Smartphones for wireless communication typically consist of a large area frontal liquid crystal display (LCD), which incorporates a metal back plate, and a back cover chassis made from metal. Leveraging this structure a new approach to construct antennas for smartphones is proposed where the complete metal back cover chassis and LCD back plate are used as the radiating element and ground plane. In the design a feedline is connected between the metal back cover chassis and LCD back plate, along with shorts at various locations between the two metal plates, to control the resonance frequency of the resulting antenna. Multiple-band operation is possible without the need for any slots in the plates for radiation. Results show that antenna frequency reconfigurability can be achieved when switching function is added to the shorts so that several wireless communication bands can be covered. This approach is different from existing metallic frame antenna designs currently available in the market. A design example is provided which uses one PIN diode for the switching shorts and the target frequency bands are 740-780MHz and 900-1000MHz & 1700-1900MHz. The optimization of LC matchings and concerns of hand effects and metallic components between the chassis and LCD metal back plate are also addressed.

A frequency-reconfigurable dipole antenna, whose dual resonant frequencies are independently controlled, is introduced. The antenna's conductor consists of radiating conductors, lumped and distributed elements, and varactors. To design the antenna, current distribution, input impedance, and radiation power including higher-order modes, are analyzed for a narrow-angle sectorial antenna embedded with passive elements. To derive the formulae used, radiation power is analyzed in two ways: using Chu's equivalent circuit and the multipole expansion method. Numerical estimations of electrically small antennas show that dual-band antennas are feasible. The dual resonant frequencies are controlled with the embedded series and shunt inductors. A dual-band antenna is fabricated, and measured input impedances agree well with the calculated data. With the configuration, an electrically small 2.5-/5-GHz dual-band reconfig-urable antenna is designed and fabricated, where the reactance values for the series and shunt inductors are controlled with varactors, each connected in series to the inductors. Varying the voltages applied to the varactors varies the measured upper and lower resonant frequencies between 2.6 and 2.9GHz and between 5.1 and 5.3GHz, where the other resonant frequency is kept almost identical. Measured radiation patterns on the H-plane are almost omni-directional for both bands.

This paper presents a new technique to enhance the bandwidth of a printed dipole antenna for ultra-wideband applications. The basic idea is to exploit mutual coupling between the feeding line, which is designed closed and paralleled to dipole arms, the dipole arms and other elements of the antenna. Dipole arms, feeding lines as well as other parts are investigated in order to expand antenna bandwidth while still retaining antenna compactness. Based on the proposed technique, we develop two sample printed dipole antennas for advanced wireless communications. One is an ultra-wideband antenna which is suitable for multi-band-mode ultra-wideband applications or being a sensing antenna in cognitive radio. The other is a reconfigurable antenna which would be applicable for wideband cognitive radios. Antenna characteristics such as radiation patterns, current distributions, and gains at different frequencies are also investigated for both sample antennas.

A feed-point-selective, asymmetrically fed dipole antenna has been proposed for multiple-input multiple-output (MIMO) applications. By using PIN diode switches, an asymmetrical antenna feed is realized so as to control antenna directivities. The two basic requirements for MIMO antenna radiation patterns, namely, a decrease in overlap and control in direction, have been achieved. Additionally, to enhance directivities for the antenna with PIN diodes, a reflector has been introduced. The gain toward the reflector decreased by 2 dB, while the gain in the direction of the maximum gain increased by 2 dB. The developed antenna can correspond to a variable power angular spectrum (PAS).