Andrew Temme

Miniaturization of Patch Antennas Using a Metamaterial-Inspired Technique

A new design methodology for producing highly miniaturized patch antennas is introduced. The methodology uses complementary split-ring resonators placed horizontally between the patch and the ground plane. By optimizing the geometry of the split rings, sub-wavelength resonance of the patch antenna can be achieved with a good impedance match and radiation characteristics comparable to those of a traditional patch antenna on a finite ground plane. Construction of the optimized antenna is straightforward, requiring only the sandwiching of two etched circuit boards. High levels of miniaturization are demonstrated through simulations and experiments, with reductions of a factor of more than four in transverse dimension achieved for a circular patch resonant at 2.45 GHz. Although miniaturization is accompanied by a decrease in antenna radiation efficiency and a loss of fractional bandwidth, antenna performance remains acceptable even for a 1/16 reduction in patch area.

In Situ Optimization of Metamaterial-Inspired Loop Antennas

A new methodology for designing metamaterial-inspired antennas using an in situ optimization technique is introduced. Through this approach, an optimization tool such as a genetic algorithm is used to design a metamaterial pattern adjacent to an antenna to enhance the antennas performance. As an example, the technique is used for miniaturization purposes where a loop antenna initially resonant at 2.45 GHz is made resonant at 960 MHz, providing a sevenfold reduction in antenna area over a conventional loop designed to operate at 960 MHz.

MNG-metamaterial-based efficient small loop antenna

In this paper, the impedance characteristic of the electrically small loop antenna has been significantly amended by introducing a layer of MNG MTM, which is formed by BC-SRRs. The 2-GHz prototype antenna has exhibited a peak gain of 5.7 dBi and efficiency of 87.8% verifying the effectiveness of the proposed SRR-based matching layer. This matching layer can, of course, be constructed using any other MNG MTM unit cells as long as they are properly aligned with the near-field magnetic field of the small loop.

Pulse Reflection from a Dielectric Discontinuity in a Rectangular Waveguide

A simple, closed-form expression for the time-domain re∞ection coe-cient for a pulsed TE10-mode wave incident on a dielectric material discontinuity in a rectangular waveguide is presented. This formula may be used to represent the transient fleld re∞ected or transmitted by a dielectric-fllled waveguide section, which is useful in material characterization routines. An exponential function approximation to the re∞ection coe-cient is presented, and the formula is validated both numerically and experimentally.

Performance enhancement of target recognition using feature vector fusion of monostatic and bistatic radar

This paper proposes a fusion technique of feature vectors that improves the performance of radar target recognition. The proposed method utilizes more information than simple monostatic or bistatic (single receiver) algorithms by combining extracted feature vectors from multiple (two or three) receivers. In order to verify the performance of the proposed method, we use the calculated monostatic and bistatic RCS of three full-scale aircraft and the measured monotatic and bistatic RCS of four scale- model targets. The scattering centers are extracted using one-dimensional FFT-based CLEAN and then used as feature vectors for a neural network classifler. The results show that our method has better performance than algorithms that solely use monostatic or bistatic data.

A dual-band tunable reflectarray

In this work, a dual-band reflectarray with reconfigurable beam angle is presented. The unit cell of the reflectarray is a square ring-patch structure which was optimized to perform within two distinct frequency bands. The full wave simulation software HFSS was used to analyze a unit cell inside a waveguide, approximating the infinite array scenario. The tuning of the unit cell was achieved by altering the capacitance of a varactor diode placed between the square ring and the patch. A 10 × 10 element array will be built and measured to demonstrate its capability of beam steering over a wide range of angles.

Determination of optimum bistatic angle for radar target identification

The transmitter and receiver positions of a bistatic radar are highly influential on its performance in radar target identification since the radar cross-section of a target varies with these positions. In this study, radar target identification performance using calculated bistatic scattering data for three full-scale models and measured data for four-scale-model targets is analyzed and compared. FFT-based CLEAN is used for shift-invariant feature extraction from the bistatic scattering data of each target, and a multilayered perceptron neural network is used as a classifier. The optimum receiver position is found by comparing the calculated identification probabilities while changing the position of the bistatic radar receiver. The identification results using calculated data and measured data show that an optimally positioned bistatic radar yields better identification results, demonstrating the importance of the positions of the transmitter and receiver for bistatic radar.

A Self-Tuning Electromagnetic Shutter

A self-tuning electromagnetic shutter is introduced, consisting of a slotted metallic surface with computer controlled switches placed across the slots. By opening and closing the switches, the transmissivity of the surface may be adjusted over a broad range of frequencies. In particular, the surface may be placed into open and closed states, creating an electronically-controllable shutter. The ability of the shutter to act as an open or a closed surface over a broad range of frequencies, incidence angles, and polarization states is investigated using simulations and measurements, and the feasibility of the system is thereby demonstrated.

Characterization and Modeling of Conjugated Polymer Sensors

In this paper the behavior of conjugated polymers as mechanical sensors is experimentally characterized and modeled. A trilayer conjugated polymer sensor is considered, where two polypyrrole (PPy) layers sandwich an amorphous polyvinylidene fluoride (PVDF) layer, with the latter serving as an electrolyte tank. A theory for the sensing mechanism is proposed by postulating that, through its influence on the pore structure, mechanical deformation correlates directly to the concentration of ions at the PPy/PVDF interface. This provides a key boundary condition for the partial differential equation (PDE) governing the ion diffusion and migration dynamics. By ignoring the migration term in the PDE, an analytical model is obtained in the form of a transfer function that relates the open-circuit sensing voltage to the mechanical input. The model is validated in experiments using dynamic mechanical stimuli up to 50 Hz.

Evaluation of material characterization systems that utilize a two-wire transmission line

Engineers in many disciplines use the electromagnetic properties of materials to evaluate and predict the performance of systems. Microwave engineers use these properties in the design of high frequency devices. Civil, mechanical, and biomedical engineers use the properties, either directly or indirectly, as indicators of the performance of structures and mechanical systems, e,g, in the evaluation of water-to-cement ratio (Mubarak, K. et al., Instrumentation and Measurement, IEEE Trans, v50, no.5, pp.1255–1263, Oct. 2001).