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We propose to control the radiation patterns of a two-dimensional (2D) point source by using impedance metasurfaces. We show that the radiation patterns can be manipulated by altering the surface impedance of the metasurface. Full-wave simulation results are provided to validate the theoretical derivations. The proposed design enjoys novel properties of isotropy, homogeneity, low profile, and high selectivity of frequency, making it potentially applicable in many applications. We also point out that this design can be implemented with active metasurfaces and the surface impedance can be tuned by modulating the value of loaded elements, like resistors, inductors, and capacitors.

Recently, the concept of metasurface has been very hot. It is two-dimensional metamaterial rather than the previously proposed bulk metamaterials. Also, it enjoys the properties of low profile and low loss, making it very flexible and easy to implement in the real applications [

The impedance metasurface also has various applications in the field of antenna. Oliner and Hessel first put forward the comprehensive analysis of propagation of leaky waves on impedance surface [

In this work, we propose a very simple model, in which a metasurface radiates under the excitation of a 2D point source (or a line source). With proper design of surface impedance of the metasurface, a specific pattern can be magnified and becomes dominant in the total field; hence, the model behaves like the radiation of this pattern. Moreover, the radiation pattern can be manipulated by employing different surface impedances. To demonstrate the validity of the theory, full-wave simulation results are given, including those mimicking the radiations of monopole, dipole, and quadripole. In order to demonstrate the flexibility of our design, the simulation for two metasurfaces is also made. These simulation results agree very well with the theoretical calculations. Throughout the paper, a time-harmonic factor

Let us first consider a cylindrical metasurface in free space. A 2D point source (i.e., a line source) is placed near the metasurface, as shown in Figure

Principle of the proposed model with a cylindrical metasurface and a line source (color online). (a) The three-dimensional depiction. (b) The two-dimensional geometry of the cross section.

In the presence of the metasurface, the induced scattered field

Using (

In order to magnify a specific pattern for radiations, the corresponding scattering coefficient is set to infinite, which can be easily achieved by setting the denominator of (

Using Huygens’ principle, the electric field in the far-field region is calculated to determine the scattering width

Next we perform full-wave simulations to verify the proposed theory, in which the working frequency is set as 10 GHz. Using (

The simulation result of a monopole radiation (color online). (a) The electric field distribution in the

In order to quantify our simulation result, the electric field on a centered circle with radius 0.1 m is extracted from the simulation result. Then the scattering width

Then we choose

The simulation result for a dipole radiation (color online). (a) The electric field distribution in the

We continue to consider the case of quadripole, and the corresponding value of surface impedance is obtained by setting

The simulation result of a quadripole radiation (color online). (a) The electric field distribution in the

Likewise, other radiation patterns, like sextupole and octupole radiations, can also be achieved by setting the order

However, the proposed metasurface can be regarded as a basic unit. And we can put several units to create many other kinds of radiation patterns. In the following part, the simulations of radiation pattern when there are two cylindrical metasurfaces with same parameters are given, in which three cases mean mode

((a), (c), and (e)) The electric field distribution in the

Using (

The total scattering widths versus frequency, in which different surface impedance is considered, including the corresponding monopole, the dipole, and the quadripole cases (color online).

Recently, active devices have been suggested to realize some negative electromagnetic parameters, which may not be attainable in nature. In our work, a negative resistor model was put forward to meet the negative conductivity requirement of an exterior cloak [

With regard to control of surface impedance, we point out that its value can be changed by modulating the parameter of some loaded elements, like resistors, inductors, or capacitors. For example, in Liu’s work, the surface impedance is tuned by voltage-modulation of a varactor diode [

In summary, we have shown that a designed radiation pattern can be achieved by using a line source to excite a metasurface. By selecting proper surface impedance, the radiation pattern of total field can be a magnified monopole, dipole, quadripole, and so forth. This makes it possible to build up a multipolar antenna system with the simple configuration. The most important property of the model is that its radiation pattern is controlled by simply changing the surface impedance rather than modifying the geometrical shape. And this surface impedance is homogeneous and isotropic in contrast with previous holographic impedance surface. Moreover, this model is ultrathin and selective in the radiation frequency.

The authors declare that there is no conflict of interests regarding the publication of this paper.

This work was supported in part by National High Tech (863) Projects (Grants no. 2012AA030402 and 2011AA010202), in part by the 111 Project (111-2-05), and in part by the National Science Foundation of China (Grants no. 60990320 and 60990324). Zhong Lei Mei acknowledges the Open Research Funds of State Key Laboratory of Millimeter Waves (Grant no. K201409) and Fundamental Research Funds for the Central Universities (Grant nos. LZUJBKY-2013-k06, LZUJBKY-2014-43, and LZUJBKY-2014-237).