The Sievenpiper high-impedance surface is a periodic structure characterized by a substrate filled with an array of vertical vias, capped by a capacitive frequency selective surface (FSS). It functions as the ideal antenna groundplane for wireless applications because it simultaneously enhances the gain of the antenna as it suppresses the surface waves associated with it (thus reducing the undesired back-lobe and the reactive coupling to nearby circuits). These two properties are known to occur approximately over the frequency bandwidth where the phase of the reflection coefficient of the surface changes from +90 to 90. Since this behavior takes place at frequencies where the unit cell of the structure is small compared to the wavelength, it can be modeled in terms of a layered homogeneous material where each layer has an anisotropic magneto-dielectric tensor. These tensors, readily derived using an effective medium model, can be designed to obtain independent control of the bandwidths of gain increase and surface wave suppression. Based on a transverse resonance model of the effective medium material model, it is shown that Sievenpiper high-impedance surfaces exist that can suppress TE surface waves alone or TM surface waves alone, or both TE and TM surface waves at the same time. Maximum TM surface wave suppression bandwidth is obtained when the distance between the vias in the via array is as close as possible to 2. Maximum TE bandwidth is obtained when the conductors of the capacitive FSS offer maximum blockage to the normal magnetic field of the wave. A reduction of the transverse resonance solution to nearly closed form is used to obtain a simple picture of the design space available when the desired operating frequency is fixed.

No abstract

It is shown using full-wave simulations that several of the conventional assumptions made for extracting permeability data from a microstrip permeameter are not justified. In particular, the proportionality between the measured effective permeability in the device and the true permeability of the film is not a constant. It is a function of the permeability of the film, its geometry and the dimensions of the microstrip permeameter. A model exploiting the analyticity of the function relating effective to true permeability is used to derive this proportionality function for our device and the results are confirmed using full-wave simulations. The error incurred by not using this method and employing a reference sample for calibration or by using saturation magnetization “Ms” and anisotropy field “Ha” is shown to be anywhere between 5% and 40% and possibly even more. Our measurement set up is capable of measuring films as thin as 300 nm with a relative permeability as low as 10.

The artificial magnetic conductor (AMC) is a textured ground plane that presents a high impedance to incident waves and nearby horizontal antennas over a prescribed frequency range. In addition, it suppresses the propagation of both transverse electric (TE) and transverse magnetic (TM) surface waves, thus concentrating the radiation from a horizontal antenna into the upper half‐space. The resulting reduced backlobe and reduced mutual coupling to any other antennas on the same surface, combined with the high input impedance, make the AMC an ideal gain‐enhancing ground plane for ultrathin antennas. It is shown that these desirable features of are derived from the AMC's effective anisotropic magnetodielectric constitutive properties. Analysis and design approaches are given that enable the control of these properties according to the desired frequency and bandwidth of operation and the amount of surface‐wave suppression needed. Examples of the latest applications of AMC are given, as well as a brief history of its inception.

No abstract