RU2407118C1 - Wideband antenna array - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: wideband antenna comprises flat dielectric base with metallised layers. In metallised layers there is a system of excitation 9 and radiating aperture connected to it. Radiating aperture is made of horn-type sources 5, 6, 7, 8, arranged in the several levels. The novelty is the fact that the left (right) generatrices of horns at all levels are arranged at current-bearing side of plate and are the continuation of microstrip conductor of excitation system, under which metallisation is removed. The right (left) generatrices are arranged on screen side of plate by means of screen cut (removal of metallisation). Generatrices cross at the angle α, forming a unit of lower (zero) level horn excitation. By means of redistribution of capacity between propagating modes, control of position of directivity patterns maximum is carried out.

EFFECT: development of wideband antenna array with high transmitted capacity and frequency-independent unit of excitation, production of controlled dynamic amplitude-phase distribution in antenna aperture.

2 cl, 6 dwg

Description

The proposed technical solution relates to electrical engineering and can be used in broadband antennas where transverse and longitudinal emitters are used.

Such emitters realize horn, lens, mirror, discrete antennas, surface wave antennas and antennas in the form of open longitudinal emitters (Kuhn R. Microwave antennas, M., Shipbuilding, 1967, p.95, 198, 258, 304, 373, 420) .

These antenna systems are effective devices that allow you to obtain the required technical parameters in a limited frequency band. When trying to create antenna systems with a bandwidth of several octaves - up to a decade - significant technical difficulties arise in ensuring high electrical parameters (radiation pattern width, low level of side lobes, gain, reflection coefficient) in the specified frequency band.

A technical solution is known, described in RF patent No. 2052878, which proposes a broadband antenna made on a dielectric substrate with metallized surfaces. On one side of the board (screen side), the main surface is occupied by a metallized (copper) conductor. On metallization, a part of the surface bounded by a radiating flat horn formed by two intersecting flat horns is removed, the tapering part of which passes into a slit line, and the intersection point of adjacent walls lies on the axis of symmetry of the radiating horn. If high-frequency energy enters through the slit lines, then the edges of the radiating horn are associated with free space. The location of the points at which the microstrip line is connected relative to the slotted line is realized by the excitation nodes, which determine the antenna impedance. On the reverse side of the board (current-carrying side) there are microstrip conductors operating as a high-frequency transmission line (excitation system). The microstrip crosses the slot line and provides capacitive coupling with the latter.

The disadvantages of this device are:

- the difficulty of matching the wave impedances of the slotted and microstrip transmission lines;

- limited (small) power transmitted by the slit line.

The technical result of the proposed technical solution is the development of a broadband antenna array with large transmitted power and a frequency-independent excitation unit, obtaining a controlled dynamic amplitude-phase distribution at the antenna aperture.

This is achieved by the fact that a broadband antenna array containing a flat dielectric base with metallized layers in which a radiating opening is made up of flat horn emitters placed at several levels is characterized in that the left (right) generators of the horns of all levels are made on the current-carrying side boards and are a continuation of the microstrip conductors of the excitation system, under which metallization is removed, and the right (left) generators are made on the screen side of the board in the form of a slice screen (removal of metallization), while the generators intersect at an angle α, forming a horn excitation node of the lowest (zero) level, which is excited by the wave of the electromagnetic field of the TEM structure, the impedance of which depends only on the opening angle of the horn.

Since the structure of the multi-level radiating aperture (broadband antenna) is built on the principle of hierarchical systems with embedded processes, its amplitude-phase distribution is dynamic, therefore, by including a controlled element (adjustable phase shifter, delay line, attenuator) in one of the levels of the excitation system (right or left) ) the change in the ratio of amplitudes of propagating modes is easily and simply carried out, which allows one to effectively control the position of the maximum of the radiation pattern.

The presented drawings explain the essence of the proposed device.

Figure 1 shows a two-level broadband antenna;

figure 2, 3 explains the principle of superposition of propagating modes for cases of in-phase, out-of-phase, uniform-amplitude and in-phase, unequal-amplitude excitation of the antenna aperture;

on figa - the principle of superposition of propagating modes for the case of out-of-phase equipotential excitation of the antenna aperture;

on figb - the principle of superposition of propagating modes for the case of in-phase non-uniform amplitude excitation of the antenna aperture;

figure 4 shows the normalized radiation patterns;

figure 5 shows a multi-level broadband antenna;

6 illustrates the hierarchy of the construction of a multi-level radiating aperture formed from horn emitters placed at several levels.

In the figures 1, 2, 3, 4, 5 are indicated:

1 - generators of flat horns made on the current-carrying side of the board in the form of microstrip conductors;

2 - generators of flat horns made on the screen side of the board in the form of a "cut" of the screen (removal of metallization);

3 - controlled element;

4 - surfaces of the screen side of the board on which metallization is removed are indicated in a circle;

5 - flat mouthpiece of the zero (lower) level;

6 - a flat mouthpiece of the first level;

7 - flat mouthpiece of the second level;

8 - flat horn of the third level;

9 is a system for exciting the aperture of a broadband antenna, made in the form of a set of parallel-sequentially connected microstrip conductors having a multi-level hierarchy of construction and symmetrical with respect to the input (points O2 ');

M is the point of spatial overlapping (intersection) of the generators 1, 2 of the horns of the zero level, in which the excitation node is implemented;

α is the angle between generators 1 and 2, which characterizes the opening angle of the zero-level horn;

O, O1, O2 - points through which the symmetry axes pass, perpendicular to the opening, they are the connection points (electrical contact) forming 1, 2 horns of zero, first, second, etc. levels respectively.

The aperture excitation system 9 of the broadband antenna - solid lines - microstrip conductors made on the current-carrying side of the board, which implement the excitation system; the shaded part of the screen side of the board corresponds to the presence of metallization, dotted lines indicate the contours of the surface of the screen side of the board on which metallization is removed.

In the microstrip transmission line, the main wave of the electromagnetic field is the wave of the TEM structure, which is characterized by the presence of only the transverse components of the electric and magnetic fields. The propagation velocity and wave impedance of the TEM wave are practically independent of frequency. For the slit line, the main wave of the electromagnetic field is the wave of the TE structure, which, in addition to the transverse components, also has a longitudinal component. Therefore, the propagation velocity and wave impedance of the TE wave strongly depend on the frequency, in addition, it has a critical frequency below which high-frequency energy is not transmitted along the slit line at all. In general, the input impedance of an antenna is complex, which has an active and reactive component. For most antennas, the active component of the input resistance is characterized by a value of about 70-100 Ohms. The slit line, made on widespread dielectric substrates with a wave impedance of 70-100 Ohms, has a slit width of the order of 0.08-0.1 mm, hundredths of a millimeter, which causes great technological difficulties in its execution (manufacturing). In addition, the small slit width sharply limits the transmitted power.

This problem can be solved if the excitation unit and the flat horn are executed not in the same plane (as was done in RF patents Nos. 2052877, 2052878), but in two parallel planes that are spatially spaced a certain distance. In this case, the flat horn will be excited by the wave of the TEM structure, which completely solves the coordination problem, and the choice of the distance between the planes solves the problem of transmitted power. From a theoretical point of view, such an “excitation unit” is ideal, since its electrical parameters are determined only by the geometry of the system (the aperture angle of the horn), it is completely independent of the frequency and has no restrictions on the transmitted power. In this case, point M does not have any features, unlike a horn, the generators of which lie in the same plane and are excited by a slit, which in turn is excited by a microstrip transmission line included in the short circuit or idle mode.

In the proposed technical solution, the goal is achieved through the implementation (execution) of the generating horns on different sides of the dielectric substrate having a certain thickness. Generator 1, made on the current-carrying side of the board, is a continuation of the microstrip conductor of the excitation system 9, under which metallization is removed; Generator 2 is made on the screen side of the board in the form of a slice of the screen (removal of metallization). At point M, the generators 1 and 2 overlap each other in space (intersect) at an angle α. Since metallization is removed under the generatrix 1, the electric field lines of the field field of the wave of the TEM structure are closed to the generatrix 2, exciting the horn 5 with the TEM wave. If the angle α is chosen small, then the structure of the TEM wave field is preserved in the horn, only the orientation of its electric field lines changes. In the excitation system 9, the electric power lines were directed from top to bottom (microstrip conductor - screen), and in the horn 5 they are directed from left to right (microstrip conductor - screen), see Fig. 1. In this case, the point M does not have any features, it simply characterizes the location of the excitation node, which determines the impedance of the speaker Z. In this case, the impedance of the speaker is a function of only the opening angle α and is determined by the expression:

.

.

A broadband antenna array, built on the principle of hierarchical systems with embedded processes, is a set of flat zero-level horns 5 (N ₀ ) with linear aperture sizes greater than half the smallest wavelength of the required frequency range, arranged in pairs one next to the other. Pairs of adjacent horn emitters should be symmetrical about the center line drawn through the point O of intersection of adjacent (adjacent internal) generators 1, 2 and perpendicular to the opening. For each pair of neighboring zero-level emitters, the external (external) generators 1, 2 (until they intersect the point O1) mutually continue for a certain length, which allows creating N ₁ horn emitters of the first level 6, in which the conditions for excitation of propagating modes as higher and lower, lower frequency range. Then, for each neighboring pair of horn emitters of the first level, the external generators 1, 2 (until they intersect the point O2) mutually continue to a certain length, which allows creating N ₂ emitters of the second level 7, in which the conditions for excitation of propagating modes, both higher lower, even lower frequency range. The described process with adjacent pairs of horns of different levels continues until the desired opening is formed, providing the required bandwidth. The continuation of the generators 1, 2 for horns of all levels does not have to be performed on a dielectric substrate, they can be made in the form of conductive rods or wires for which the environment (free space) is the dielectric base, see Fig. 5. Also, they do not have to be straight, but can be broken or exponents - this is determined already by the features of a particular performance. From a theoretical point of view, there are no restrictions on creating a broadband antenna with any required bandwidth (on the proposed principles). In this case, the broadband antenna includes:

- the number of elements of the zero level N ₀ = 2 ^m ;

- the number of elements of the first level N ₁ = 2 ^m-1 ;

- the number of elements of the second level N ₂ = 2 ^m-2 ;

- the number of elements of the level m N _m = 2 ^mp ;

- the number of elements of the highest level when p = m, N = 1;

- the total number of elements forming the extended structure of a broadband antenna with dynamic amplitude-phase distribution is determined by the expression N = Σ2 ^mp , where m is the number of level transitions; p is the level number.

For figures 1 and 5, p = 1 and 3, and N = 3 and 15, respectively.

A feature of constructing the structure of a broadband antenna array is that the elements of any level (except the zero) are constructed according to the same scheme, the mechanism for forming the field structure in the aperture of elements of all levels is exactly the same, and they differ only in boundary conditions. Therefore, the structure for constructing a broadband antenna is strictly subordinate to the theory of hierarchical systems with embedded processes, this is especially clearly seen in Fig.6. From figure 1, 5, 6 it follows that the broadband antenna in a first approximation can be considered as a rolled-up horn, which is characterized by the coefficient of spatial shortening (compression):

,

,

where L _h is the length of the original speaker, and L _fh is the length of the folded speaker representing a broadband antenna. If the original speaker has only one entry point (control) O2 ', then the folded speaker is characterized by the number of control points n = 2 for figure 1 and n = 8 for figure 5.

The amplitude-phase distribution at the aperture of a broadband antenna is dynamic, easily controlled at any of the entry points. Figure 2, 3 shows the superposition for the simplest case of a two-level antenna with in-phase uniform-amplitude (Fig. 2), unequal-amplitude (Fig. 3b) and antiphase uniform-amplitude excitation of the aperture (Fig. 3a). As follows from FIGS. 2, 3a, with equal-amplitude excitation, the resulting distribution in the aperture is symmetric with respect to the center, and with unequal-amplitude excitation, it is asymmetric (biased), and the magnitude of this shift depends on the ratio of the amplitudes of the propagating modes. Spatial modes are characterized by different angular-frequency dependences; therefore, the ratio of their amplitudes determines the direction of the maximum position of the antenna pattern. For the simplest case of excitation of an even and odd aperture by propagating modes, the distribution of the electric field in the aperture can be represented as

;

;

;

;

where A ₁ , ψ ₁ is the amplitude and phase of the lowest mode H ₁₀ ;

A ₂ , ψ ₂ — amplitude and phase of the higher mode H20;

β, ψ ₁₂ — amplitude ratio and phase difference of the higher and lower modes.

The normalized values of the gain function of the aperture with distribution (1) are described by the expression

- обобщенная угловая координата,Where

- generalized angular coordinate,

sinΘcosφ - direction cosines,

λ is the wavelength in free space;

Θ, φ are the spatial angles of the spherical coordinate system,

a is the linear size of the aperture (aperture),

- размер раскрыва, нормированный к длине волны.

- the size of the aperture, normalized to the wavelength.

, из которых следует, что посредством перераспределения мощности между распространяющимися модами (изменения отношения амплитуд) можно очень эффективно управлять положением максимума диаграммы направленности в пространстве, при этом форма ДН практически не изменяется, а уровень боковых лепестков не превышает стандартных значений; β=0 соответствует случаю синфазного равноамплитудного возбуждения раскрыва - фиг.2; β=0.5…2 соответствуют случаю неравноамплитудного синфазного возбуждения раскрыва - фиг.3б. При размере раскрыва а=1.8λ ширина диаграммы направленности по уровню половинной мощности 2Θ_0.5p=38°. При отношении амплитуд распространяющихся мод β=0.5…2 и пространственном фазовом набеге между ними

максимум диаграммы направленности смещается на угол Θ=17.5° и 25° соответственно (фиг.4), то есть более чем на половину ширины диаграммы; при этом форма диаграммы направленности практически не изменяется, а уровень боковых лепестков не превышает стандартных значений. В обычных антеннах, и даже фазированных антенных решетках, с указанным размером апертуры и одним управляемым элементом такой результат недостижим.In Fig. 4, normalized radiation patterns are constructed according to expression (2), where ψ ₁₂ = 0.5π;

, from which it follows that by redistributing the power between the propagating modes (changing the amplitude ratio), it is possible to very effectively control the position of the maximum radiation pattern in space, while the shape of the pattern remains practically unchanged, and the level of the side lobes does not exceed standard values; β = 0 corresponds to the case of in-phase equal-amplitude excitation of the aperture - figure 2; β = 0.5 ... 2 correspond to the case of unequal in-phase excitation of the aperture - Fig.3b. With the aperture size a = 1.8λ, the width of the radiation pattern at the half power level is _{2Θ 0.5p} = 38 °. With the ratio of the amplitudes of the propagating modes β = 0.5 ... 2 and the spatial phase incursion between them

the maximum of the radiation pattern is shifted by an angle Θ = 17.5 ° and 25 °, respectively (figure 4), that is, more than half the width of the diagram; the shape of the radiation pattern remains virtually unchanged, and the level of the side lobes does not exceed standard values. In ordinary antennas, and even phased antenna arrays, with the indicated aperture size and one controlled element, such a result is unattainable.

From the foregoing, it becomes obvious that the tasks posed in the development of this technical solution are completely solved by the proposed design of the broadband antenna array, which has a frequency-independent excitation unit with a large transmitted power, a controlled dynamic amplitude-phase distribution at the aperture, which makes it possible to solve the problems quite simply bandwidth expansion, matching, transmit power and radiation pattern control. The proposed technical solution is a perfect microstrip antenna, performed using modern technology of printed circuit boards, characterized by compactness, low weight and high adaptability. A broadband antenna will be especially effective in applications where ultrashort pulses are used for radiation, of the order of picosecond and nanosecond durations - these are digital communication and data transmission systems, subsurface location, radar superresolution, systems for simulating a nuclear pulse of a nuclear explosion, and also in wireless transmission lines electrical energy.

Claims (2)

1. A broadband antenna array containing a flat dielectric base with metallized layers in which a radiating opening is made up of flat horn radiators placed at several levels, characterized in that the left (right) generators of the horns of all levels are made on the current-carrying side of the board and are a continuation of the microstrip conductors of the excitation system, under which the metallization is removed, and the right (left) generators are made on the screen side of the board in the form of a cut of the screen (removal of metal llizatsii), thus forming intersect at an angle α, forming a lower excitation horn assembly (zero) level, which is excited by the electromagnetic wave field TEM structure, the impedance of which depends only on the angle of aperture of the horn. 2. The device according to claim 1, characterized in that in one of the levels of the excitation system, right (left), a controlled element is included, by means of which the amplitude ratio of the propagating modes is changed.

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