JPH036683B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a radio wave lens that electronically controls the refraction direction of a beam using an external control signal.

[Prior art]

Figure 1 is an example from Microwave Journal 19812.
This is a diagram showing the conventional radio wave lens that electronically controls the refraction direction of the beam, shown on pages 45 to 53 of the monthly issue. In the diagram, 1 is a metal grid, and 2 is a polarity of the applied bias voltage. 3 is a dielectric plate for fixing the metal grid 1 and the pin diode 2 in space; 4 is a horn antenna for irradiating radio waves to the radio lens; 5 is a pin diode that equivalently shows short or open characteristics. is a single-layer lens plate composed of the metal grating 1, pin diode 2, and dielectric plate 3; 6 and 7 are lenses that are made by stacking a plurality of these single-layer lens plates to refract the beam left and right and up and down, respectively; 8 is a lens that refracts the beam horizontally and vertically; Indicates the direction of the electric field of radio waves.

FIG. 2 is a diagram showing the operating principle of the single-layer lens plate 5, FIG. 2 a is a configuration diagram, and FIG. 2 b and c are diagrams when a forward or reverse bias voltage is applied to the pin diode 2, respectively. An equivalent diagram of FIG. 2d is a diagram illustrating the principle of beam refraction. still,
In the figure, 1 to 8 are the same as in Figure 1, and 9 is the wavefront of the radio wave.
10 is the traveling direction (beam direction) of the radio waves.

Now, by setting the mounting interval of the pin diodes 2 to a dimension of 1/2 wavelength or less in FIG. 2a, and setting the width and spacing of the metal grating 1 to predetermined dimensions, the metal gratings shown in FIGS. 2b and c are obtained. 1 acts as an inductive circuit element and a capacitive circuit element, respectively, for radio waves having an electric field parallel to the metal grid 1 passing through them, and the transmitted phase amount of the radio waves leads and lags respectively.

As shown in FIG. 2d, for example, by applying a forward bias (● in the figure) to the upper half of one single layer lens plate 5 and a reverse bias (● in the figure) to the lower half (respectively to the pin diode 2 in the figure), As mentioned above, the phase advances in the upper half and the phase lags in the lower half, so the wavefront 9 of the radio wave changes, equivalently seen as shown by the broken line in the figure, and the traveling direction 10 of the radio wave is refracted downward. .

However, as mentioned above, the conventional radio wave lens shown in Figure 1 combines a pin diode and a metal grating, and changes the amount of transmission phase by switching the bias voltage in the forward/reverse direction to refract the beam. When this radio wave lens is combined with a fixed beam antenna to form an electronic scanning antenna, if the transmission phase amount is changed every Δφ radian, the number of layers of the single layer lens plate in the direction of propagation of radio waves is N. is expressed by the following equation assuming that the beam is scanned vertically and horizontally.

N=2 (2π/Δφ−1) ………(1) For example, if Δφ is π/8 radian used in a normal electronic scanning antenna, the number of layers N is 30
This method requires pin diodes to be used in layers, and pin diodes must be used at intervals of half a wavelength or less per layer, so the number of pin diodes required is enormous, and there are disadvantages such as high cost and difficulty in assembly. Ta.

Furthermore, as the frequency increases, such as in the millimeter wave band and submillimeter wave band, the effect of the junction capacitance of the pin diode increases, and even if reverse bias is applied, it does not become completely open, resulting in transmission during forward/reverse bias switching. This had the drawback that the change in phase amount became small, making it difficult to refract the beam.

[Summary of the invention]

This invention was made with the aim of improving such drawbacks, and it changes the amount of transmission phase in accordance with the number of bits in order to reduce the number of layers in the direction of propagation of radio waves, and it This project proposes a radio wave lens that can be used up to high frequency ranges.

[Embodiments of the invention]

FIG. 3 is a diagram showing an embodiment of the present invention,
In the figure, 4 and 8 are the same as in Figure 1, and 11
is a phase shifter constituting a radio wave lens according to the present invention.

FIG. 4 is a partially missing diagram showing an example of the configuration of the phase shifter, and in this case, a 4-bit phase shifter is shown as an example. In the figure, 12 is a phase shift element corresponding to each bit constituting the phase shifter, 13, 1
4 and 15 constitute each phase shift element, and include two sets of dielectric thin plates facing each other, a set of conductive thin plates parallel to and facing the direction of propagation of radio waves, and a cell filled with the thin plates; The reference numeral 16 indicates a connection line for applying a bias voltage.

In the phase shift element 12 configured as described above, the amount of phase shift of the radio wave is mainly determined by the permittivity of the liquid crystal in the direction of the electric field, and if this is now ε, then the amount of phase shift of the radio wave Φ is expressed by the following equation. Can be approximated.

Φ=2π/λd(√〓−1) (radians) ......(2) where d: Thickness of the liquid crystal layer of one phase shift element in the direction of propagation of radio waves λ: Wavelength of radio waves Applied to Figure 5 FIG. 2 is a cross-sectional view of an example showing the relationship between voltage and molecular orientation of liquid crystal, where a shows the case where no voltage is applied, and b shows the case where the voltage is applied.
In the figure, 8 and 13 to 16 are the same as in FIG. 4, 17 is a liquid crystal molecule whose long direction indicates the direction of molecular orientation, and 18 and 19 are a power source and a switch for applying a bias voltage, respectively. As shown in FIG. 5a, when no voltage is applied, the molecules are orientated in advance so that they are orthogonal to the direction of the radio waves. As shown in FIG. 5b, when a voltage is applied, the molecules are oriented in the direction of the electric field of the radio wave.

FIG. 6 is a diagram illustrating an example of the frequency characteristics of the dielectric constant of a liquid crystal, comparing the molecular orientation direction and the direction orthogonal to the orientation direction. In the figure, the horizontal axis is the frequency (Hz), and the vertical axis is the dielectric constant, where the solid line represents the dielectric constant in the orientation direction of the molecules, and the broken line represents the dielectric constant in the direction perpendicular to the orientation direction.

As mentioned above, the orientation direction of molecules in liquid crystals can be changed by applying an external voltage, and since the dielectric constant in the orientation direction and in the direction orthogonal to it differs at most frequencies, this property of liquid crystals can be changed. By turning the applied voltage ON/OFF, the dielectric constant ε〓 of the liquid crystal in the direction of the electric field of the radio wave can be changed. The amount of phase shift changes.

Now, if the relative permittivity of the liquid crystal in the alignment direction is ε _d and the relative permittivity in the direction perpendicular to the alignment is ε _c , then the voltage to the liquid crystal is
Change in phase shift amount ΔΦ due to switching from OFF to ON
is approximated by the following equation.

ΔΦ=2π/λd (√ _c −√ _d ) (radians)……(
3) From the relationship in equation (3), find the thickness d at which the absolute value of ΔΦ is π, π/2, π/4, and π/8 radians, respectively, and calculate it as the radio wave of the phase shift element for each bit. A 4-bit phase shifter can be formed by adjusting the thickness of the liquid crystal in the advancing direction.

FIG. 7 is a diagram showing the principle of refraction of radio waves by the radio wave lens according to the present invention. In the figure, 8 to 10 are the same as in Figure 2, 11 is the same as in Figure 3, and 1
2A, 12B, 12C, 12D are respectively π,
Phase shift elements of π/2, π/4, and π/8 radians are shown. Here, it is assumed that the phase shift elements shaded with diagonal lines are biased so that the phase is delayed.
Now, the four phase shifters 11 each move from top to bottom by π/
Since the phase shift of the transmitted wave is delayed by 8 radians, the wavefront of the radio wave equivalently becomes like a broken line, and the direction of propagation of the radio wave is refracted downward.

Although the above description has been made regarding the case of 4 bits, this radio wave lens is not limited by the number of bits due to its structure, and can arrange as many phase shift elements as required in the direction of propagation of radio waves.

[Effects of the Invention] As explained above, the present invention can significantly reduce the number of layers (number of elements) in the direction of propagation of radio waves when using the same minimum phase shift amount compared to conventional electronically controlled radio wave lenses. In addition, when used at high frequencies such as millimeter wave and submillimeter wave bands, it is possible to reduce costs by using liquid crystals instead of using pin diodes, which were a problem with conventional radio lenses. It has the effect of solving problems when used in

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a conventional radio wave lens, Fig. 2 is a diagram showing the operating principle of a single-layer lens plate, Fig. 3 is a diagram showing an embodiment of the present invention, and Fig. 4 is a diagram showing the configuration of a phase shifter. Some partially missing figures showing an example, Figure 5 is a cross-sectional view of an example showing the relationship between applied voltage and molecular orientation of liquid crystal, Figure 6 is a diagram showing frequency characteristics of relative dielectric constant of liquid crystal, and Figure 7 is FIG. 3 is a diagram showing the principle of refraction of radio waves by the radio wave lens according to the present invention. In the figure, 11 is a metal grid, 2 is a pin diode, 3 is a dielectric plate, 4 is a horn antenna, 5 is a single layer lens plate, 6 and 7 are lenses, 8 is the direction of the electric field of the radio wave, 9 is the wavefront of the radio wave, 10 is the traveling direction of the radio wave,
11 is a phase shifter, 12 is a phase shift element, 13 is a dielectric thin plate, 14 is a conductive thin plate, 15 is a liquid crystal, 16 is a connection line, 17 is a liquid crystal molecule, 18 is a power source, and 19 is a switch. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1 In a radio wave lens that electronically controls the refraction direction of the beam using signals such as external voltage,
A cubic or rectangular parallelepiped cell consisting of two sets of dielectric thin plates facing each other and a set of conductor thin plates facing and parallel to the direction of propagation of radio waves; the cell is filled with a voltage applied from the outside through the conductive thin plates; By changing the orientation direction of molecules, a phase shift element consisting of a liquid crystal having dielectric anisotropy that changes accordingly is divided into predetermined lengths corresponding to the number of bits of a control signal, A radio wave lens characterized in that a required number of phase shifters arranged in the direction of propagation of radio waves corresponding to the number of bits are arranged in a plane orthogonal to the direction of propagation of radio waves in order to refract the beam.