RU2470424C1 - Small-size capacitive antenna with matching inductance coil - Google Patents

Abstract

FIELD: physics, radio.

SUBSTANCE: invention relates to antenna equipment and can be used in designing small-size antenna devices for communication equipment and transmitting data in MW, SW and USW frequency ranges. The small-size capacitive antenna with a matching inductance includes series-connected inductance coil and capacitive element whose plates are in form of coaxial cylindrical current-conducting surfaces placed vertically one above the other. Connection of the elements forms an antenna oscillatory circuit with resonance at the given frequency of the transmitted or received electromagnetic signal. The antenna is fed through a coaxial line connected to the matching inductance coil which is connected in series to the inductor of the antenna circuit and is placed coaxially with it. All components of the antenna are made on a cylindrical base made of a radiotransparent dielectric.

EFFECT: higher efficiency of the antenna during radiation, higher responsiveness and simpler method of matching the antenna with the characteristic impedance of the feed line during operation.

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Description

The invention relates to antenna technology and can be used to create small-sized antenna devices for communication equipment and data transmission in CB, KB and VHF frequency bands.

As is known, the use of short-wave and ultra-short-wave full-size (half-wave) antennas in radio communications is often associated with difficulties due to their large size. So, for example, a half-wave dipole tuned to a frequency of 2 MHz has a length of about 75 meters. In addition, for its effective operation, a large installation height of the antenna relative to the ground is required, which in many cases is unacceptable.

Small-sized shortened (in the electrical sense) antennas, usually used in mobile radio communications, have a low radiation efficiency and a small reception gain. This significantly reduces the real range of radio communications.

Capacitive antennas are more effective than shortened ones (see, for example, patent: Inductive-capacitive antenna, Russia, No. 2383974, H01Q 9/00, 09/05/2008). The antenna contains two main elements, one of which is made in the form of a flat inductor, and the other is in the form of a conductive surface on a dielectric pipe, which performs the function of a capacitor plate. The disadvantage of this antenna is the design complexity, which makes it difficult to use it on mobile radio communications.

The closest analogue is the "Coaxial inductor and dipole EH antenna" (US Patent No. US 6956535 B2 dated 10/18/2005). This known antenna, taken as a prototype, contains a capacitive element in the form of two coaxially arranged conductive cylinders and an inductor connected in such a way that together they form an oscillating circuit tuned to the frequency of the emitted or received signal. The disadvantages of such an antenna are the inability to fully realize the potential of the antenna during radiation, as well as the difficulty of matching it with the feeder line.

The aim of the invention is to increase the efficiency of the antenna during radiation, as well as improving the efficiency and simplification of the method of matching the antenna with the impedance of the feeder line during operation.

The technical result is achieved by the fact that:

- in order to increase the efficiency (efficiency) of the antenna during radiation, the connection points of the conductive cylinders have been changed;

- in order to increase the efficiency and simplify the technique of matching the antenna with the feeder line, a matching design inductor is used, which allows changing the input impedance of the antenna during operation.

The drawings show:

figure 1 - the design of a small capacitive antenna with a matching inductor, where the numbers indicate:

1 - a cylindrical base made of a translucent dielectric (for example, fiberglass or polypropylene), on which all the antenna components are mounted;

2 - plates of the capacitive element of the antenna circuit, made in the form of cylindrical conductive surfaces (for example, copper foil);

3 - inductance coil of the antenna circuit;

4 - matching inductor for matching the input impedance of the antenna with the impedance of the feeder line;

5 is a frame of a matching inductor having a helical circular groove on the surface for laying turns of a copper wire made of an elastic dielectric (for example, silicone);

6 - upper fixed dielectric flange with a threaded insert;

7 - threaded insert;

8 - lower movable dielectric flange;

9 - dielectric threaded rod;

10 - drive rotation of the dielectric stud;

figure 2 - distribution of bias currents in the space around the capacitive antenna, where the numbers indicate:

1 - conduction current;

2, 3 - bias currents;

4 - polarization current;

5 - magnetic field;

figure 3 - distribution of bias currents in space with different methods of connecting a capacitive element.

A small-sized capacitive antenna with a matching inductor (capacitive antennas see: Aizenberg GZ and other VHF antennas. Part 1. M .: Communication, 1977, p. 82), made on a cylindrical base 1, consists of a space-deployed one capacitive element 2 formed by two cylindrical conductive surfaces, for example, of copper foil. In series with it, an inductor 3 is connected, forming an oscillating circuit (antenna circuit) with a capacitive element 2, tuned to the frequency of the emitted or received electromagnetic signal (see Fig. 1). To the antenna circuit using a matching inductor 4 connected to the feeder line that feeds the antenna.

When emitted by a feeder line electrically matched with the antenna, a high frequency signal voltage is supplied from the transmitter. At the resonance between the cylindrical plates of the capacitive element deployed in space, an alternating high-frequency voltage arises, which is Q times the input voltage (Q is the quality factor of the antenna circuit). At the same time, a strong high-frequency electric field is formed around the cylinders, the change of which in time induces eddy displacement currents in the surrounding space (Eichenwald A.A. Electricity, ed. Fifth, M.-L .: State publishing house, 1928, the first Maxwell equation), which form high frequency electromagnetic field.

Some part of the bias currents remains connected with its source (G. Eisenberg and other VHF antennas. Part 1. M .: Svyaz, 1977, p. 84) since it circulates through closed loops (see Fig. 2), in which on the part of the path they are in the nature of conduction currents 1 (in a conductor) or polarization currents 4 (in a dielectric). “Bound” bias currents correspond to “coupled” (reactive) power, which is not radiated into space, but is dissipated during the periodic exchange of energy between the capacitance and inductance.

Another part of the bias currents (“free” bias currents) loses contact with the source and propagates in the surrounding space. "Free" bias currents correspond to radiated power. The magnitude of the ratio of the reactive and radiated powers depends on the magnitude of the efficiency of the antenna (with radiation).

In an antenna circuit with an open capacitive element, the associated power is minimal, so the radiated power and antenna efficiency will be greatest. In addition, at resonance, when the reactance of the antenna circuit is minimal (ideally equal to zero), the losses in the antenna will mainly be determined by the active (ohmic) resistance of the inductor. If it is wound with a copper wire of a relatively large cross section, and the number of turns is less than a certain limiting value, then the radiation loss does not exceed 10% and the antenna efficiency can reach 90-95 percent. In traditional shortened antennas, this value is significantly less - 0.5-50 percent, depending on the frequency and design of the antenna.

In order to fully realize the potential capabilities of a small-sized capacitive antenna and to obtain the highest possible efficiency value, it is necessary to change the position of the connection points of the conductive cylinders in comparison with the prototype. The positive effect obtained in this case is due to the following. If the feeder line and the inductance of the antenna circuit are connected, as in the prototype, between the inner ends of the conductive surfaces, then bias currents are formed in space, firstly, by a conductivity current 1 flowing along the upper conductive surface (see Fig. 3a, bias current 2), and secondly, a polarization current 4 flowing in a relatively short dielectric gap between the cylinders (figa, bias current 3). The bias currents induced by these sources are directed in the opposite direction, so the total field around the antenna will be determined by their difference.

If the connection points are transferred to the outer ends of the cylinders (Fig.3b), then the spatial bias currents will be induced by the conduction currents 1 in the conductive cylinders 2 and the polarization current 4 in the dielectric, flowing in one direction. In this case, the bias currents will be summed, and the electromagnetic energy emitted by the antenna will increase. Measurements show that due to this, the electromagnetic field strength near the antenna increases by 1.5-2 dB.

A characteristic feature of a small capacitive antenna that distinguishes it from known types of both small and other types of antennas is that in the electromagnetic field that it forms, the voltage vectors of the electric component E and magnetic component H turn out to be in-phase in time in the immediate vicinity of antennas. This is confirmed by multiple instrument measurements. Consequently, an electromagnetic wave (Poynting vector) in a capacitive antenna is formed simultaneously with the appearance of an electric field between the plates of the capacitive element. In other types of antennas (full-sized and shortened), an electromagnetic wave is formed in the far zone at a distance of several wavelengths from the emitter. Therefore, the linear dimensions of capacitive antennas turn out to be significantly less than the wavelength of the emitted (received) electromagnetic signal.

The optimal electrical mode of operation of the antenna is ensured by tuning it to a minimum standing wave coefficient (SWR) while matching the input impedance of the antenna with the impedance of the feeder line. Various coordination methods are known. For example, (US Patent Nos. US 6486846 B1, 11.26.2002; No. US 6864849 B2, 03/08/2005), a method for matching a capacitive antenna using external matching devices, namely the Bushero Bridge (German Patent No. DE 603816, 1932), is considered. In this case, to change the matching parameters, it is necessary to use variable capacitors and (or) inductance. However, for matching small-sized capacitive antennas, the use of such capacitors is impractical due to the strong dependence of their parameters on atmospheric influences and the presence of sliding contacts with large and unstable electrical resistance. It was experimentally established that an increase in the active electrical resistance of the antenna circuit by tenths of an ohm can lead to a decrease in the intensity of the electromagnetic field in space by 25-30 percent.

The use of a ferromagnetic core to change the inductance of the coil is also impractical due to the presence of large losses in the core at a high frequency in the radiation mode.

The use of a variable inductance coil (variometer) as a matching element is not justified, because, firstly, the presence of sliding contacts in the variometer significantly increases the active losses in the antenna; and, secondly, this can lead to several resonances in the antenna and its detuning.

In order to ensure the operational adjustment of the antenna to a minimum of SWR, it is proposed to use a matching design inductor 4 (see Fig. 1) of a special design for matching the antenna with the feeder line, connected in series with the antenna circuit inductance coil. The matching coil is made on the frame of an elastic dielectric having a helical circular groove on the surface in which the coils of the copper wire are laid.

A matching inductor is located between the rigid dielectric flanges. The upper flange of the coil is fixed at the base of the antenna below and coaxially with the inductor of the antenna circuit and has a threaded insert in the geometric center into which a dielectric threaded rod is screwed. The lower end of the stud passes through an opening in the lower movable flange and is mechanically connected to the rotation drive. The rotation of the stud leads to the displacement of the lower flange in the axial direction, resulting in compression (tension) of the frame of the matching coil. In this case, the distance between its turns changes and, as a result, the reactance of the matching coil and the input impedance of the antenna change. This allows you to quickly adjust the matching antenna in the process. At high antenna heights, the rotation drive can be remotely controlled.

An instrumental assessment of capacitive antenna parameters showed that, compared with other types of small antennas that are widely used in practice, they have the following advantages:

- high efficiency (up to 90-94 percent) in radiation, while in traditional ones - in the range of 0.5-50 percent, depending on the wavelength and design features of the antenna;

- significantly smaller dimensions (20-40 times depending on the wavelength);

- less dependence on the influence of the surface of the earth, which reduces the height of the antenna;

- replacing standard antennas with small-sized capacitive ones in commercially available mobile VHF radio stations increases their real range by 2-2.5 times with constant transmitter power.

The capacitive antenna installed on the drive radio station of the Seltso airfield (Leningrad Region) has been tested for three years. In this case, the regulatory range of the aircraft’s drive is provided using a capacitive antenna, the overall dimensions of which are not commensurate with the characteristics of a standard antenna, commercially available drive radio station PAR-10, and the power supplied to the antenna from the transmitter is several times lower than in PAR-10.

Claims (6)

1. Small-sized capacitive antenna with a matching inductor, containing a capacitive element in the form of two coaxially arranged cylindrical conductive surfaces and an inductor, characterized in that the antenna circuit includes a matching inductor, the upper tap of which is connected to the central conductor of the feeder line and to the lower retraction of the inductance coil of the antenna circuit, the upper tap of which is connected to the upper end of the upper conductive surface; the lower tap of the matching inductor is connected to the lower end of the lower conductive surface and to the outer braid of the feeder line. 2. A small-sized capacitive antenna with a matching inductor according to claim 1, characterized in that all the structural elements of the antenna are made on a cylindrical base from a radio-transparent dielectric. 3. A small capacitive antenna with a matching inductor according to claim 1, characterized in that the matching inductor is made on the frame of an elastic dielectric having a helical circular groove on the surface into which the turns of a copper wire are laid. 4. A small capacitive antenna with a matching inductor according to claim 1, characterized in that the matching inductor is located between two rigid dielectric flanges, the upper of which is rigidly fixed below and aligned with the antenna coil and has a threaded insert in the geometric center into which a threaded dielectric screw is screwed. 5. A small capacitive antenna with a matching inductor according to claim 1, characterized in that in the matching inductor, the lower end of the threaded dielectric stud passes through an opening in the lower movable dielectric flange and is mechanically connected to the rotation drive. 6. A small-sized capacitive antenna with a matching inductor according to claim 1, characterized in that in the matching inductor the rotation of the dielectric pin moves the axial direction of the lower dielectric flange, resulting in compression (tension) of the coil frame and the input impedance of the antenna .

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