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Analiza pełnofalowa anteny skanującej na podłożu ferroelekrycznym

Jaszczyszyn E.

Kwartalnik Elektroniki i Telekomunikacji

2004

Vol. 50, z. 2

287-311

W pracy przedstawiono koncepcję i opracowano nowy rodzaj skanującej anteny paskowej na podłożu ferroelektrycznym bez konieczności wykorzystania przesuwników fazy. Ponadto opracowano uogólnioną metodę analizy elektrodynamicznej rozpatrywanej struktury promieniującej wraz z metodą analizy numerycznej. Wyniki badań anteny skanującej wskazują na możliwość szerokiego jej zastosowania, a przedstawiona metoda analizy pełnofalowej do projektowania struktur promieniujących.

Electronically scanned microwave antennas is accomplished by electronically altering the phase across the antenna radiating aperture (by means of discrete phase shifting elements or by changing frequency). This conventional inertialess scanning techniques in the microwave region are not cheap. A new scan antenna concept that realizable design using low-cost fabrication processes is presented. This concept is based on the first higher order mode on a microstrip line, which substrate is made using ceramic-polymer composite with modified ferroelectric powder Ba0,65Sr0,35TiO3 and appropriate polymer (grains of the powder have been sprayed into polymer with specific method). This ceramic-polymer composite was designed to change permittivity in response to an applied electric control field. The property of ferroelectric materials having a dielectric constant which can be modulated at high frequencies is very attractive. The feasibility of dielectric scanning (changing the direction of the beam by varying the relative permittivity of the electrically controlled ceramic-polymer composite) has been investigated. The radiation characteristics of such antenna have been accurate evaluated. Both longitudinal and transverse currents are treated. The method of solution used is an extension of the Fourier integral method which is used in conjunction with the method of moments (Galerkin solution). The propagation constant kx for higher order modes in open microstrip were calculated. In the present structure the complex propagation constant can be changed by changing the frequency or by changing the dielectric constant of the substrate (E2) as in the case of electrically controlled ferroelectric ceramic-polymer composite. In general, the direction of the radiated beam is given by Om = sin-1 (B), where kx (E2) = B(E2) = j * A(E2). For frequencies not far above the cut-off frequency, that means for B/k 0 < 1 (B in phase constant of the first higher order mode), the fields of the first higher order mode on the microstrip line are coupled to the line very loosely resulting in a considerable radiation.

Synteza paskowych szyków antenowych na podłożu ferroelektrycznym

Jaszczyszyn E., Modelski J.

Kwartalnik Elektroniki i Telekomunikacji

2002

Vol. 48, z. 1

67-80

W pracy przedstawiono nową metodę syntezy anten paskowych, przydatnych do zastosowań w systemach adaptacyjnych. Proponowana metoda polega na poszukiwaniu optymalnych kształtów charakterystyk promieniowania pojedynczych radiatorów w szyku antenowym (przez zmianę przenikalności elektrycznej podłoża ferroelektrycznego radiatora paskowego) bez konieczności stosowania przesuwników fazy i tłumików. W pracy przedstawione wyniki syntezy oraz porównanie proponowanej metody z ogólnie stosowanymi.

ln modern radio system smart beamforming is often required. Communications antennas must offer a large number of operating modes (including pencil and shaped beams with fast switching between them) in order to ensure the best coverage of the service area. Therefore in designing smart antennas one of the main challenges is to provide a prescribed shaped antenna pattern that simultaneously suppresses interference signals (which locations are either known or unknown). As a rule this problem is solved with the use of phased-array antennas. This type of array consists of multiple stationary antenna elements which are fed coherently and use variable phase or time-delay control at each element to scan the beam to given angles in space. Variable amplitude control is sometimes also provided for pattern shaping. Performance of each radiating element bas significant influence on the parameters of antenna array, e.g. pattern, beamwidth, directivity gain, sidelobes, cross-polarization levels etc. Reducing the cost of phased array antennas has recently become the subject of considerable interest. The most prominent obstacle to this is the cost of current phase shifter elements (p-I-n diodes, MESFETs, ferrite). AIl of these are expensive, constituting a significant portion of the total receive-array cost. Additionally, p-I-n diodes and MESFETs introduce significant losses. These losses necessitate additional amplification of signal thus complicate the overall system design. New developments in MEMS and ferroelectric technologies promise low loss/high performance phase shifters. Both technologies provide low losses with beam capabilities, high isolation, good power handling ability, and low intermodulation distortion. Ferroelectrics are beneficial for applications operating at microwaves range, offering large phase shift per loss, low losses (0.2-0.3 dB, depending on frequency and matching), and large power handling capability. Bulk ferroelectric are beneficial for large phased array antennas because acceptable radiation characteristics may be achieved with fewer elements, lower cost, smaller size, and weight and lower power consumption. The design of a low-cost antenna array with 2D steering capability is very important for radiocommunication. As the satellite and mobile wireless communications technologies continue to utilize higher frequencies in the 20 to 60 GHz range, the design of a phased array antenna becomes prohibitively expensive. Also the realization od 2D scanning capability to track the satellite or to provide adequate urban communications systems becomes increasingly difficult to realize at a sufficiently low-cost suitable for the consumer market. The aim of this paper is to present a new method of array pattern synthesis by taking into consideration pattern of each radiator specially of the ferroelectric one. Radiating elements employing ferroelectric materials may give much better performance compared with ferrite ones, because of their high power handling capability, low drive power, full military temperature range of operation and low cost. The main feature of the ferroelectric antennas is the change of ferroelectric material permittivity with an applied dc control voltage. The permittivity change by varying the dc bias enables to create different radiation patterns. This permits to use such radiating element in several applications, e.g. smart antenna arrays. In this paper, new method of pattern synthesis of antenna arrays without phase shifters and attenuators has been presented. This concept is based on utilizing voltage-controlled ferroelectric array, where variable pattern of each antenna element is used to synthesize array pattrern.