RU2400879C1 - Double-channel duel-band quadrifilar antenna - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: spiral radiators (SR) are conical, and each of them is made in the form of piece (3) of transmission line, which contains the main and auxiliary conductors (C), as well as radiating (4) C. Feed circuit is made in the form of two quadrature four-channel power dividers with one input (15) and four outputs (13) and (14). Outputs (13) and (14) of feed circuit contain eight central (1) C and one common (2) C. The main C of pieces of (3) transmission lines are connected on one side to central (1) C of outputs of feed circuit, and on the other side to radiating (4) C; at that, central (1) C of pieces (3) of transmission lines of various groups (5) and (6) SR are connected to central (1) C of outputs (13) and (14) of various quadrature power dividers. Auxiliary C of pieces (3) of transmission lines are connected to common (2) C of feed circuit. Radiating (1) conductors of SR are offset relative to each other through 180 degrees and connected to each other with connection straps (9). Concentrated resonant circuits are connected to radiating (4) C. Resonant frequencies (RF) of circuits connected to radiating (4) conductors of SR of one group have similar RF differing from RF of the circuits connected to radiating (4) conductors of SR of the other group.

EFFECT: enlarging working frequency band, separation of signals of two frequency bands as to various inputs, and reducing aerodynamic resistance.

6 cl, 8 dwg

Description

The invention relates to antenna technology and can be used as an antenna of a receiving device for satellite navigation.

Spiral antennas are widely used in various electronic systems, including navigation systems. Their advantages include simplicity of design, relatively small dimensions and, at the same time, one-sided directivity of radiation. Antennas based on a single helix are well known (Kraus J.D. "A 50-Ohm Input Impedance for Helical Beam Antennas" IEEE AP. V. AP-25. No. 6. P.913). The disadvantages of such antennas are their large dimensions, due to the fact that for the satisfactory operation of the antenna requires a large number of turns for the formation of a wave running along the spiral.

Multiple-helixes, most often two- and four-way, can have significantly smaller dimensions, since they can function as resonant antennas. Resonance in the antenna occurs when the length of the conductors is a multiple of a quarter of the wavelength in free space. The most widespread are antennas with quarter- and half-wave shoulders. The smallest dimensions are quarter-wave two- and four-way helical antennas.

The proposed solution relates to four-way helical antennas, which are also called quadrifilar antennas. The advantage of such antennas is the possibility of realizing circularly polarized radiation in a fairly wide frequency range. In antenna technology, the radiation pattern is a complete radiation pattern. A simpler characteristic adopted for the description of antennas of small electrical dimensions is the ratio of the radiation intensity forward to the radiation intensity back (OIVN). This parameter is often used to describe multiple helix antennas that have a maximum radiation along the axis of the spiral in one direction and a minimum along the same axis, but in the opposite direction.

Quadrifilar antennas differ in different power circuits, significantly affecting their functioning. Known quadrifilar antenna with one battery (US patent, No. 5170176, 1992). The disadvantage of this technical solution is the contradiction between the requirements for radiation ellipticity and the requirement of matching the antenna. The ellipticity of a circularly polarized antenna is characterized by an ellipticity coefficient (FE), which is ideally equal to unity. In an antenna with one battery, it is impossible to simultaneously provide perfect matching and FE equal to one. Therefore, usually one of the important parameters has to be compromised. In addition, such an antenna has a relatively narrow band of operating frequencies.

The closest technical solution to the claimed antenna is a dual-band quadrifilar antenna (US patent No. 4008479, 1977), containing a power circuit and eight helical emitters having a common axis of symmetry and located with a shift of 45 degrees relative to each other, combined in two groups of four identical spiral emitters shifted relative to each other by 90 degrees, the spiral emitters of one group are made with a length different from the length of the spiral emitters of the other group.

This antenna has a power circuit and eight helical emitters, bent along spirals having a common axis. They differ in an angular shift of 45 degrees relative to each other. Spiral conductors are combined in two groups of four identical conductors, 90 degrees offset from each other. Spiral conductors in different groups have different lengths. The excitation of spiral emitters is carried out using a power circuit that has one input and four outputs. The power circuit generates voltages with the same amplitude and a phase shift of ± 90 degrees at its outputs. The presence of a phase shift together with the spiral shape of the emitters provides, on the one hand, the circular polarization of the emitted field, and on the other hand, a high value of the SIR.

For reasons that impede the achievement of the technical result indicated below, when using the known antenna adopted for the prototype, there is an extremely low input impedance of helical emitters, which is units of Ohms. Coordination of such resistance with other circuits, usually designed to work with loads of 50 Ohms, is carried out using special impedance transformers. The use of such transformers increases the dimensions of the antenna, narrows its frequency band, increases the cost.

The disadvantages of this antenna also include the fact that it is a single-input (single-channel) antenna, in which when working at the reception, signals of different frequency ranges are allocated at the common input.

Another disadvantage of this antenna is its high aerodynamic drag, which complicates the installation of the antenna in the bow of the aircraft, which has a conical shape. The installation of a cylindrical antenna in this place either increases the aerodynamic drag of the aircraft, or increases the volume that the antenna occupies.

The proposed technical solution is aimed at obtaining a technical result, which is expressed in expanding the working frequency band, separating the signals of two frequency ranges at different inputs and reducing aerodynamic drag.

The specified technical result during the implementation of the invention is achieved by the fact that the spiral emitters are made in the form of conical spiral emitters, each of which is made in the form of a segment of the transmission line containing the main and auxiliary conductors, as well as the radiating conductor, the power circuit is made in the form of two quadrature four-channel power dividers with one input and four outputs, the outputs of the power circuit contain eight central conductors and one common conductor, the main conductors of the line segments the transmission are connected on one side with the central conductors of the outputs of the power circuit, and on the other hand with radiating conductors, the central conductors of the segments of the transmission lines of various groups of spiral radiators connected to the central conductors of the outputs of various quadrature power dividers, the auxiliary conductors of the segments of the transmission lines are connected to a common conductor power circuits emitting the conductors of spiral radiators are shifted relative to each other by 180 degrees and connected to each other with bridges, and concentrated resonant circuits are included in the radiating conductors, and the resonant frequencies of the circuits included in the radiating conductors of the spiral radiators of one group have the same resonant frequencies, which differ from the resonant frequencies of the circuits included in the radiating conductors of the spiral radiators of another group.

There are additional options for performing a dual-channel dual-band quadrifilar antenna, in which:

- a dielectric cone is additionally introduced into the antenna, and spiral radiators are located on the surface of the specified dielectric cone;

- segments of transmission lines are made in the form of segments of coaxial lines;

- segments of transmission lines are made in the form of segments of two-wire strip lines, and radiating conductors are made in the form of strip conductors;

- the resonant circuits are made in the form of parallel loops, the resonant frequencies of the loops included in the radiating conductors of spiral radiators with a shorter length than the resonant frequencies of the loops included in the radiating conductors of spiral emitters with a longer length;

- the resonant circuits are made in the form of sequential circuits, the resonant frequencies of the circuits included in the radiating conductors of spiral radiators with a shorter length than the resonant frequencies of the circuits included in the radiating conductors of spiral radiators with a shorter length.

An embodiment of a dual channel dual band quadrifilar antenna is shown in FIG. It consists of a power circuit that has eight outputs. Each output has two conductors: a common conductor (2) and a central conductor (1). The antenna consists of eight helical emitters, curved along a conical spiral. The emitters are located symmetrically with respect to the axis of symmetry of the antenna, which simultaneously coincides with the axis of the real or virtual cone, on the surface of which spiral emitters are located. Spiral emitters are located with an angular shift of 45 degrees.

Spiral emitters are made of two parts. One of them is the segment (3) of the transmission line, the other part is the radiating conductor (4). The segment (3) of the transmission line contains two conductors, which can conditionally be called the main and auxiliary. Figure 1 shows an embodiment of a two-channel, dual-band quadrifilar antenna with segments (3) of transmission lines in the form of coaxial lines. In this case, the central conductor of the coaxial line plays the role of the main conductor of the transmission line segment (3), and the screen of the coaxial line plays the role of the auxiliary conductor of the transmission line segment (3). The radiating conductor (4) is electrically connected at one end to the main conductor of the transmission line segment (3), and at the other end with a jumper (9) connecting the radiating conductors (4) of the spiral emitters shifted by 180 °.

The other end of each of the main conductors of the segment (3) of the transmission line is electrically connected to the central conductor (1) of one of the outputs of the power circuit. The auxiliary conductors of the segments (3) of the transmission lines are electrically connected to a common conductor (2) of the power circuit. Due to the significant influence on the microwave parasitic reactances of the connecting wires, the connection point of the auxiliary conductor of the transmission line segment (3) should be located as close as possible to the connection of the main conductor of the transmission line segment (3) and the common conductor (2) of the power circuit, as shown in Fig. 1 .

Spiral emitters are divided into two groups (5) and (6) of four emitters. In each group they are located with an angular shift of 90 degrees. Each group of emitters ensures the functioning of the antenna in its frequency range (let's call them first and second), which have center frequencies f _1.2 . For definiteness, let f ₁ <f _2. Then the group (5) of spiral emitters having a large length operates in the first range with a central frequency f ₁ , and the group (6) of emitters works in the second range with a central frequency f ₂ .

The radiating conductors (4) include concentrated resonant circuits (7) and (8). These circuits can be either sequential or parallel. The contours in each group (5) and (6) of spiral emitters have the same resonant frequencies. The resonant frequencies of the circuits (7) and (8) included in different groups of spiral radiators have different resonant frequencies. If the circuits are parallel, then they have an infinite reactance at the resonant frequency. In this case, the resonant frequencies f _{r1 of the} circuits (8) in the group (5) of spiral radiators operating in the first (lower) frequency range close to the resonant frequency f ₂ . Accordingly, the resonant frequencies f _{r2 of the} circuits (7) in the group (6) of spiral radiators are close to the frequency f ₁ . Thus, the inequality f _r2 <f _r1 holds _.

When performing the circuits in a sequential circuit at the resonant frequency, they have zero reactance and therefore the resonant frequency f _r1 should be close to f ₁ and the resonant frequency f _r2 should be close to f ₂ . Accordingly, the resonant frequencies are related by the following inequality: f _r2 > f _r1.

Another embodiment of a dual channel dual band quadrifilar antenna is shown in FIG. Its feature is that the segment (3) of the transmission line is made in the form of a two-wire transmission line, and all its conductors, as well as radiating conductors (4) are made in the form of printed conductors, which can be located on a common substrate of a film dielectric. The substrate is wound on a dielectric cone (10), which gives the structure additional mechanical strength. The implementation of segments (3) of transmission lines and radiating conductors (4) in the framework of printing technology significantly reduces the cost of the antenna and increases its manufacturability.

The power circuit consists of two quadrature four-channel power dividers (we will call them the first and second divider), each of which ensures the functioning of the antenna in its own frequency range. In addition, each divider has one input and four outputs. The central conductors (1) of the outputs are connected to the main conductors of the segments (3) of the transmission lines. The first divider is connected to spiral emitters operating in the first frequency range, and the second divider to spiral emitters of range 2. Each of the dividers is conveniently designed as a strip board, the screen of which simultaneously functions as common conductors (2) of the power circuit outputs. These boards have a common screen forming a common conductor (2) of the power circuit, and their strip conductors (11) and (12) are located on opposite sides of the common conductor (2), as shown in Fig. 3. The outputs (13) of the first quadrature power divider are made in the form of conductors connected to strip conductors (11). They pass through the dielectric substrates of the strip boards and are connected to the main conductors of the segments (3) of the transmission lines. The outputs (14) of the second quadrature power divider are also made in the form of conductors that are connected to strip conductors (12). They are located outside the dielectric substrates and are directly connected to the main conductors of the segments (3) of the transmission lines.

An example of the implementation of the first quadrature power divider in the form of a strip board is shown in figure 4. The circuit uses common-mode power dividers with a division ratio of 1: 1 and phase shifters on segments of strip transmission lines. The use of phase shifters provides a phase shift between the voltages in the output channels by ± 90 degrees, and the use of common-mode equal-amplitude power dividers ensures the same amplitudes of the above voltages. The quadrature power divider shown in FIG. 4 has one input (15) and four outputs (13), which are made in the form of metallized holes passing through the dielectric substrate.

Consider the operation of the antenna. Due to the reciprocity of the structure, its work can be considered both in the receiving and in the transmitting modes. We consider it for definiteness in the transmitting mode.

Let the wave from the microwave generator arrive at the input of the first divider. The first divider generates at its outputs voltages with the same amplitudes and a phase shift of ± 90 degrees. The sign of the phase shift determines the type of circular polarization that the antenna emits: right- or left-handed. The output voltages of the first divider through the central conductors (1) are applied to the central conductors of the segments (3) of the transmission lines. These voltages excite waves in segments (3) of transmission lines that propagate along these segments and form voltages at their outputs, excite electric currents flowing along radiating conductors (4), as well as along the external surfaces of segments (3) of transmission lines. The excited currents, in turn, excite waves in free space and form circularly polarized radiation with the desired radiation pattern.

The formation of directional radiation of circular polarization is illustrated in figure 5. Figure 5 presents a simplified diagram of a quadrifilar antenna. In it, the spiral emitters are replaced by inclined rectilinear emitters, and the voltages at the outputs of the segments (3) of the transmission lines are replaced by voltage generators U ₁ -U ₄ , while

и

, текущих по наклонным излучателям, и из токов I_x1,4, текущих по горизонтальным проводникам. Нижний горизонтальный проводник моделирует общий проводник схемы питания, а верхний горизонтальный проводник - перемычки, соединяющие излучающие проводники. Токи

обычно ослаблены по сравнению с токами, текущими по горизонтальным проводникам, так как распределение тока имеет нуль в середине наклонного проводника. Поэтому можно приближенно принять, чтоDue to the fact that the supply voltages have the same amplitude and are 90 degrees out of phase, the currents in the arms of the quadrifilar antenna 1-4 are also the same in amplitude and 90 degrees out of phase. Note that the currents in rectilinear emitters have all three components, but the vertical component I _Z does not emit along the axis of the antenna, that is, along the axis 0z. Therefore, it does not affect the ratio of radiation intensity forward - backward. Consider the current component I _x . It is made up of currents

and

flowing along inclined radiators, and from currents I _x1.4 , flowing along horizontal conductors. The lower horizontal conductor models the common conductor of the power circuit, and the upper horizontal conductor models jumpers connecting the radiating conductors. Toki

usually weakened compared to currents flowing along horizontal conductors, since the current distribution has zero in the middle of the inclined conductor. Therefore, we can approximately assume that

These currents are located at different heights and are phase shifted relative to each other. Let the currents I _{x1 be} located at zero height, the currents I _x2 at a height h, the currents I _x3 at a height of 2h, and the currents I _x4 at a height of 3h. The currents I _x2 and I _x4 have a phase shift of 90 ° relative to the currents I _x1 and I _x3 .

An analysis of the radiation of such currents shows that their radiation pattern F (θ) in the vertical plane (the angle θ is measured from the axis 0z, the zero angle corresponds to the radiation forward) is described by the following formula:

where k is the wave number of free space.

The OIVN parameter is determined as follows:

, то есть расстояние между токами равно четверти длины волны в свободном пространстве. При меньших расстояниях ОИВН может быть достаточно большой, но конечной величиной.From relation (4) it can be seen that the OIVN parameter tends to infinity (there is no radiation back), when

, that is, the distance between the currents is equal to a quarter of the wavelength in free space. At shorter distances, the SIR can be quite large, but finite.

The radiation of circularly polarized waves in the quadrifilar antenna shown in FIG. 5 is easy to explain from the analysis of currents flowing along the conductors. Circular polarization occurs when there are currents of the same amplitude, shifted in space by 90 degrees and also having a phase shift of 90 degrees. It follows from the foregoing that this is precisely the situation observed in a quadrifilar antenna. If we consider the currents on the pairs of emitters 1-3 and 2-4, we can see that in space they are rotated 90 degrees, their amplitudes are equal, and the phases differ by 90 degrees.

The execution of part of the spiral emitter in the form of a segment (3) of the transmission line leads to the fact that the point of inclusion of the voltage generator can move along the length of the emitter. This implements a value of the input resistance of the emitter convenient for practical use, which, as a rule, is in the range of 50-100 Ohms.

The choice of the required input resistance value is illustrated in Fig.6, which shows the distribution of the electric current flowing over the surface of the spiral emitter. The z coordinate is directed along the axis of the emitter. The point z = 0 corresponds to the lower part of the emitter located near the power circuit, and the point z = L corresponds to the upper end of the emitter, which coincides with the breakage of the radiating conductor (4). The switching point of the voltage generator is located at a distance L ₁ from the bottom of the emitter.

. Тогда входное сопротивление излучателя Z оказывается пропорциональным отношению ЭДС генератора E к току I(z) в точке его включения:The current distribution I (z) can be approximately described by the trigonometric function

. Then the input impedance of the emitter Z is proportional to the ratio of the emf of the generator E to the current I (z) at the point of its inclusion:

From relation (5) it can be seen that by varying the distance L ₁ , it is possible to vary the input resistance Z over a wide range.

The length of the spiral emitter determines its operating frequency. This is due to the fact that such an emitter is a resonant device operating in a certain limited frequency band. Approximately the resonance condition can be written as follows:

where λ is the wavelength in free space. From relation (6) it is seen that the length of the emitter is inversely proportional to the center frequency of its operating range. For this reason, spiral emitters operating in the lower frequency range have a length greater than spiral emitters operating in the upper frequency range.

A feature of the dual-band quadrifilar antenna is its simultaneous operation in two different frequency ranges, which is significantly complicated by the interconnection of groups (5) and (6) of spiral radiators, which occurs through free space and cannot be eliminated through power circuits. The presence of such a relationship leads to a number of negative phenomena, which include the following. Part of the energy emitted by a group of emitters at its tuning frequency is received by emitters of another group and is dissipated in the load of the input of its power subcircuit. This results in power loss and reduces the antenna gain. In addition, the presence of mutual coupling complicates the tuning of the antenna, since it changes the natural resonant frequencies of the emitters, which leads to a shift in the working frequency ranges when working together as part of a dual-band antenna.

To weaken the connection between the two groups (5) and (6) of spiral radiators, resonant circuits on lumped elements are introduced into their radiating conductors (4). These circuits can be either parallel or sequential. When using sequential circuits, their resonant frequencies f _r1 in the group (5) of spiral radiators are chosen close to the center frequency of the first frequency range f ₁ , and the resonant frequencies of the circuits f _r2 in the group (6) of spiral radiators are chosen close to the center frequency of the second frequency range f ₂ . In this case, within their operating ranges, the circuits have a low reactance and do not affect the operation of their groups (5) and (6) of spiral radiators. When the frequency detuning from the resonance, the reactance of the circuit increases rapidly, and therefore the circuits in groups (5) and (6) of spiral radiators at frequencies f ₂ and f _1, respectively, have large resistances. Therefore, the currents induced by the spiral emitters of group (5) on the spiral emitters of group (6) at a frequency f ₁ are small. The currents induced by the spiral emitters of group (6) on the spiral emitters of group (5) at a frequency f ₂ also turn out to be small. A decrease in currents leads to a weakening of the interconnection of groups of emitters. It should be noted that the use of sequential circuits ensures the complete absence of their influence on your group of emitters. The degree of current suppression on an adjacent group of emitters is a finite value, that is, there is no complete current suppression.

The use of parallel loops, on the contrary, provides infinite reactance of the group (6) of helical emitters at a frequency f ₁ due to the choice of the resonant frequencies of the loops of this group f _r2 = f ₁ . Similarly, in the group (5) of emitters, the parallel circuits have resonant frequencies f _r1 = f ₂ , which ensures a minimum of induced currents in this group of emitters at a frequency f ₂ . In this case, the influence of the circuits on the operation of their groups of emitters remains finite. This makes it necessary to configure these emitters taking into account the presence of contours in them.

The experimental radiation patterns obtained in the L1,2 bands with center frequencies of 1590 MHz and 1245 MHz are respectively shown in Figs. 7 and 8. The graph in Fig. 7 corresponds to the L1 band, and in Fig. 8 to the L2 band.

Thus, the above information indicates the fulfillment of the following set of conditions when using the claimed invention:

- an antenna device embodying the claimed invention is intended for use in industry, namely in antenna technology, for example, as a receiving antenna of a satellite navigation device;

- for the claimed device in the form described in the independent clause of the claims, the possibility of its implementation using the means described in the application is confirmed;

- an antenna device embodying the claimed invention allows to realize the following technical result: to expand the operating frequency band, to separate the signals of two frequency ranges at different inputs, to reduce aerodynamic drag and thus reduce the cost and increase the manufacturability of electronic systems.

Claims (6)

1. Two-channel dual-band quadrifilar antenna containing a power circuit and eight helical emitters having a common axis of symmetry and located with a offset of 45 ° relative to each other, combined in two groups of four identical spiral emitters, 90 ° offset from each other, spiral emitters of one groups are made with a length different from the length of the spiral emitters of another group, characterized in that the spiral emitters are made in the form of conical spiral emitters, each of which is made nen in the form of a segment of a transmission line containing the main and auxiliary conductors, as well as a radiating conductor, the power circuit is made in the form of two quadrature four-channel power dividers with one input and four outputs, the outputs of the power circuit contain eight central conductors and one common conductor, the main conductors of the segments transmission lines are connected on the one hand with the central conductors of the outputs of the power circuit, and on the other hand with radiating conductors, the central conductors of the line segments transmissions of various groups of spiral radiators are connected to the central output conductors of various quadrature power dividers, auxiliary conductors of transmission line segments are connected to a common power circuit conductor, the radiating conductors of spiral radiators are 180 ° offset from each other and connected to each other by jumpers, and into radiating conductors lumped resonant circuits are included, and the resonant frequencies of the circuits included in the radiating conductors of the spiral emitters of one load pp, have the same resonant frequencies, which differ from the resonant frequencies of the circuits included in the radiating conductors of the spiral emitters of another group. 2. The antenna according to claim 1, characterized in that it is additionally introduced a dielectric cone, and spiral emitters are located on the surface of the specified dielectric cone. 3. The antenna according to claim 1, characterized in that the segments of the transmission lines are made in the form of segments of coaxial lines. 4. The antenna according to claim 1, characterized in that the segments of the transmission lines are made in the form of segments of two-wire strip lines, and the radiating conductors are made in the form of strip conductors. 5. The antenna according to claim 1, characterized in that the resonant circuits are made in the form of parallel loops, the resonant frequencies of the loops included in the radiating conductors of the spiral emitters with a shorter length than the resonant frequencies of the loops included in the radiating conductors of the spiral emitters with a longer length. 6. The antenna according to claim 1, characterized in that the resonant circuits are made in the form of sequential circuits, the resonant frequencies of the circuits included in the radiating conductors of spiral radiators with a shorter length than the resonant frequencies of the circuits included in the radiating conductors of spiral radiators with a shorter length.

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