XIV Международная студенческая научная конференция Студенческий научный форум - 2022

Development of antenna technology throughout the evolution of radio was accompanied by and was closely associated with the development of the antenna devices theory. The first work of Heinrich Hertz on the experimental proof of the existence of electromagnetic waves was supplemented by him with theoretical research on the radiation of a dipole. One of the main elements of the invention of the radio by Alexander Popov was the receiving antenna. It was the connection of the antenna with the Hertz vibrator and the receiving circuit that allowed A.S. Popov to increase the length of the radio communication line, step over the walls of the laboratory and thereby lay the foundation for radiotelegraphy and radio engineering as a new field of technology. The technique of antenna devices has come a long and difficult way since the discovery of radio. The development of new wave ranges, new applications of radio engineering have always caused improvements in old ones and the appearance of the fundamentally new antenna devices. The main areas of the radio electronics use - communications, television, radar, radio control, radio astronomy, as well as systems for determining nationality, instrumental landing, electronic countermeasures, telemetry and others are impossible without the use of antennas with different characteristics. In the process of development of antennas, they became more complicated, fundamentally new classes of them have appeared, their functions expanded, and antennas often turned from simple reciprocal devices into complex dynamic systems containing, in most cases, hundreds, thousands of different elements.

Let us define what is antenna. Antenna is a conductor used to emit electromagnetic energy into the surrounding space or collect electromagnetic energy from the surrounding space. There are many different types of antennas used in technology, but here we will focus only on those antennas that perform the work of transmitting and receiving signals in radar measurement and control devices designed to automate technological processes.

There are two types of microwave antennas:

1. Horn antenna;

2. Parabolic antenna.

The choice of this or that type depends on the task of detection, control, measurement.

A horn antenna is a simple device; it is simply an expanding waveguide that can amplify and direct microwave radiation. An ordinary parallel waveguide itself is an inefficient emitter – at the output, the impedance change from the wave impedance to the ambient space impedance is interrupted. When radio waves travel through the waveguide collide with an open output, a significant part of the energy of the radio waves is reflected back towards the source, which is why part of the radiation power is extinguished. The reflected waves form standing waves in the waveguide, increasing their coefficient, which leads to a loss of energy and, possibly, heating of the transmitter. In addition, due to the small opening of the waveguide (less than one wavelength), there is a significant diffraction, as a result of which we get widespread, but not directed radiation.

By expanding the waveguide in the form of a bell, it is possible to greatly improve its characteristics, to achieve amplification and directivity of radiation. A continuation of the circular waveguides used by industrial rangefinders is a cone-shaped horn.

The gain depends on the important geometrical parameters of the antenna: the length of the horn; the opening area; the expansion angle. The horn length is selected in the range from 2 to 5 working wave length. The opening area is the area of the outlet mouth of the bell, the larger it is, the higher the gain and the better the radiation directivity. The amplification of the horn antenna is determined by the area of its opening and can be calculated by the formula: where: λ is the wavelength, S is the area of the opening of the horn, v-KIP (horn surface utilization factor), equal to 0.6 for the case when the difference in the course of the central and peripheral rays is less than, but close to π/2, and 0.8 when using devices that equalize the phase of the wave.

A parabolic antenna, otherwise called a "parabolic reflector" is the most common among all microwave antennas. This type of antenna comes from optics, which is quite understandable, since microwaves are in the transition region between ordinary radio waves and visible infrared radiation. A parabolic reflector, as such, is not an emitter. It reflects the waves sent in its direction by the so-called irradiator located at a certain focal length. Due to the shape of the parabola, the reflected waves converge into a parallel beam, which ensures their narrow orientation. The larger the reflector relative to the wavelength, the narrower the beam. Parabolic antennas, among others, are characterized by the best gain and the highest directivity coefficient.
The gain of a parabolic antenna can be calculated using the formula:
where: A is the area of the antenna opening, which is the mouth of the parabolic reflector, d is the diameter of the parabolic reflector, λ is the wavelength, eA is an abstract parameter between 0 and 1, called the "opening efficiency". The typical opening efficiency for parabolic antennas ranges from 0.55 to 0.70. It can be seen that the larger the opening area, comparable to the wavelength, the higher the gain.

Antennas are designed to form the directivity and send the maximum power in the direction of propagation of microwave radiation. In practice, it is impossible to focus all the energy in one direction, some of it spreads out to the sides and generates the so-called side lobes of directivity relative to the main lobe located in the center of the diagram. The side lobes have a smaller amplitude. The purpose of a directional antenna is to increase the power of the main lobe by reducing the power of the side lobes. The beam width that characterizes the antenna is determined by the width of the main lobe of the BOTTOM at the half-power level (which is 2 dB lower than the maximum gain along the main axis of the BOTTOM). The higher the antenna gain, the narrower the BOTTOM beam. The beam width of the antenna usually narrows as the size of the reflector increases. The beam width is usually expressed in terms of the divergence angle. The directional pattern of a horn antenna is characterized by a wider divergence angle and lower gain compared to a parabolic antenna, so horn antennas are used where it is necessary to spread microwave radiation over a larger area, and parabolic antennas are used where a point-to-point orientation is required at a greater distance.

Microwave technologies are used for non-contact detection and control of the position of objects, measuring distance and level in very severe operating conditions associated with high temperature, smoke, steam, dust and dirt. The principles of detection and measurement of microwave devices are based on the reflection of radio waves caused by a sharp change in the macroscopic parameters of the medium that characterize the propagation of radio waves: dielectric and magnetic permeability. The conditions mentioned above, which impair the optical properties of the medium and prevent the propagation of light radiation, do not affect the propagation of radio waves. Basically, radio waves and optical waves obey the same laws. When radio waves collide with a smooth surface, there is a "mirror" reflection, which is described by Fresnel formulas, and when they collide with a rough surface, diffuse reflection occurs. Microwave rangefinders for industrial automation perform detection and measurement based on the spectral analysis of a mixture of carrier, transmitted and reflected waves using the fast Fourier transform (FFT) algorithm. The ability to detect and measure, independent of the optical and mechanical properties of the medium, determines the applicability of radio wave technologies in such industries as metallurgy, mining and processing industry, chemical industry, production of building materials, etc.

This invention became one of the greatest in the history of science and technology - it was ultimately the forerunner of today's information society, making ultra-fast news delivery possible for the first time.

Bibliography:

Radar Fundamentals (Part II ) – Aircraft 101 (wordpress.com)

Omni Antenna vs. Directional Antenna - Cisco