Wideband Active Region Metasurface Antennas

Abstract

Modulated metasurface (MTS) antennas with broadside beam rely on the interaction between a radially modulated equivalent impedance and a surface wave (SW) with cylindrical wave-front, launched by a point source. At the frequency where the SW wavelength matches the period of the impedance modulation, the-1 indexed (leaky) mode of the Floquet-mode expansion in cylindrical-coordinates provides a broadside beam. The mismatch between the SW wavelength and the period of the modulation imposes a limitation on the product bandwidth-gain. Here, we overcome this limitation by exponentially stretching the radial period of the impedance modulation. Doing so, an annular active region is generated on the antenna aperture, which moves from the antenna center to the circular rim as the frequency decreases. This mechanism enables a broadside beam over an extreme large bandwidth. We therefore extend significantly the applicability of these antennas, e.g., to requirements of 30 1.5 dB  gain over 30% bandwidths. Here, an analytical formulation is proposed to treat the active region migration and edge outgoing by a Fresnel-type transition function. This function predicts in closed form the antenna bandwidth and average gain. A more accurate gain versus frequency response is also introduced by an integral formula that accounts for the frequency dependent amplitude distribution of the aperture fields. The theory is validated by full-wave simulations and by measurements of a prototype realized by subwavelength elliptical patches. The presented results show that these antennas can provide a performance difficult to reach by any other flat antennas based on printed technology.

Multibeam Si/GaAs Holographic Metasurface Antenna at W-Band

“…10, when fed through the central port (port 1), the metasurface antenna forms a beam steered at (θ=15°, ϕ=0°) with the antenna directive gain being recorded as 31.9 dBi (measured) and 31.9 dBi (simulated). Similar to the work presented in [23], we use the directivity of the metasurface to calculate the aperture efficiency, which is reported to be 59% for this scenario. Activating port 2, as shown in Fig.…”

Flat Gain Broadband Metasurface Antennas

“…The bandwidth performance can be significantly improved by adopting a period d that changes as a function of the aperture radius [17], [18]. The period d of the modulation in [18] increases exponentially along the radial distance to match the SW wavelength in different annular regions (Fig. 1).…”

Millimeter-Wave and Sub-THz Modulated Metasurface Antennas

“…Practical values of ∆f /f 0 may vary between 3% and 9% when the antenna gain goes from 40 to 28.5 dB. Nonetheless, one can trade gain for larger bandwidths as explained in [4]. Another crucial aspect consists in choosing the most appropriate fabrication technique at each frequency band.…”

“…The IBC modulation in MTS antennas is typically periodic and, by properly choosing the period of this modulation, the -1 mode in the Floquet expansion can enter the visible region and provide the desired radiation effect. Besides polarized and shaped beams [2], this class of antenna can provide multiple-beams [3] and broadband operation [4].…”