As a classical physical phenomenon, the Brewster effect describes the zero-reflection behavior of a polarized planar electromagnetic wave impinging on the surface of a linear homogeneous isotropic non-magnetic media. Traditionally, this classical effect is usually restricted to particular incident angle and polarization due to the scarcity of natural material with ideal magnetic response, and the research on generalizing the classical Brewster effect was only of theoretical interest. Nevertheless, the advent of metamaterials and metasurfaces brings new vitality to the research field of the so-called generalized Brewster effect (GBE), where many efforts have been done for seeking zero-reflection of planar wave at any frequency, any polarization and any incident angle. The physical implementation of GBE has enabled people to gain a greater degree of freedom for modulating electromagnetic waves in a wide range of frequency, polarization and angle of incidence. Therefore, the GBE has been demonstrated to have important applications in many fields such as wireless communications, phased array antennas, nanophotonics and even chemical sensing.

So far, both physical mechanisms and experimental methods of GBE have been explored in a variety of physical systems. Many theoretical methods for explaining the GBE mechanism have been proposed, such as optical filter theory, transfer matrix method, molecular optics method and so on. However, most of these methods are either lack of intuitive physical understanding or only applicable to specific physical scenes, and thus cannot provide useful guidelines for GBE design. Moreover, in the past research, the realized GBEs are often fixed at some frequencies or incident angles and untunable, limiting their application in varied situations. Hence, a universal and intuitive GBE design principle is highly demanded, and it is important to summarize the existing research on both the general design method and arbitrarily tunable GBE realization. Furthermore, the application aspect of GBE is rarely discussed in literature, and it is worth discussing some novel applications to fill this gap.

In this article, the recent work of our group for realizing tunable dual-polarized GBE is introduced, and two novel applications in the field of millimeter-wave communication and phased array antenna are presented. First, the mechanism and implementation of various published GBE systems are summarized, among which a physical interpretation based on the generalized Kerker effect (GKE) is discussed in detail due to its profound physical insight (Fig. 1, Fig. 2). From the perspective of GKE or multipole destructive interference, a simple and universal design principle for implementing GBE is proposed (Fig. 3), that is, we can construct artificial multipoles to coherently eliminate the radiation of the multipoles intrinsic in the original system at some particular angles. Under the guidance of this principle, we proposed a metasurface composed of artificial metallic structure, and realized an arbitrarily tunable GBE in the microwave band (Fig. 4), where the zero reflection can be realized at the same frequency and same incident angle for the two different polarized incident waves. After that, an application in the scenario of 5G millimeter-wave communication is presented, that is, we designed a single-layer metasurface for realizing dual-polarized ultra-wide-angle high transmission (Fig. 5) and a near-isotropic electromagnetic window suitable for engineering application in 5G communication (Fig. 6). Besides, we noted the consistency between the ideal planar phased array model and the Fresnel reflectance model in the sense of physical image, and pointed out the implications of GBE for wide-angle impedance matching of phased array antennas (Fig. 7). Under this heuristic design idea, a planar slot antenna array with ultra-wide angle scanning performance is presented and discussed (Fig. 8).

The realization of generalized Brewster effect provides the possibility for people to arbitrarily modulate electromagnetic waves of vatious frequencies, polarization and incident angles, and is expected to provide solutions for challenges in both academic and engineering aspects, such as electromagnetic window, wide-angle scanning phased array, angle filter and so on. So far, the GBE has been well studied both theoretically and experimentally, but some research gaps still exist. To sum up, in-depth study is still needed in this field and the future directions may include: the realization of wide-band wide-angle GBE; the application in designing electromagnetic window with angle filter characteristics; the application in designing wide-band wide-angle phased array antennas and the influence of GBE metasurface on antenna performance, and others.