Department of Radio Engineering and Specialized Training
Speciality: Radioelectronical devices, systems and complexes
Subject urgency. At the present stage of development of radio engineering it is necessary to mark the considerable extension of area of the tasks solved by the modern radio engineering systems and, as consequence, increase of requirements to quality indicators and design data of radio-electronic equipment [1]. In particular, such increase of requirements is characteristic for antennas, and for super high frequency (SHF) devices who play a crucial role in the organization of systems and radio communication networks. It is necessary to carry efficiency of establishment of direct communication to primary benefits of a radio communication on defined distance and simplicity of the organization of communication with nonstationary objects, however, radio communications are peculiar as well certain lacks, such as complexity of the organization of wireless links of communication in underground constructions (in tunnels, in adits and etc.) Various character of a dying down of signals on radio communication routes, rather low noise immunity. In practice, at the organization of channels of a radio communication in constructions and buildings, the wide circulation was received by communication systems at which there is a central office and some basic stations, thus data transfer between central and basic stations will be organized on the waveguide (including optical fiber) or wire (feeder) communication lines, and data transfer on the device the networks which are not basic or central stations, is carried out by basic station through a radio channel. Such communication systems include, in particular, so-called radio over fiber (RoF) systems.
In modern lines of development of radio engineering tendencies of are accurately tracked that to communication systems more strict demands concerning many parameters, such as bandwidth, operational frequency, electromagnetic compatibility and etc. obviously will be made permanently that observance of these requirements demands innovative decisions.
There is a considerable quantity of directions of researches for the purpose of the decision of existing problems of radio engineering, the special place among these directions is occupied with development of new devices, in particular, what would fulfill specific functions (tasks), had as more as possible simple construction (structure) and minimum power consumption.
Perspective directions of development of radio engineering, in particular telecommunications, is fiber lines of communication and a communication radio-frequency line. Therefore to creation of simple devices the aspiration is natural to conversion of an optical signal to an electromagnetic signal and on the contrary, thus a signal, in that case, is considered as the information medium. Usage of photonic devices and fiber-optic communication lines (fiber-optic links) opens new possibilities and allows to raise productivity of radio engineering systems. This circumstance promoted appearance of the new task in radio engineering — tasks of development of photonic-controlled antennas.
Relatively recently the new concept of creation of devices for converting the optical signal into an electromagnetic signal and on the contrary has been offered, these are so-called photonic antennas [2] - [4]. The term «photonic antennas»[2] - [4] is the reduced title of the photonic active integrated antennas (PhAIAs) [5], [6]. For photonic antennas that the signal to the antenna, in case of the transferring antenna, and from the antenna, in case of the receiving antenna, is spread on an optical fiber is characteristic. The photonic antenna consists of the microstrip antenna and the photonic device (the photodiode or the laser, according to that what it it is transferring or a reception — the antenna) [5], [6]. Simplicity of a construction of such device predetermines interest it. Its properties and real possibilities of usage in communication systems haven't been carefully researched, hence, profound research of possibilities of photonic antennas is the actual task.
Purpose of master's work consists in research of real possibilities of usage of photonic antennas (PhAIAs [2] - [6]) in communication systems, and development of new constructive and technical decisions of the photonic active integrated antennas (PhAIAs) with the refined characteristics which would satisfy to the specific in advance predetermined conditions of application of photonic antennas is better.
Object of research are the electromagnetic phenomena accompanying operation of photonic antennas (PhAIAs).
Subject of research are principles of operation and property of photonic antennas (or photonic active integrated antennas).
Methods of researches. In the master's work is supposed to use methods of the theory of analysis and design of SHF microstrip devices, the use of mathematical formalism of electrodynamics and experimental methods for studying the characteristics of antennas.
Practical value. It is supposed that the received results can be used at creation of real communication systems and also by development of similar devices (modifications).
Keywords: active antennas, microstrip devices, semiconductor laser, photodiode, photonic devices, integrated devices, photonic antenna, photonic active integrated antennas, PhAIAs, the frequency properties, pattern, communication systems, radio communication.
Information search in a subject of operation as of 01.04.11 has shown that research on the given subjects (photonic antennas, and their usage in communication systems) in DonNTU weren't led, also is revealed that in the Internet sources there is any information on results of researches on the given subjects made in Ukraine. From the Internet sources also it is known that in the world the given subjects are considered and researched in Europe (in Great Britain, Poland, Belarus, Russia), America (in the USA) and Asia (in Thailand).
The concept of photonic antennas (PhAIAs [2] - [6]) is close to the concept of integration of photonic devices with the microstrip antennas [7], and it's the extension for a long time the known concept of the active integrated antennas (AIA) [8]. In a basis of photonic antennas the idea of usage of photonic devices for control in parameters of antennas is supposed.
Principal difference of photonic antennas (PhAIAs) from normal microstrip antennas (MSA) and active integrated antennas (AIA) consists that SHF signal to and from MSA is transferred on a coaxial cable, and in case of photonic antennas a coaxial cable is replaced by an optical fiber. Also an important singularity of PhAIA-aerials is their unidirectional properties, i.e. one antenna can work only on transmission or reception of a signal depending on what photonic device (photodiode or semi-conductor laser) is integrated in MSA. The diagram of transmission system of the information (digital data) with usage of photonic antennas has the following appearance displayed in a figure 1.
Figure 1. System configuration of information transmission using photonic antennas.
(Pay attention to a construction of the PhAIA operating on reception of a wireless signal, and on a construction of the PhAIA operating on transmission of a wireless signal)
(This figure is animated. File size: 20 KB; size: 730 × 252, number of frames: 17; number of cycles of repetition: 7)
In figure 1, the following notation: PhAIA — photonic active integrated antenna (photonic antenna), VCSEL — vertical-cavity surface-emitting laser, Photodiode — the photodiode.
In the design of photonic antennas photonic devices are used as photoreceptions and phototransmission devices.
Figure 2. Сoncept of photonic antennas (PhAIAs) for radio transmission [4].
In figure 2 dashed line designates the photonic antenna (PhAIA).
For most of existing concepts of photonic-controlled antennas [7], and photonic antennas, in particular, questions of technology of photoelectronic devices is critical. It is caused by need for photoelectronic devices which will specific image to react to change of value of illuminance. Therefore the most part of operations is devoted learning and development of photoelectronic devices (preferentially semiconductor photodiodes) which would satisfy to certain needs.
For creation of the photonic active integrated antennas as photonic devices as it is specified in the literature [2] - [6], are used PIN photodiodes, and VCSEL laser diodes. And as the device for radiation and reception of radio-waves — the microstrip antenna. We will consider these instruments in more details.
A PIN photodiode is a photodiode at which between two areas of opposite conductivity average is allocated intrinsic semiconductor. The majority of photons are absorbed in intrinsic semiconductor (i-region), it effectively promotes the formation of photo-current.
In comparison with normal a PN photodiode a PIN photodiode has thicker the impoverished region that causes a large quantum efficiency, and also leads to power lowering and by that provides more throughput high level [10, p. 499]. At application of sufficiently large voltage, it penetrates i-region and the free carriers, appeared at the expense of photons at an irradiation, are accelerated by electric field p-n passages. It causes a speed gain and sensitivity of the device. High-speed performance increase in PIN photodiode is caused by change of process of diffusion on drift of electrical charges in the strong electric field.
Advantages:
1) there is a possibility of support of sensitivity in a long-wave part of a spectrum at the expense of change of width i-region;
2) high sensitivity and high-speed performance;
3) low operating voltage.
Disadvantages: technological complexity of obtaining of high purity i-region.
In view of the aforesaid it is clear that usage PIN of photodiodes is appreciably due to their high-speed performance and high sensitivity.
VCSEL — vertical-cavity surface-emitting laser — is a type of semiconductor laser diode with laser beam emission perpendicular from the top surface, contrary to conventional edge-emitting semiconductor lasers (also in-plane lasers) which emit from surfaces formed by cleaving the individual chip out of a wafer.
VECSEL, because of the small circular delay resonator can be modulated by high frequencies, including gigahertz range, this makes them useful, for example, for optical fiber communications. For VECSELs are characterized by low current density of excitation in the active element of the laser, ie, characterized by a low threshold current (a few microamperes).
Advantages:
1) high wavelength stability;
2) low temperature sensitivity;
3) heightened power on area unit;
4) high quality of a luminous bundle.
Microstrip antennas (MSA) or patch antennas have rather simple structure, however their analysis it is added enough. The primary complicating factor is the planar construction and presence of a dielectric substrate on which horizontal plane the conductor layer is allocated. Research of allocation of currents on a conductor layer surface has led to appearance of a large quantity of approaches to the analysis and modeling. The first models of the microstrip antennas were rather simple, from reasons of geometrical design, however till now it is difficult to consider all physical properties which it are inherent. The modern microstrip antennas have set of forms and configurations which can be analyzed, but don't give accurate representations about that, how it is necessary to make a choice of the form of the elementary radiator of the microstrip antenna (patch).
Exact approaches to mathematical and electrical modeling of the microstrip antennas, including those approaches which use differential equations, allow to receive hair accuracy and adequacy, but demand very difficult numerical calculations. As consequence, for engineering operations it is more convenient to use the simplified approaches.
Elementary radiators MSA are characterized by various operation modes: resonance and nonresonance, their combinations [9]. MSA have a considerable quantity of possible power supply circuits: the coaxial cable, a square-topped wave guide, a transmission strip line.
Microstrip antennas aren't included in section devoted to elements with distributed parameters, nor to section of aperture elements as radiation MSA, and all its properties, can be formulated from any point of view. Therefore the microstrip patch can be used and as an element of the microstrip lines, and as the microstrip antenna.
Resonator rectangular patches are structurally simple and quite convenient to consider the physics of the processes in MSA.
Figure 3. Elementary rectangular microstrip antenna and electric field distribution.
(On the figure^ W and L - the geometric dimensions of the resonant MSA; L - determines the resonant frequency of antenna)
Consider the rectangular microstrip antenna which eats from the microstrip line (fig. 3). When the wave in the microstrip line receives sharp change of width of a line on an input an antenna patch, a wave is radiated. On passage boundary the microstrip line — the microstrip antenna is formed a dispersion field, as is shown in a picture 3. After passage, the patch is considered as other microstrip line. The field is spread on this line, yet will not reach other edge. Here the sharp breakaway of a line creates again a dispersion field. Edges of the MSA behave as condensers shorted on the earth, and changes in electric field allocation are more considerable than magnetic field changes. The equivalent circuit for a rectangular microstrip elementary radiator looks like two parallely connected conductivities: YS1 = G + jωC1 and YS2 = G + jωC2.
In the master's work the actual scientific and technical task which is devoted research and modification of the integrated antenna systems with photonic devices — photonic antennas — for the purpose of their possible usage in communication systems. Profound research of properties of photonic antennas allows to confirm or refute efficiency of usage such devices in communication systems under various operational conditions.
Usage of such antenna systems in radio communication systems with optical backbone allows significantly simplify data circuit-terminating equipment (DCE) of radio over fiber (RoF) system.
© 2011 DonNTU. Restrictions apply.
© 2011 Gogolenko I.