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A differentially fed dual-polarized antenna with low cross-polarization is proposed for sub-6 GHz applications. The main patch is fed through two pairs of symmetrical ports, and annular-ring slits are etched around the feedings. The broadband 180° phase shifter provides a stable differential feeding structure, and a 1 mm thick radome with a parasitic patch printed on its inner surface is utilized to expand the impedance bandwidth. The impedance bandwidth of the proposed antenna ranges from 3.3 to 6.0 GHz, covering the entire sub-6 GHz band. The 4-element antenna array features low profile, wide bandwidth, low cross-polarization level, and stable gain over the entire operating band. The prototype of the antenna array is fabricated and measured, and the design is well validated by experimental results.

A small-size 2×2 broadband circularly polarized microstrip antenna array is proposed in this article. The array has four broadband dual-feed U-slot patch antenna elements with circular polarization, and the sequential feeding technique is used to further enhance the 3 dB axial ratio bandwidth. The lateral size of the fabricated array is as small as 1.33λ0×1.33λ0, and the profile is only 0.04λ0. Measured results show that the overlapped −10 dB reflection coefficient and the 3 dB AR bandwidth is 53%, and the variation of the measured realized gain is less than 1 dB for S-band satellite communications (1.98–2.2 GHz).

A 2×2 circularly polarized magnetic-electric dipole array which adopts sequential-rotated feeding technique to broaden the bandwidth with the total size of 1.68λ 0 × 1.68λ 0 × 0.08λ 0 is presented in this paper. The antenna element utilizes an obtuse-triangular structure to reduce the antenna profile to only 0.08λ 0 . The simulated results show that an impedance bandwidth of 21.4% (VSWR

A 4 × 4 dual-polarized patch antenna array working at Ku band is proposed in this paper. Based on the slot-coupled structure, via holes are inserted into the substrates around the feeding lines to improve the impedance matching. In order to enhance the isolation and flexibility for planar antenna array, the feeding network is designed on two separated substrates. In addition, the anti-phased technique is also employed to reduce the cross-polarization level. Numerical results indicate that the presented antenna can realize an impedance bandwidth of 16% for horizontal polarization and 16.8% for vertical polarization with VSWR less than 1.6. The isolation between two feeding ports is larger than 47 dB and cross-polarization levels are less than −40 dB in principal planes.

In this paper, a novel design to reduce radar cross section (RCS) for microstrip antenna with a chessboard structure is proposed. The chessboard structure is composed by two different types of artificial magnetic conductor (AMC) unit cells which exhibits 180° phase difference. It can dramatically reduce the antenna RCS in a broadband including the in band and out of band from 12 to 24GHz. Compared with the reference antenna, the proposed antenna shows RCS reduction larger than 10dB, and the maximum reduction can reach more than 36dB. In addition, the radiation performance of the proposed antenna is preserved well.

We propose the design of a reconfigurable graphene leaky wave antenna based on dielectric grating. By simply adjusting the biased voltage applying to the graphene, the radiation pattern and operation frequency can be tuned.

As a spatial filter, frequency selective surface (FSS) has been intensively investigated for many years. The applications of FSS are always needed to be conformal. So modeling and analysis conformal FSS (CFSS) is particularly important. In this paper, three projection methods for modeling the doubly-curved frequency selective surfaces (DCFSS) are investigated. We compare the different effects of these methods on the performance of FSS. Then, a hyperboloid, as a sub-reflector in 93GHz Cassegrain system, is designed as an example. We find that the projection methods all could be successfully applied in the design if the curved surface within electrically large size and small curvature.

A fast and accurate method based on the modified surface integration (MSI) method is proposed to analyze the transmit fields through the radome in the receiving mode. Compared to the original MSI method, the reflection on the inner surface of the radome wall is considered in this method. And the computational time of the proposed fast method is reduced significantly. Numerical results are in excellent agreement with the results of the full-wave method.

More accurate hybrid PO-MOM process combining physical optics (PO) with method of moment (MOM) is employed to analyze an electrically large antenna-radome structure. The mutual interactions among the antenna, the inner and outer surfaces of the radome are considered through a group of associated integral equations. In the analysis, the antenna surface and the sharp tip part on the radome surface are modeled accurately by using MOM while the rest smooth parts on the radome surfaces are approximated by using PO. Numerical results indicate that the hybrid process presented in this paper is much more accurate than the conventional PO-MOM ones.

The dual feed circularly polarized (CP) U-slot microstrip antenna (MSA) has recently been proposed to provide more than 20% bandwidth that VSWR ≤ 1.5 and AR ≤ 3 dB overlapped, even with very small size. However, the working principles of the antenna and the design rules for it have not been yet presented. In this paper, simple formulations to estimate the resonant frequencies of the dual feed antenna are derived, and an iterative design procedure to determine the initial geometric sizes of the antenna is also given. Compared to the final dimensions of the antenna obtained by numerical simulations, the accuracy of the proposed approximate computer-aided-design (CAD) formulas is within 5.3%.

Based on the dielectric grating structure, the concept and design method of a novel reconfigurable graphene leaky-wave antenna (LWA) working at terahertz band is presented. The leaky-wave mode is excited by using the dielectric grating, while the applied bias voltage is varied to control the surface plasmon polariton in the graphene. Radiation pattern reconfigurability of the LWA can be realized at a fixed frequency or over a wide frequency range at the terahertz band.

In this letter, the performance of wire antennas enclosed by a small/moderate-size dielectric radome with arbitrary shape is investigated by using the coupled surface integral equation (CSIE). PMCHWT formula is applied on the surfaces of the radome, while the EFIE is employed to model the equivalent strip structure of wire antennas. The advantages of this approach over other methods are (1) all of the mutual interactions between antennas and radome are taken into account so that the performance of the composite antenna-radome system can be predicted rigorously and accurately; (2) one can use only one type of basis function (e.g. RWG functions) to represent the equivalent currents on both antenna and radome surfaces; (3) A simple delta-gap feed model can be conveniently incorporated in the method of moments (MoM) with good accuracy. Numerical results of wire antenna covered by radomes with both spherical shell and Von Karman shapes are presented to validate the proposed method.

In this paper, a Frequency Selective Surface (FSS) radome with a horn system was analyzed. A new coupled resonator spatial filter (CRSF) consisting of hexagon patch and circular aperture was firstly used in W-band. The FSS element shows stable performance with the polarization state and angle of incident wave. The horn composed of the FSS radome placed in its near-field region was designed. The antenna patterns shows that the FSS radome keeps good insertion loss, radiation patterns of horn within the designed pass-band, and reflects signal within the stop-band. The design of FSS radome shows performance advantage in reducing RCS at stop-band for its planar shape. The results provide the basis for our later studies of conformal shape radome.

A compact single-feed circularly polarized microstrip antenna is proposed to achieve symmetric radiation pattern over a wide range of observation angles. In order to reduce the radiation aperture and consequently broaden the circular polarization (CP) and the half power beamwidth (HPBW) of the antenna, a partially etched superstrate and a conducting cavity are employed in the design. Further, reasonable axial ratio (AR) and impedance bandwidths are realized within the compact structure by using a simple series crossed-slot aperture coupled feeding. As a consequence, the overall dimension of the fabricated prototype is 0.32λ0× 0.32λ0× 0.12λ0at the center operating frequency of 1.56 GHz, and a 3.0% overlapped bandwidth of 10 dB return loss (RL) and 3 dB AR is obtained. Within the bandwidth, symmetric CP radiation pattern over almost the entire upper hemisphere is observed and the HPBW is also increased from 60° to 106°.

A design of the compact cavity-backed antenna with I-type crossed-slot for circular polarization is presented. Parametric study is carried out to numerically investigate the effects of various dimensions of the antenna, including the length and width of the main arm of the crossed-slot, the size of the folded part at the end of the slot, and the finite ground plane, on the performance of the antenna. Numerical results show that good circular polarization can be achieved within the 4.8% impedance bandwidth as the size of the cavity is only 42mm (0.31λ 0 at the central frequency).

The hybrid method combining physical optics (PO) and method of moments (MOM) is proved to be an excellent method for an electrically large radiation system. In this paper, a simple and efficient method for dealing with the shading problem is presented to analyze an antenna-radome system with a PEC reflector, which also roots in the basic PO and IPO theory used in shading analysis for the scattering problem. Furthermore, the division principle of PO and MOM regions is discussed carefully for less computer cost.

The effects of the electrically large rotation ellipsoid radome on the radiation characteristics of two kinds of wire antennas are analyzed by an improved hybrid method, which combines the method of moments (MOM) and physical optics (PO). Based on a group of associated integral equations, the mutual interactions among the antenna, the inner and outer surfaces of the radome are all considered. In the analysis, the antenna surface and the sharp tip part on the radome surface are modeled accurately by using MOM, while the smooth parts on the radome surfaces approximated by using PO method. Numerical results indicate that the radome parameters can affect the antenna radiation characteristics seriously.

A full wave method is proposed to analyze the characteristics of the aperture coupled cylindrically conformal microstrip antennas. The near field of the antenna is obtained through conformal FDTD method in cylindrical coordinates and then the equivalence and duality theorems combined with the modified spectral domain dyadic Green's functions for cylindrically stratified media are used to calculate the radiation patterns. As well, a broadband antenna of this type with stacked structure is realized.