Tailoring methodology is proposed in this communication to achieve arbitrary frequency response within a wide absorption band. An ultra-wideband absorber utilizing multiple resonances in the unit cell of 3-D frequency-selective structure is utilized as the textile for the proposed designs. Two types are proposed; one is absorptive frequency-selective reflection structure and the other is absorptive frequency-selective transmission structure. These structures have reflection/transmission band within a wide absorption band. Two prototypes are designed, fabricated, and measured to validate the proposed methodology. The first one is an ultra-wideband absorber with 155.7% absorption bandwidth from 1.8 GHz to 14.4 GHz with structure’s thickness of 0.12 λ0 at the lowest absorption frequency. The second one is an absorptive frequency-selective transmission structure with wide absorption bands at both sides of its transmission window. It exhibits 54% and 76% for the lower and upper absorption bands, respectively, with 1 dB insertion-loss in the transmission window. A good agreement is achieved between simulated and measured results.

A methodology for designing a frequency selective reflector with two-sided absorption bands is proposed. This method is based on utilizing multi-mode resonators inside a 3-dimensional (3-D) unit cell to obtain an absorption-reflection -absorption response. Detailed analysis of this 3-D absorptive frequency selective reflector (AFSR) is provided with the aid of an equivalent circuit model to reveal the operating principle. To show the benefit of the new structure in antenna’s radar cross section reduction (RCSR), a dual-polarized 3D-AFSR integrated with monopole and dipole antennas are simulated, fabricated and then measured. Compared with their counterparts with normal ground plane, AFSR-backed antennas have shown a remarkable out-of-band RCSR. The -10 dB RCSR has a fractional bandwidth of at least 64.7% and 41% with center frequencies of 3.4 GHz and 8.3 GHz, respectively. The radiation characteristics of AFSR-backed antennas are nearly maintained. The realized gains are enhanced by 0.9dB and 2.3 dB for monopole and dipole antennas mounted on a 3D-AFSR, respectively.

This paper presents a methodology to control the reflection phase response from a 3-D bandstop structure backed with an absorbing material. An absorptive frequency-selective reflection structure using the cascaded arc-shaped strip resonators and absorbers is utilized to obtain an absorption-reflection-absorption response. The reflection phase response of the structure within the reflection band is then flexibly controlled by top-loaded metallic patches with variable size. An application of this methodology is demonstrated by designing a high-gain and low-radar cross section (RCS) reflectarray. The in-band phase profile of the reflecting surface is constructively designed to collimate the beam in the far field. Meanwhile, the out-of-band scattering from the planar reflector is significantly reduced. Compared with a conventional reflectarray, the radiation performance of the proposed antenna is maintained with an aperture efficiency of 50.1% and directivity of 23.5 dBi. Significant RCS reduction has been achieved with a fractional bandwidth of 76.9% and 17.1% for the lower and upper bands with reduction levels of 10 and 8 dB, respectively.

The replacement of lumped resistors with absorbing materials for absorptive frequency-selective transmission (AFST) structures enables a wider range of applications in low radar cross section (RCS) radomes. However, the transmission band within the absorption band for most absorbers is naturally nonexistent. It is shown that such a limitation can be overcome with the engineered frequency-selective surfaces (FSSs) and microwave absorbers to obtain a frequency response of absorption–transmission–absorption. In particular, a transmission window of low insertion loss within the absorption band is introduced by the integration of bandpass FSS and wideband absorber, while a bandstop FSS in the front minimizes the insertion loss in the passband. This design methodology is successfully demonstrated by two examples of AFST structures with single and dual polarizations.

This paper presents an approach to designing a beam-steerable dipole array with low radar cross section (RCS). A 2-D periodical array of dipole antennas is co-located with absorptive frequency-selective reflection structures (AFSRs) to effectively reduce the out-of-band RCS and maintain a high gain at the in-band frequencies. The AFSR structures consist of 3-D bandstop frequency-selective structure (FSS) and pyramidal-shaped absorbers to provide a reflection band for the dipole array with enhanced front-to-back ratio. Compared with the reference array, the radiation performance of the proposed array is maintained with an aperture efficiency of 70% and a measured peak gain of 21.5 dBi. The beam steering angle is up to ±45°. Meanwhile, more than 10 dB two-sided out-of-band RCS reduction is achieved with a bandwidth of 96.5% and 30% for co-polarization and 142% for cross-polarization, respectively, and the in-band RCS is unchanged.