Modeling Approaches for Active Antenna Transmitters

The rapid growth of data traffic in mobile communications has attracted interest to Multiple-Input-Multiple-Output (MIMO) communication systems at millimeter-wave (mmWave) frequencies. MIMO systems exploit active antenna arrays transmitter configurations to obtain higher energy efficiency and beamforming flexibility. The analysis of transmitters in MIMO systems becomes complex due to the close integration of several antennas and power amplifiers (PAs) and the problems associated with heat dissipation. Therefore, the transmitter analysis requires efficient joint EM, circuit, and thermal simulations of its building blocks, i.e., the antenna array and PAs. Due to small physical spacing at mmWave, bulky isolators cannot be used to eliminate unwanted interactions between PA and antenna array. Therefore, the mismatch and mutual coupling in the antenna array directly affect PA output load and PA and transmitter performance. On the other hand, PAs are the primary source of nonlinearity, power consumption, and heat dissipation in transmitters. Therefore, it is crucial to include joint thermal and electrical behavior of PAs in analyzing active antenna transmitters. In this thesis, efficient techniques for modeling active antenna transmitters are presented. First, we propose a hardware-oriented transmitter model that considers PA load-dependent nonlinearity and the coupling, mismatch, and radiated field of the antenna array. The proposed model is equally accurate for any mismatch level that can happen at the PA output. This model can predict the transmitter radiation pattern and nonlinear signal distortions in the far-field. The model\u27s functionality is verified using a mmWave active subarray antenna module for a beam steering scenario and by performing the over-the-air measurements. The load-pull modeling idea was also applied to investigate the performance of a mmWave spatial power combiner module in the presence of critical coupling effects on combining performance. The second part of the thesis deals with thermal challenges in active antenna transmitters and PAs as the main source of heat dissipation. An efficient electrothermal modeling approach that considers the thermal behavior of PAs, including self-heating and thermal coupling between the IC hot spots, coupled with the electrical behavior of PA, is proposed. The thermal model has been employed to evaluate a PA DUT\u27s static and dynamic temperature-dependent performance in terms of linearity, gain, and efficiency. In summary, the proposed modeling approaches presented in this thesis provide efficient yet powerful tools for joint analysis of complex active antenna transmitters in MIMO systems, including sub-systems\u27 behavior and their interactions

Active Transmitter Antenna Array Modeling for MIMO Applications

The rapid growth of data traffic in mobile communications has attracted interests to the Multiple-Input-Multiple-Output (MIMO) communication systems at millimeter-wave (mmWave) frequencies.\ua0 MIMO systems exploit active transmitter antenna arrays for higher energy efficiency and providing beamforming flexibility. The close integration of multiple PAs and antennas increases the transmitter analysis complexity. Moreover, due to the small antenna element spacing at mm-wave frequencies, isolators are too bulky and cannot be used. Therefore, including the effects of interactions between the antenna array and PAs is a significant aspect in the analysis of MIMO transmitters. For large active arrays, applying joint circuit and EM simulation tools for the analysis is a complicated and time-consuming task. In these occasions, behavioral models are the key to the fast and accurate evaluation of active transmitter antenna arrays.In this thesis, a technique for modeling the active transmitter antenna array performance is presented. The proposed model considers the effect of PAs nonlinearity as well as the coupling and mismatch in the antenna array. With this model, a comprehensive prediction of radiation pattern and signal distortions in the far-field is feasible. The model is experimentally verified by a mmWave active subarray antenna for a beam steering scenario and by performing over-the-air measurements. The measurement results effectively validate the modeling technique for a wide range of steering angles.\ua0\ua0 Furthermore, a linearity analysis is provided to predict transmitter performance in conjunction with beam-dependent digital predistortion (DPD) linearization. The study reveals the model potential in evaluating different DPD approaches as well as predicting the performance of linearized transmitters. The demonstration shows that the variation of nonlinear distortion versus steering angle depends significantly on the array configuration and beam direction.In summary, the proposed model allows for the prediction of the active transmitter antenna array performance in the early design stages with low computational effort. It can provide design guides for developing large-scale active arrays and can be employed for evaluating the DPD and transmitter linearity performance

Hybrid Beamforming Transmitter Modeling for Millimeter-Wave MIMO Applications

Hybrid digital and analog beamforming is an emerging technique for high-data-rate communication at millimeter-wave (mm-wave) frequencies. Experimental evaluation of such techniques is challenging, time-consuming, and costly. This article presents a hardware-oriented modeling method for predicting the performance of an mm-wave hybrid beamforming transmitter. The proposed method considers the effect of active circuit nonlinearity as well as the coupling and mismatch in the antenna array. It also provides a comprehensive prediction of radiation patterns and far-field signal distortions. Furthermore, it predicts the antenna input active impedance, considering the effect of active circuit load-dependent characteristics. The method is experimentally verified by a 29-GHz beamforming subarray module comprising an analog beamforming integrated circuit (IC) and a 2 times 2 subarray microstrip patch antenna. The measurement results present good agreement with the predicted ones for a wide range of beam-steering angles. As a use case of the model, far-field nonlinear distortions for different antenna array configurations are studied. The demonstration shows that the variation of nonlinear distortion versus steering angle depends significantly on the array configuration and beam direction. Moreover, the results illustrate the importance of considering the joint operation of beamforming ICs, antenna array, and linearization in the design of mm-wave beamforming transmitters

High gain V-band planar array antenna using half-height pin gap waveguide

With growing demand for mm-Wave applications, gap waveguide technology introduced many advantageous features compared to hollow waveguides or SIW. Till now several wideband, high-efficiency and highly directive planar gap waveguide antennas have been proposed. Recently, a new form of pins, the so called half-height pin, is proposed for realizing gap waveguide technology. In this paper, a wide-band, high gain, and high efficiency 8 78-element slot array antenna for 60 GHz band based on the new form of pins is introduced. The simulation shows a very good performance of the antenna, with 14% bandwidth of the 10 dB return loss, 26 dBi realized gain and close to 80% aperture efficiency. The antenna has less difficulty in manufacturing because of new pin form and therefore is suitable for the low cost mass production of mm-Wave antennas

Magnetic Field Effect on Natural Convection Flow with Internal Heat Generation using Fast – Method

The magnetic field effect on laminar natural convection flow is investigated in a filled enclosure with internal heat generation using two-dimensional numerical simulation. The enclosure is heated by a uniform volumetric heat density and walls have constant temperature. A fixed magnetic field is applied to the enclosure. The dimensionless governing equations are solved numerically for the stream function, vorticity and temperature using finite difference method for various Rayleigh (Ra) and Hartmann (Ha) numbers in MATLAB software. The stream function equation is solved using fast Poisson's equation solver on a rectangular grid (POICALC function in MATLAB), voricity and temperature equations are solved using red-black Gauss-Seidel and bi-conjugate gradient stabilized (BiCGSTAB) methods respectively. The results show that the strength of the magnetic field has significant effects on the flow and temperature fields. For the square cavity, the maximum temperature reduces with increasing Ra number. It is also observed that at low Ra number, location of the maximum temperature is at the centre of the cavity and it shifts upwards with increase in Ra number. Circulation inside the enclosure and therefore the convection becomes stronger as the Ra number increases while the magnetic field suppresses the convective flow and the heat transfer rate. The ratio of the Lorentz force to the buoyancy force (Ha2/Ra) is as an index to compare the contribution of natural convection and magnetic field strength on heat transfer

Low-profile planar eleven antenna over a magnetic plane

The eleven antenna has been greatly used in many applications to achieve low reflection coefficient and stable-pattern over ultra-wide-bands. However, arraying in the eleven configuration forces the antenna designer to tilt the antenna over an electric conducting ground plane, and this makes it mechanically complicated and increases the profile of the antenna. Seeking new capabilities, the theory of putting log-periodic dipoles in the eleven configuration over magnetic ground is developed. The eleven antenna is formed by two printed folded-dipoles, and we evaluate the performance for a single-pair of dipoles and five-pairs of dipoles. The results are extracted for the cases of PEC ground, PMC ground and without ground. The results are in a good agreement with theory. Also, some discussions are provided for the realization of the artificial-magnetic-ground

Oil Immersed Distribution Transformer HST Reduction using Vegetable Oils and ONAN Cooling

Today, the use of electricity sources is increasing as cities are growing. With the increasing use of mineral oils for transformers cooling in the distribution network, due to the problems encountered using these oils, an alternative fluid should be used inside the transformers instead of mineral oils. Therefore, mineral oils should be replaced with fluids that are more compatible with nature due to the environmental hazards and high costs. Hence, vegetable oils can be used as suitable alternatives for the mineral oils in transformers due to their low risk and the renewability. On the other hand, compared to the mineral oils that have a fire point of about 151 Celsius degrees, vegetable oils have fire points higher than 311 Celsius degrees. As a result, from this viewpoint, they are considered as harmless fluids. Vegetable oils are simply degraded in the nature, and due to their different chemical structures compared to the mineral oils, they can increase the life of the equipment. Besides, the most important point is that they improve the transformer cooling performance, in terms of thermal analysis. Thus, in this paper, the distribution transformer electromagnetic-thermal analysis and conjugate heat transfer, in presence of different types of vegetable oils, and different types of cores such as grain-oriented silicon steel, amorphous and vitroperm alloy are investigated. Afterwards, the obtained results, especially hot spot temperature, are compared with distribution transformer containing mineral oil. ANSYS software has also been used for simulations

A Wideband and Low-Loss Spatial Power Combining Module for mm-Wave High-Power Amplifiers

We present a low-loss power combiner, providing a highly integrated interface from an array of mm-wave power amplifiers (PAs) to a single standard rectangular waveguide (WG). The PAs are connected to an array of parallel and strongly coupled microstrip lines that excite a substrate integrated waveguide (SIW) based cavity. The spatially distributed modes then couple from the cavity to the rectangular WG mode through an etched aperture and two stepped ridges embedded in the WG flange. A new co-design procedure for the PA-integrated power combining module is presented that targets optimal system-level performance: output power, efficiency, linearity. A commercial SiGe quad-channel configurable transmitter and a standard gain horn antenna were interfaced to both ends of this module to experimentally demonstrate the proposed power combining concept. Since the combiner input ports are non-isolated, we have investigated the effects of mutual coupling on the transmitter performance by using a realistic PA model. This study has shown acceptable relative phase and amplitude differences between the PAs, . within +/- 15 degrees and +/- 1 dB. The increase of generated output power with respect to a single PA at the 1-dB compression point remains virtually constant (5.5 dB) over a 42% bandwidth. The performed statistical active load variation indicates that the interaction between the PAs through the combiner has negligible effect on the overall linearity. Furthermore, the antenna pattern measured with this combiner shows negligible deformation due to non-identical PAs. This represents experimental prove-of-concept of the proposed spatial power combining module, which can be suitable for applications in MIMO array transmitters with potentially coupled array channels

Assessing the toxic effects of hydroalcoholic extract of Stachys lavandulifolia Vahl on rat's liver

Aims: Stachys lavandulifolia Vahl is a frequently used plant to treat different diseases, but its probable toxic effects have not been reported yet. This study aimed to study the toxicity of the extract on rats' liver. Methods: In this experimental study, 100 rats were designated into 10 groups and injected normal saline or Stachys lavandulifolia Vahl extract at 50, 100, 150, and 200 mg/kg, intraperitoneally for 28 days. Four case groups and one control group were examined for ALT, AST and ALP after one month and the other groups were evaluated after two months. Results: In the first month, the increase of ALP at all doses and the increase of AST at 200 mg/kg was significant, compared to the control group (p<0.05). In the second month, AST increased at the dosage of 150mg/kg, and ALP decreased at the dosage of 100 mg/kg, compared to the control group (p<0.05). Histopathological assessment showed a significant dose dependent increase both in necrotic-inflammatory reactions and fibrotic lesions, in the first and second months, compared to the control group (p<0.001). Conclusions: The Stachys lavandulifolia extract injected intraperitoneally has hepatotoxic effect, which is not eliminated by the drug withdrawal. Therefore, it is necessary to be consumed with caution (Tab. 4, Fig. 1, Ref 21). Text in PDF www.elis.sk