We study the radar cross section (RCS) property of an aircraft considering the electromagnetic (EM) characteristics of a frequency selective surface (FSS) radome, mounted on the aircraft. Instead of full-wave methods, we utilize high-frequency methods, such as the shooting and bouncing rays (SBR), physical theory of diffraction (PTD), and flat model, taking a significant computational efficiency. Based on the developed algorithm, we analyze monostatic and bistatic RCSs of the aircraft equipped with either single- and multi-layer dielectric, FSS, or PEC radomes in terms of frequency and polarization. Our calculations are validated by comparing with those of the commercial EM simulator with significant computational efficiency. The present numerical study indicates that including the radome EM characteristics into the overall aircraft RCS study is crucial for the accurate RCS estimate

In this paper, we analyze the radar cross section (RCS) of an integrated mast and present the optimized mast shape for RCS reduction. The RCS is simulated using commercial electromagnetic (EM) software based on the shooting and bouncing rays (SBR) method and the diffraction fields at the edges are also considered. Threat frequencies, threat regions and cardinal points are first defined considering the operational environments of a naval vessel. We calculate and analyze the RCS of the integrated mast in terms of the threat frequencies, the shapes of the integrated mast and the direction and polarization of the incident waves. The shape of the integrated mast is optimized based on the shaping technique. The optimized mast has low RCS properties in the primary threat sectors except for the exceptional angle regions.

In this paper, we numerically study a curved frequency selective surface (FSS) radome, which encloses a waveguide slot array antenna operating at 10GHz, using the ray tracing technique and flat model. The transmission loss (TL) and boresight error (BSE) are calculated for various degrees of freedom, such as elevation and azimuth angular scanning or gimbal systems of array antennas to examine the electromagnetic properties of the curved FSS radome. Our calculations of radiation patterns, TL, and BSE for a multi-layered dielectric radome are compared with those of a commercial EM solver for validation. Importantly, we quantify phase distortions, incurred by the curved FSS radome, using the insertion phase delay (IPD) of transmitted fields on the radome surface. Thereby, we demonstrate that the BSEs strongly depend on (1) the spatial distribution of phase distortions on the radome surface and (2) their average level. The present method is highly suited for analyzing radomes with arbitrary surface patterns inserted.

This work introduces a refined technique for the estimation of films permittivity within the Ka-band using free-space measurement method. Addressing the challenge of wrong solutions in permittivity estimation, our approach incorporates a frequency-dependent objective function, to find a unique estimation solution. We apply this technique to a variety of thin and flexible substrates, including cycloolefin polymer (COP), polyethylene terephthalate (PET), and polyimide (PI) films, and quantitatively analyze the uncertainty on the estimated permittivity and loss tangent. The proposed technique can offer a method for determining the permittivity of not only thin media but also flexible printed circuit boards used for circuits and antennas.

This paper presents a fan-beam lens antenna design for IR-UWB through-wall human detection radar applications operating in the 1-8 GHz. The proposed fan-beam lens antenna integrates a dielectric lens, designed by adjusting the lengths of dielectric slabs and air layers, with a Vivaldi antenna to achieve a fan-beam pattern characterized by a narrow beam width in the E-plane while maintaining a wide beam width in the H-plane. The antenna demonstrates excellent time-domain characteristics with a high fidelity factor exceeding 0.93, low reflection signal ringing, and maintained narrow beam width in the E-plane for far-field pulse radiation patterns. Through experimental validation, the antenna achieved SNR improvement due to concentrated signal propagation, enabling stable human detection at distances beyond 5m through walls. The wide H-plane beam width allows effective detection of subjects in various postures, including lying positions. The proposed antenna design shows promising potential for various applications including disaster site search and rescue, building surveillance, fall detection in care facilities, non-contact vital sign monitoring, and smart home occupancy detection systems.

This paper presents an ultra-thin, ultra-wideband linear-to-circular (LTC) polarization converter based on the crossed-dipole-shaped metasurface. The unit cell of the crossed-dipole-shaped metasurface is made up of two identical T-shaped dipole arms, which are orthogonal to each other and are connected with a diagonal microstrip line. The LTC polarization converter is placed on the top side of an ultra-thin single-substrate layer with a profile size of 0.035 λ _o , where λ _o is a free space wavelength at the center frequency of the axial ratio bandwidth (20.89 GHz). The proposed design shows nearly equal transmission amplitude and stable phase difference of nearly 90° of the two orthogonal components of transmitted waves in a wide frequency range. The right-hand circularly polarized (RHCP) component of the transmitted wave is much larger than the left-hand circularly polarized, and thus, the transmitted wave is RHCP. Numerical and experimental results showed that the polarizer could realize an ultra-wideband LTC polarization conversion at both x- and y-polarized incidences in the frequency range from 11.66 to 30.12 GHz, which is a fractional bandwidth of 88.4%, and it can maintain a stable polarization conversion performance under large-range incidence angles. In addition, a high total transmittance of the electromagnetic wave was obtained.