Joey R. Bray

A Wideband Transmitarray Using Dual-Resonant Double Square Rings

A four-layer transmitarray operating at 30 GHz is designed using a dual-resonant double square ring as the unit cell element. The two resonances of the double ring are used to increase the per-layer phase variation while maintaining a wide transmission magnitude bandwidth of the unit cell. The design procedure for both the single-layer unit cell and the cascaded connection of four layers is described and it leads to a 50% increase in the -1 dB gain bandwidth over that of previous transmitarrays. Results of a 7.5% -1 dB gain bandwidth and 47% radiation efficiency are reported.

Theory and Design of a Tunable Antenna on a Partially Magnetized Ferrite LTCC Substrate

For the first time, a theoretical model is presented to predict the frequency tuning of a patch antenna on a partially magnetized ferrite substrate. Both extraordinary (E) and ordinary (O) modes of the antenna are studied. The permeability tensor of the partially magnetized ferrite is calculated through the proposed theoretical model and is subsequently used to analyze the antennas performance in a microwave simulator. Prototype antennas were built, using two different bias windings, embedded in a multilayer ferrite LTCC substrate, to demonstrate E and O mode tuning. The use of embedded windings negates the requirement of bulky electromagnets, thus providing miniaturization. The concept also eliminates the demagnetization effect, thus reducing the typically required bias fields by 95%. The prototype measurements at 13 GHz demonstrate an E-mode tuning range of 10%. The proposed theoretical model has been validated by simulations and measurements. The design is highly suitable for compact, light-weight, tunable and reconfigurable microwave systems.

Ferrite LTCC-Based Antennas for Tunable SoP Applications

For the first time, ferrite low temperature co-fired ceramic (LTCC) tunable antennas are presented. These antennas are frequency tuned by a variable magnetostatic field produced in a winding that is completely embedded inside the ferrite LTCC substrate. Embedded windings have reduced the typically required magnetic bias field for antenna tuning by over 95%. The fact that large electromagnets are not required for tuning makes ferrite LTCC with embedded bias windings an ideal platform for advanced tunable system-on-package applications. Measurements of rectangular microstrip patch antennas on a ferrite LTCC substrate display a maximum tuning range of 610 MHz near 12 GHz. Two different bias windings and their effect on the antenna performance are discussed, as is the effect of antenna orientation with respect to the bias winding. The antenna radiation patterns are measured under biased and unbiased conditions, showing a stable co-polarized linear gain.

Microwave and Magnetostatic Characterization of Ferrite LTCC for Tunable and Reconfigurable SiP Applications

The material property extraction techniques for an emerging commercial ferrite LTCC (low temperature co-fired ceramic) tape are presented. These properties are evaluated in the context of tunable and reconfigurable microwave components for wireless communications. Relevant parameters for microwave design, including relative permittivity epsivr, relative permeability mur and loss tangent tandelta, are presented. Measurements performed at 9.86 GHz and 27.2 GHz yield an epsivr of 13.6 and tandelta values of 0.004 and 0.001 respectively. For the first time, a completely embedded LTCC toroid transformer is utilized to extract the magnetostatic properties with greater accuracy than a solenoid transformer. These measurements reveal a saturation flux density of nearly 400 mT, a remanence of 250 mT, and a coercivity of 430 A/m. The peak relative linear permeability of the ferrite is 370. The low loss tangent and the high degree of variability of the ferrite properties with bias indicate its suitability for tunable and reconfigurable microwave SiP (system in package) applications.

A broadband transmitarray using double square ring elements

Dual-resonant double square ring elements are applied to the design of a four-layer transmitarray operating at 30 GHz. The design procedure is described and results of a 7.5% −1 dB gain bandwidth and 47% radiation efficiency are reported.

Analysis of Electrically Small Slot-Fed Substrate Lens Antennas Using the Physical Optics Hybrid Method

Typical limitations of integrated antennas such as bidirectional radiation, power loss via substrate modes, and broad radiation patterns can be corrected using a substrate lens. In this paper, various slot-fed substrate lens antenna (SLA) configurations are examined, and a novel hybrid physical optics analysis technique, suitable for electrically small geometries, is presented. Based on this method, directivity and reflection loss calculations for elliptical and hyperhemispherical synthesized lenses are carried out. It is found that the conditions for maximum directivity and minimum reflection loss do not coincide, and thus certain performance compromises are necessary. The results are confirmed experimentally.

Induced currents on electric detonators for improvised explosive device pre-detonation

Electric hotwire detonators are commonly used in the construction of improvised explosive devices. This paper explores the electromagnetic susceptibility of a commercial detonator when it is exposed to continuous wave, linearly-polarized plane wave radiation. The aim is to assess the feasibility of inducing sufficient current in the detonator to cause its explosion. For selected lead wire configurations, analytical formulae are used to predict the resonant frequencies of the detonators. Computer modeling is then used to simulate the induced current on the detonators bridge wire during electromagnetic illumination. The predictions are compared with experimental measurements of induced current on commercial detonators.

Ferrite-Filled Antisymmetrically Biased Rectangular Waveguide Isolator Using Magnetostatic Surface Wave Modes

The complex dispersion diagram of an antisymmetrically biased ferrite-filled rectangular waveguide (RWG) is investigated, revealing that the waveguide supports a band-limited unidirectional magnetostatic surface wave mode. This mode is subsequently used to design a novel RWG isolator. A parametric analysis including loss is performed to characterize the isolation band. A prototype waveguide isolator has been fabricated using a small metallized ferrite substrate measuring 30-mm long, 6-mm wide, and 0.8-mm high. Measurements in the 10-20-GHz range confirm the theory and mark the first time that a ferrite isolator has been built using a completely filled RWG. The fabricated 6-mm-long waveguide isolator provides a peak isolation figure-of-merit (IFM) of 42.5 dB at 15.4 GHz. An IFM of over 16.2 dB is sustained from 15.2 to 18.3 GHz (18.5% bandwidth). The simplicity of this compact isolator makes it amenable to package-scale integration, such as in ferrite low-temperature co-fired ceramic, where it could be readily embedded within a multichip package.

Study of a Ferrite LTCC Multifunctional Circulator With Integrated Winding

This paper shows a study of a new ferrite low-temperature cofired ceramic (LTCC) circulator with integrated winding. The external magnets used in traditional circulators must be strong to overcome the ferrites demagnetization factor. The novel circulator presented herein uses an embedded winding within the ferrite to magnetize the material from the inside, thereby significantly reducing the demagnetization effects. Because of the controllability of the bias field, the resulting device is also multifunctional: when the windings are energized by a current, the device operates as a dynamic circulator in which the circulation direction can be changed by switching the direction of the current. If an external magnet is placed on the circulator, its operating frequency can be changed by adjusting the bias current. Unlike other LTCC circulators with external magnets, the proposed device can even operate as a power splitter by removing the bias current. A circulator prototype has been characterized in three states: unbiased, biased by windings, and biased by windings and external magnets. When no current is applied, the transmission of each port is about -5 dB with a return loss better than 20 dB at 14.8 GHz. When a current of 300 mA is injected into the windings, the measured insertion loss and isolation of the circulator are approximately 3 and 8 dB, respectively, whereas the return loss is better than 20 dB at 14.2 GHz. When external magnets are added in addition to a current of 200 mA, the insertion loss and isolation improve to 1.6 and 23 dB, respectively, at 14.2 GHz. The variation of the circulators working frequency is 0.6 GHz. This is achieved first by the change of internal magnetization M when current is less than 120 mA, then the heat due to the winding increases the ferrites μeff, leading to more frequency shifting. The total size(L×W×H)is8mm×8mm×1.1mm.

Left-handed behaviour in a ferrite-filled, antisymmetrically-biased rectangular waveguide phase shifter

Over the last few years, artificial materials (metamaterials) demonstrating so-called left-handed behaviour have been reported [1,2]. Left-handed materials have a peculiar property in that their group velocity is negative with respect to their phase velocity. During the course of an investigation into a new rectangular waveguide phase shifter, it was discovered that the ferrite also supports left-handed propagation, albeit over a very limited range of frequencies. Left-handedness thus also appears to be possible in natural materials, not just in artificial ones. In this paper, the salient features of the ferrite medium inside the phase shifter are presented, and the longitudinal component of the Poynting vector is examined throughout the guides cross-section at multiple frequencies.