An extremely ultrawideband (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 the 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.

This paper 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 dual-wideband dual-polarized dipole antenna for base-station applications is proposed. This antenna consists of a pair of crossed dipoles, a circular director, and a metallic reflector. The crossed dipoles are fed by two 50 Ω coaxial cables to achieve ±45° polarized radiation over a wide frequency band, while four T-shaped slots are cut in the dipole arms to produce two wide operating bands. The circular director is employed and located above the dipoles to enhance the impedance matching and further stabilize the radiation pattern at the higher frequency band. To further stabilize the pattern, four baffles are added along the edge of a square reflector. Measured results demonstrate that this antenna has two broad bandwidths of 47.8% (1.67–2.72 GHz) and 16.6% (3.3–3.9 GHz) for VSWR < 1.5 at the lower and higher frequency bands, respectively. Stable half-power beamwidths of 67.5°±8.5° for the lower frequency band and 64°±5° for the higher frequency band are obtained. The measured gains are stabilized at 8.1±0.5 dBi for the lower band and 8.35±0.25 dBi for the higher band. This antenna is potentially attractive for mobile communications.

A compact broadband patch filtenna with enhanced stopband suppression is presented in this letter. The designed antenna is configurated with a simple structure having two substrates of 0.04 λ0 spacing (λ0 is the free space wavelength at the center frequency). A rectangular patch with Π-, Γ- and inverted Γ-shaped slots is printed on the top substrate and fed by a coaxial probe. The above three slots create additional resonance modes to broaden the impedance bandwidth and generate two out-of-band radiation nulls to enhance the stopband suppressed level. An antenna prototype with a dimension of 0.56 λ0 × 0.56 λ0 × 0.06 λ0 is fabricated to demonstrate its characteristic. A stable gain of 7.2 ± 0.4 dB over the wide impedance bandwidth of 17% (1.88 - 2.23 GHz) is achieved, and the out-of-band suppression level is beyond 20.6 dB. These features make the filtenna a promising candidate for the PCS 1900/UMTS 2000 bands in mobile communication systems.

This communication presents an ultra-wideband dual-polarized antenna consisting of a main radiator, parasitic elements, and a ground plane. The main radiator is composed of two pairs of dual-dipoles, which are cross-arranged and fed by coplanar-strip lines in order to achieve ±45° dual-polarization within a wide frequency band. Parasitic elements including a circular patch and four pairs of dipole strips are employed for improving the radiation performance in the high frequencies, which is very essential for stabilizing the radiation pattern over the entire bandwidth. The proposed antenna can cover the frequency range from 1.7–5.1 GHz for both polarizations, corresponding to an ultra-wide bandwidth of 100%. The gain and half-power beamwidth (HPBW) are very stable within the entire bandwidth, which are 8.2±0.7 dBi and 65°±5°, respectively. Measured results agree well with simulated ones, indicating that the proposed antenna is a very promising candidate for the future base station communication system.

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 TM ₂₂ mode with TM ₂₀ -like radiation pattern is obtained, which combines with the TM ₂₀ 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 $0.038~\lambda _{0}$ , 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 high out-of-band suppression of over 15 dB.