This paper investigates the performance of a Windowing Based Crest Factor Reduction (CFR_WB) technique, to enhance the power efficiency of Radio Frequency (RF) power amplifiers. In particular, CFR_WB is implemented on a Doherty Power Amplifier (DPA) in conjunction with Generalized Memory Polynomial (GMP_DPD), and Volterra series based Digital Predistortion (V_DPD) techniques. Key features like spectral regrowth, Peak to Average Power Ratio (PAPR) reduction, efficiency improvement and Error Vector Magnitude (EVM) have been used to measure the efficacy of the proposed method. Both simulation and experimental results show that the proposed combination of CFR_WB technique with GMP_DPD and V_DPD is able to reduce the PAPR of the complex input signals by nearly 60%, with minimal degrading of the EVM and spectral regrowth. Moreover, such signal with reduced PAPR can be used to overdrive the DPA, allowing for a relevant average efficiency enhancement (i.e., up to 25%), while fulfilling the requirements of modern communication standards such as Wideband Code Division Multiple Access (WCDMA) and long-term evolution (LTE).

In this paper, a Rectangular Dielectric Resonator Antenna (RDRA) with a modified feeding line is designed and investigated at 28 GHz. The modified feed line is designed to excite the DR with relative permittivity of 10 which contributes to a wide bandwidth operation. The proposed single RDRA has been fabricated and mounted on a RT/Duroid 5880 (ε_r=2.2 and tan δ=0.0009) substrate. The optimized single element has been applied to array structure to improve the gain and achieve the required gain performance. The radiation pattern, impedance bandwidth and gain are simulated and measured accordingly. The number of elements and element spacing are studied for an optimum performance. The proposed antenna obtains a reflection coefficient response from 27.0 GHz to 29.1 GHz which cover the desired frequency band. This makes the proposed antenna achieve 2.1 GHz impedance bandwidth and gain of 12.1 dB. Thus, it has potential for millimeter wave and 5G applications.

Single-layer circularly polarized (CP) reflectarrays in the Ka-band are presented in this paper. Three reflectarray (RA) models are designed and measured, using geometrically dissimilar elements. Each element is analyzed individually and optimized to obtain good performance within the operating frequency band. To compensate the spatial delay from feed to the elements at RA surface, the angular rotation technique has been employed for obtaining reflected phase curve. The performances of the antennas are analyzed at 30 GHz, exhibiting 13.3% of 1.5 dB gain bandwidth, while the axial ratio bandwidth is less than 3 dB in the whole operating band.

An approach of reducing Mutual Coupling between two patch antennas is proposed in this paper. Here, a meander line resonator is placed in between the radiating elements. By inserting the meander line resonator between the patch antennas with the edge-to-edge distance less than λ/18, about 8 dB reduction of Mutual Coupling throughout the 10-dB bandwidth has been achieved without degrading the radiation pattern.The circuit model of the proposed configuration is carried out in this paper and envelope correlation coefficient is also computed. The proposed structure has been fabricated and measured.

In this paper, the uniaxial anisotropic perfectly matched layer (UPML) absorbing boundary condition in unconditionally stable five-step locally one-dimensional finite-difference time-domain (LOD5-FDTD) method is deduced. The UPML absorbing boundary condition (ABC) is validated based on comparison with a simulation in larger domain (and thus without reflection) in the first test. Then using a sinusoidal source, target field phase distribution surrounded by the UPML-ABC is analyzed. The results further illustrate the stability and efficiency of the UPML absorbing boundary condition.

This paper presents the theoretical framework for a new technique in the field of linear antenna arrays with amplitude control called error coefficient matrix. First of all, the array factor is expressed as a summation of contribution from the elements of the array. It will be shown that for small errors in excitation amplitude, the error in the overall radiation pattern at a given angle is a summation of errors contributed by the individual elements of the array at that angle. An error coefficient matrix is proposed, and its properties are discussed in great detail. The accuracy of the proposed method is investigated for varying levels of errors in weights and for varying number of error elements, using Monte-Carlo simulation. Finally, the applications of this new technique in the field of antenna arrays are presented.

Current microwave hyperthermia applicators are not well suited for uniform heating of large tissue regions. The objective of this research is to identify an optimal microwave antenna array for clinical use in hyperthermia treatment of cancer. For this aim we present a novel 434 MHz applicator design based on a metamaterial zeroth order mode resonator, which is used to build larger array configurations. These applicators are designed to effectively heat large areas extending deep below the body surface and in this work they are characterized with numerical simulations in ahomogenous muscle tissue model. Their performance is evaluated using three metrics: radiation pattern-based Effective Field Size (EFS), temperature distribution-based Therapeutic Thermal Area (TTA), and Therapeutic Thermal Volume (TTV) reaching 41-45°C. For 2×2 and 2×3 array configurations, the EFS reaching > 25% of maximum SAR in the 3.5 cm deep plane is 100% and 91% of the array aperture area, respectively. The corresponding TTA for these arrays is 95% and 86%, respectively; and the TTV attaining > 41°C is over 85% of the aperture area toa depth of over 3 cm in muscle, using either array configuration. With theoretical heating performance exceeding that of existing applicators, these new metamaterial zero order resonator arrays show promise for future applications in large area superficial hyperthermia.

A 3D printed dual-ridged horn antenna (DRHA) is presented. The antenna design is optimized for additive manufacturing and is 3D printed using acrylonitrile butadiene styrene (ABS) and then painted with nickel based aerosol spray. The coaxial transition is also included in the 3D printed prototype. The antenna was manufactured with the intention of improving learning and education of electromagnetism and antennas for undergraduate students using a low-cost personal desktop 3D printer. The painted DRHA has a 10 dB return-loss bandwidth of 6621 MHz (1905 MHz-8526 MHz) with a peak gain of 11 dBi. This prototype is the first known ABS based horn antenna with the coaxial transition embedded into it.

This paper reports the design and performance of a compact planar arrangement of concentric rings designed with defected ground plane. The radiating circular patch and ground plane of antenna are modified in several steps to achieve a broadband circularly polarized antenna. In each stage of modification, antenna is simulated by applying CST Microwave Studio simulator, and finally, a prototype is developed and tested in free space. The developed prototype efficiently operates at frequencies 2.34 GHz and 4.41 GHz, and provides an overall impedance bandwidth close to 2.31 GHz or 67.45% with respect to central frequency 3.425 GHz. This antenna provides nearly flat gain in the desired frequency band with maximum measured gain close to 2.94 dBi at frequency 3.02 GHz. It also provides circularly polarized radiations in the frequency bands extended from 2.67 to 3.05 GHz and 3.44 to 3.57 GHz. The co-polar and cross-polar radiation patterns of the antenna in azimuth and elevation planes are obtained at frequencies 2.316 GHz and 4.41 GHz. The proposed antenna can be used for mobile and lower bands of Wi-Max and UWB communication systems.

A compact microstrip antenna loaded with periodic patterns etched in the ground plane is proposed. The etched patterns are Jerusalem crosses which look the same as one of the common electromagnetic band gap structures, uni-planar electromagnetic band gap. In this paper, the dielectric backed with etched ground plane is analysed in terms of metamaterial. The permittivity and permeability are derived from the simulated reflection and transmission coefficients. Then a patch is stacked on the metasubstrate, and the antenna is designed to operate at 2.4 GHz. The proposed antenna has a small dimension in comparison to two other published compact antennas. Compared to the conventional patch antenna, the proposed antenna achieves a 68.38% miniaturization of the patch, and a 2.84 times impedance bandwidth broadening. Furthermore, the operating frequency of the proposed antenna can be tuned over a large range of frequencies by physically adjusting the length of the surrounding slots or by voltage adjusting of the voltage controlled tunable inductive elements. The proposed antenna is fabricated and measured. The measurement results are found to agree well with the simulation ones.

The effects of anisotropic turbulence on the wander and spreading of Gaussian-Schell model beams propagating in non-Kolmogorov marine-atmospheric channel are investigated. Expressions for beam wander and long-term beam spreading are derived in all conditions of marine-atmospheric turbulence. Our results indicate that the beam wander and spreading of Gaussian-Schell model beams are lower in the anisotropic turbulence than the beam in isotropic turbulence. This model can be evaluated ship-to-ship/shore optical laser communication system performance.

A novel feeding network is investigated both theoretically and experimentally. The proposed system with combination of a Wilkinson power divider and two branch-Line couplers is established. The output signals of the system have the same amplitude and 900 phase difference with each other. The size reduction technique is applied to minimize the physical size of the proposed network. In this technique, the ground of the structure is defected, and distributed capacitors and inductors are added to empty space of the branch-line couplers. Moreover, meandered lines are used in order to match the output impedance of the Wilkinson power divider arms and reduce its size. The initial design realized in 2.5 GHz shows the fractional bandwidth of 24%. Then a miniaturized structure is fabricated with 42% smaller size than the main structure while it shows similar electrical performance. For both cases, measurement and simulation results are in good agreement with each other.

Multiple-input-multiple-output antennas are investigated for terrestrial point-to-point wireless link. The lack of rich scatters in a terrestrial wireless channel results in an ill-conditioned channel matrix for a long range link with compact arrays, which can cause a high bit error rate. This paper demonstrates that the channel matrix can be improved by carefully selecting the antenna spacing. Unfortunately, an optimum antenna spacing that guarantees a good channel matrix is too large to implement for most long range terrestrial wireless links. On the other hand, a channel capacity study of an 8×8 link reveals that multiple antennas do provide more capacity even with small antenna spacing. Constellation multiplexing is then applied to the compact array configuration to solve the unreliable communication problem. In addition, a multilevel maximum ratio combining technique is introduced to improve detection efficiency.

In this paper, the application of Artificial Neural Network (ANN) with back-propagation algorithm and weighted Fourier method are used for the synthesis of antenna arrays. The neural networks facilitate the modelling of antenna arrays by estimating the phases. The most important synthesis problem is to find the weights of the linear antenna array elements that are optimum to provide the radiation pattern with maximum reduction in the side lobe level. This technique is used to prove its effectiveness in improving the performance of the antenna array. To achieve this goal, antenna array for Wi-Fi IEEE 802.11a with frequency at 2.4 GHz to 2.5 GHz is implemented using Hybrid Fourier-Neural Networks method. To verify the validity of the technique, several illustrative examples of uniform excited array patterns with the main beam are placed in the direction of the useful signal. The neural network synthesis method not only allows to establish important analytical equations for the synthesis of antenna array, but also provides a great flexibility between the system parameters in input and output which makes the synthesis possible due to the explicit relation given by them.

This paper presents the design and fabrication of a broadband UHF RFID tag for bio-monitoring applications. The proposed tag is realized with a thin FR4 substrate of 200 μm, which can be considered as flexible. It shows good performances both in free space and placed on human body. For instance, in free space, the tag can be read at 14 m in the UHF RFID band and at an average distance of 4.6 m when it is placed on the human body. The overall tag size is only 80 mm × 50mm × 200 μm.

This paper presents the use of micro-electromechanical systems (MEMS) switches to realize the radiation pattern reconfiguration of microstrip antenna, which works in Ka-band. The antenna was fabricated on a silicon substrate and designed to reconfigure radiation pattern at the operation frequency of 35 GHz. The simulation results show that by controlling the states of MEMS switches between the driven element and two parasitic elements, the antenna can achieve reconfigure into three maximum radiation directions in the H-plane (θ=0°, ψ=90°, θ=14°, ψ=90°, and θ=-14°, ψ=90°, respectively). The measured maximum radiation directions of modes-1, modes-2, modes-3, modes-4 are θ=17°, -25°, 3.5°,0.7° and gains of four modes at the maximum radiation direction are 5.78 dBi, 6.49 dBi, 7.24 dBi, 6.31 dBi, respectively. The measured results are closely consistent with the simulation ones. The proposed antenna can be applied to satellite communication.

In the present paper we focus on the study of polarization properties of biaxial metamaterial, which consist of alternate ferrite and semiconductor layers, located on an ideally conducted metal substrate. The system is placed into an external magnetic field along the boundaries of the layers. The effective medium theory is applied. Effective linear-to-elliptic polarization conversion has been shown, by means of physical and geometrical parameters of the system under consideration.

A categorized radio channel modeling for wireless ultra-wideband on-body body area networks is discussed. Measurements in an anechoic chamber at fourteen antenna locations are conducted in a 2-8 GHz band. The dipole and double loop antenna types are used. Six link classes are formed based on the antenna spots on the torso, head or limb. The limb-limb and the head-limb links have the lowest and highest path losses, respectively. The head-limb links have the shortest channel impulse responses (CIRs) and limb-limb links the longest ones. The CIR amplitudes follow the inverse Gaussian distribution. The tap indexes and the total excess delays are modeled with the negative binomial distribution. In most cases, the CIRs decay faster for the dipole. Otherwise no major differences exist between the antennas.

A compact broadband bandpass filter (BPF) on Composite right/left-handed (CRLH) Quarter-Mode Substrate Integrated Waveguide (QMSIW) is presented and analyzed in this paper. A size reduction is implemented by etching the CRLH interdigital slots (CRLH-IS) in the compact QMSIW cavity to introduce a lower resonant frequency less than that of the QMSIW. The influence of the rotation angle of the CRLH-IS on the frequency response of the CRLH QMSIW BPF is analyzed, and the optimal rotation angle is used to implement a BPF with good out-band rejection. The proposed CRLH QMSIW shows the characteristics of low quality factor and high coupling coefficient that make it a good solution to design a broadband bandpass filter. The measured insertion loss is less than 1.8 dB at 4.43 GHz with a fractional bandwidth (FBW) of around 22%. The measured results agree well with the simulated ones.

In this letter, a new design for patch antenna, which can obtain low radar cross section (RCS) and high gain performance simultaneously, is proposed on the basis of a metamaterial (MTM) superstrate. The superstrate consists of two metallic layers with different patterns on both sides of a dielectric substrate. Low reflection and transmission are obtained from the upper surface which can absorb most of the incident wave to reduce the antenna RCS. The bottom surface, which has partial reflectivity, is used to construct a Fabry-Perot resonance cavity with the ground plane of the patch antenna to improve its directivity. Measured results show that the proposed antenna can achieve RCS reduction in a broad frequency band ranging from 2 to 14 GHz with maximum RCS reduction value of 28.3 dB, and high gain performance is enhanced by 4.3 dB at most compared with the original antenna in the working frequency band extending from 10.9 GHz to 12 GHz. The measured results agree well with the simulated ones.