Abstract-The recent extension of the orbital angular momentum (OAM) concept from optical to microwave frequencies has led some researchers to explore how well established antenna techniques can be used to radiate a non-zero OAM electromagnetic field. In this frame, the aim of the present paper is to propose a new approach to generate a non-zero OAM field through a single patch antenna. Using the cavity model, we first analyze the radiated field by a standard circular patch and show that a circular polarized (CP) TM nm mode excited by using two coaxial cables generates an electromagnetic field with an OAM of order ±(n − 1). Then, in order to obtain a simpler structure with a single feed, we design an elliptical patch antenna working on the right-handed (RH) CP TM 21 mode. Using full-wave simulations and experiments on a fabricated prototype, we show that the proposed antenna effectively radiates an electromagnetic field with a first order OAM. Such results prove that properly designed patch antennas can be used as compact and low-cost generators of electromagnetic fields carrying OAM.
We present the design of an innovative wire antenna able to automatically hide or reveal its presence depending on the waveform of the received/transmitted signal. This unconventional behaviour is achieved through the use of a novel waveformselective cloaking metasurface exploiting a meander-like unit cell loaded with a lumped-element circuit capable to engineer the scattering of the antenna depending on the waveform of the impinging signal. Due to the time-domain response of the lumped-element circuit, the antenna is able switching its scattering behaviour when interacts with either a pulsed wave (PW) or a continuous wave (CW) signal. The proposed configuration paves the way to a new generation of cloaking devices for intelligent antenna systems, extending the concept of antenna as a device capable to sense the external environment and change its electromagnetic behaviour accordingly.
Recently, our group has proposed a self-filtering linearly polarized horn antenna that can be used to reduce the noise captured by regular horn feeds. However, the approach used in that design is inherently limited to linear polarization, while possible interesting applications are likely in satellite receiving systems, which are typically based on circularly polarized signals. In this letter, we propose a new approach to obtain a filtering horn antenna working in circular polarization. The proposed solution is based on the design of a linear-to-circular polarization transformer that consists of a complementary electrically small resonator etched on a metallic screen. We first show that this component is able to transform the linear polarization of a regular rectangular waveguide working on the fundamental mode into a circular one. Then, integrating this polarization transformer in a conical horn, we show how it is possible to obtain a circularly polarized filtering horn antenna. The numerical simulations and the measurements performed on a prototype prove that the proposed structure can be effectively used to design a bandpass filtering horn antenna for circularly polarized signals
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