A novel method for a beam pattern reconfigurable circularly polarized (CP) transmitarray antenna based on passive metasurface is proposed by a rearrangement of source antennas. Two source antennas among eight source antennas are selected for the fine beam steering. The beam steering angle can be finely controlled by the positions and phase difference of the source. Moreover, this kind of transmitarray antenna can be utilized to generate multibeam by the combination of the source antennas for radiation to different directions. To verify its feasibility, the planar CP source antenna is designed to operate at 5.8 GHz. Also, the metasurface consists of four layer separated by four substrates to cover full transmission phase variation of 2π, and the metallic layers are designed to circular patches. As a result, the steering angle is experimentally observed at each 0, +20, and +40°, and dual beam radiating to −30 and +30° also is measured.

In this paper, we have presented an equation for estimating the gain of a Fabry-Perot cavity (FPC) antenna with a finite dimension. When an FPC antenna has an infinite dimension and its height is half of a wavelength, the maximum gain of that FPC antenna can be obtained theoretically. If the FPC antenna does not have a dimension sufficient for multiple reflections between a partially reflective surface (PRS) and the ground, its gain must be less than that of an FPC antenna that has an infinite dimension. In addition, the gain of an FPC antenna increases as the dimension of a PRS increases and becomes saturated from a specific dimension. The specific dimension where the gain starts to saturate also gets larger as the reflection magnitude of the PRS becomes closer to one. Thus, it would be convenient to have a gain equation when considering the dimension of an FPC antenna in order to estimate the exact gain of the FPC antenna with a specific dimension. A gain versus the dimension of the FPC antenna for various reflection magnitudes of PRS has been simulated, and the modified gain equation is produced through the curve fitting of the full-wave simulation results. The resulting empirical gain equation of an FPC antenna whose PRS dimension is larger than 1.50 has been obtained. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. ⓒ

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In this letter, the null steering of a circular array is presented using a modified array factor (AF) for a global positioning system (GPS) anti-jam. The seven radiating elements were designed using a mu-zero resonance (MZR) circularly polarized (CP) antenna arranged toward the center. Since the radiating elements, which are arranged toward the center, have a CP characteristic, the AF of the seven radiating elements has to be modified considering the rotation angle of the nth radiating element. The phases of input ports can be calculated to implement a nulling of radiation patterns where the modified AF is zero. To verify the modified AF for null steering in the desired direction, two cases of power dividers operating in L2 band (1.2276 GHz) were fabricated to achieve pattern nulling at a certain angle. The modified AF can be confirmed by a comparing the simulated and measured radiation patterns.

Stimuli‐responsive materials can sense environmental conditions and respond in predesigned ways. Such intelligent materials have a wide range of potential applications; however, they are usually limited to rather simple geometries. 3D printing is suitable for complex 3D objects with fine details. In particular, four‐dimensional (4D) printing of smart materials can be ideal for various stimuli‐responsive structures with highly enhanced functionalities. However, no studies on active, reconfigurable photonic structures in which external stimuli can induce a drastic response change have been reported. The 4D printing of stimuli‐responsive, Fano‐resonant structures that can exhibit sharp spectral resonances in an optimized lattice structure is demonstrated here. Specifically, shape memory polymers are employed and resonant microwave structures that undergo structural reconfiguration upon heating are demonstrated. When heated above the glass‐transition temperature, disordered lattices are transformed into a permanent, ordered lattice, resulting in a drastic change in their transmission spectrum. The origin of the sharp Fano resonance and spectral collapse is further elucidated using angle‐dependent transmission spectra. 4D printing could be a very interesting route for microwave active photonics. It can enable active reconfiguration without an electric power supply. It could therefore be useful in remote sensing applications such as long‐distance environmental monitoring.