Multiport Antenna Research Articles

SAR Reduction With Antenna Cluster Technique

An efficient and straightforward antenna design method is presented that maximizes the ratio of total efficiency and specific absorption rate (SAR). This goal is achieved with a multiport antenna cluster technique where several ports are excited collectively with appropriate feeding weights. These weights are found as an eigenvalue solution formulated in terms of the radiated and near-field power of an antenna. The method relies on both the near-field (SAR) and far-field (radiation) physics of an antenna and it can be applied to various design cases. The importance of the maximization of total-efficiency-SAR ratio and the feasibility of the proposed approach are demonstrated with a simple multiple-dipole antenna example and with a more realistic antenna design where a metal-rimmed antenna is held in the user’s hand.

Some Excitation Independent Bounds for the Total Active Reflection Coefficient of Antenna Arrays

The total active reflection coefficient (TARC) is a key parameter in the characterization of multiport antenna arrays used in multiple-input multiple-output (MIMO) platforms. The TARC dependency on scattering parameters and port excitations is expressed using matrix <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$p$ </tex-math></inline-formula> - and Frobenius norms. It is demonstrated how coupling and excitation effects can be separated from each other by mathematical manipulations of the TARC equation and represented in the form of inequalities. The derived inequalities are used to determine excitation-independent upper bounds or approximations for the TARC. It is shown that the proposed bounds can be used to define proper margins for efficient prediction of the TARC variations without a priori information about port excitations. In addition to the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$p$ </tex-math></inline-formula> - and Frobenius norm inequalities, the extrema of the TARC as a function of the port phases are analytically calculated using the Hessian matrix. Finally, the derived bounds are verified and compared numerically via simulating different antenna arrays in both random and uniform configurations with different port excitations corresponding to different beamsteering directions. It is shown that the TARC values are fluctuating very close to the tightest proposed bounds which are defined based on the Frobenius and 2-norm of the array <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> -matrix.

Multiport Pixel Antenna Optimization Using Characteristic Mode Analysis and Sequential Feeding Port Search

An optimization approach for multiport pixel antenna design using <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}$ </tex-math></inline-formula> -port characteristic mode analysis (CMA) and sequential feeding port selection is proposed. CMA is utilized to characterize the maximum number of independent or orthogonal resonant modes that can be formed in the limited space constrained by the size of the pixel antenna. Once the maximum number of orthogonal resonance modes is found sequential feeding port selection is proposed to find the optimum feed positions to independently excite each of the orthogonal resonance modes. The resulting design does not need additional complex feeding networks or impedance matching circuits, making the physical implementation of the design straightforward, compact and practical. Two examples are provided to verify the performance of the proposed approach, including a 3-port pixel antenna and a 4-port pixel antenna operating at 2.4 GHz. The performance of the optimized antennas is very good, and verifies the usefulness of the proposed approach.

2-D Printed 8-element compact UWB diversity antenna for multi-service-multi-mode applications

A 2-D compact 8-element UWB diversity antenna of dimension 28 mm × 28 mm each, is proposed to operate from (4.1–24) GHz with 141.63% IBW for multi-service-multi-mode (MS2M) applications. With self-similar antennas, the antenna design embodiment is constructed by asserting cross-coupled inter-connect bridge substrates to accomodate eight radiating elements in a compact footprint. This configuration results in good isolation between non overlapped antenna clusters, the ortho-centric antenna arrangement asserts pattern diversity and avoids the dependancy of additional decoupling network. The performance metrics consists of isolation coefficient of >20 dB at all ports, realized gain varies from (4.5–8.1) dBi and ECC from far-field magnitude < 0.08, which makes it suitable for UWB diversity applications. To validate the multi-port antenna performance, a full-wave simulation PTFE shield enclousure with volume of 40 mm × 40 mm × 40 mm has been demonstrated, which shows good results in correlation to EM-simulation. With good performance attributes in the shield enclousure, the multi-port antenna can be exported to a fully fledged plastic jacketed cage for real-time environment. Finally, a prototype antenna is fabricated and measured with good agreements to validate the overall RF performances.

Characteristic Mode-Inspired Advanced Multiple Antennas: Intuitive insight into element-, interelement-, and array levels of compact large arrays and metantennas

This article, as part of the special issue on characteristic modes (CMs), updates the recent progress in developing advanced multiple antenna systems based on CM analysis (CMA). The multiple antennas include antenna arrays of multiple radiating elements fed by one single signal port, arrays of multiple antennas fed by multiple signal ports simultaneously, and combinations thereof. The challenges, opportunities, and the way in which CMA assists in the design of antenna elements, multiple antennas, and antenna arrays are addressed, including physical insights and dedicated advanced CMA methods. Two types of advanced multiple antenna systems inspired by the CMs are discussed as examples. One is the multimode, multiport antenna (M³PA). The other is the CMA-enabled metasurface (MTS) antenna (metantenna). Both types can serve as unit cells of massive multiple-input, multiple-output (MIMO) antennas.

Antenna Element Design Using Characteristic Mode Analysis: Insights and research directions

This article provides a comprehensive review of recent applications of characteristic mode analysis (CMA) to innovative antenna element designs, including multiport, circularly polarized, wideband, reconfigurable, and dielectric resonator antennas (DRAs). Emphasis is placed on the interpretation of the characteristic modes (CMs) for those unfamiliar with the method and physical insights gained from the characteristic eigenvalues and eigenvectors of an antenna. In addition, we review CMA-based design strategies and specific design examples that highlight the application of CMA to various types of antennas. Ultimately, this article seeks to demonstrate the value of CMA-based design insights for antenna engineering and look toward promising new research directions for CMA and antenna research.

Synthesis, Control, and Excitation of Characteristic Modes for Platform-Integrated Antenna Designs: A design philosophy

Electrically compact antennas that exploit the characteristic modes (CMs) of their platforms have recently attracted much attention in military and terminal device antenna research. Conventionally, to design an antenna on a platform, the antenna element is first synthesized in a stand-alone manner, without explicitly considering the platform structure. Electromagnetic compatibility issues may arise since the size of the antenna is usually comparable to the wavelength of operation. In contrast, CM-based platform-integrated antenna design takes advantage of the natural resonant modes of the platforms to achieve the desired properties, such as multiband/wideband operation, polarization or pattern reconfigurability, high isolation between ports (in the case of multiport antennas), and achievement of the specified gain.

Optimizing the Mutual Information of Frequency-Selective Multi-Port Antenna Arrays in the Presence of Mutual Coupling

As larger bandwidths are used in multiple antenna wireless systems, the frequency selectivity of the antenna arrays starts to impact rate. Motivated by optimizing the achievable rate in compact antenna arrays, we present a system model that incorporates the effects of mutual coupling (MC) of wideband physically realizable single-input multiple-output (SIMO) and multiple-input single-output (MISO) antenna systems. For the SIMO system setup, we extract the noise correlation matrices for two different antenna array configurations (parallel and co-linear). We optimize the inter-element spacing in each alignment while maximizing the achievable rate and fixing the transmit power. Then, we compare the two compact antenna designs to a perfectly matched single omni-directional antenna while accounting for MC. Likewise, for the MISO antenna system, we derive the optimal beamformer that maximizes the achievable rate using the same antenna configurations as the SIMO system. Then, we study the impact of MC and develop a new single-port matching technique for wideband antenna arrays. Finally, we provide reciprocity plots to compare the performance of the SIMO-MISO systems using different channel models.

Extremely Low-Profile Tunable Multiport Handset Antenna

This article presents an extremely low-profile tunable antenna design for smartphones with height of only 0.75 mm. The proposed antenna is integrated into the back cover of the device to utilize the existing gap between the battery and the back cover as efficiently as possible. By utilizing both tunable components and adjustable feeding weights, the designed multiport antenna system covers 3300–4200 MHz frequency range with 100 MHz instantaneous bands. In addition to just frequency tuning, these tunable elements can be utilized to adapt the antenna for different operation environments, such as changes in the structure of the device or the user effect. We show that the proposed antenna can be extended for two- and four-element multiple-input multiple-output (MIMO) operation. The proposed design is manufactured and measured, and the results confirm good antenna performance with average total efficiencies of 35% and 25% in free space and with a hand phantom, respectively.

The Radiation and Transducer Efficiencies of a Multiport Antenna Array

The Radiation and Transducer Efficiencies of a Multiport Antenna Array

Bayesian In-Situ Calibration of Multiport Antennas for DoA Estimation: Theory and Measurements

The DoA of radio waves is used for many applications, e.g. the localization of autonomous robots and smart vehicles. Estimating the DoA is possible with a multiport antenna, e.g. an antenna array or a multi-mode antenna (MMA). In practice, DoA estimation performance decisively depends on accurate knowledge of the antenna response, which makes antenna calibration vital. As the antenna surroundings influence its response, it is necessary to measure the entire device with installed antenna to obtain the installed antenna response. Antenna calibration is often done in a dedicated measurement chamber, which can be inconvenient and costly, especially for larger devices. Thus, auto- and in-situ calibration methods aim at making antenna calibration in a measurement chamber redundant. However, existing auto- and in-situ calibration methods are restricted to certain antenna types and certain calibrations. In this paper, we propose a Bayesian in-situ calibration algorithm based on a maximum a posteriori (MAP) estimator, which is suitable for arbitrary multiport antennas. The algorithm uses received signals from a transmitter, noisy external DoA observations, takes multipath propagation into account and does not require synchronization. Furthermore, we take an estimation theoretic perspective and provide an in-depth theoretical discussion of in-situ antenna calibration in unknown propagation conditions based on Bayesian information and the Bayesian Cramér-Rao bound (BCRB). Extensive simulations show that the proposed algorithm operates close to the BCRB and the achieved DoA estimation performance asymptotically approaches the case of a perfectly known antenna response. Finally, we provide an experimental validation, where we calibrate the antenna on a robotic rover and evaluate the DoA estimation performance using measurement data. With the proposed in-situ antenna calibration algorithm, DoA estimation performance is considerably improved compared to using an antenna response obtained by simulation or in a measurement chamber.

A Method to Co-Design Antenna Element and Array Patterns

In this paper, we develop a novel method to design the elements of an antenna array and their feed weights simultaneously. The method is based on formulating the design problem as a non-linear multi-objective optimization model that estimates the realized gain at certain angles as a function of the element-level port signals and impedances, and the array-level weights for the elements. This enables utilization of genetic algorithms to find optimal signals, impedances, and weights for given steering range requirements. As an example, an array consisting of multi-port antenna elements is simulated and modeled with its impedance and radiation matrices. These matrices are used in the calculation of realized gain with the model. The model is then applied as part of the method to find as wide scanning range for the array as possible. The antenna elements are designed such that the multi-port system can be reduced to a single feed with physically realizable matching components and a matching network. The array designed with the proposed method is also compared to a reference antenna array of the same size. Both the simulations and measurements verify that the method can provide substantial improvements in the scanning range as compared to the reference.

Pattern diversity and defected ground structure for decoupling planar Yagi MIMO antenna

In this paper, a novel decoupling technique both in pattern diversity (PD) and defected ground structure (DGS) is proposed for planar Yagi multiple-input multiple-output (MIMO) antenna arrays. The proposed planar Yagi antenna (PYA) is composed of two symmetrical printed dipoles and U-/V-shape directors. Based on the redirection effect of the directors, the desired pattern diversity and isolation improvement are achieved. DGS is added outside the excitation dipoles for closely packed elements, which achieves decoupling and better impedance matching. Through the whole frequency bandwidth (5.5–6.1 GHz), the mutual coupling between two-ports Yagi antenna elements is lower than −25 dB, and the stable gain is above 8 dBi with the variation of 1 dBi. Moreover, the validation of the proposed decoupling method is carried out on three and four-ports MIMO antenna arrays. By combining two kinds of directors and asymmetric DGS, the imbalance problem of the multi-port antennas is solved. The simulated and measured results validate the effectiveness of PD-DGS in MIMO directional antenna systems with high isolation and gain for 5.8 GHz WLAN application.

Dual-Beam Rectenna Based on a Short Series-Coupled Patch Array

The multibeam multiport antenna is a promising solution for effectively harvesting wireless low-density power in a wide angle range. The traveling-wave series-fed patch array antenna without the requirement of additional beamforming circuits is a good option. However, its application is limited by its large length or low radiation efficiency. In this work, a periodic circuit model consisting of coupled resonators is proposed and analyzed for enhancing the radiation attenuation. A series-coupled patch array based on the model is then designed. It presents a much shorter configuration and could be well applied in a scenario where a tradeoff between size and gain exists. The dc combining method that accumulates currents of rectifying branches corresponding to multiple beams is adopted in the rectifier design. The rectenna exhibits an enhanced spatial or angular coverage with a simple configuration. In the measurement, the output dc power can be more than 0.5- 32 μW in an angle range of 90° in the H-plane and reach a maximum value of 1.1- 50.3 μW and a maximum efficiency of 19.5%-44.6% when the power density ranges from 0.05 to 1 μW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 2.45 GHz.

Digital pattern synthesis with a compact MIMO antenna of half-wavelength diameter

The paper presents a compact multiport antenna, with beamforming capabilities and a realized gain of 4.31 dBi with the size of λ/2. The antenna allows digital beamforming with independent control over three parameters: main-beam direction, beamwidth, and null-depth. Those parameters can be dynamically adjusted within a continuous range, create multiple beams for different frequency channels, and simultaneously generate multiple digital patterns. Due to digital beamforming capabilities, the proposed antenna offers much greater flexibility over switch-based analogue beamforming of Electronically Steerable Parasitic Array Radiator (ESPAR) antennas. The reconfiguration properties are achieved by using superposition of three dipole-like radiation patterns, where each radiator generates different spherical mode, i.e. with different angular phase distribution in the horizontal plane. This allows beamsteering with compact size, while the use of different modes ensures low Envelope Correlation Coefficient (ECC) from 10−4 to 3.2 × 10−5 for the operating frequency of 2.4 GHz. The proposed technique allows for significantly greater pattern reconfiguration than any reconfigurable antenna or array of comparable size and is a perfect candidate for Software Defined Radios.

Integration of coupling resonator as port-isolator and MMLC-Minkowiski fractal loop for Wi-Max rejection in 4-port compact UWB MIMO antenna

This paper presents a 4-port compact UWB MIMO antenna. It has 45 tilted offset feed for better impedance matching and connected to cornered cut-out quad-radiators. Radially symmetric resonators are provided for impedance matching and isolation improvements. A miniaturized magnetic LC (MMLC) Minkowiski fractal loop acts as a magnetic shield between electric walls of feed and resonator for Wi-max band rejection. The contra-rotational symmetry of resonator and rotationally asymmetric strips in ground enhances isolation. To validate, a prototype antenna is fabricated and measured which shows good agreements. The proposed antenna has a compact dimension 31 mm × 31 mm, operates from 2.27 to 11.7 GHz and reject bands at 3.0–4.2 GHz. The average gain is > 4 dBi with ECC < 0.16 in the operating band. An equivalent circuit topology is also modelled which validates the design. The multi-port antenna system can be used for microwave imaging, RF-sensing and radar applications.

Metamaterial Based Design of Compact UWB/MIMO Monopoles Antenna with Characteristic Mode Analysis

In this article, a novel metamaterial inspired UWB/multiple-input-multiple-output (MIMO) antenna is presented. The proposed antenna consists of a circular metallic part which formed the patch and a partial ground plane. Metamaterial structure is loaded at the top side of the patches for bandwidth improvement and mutual coupling reduction. The proposed antenna provides UWB mode of operation from 2.6–12 GHz. The characteristic mode theory is applied to examine each physical mode of the antenna aperture and access its many physical parameters without exciting the antenna. Mode 2 was the dominant mode among the three modes used. Considering the almost inevitable presence of mutual coupling effects within compact multiport antennas, we developed an additional decoupling technique in the form of perturbed stubs, which leads to a mutual coupling reduction of less than 20 dB. Finally, different performance parameters of the system, such as envelope correlation coefficient (ECC), channel capacity loss (CCL), diversity gain, total active reflection coefficient (TARC), mean effective gain (MEG), surface current, and radiation pattern, are presented. A prototype antenna is fabricated and measured for validation.

Spatial diversity improvement in frequency-diverse computational imaging with a multi-port antenna

In this paper, we study an additional spatial diversity mechanism added to a cavity-backed frequency-diverse aperture for computational imaging applications at X-band frequencies. It is shown that the dynamic variation of cavity modes achieved by means of a simple, multi-port excitation mechanism can significantly simplify the diversity constraints on the frequency-diversity technique for computational imaging and can substantially improve the fidelity of the reconstructed microwave images. Leveraging the proposed technique, we present that, for the selected number of measurement modes, the condition number of the studied computational imaging problem is improved by 8.5 times in comparison to using the frequency-diversity as the only diversity mechanism. The reconstructed X-band images of various targets, including the letters “Q”, “U” and “B” reflect on this improvement and exhibit a higher reconstruction quality, significantly assisting in the identification of the imaged objects. We also present that the resolution limits of the frequency-diverse computational imaging system synthesized using the proposed multi-port cavity are in excellent agreement with the theoretical resolution limits.

Анализ эффективности многопортовой печатной антенны

The article considers the patch antenna with several ports to excite a circular polarization. The effect of excitation ports number on the total efficiency of antenna was investigated. Taking into account the mutual coupling of the antenna ports, the total active reflection coefficient was estimated. A comparison of the calculated characteristics and the data obtained by CAD-modeling was carried out. It was shown that the total efficiency of the multiport patch antenna is independent from the number of excitation ports

Directive 2-D Beam Steering by Means of a Multiport Radially Periodic Leaky-Wave Antenna

A multifed radially periodic two-dimensional leaky-wave antenna is proposed for the generation of a directional beam continuously scanning in elevation by changing the frequency, and over a discrete number of directions in azimuth when activating different elements of the feeding system. The structure is planar and constituted by a circular grounded dielectric slab loaded with microstrip rings, properly positioned around the sources to support the propagation of an angularly directional surface wave over a sector determined by the corresponding activated feeder. This produces a perturbation of the surface wave, resulting in the generation of a directional leaky wave over the aperture, whose complex propagation constant is described by a single fast backward spatial harmonic. The antenna radiation features are numerically investigated in conjunction with the dispersion analysis of the structure, validated through a conventional generalized-pencil-of-function approach. Full-wave simulations have been developed to design a practical feeder, which is constituted by a circular arrangement of commercial coaxial connectors. The proposed multiport antenna is validated by means of measurements performed on a microwave manufactured prototype. The design represents an attractive simple and cost-effective solution to achieve a high-gain beam scanning over the three-dimensional space, alternative to more conventional phased-array design based on cumbersome and lossy feeding networks.