Raoul O. Ouedraogo

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.

An origami tunable metamaterial

The transmission characteristics of a folded surface decorated with a periodic arrangement of split-ring resonators is investigated. The folding pattern has one displacement degree of freedom, allowing motion that can be used to adjust the separation between the rings. When the geometry of the folded surface is varied by mechanical means, the change in spacing between the rings causes a shift in resonance frequency, making the surface mechanically tunable.

A Reconfigurable Microstrip Leaky-Wave Antenna With a Broadly Steerable Beam

A half-width microstrip leaky-wave antenna with an electronically steerable main beam is introduced. Lumped capacitors are connected between the free edge of the antenna and the ground plane through computer controlled switches, allowing the phase constant of the propagating wave to be varied. Consequently, the main beam of the antenna can be directed along any chosen direction in the longitudinal plane, at any frequency within the operating band of the antenna. By recalling stored switch combinations, the antenna may be steered at a certain frequency, or the antenna may be frequency-scanned while maintaining the beam at a fixed angle. The antenna may also be operated in a dynamic mode using a feedback system, where appropriate switch configurations are determined in real time using an efficient search algorithm. As a proof of concept, simulations are used to determine switch states to allow beam steering through nearly a full 180 degree scan range and also to keep the main beam at a fixed angle across a broad frequency spectrum.

Origami Tunable Frequency Selective Surfaces

A foldable frequency selective surface (FSS) is introduced that may be tuned by changing the folding state. The FSS comprises periodic elements arranged in an origami-like fashion on a dielectric sheet. By folding and unfolding the FSS, the interaction with the incident field and the mutual interactions between the elements may be altered, resulting in a shift in resonance frequency. A sample design of a tunable FSS folded into a chevron pattern and decorated with cross-shaped copper prints allows a 19% shift of resonant frequency with a change in folding angle of 60°.

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.

A Self-Structuring Patch Antenna: Simulation and Prototype

A self-structuring patch antenna (patch SSA) is proposed. It combines the operating principles of the original self-structuring antenna with the desirable properties of a classic microstrip patch antenna. The patch self-structuring antenna has several computer-controlled shorting pins inserted between the patch and the ground plane. By opening and closing these pins, the antenna may be configured to operate at any arbitrary frequency within a very large bandwidth. Additionally, the patch self-structuring antenna may be configured to operate at several simultaneous frequencies that when placed near each other can be used to dramatically expand the instantaneous bandwidth of the antenna. A proof-of-principle study is undertaken both in simulation and by performing measurements on a prototype antenna.

Metamaterial inspired patch antenna miniaturization technique

Over the past decade, the need for small, compact and low cost antennas has increased tremendously for applications such as wireless communications and radar. Microstrip patch antennas, though popular for these applications, are difficult to miniaturize, since their resonant frequency is determined by the dominant (TMZ110) mode of the patch cavity (the region immediately beneath the patch). Nevertheless, numerous miniaturization techniques using shorting posts, active loading or high permittivity dielectrics [1] have been conceived to lower the resonant frequency of patch antennas without increasing their size. Unfortunately, as the demand for ever smaller patch antennas increases, these techniques fail to produce the required size reductions.

A Tunable Dual-Band Miniaturized Monopole Antenna for Compact Wireless Devices

A technique for producing miniaturized tunable planar monopole antennas for wireless communication applications is introduced. Miniaturization is achieved by optimizing the geometry of a pixelated metallic patch surrounding the monopole antenna. Tuning of the antenna is implemented by varying the capacitance of a varactor diode loaded between the pixelated metallic patch and the ground plane. The result is an ultra-compact, dual band, folded monopole antenna that fits into a hemisphere of radius λ0/20 at 2.1 GHz. Varying the capacitance of the varactor diode enables the two resonance frequencies to be tuned simultaneously, covering multiple frequency bands for different wireless applications. A prototype antenna has been fabricated and measured, confirming the feasibility of the proposed design.

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.

A Self-Structuring Electromagnetic Scatterer

A novel self-structuring electromagnetic scatterer (SSES) is proposed. The SSES can alter its electrical shape to fulfill various operational objectives, such as radar cross section (RCS) reduction or enhancement. The SSES template comprises segments of metallic thin strips interconnected via voltage-controlled switches. By opening or closing the switches, the phase of the field scattered by the strips changes, resulting in destructive or constructive interference in the total scattered field. The RCS of the SSES can thus be controlled. An efficient search algorithm based on the fractional factorial designs of experiments (FFD) is adopted to find a suitable switch configuration for the SSES. The FFD estimates the effects of the switches on the scattering properties, and identifies the significant effects. For a given operational objective, a combinatorial optimization problem can be formulated in terms of these effects and solved for a suitable switch configuration. A SSES prototype was built and a series of RCS measurements were performed to demonstrate its capability to adaptively control the RCS. It is shown that the bistatic RCS can be significantly reduced in any specified direction and that the main beam maximum of the RCS pattern can be enhanced and steered within an angular range of 30° . Importantly, the proposed method requires only one sixth of the number of experiments needed by a genetic algorithm to locate a comparable solution.