Analysis of a novel folded loop antenna for handset is described along with the advanced design concept for handset antennas. The design concept shown in this paper meets the foremost requirement for handset antennas such as (1) small size and yet (2) has capability of mitigating degradation of antenna performance due to the body effect, and (3) of reducing SAR value in the human head at the handset talk position, in addition to the indispensable requirements for handset antennas such as (4) low profile, and (5) light weight. The technology applied is to make this antenna (a) an integrated structure, which is a typical application of the fundamental concept of making antennas small and (b) a balanced structure which has been proved to be very effective to satisfy the requirements (2) and (3). The antenna is essentially a two-wire transmission line, folded at about a quarter-wavelength to form a half-wave folded dipole, and yet appears to be a loop of one-wavelength. It does not have really a balanced structure, as is fed with an unbalanced line; however, the antenna structure itself can eliminate the unbalanced current flow on the feed line as in the balanced antenna system. Both theoretical and experimental analyses have been shown and the usefulness of the antenna is discussed. This paper may suggest the advanced technology and design concept that will be applied to the development of handset antennas toward the future.

A polarization diversity planar inverted-F antenna (PIFA) on portable telephone in the practical use near the operator's body is investigated at 1,800 MHz under multipath urban environment. The antenna structure comprises a center-fed square patch with one permanent short-pin and two RF-switches on three corners. The RF-switches perform as the polarization branch switches for dominantly vertical polarization (VP) or dominantly horizontal polarization (HP) modes. The radiation efficiency of the polarization diversity PIFA is 58% and 53% for VP and HP modes, respectively, which is higher than the 52% efficiency of the reference λ/4 monopole antenna under the same condition. The mean effective gain (MEG) of VP and HP modes decrease with respect to the increasing cross-polarization power ratio (XPR). The correlation coefficient of two diversity branches is between 0.66 through all the possible XPR ranging from -10 dB to +10 dB. The diversity gain is computed from the MEG and correlation coefficient to determine the diversity antenna gain (DAG). The diversity gain, based on 10-3 BER for selective combining, is 7.5 dB over non-diversity reception. The DAG is -1.2+2.8 dBi which is approximately 4 dB lower than the case without human body. In other words, the presence of the human body degrades the communication performance by a half.

This paper presents a novel design method for reducing the complexity of the design procedure for diversity antennas on the hand-held phone. Recently, antenna selection diversity has been widely used for hand-held phones in order to overcome a problem of fading. A monopole antenna and an inverted-F antenna are the typical combination for this purpose. In the case of the conventional design method, the mutual coupling between two antennas are used for improving the diversity performance. However, strong mutual coupling often makes the diversity antenna design difficult and degrades the radiation performance. The proposed design method suppresses this coupling by tuning the terminating impedance on the unselected antenna and improves the diversity performance by modifying the shape of inverted-F antenna. The validity of the proposed method is investigated under the effect of the user's hand and head by FDTD simulation.

In this paper, a novel three-port antenna structure, named 180 antenna hybrid, is proposed and demonstrated. This structure is composed of a Wilkinson power divider with the isolation resistor replaced by an aperture-coupled patch antenna. The equivalent series impedance of the antenna can be adjusted to the required one by properly choosing the dimensions of the patch and the coupling aperture. When a signal is fed to the balanced port of this antenna hybrid, the power is equally split, with equal phases, to the two unbalanced ports. No power is radiated out from the antenna. In the other hand, a signal received from the antenna will be split with equal power but 180 phase difference to the two unbalanced ports. The balanced port is an isolation port. The measurement results showed good agreement with the characteristics to be designed. Three applications of this 180 antenna hybrid are introduced, that is, a balanced mixer, an active transmitting antenna, and a dual-radiation-mode antenna array. The balanced mixer was constructed with diodes directly mounted on the two unbalanced ports of the antenna hybrid. The LO signal is fed from the balanced port and RF signal is received from the antenna. The active transmitting antenna was implemented with feedback configuration. The route from one of the unbalanced port to the balanced port of the antenna hybrid was used as the feedback path. A locking signal may be injected from the other unbalanced port. Finally, through a three-quarter-wavelength microstrip line, the balanced port of the antenna hybrid was connected to another aperture-coupled patch antenna to form a dual-radiation-mode antenna array. The in-phase and out-of-phase radiation patterns of this two-element array can be obtained from two unbalanced ports of the antenna hybrid, respectively.

Beam reconfiguration by structural reconfigurable antenna, such as the small multi-panel reconfigurable reflector antenna, has an aspect of great concern, that is the effects due to the use of a number of small panels to form the reflecting surface. It is thus a matter of great interest to numerically investigate all possible factors affecting the performance of this type of antenna such as: neighboring panels blocking, diffraction. The "null-field hypothesis" and PTD are employed to account for the effects of both phenomena on the main beam steering ability and the cross-polar level. In addition, the transformation of the polygonal flat domains into the square domains is applied in calculating the PO radiation field due to the various irregular polygonal flat sections of the arbitrary initial approximate reflector e.g., the flat circular reflector and the paraboloidal reflector. It is found that the main contribution to the total cross polarization is depolarization due to the finite size of the panels. The maximum cross-polar gain predicted using PTD is around -30 dB. The blocking effect has minor influence on cross-polarization. Both effects cause distortion on the co-polar pattern for the observer far from boresight but blocking has more influence than edge diffraction. Both effects have minor influence on the co-polar gain. The co-polar gain has variation of less than or equal to 0.07 dB in the flat case and 0.16 dB in the paraboloid case.

An optically controlled beamforming technique is a very effect procedure for phased array antenna control. We have built a Fourier optical processing beamforming network. In the optical processor, we use optical waveguide arrays and a GRIN micro lens in order to reduce the size and weight of the processor, optical coupling losses, mechanical destabilization, and optical alignment difficulties. This paper describes the characteristics of a one-dimensional Fourier optical processor, and shows the configurations of both its transmitting and receiving modes, which we have constructed. We demonstrate multiple signal generation, and beam steering for transmission in the X-band. Furthermore, we configure the beamformer for reception using the phase information of local signals form the optical processor. We additionally demonstrate the beam steering of the received X-band RF signal. Experimental results confirm the feasibility of the Fourier optical processing beamforming network.

A novel millimeter-wave planar leaky-wave antenna is described which consists of a dielectric slab loaded by metallic periodic strips. Several new techniques are discussed, such as an air-gapped dielectric waveguide to reduce conductor loss of the ground plane, a canceling array to suppress the reflections in the waveguide due to the metallic strips, a compact feed, and a simple polarizer. By applying these new techniques, we achieved an excellent antenna efficiency, exceeding 70% at 76 GHz band for both vertical and 45-degree inclined linear polarizations.

The European Commission, through RACE, ACTS and now the IST programmes, has funded numerous consortium based research projects addressing capacity enhancement by means of Smart or Adaptive Antenna Technology. In addition to capacity enhancement, these projects have also considered the additional operational benefits, such as multipath mitigation and range extension, that this technology can offer to wireless network deployments. This paper provides an overview of the results obtained from the test-bed and field trial evaluations conducted under the ACTS TSUNAMI project. Here, a test-bed facility was developed by the project partners in order to appraise the potential merits of a Smart antenna facet deployment at the base-station cell site of a DCS1800 network. Details of the test-bed hardware and adaptive control algorithms are given, as well as results from the user tracking, traffic bearer quality assessments and range extension experiments. These results help substantiate many of the claims put forward by the proponents of Smart antenna technology, as well as ranking the relative performance of the family of adaptive control algorithms evaluated here. Further, new research activities, which embody Smart Antenna Technology, now supported under IST funding are also introduced.

This paper presents the design of low sidelobe single-layer slotted waveguide arrays. The Taylor distribution with -25 dB sidelobe level is synthesized in two orthogonal directions in the aperture. The multiple-way power divider consisting of a cascade of novel π-junctions is introduced; each π-junction, two-way power divider, is so designed as to accept unequal power dividing by adopting an offset window. The smooth Taylor distribution is realized at the output of the multiple-way power divider, which was originally developed only for uniform distribution. A model antenna for Taylor distribution is tested at 76 GHz. The measured sidelobe level is below -24 dB in both E- and H-plane. The highest gain is 34.5 dBi with 50% efficiency which is only 15% lower than that for uniform aperture illumination.

A novel millimeter-wave slotted waveguide array antenna is developed for automotive radar systems. An antenna structure suitable for mass-production is proposed in this paper. The waveguide is composed of two parts; an upper plate and a bottom plate. It is not necessary to contact each other closely because they are divided at the center of the broad wall of the waveguide where the electric current is small. In addition, grating lobes are suppressed by using a cylindrical cavity around each slot and by controlling the slot arrangement without using dielectric material in the waveguide. We have fabricated the proposed antenna by metal injection molding. The measured antenna efficiency results in 55%, which is quite high in comparison with any other conventional low cost millimeter-wave antenna. This efficiency is almost the same as that of the antenna fabricated by precision metal machining. In this paper, it is confirmed that the proposed antenna could be manufactured with low cost.

Broadband fixed wireless access (FWA) systems offer significantly higher bit rates than current cellular systems to which adaptive arrays are partly applied. Digital beam forming is being eagerly explored on account of its flexibility, but it will be difficult to apply to the high-speed systems, because its digital signal processing requires huge resources and power consumption. Conventional phased arrays, on the other hand, utilize phase shifters through RF or IF signal lines, but the phase shifters are usually both bulky and expensive. The authors propose an adaptive array steered by IF local signal phase shifters in this paper. The phase shift and the frequency shift of the signal from each antenna element can be simultaneously accomplished at the down conversion stage by the phase-controlled local signal. A prototype receiver operated in the K-band with the proposed configuration and its beam pattern measurement results are also described.

This paper describes an estimation method for an antenna current distribution including the interaction between a cellular telephone antenna and a human body. In our experiments, current distributions on a half wavelength dipole antenna at 900 MHz are evaluated by measuring the magnetic field near the antenna, when a human head-sized phantom model is located near the dipole antenna. From the experiments, the antenna current around a feed point is confirmed to increase by 30% due to the interaction effect. This result shows that antennas of portable phones should be designed by considering the effect of a human presence for the development of the higher performance antenna, and our estimation method will contribute to optimizing the design of such antennas.

The analysis of the radiating properties of a multilayer structure where chirality is introduced is here addressed. Both the effects on the resonant behaviour and on the radiation patterns have been considered for different multilayer structures. The adopted procedure is full wave and leads to the numerical analysis performed via the Methods of Moment in the spectral domain.

Coupling between two slot antennas on an infinite ground plane and radiation patterns on a finite ground plane are calculated. We introduce a parasitic wire between slot antennas to reduce coupling. Two typical cases with a monopole or a half-loop are considered in this paper. Numerical results show that the reduction of 13.9 dB is obtained by adjusting a monopole height to about a quarter wavelength of the operating frequency. Also a properly adjusted parasitic half-loop reduces the coupling coefficient by 24 dB. Radiation patterns of the antennas on a 365 mm 465 mm ground plane at 1.5 GHz are calculated where the diffracted fields are taken into account. It is found that the parasitic elements little affect the antenna patterns around the +z-axis that is perpendicular to the ground plane although the reduction of coupling between slot antennas is obtained.

Sector antennas provide many advantages such as when combined with a narrow beam antenna, they become particularly effective in achieving high-speed wireless communication systems and they aid in simplifying the structure. These antennas have a drawback in that as the number of sectors increases, the antenna size rapidly increases. Therefore, downsizing the sector antenna has become a major research topic. A promising candidate is utilizing a phased-array type antenna; however, this antenna requires a phase-shifter circuit for beam scanning and generally the feeding circuit for this type of antenna is very complicated. To address these issues, we propose a self-selecting feeding circuit that is controlled by the same control circuit and is operated similarly to the conventional single port n-th throw (SPNT) switch. We fabricated a small cylindrical 12-sector antenna at 19 GHz employing the proposed feeding circuit for verification purposes. Furthermore, this paper clarifies the design method of this feeding circuit where the antenna diameter is 71 mm, and the results clearly show that the gain is more than 12 dBi.

Electric beam scanning reflector antennas provide beam scanning and pattern control, and can create narrow beams efficiently. However, they are not popular because the beam control circuit is large and difficult to realize. This paper proposes a new BFN configuration for cluster feeding of highly functional scanning antenna. The Enhanced PAttern Control nonswiTch (EPACT) BFN simplifies the beam control circuit and its control algorithm by using a fast Fourier transform (FFT) circuit, phase shifters, and a power divider. Furthermore, this paper proposes a design technique that uses modules to implement the FFT circuit and a method that optimizes amplifier placement to improve antenna efficiency. The design technique facilitates the manufacture of large-scale FFT circuits. The optimized amplifier location improves the antenna efficiency by eliminating the partial concentration of signal power.

A low-profile bi-directional cavity antenna has been developed for the IMT-2000 indoor base stations. The geometrical relationships required for the design of an antenna with broadband impedance characteristics, which are obtained as a superposition of two resonant modes (M-antenna + metal case), are presented. The approximate equations describing the resonant frequencies associated with the two resonant modes are derived. By using the equations, a cavity antenna with dimensions of 120 mm 120 mm 12 mm and a fractional bandwidth of 18.3% (VSWR <2) that meets the IMT-2000 specification can be designed successfully. The proposed design procedure of the antenna is confirmed by the measurements.

In this paper, a novel beam selection transmit diversity (BSTD) scheme is proposed for the downlink transmission of frequency division duplex (FDD) based DS-CDMA system. As a combination of selection transmit diversity and steering vector based beamforming, the BSTD scheme provides diversity gain as well as reducing multiple access interference in downlink. Moreover, to have a better understanding, the performance of the BSTD is also compared with other schemes. The comparison results show that the BSTD would be a promising candidate for the downlink transmission if both performance and implementation complexity are considered.

An uplink synchronised CDMA system through transmission timing control at mobile users has been proposed to improve the uplink capacity. This Letter mathematically investigates its capacity, considering perfect fast TPC and two antenna diversity reception in a single cell environment and compares it with that of a conventional CDMA system.

As the capacity of a personal computer and workstation increases rapidly, many electromagnetic simulators solving antenna problems are widely used. In this paper, the IE3D electromagnetic simulator, which is a commercial software product, is applied to the analysis of handset antennas in the vicinity of the human body. Firstly, basic characteristics of popular handset antennas such as whip and planar inverted-F antennas are obtained by the IE3D electromagnetic simulator and calculated results are compared with measured results quoted from the referenced paper. Secondly, on the basis of newly considered design concept for a handset antenna, a loop antenna system for the handset, which we have proposed in order to reduce the influence of human body, is taken as an example of a balance-fed antenna and is analyzed theoretically and experimentally including the influence of the human body. In a result, calculated results by the IE3D electromagnetic simulator are in good agreement with measured results and it is confirmed that the simulator is very effective in analyzing the handset antenna in the vicinity of the human body.