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An extremely ultra-wideband (UWB) antipodal Vivaldi antenna with a high gain and excellent impedance matching is proposed. An elliptical-shaped director embedded in an exponentially tapered slot is employed to enhance the gain at the high frequency band, while a metamaterial inspired structure is employed to enhance the gain around center frequency band and the symmetry of radiation pattern at the low frequency band. Furthermore, two sets of rectangular slits are symmetrically embedded around the tapered slot to improve the impedance matching at the low frequency band. Based on this novel structure, an antipodal Vivaldi antenna with good impedance matching and a high gain over an extremely UWB band is successfully designed. The reflection coefficient is lower than -12 dB at 1-4.16 GHz and lower than -16 dB at 4.16-28 GHz. The gain is 4.9-11.6 dBi at 1-8 GHz and higher than 11.6 dBi at 8-28 GHz.

A dual-beam filtering patch antenna with two absorptive band-edge radiation nulls and four reflective stopband radiation nulls is proposed. By loading a pair of T-shaped metallic strip underneath the radiating patch, a modified TM22 mode with TM20-like radiation pattern is obtained, which combines with the TM20 mode of the radiating patch, generating a wide operating band with symmetrical dual-beam radiation pattern. Two reflective radiation nulls are generated in both upper and lower stopbands for suppressing the out-of-band radiation. Through embedding two pairs of shorted small patch in the radiating patch, one absorptive radiation null combining with one absorptive resonant mode is produced at each band edge to absorb the band-edge incident energy, leading to a reduced reflection and sharp roll-off at both band edges, and therefore, the transceiver can be protected. With a total height of 0.038 λ0, a prototype is designed, fabricated and measured, showing a -10 dB impedance bandwidth from 4.63 to 6.10 GHz with sharp band-edge roll-off, two radiation beams directed at ± 40° with an in-band gain of 6.0 dBi, and a high out-of-band suppression of over 15 dB.

This article presents a wideband ±45° dual-polarized six-element antenna array with stable radiation pattern for base-station applications. Each element consists of four folded dipoles, a parasitic patch, and a convex-shaped reflector. To generate ±45° dual-polarized radiation pattern, the four close-in folded dipoles are arranged uniformly in a square shape and excited simultaneously by two integrated baluns. The parasitic patch is placed above the folded dipoles to enhance the impedance bandwidth for reaching 64.7% (VSWR < 1.5 within 1.4–2.77 GHz), while the reflector is designed in a convex shape to stabilize the horizontal radiation pattern. To further optimize the horizontally 3 dB beamwidth in the whole frequency band, six antenna elements are divided into three element pairs. Each element pair consists of two antenna elements which are misaligned in the horizontal plane. Using this method, the 3 dB beamwidth is stabilized within the range of 65.7° ± 3.2°. The impedance bandwidth is measured to be 64.8% (1.39–2.76 GHz) for VSWR < 1.5. Port-to-port isolation of 27 dB and side-lobe level better than 16 dB are obtained. These results make the proposed design attractive in wideband base-station applications.

A broadband ± 45° dual-polarized dipole antenna with stable radiation pattern is proposed. The antenna consists of four dipoles, a shaped reflector and a broadband feeding network. To realize ± 45° dual-polarize radiation pattern, the dipoles are formed as a square loop and fed by the feeding network. The feeding network is formed by four baluns and two 1-to-2 power dividers. The baluns and the power dividers are used to feed the dipoles for achieving better performance in impedance matching and bandwidth. The square reflector is employed to stabilize the radiation. With this method, the antenna obtains the impedance bandwidth for 58.5% (|S11|>15 dB within 2.3–4.2 GHz), and the 3-dB beamwidth of the proposed antenna is within 65° ± 5° in the horizontal plane.

A compact wideband dual-polarized omnidirectional antenna array for base-station applications is proposed. It consists of ten antenna units. To generate ±45° dual-polarized ominidirectional radiation with low gain variation for each unit, three close-in crossed-dipole elements are uniformly arranged in a regular triangle shape and excited by two 1-to-3 power dividers with equal magnitude and phase, acting as a dual-polarized loop antenna. To obtain wide impedance bandwidth for each unit, the dipole element and power divider are designed to operate in a wide and well-matched band. Moreover, the unit features steady structure, easy fabrication, and high scalability, which makes it convenient to form an antenna array. To achieve a high gain for base-station applications, a ten-unit antenna array is designed, fabricated, and measured. A wide impedance bandwidth of 52.3% (1.62–2.77 GHz) for standing-wave ratio (SWR) < 1.5 and a high port-to-port isolation of 26 dB are realized. It also features a high gain of 10.3 ± 0.9 dBi and a small gain variation of less than 2.5 dB in the horizontal plane. Additionally, the sidelobe suppression of 18 dB and null filling below the main vertical beam are obtained by the designed feeding networks. These results make the proposed design attractive in base-station applications.

This paper presents a wideband dual-polarized $4\,\times \,6$ antenna array with two beams for base-station applications. It consists of three $4 \times 2$ subarrays. For obtaining ± 45° dual-polarized radiation, a wideband crossed dipole is employed as a basic element. For each $4 \times 2$ subarray, the lower and upper $4 \times 1$ subarrays are misaligned in the horizontal plane. By using this innovative scheme, the $4\,\times \,2$ subarray is equivalent to an $8 \times 1$ subarray with a half adjacent-element spacing, resulting in good grating-lobe suppression. For achieving stable two-beam radiation with low sidelobe over a wide frequency band, specific wideband beam-forming networks with little magnitude and phase imbalances are designed. Moreover, the adjacent-element spacing is optimized to obtain stable 10 dB beamwidth around 120°, thus satisfying the coverage requirement of 120° in the horizontal plane for base-station applications. For demonstration, the proposed $4 \times 6$ antenna array is designed, fabricated, and measured. The array exhibits two beams with stable 10 dB beamwidth around 120° in the horizontal plane and around −10 dB cross level between two beams. The impedance bandwidth is measured to be 56.1% (1.64–2.92 GHz) for VSWR < 1.5 and horizontally, sidelobe and grating-lobe levels of the two beams are measured to be better than 18 dB. Moreover, the proposed method can easily be extended to multibeam base-station antenna array designs.

This communication presents a broadband horizontally polarized (HP) omnidirectional antenna array with low gain variation for base-station applications. It consists of six omnidirectional antenna units. In order to generate HP omnidirectional radiation patterns for each unit, three wideband planar dipoles are employed as basic elements and they are connected by a wideband three-way power divider with equal magnitude and phase, conducting as a loop antenna. Based on such a configuration, the antenna unit obtains an HP omnidirectional pattern as well as a wide bandwidth of 48.2% (VSWR < 1.5 within 1.67–2.73 GHz). However, the gain variation is more than 2.5 dB, which is relatively large. To reduce the gain variation, a novel approach is proposed by dividing the six antenna units into three unit pairs. Each unit pair consists of two antenna units which are complementary in radiation pattern. Using this method, the number of basic elements in each antenna unit is not increased, but the simulated gain variation is effectively reduced to about 1.24 dB.

A compact dual band-notched ultra-wideband slot antenna with sharp band-notched characteristics and controllable notched bandwidths is presented. The antenna is formed by a rectangular slot with chamfered corners on a printed circuit board ground plane, a T-shaped stub and two sets of compound band- notched structures. The compound band-notched structures are employed to generate desired lower and upper rejected bands with satisfactory skirt characteristics and su-cient rejection bandwidths. Moreover, the bandwidth of either the lower or upper rejected band can be independently adjusted by changing the size and location of the corresponding band-notched structure. Finally, a UWB slot antenna with two rejected bands at WiMAX/WLAN frequencies is successfully simulated, designed, and measured, showing good impedance matching, stable gain and near omnidirectional radiation patterns.

A compact CPW-fed dual-wideband antenna formed by a rectangular ring monopole and a rectangular monopole is presented. The measured 10 dB bandwidths for return loss are achieved to be 46.3% (2.36–3.78 GHz) and 31.4% (5.1–7 GHz) in the lower and upper band, respectively, covering all the 2.4/5.2/5.8 GHz WLAN bands and the 2.5/3.5/5.5 GHz WiMAX bands. Further, the proposed antenna has a simple planar structure and occupies a small size of 28 × 36 mm2, including the finite ground CPW feeding mechanism. Good monopole-like radiation characteristic are obtained over the operating bands. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1228–1231, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25156

In this paper, we have proposed a novel wideband 180degout-of-phase power divider. By means of using a slot T-conjunction which operates like a waveguide E-T, the frequency independent 180deg out-of-phase characteristic between the two output ports is achieved. The simulated and measured results of the proposed divider show equal power division with high stability of phase, good input return loss within 1.85-3.5 GHz band.

In this paper, a simple and effective method using two sets of lambda/4 resonators for designing dual-band filter has been investigated, and a practical filter has been fabricated, which provides two passbands at 2.4 and 5.2 GHz for WLAN application. The dual-passband characteristics are generated by adjusting the physical dimension of the top and bottom lambda/4 resonators. The bandwidth of each passband could be controlled independently by tuning the coupling gap. The measured insertion losses are 1.1 dB and 1.8 dB and the return losses are 24 dB and 20 dB at 2.4 and 5.2 GHz, respectively.