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

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

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

Temperature-dependent Characterization of Power Amplifiers Using an Efficient Electrothermal Analysis Technique

In this paper, we propose an efficient methodology for the electrothermal characterization of power amplifier (PA) integrated circuits. The proposed electrothermal analysis method predicts the effect of temperature variations on the key performances of PAs, such as gain and linearity, under realistic dynamic operating conditions. A comprehensive technique for identifying an equivalent compact thermal model, using data from 3-D finite element method thermal simulation and nonlinear curve fitting algorithms, is described. Two efficient methods for electrothermal analysis applying the developed compact thermal model are reported. The validity of the methods is evaluated using commercially available electrothermal computer-aided design (CAD) tools and through extensive pulsed RF signal measurements of a PA device under test. The measurement results confirm the validity of the proposed electrothermal analysis methods. The proposed methods show significantly faster simulation speed comparing to available CAD tools for electrothermal analysis. Moreover, the results reveal the importance of electrothermal characterization in the prediction of the temperature-aware PA dynamic operation

Half-height-pin GapWaveguide Technology and its Applications in High Gain Planar Array Antennas at MillimeterWave Frequency

This paper presents a new form of gap waveguide technology -- the half-height-pin gap waveguide. {The gap waveguide technology is a new transmission line technology introduced recently, which makes use of the stopband of wave propagation created by a pair of parallel plates, one PEC (perfect electric conductor) and one PMC (perfect magnetic conductor), with an air gap in between less than a quarter of the wavelength at operation frequency. Applying this PEC/PMC gap plate structure to ridged waveguides, rectangular hollow waveguides and microstrip lines, we can have the ridged gap waveguides, groove gap waveguides and inverted gap waveguide microstrip lines, respectively, without requiring a conductive or galvanic contact between the upper PEC and the lower PMC plates. This contactless property of the gap waveguide technology relaxes significantly the manufacturing requirements for devices and antennas at millimeter wave frequencies. PMC material does not exist in nature, and an artificial PMC boundary can be made by such as periodic pin array with the pin length about a quarter wavelength. However, the quarter-wavelength pins, referred to as the full-height pins, are often too long for manufacturing. In order to overcome this difficulty, a new half-height-pin gap waveguide is introduced.} The working principles and Q factors for the half-height-pin gap waveguides are described, analyzed and verified with measurements in this paper. {It is concluded that half-height-pin gap waveguides have similar Q factors and operation bandwidth to the\ua0 full-height-pin gap waveguides.} As an example of the applications, a high gain planar array antenna at V band by using the half-height-pin gap waveguide\ua0 {has been designed and} is presented in the paper\ua0 {with a good reflection coefficient and high aperture efficiency}

Half-Height-Pin Gap Waveguide Technology and Its Applications in High Gain Planar Array Antennas at Millimeter Wave Frequency

This paper presents a new form of gap waveguide technology -- the half-height-pin gap waveguide. {The gap waveguide technology is a new transmission line technology introduced recently, which makes use of the stopband of wave propagation created by a pair of parallel plates, one PEC (perfect electric conductor) and one PMC (perfect magnetic conductor), with an air gap in between less than a quarter of the wavelength at operation frequency. Applying this PEC/PMC gap plate structure to ridged waveguides, rectangular hollow waveguides and microstrip lines, we can have the ridged gap waveguides, groove gap waveguides and inverted gap waveguide microstrip lines, respectively, without requiring a conductive or galvanic contact between the upper PEC and the lower PMC plates. This contactless property of the gap waveguide technology relaxes significantly the manufacturing requirements for devices and antennas at millimeter wave frequencies. PMC material does not exist in nature, and an artificial PMC boundary can be made by such as periodic pin array with the pin length about a quarter wavelength. However, the quarter-wavelength pins, referred to as the full-height pins, are often too long for manufacturing. In order to overcome this difficulty, a new half-height-pin gap waveguide is introduced.} The working principles and Q factors for the half-height-pin gap waveguides are described, analyzed and verified with measurements in this paper. {It is concluded that half-height-pin gap waveguides have similar Q factors and operation bandwidth to the\ua0 full-height-pin gap waveguides.} As an example of the applications, a high gain planar array antenna at V band by using the half-height-pin gap waveguide\ua0 {has been designed and} is presented in the paper\ua0 {with a good reflection coefficient and high aperture efficiency}

A Methodology for Analysis of mm-Wave Transmitter Linearization Trade-offs Under Spectrum Constraints

This paper presents a simple method to estimate the efficiency and modulated RF performance for pre-distortion linearized PAs. The method is based on AM/AM and AM/PM and DC power data obtained from single tone measurements or simulations. This method allows us to investigate the tradeoffs between efficiency, output power, and predistortion complexity in PAs, under spectrum mask requirements. This is particularly important for in mm-wave applications. For demonstration, a 29 GHz GaAs PA has been modeled and used to study how biasing and pre-distortion complexity shape the output in terms of power and efficiency