Aurora Andújar

Ground Plane Boosters as a Compact Antenna Technology for Wireless Handheld Devices

The increasing demand for multifunctional wireless devices has fostered the need to reduce the space devoted to the antenna in order to favor the integration of multiple and new functionalities. This fact becomes a challenge for the handset antenna designers who have to develop antennas capable of providing multi-band operation constrained by physical limitations. This proposal consists in a radiating system capable of providing multi-band operation without the need of an antenna element, by properly exciting the efficient radiation modes associated to the ground plane structure. In this sense, the typical volume devoted to a handset antenna is reduced by a factor of 20. The electrical model approximation of the radiating structure leads to the radiofrequency system design able to provide multi-band operation. The feasibility of the proposal has been tested by electromagnetic simulations as well as by experimental measurements regarding the main antenna parameters: reflection coefficient, efficiency, and radiation patterns. Furthermore, the human head interaction concerning biological compatibility in terms of SAR (Specific absorption rate) has been measured and a solution for its reduction is presented. As a result, a promising standard solution for a radiating system capable to operate in the main communication standards GSM850, GSM900, DCS, PCS and UMTS is provided with a volume reduction factor around 20.

Multiband and Small Coplanar Antenna System for Wireless Handheld Devices

Multiband and small antennas are strongly demanded in current wireless handheld or portable devices that require multiband operation. Nowadays, trends are focused on exciting ground plane radiation modes in order to reduce as much as possible the volume devoted to the antenna element. This paper studies different geometries for determining which one better excites a ground plane radiation mode at different frequency regions. The results demonstrate that a non-resonant pad element attains the best tradeoff between performance and geometry complexity. A multiband antenna system featuring small coplanar pad elements is proposed for providing operation at the communication standards LTE700 (698-787 MHz), GSM850 (824-894 MHz), GSM900 (880-960 MHz), GSM1800 (1710-1880 MHz), GSM1900 (1850-1990 MHz), UMTS (1920-2170 MHz), LTE2100 (1920-2170 MHz), LTE2300 (2300-2400 MHz), LTE2500 (2500-2690 MHz) as well as at the satellite positioning systems GPS (1575 MHz), Galileo L1 (1559-1591 MHz), Glonass (1592-1609 MHz). A radiofrequency system comprising broadband matching networks is included to provide the required impedance bandwidth. Numerical results give physical insight into the behavior of the proposed planar element. A prototype is built to demonstrate the feasibility of the proposal. The proposed radiating system is appealing for the new wireless handheld devices due to its small size (153 ), planar profile, and multiband performance.

Advances in Antenna Technology for Wireless Handheld Devices

The constant evolution of wireless handheld devices together with the apparition of multiple wireless communication systems fosters the antenna community to design new radiating and measurements systems capable of satisfying the market demands. It is an object of the present paper to provide an overview of the evolution that wireless handheld technology has experienced in the last years. In this sense, a description of the evolution of wireless handheld devices, regulations, challenges in today’s smartphones, and handset characterization is reviewed. Finally, recent advances in antenna technology for wireless handheld or portable devices are presented.

Analysis of the Human Head Interaction in Handset Antennas with Slotted Ground Planes

The interaction between the human head and handset antennas needs to be taken into account, since mobile phones have to be functional, and, at the same time, guarantee biological compatibility. The present research analyzed the performance of several handset antennas with different slotted ground planes in free space and also in the presence of the human head. The main objective was to compare the measured bandwidth and efficiency in both environments (free space and human interaction), and the impact on the measured SAR (Specific Absorption Rate) of such antennas as functions of the slot configuration in the ground plane and the antennas location. Results showed that slots may be useful for increasing bandwidth and efficiency while keeping similar SAR values compared to the non-slotted ground plane. Changing the antennas location was a good way to achieve a significant SAR reduction. In some cases, when the antenna was at the lower edge of the ground plane (down position), the SAR could be reduced by a factor of two. Impedance, efficiency, and radiation patterns were measured and analyzed with a phantom head in order to understand the human heads effect on the antennas performance. Although all antennas suffered from changes, shorted-end slots were more robust for human interaction than open-ended slots.

HUMAN HEAD INTERACTION OVER GROUND PLANE BOOSTER ANTENNA TECHNOLOGY: FUNCTIONAL AND BIOLOGICAL ANALYSIS

Handset antennas strongly interact with the human body. When a user holds a handset during a phone call, the proximity of the human head considerably afiects the antenna performance and eventually the quality of the wireless connection. Consequently, the assessment of the antenna parameters regarding free-space conditions is not enough to fully characterize the performance of handset antennas and a further analysis taking into account human head interaction is required. In this sense, this paper presents a study that deals with the human head interaction concerning two aspects: functional and biological. The flrst one analyzes the efiect of the human head over the main antenna parameters (re∞ection coe-cient, e-ciency, and radiation pattern) whereas the second one evaluates the impact of the antenna over the human head in terms of Speciflc Absorption Rate (SAR). Four representative prototypes of radiating structures are measured in both conditions in order to compare their performance: a dual-band Planar Inverted F Antenna (PIFA), a hexa-band PIFA with a slotted ground plane, a set of coupled monopoles, and a new architecture referred as compact radiating system based on the excitation of the ground plane through a set of non-resonant ground plane boosters. A flgure of merit that relates the antenna e-ciency with the SAR values is proposed for comparison purposes. The results demonstrate that losses caused by the human head power absorption

Ground Plane Contribution in Wireless Handheld Devices Using Radar Cross Section Analysis

The ground plane of wireless handheld devices plays a significant role in the electromagnetic behavior determining bandwidth, efficiency, and radiation patterns. Therefore, it is necessary to determine the frequency region where the ground plane can be better excited, especially for low frequencies where the performance of the radiating system is critical due to size limitations with respect to the operating wavelength. A fast method based on the radar cross section (RCS) is presented for computing the frequency at which the ground plane is better excited. The proposal is applied to three typical wireless platforms: a handset phone, a smartphone, and a clamshell phone. The method is compared with characteristic mode analysis and the results demonstrate a very good agreement in the resonant frequency prediction. In addition, complex platforms using metallic strips and slots in the ground plane are analyzed using RCS which gives physical insight into the electromagnetic performance.

Nonuniform Overlapping Method in Designing Microstrip Patch Antennas Using Genetic Algorithm Optimization

Genetic algorithm (GA) has been a popular optimization technique used for performance improvement of microstrip patch antennas (MPAs). When using GA, the patch geometry is optimized by dividing the patch area into small rectangular cells. This has an inherent problem of adjacent cells being connected to each other with infinitesimal connections, which may not be achievable in practice due to fabrication tolerances in chemical etching. As a solution, this paper presents a novel method of dividing the patch area into cells with nonuniform overlaps. The optimized design, which is obtained by using fixed overlap sizes, shows a quad-band performance covering GSM1800, GSM1900, LTE2300, and Bluetooth bands. In contrast, use of nonuniform overlap sizes leads to obtaining a pentaband design covering GSM1800, GSM1900, UMTS, LTE2300, and Bluetooth bandswith fractional bands with of 38% due to the extra design flexibility.

Distributed Antenna Systems for Wireless Handheld Devices Robust to Hand Loading

The performance of handset antennas is strongly affected by the user interaction. In particular, the close proximity of the users hand when holding the phone usually degrades the behavior of the antenna by introducing detuning effects and efficiency decrements. With the aim of mitigating such negative effects, the present paper proposes a distributed antenna system comprising three monopoles strategically arranged along the ground plane of a wireless handheld device. This configuration not only improves the performance of the radiating system with respect to that attained with a single monopole antenna or a distributed antenna system of two monopoles, but also increases its robustness to the hand loading effect. In order to assess the benefits of the proposed technique, simulated and measured results in free-space as well as regarding the presence of a hand phantom are compared with previous techniques based on a single monopole and a distributed antenna system of two monopoles. The experimental results demonstrate that the proposed distributed antenna system of three monopoles improves the bandwidth (34% for SWR ≤ 3 (693-978 MHz)), the efficiency in free-space, and becomes more robust to the hand loading effects than a single monopole solution and a distributed system of two monopoles.

On the Radiation Pattern of the L-Shaped Wire Antenna

An objective of the present study is to make a physical insight into the radiation properties of an L-shaped wire antenna. More specifically, the study is focused on the effects of the antenna geometry over the characteristic radiation pattern of an L-shaped wire antenna. Regarding the basic equations for the radiated field, three main regions according to the length-height ratio of an L-shaped wire antenna have been determined. The said regions depict the geometrical boundaries where the L-shaped wire antenna loses its characteristic monopoletype radiation pattern. In this sense and relating to the aspect ratio of the L-shaped antenna, the said radiation properties can be easily varied in order to achieve a half isotropic radiation pattern or even, a patch-type radiation pattern. Thus, the method described herein demonstrates that simple modifications applied to the geometry of a basic structure, allow obtaining radiation properties associated to more complex structures.

High-directivity genetic microstrip patch antenna

A high-directivity microstrip patch antenna (MPA) is attractive, since a narrow broadside beam can be obtained without using an array of antennas. Therefore, the solution becomes simpler as there is no complex feeding network as in an array. In this sense, this letter presents a single-element high-directivity MPA, which can substitute a 2 × 2 array operating in the fundamental mode. The novel MPA is designed by using genetic algorithms to fit the patch inside an area of 1λ × 1λ, resulting in a directivity of 13.2 dBi in the broadside direction. The MPA is fabricated and the simulation results are in good agreement with the measurements. The element is attractive for antennas with moderate directivity as those used in hot-spots.