Sharif Digital Repository

In this paper, a novel travelling-wave printed Frequency Scanning Antenna (FSA), which can be used for imaging purposes, is proposed. All sample designs scan the space symmetrically about the broadside direction. For different scanning ranges, two low profile antennas are designed on a 6.6 mils thick Rogers 4350 board substrate layer. Impedance bandwidth of the first one covers 6.5GHz, from 29.5GHz to 36GHz, and this antenna scans 56° in angular space. The second antenna has 5.6GHz bandwidth from 30.6GHz to 36.2GHz, and scans 98° in angular space by means of switching the input port. The average gain and the Side-lobe level (SLL) of the first and the second antennas are 11.46dBi, 12.8dB, and... 

In this paper a closed-form expression is introduced to calculate slot shape of long slot leaky wave waveguide antennas at its fundamental mode of operation with minimum side lobe level (SLL). The derived equation is a function of geometrical parameters of the structure. This is an advantage because they show a clear relationship between geometrical parameters of the antenna and radiated field that allows intelligent modification of the pattern. The Gaussian slot is used to obtain the best radiation pattern with lowest SLL. The results obtained by introduced formula are compared with the full wave commercial simulator such as HFSS software which confirms the accuracy of the introduced... 

we propose a graphene-covered subwavelength metallic grating where the Fermi level of graphene is sinusoidally modulated as a leaky-wave antenna at terahertz frequencies. This structure can convert spoof surface plasmon guided waves to free-space radiation due to the tunability of graphene. Analysis and design of the proposed leaky-wave antenna are discussed based on sinusoidally modulated surface impedance. The surface impedance is obtained by an analytical circuit model. The sinusoidal surface impedance is realized using modulation of the conductivity of graphene by applying a bias voltage. The proposed leaky-wave antenna is capable of electronic beam scanning with an almost constant gain... 

In this work, the authors experimentally show Dirac Leaky Wave Antennas (DLWAs) at upper microwave frequencies. For the first time, DLWAs are implemented using simple Parallel plate waveguide (PPW) technology, while yielding desirable radiation features and continuous beam scanning through broadside, as well as extremely low profile, with significant ease of fabrication, making them well suited for Ku band applications such as satellite communication, radar and emerging fifth-generation (5G). A planar Dirac photonic crystal in PPW is shown with a closed bandgap and linear dispersion around broadside. In this work, 1D and 2D PPDLWAs are designed that provide scannable fan and pencil beams,... 

Array scanning method (ASM) is employed to study the input impedance and radiation pattern of a two-dimensional periodic leaky-wave antenna (LWA). The antenna consists of a narrow horizontal strip dipole of arbitrary length underneath a two-dimensional (2D) periodic screen of metallic patches, which acts as a partially reflective surface (PRS), and backed by a ground plane. First, the Green's function in the presence of the 2D array of metallic patches is calculated by means of the ASM and then the current distribution and input impedance of the source dipole are calculated through the electric field integral equation and method of moments. The far-field pattern is computed using the... 

Dirac leaky-wave antennas (DLWAs) are derived from photonic crystals exhibiting Dirac cone dispersion around their Γ-point. DLWAs provide high directive beams and continuous frequency beam scanning, non-fluctuating leakage constant and real non-zero Bloch impedance at and around broadside, due to the closed and linear Dirac dispersion relation around broadside. These features, along with their inherent compatibility for higher frequency designs (larger unit cells compared to metamaterials), make DLWAs an ideal candidate for the upper microwave, mm-wave and terahertz frequencies, and for applications such as radar, 5G, spectroscopy, etc. In this review, we cover the recent developments on... 

Dirac dispersion cones enable remarkable wave phenomena in electronics as well as electromagnetic systems. In this work, the authors experimentally demonstrate for the first time the Dirac leaky wave antennas (DLWAs) at millimetre-wave (mm-wave) frequencies. The demonstrated DLWAs are implemented in the substrate integrated waveguide technology, delivering unprecedented features at high frequencies such as radiation at, and continuous beam scanning through broadside, with ease of fabrication, making these designs well suited for mm-wave applications such as emerging fifth generation and Internet of Things, radar and imaging. It is shown that a planar Dirac photonic crystal can be realised... 

In the majority of leaky-wave antennas (LWAs), the lack of broadside radiation is due to the existence of an open-stopband (OSB) at broadside. In this letter, we present a study on the OSB suppression in LWAs. In particular, we start from a simple unit cell comprising a planar waveguide having alternating open and short sidewalls. The analytical and simulated band structures testify consistently that OSB suppression can indeed be realized by proper design, analytically studied using mode-matching, and further supported by full-wave simulations. An LWA is then implemented using the substrate integrated waveguide (SIW) technology, which provides interesting features such as a high directive... 

In this work, we present a study on the existence of Dirac type dispersion in the simplest of periodic metallic waveguide structures. It is shown that periodic repetitions of two dissimilar waveguides (WGs) can be properly designed to lead to a Dirac type dispersion. A simple theory using circuit modeling is presented to find the condition for Dirac point operation. In addition, mode-matching followed by full-wave simulations validate that the band structure matches that of the theory and shows that a Dirac dispersion can be realized. A Dirac Leaky-Wave Antenna (DLWA) is then implemented using this simple arrangement in substrate-integrated-waveguide (SIW) technology. This DLWA has the...