Dual-Band and Triple-Band Metamaterial-Based Microwave Devices and Antennas for Modern Communication Systems
Institut za Fiziku
Ministry of Science and Environmental Protection
National Development Project
In this project, the newest technology based on metamaterials will be applied. Metamaterials are artificial periodic structures which exhibit advantageous and unusual electromagnetic properties, generally not found in nature. They are composed of miniature unit cells whose size is typically smaller than one tenth of the propagating signal wavelength. Due to this fact, metamaterials can be considered as continuous media with effective dielectric permeability and effective magnetic permittivity. By a proper choice of the type and geometrical arrangement of constituent unit cells, the effective parameters of metamaterials can be made arbitrarily small or large, or even negative. By tailoring characteristics of the metamaterial according to the designer needs, RF and microwave circuits with improved performances can be obtained, such as small dimensions, dual- or triple-band operation, arbitrary antenna scanning angle, etc.
Double-negative (DNG) or left-handed (LH) metamaterials, which simultaneously exhibit negative effective permeability and negative effective permittivity in a certain frequency range, were first theoretically studied by Russian physicist Victor Veselago. The first structure that exhibits negative permittivity at microwave frequencies by decreasing the plasmon frequency was proposed in mid-nineties. Soon afterwards, negative permeability was obtained by a new sub-wavelength particle called split-rings resonator (SRR). By combining those two particles into one unit cell, the first experimental verification of LH behavior was performed in 2001.
Since the first experimental proof-of-principle some years ago, the field of metamaterials has seen a tremendous growth world-wide, as is testified by the exponential growth in publications dealing with this topic. Several programs within DARPA and DoE dedicated to this issue have been launched in the USA by several universities, but this topic is now also actively supported by Japan and China. Europe so far has been pioneering in several aspects, with a strong research base present, and with the tendency to structure the research community at a European level around a common strategic objective in this field.
The aim of the proposed project is the development of LH-metamaterial-based dual-band and triple-band microwave circuits and antennas. Due to the pronounced dispersion of LH metamaterials, circuits that simultaneously operate in two or even three arbitrary frequency bands can be designed. This is extremely important for microwave links that operate in precisely defined frequency bands according to ITU recommendations. In the conventional technology, every link has separate microwave transceiver which depends on the operating frequency: 4GHz, 7.5GHz, 13GHz, 15GHz, 18GHz, 23GHz and 26GHz, while the baseband processing is the same for all, and depends on the capacity of the system, i.e. the transmission rate. The prices of microwave links are constantly dropping, due to the great demand of the mobile-telephony market. It seems that the application of new technologies is the only way to insure survival of small producers, such as IMTEL Communications. By applying dual-band circuits in microwave transceiver, the number of different microwave circuits that need to be designed and fabricated would be significantly reduced, which would allow application of the same hardware on two or three operating frequency bands. By using the conventional technology, maximally two harmonic-related frequency bands can be covered simultaneously, while application of metamaterials allows usage of two or three arbitrary (non-harmonic related) frequency bands. This is due to highly nonlinear dispersion characteristic of metamaterials.
The need for dual- or, generally, multi-band circuits exists also in personal wireless communication systems for Internet access, such as lap-top computers, PDA, iPOD, etc. In all these applications microwave multi-band circuits with standard number of ports are used.
Dual- or multi-band operation is also important for wireless sensors for heart-rate monitoring (EKG recording) and monitoring of respiratory organs. In such systems, multi-band multi-port components are used, due to the fact that microwave circuit or antenna must have a separate access for every operating frequency, since signal processing performed on different frequencies allows separation of the signal caused by heart operation from that caused by respiration.
In this project, multi-band circuits with standard number of ports will be designed, for the application in microwave links and personal devices for Internet access, as well as multi-band circuits and antennas with separate ports for each operating frequency band.