Corbett Rowell

Toward green and soft: a 5G perspective

As the deployment and commercial operation of 4G systems are speeding up, technologists worldwide have begun searching for next generation wireless solutions to meet the anticipated demands in the 2020 era given the explosive growth of mobile Internet. This article presents our perspective of the 5G technologies with two major themes: green and soft. By rethinking the Shannon theorem and traditional cell-centric design, network capacity can be significantly increased while network power consumption is decreased. The feasibility of the combination of green and soft is investigated through five interconnected areas of research: energy efficiency and spectral efficiency co-design, no more cells, rethinking signaling/control, invisible base stations, and full duplex radio.

Reduction of Mutual Coupling Between Closely-Packed Antenna Elements

A simple ground plane structure that can reduce mutual coupling between closely-packed antenna elements is proposed and studied. The structure consists of a slitted pattern, without vias, etched onto a single ground plane and it is therefore low cost and straightforward to fabricate. It is found that isolations of more than -20 dB can be achieved between two parallel individual planar inverted-F antennas (PIFAs) sharing a common ground plane, with inter-antenna spacing (center to center) of 0.116 lambdao and ground plane size 0.331lambdao 2. At 2.31 GHz it is demonstrated that this translates into an edge to edge separation between antennas of just 10 mm. Similarly the structure can be applied to reduce mutual coupling between three or four radiating elements. In addition the mutual coupling between half wavelength patches and monopoles can also be reduced with the aid of the proposed ground plane structure. Results of parametric studies are also given in this paper. Both simulation and measurement results are used to confirm the suppression of mutual coupling between closely-packed antenna elements with our slitted ground plane.

A capacitively loaded PIFA for compact mobile telephone handsets

A capacitively loaded planar inverted-F antenna (PIFA) is proposed and studied. It is found that the capacitive load reduces the resonance length of the PIFA from /spl lambda//4 to less than /spl lambda//S. A design with a bandwidth of 178 MHz centered at 1.8 GHz is provided to demonstrate that compact antennas for mobile telephone handsets can be constructed using this approach. The finite-difference time-domain (FDTD) method is used in the study and experimental verification is also provided.

A compact PIFA suitable for dual-frequency 900/1800-MHz operation

Planar inverted F antennas (PIFA) have been proposed as possible candidates for mobile telephone handsets. We describe the design of a compact PIFA suitable for operation at 900 MHz. In addition, we provide modifications to this design that allow it to operate in dual-frequency bands at 300 and 1800 MHz. Finite-difference time-domain (FDTD) and experimental results are provided.

Isolation Enhancement Between Two Closely Packed Antennas

This paper introduces a coupling element to enhance the isolation between two closely packed antennas operating at the same frequency band. The proposed structure consists of two antenna elements and a coupling element which is located in between the two antenna elements. The idea is to use field cancellation to enhance isolation by putting a coupling element which artificially creates an additional coupling path between the antenna elements. To validate the idea, a design for a USB dongle MIMO antenna for the 2.4 GHz WLAN band is presented. In this design, the antenna elements are etched on a compact low-cost FR4 PCB board with dimensions of 20times40times1.6 mm3. According to our measurement results, we can achieve more than 30 dB isolation between the antenna elements even though the two parallel individual planar inverted F antenna (PIFA) in the design share a solid ground plane with inter-antenna spacing (Center to Center) of less than 0.095 lambdao or edge to edge separations of just 3.6 mm (0.0294 lambdao). Both simulation and measurement results are used to confirm the antenna isolation and performance. The method can also be applied to different types of antennas such as non-planar antennas. Parametric studies and current distribution for the design are also included to show how to tune the structure and control the isolation.

Large-scale antenna systems with hybrid analog and digital beamforming for millimeter wave 5G

With the severe spectrum shortage in conventional cellular bands, large-scale antenna systems in the mmWave bands can potentially help to meet the anticipated demands of mobile traffic in the 5G era. There are many challenging issues, however, regarding the implementation of digital beamforming in large-scale antenna systems: complexity, energy consumption, and cost. In a practical large-scale antenna deployment, hybrid analog and digital beamforming structures can be important alternative choices. In this article, optimal designs of hybrid beamforming structures are investigated, with the focus on an N (the number of transceivers) by M (the number of active antennas per transceiver) hybrid beamforming structure. Optimal analog and digital beamforming designs in a multi-user beamforming scenario are discussed. Also, the energy efficiency and spectrum efficiency of the N × M beamforming structure are analyzed, including their relationship at the green point (i.e., the point with the highest energy efficiency) on the energy efficiency-spectrum efficiency curve, the impact of N on the energy efficiency performance at a given spectrum efficiency value, and the impact of N on the green point energy efficiency. These results can be conveniently utilized to guide practical LSAS design for optimal energy/ spectrum efficiency trade-off. Finally, a reference signal design for the hybrid beamform structure is presented, which achieves better channel estimation performance than the method solely based on analog beamforming. It is expected that large-scale antenna systems with hybrid beamforming structures in the mmWave band can play an important role in 5G.

Reconfigurable Multiband Antenna Designs for Wireless Communication Devices

New designs for compact reconfigurable antennas are introduced for mobile communication devices. The uniqueness of the antenna designs are that they allow various groups of their operating frequency bands to be selected electronically. In particular, each group of frequency bands, or mode, can be made to serve several different communication systems simultaneously. These systems may include various combinations of GSM, DCS, PCS, UMTS, Bluetooth, and wireless local-area network (LAN). Therefore, by electronically selecting different antenna modes, a variety of communication systems can be conveniently served by only one antenna. One advantage is that through the different operational modes, the total antenna volume can be reused, and therefore the overall antenna can be made compact. In these designs, the selection of the different modes is achieved by either i) switching different feeding locations of the antenna (switched feed) or ii) switching or breaking of the antennas connection to the ground (switched ground). This paper demonstrates these two designs. For the first design of switched feed, it can support GSM, DCS, PCS, and UMTS. In the second design, the antenna makes use of a switched-ground technique, which can cover GSM, DCS, PCS, UMTS, Bluetooth, and 2.4 GHz wireless LAN. The designs are investigated when ideal switches and also various realistic active switches based on PIN diodes, GaAs field effect transistor, and MEMs configurations. The designs are verified through both numerical simulations and measurement of an experimental prototype. The results confirm good performance of the two multiband reconfigurable antenna designs.

Mobile-Phone Antenna Design

This paper is a survey of internal antennas in mobile phones from 1997 to 2010. It covers almost 60 GSM and 3G handsets, ranging from the first GSM handset with an internal antenna to the current Nokia, Sony-Ericsson, Motorola, and Apple handsets. The paper discusses different types of mobile-phone antennas, feeding structures, active antennas, isolation, and antenna loading techniques. This paper examines different design techniques for mobile-phone antennas, and the limitations of antenna design due to manufacturing technologies and the effect of handset materials. Antenna performance parameters, including S parameters, radiation efficiency, SAR, and TRP/TIS are reported for the surveyed handsets. The effective antenna volume for every antenna is calculated, in order to determine the average volume/space required for each antenna type and the corresponding performance. Some of the handsets are further simulated using commercial electromagnetic simulators to illustrate the electromagnetic-field distributions. This paper summarizes the antenna design parameters as a function of handset performance, and presents a short summary of design procedure.

Low Cost Reconfigurable Landstorfer Planar Antenna Array

In this paper, we introduce a practical design for a Landstorfer planar antenna that can be implemented as a compact and low cost reconfigurable planar antenna array. The array, we propose, can have 360-degree coverage in azimuth and allows a wide variety of directive beams to be electronically selected while maintaining a simple structure, ease of manufacture and low cost with high efficiency. One of the possible applications for this array is in WLAN systems where high gain and low cost adaptable antennas promise increases in capacity and coverage. The array design utilizes key innovations in the design of Landstorfer antennas and feed/switching network. The Landstorfer antenna exhibits a high gain with 9.5 dBi and low mutual coupling between elements. A proposed reflector for the Landstorfer antenna is implemented and it allows the antenna array to be fabricated on a 2-layer PCB board. We also present a low cost feed/switching network which allows flexible control of the antenna patterns. The design makes use of PIN diodes as switching elements and a resonant inductor to improve the isolation of the PIN diodes. By integrating the antenna elements, feed/switching network and array configuration, a low cost reconfigurable Landstorfer planar array can be formed.

Large scale antenna system with hybrid digital and analog beamforming structure

Large scale antenna systems (LSAS) are expected to significantly enhance the energy efficiency (EE) and spectrum efficiency (SE) of wireless communication systems. However, there are many open issues regarding the implementation of digital beamforming (BF) structures: calibration, complexity, and cost. In a practical LSAS deployment, hybrid digital and analog BF structures with active antennas can be an alternative choice. In this paper, an N (the number of transceivers) by M (the number of active antennas per transceiver) hybrid BF structure is investigated, where the analog BF is performed per transceiver and digital BF is performed across N transceivers. Analysis of the N by M BF structure includes: the optimal analog and digital BF design, EE-SE relationship at the green point (i.e. the point with highest EE) in EE-SE curve, impact of N on EE performance at a given SE value, and impact of N on the green point EE. Numerical simulations are provided to support the analysis.