K. W. Whites

Multiple superstrates technique for a broadband cavity resonance antenna (CRA)

A cavity resonance antenna (CRA) with three dielectric superstrates is examined and its performance is compared to those of the single superstrate CRAs of the lowest two resonances. The broadside directivity, bandwidth, and directivity-bandwidth product of all three antennas are investigated. When compared to the single superstrate CRAs, an appropriately designed three superstrate CRA can enhance to the maximum directivity, the bandwidth, or both, a result that is reflected as more than 75% increase to the directivity-bandwidth product in some cases. Theoretical results are validated by simulation using commercial numerical electromagnetics software.

Economical resistive tapering of bowtie antennas

Resistively loaded bowtie antennas built with discrete resistors have been shown to be a cost effective alternative to resistively graded sheets. Resistors of appropriate values and sizes are commonly available and the additional construction costs in comparison to an unloaded bowtie antenna are minimal.

Easily designed and constructed high impedance surfaces

In this paper, we propose a type of new high impedance surface that is extremely easy to design and fabricate. These new surfaces are formed by properly lumped loading a periodic screen on a metallic-backed substrate. This can result in an extremely effective high impedance surface. In particular, we have shown here that capacitive lumped-element loading of a periodic inductive screen is an easily designed and effective surface that would be inexpensive to fabricate. For practical unit cell sizes on the order of a few millimeters, capacitors on the order of a few picofarads are all that is needed to operate this high impedance surface in the commercial wireless communications bands (0.9-6 GHz). Such capacitors are cheap, readily available and will operate nearly to 10 GHz.

Advances in direct-write printing of RF-MEMS using M3D

We report an additive manufacturing process using in-house custom-made inks for the fabrication of ohmic contact RF MEMS switches. The fabrication involves multiple steps of additive printing using a conductive silver ink and a PMMA [poly(methyl methacrylate)] photoresistive polymer ink. The inks comply with the rheology requirements of the M3D material deposition system. Deposition is made at 40°C and feature sizes involve 10-20μm. The maximum temperature of the process depends on ink curing and was 250°C. A functional ohmic contact cantilever RF MEMS switch on flexible Kapton™ substrate was fabricated and tested successfully, and results are presented.

Using anisotropic high impedance surfaces for tuning antenna performance

More recently, structures capable of being produced inexpensively and operated in the more commercially viable bands have been proposed. Unfortunately, high impedance (high-Z) surfaces capable of operating at lower frequencies tend to be far more susceptible to fabrication errors because of complex surface patterns. In most cases, standard circuit board manufacturing tolerances are too loose to create such high-Z surfaces to the necessary accuracy. To circumvent these difficulties in fabrication, we propose that adding a small degree of anisotropy to high-Z surfaces can enable compensatory tunability for certain planar antennas located on the surface by simply rotating the antenna. Doing so allows fabrication tolerances to be loosened to those available for large scale, inexpensive fabrication

Application of a dielectric puck for a high gain-bandwidth resonant cavity antenna

We propose a new type of resonant cavity antenna (RCA) that employs a small dielectric puck instead of the large dielectric superstrate layer used in the traditional RCA. The diameter of the puck is studied to determine its influence on the gain-bandwidth product (G·BW) of the RCA. Simulations of the waveguide-fed RCA demonstrate that the G·BW of the RCA with puck can be four times larger than that of the traditional RCA. Moreover, the antenna with puck is compact and can be easily fabricated, which makes it attractive for future high-frequency and very directive point-to-point communication links.

A miniaturized ultrawideband monocone antenna by using intelligent dielectric loading

We propose a miniaturized ultrawideband monocone antenna. The size reduction was achieved by loading a dielectric material of high dielectric constant around the antenna in an intelligent manner. In order to maintain the impedance bandwidth characteristics, a spatial quarter wave transformer was applied. A preliminary antenna was fabricated and tested, and the measured results have shown good agreement with the simulated data.

Characterization of high impedance surfaces using magnitude measurements

High impedance surfaces are generally characterized by reflection coefficient measurements. Other methods such as surface wave suppression measurements are used but do not provide as useful information. For ideal lossless high impedance surfaces the reflection coefficient magnitude is one while the phase angle varies greatly with frequency. However, by placing a resistive sheet near the high impedance surface, the magnitude of the reflection coefficient can also be made to vary with frequency

Direct-write printing of an RF-MEMS Cantilever

This paper presents the manufacturing of a simple RF MEMS cantilever ohmic contact switch using only a custom made silver nanoparticulate ink and PMMA [poly(methyl methacrylate)]. The manufacturing is additive in nature and only the PMMA layer is subtractive. The MEMS switch is printed on Kapton substrate using an Optomec Aerosol Jet printer. Then, it is cured at 200°C. Finally it is soaked in chloroform to remove the PMMA layer and complete the process. The printed MEMS were tested successfully and results are presented here.

Two-cavity model for creating two high-directivity bands of the resonant cavity antenna with flexible and dynamic control

We present a simple method to design a resonant cavity antenna (RCA) that resonates in two bands by employing two dielectric superstrates of thicknesses and positions determined by a step-by-step, non-iterative process. The method models the RCA as two cavities, each corresponding to one operational band, which allows for a dynamic control of the separation between the bands. The antenna is analytically designed and performance is evaluated using a commercial software.