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Because of the large wavelength in very high-frequency (VHF) band, conventional design concepts for flush-mounted VHF band antenna arrays over aircraft platforms meet many challenges. This article presents an approach for the design of VHF aircraft-integrated antenna arrays with switchable beams by using the characteristic modes (CMs) of the aircraft platform. The CMs of the aircraft platform provide the modal significances, modal currents, and modal radiation fields of each mode. An in-depth investigation over the useful CMs information is performed to prove the feasibility of design VHF band antenna array using the CMs of the platform. Switchable radiation patterns with horizontal polarization are then synthesized from these CMs. The switchable beams and polarization constraint make it more challenging than CM-based fixed power pattern synthesis. The polarized switchable beam synthesis is carried out with a multiobjective evolutionary algorithm. A trade-off among the synthesized current distributions for different beam steering angles is made to determine the optimal current excitation locations for antenna array development. Meanwhile, a novel bandwidth enhanced triple-couple-line coupling element is proposed to allow aircraft platform flush-mounted designs. A scaled model of the proposed aircraft-integrated antenna array system was fabricated to experimentally verify the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

A systematic approach for in-band scattering cross-section (SCS) reduction of a U-slot patch antenna is proposed in this letter. Characteristic mode (CM) analysis is conducted on the U-slot patch antenna to visualize the resonant behavior of the radiating patch. By examining the modal current distributions, an impedance-loading location for SCS reduction is determined. Value of the loading impedance is directly calculated from the proposed approach to cancel out the scattering-mode SCS and residual SCS. Prototypes of the U-slot patch antennas with reduced SCS and a reference antenna are fabricated. The experimental results show that a maximum in-band SCS reduction of 26 dB has been achieved with the proposed approach. [ABSTRACT FROM AUTHOR]

The large wavelength at high-frequency (HF) band imposes critical challenges in platform conformal HF antenna designs, especially when multiple HF antennas are required in multifunction aircraft electronic systems. This paper presents an approach for the design of the aircraft-integrated multiantenna system based on the theory of characteristic modes (CMs). By investigating the CMs of the aircraft body in the entire HF band, three types of radiation patterns are synthesized at three frequency bands centered at 8, 18, and 28 MHz, respectively. The synthesis is achieved through the linear weighting combinations of the first few dominant CMs, and a multiobjective evolutionary algorithm is implemented to seek the complex weighting coefficients in each band. Following the theoretically synthesized radiating currents, three pairs of exciters are then designed and flush mounted on optimal locations over the aircraft. Furthermore, properly designed LC matching networks are introduced in each exciter to get good impedance matching in each band. Because of the large physical size of the aircraft, scaled model of the proposed aircraft-integrated multiantenna system was fabricated and experimentally verified. Measurement results are in good agreement with simulated results and demonstrate the effectiveness of the proposed approach in the designs of HF aircraft-integrated multiantenna systems. [ABSTRACT FROM AUTHOR]

This paper proposes a dual-band dual-polarized planar antenna array with flat-top and sharp cutoff radiation patterns for 2G/3G/LTE base stations. The array consists of $8 \times 8$ antenna elements arranged with nonuniform spacings and is assigned with optimized nonuniform excitations to achieve flat-top and sharp cutoff radiation patterns with low sidelobes. The radiating element consists of two square-shaped PCB boards. Extra adjustable coupling elements are introduced in the H-shaped patches to improve the impedance matching performance in an array environment as well as to reduce the size of the antenna element. In the 1.71–2.69 GHz band, the dual-polarized radiating element exhibits stable radiation patterns, excellent impedance matching (VSWR < 1.5), and high isolations (>40 dB). Frequency band selective variables are defined to group the antenna elements. They are optimized along with the element spacings and complex excitations in the optimizer to ensure stable flat-top radiation patterns. Rectangular-shaped baffles are introduced to reduce mutual couplings. A prototype of the $8 \times 8$ antenna array has been fabricated and measured. The results indicate that the proposed dual-band dual-polarized planar array achieves a half-power beamwidth of 50° ± 5° in both the H-plane and E-plane. The proposed antenna and its array exhibit attractive potentials for 2G/3G/LTE base station applications. [ABSTRACT FROM AUTHOR]

In this letter, a wideband dual-polarized slot antenna is presented. The proposed antenna is designed in a systematic way using the theory of characteristic modes for slot apertures. An H-shaped slot in an infinite ground plane is used as the initial structure for further optimization design. Magnetic characteristic currents for the first four modes of the slot are investigated. To enhance the bandwidth (BW) of the antenna, the geometry of the slot antenna is then modified based on the clear physical insights obtained from the modal analysis. In addition, two pairs of differentially fed capacitive coupling elements are introduced to excite the first two modes of the slot, and an integrated wideband feeding network is designed. An antenna prototype in WLAN 2.4 GHz band is fabricated. Experimental and simulated results show that the proposed dual-polarized slot antenna has a wide BW and good dipole-like radiation characteristics. Compared with the initial H-shaped slot antenna, the BW of the proposed antenna is enhanced from 17% to 46%. The measured port isolation over the entire frequency band is about 26 dB, and the cross-polarization level is over 28 dB for the two polarizations. [ABSTRACT FROM AUTHOR]