Hisashi Morishita

Design concept of antennas for small mobile terminals and the future perspective

With the progress and rapid increase in mobile terminals, the design of antennas for small mobile terminals is acquiring great importance. In view of this situation, the design concept of antenna systems for small mobile terminals and its future perspective are discussed, referring to the trends in modern mobile communications and the demands for the antenna system. The design concept of antenna systems has changed along with the progress of mobile systems. In the conventional design, the conducting material of the equipment case, existing near the antenna element, is included as a part of the radiator in the antenna system, without regard to whether or not it has been considered. In the latest mobile phones, the design concept has been advanced to aim at improving the antennas performance, and the treatment of the case, etc., has become a part of this. Some particular considerations for the design are to relieve the degradation of the antennas performance due to the human-body effect, to overcome the SAR problems, and yet to make the size small. Furthermore, it is now time to proceed to the more-advanced concept, in which implementation of adaptive control and software is considered, even in small mobile terminals. Typical trends in modern communications systems are discussed, and the demands of these trends-which are summarized as down-sizing, function, and intelligence-are taken up for future antenna structures. Small-antenna technology and the application of the integration technology to antenna systems are essential for realizing such future structures.

Analysis of a cavity-backed annular slot antenna with one point shorted

Analysis of a cavity-backed annular slot antenna with one point shorted is performed experimentally and theoretically. Resonance frequencies, bandwidths, and radiation patterns are studied with respect to slot width, cavity depth, and slot shorting position. In the theoretical analysis, the method of moments is applied to find the magnet current on the slot, and the Greens function for the field inside the cavity has been newly derived. By selecting a slot shorting position, circular polarization, and a bandwidth of more than 10%, the voltage standing-wave ratio (VSWR) >

Wideband Planar Folded Dipole Antenna With Self-balanced Impedance Property

A planar folded dipole antenna that exhibits wideband characteristics is proposed. The antenna has simple planar construction without a ground plane and is easy to be assembled. Parameter values are adjusted in order to obtain wideband properties and compactness by using an electromagnetic simulator based on the method of moments. An experimental result centered at 1.7 GHz for 50 impedance matching shows that the antenna has bandwidth over 55% . The gains of the antenna are almost constant (2 dBi) in this frequency band and the radiation patterns are very similar to those of a normal dipole antenna. It is also shown that the antenna has a self-balanced impedance property in this frequency band.

Characteristics of a balance-fed loop antenna system for handsets in the vicinity of human head or hand

In this paper, in order to confirm the effectiveness of using the balanced antenna structure, the performance of the balance-fed antenna system for a handset under the influence of a human head or hand is analyzed numerically and experimentally. As a human head model, the COST (European Cooperation in the field of Scientific and Technical Research) 244 model, which has a spherical or cubic form, is used. The hand is simply simulated as the combined rectangular prism on the basis of the average size of human hands. The electromagnetic IE3D simulator by Zeland Software is used to obtain the antenna characteristics such as the current distribution and radiation pattern.

Built-in folded dipole antenna for handsets

One of the trends observed in mobile telephone technologies is the reduction in the size and weight of the handset. Accordingly, antennas used for such handsets must also follow the downsizing of the handset unit. Especially, built-in antennas are required for the latest handset antenna designs. A built-in folded dipole antenna (BFDA) for a handset is introduced and analyzed. The structure of the BFDA gives it a low profile. In the analysis, the electromagnetic simulator IE3D based on the method of moments (MoM) is applied to calculate antenna characteristics such as VSWR, current distribution and radiation patterns. The antenna has a self-balanced effect and a bandwidth of about 13%.

Compact Built-In Handset MIMO Antenna Using L-Shaped Folded Monopole Antennas

A compact built-in handset antenna for multiple-input multiple-output (MIMO) system at 2GHz, comprising two elements array of newly proposed L-shaped folded monopole antenna (LFMA), is evaluated under the multipath radio wave propagation environments. By analyzing the fundamental characteristics, mean effective gain (MEG), correlation, and channel capacity, the significant enhancement in the capability, as a handset MIMO antenna under practical use conditions, was confirmed. The performances were also compared to those of an array antenna comprising two planar inversed-F antenna (PIFA) elements in order to verify the effectiveness of the proposed antenna. The results show that the equivalent or improved performances can be realized, by using the proposed LFMA array with a compact size, taking only the volume of 44% of a PIFA array. The LFMA array provides almost the same bandwidth and enhanced isolation compared with a PIFA array, and the sufficiently low correlation and acceptable effective gain are obtained under the multipath radio wave propagation environments. In addition, a greater channel capacity than a PIFA array is achieved especially when the proposed LFMA array is inclined for the display-viewing mode, and moreover, an almost doubled increase in the channel capacity is obtained by using MIMO transmission compared with single-input single-output (SISO). This study also show that the MEG has much effects on the channel capacity, rather than the correlations, for the proposed antenna.

Analysis of decoupling method between J-shaped folded monopole antennas for IEEE 802.11b/g on handset

This letter presents a mutual coupling reduction method between two J-shaped folded monopole antennas (JFMA), which cover Wireless Local Area Network (WLAN), especially for IEEE 802.11b/g band on handset. IEEE 802.11b/g is used to 2.4GHz (2400-2484MHz) band. We proposed an effective method to reduce mutual coupling by using a bridge line that links two antennas. As the analytical results, by linking the shorting strips of two JFMA elements with a bridge line, we obtained a sufficiently reduced mutual coupling and improved total antenna efficiency.

Characteristics of Built-In Folded Monopole Antenna for Handsets

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 electro-magnetic 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.

A study on mutual coupling reduction between two inverted-F antennas using mushroom-type EBG structures

The mutual coupling reduction between two inverted-F antennas has been investigated when mushroom-type EBG structures are arranged between two inverted-F antennas at intervals of a half wavelength on a finite ground plane of 200 times 200 mm. The mutual couplings on the normal finite ground plane and with the choke structure were simulated as conventional techniques for the mutual coupling reduction. The mutual coupling of -48 dB was achieved by adjusting the arrangement of the EBG structures W and G. The effect of the mutual coupling reduction of mushroom-type EBG structures was clarified through the analysis. The low profile and high isolation antennas were realized without using the choke structure. In addition, the measured and calculated results of the input impedance and radiation characteristics are in good agreement and validity of calculated results has been confirmed.

Study on the reduction of the mutual coupling between two L-shaped folded monopole antennas for handset

In this study, we analyzed the change on the mutual coupling with respect to the spacing between two LFMA elements and propose the effective method to decrease the mutual coupling, by using a bridge line linking two antennas. As the analytical results, by linking the feeding strips of two LFMA elements with a bridge line, we obtained a sufficiently reduced mutual coupling and improved total antenna efficiency.