RU2400880C1 - Printed antenna - Google Patents

Abstract

FIELD: radio engineering. ^ SUBSTANCE: in printed antenna which contains lower dielectric layer (1), upper dielectric layer (2), lower metal layer (3) located on lower surface of lower dielectric layer (1), middle metal layer (4) located between upper dielectric layer (2) and lower dielectric layer (1) and upper metal layer (5) located on upper surface of upper dielectric layer (2) and excitation elements (8), there introduced are four connection straps (6) connecting upper metal layer (5) and lower metal layer (3) without electrical contact to middle metal layer (4), and crossed slot (7) is made in upper metal layer (5). ^ EFFECT: decreasing dimensions, providing reception and transmission of waves with circular polarisation at maintaining working frequencies. ^ 5 cl, 11 dwg

Description

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

Printed antennas, including single emitters and arrays, are widely used in various electronic systems. Their advantages include small dimensions, high adaptability and low cost, reliability, etc. The simplest printed antennas are known having a single dielectric layer on the surface of which metal layers are applied (T. Haddrell, J P. Bickerstaff, M. Phocas. Realisable GPS Antennas for Integrated Hand Held products. ION GNSS 18th International Technical Meeting of the Satellite Division, 13-16 September 2005, Long Beach, CA). Typically, the dielectric and metal layers have a rectangular shape or a circle shape. The connection of such an antenna with external devices is provided using an excitation element. Often a coaxial cable is used as an excitation element, the central conductor of which has contact with one metal layer, and the external conductor with another. Other excitation elements are also possible, for example, a technological excitation element by a strip line through a slit.

Circularly polarized printed antennas are also known. They may be in the shape of a circle or square (US Patent No. 6326923) or close to them. The exact choice of shape depends on the number of excitation elements that are used to communicate with the external circuit. If the antenna has one communication element, then the shape of the antenna, that is, the shape of the dielectric and metal layers, is close to a square or circle, but does not completely coincide with them. When using two communication elements, the antenna has a strictly round or square shape. In a more general case, its shape should have a 90 degree rotation symmetry.

The closest technical solution to the claimed antenna is a printed antenna containing two dielectric layers located one above the other and three metal layers (US Patent No. 5124733). Such an antenna provides operation in two separated frequency ranges. The disadvantage of this antenna is its large dimensions. The dimensions of the printed antenna are approximately determined by the resonance conditions in the resonator formed by two metal layers and a dielectric layer located between them. The antenna functions effectively when the operating frequency is close to the resonance frequency. The conditions determining the resonant frequency of a rectangular antenna are as follows:

where a is the length of one of the sides of the antennas, λ ₀ is the wavelength in free space, ε is the relative permittivity of the dielectric layer. From formula (1) it can be seen that at a fixed wavelength (frequency), the dimensions of the printed antenna can only be reduced by increasing the dielectric constant. This method is often used in practice, but the cost for reducing the size is to increase the Q factor of the Q antenna and, as a result, narrow its operating frequency band.

It is known that the dimensions of a printed antenna can be reduced by using short-circuiting devices (S. Dey and R. Mittra, "Compact microstrip patch antenna", Microwave and Optical Technology Letters, 1996, N13, p.12-14). The size of such an antenna is half that of the case discussed above. They are close to a quarter of the wavelength in a medium with a permittivity of the dielectric layer. The disadvantage of this antenna is the inability to work on the circular polarization of the emitted (received) waves.

The proposed technical solution is aimed at obtaining a technical result, expressed in reducing the size of the printed antenna, providing reception and transmission of waves with circular polarization while maintaining the operating frequency band.

These problems are solved due to the fact that in the printing antenna containing the lower dielectric layer, the upper dielectric layer, the lower metal layer located on the lower surface of the lower dielectric layer, the middle metal layer located between the upper and lower dielectric layers, and the upper metal layer, located on the upper surface of the upper dielectric layer, and the excitation elements, four jumpers are introduced connecting the upper metal layer and the lower metal layer without electric nical contact with secondary metal layer, and a top metal layer formed cruciform slot.

There are additional options for the implementation of the printed antenna, in which:

- the lower dielectric layer and the upper dielectric layer, as well as the lower metal layer, the middle metal layer and the upper metal layer are square in shape, and the cross-shaped slit has a length equal to the side of the upper metal layer, jumpers are located on the diagonals of the lower dielectric layer at the same distance from it center and made in the form of metal conductors connecting the lower metal layer and the upper metal layer without electrical contact with the middle metal layer ;

- the printed antenna contains two excitation elements located in the lower dielectric layer at the same distance from its center, and the angle between the straight lines connecting the excitation elements and the center of the lower dielectric layer is 90 degrees;

- the printed antenna contains four excitation elements located in the lower dielectric layer at the same distance from its center, and the excitation elements are mounted on orthogonal lines parallel to the plane of the lower dielectric layer and passing through its center;

- the printed antenna contains one excitation element located in the lower dielectric layer on its diagonal, and the middle metal layer is made in the form of a figure having two orthogonal planes of symmetry perpendicular to the lower and upper dielectric layers.

One possible embodiment of a printed antenna is shown in FIGS. 1, 2. FIG. 1 shows a general view of an antenna comprising a lower dielectric layer (1), an upper dielectric layer (2), a lower metal layer (3), a middle metal layer ( 4) and the upper metal layer (5), jumpers (6), a cross-shaped slit (7), and figure 2 shows the lower dielectric layer (1), the lower metal layer (3), the middle metal layer (4), jumpers ( 6) and the element (8) of excitation. All layers are square.

The functioning of a printed antenna can be understood in the simplest way, considering it as a cavity resonator having a number of natural oscillations characterized by resonant frequencies, Q factors, and field distribution. An analysis of the natural oscillations of the cavity resonator is usually carried out without taking into account the excitation element, which is easy enough to take into account later for calculating the external parameters of the antenna.

It is convenient to consider the natural vibrations of a cavity resonator having two planes of symmetry within the framework of the principle of symmetry. In accordance with this principle, the analysis of the electromagnetic field in a structure having two planes of symmetry can be reduced to an analysis of the four partial structures shown in FIG. For simplicity, we will consider the case when all layers have a square shape and the same size. Let the side length of the square be a. We also consider the case of identical permeabilities of the upper and lower dielectric layers.

Each of the partial structures is a quarter of the initial structure obtained by its section along the planes of symmetry. Partial structures differ from each other in the type of boundary conditions established in the planes of symmetry. These can be conditions for the tangential components of the electric field to be equal to zero:

or magnetic field:

In the first case, they speak of an electric wall, and in the second, of a magnetic wall.

Working vibrations are vibrations 1 and 2. They are formed by re-reflections of the T-waves of the lower dielectric layer (1) and the upper dielectric layer (2) with metallized surfaces. Let us consider this process in more detail using the example of oscillation 2. The T-wave runs along the lower dielectric layer (1) from the electric wall in the direction indicated by the upper arrow. She reaches the jumper (6) and passes to the upper dielectric layer (2), while changing the direction of movement to the opposite, as shown in Fig.4. To transfer T-wave energy from the lower dielectric layer (1) to the upper dielectric layer (2), the jumpers (6) should not have electrical contact with the middle metal layer (4). Next, the T-wave reaches a cross-shaped slit (7), in the middle of which there is an electric wall. A slit with an electric wall passes a wave, which is partially emitted through a cross-shaped slit (7) into free space. Radiation into free space is equivalent to power losses, due to which the resonator Q factor has a finite value. The remaining part of the power is reflected from the cross-shaped slit (7) and moves in the opposite direction, passing through the jumpers (6) to the lower dielectric layer (1) and reaching the electric wall. The process is then repeated periodically. Note that the transition from layer to layer through a slit with a magnetic wall is impossible.

Thus, each partial resonator (see FIGS. 3 and 4) is a segment of a transmission line that is shorted by an electrical wall at one end and has an idle load at the other end. This load simulates a crosswise gap (7). Resonance in such a resonator occurs when the line length is equal to a quarter of the wavelength in the medium filling the line. It is easy to see that the resonance conditions in the case under consideration are written as follows:

Comparing formulas (1) and (4), it is easy to see that the proposed antenna has half the size compared to the known printed antenna.

Oscillations 1 and 2 differ from each other only in the structure of the fields. They are identical except for a rotation of 90 degrees. This rotation is due to the fact that the walls with the same boundary conditions are also rotated relative to each other by 90 degrees. The identity of the fields of both oscillations determines their identical resonant frequencies. Thus, we can conclude that in the resonator under consideration there are two oscillations with the same resonant frequencies, which are rotated 90 degrees relative to each other. This creates the possibility of radiation (reception) of waves with circular polarization. A circularly polarized wave is a superposition of two linearly polarized waves. Moreover, these waves are rotated in space by 90 degrees and oscillate with a phase shift also by 90 degrees. If vibrations 1 and 2 are excited with a phase shift of 90 degrees, they will emit a wave with circular polarization into free space, since in space they are already deployed to the desired angle.

Fluctuation 3 is not working. The movement of T-waves with this arrangement of electric walls is impossible, since each of them is located along the direction of propagation of one of the T-waves and, thus, prevents its movement. In a transmission line with a longitudinal electric wall, waveguide waves are formed. Oscillations based on them have resonant frequencies far exceeding the resonant frequencies of the working oscillations 1 and 2.

Finally, oscillation 4. It also belongs to the number of non-working ones, since it does not have gaps with an electric wall and waves cannot be emitted into free space, since a gap with a magnetic wall does not transmit electromagnetic radiation.

It was already said above that the implementation of the circular polarization regime requires the excitation of two working oscillations with a phase shift of 90 degrees. Such excitation is realized using different schemes, differing in the number of excitation elements. The first circuit contains one element (8) of excitation. She is shown in figure 5.

In this case, the middle metal layer (4) is made in the form of a geometric figure having two planes of symmetry. In the particular case shown in figure 5, this figure can be a rectangle with sides a and b. The intersection planes of symmetry form a straight line that coincides with the axis of symmetry of the lower dielectric layer (1), which has the shape of a square. This axis passes through the center of the square and is perpendicular to its plane. The element (8) of the excitation is located on the diagonal of the lower dielectric layer (1).

The lack of 90 degree rotation symmetry in the middle metal layer leads to the fact that the resonance frequencies of oscillations 1 and 2 are a little upset: f ₁ ≠ f ₂ . Due to the fact that the excitation element (8) is located on the diagonal of the lower dielectric layer (1), it excites both oscillations with a similar intensity. Each oscillation emits a linearly polarized wave. In particular, vibration 1 emits a wave having an electric field component E _y in the direction of the 0z axis, and vibration 2 - component E _x . The frequency dependence of the amplitudes of these field components is described by the following formulas:

where Q is the quality factor of the oscillation. From formulas (5) it can be seen that if the oscillations are disordered into the bandwidth of the circuit:

then at the center frequency f _{0 the} orthogonal field components have the same amplitude and are 90 degrees out of phase. Thus, the required mode of excitation of the working oscillations is achieved, which ensures radiation of the field with circular polarization.

The disadvantage of the above-described excitation scheme is that the fulfillment of the conditions for circular polarization contradicts the condition for matching the antenna. Figure 6 shows a typical dependence of the modulus of the reflection coefficient on frequency for oscillations detuned in accordance with formulas (6).

From Fig.6 it can be seen that at the center frequency the antenna cannot fundamentally be fully matched, which leads to a decrease in its gain. Thus, we are dealing with a technical contradiction between the requirement of matching and the requirement of ensuring circular polarization. This contradiction cannot be eliminated within the framework of a power supply circuit with one excitation element. It is eliminated in power circuits with several excitation elements. The greatest positive effect is provided by the circuit with four elements (8) of excitation. She is shown in figb.

When using four excitation elements (8), all dielectric and metal layers are square in shape. The voltage on the elements (8) of the excitation 1-4 have the same amplitude and are phase shifted relative to each other by ± 90 degrees. The sign of the phase shift determines the type of circular polarization - right or left screw. The resonant frequencies of the working oscillations are the same in this case. The phase shift between them is achieved not due to the detuning of oscillations, but due to phase shifts of the supply voltage. Moreover, the matching of the antenna is in no way connected with the polarization of the radiation. In order for the working oscillations to be excited with the same amplitude, the excitation elements (8) must be located at the same distance from the center of the lower dielectric layer (1). In addition, operating oscillations must be excited with a phase shift of 90 degrees. This is achieved not only by a phase shift between the voltages on the excitation elements (8), but also by their spatial arrangement on two orthogonal lines passing through the center of the lower dielectric layer (1).

Four-cell power supply requires the use of special circuits that provide the required amplitude-phase relationships between exciting voltages.

On Fig shows a parallel (figa) and serial (figb) circuit. They contain phase shifters 90 and 180 degrees, which can be made in the form of segments of transmission lines. The serial circuit is more compact. However, when performing it on the basis of segments of transmission lines, lines with very different wave impedances appear in it, which are rather difficult to technologically implement. The parallel circuit is devoid of this drawback, but has significantly large dimensions. Figure 9 shows the topology of the printed circuit board of a parallel strip power circuit.

Four-element power circuits are quite complex devices that can introduce significant losses in the microwave range that reduce the efficiency of the antenna. Therefore, two-element excitation is often used (see Fig. 7a). In this case, the elements (8) of the excitation are located at the same distance from the center of the lower dielectric layer (1). Due to this, the excitation of working vibrations with the same amplitude is achieved. The required phase shift between the field strengths of the working oscillations of 90 degrees is provided by the phase shift of the stresses on the excitation elements (8), as well as their spatial arrangement on the lines passing through the center of the lower dielectric layer (1), and the angle between these lines is 90 degrees.

Jumpers (6) are conductors that galvanically connect the lower metal layer (3) and the upper metal layer (5). Jumpers (6) should not have electrical contact with the middle metal layer (4). In real constructions, jumpers (6) are conveniently made in the form of metallized holes. Thus, the entire antenna can be manufactured using printed circuit board technology, which significantly reduces its cost.

The final selection of the parameters of the printed antenna should be made using modern means of engineering design of microwave devices, such as electrodynamic modeling and experimental studies. Electrodynamic modeling can be implemented using well-known programs such as HFSS or Microwave Studio. Figure 10 shows the results of calculating the reflection coefficient from a printed antenna when it is powered by two excitation elements. The calculations were carried out in the Microwave Studio system for the following parameters:

- all layers have a square shape, the length of the side of the square is 17 mm;

- the thickness of the dielectric layers is 4 mm;

- the permeability of the dielectric layers is 10;

- the width of the cross-shaped slit - 9 mm;

- thickness of metal layers - 0.03 mm;

- jumper width - 0.5 mm;

- dimensions of the metal screen - 80 × 80 mm.

Figure 10 shows that the curve of the reflection coefficient has a resonant single-humped character. 11 shows a three-dimensional radiation pattern of a printed antenna in power. It can be seen that it has a directivity, which is due to the presence of a metal screen that reduces radiation in the lower half-space.

Claims (5)

1. A printed antenna comprising a lower dielectric layer, an upper dielectric layer, a lower metal layer located on the lower surface of the lower dielectric layer, a middle metal layer located between the upper and lower dielectric layers, and an upper metal layer located on the upper surface of the upper dielectric layer , and excitation elements, characterized in that four jumpers are inserted into it, connecting the upper metal layer and the lower metal layer without electric contact with the middle metal layer, and a cross-shaped slit is made in the upper metal layer. 2. The printed antenna according to claim 1, characterized in that the lower dielectric layer and the upper dielectric layer, as well as the lower metal layer, the middle metal layer and the upper metal layer are square in shape, and the cross-shaped slit has a length equal to the side of the upper metal layer, jumpers are located on the diagonals of the lower dielectric layer at the same distance from its center and are made in the form of metal conductors connecting the lower metal layer and the upper metal layer without electricity contact with the middle metal layer. 3. The printed antenna according to claim 2, characterized in that it contains two excitation elements located in the lower dielectric layer at the same distance from its center, and the angle between the straight lines connecting the excitation elements and the center of the lower dielectric layer is 90 °. 4. The printed antenna according to claim 2, characterized in that it contains four excitation elements located in the lower dielectric layer at the same distance from its center, and the excitation elements are mounted on orthogonal lines parallel to the plane of the lower dielectric layer and passing through its center. 5. The printed antenna according to claim 2, characterized in that it contains one excitation element located in the lower dielectric layer on its diagonal, and the middle metal layer is made in the form of a figure having two orthogonal planes of symmetry perpendicular to the lower and upper dielectric layers.

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