This paper presents the detailed investigations on a simple multi-band method that allows inverted-F antennas (IFAs) to achieve good impedance matching in many different frequency bands. The impressive simplicity of the method arises from its sharing of a shorting strip among multiple branch elements to simultaneously generate independent resonant modes at arbitrary frequencies. Our simulation and measurement results clarify that, by adjusting the number of branch elements and their lengths, it is very easy to control both the total number of resonant modes and the position of each resonant frequency with impedance matching improved concurrently by adjusting properly the distance ds between the feeding and shorting points. The effectiveness of the multi-band method is verified in antenna miniaturization designs, not only in the case of handset antenna, but also in the design upon an infinite ground plane. Antenna performance and operation principles of proposed multi-band models in each case are analyzed and discussed in detail.

This study presents a proposal for space-saving design of built-in antennas for handset terminals based on the concept of requisite design antenna volume. By investigating the relation between antenna input characteristic and electric near-field around the antenna element and surrounding components inside the terminal, and then evaluating the requisite design antenna volume, we propose the most effective deployment for both the antenna and surrounding components. The results show that our simple proposal can help reduced, by about 17% and 31.75%, the space that the antenna element actually requires at least for stable operation inside the terminal, in the single-band designs for the cellular 2GHz band (1920-2170MHz) and 800MHz band (830-880MHz), respectively. In the dual-band design, we verify that it can reduce, the antenna space by about 35.18%, and completely cover the two above cellular bands with good antenna performance.

This paper presents a spatial fading emulator for evaluating handset MIMO antennas in a cluster environment. The proposed emulator is based on Clarke's model and has the ability to control RF signals directly in spatial domain to generate an accurate radio propagation channel model, which includes both uniform and non-uniform angular power spectra (APS) in the horizontal plane. Characteristics of a propagation channel such as fading correlations, eigenvalues and MIMO channel capacities of handset antennas located in the vicinity of the emulator's ring can be evaluated. The measured results show that the fading emulator with 31 antenna probes is sufficient to evaluate fading correlation and MIMO channel capacity of handset antenna in the case of a narrow APS with the standard deviation of more than 20 degrees.

This paper describes a spatial fading emulator based on Clarke's model that can evaluate spatial correlation characteristics between signals received by handset antennas including human-body effect under emulated multipath propagation environments. The proposed model is composed of scatterers, phase-shifters and attenuators. The scatterers are located at equal intervals on the circumference of a circle. Phase shifters and attenuators in a control circuit are used to control the phase and amplitude of each wave radiated from the scatterers in order to emulate multi-path propagation environments, such as Rayleigh or Nakagami-Rice distribution, to be generated at their center. In this paper, the maximum distance between receiving antennas that could be used to evaluate spatial correlation characteristics between antennas was investigated experimentally. The measurement results show that 15 scatterers with a radius of 1.5 m are sufficient to evaluate spatial correlation characteristics within the branch separation of 1.7 λ when parallel dipole antennas are used as receiving antennas.

A folded loop antenna for handsets has already been introduced and shown as one of balance-fed antennas for handsets, which is very effective to mitigate the antenna performance degradation due to the body effect. In order to meet the requirements for the latest handsets such as low profile and small size, a folded loop antenna is modified. The antenna, which is possibly built in the handsets, is newly proposed. Low profile and small size is achieved by consisting of the half of low profile folded loop antenna, which has a structure folded loop elements sideways so that the antenna can be placed on the ground plane (GP). In the analysis, the electromagnetic simulator based on the FDTD (Finite Difference Time Domain) method is used and the design parameters useful in practical operation are found. The electromagnetic simulator based on the Method of Moment (MoM) is used to calculate the current distribution on the antenna element and the GP. An example of low profile and small size antenna which has wideband characteristics are designed based on these parameters, and the antenna characteristics such as VSWR, the current distributions and the radiation patterns are compared with Planar Inverted-F Antenna (PIFA), which is one of conventional built-in antennas for handset. As a result, it has been confirmed that the physical volume of the antenna, which has been introduced here, becomes smaller than that of PIFA. In addition, the radiation efficiency of these antennas is measured and the results are compared with each other.