Nicolas Capet

Continuous Transverse Stub Array for Ka-Band Applications

This paper presents a flat, high gain, wide scanning, broadband continuous transverse stub (CTS) array. The design procedure, the fabrication, and an exhaustive antenna characterization are described in details. The array comprises 16 radiating slots and is fed by a corporate-feed network in hollow parallel plate waveguide (PPW) technology. A pillbox-based linear source illuminates the corporate network and allows for beam steering. The antenna is designed by using an ad hoc mode matching code recently developed for CTS arrays, providing design guidelines. The assembly technique ensures the electrical contact among the various stages of the network without using any electromagnetic choke and any bonding process. The main beam of the antenna is mechanically steered over ±40° in elevation, by moving a compact horn within the focal plane of the pillbox feeding system. Excellent performances are achieved. The features of the beam are stable within the design 27.5-31 GHz band and beyond, in the entire Ka-band (26.5-40 GHz). An antenna gain of about 29 dBi is measured at broadside at 29.25 GHz and scan losses lower than 2 dB are reported at ±40°. The antenna efficiency exceeds 80% in the whole scan range. The very good agreement between measurements and simulations validates the design procedure. The proposed design is suitable for Satcom Ka-band terminals in moving platforms, e.g., trains and planes, and also for mobile ground stations, as a multibeam sectorial antenna.

Active Impedance of Infinite Parallel-Fed Continuous Transverse Stub Arrays

This paper introduces a rigorous and effective modeling framework for the continuous transverse stub (CTS) array, based on a spectral Greens function approach. A multimodal expansion of the equivalent currents over the slots is used to derive an accurate expression for the active impedance of an infinite array. This formula is validated through comparisons with full-wave simulations when the array scans are in principal planes. The mathematical formulation highlights the broadband properties of CTS arrays and accurately predicts the impact of the geometrical parameters on the active impedance, as a function of frequency and scan angle. The discussion of the results provides physical insights to outline effective design strategies.

Optimum High Impedance Surface Configuration for Mutual Coupling Reduction in Small Antenna Arrays

In this paper, the electromagnetic properties of two difier- ent High Impedance Surfaces (HIS) with or without Electromagnetic Band Gap (EBG) in difierent conflgurations are investigated for mutual coupling reduction in small antenna arrays. The resonant mechanisms of these structures are studied using transmission calculations in a par- allel plate waveguide. An optimum conflguration is then proposed. It is shown that a good isolation performance can be achieved without the need of metallic vias when the structure is embedded in a metal- lic cavity, which limits signiflcantly the number of HIS cells needed to perform a good isolation and the cost of manufacture.

Field distribution of rectangular waveguides with anisotropic walls by using the modal theory

This article presents a new analytical approach to calculate very rapidely the field distribution in rectangular waveguides with anisotropic walls.

Modal Theory for Waveguides With Anisotropic Surface Impedance Boundaries

The modal theory for propagation in structures with constant anisotropic surface impedances as a boundary condition is developed for cylindrical waveguides and rectangular waveguides with vertical anisotropic surfaces. Dispersion diagrams for these waveguides are computed for various sets of surface impedances. The results are then validated by comparison, using commercial software. These results confirm a number of interesting properties of such waveguides with anisotropic surface impedances: the cutoff frequency can be drastically lowered, and left-handed mode propagation in a given frequency band can be obtained. The development of this theory can open the door to the development of new design tools for various applications using guided structures such as small waveguides, filters, positive phase shifters, or horns with excellent radiation properties.

Implementation of Radiating Aperture Field Distribution Using Tensorial Metasurfaces

This paper deals with the design of tensorial modulated metasurfaces able to implement a general radiating aperture field distribution. A new aperture synthesis approach is introduced, based on local holography and variable impedance modulation. In particular, it is shown that tensorial metasurfaces can be used to generate general radiating distribution (phase and amplitude). In addition, a step-by-step algorithm is presented. In order to validate the method, several solutions are presented at 20 GHz which implement aperture distributions able to radiate different beams with general polarization.

Mode Matching Analysis of an E-Plane

We present a numerical model for the analysis of an E-plane right-angle bend in parallel-plate waveguide (PPW), with a single square step for matching purposes. This design can achieve wideband matching and can be implemented using hollow waveguides as well as multilayer printed circuit boards. An even-and odd-mode analysis is performed exploiting the symmetry of the structure. Two auxiliary problems are defined considering the bisecting plane of the bend as a perfect electric conductor or a perfect magnetic conductor, respectively. They are solved using a mode matching method. The mathematical derivations are discussed in detail. The proposed procedure can be embedded in efficient tools for the analysis of complex PPW systems, such as feed networks for antenna arrays.

90^{\circ }

A new method to rapidly design 2D metamaterials for rectangular waveguides by rebuilding their dispersion properties is proposed. The Modal Expansion Theory (MET) is revisited for theoretical surfaces with fixed surface impedances ZS . Then, it is pursued for real dispersive anisotropic surfaces, which have surface impedances that are dependent on the frequency and the incidence angle. An algorithm which calculates the correct incidence angle of the guided electromagnetic mode at each frequency is presented. By including this algorithm in the MET and by combining it with a code based on the Finite Element Method (FEM) to calculate the surfaces impedances, dispersion diagrams of waveguides with real 2D anisotropic walls are correctly rebuilt. This is validated by comparing the results for two different metamaterials, corrugationand T-structure, with those obtained using a commercial software.

Bend With a Square Step in Parallel-Plate Waveguide

In order to clearly analyze the fundamental changes when dealing with OAM waves, we try to simplify a conventional point to point microwave link. The geometrical configuration is then reduced to face to face, co-axial, annular antenna arrays. Under assumptions of uncoupled elementary sources and ideal Beam Forming Network, the global link budget is derived from an original asymptotic development and analytically exhibits the topological charge effect. A new expression for antennas Gain is then obtained, surprisingly increasing with the topological charge l. The specific decrease previously discussed by Tamagnone with respect to the distance is found again.

Modal Analysis of Rectangular Waveguides with 2D Metamaterials

We present a low-profile, high-gain continuous transverse stub (CTS) array with wide-scanning capabilities. It achieves state-of-the-art performance by employing just 16 slots fed by a corporate feeding network in parallel plate waveguide technology. A pillbox coupler, based on a parabolic reflector, provides the linear source exciting the network. The beam is steered in H-plane by moving the input horn in the focal plane of the reflector. The radiated properties have been optimized in the 27.5-31 GHz band, but are stable up to 40 GHz. In the targeted band, the antenna is matched below -15 dB and the efficiency is > 80% within a ±30° scanning range. For broadside operation at 29.25 GHz, efficiency and peak gain are 93% and 28.9 dBi, respectively. This design represents a flat and cost-effective solution for high-performance Satcom Ka-band terminals and mobile ground stations.