500, etc.