Due to the demand of dual-band modern wireless communications, this paper presents a dual-band patch antenna for IEEE802.11 a and g wireless local area network (WLAN) system. The antenna has bidirectional patterns that can be switched by an RF switch to select the feeding probe positions. The 2.4 GHz and 5.2 GHz patches are stacked on a ground plane and are matched to the RF switch by open stubs. Analysis and design are illustrated and throughput improvement is demonstrated in an indoor environment.

This paper proposes an adaptive antenna using a combination of on-off and CMA algorithms. With the proposed technique, the on-off algorithm is first employed to search for a desired signal direction in which maximum received power is achieved. Then, interference is suppressed by performing CMA. Simulations are conducted according to the potential application of the proposed adaptive antenna. The simulation results show the SINR improvement implying that the proposed adaptive antenna can be applied to microwave RFID systems in order to resolve reader collision. Furthermore, the proposed adaptive antenna is implemented and then experimented. The experimental results verify that the proposed adaptive antenna can reduce interference resulting in the collision problem.

In this paper, CPW-fed slot antennas using loading metallic strips and a widened tuning stub (CPW-FSLW) which provides wideband operation on the flat, a Λ-shape reflector with horizontal plate that prevents the back radiation and provides the uni-directional radiation are investigated. We observe that the size and shape of the reflector have significant impact on the impedance matching and radiation patterns. By fabricating the CPW-FSLW on the Λ-shape reflector with horizontal plate structure, noticeable enhancements in both radiation pattern and bandwidth are achieved. The antennas are verified both through numerical simulations and also measurements of the experimental prototypes and these confirm the good performance antennas. It is found that the proposed antenna can deliver a measured impedance bandwidth of 64% from 1.6 to 3.1 GHz for VSWR ≤ 2. The antennas are designed to have wideband operation suitable for applications in GSM1800, GSM1900, PCS, IMT-2000 and WLAN bands.

In this paper, the analysis, design and experimental results of active array applicator are presented. The injection-locking technique is used to alter the magnitude of the microwave sources so that the steering of near fields can be achieved. This technique can be applied for microwave hyperthermia cancer treatment to provide the large uniform temperature distribution. The complexity of the system can be reduced by using this technique. The study shows that the temperature distribution can be controlled by varying the modulation index, modulating frequency and initial phase of modulating signal. The temperature distribution is also affected by applicator configuration, spacing between applicators, and heating time. The Spectral Domain approach is used to analyze the near field and then the near field data are used to find the temperature distribution by using the Finite Difference method. The study is carried out at frequency of 2,450 MHz. This design is useful for implementation of the low cost steerable applicator.

This paper presents a simple and cost-effective bidirectional antenna using a probe excited circular ring. The structure of the antenna is simple i.e., a linear electric probe surrounded by the circular ring. The principle of the antenna design is easy and straightforward. A choice of the ring radius is first chosen to achieve the condition that only the dominant mode can be propagated. Furthermore, it is found that for a specific ring radius, the radiation patterns of the antenna are varied as the ring width. Then, the optimum ring width that provides the maximum directivity is determined. The criterion of the selection of the ring width for various ring radii is illustrated as the guidelines for the antenna design. The fabricated antennas at the operating frequency of 1.9065 GHz are measured and compared with the theoretical predictions. It is apparent that these results are in reasonable agreement. The bidirectional pattern with the gain of 5.4 dBi over the bandwidth of 17% is obtained. Moreover, the antenna can be easily fabricated with the low production cost. Therefore, this antenna is suitable for installing at the base station in the street cell.

This paper presents the analysis of the impedance characteristics of a sectoral cylindrical cavity-backed axial slot antenna excited by a probe. The integral equations are derived based on boundary conditions of the proposed structure and they are expressed in terms of dyadic Green functions and unknown current densities. The dyadic Green functions are obtained by using the eigenfunction expansion method together with application of scattering superposition techniques. The unknown current densities are solved by the Method of Moments. The input impedance is subsequently determined from the unknown electric current density at the probe. Numerical results of input impedance and return loss are demonstrated as functions of frequency for various parameters such as cavity length, cavity radius ratio, slot location in φ direction, slot length and probe length. Calculated results are validated by the measurements. At the operating frequency, it is found that the result is sufficiently accurate. The results from this study are very useful for the design of a sectoral cylindrical cavity-backed axial slot array antenna excited by a probe with omnidirectional beam radiation.

A probe-fed U-shaped cross-sectional antenna with tuning stubs on a U-shaped ground plane is proposed for wideband applications. The bottom of the antenna is etched to form tuning stubs for impedance matching. The simulated results of return loss, co- and cross-polarized patterns are presented and compared with the measured ones. Characteristics of a constructed antenna prototype at the operating frequency show that the antenna has an impedance bandwidth (2:1 VSWR) of 37.44% and average gain level of 8.5 dBi. Good radiation characteristics of the proposed antenna have been obtained that is the cross-polarization level and front-to-back ratio in both E- and H-planes across the large bandwidth are better than 22 dB and 12 dB, respectively.

This paper presents the radiation characteristics of a circularly polarized conical beam spherical slot array antenna for applying to the mobile satellite communication subscriber. The structure of the antenna is easy to fabricate i. e. , a ring of perpendicular slot pairs cut on an outer surface of a concentric conducting spherical cavity enclosed by the conducting conical surface with the simple feeding structure, and a linear electric probe excited at the center of the inner surface of the cavity. Radiation fields of a spherical slot array antenna are calculated by superposing the patterns of all the slots. From the numerical results of the radiation pattern, in both elevational and azimuthal planes, it is obvious that the conical beam is realized. The elevational beam direction is low, which is suitable for installing in the land mobile subscriber unit located far from the equator. The tracking system is not necessary because the azimuthal pattern is omnidirectional. Directivity of the antenna for various spherical radii and angles of slot positions are illustrated as the guidelines for the design. Experimental results are in good agreement with the predictions.

This paper presents a pattern reconfigurable Yagi-Uda antenna on an FR-4 printed circuit board (PCB) for 2.435-2.465GHz-frequency short-range radiocommunication devices. To realize the antenna, pin diodes are attached onto the antenna's driven elements and parasitic elements. The direction of the beam is shifted by alternating the pin diodes status between ON and OFF to induce a quad-directional operation so that E-plane maximum beams are formed in the directions of 135°, 45°, 310° and 225° (i.e. regions 1, 2, 3, 4), respectively. A series of simulations are performed on four parameters: microstrip-to-CPS (coplanar stripline), inter-parasitic spacing, parasitic length, and modes of parasitic elements (i.e. director/reflector) to determine the optimal antenna design. A prototype is fabricated based on the optimal simulation results. The experiments showed very good agreement between the simulation and measured results with regard to the reflection coefficients, radiation patterns and gains for all four beams.

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.