Microwave ferroelectric and reconfigurable antennas

Nowadays, radioelectronic systems employ multiple antenna systems. Reconfigurable apertures are derived from a new class of antennas, which consist of a matrix of conducting patches with switches between some or all of the patches. These reconfigurable apertures can change functionality by opening or closing different connections between these patches. An example of the second group is the plasma regions with fairly high electrical conductivity, which are temporarily created on a silicon substrate. These regions define the antenna structure, and they can be changed to create different antennas. The key element of the antenna is a semiconductor chip that contains a set of individually controlled PIN structures. Electromagnetic waves propagate through the chip, which also serves as a planar dielectric waveguide. The PIN structures locally affect the wave propagation velocity, and the antenna can form a beam in practically any direction within a wide steering angle (like a leaky-wave antenna). The first investigations of the reconfigurable antennas, which are carried out at our Institute, show the extensive functionalities of this type of antenna. First of all, the reconfigurable antenna can be used as the conventional frequency scanning antenna. It is easy to see, that the reconfigurable antenna can direct radiation beam to desire direction. The first additional possibility in comparison with the conventional waveguide slot antenna, is that the reconfigurable antenna can be used for operating at one frequency, but with generating two or more different radiation patterns at different moments. The second extending possibility of the presented reconfigurable antenna is that the antenna can operate at different frequencies with supporting radiation in the same direction. Presented reconfigurable antenna consists of the reconfigurable aperture which is placed on, instead of the narrow wall of a rectangular waveguide. Aperture consist of a number of the reconfigurable elements which are made as the surface PIN diodes (SPIN), and are excited by means of an electromagnetic field existing in a waveguide. The main drawback of the presented electronically reconfigurable antenna concept is fact that the directions of the beam can be chosen in a discrete way. Increasing the number of the reconfigurable elements causes decreasing of the angle distance between two neighbouring beam directions. However, some parameters of the SPIN diodes made the limitations of their utilization on microwave. Advances in several areas of materials science have led to a variety of new materials with strong potential applications to microwave and millimeter-wave components. The high tunability and low dielectric losses are only the desired properties of material which can be applied in the tunable micro- and mm-wave devices. Despite the enormous effort made to reduce the cost of the tunable devices, the desired progress has yet to be achieved. However a number of the device configurations are a promising solution to inexpensive steering. A new low-cost scan antenna concept (without phase shifters), applying ferroelectrics, has been presented. The property of ferroelectric materials having a dielectric constant which can be modulated at high frequencies, under the effect of an electric field bias operating perpendicular to the direction of propagation of the signal, is very attractive and can be used to develop a new family of devices operating in the microwave and mm-wave range. Ferroelectric materials are in many ways dual to ferromagnetic materials. However, they have a number of advantages over the magnetically controlled ferrites. In ferroelectric, the driven energy required to change the property of material goes primarily to change in the stored energy and is not dissipated in the ferroelectric material. As a consequence, less power is required to control the property of material. Ferroelectrics also allow for faster tuning compared to ferromagnetic materials, they have smaller and lighter structure, and allow for high power capacity. The electrical scan property permits to expand functional possibilities of the known frequency scan leaky-wave antennas. The substrate of the presented microstrip antenna has been made using a ceramic-polymer composite with modified ferroelectric powder Ba0,65Sr0,35TiO3 and an appropriate polymer (grains of the powder were sprayed into polymer with the use of a specific method). The ceramic-polymer composite was designed to change permittivity in response to an applied electric control field for antenna utilization. The main advantage of the developed composites over typical ceramic ferroelectric materials is that the first one is elastic and can have any dimensions (even 1 m), it has also got a very low permittivity and a high tunability. It allows to electrically change the phase constant of the propagation wave and, in turn, changes the main beam direction. It has been shown that the beam angle changes over 300 when the dc-bias field is applied up to 200 V. The rigorous full-wave analysis of the developed scan antenna on a ferroelectric substrate has taken into account the current distributions of the first higher order modes, and radiation characteristics have been investigated. The comparison with experimental results has fully confirmed the usefulness of the scan-antenna concept. Presented results of the electrical scanned antenna investigation are promising, especially for fixed-frequency operation, where frequency scanning is impossible.