Analysis, Simulation and Measurements of CBS Antennas Loaded With Non-Uniformly Biased Ferrite Material

Abstract

When ferrite materials are used in antenna designs, they introduce some interesting and unique performance characteristics. One of the attractive features, for example, is the ability to reconfigure the center frequency of the antenna. In addition, ferrite materials also introduce a number of challenges in the modeling and simulation of such antennas.In order for the ferrite material to be useful in an antenna design, it usually is subjected to an external magnetic field. This field induces the internal magnetic field inside the ferrite material. The internal field plays a pivotal role in the radiation characteristics of the antenna. Thus, from the numerical point of view, accurate computation of this field is critical to the overall accuracy of the analysis. Usually the internal field is non-uniform and its computation is often a rather complex and nontrivial task. Therefore, to facilitate the modeling, simplifying assumptions, which introduce some kind of averaging, are often made.In this study, ferrite-loaded cavity-backed slot antennas are used to demonstrate that averaging procedures can lead to very unsatisfactory results. For instance, it is common practice to assume that the external field is uniform by averaging its distribution. One of the pivotal points in this study is the demonstration that the external magnetic field plays a very significant role and should be included in the modeling without averaging, if the accurate results are to be attained. Results presented in this study clearly support this argument. A procedure which avoids such averaging is presented and verified by comparing simulations with measurements. In contrast to the previous formulations, the modeling methodology developed in this dissertation leads to accurate results which compare very well with measurements for both uniform and non-uniform field distributions. The utility of this methodology is especially evident for the case when the magnetic field is severely non-uniform. i

Gain and Bandwidth Enhancement of Ferrite-Loaded CBS Antenna Using Material Shaping and Positioning

“…Such an electric field distribution, with weak electric fields both at the aperture and corners, leads to a low gain and impedance mismatch. This resonant frequency is much higher than that of the geometry investigated in [1]. To maintain the resonant frequency low, larger currents were applied to the coil One of the solutions to overcome the reduction in the resonant frequency sensitivity is to introduce more ferrite material on both sides of the cavity, as shown in Fig.…”

“…The first step is to find out the reasons for the low gain and poor impedance match of the ferrite-loaded CBS antenna which was reported in [1]. To overcome these drawbacks, other configurations of ferrite material will be suggested.…”

“…In [1], the emphasis was on the modeling of the non-uniform applied magnetic field and non-uniform magnetic field within the ferrite specimen. It was demonstrated that assuming a uniform magnetic field does not always lead to an acceptable approximate solution.…”

Gain and bandwidth enhancement of ferrite-loaded circular cross-section CBS antenna

“…In [1], the nonuniform applied magnetic field and nonuniform magnetic field internal to the ferrite specimen was modeled. In [2], some design guidelines to enhance the gain, impedance match and tunable bandwidth of a rectangular cross-section cavity was developed.…”

Electrically small ferrite antenna gain with dc magnetic field for mobile device application

“…Therefore, low loss ferrite having large l r and e r is indispensable [8,9]. A dc bias magnetic field was applied to a ferrite antenna to lower magnetic tangent loss, thereby improving antenna gain [10][11][12][13][14][15][16][17]. It was observed that antenna gain was improved with the dc magnetic field.…”