David M. Klymyshyn

On the Two Segmented and High Aspect Ratio Rectangular Dielectric Resonator Antennas for Bandwidth Enhancement and Miniaturization

The goal of this communication is to maintain wide impedance bandwidth while miniaturizing a microstrip-fed dielectric resonator antenna (DRA). The approach of using high aspect ratio structures is proposed, discussed, and compared with the two segmented structures approach. Finite element method parametric study of high permittivity high aspect ratio structures is used to demonstrate how two appropriate resonant modes can be merged to obtain miniaturized antennas with broadband operation, stable radiation patterns, and low cross polarization levels. To show the effectiveness of the approach, a set of microstrip-fed two segmented and high aspect ratio DRAs is fabricated, characterized, and the results are compared with Ansoft HFSS simulations. A high aspect ratio DRA with cross section as small as 0.08lambda by 0.12lambda has better than 11 percent bandwidth and is especially attractive for compact array applications.

Active frequency-multiplier design using CAD

A tutorial paper on active frequency multiplier design is presented. Rough calculations for a /spl times/2 multiplier using classical theory are developed and used as a starting point for implementation with nonlinear computer-aided design (CAD) software. The power of the nonlinear CAD software for visualizing and understanding concepts important to frequency multiplier design, and also for optimization of critical design parameters is demonstrated through realistic examples. Important design considerations for higher order multipliers are discussed, including design of output termination circuitry for a /spl times/4 multiplier at 28 GHz.

Compact Wideband Multimode Dielectric Resonator Antennas Fed With Parallel Standing Strips

As the number of resonances increases, it becomes difficult to improve and maintain the performance of dielectric resonator antennas (DRAs), over the expanded impedance bandwidth. To remove unwanted modes, adjust the frequency distance between individual modes, reduce antenna size and cross polarization, and preserve radiation patterns in a wideband configuration, a dielectric resonator antenna fed with parallel standing strips is proposed in this paper. The use of parallel standing strips provides several degrees of freedom in the design procedure to enhance the DRA characteristics. To validate the effectiveness of this approach, two DRAs with parallel standing strips were fabricated using different procedures. The antennas were tested and characterized. The measured results are in good agreement with simulation ones. A 46% size reduction was achieved for the multimode DRA. The impedance bandwidth of the proposed DRA of simple rectangular shape was over 60% with a measured gain ranging from 5.5 to 9.5 dBi. Broadside radiation patterns with fairly low cross polarizations can be maintained over the impedance bandwidth. The simulated radiation efficiency is more than 96% within the frequency band.

Dielectric characterization of materials using a modified microstrip ring resonator technique

The goal of this study is to present a simple model based on the ring-resonator technique to measure nondestructively the permittivity and loss tangent of dielectric materials. The proposed measurement model utilizes a modified ring-resonator technique in one-layer and two-layer microstrip configurations. This method eliminates the requirement to metalize the samples and enables characterization of permittivity and dielectric loss from 2 to 40 GHz. The effects of conductor and radiation losses that may introduce significant errors in the calculation of the loss tangent, especially at very high frequencies, are minimized. The measurement precision is evaluated by comparing the results with those obtained by using two well-known standard techniques. Uncertainties associated with the proposed model are addressed.

High Aspect Ratio Vertical Cantilever RF-MEMS Variable Capacitor

An electrostatically actuated, microwave microelectromechanical system variable capacitor fabricated using deep X-ray lithography is presented. A single exposure has been used to produce the novel high aspect ratio microstructure, which includes a thin, vertically oriented, movable nickel cantilever beam and a 40:1 vertical aspect ratio capacitance gap. The 0.8-pF capacitor operates in the 1-5GHz region and has Q-factors of 36 at 4GHz and 133 at 2 GHz. The variable capacitance ratio is 1.24:1 over a 20-V tuning range at 4GHz

Characterization of effective bandwidth as a metric of quality of service for wired and wireless ATM networks

The concept of effective bandwidth has been recently introduced to analyze the call admission, congestion control, and resource management in ATM networks. In this paper, the effective bandwidth is proposed as a metric of quality of service for wired and radio ATM. Using traditional and self-similar models of traffic sources, the effective bandwidth for an ideal channel is computed. The results are extended to random error and burst error channels by computing cell loss ratio. Using a modified fluid flow model, analytical approaches are examined using an ATM-simulator with different buffer sizes and Hurst parameters. The results can be used by the ATM system designer when dealing with bandwidth restricted channels, e.g., radio ATM.

Deep x-ray lithography processing for batch fabrication of thick polymer-based antenna structures

Deep x-ray lithography is applied for the first time to fabricate polymer-based antenna structures with different portions of ceramic contents. To produce successful and viable antenna structures, three different methods are proposed using positive and negative tone resists. In the first method the structures are lithographically fabricated avoiding an intermediate molding step using SU-8 as a photosensitive resist filled with fine ceramic powder with particles in the submicron range. In the second and third methods a polymethylmethacrylate (PMMA) mold is first fabricated by x-ray lithography, and then SU-8/MMA mixed with the high ceramic powder content is injected into the mold. In these methods a final step of crosslinking for SU-8 and polymerization for MMA is also required. Optimized fabrication parameters allow the production of high quality antenna structures as thick as 2.3 mm. X-ray lithography capabilities in fabrication of antennas and other passive microwave components with special features reinforce the idea of fabricating integrated passive microwave circuits along with active circuits using this emerging technology.

Reducing pull-in voltage by adjusting gap shape in electrostatically actuated cantilever and fixed-fixed beams

A gap with variable geometry is presented for both cantilever beam and fixed-fixed beam actuators as a method to reduce the pull-in voltage while maintaining a required displacement. The method is applicable to beams oriented either in a plane parallel to or perpendicular to a substrate, but is most suitable for vertically oriented (lateral) beams fabricated with a high aspect ratio process where variable gap geometry can be implemented directly in the layout. Finite element simulations are used to determine the pull-in voltages of these modified structures. The simulator is verified against theoretical pull-in voltage equations as well as previously published finite element simulations. By simply varying the gap in a linear fashion the pull-in voltage can be reduced by 37.2% in the cantilever beam case and 29.6% in the fixed-fixed beam case over a structure with a constant gap. This can be reduced a further 4.8% by using a polynomial gap shape (n = 4/3) for the cantilever beam and 1.2% for the fixed-fixed beam by flattening the bottom of the linearly varying gap.

On the Matching of Microstrip-Fed Dielectric Resonator Antennas

As the permittivity of dielectric resonators decreases, it becomes difficult to feed the dielectric resonator antennas (DRAs) using direct microstrip lines. The variation of the resonant input resistance with the feed location becomes smaller, while the maximum achievable peak resistance dramatically drops to lower than 50 Ω in most cases. To satisfy the impedance matching, field matching, improve coupling to low-permittivity dielectric resonators, and further increase the antenna bandwidth associated with the dominant mode, without disturbing far-field properties, tapered microstrip line-fed DRAs are proposed, designed, fabricated and evaluated in this communication. Both measurements and simulation investigations are presented and the results are compared with other forms of microstrip feed lines. The impedance bandwidth can be 75% larger than the bandwidth achieved by the step-shape microstrip-fed DRA. Symmetrical radiation patterns with low cross-polarization levels (lower than -22 dB) and a gain ranging from 4.9 to 6.8 dBi, within the impedance bandwidth of the antenna, are observed in the measurements. It is also shown that the proximity coupled tapered microstrip line is an ideal feeding for high-permittivity DRAs in situations where the microstrip line cannot be positioned underneath the dielectric resonator. To verify, one such antenna is designed, simulated and experimentally investigated, obtaining satisfactory results.

Development of Polymer-Based Dielectric Resonator Antennas for Millimeter-Wave Applications

The goal of this paper is to use polymer-based materials (instead of hard ceramics) in fabrication of dielectric resonator antennas at millimeter-wave frequencies. The soft nature of polymers facilitates machining of antennas, while the low permittivity of polymers naturally enhances the bandwidth. More importantly, advantageous properties (e.g., ∞exibility and photosensitivity) of some polymers introduce special capabilities which can not be achieved by ceramics. A photosensitive polymer is utilized in this paper to fabricate polymer-based resonator antennas. As a result, deep X-ray lithography is enabled to produce high quality antenna structures. The proposed dielectric resonator antennas which inherently have very low relative permittivity (usually in a range from 3 to 5) are excited efiectively using a slot-coupled feeding method and analyzed in both the frequency and time domains. Impedance and radiation properties are compared with higher permittivity ceramic antennas. Impedance bandwidths up