Yuanhua Sun

Wide-angle and polarization-independent metamaterial absorber based on snowflake-shaped configuration

A metamaterial absorber (MA) based on snowflake-shaped resonators is designed and experimentally demonstrated in this paper. Such an MA possesses a nearly perfect absorption with wide angle of incidence and polarization independence. The measurement in a rectangular waveguide system shows the absorptivity as high as 99.5% at 11.28 GHz. Furthermore, the operating frequency can be flexibly controlled by adjusting the lengths of the snowflakes branches, while keep the peak absorptivities nearly uniform (>97.5%). The proposed MA is sure to find wide applications in, for instance, stealth technology, thermal detector and imaging.

A Wideband Conformal End-Fire Antenna Array Mounted on a Large Conducting Cylinder

The radiation characteristics of a wideband conformal end-fire antenna array mounted on a large conducting cylinder are investigated in this communication. By employing balanced Vivaldi antenna element, the antenna array has ultra-wide bandwidth, low cross-polarization levels, and wide 3 dB beam-width. It is shown that using a larger antenna height, shorter distance away from the edge of a hollow conducting cylinder, and bigger slant angle of antenna element leads to better end-fire radiation performances. Measured radiation patterns are compared with simulated values and a good agreement is observed. A radome-antenna system is also studied and it is found that the antenna has a larger beam-pointing angle in the H-plane owing to the electromagnetic waves reflected from a dielectric radome surface, while retaining its symmetric pattern in the E-plane. These findings may provide useful insights and guidelines for the design of large radome-antenna systems mounted a cylindrical platform.

DESIGN OF MODIFIED 6-18 GHz BALANCED ANTIPODAL VIVALDI ANTENNA

In this paper, a modifled planar balanced Vivaldi antenna with endflre characteristics near the metal surface is proposed for 6{18GHz applications. The proposed antenna structure consists of three copper layers, among which two external layers locate on the two outsides of two dielectric substrates, and the central layer is sandwiched by these two dielectric substrates. To further enhance the end-flre radiation characteristic, a number of novel techniques are proposed, including elongation and shaping of the supporting substrate of a conventional balanced antipodal Vivaldi antenna beyond its aperture, using an I-shaped slot loaded radiation patch and cutting a triangle on the edge of three copper layers. Measured and simulated results show that the proposed antenna not only exhibits good impedance bandwidth, but also improves the end-flre performance in the operational frequency of 6{10GHz and achieves high gain in the end-flre direction, low cross-polarization and high front-to-back (F-to- B) ratio.

Design of wideband conformal end-fire antenna array on a large conducting cylinder

In this paper, one-element and six-element antenna arrays, conformal to electrically large cylinders of finite length, are simulated. When the length of conducting cylinder changes, the proposed antenna maintains stable radiation patterns. Moreover, the proposed antenna array provides end-fire radiation patterns with a high gain and high front-to-back ratio.

A 6–18 GHz log-periodic monopole end-fire antenna based on microstrip-to-slotline transition

This paper presents a novel wideband log-periodic monopole end-fire antenna fed by a microstrip-to-slotline transition feeding network. The proposed transition consists of a microstrip stub and slot stub to achieve the wideband impedance matching, and remove the inverting converter and correct the errors in conventional log-periodic antenna array. The proposed novel log-periodic monopole antenna covers 6 GHz–18GHz (S11< −10 dB) with flat gain of 7–8 dBi, and front-to-back ratio better than 18 dB.

A compact dual-band circularly polarized squarering slot antenna with a wide angle circularly polarization performance

A compact dual-band circularly polarized (CP) square-ring slot antenna with wide angel CP performance is proposed. The antenna is a two-layer structure. A cross strip is placed in the centerline of the slot to achieve a compact size. Two different kinds of perturbations are applied to the slots on the diagonal line of the slots for splitting the fundamental mode into two degenerate resonant modes with equal amplitudes and 90° phase-difference for CP performance. Due to the special structure, a wide angle CP performance is observed.

A novel low profile rectangle waveguide planar magic-T of Ka-band

With the research and application of monopulse antenna, Sum and Difference become an essential element. As the basic component, the magic-T should be paid attention to. Due to the drawback of large profile in traditional magic-T, one planar magic-T structure working at the Ka-band have been designed and simulated in this letter. The E-arm fed through a longitudinal coupling gap in the proposed structure is coplanar with other arms for saving valuable space in a minimization device such as Sum and Difference network. In order to fine return loss properties, one copper cylinder is added act as inductance element to disturb the electromagnetic field for improving impedance matching. As a result, the bandwidth (VSWR<;1.45) with 4 GHz is obtained at the resonance frequency of about 35.5 GHz. The performance of low loss, equal power divide, Low VSWR and high isolation have all been achieved and it is of significance in design sum-and-difference network which can work in Monopulse antenna acting as feeding network.

Broad bandwidth endfire antenna using log-periodic directors

This paper presents the design and implementation of a novel broad bandwidth endfire antenna with log-periodic directors. The feeding structure of the proposed antenna includes a balun which is formed using a pair of microstrip to slotline transitions. The proposed antenna has three resonant frequencies in the operating frequency band. Both simulation and measurement results show that the operating frequency band of the antenna can cover wide bandwidth (5GHz-10GHz), and the relative bandwidth is 67%. Far field measurements in azimuth plane and elevation plane show that the radiation patterns are stable and end fire within the operating band at frequencies of 5GHz, 7GHz, 8GHz, 10GHz. The proposed antenna radiates a well defined endfire beam, with a front-to-back ratio > 18dB and cross polarization level below -28dB. The dimension of the proposed antenna is 26mm × 27mm. Good return loss and radiation pattern characteristics are obtained and measured results are presented to validated the usefulness of the proposed antenna structure for wide bandwidth endfire applications.

A novel low profile high power Ka-band planar Sum and Difference Network

This letter introduces a Sum and Difference Network working at the centre frequency of 35.5GHz of Ka-Band. The Monopulse radar needs to be fed with the Sum and Difference Network for its requirement for sum and difference signals. Due to the requirement for sum and difference signals, the Monopulse radar was added to be fed with the Sum and Difference Network In this paper, the proposed structure adopts a kind of planar Magic-T with its E-arm bent to the parallel side and the E-arm is fed through a longitudinal coupling gap. This structure working at the center frequency of 35.5GHz is impedance bandwidth and can be up to 2 GHz for 10-dB return loss. Nonstandard waveguide is employed to get better performance. Furthermore, to get better impedance performance, four metal cylinders is used in this structure. The waveguide Sum and Difference has the merits of small in size and high power capacity, thus it is promising in radar system.

A novel stacked-patch endfire antenna

This paper presents a novel stacked patch antenna design with stable radiation and high gain characteristics. The presented antenna provides the bandwidth from 2.4 GHz to 2.483GHz. This bandwidth is realized by stacking the copper sheet. The bandwidth of the stacked antenna is narrow, but results in stable radiation patterns and high gain in the operating band, and the main gain can achieve 8.9dBi.