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A planar pattern reconfigurable patch antenna is proposed. The proposed antenna is a circular array composed of three radiating elements, and each element can generate a horizontally polarized main beam with a half‐power beamwidth of about 135°. To switch the beam direction, a single‐pole three‐through circuit is designed on the same printed circuit board as the radiating elements, and the total area of the integrated planar antenna is a circular shape of diameter 0.37λ0. A prototype operated at 2.45 GHz is constructed, and the measured results demonstrate that the pattern reconfigurable antenna can give three steerable beams in the E plane, and the gain and the front‐to‐back ratio of each beam are 3.2 dBi and 15 dB, respectively; moreover, an operation bandwidth of more than 10% is also achieved. Simulated analyses are also performed to explain the antenna performances mentioned above, and they have good agreements with the experimental data. [ABSTRACT FROM AUTHOR]

A strip‐typed patch antenna covered with a dielectric is studied. The antenna is excited with a differential feeding mechanism to obtain a low cross‐polarization level. When the patch antenna is totally covered with a dielectric, it can be operated at lower frequencies without tuning antenna dimensions. The simulated results show that as the relative permittivity of the dielectric is increased from 1 to 9.2, the antenna operation frequency is reduced from 4.25 to 2.38 GHz, and the cross‐polarization level is lower than −25 dB for each operation frequency. Based on such an antenna, a 1 × 8 dual‐polarized phased array is developed. The simulated results indicate that for each polarization mode, the gain variations of the array are less than 2 dB when the main beam is scanned from 60° to −60°; bedsides, a cross‐polarization level of less than −20 dB is also achieved. An array prototype is constructed, and measured data validate the simulated results. [ABSTRACT FROM AUTHOR]

A strip‐typed antenna with the advantages of simple structure and easy fabrication is first proposed. When the antenna is mounted on a planar circuit board, it has the same radiation characteristics as a traditional microstrip antenna operated in the fundamental mode; however, the proposed antenna only occupies a space of a linear length for the surface of the circuit board. Then, A 1 × 4 array with ± 45° polarizations is realized using the strip‐typed antenna as a radiating element. The dual‐polarized array is excited with a pair of coplanar corporate feed networks. Simulated results show that the gains of the radiating element and array are up to 8 and 13 dBi, respectively; in addition, the isolation between the two input ports of the array is higher than 27 dB within an impedance bandwidth of around 11%. Experiments are also carried out, and they validate the simulated results. Details of the designs are presented. [ABSTRACT FROM AUTHOR]

A design for reconfigurable circularly polarized (CP) microstrip antennas with frequency agility is described. The main radiating element of the antenna is a suspended patch, and it is connected with two vertical feed probes. When one feed probe is used as a signal input port, the other probe can serve as a perturbation element of the microstrip antenna resonant at the fundamental mode, and consequently a CP radiation is generated. Because the dual probes are arranged in an orthogonal fashion, the antenna can be operated in right‐handed and left‐handed circular polarization modes. To vary the CP operation frequency, four varactors are mounted on the ring slot embedded on the radiating patch. Simulated results indicate that the CP frequency can be continuously tuned from 1.2 to 1.9 GHz with decreasing the capacitance of the varactors. A prototype is also fabricated, and only one DC bias is required to realize the reconfigurable antenna. The design concept of the proposed antenna is shown, and CP performances at different frequencies are also presented. [ABSTRACT FROM AUTHOR]

A design is described of a broadband circularly-polarized (CP) slot antenna. A conventional annular-ring slot antenna is first analyzed, and it is found that two adjacent CP modes can be simultaneously excited through the proximity coupling of an L-shaped feed line. By tuning the dimensions of this L-shaped feed line, the two CP modes can be coupled together and a broad CP bandwidth is thus formed. The design method is also valid when the inner circular patch of the annular-ring slot antenna is vertically raised from the ground plane. In this case, the original band-limited ring slot antenna is converted into a wide-band structure that is composed of a circular wide slot and a parasitic patch, and consequently the CP bandwidth is further enhanced. For the patch-loaded wide slot antenna, its key parameters are investigated to show how to couple the two CP modes and achieve impedance matching. The effects of the distance between the parasitic patch and wide slot on the CP bandwidth and antenna gain are also presented and discussed in details. Index Terms--Broadband operation, circular polarization (CP), slot antenna.

A circularly-polarized (CP) slot antenna comprises of a triangular wide slot, a director patch, and a metallic reflector is proposed and studied in this paper. The CP radiation of the slot antenna is excited by the proximity coupling of an L-shaped strip. To obtain an optimum peak gain and a broad CP bandwidth, the effects of varying the positions of the director and reflector on the antenna performances are respectively investigated. Several prototypes were constructed, and the measured results show that the proposed antenna can provide an average gain of 10 dBi within a CP operating bandwidth of 23% and a front-to-back ratio of over 10 dB. Simulation analyses are also carried out to validate the experimental results. Index Terms--Broadband operation, circular polarization, slot antenna.

A single-fed reconfigurable microstrip antenna that can provide various polarization diversities is presented in this paper. The antenna is excited by a microstrip feed line through aperture coupling. When two PIN diodes are used to respectively reconfigure the coupling slot and the open stub of the feed line, the polarization of the microstrip antenna can be switched between vertical and horizontal polarizations. For the reconfigurable antenna with the linear polarization diversity, it can be converted to a circularly-polarized antenna with switchable polarization sense by introducing a perturbation segment. Moreover, an antenna with the quadri-polarization diversity, including dual orthogonal linear polarizations and two circular polarizations, is also developed from the structure of the switchable circular polarization microstrip antenna, and only three diodes are required. Details of the antenna design are shown, and the measured results for the constructed prototype are also exhibited and discussed. Index Terms--Aperture coupling, microstrip antennas, polarization switching.

The designs of dual-band and wide-band microstrip patch antennas with conical radiation patterns are presented in this paper. The antenna is composed of a square-ring patch that is shorted to the ground plane through four shorting walls. Three resonant modes with conical radiation patterns can be simultaneously excited in the antenna structure by a patch-loaded coaxial probe inside the square-ring patch, and they can be designed as a dual-band operation. Moreover, by adjusting the width of the shorting walls, the three modes can be coupled together to realize a wide-band operation. From the obtained results, the 10 dB impedance bandwidths at lower and higher operating frequencies are respectively 42 and 8% for the dual-band antenna design, and the wide-band design exhibits an impedance bandwidth of about 70%. Index Terms--Conical radiation, dual-band, patch antenna, wideband.

A single-feed reconfigurable square-ring patch antenna with pattern diversity is presented. The antenna structure has four shorting walls placed respectively at each edge of the square-ring patch, in which two shorting walls are directly connected to the patch and the others are connected to the patch via pin diodes. By controlling the states of the pin diodes, the antenna can be operated at two different modes: monopolar plat-patch and normal patch modes; moreover, the 10 dB impedance bandwidths of the two modes are overlapped. Consequently, the proposed antenna allows its radiation pattern to be switched electrically between conical and broadside radiations at a fixed frequency. Detailed design considerations of the proposed antenna are described. Experimental and simulated results are also shown and discussed. Index Terms--Patch antennas, pattern diversity, reconfigurable antennas.

The design of an aperture-coupled microstrip antenna with switchable polarization is presented. The antenna is excited by a series microstrip-line-feed configuration through the coupling of a ring slot in the ground plane. For the ring-slot-coupled microstrip antenna, it is found that the minimum axial ratio in the 10 dB-input-impedance bandwidth can be varied between 0.4 and 23 dB when the length of the series stub is changed. Therefore, the antenna can radiate linear or circular polarization with good performances by selecting a proper length of the stub. To realize the voltage-controlled polarization switching, one PIN diode is integrated into the ring-slot-coupled microstrip antenna. Two typical layouts are indicated and their antenna prototypes are implemented. Details of the measured and simulated results are also presented. Index Terms--Aperture coupling, microstrip antennas, polarization switching.

The design of a short-circuited triangular patch antenna with broadband operation is presented. By placing two shorting walls at the opposite edges of a tip-truncated triangular patch antenna with a V-shaped slot, two resonant modes can be excited simultaneously and they can be coupled together to achieve the broadband operation. The key parameters of the proposed antenna are investigated experimentally to show how to obtain 50 [OMEGA] input impedance and optimum bandwidth. An antenna prototype designed for covering UMTS and ISM bands (1.92-2.48 GHz) is completed and tested. The measured results show the 10 dB impedance bandwidth is more than 25%, and the antenna height is less than 0.06 free-space wavelengths. Index Terms--Broadband antenna, conical pattern, short-circuited patch antenna.

The design of a monopolar square-ring patch antenna with wideband operation is presented. The antenna consists of a parasitic square-ring patch antenna that is shorted to the ground plane through two shorting walls and is excited by a top-loaded coaxial probe. The key design parameters to obtain 50 [OMEGA] input impedance and optimum bandwidth are investigated experimentally. The effects of the inner slot size of the square-ring patch on the operating frequency of the proposed antenna are also studied. From the obtained results, a 10 dB-input-impedance bandwidth of more than 50% can be achieved while the side length of the square-ring patch is about 0.3 free-space wavelengths and the antenna height is less than 0.1 free-space wavelengths. Also, the antenna can provide stable monopole-like conical radiation patterns across the impedance bandwidth. Index Terms--Conical pattern, patch antenna, wideband antenna.

A new design of a circularly polarized square-ring slot antenna is proposed. The circular polarization is achieved by a series microstrip-line-feed configuration coupling to two orthogonal sides of the square-ring slot. A parametric study is conducted using a commercial simulation software based on the method of moments, and the design procedure is established. The required ground-plane size of the proposed design for a given frequency is also indicated. Three antenna prototypes respectively operated at distinct frequency bands are constructed and measured for providing the simulation validation. Experimental results show that the proposed antenna has good circularly polarized radiations and the 3 dB axial-ratio bandwidth is more than 6%. Index Terms--Circular polarization, slot antenna.

The design of an aperture-coupled annular-ring microstrip antenna for circular polarization (CP) is presented. The CP radiation of the annular-ring microstrip antenna is achieved by a series microstrip-line-feed configuration through the coupling of a ring slot in the ground plane. The key parameters of the proposed design are investigated using a commercial simulation software based on the Method of Moments to show how to obtain the 50 [ohm] input impedance and optimum axial ratio. The proposed design can be applied to the annular-ring microstrip antennas with different inner radii and substrate thickness, and several antenna prototypes are constructed and measured. Details of the experimental results of the CP performance are presented and discussed. Index Terms--Aperture coupling, circular polarization, microstrip antennas.

Analysis of the resonance problem of a cylindrical wraparound microstrip structure with superstrate is presented. In this study the rigorous full-wave formulation and Galerkin's method are used. The numerical convergence for the selected sinusoidal basis functions with edge singularity is also discussed. Numerical results of the superstrate loading effects on the real and imaginary parts of complex resonant frequency of the structure as a radiator at T[E.sub.01] mode and as a resonator at H[E.sub.10] mode are calculated and analyzed.

The resonance problem of the cylindrical-rectangular microstrip structure with an airgap between the substrate layer and the ground conducting cylinder is studied by using a rigorous full-wave approach and a moment method calculation. The resonance condition is satisfied by complex resonant frequencies, which provide the information of resonant frequency and half-power bandwidth of the structure. Numerical results indicate that, with the increasing of the airgap thickness, the half-power bandwidth of the structure at the efficient radiating mode of H[E.sub.01] is considerably increased, which improves the narrow bandwidth characteristics of microstrip structures. Details of the numerical results, including the results for the planar rectangular microstrip structure with an airgap, are presented and analyzed.

The complex resonant frequency of a superstrate-loaded rectangular microstrip structure is investigated. The study is performed by using a full-wave analysis and Galerkin's moment method. The numerical convergence using sinusoidal basis functions, with and without considering the edge singularity to expand the unknown surface current distribution on the rectangular patch, is discussed. Numerical results for the effects of superstrate permittivity and thickness on the complex resonant frequency of the rectangular microstrip structure are also presented.

The complex resonant frequencies of the cylindrical-rectangular microstrip structure loaded with a dielectric superstrate layer is studied by using a rigorous full-wave analysis and the numerical results are obtained by using the Galerkin's moment method calculation. The numerical convergence for the selected sinusoidal basis functions with and without the edge singularity condition is also discussed. Numerical results for the dependence of the real and imaginary parts of the complex resonant frequencies on the superstrate permittivity and thickness are calculated and analyzed, which are also compared with those obtained for the planar microstrip structure.

A pattern reconfigurable design realized by a planar array integrated with a switchable feed network is presented. The array has 16 radiating elements, and each element is a printed dipole backed with a metallic box. These elements are divided into four groups, and the excitation state of each group can be controlled with the feed network. By varying the number of the active groups, the radiation pattern of the array is reconfigured. Simulated results demonstrate that the proposed array can generate broadside beams with a front‐to‐back ratio of higher than 25 dB, and the half‐power beamwidths of these main beams in E‐plane or H‐plane can be switched among 20°, 26°, and 46°; besides, the array can produce three different side lobe levels, including −1, −12, and − 25 dB, in the two principal planes. For the proposed pattern reconfigurable array, a prototype is constructed, and its experimental results are also exhibited to validate the simulated data. [ABSTRACT FROM AUTHOR]

A simple impedance-matching technique for the patch antennas fed by a coplanar microstrip line is presented. By placing a shorting through hole at a proper position, the resonant input resistance of the edge-fed patch antenna can be easily tuned to 50 [ohm]. For the cases of the patch antennas with the aspect ratios varied from 0.5 to 2, both theoretical and experimental investigations of the proposed technique are carried out. From the obtained results, it is shown that, to acquire the 50 [ohm] input impedance, the position of the through hole is only related to the length of the radiating edge of the patch antenna. Details of the antenna design are presented. Index Terms--Impedance match, patch antenna.

This paper presents the performance of a single-feed triangular planar inverted-F antenna with a V-shaped slot. Several prototypes of the proposed antennas with different shorting-wall widths are studied experimentally. The obtained results show that, by selecting a proper shorting-wall width, the proposed antenna not only has dual-frequency characteristic but also can achieve the impedance bandwidth of more than 30% in higher operating frequency band. In addition, the radiation pattern across the entire operating bandwidth is measured and discussed. Index Terms--Compact antenna, dual-band antenna, planar inverted-F antenna (PIFA).

A 2 × 2 array with reconfigurable pattern and polarization is presented. The element of the array is a circularly polarized (CP) antenna, which is mainly composed of a monopole slot, a dipole, and a cylindrical copper tube. By manually moving the dipole arms, the element can be operated at right‐handed and left‐handed circular polarization states; besides, each CP element can be electrically rotated with a servo motor, whereby the phase of its radiated fields is varied with rotation angle. Based on such a mechanically reconfigurable element, the resultant array at each CP state can be operated in different radiation modes, including broadside mode, conical mode, and steerable beam mode. In addition, the array operated in the broadside mode can also provide a linearly polarized radiation with 360° polarization scanning. Simulations for typical radiation modes of the proposed array are performed, and they are validated with experiments. [ABSTRACT FROM AUTHOR]

A wideband antenna with conical radiation is first studied in this article. The antenna has the advantages of low profile and simple structure, and it can provide a stable radiation pattern within an impedance bandwidth of about 108%. Then, five radiating elements, including four dipole antennas and one ring slot antenna, are excited from the wideband antenna structure, forming a six‐port antenna. The integrated antenna at 3.5 GHz band can offer a broadside pattern with 9.3 dBi gain, a conical pattern with 4.3 dBi gain, and four symmetrical endfire patterns with 6.4 dBi gain. The design process of the integrated antenna is explained in details, and a prototype is fabricated. The experimental results indicate that the operation bandwidth of the pattern diversity antenna is about 14%, and the isolation between input ports is lower than −16 dB within the bandwidth. Simulated results also validate the experiments. [ABSTRACT FROM AUTHOR]

A design of pattern reconfigurable arrays realized with mechanical mechanism is presented. The radiating element of the array is a printed dipole backed with a metallic box, and it has a broad impedance bandwidth as well as a high front‐to‐back ratio. Four of the elements are connected together by using a mounting fixture with rotatable joints. When the joints are rotated manually, the array configuration is changed, and each array configuration can generate a specific radiation pattern. For the proposed array, a prototype designed at the frequency band from 4.8 to 5.9 GHz is constructed. Measured results for the prototype operating in three typical radiation modes are exhibited, including high‐directivity radiation mode, two‐beam radiation mode, and omnidirectional radiation mode. Simulated results also validate the experiments. [ABSTRACT FROM AUTHOR]