JPH0239835B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a microwave barrier device having a microwave transmitter having a transmitting antenna and a microwave receiver having a receiving antenna.

[Problems with conventional technology]

Microwave barrier devices are used to prevent intruders from entering an area or protected zone, with microwave transmitters and microwave receivers located at either end of the monitored area. When the microwave antenna beam is completely or partially obstructed by an intruder, a circuit provided in the receiver issues an alarm signal.

The area covered by such a microwave barrier device must reach to the ground on the one hand (so that intruders cannot crawl under the beam) and on the other hand must reach a sufficient height. (Prevent intruders from jumping over the beam).

Conventional microwave barrier device (UK patent no.
No. 1475111) uses only one antenna beam or multiple antenna elements that determine only one beam propagation angle. this is,
As will be explained in more detail below, the need for good monitoring near the ground (prevention of passing under the beam) and at height (prevention of jumping over the beam) cannot be fully satisfied.

Microwave barrier devices must generally have a range (length of protected area) of 10 to 200 m. An alarm should be sounded when an intruder attempts to pass under the microwave barrier beam or pass through or jump over the guard beam. To meet these requirements, the monitoring area must extend to the ground on the one hand and reach a height of more than 2 m on the other hand.

To meet both requirements, it is advantageous to use an antenna beam that extends over a relatively large vertical distance within the operating area of the transmitter and receiver. The following relationship exists between the beam width, the geometric dimensions of the microwave antenna, and the radiation wavelength.

Beam width (degrees) λ/a however, λ = wavelength a = antenna aperture.

Therefore, a small antenna aperture is required to obtain a large beamwidth. The beam width corresponds to the propagation angle of the radiation waves from the antenna.
It corresponds numerically to the angular range in which most of the microwave signal is focused.

If an antenna with an aperture of 20 cm is placed at a height of 1 m above the ground (see Figure 1), the beam width will be 8.6° at a wavelength of 3 cm. The antenna beam therefore extends upward and downward by 4.3°. At a distance of 12 cm from the transmitter or receiver, this antenna beam intersects the ground and a line at a height of 2 m.

As the antenna aperture is reduced, the antenna beam spread increases. That is, the point at which the antenna beam reaches the ground or a height of 2 meters is closer to the transmitter or receiver. Although this is advantageous for surveillance, it faces the serious problem of ground reflections.

When there is no intruder, the signal received by the receiver consists of two main components. namely, the direct signal and the ground radiation signal (see Figure 2).

The received electric field strength Er is given by the following formula.

Er=E ₁ (1+αe ^j 〓) However, E ₁ = Electric field strength due to linear signal α = Ratio of ground reflected signal λ = Wavelength h = Mounting altitude of the device R = Distance from transmitter and receiver.

In this way, the two components of the received signal have a phase difference φ. The magnitude of the received signal is the ground reflection component (α)
It is determined by the magnitude of and the phase difference (φ).

If the angle θ' (see FIG. 2) that the antenna beam makes with the ground is very small, the magnitude of the ground reflected component is equal to the direct component. The 180° phase shift that the ground-reflected wave undergoes upon reflection also occurs in horizontally and vertically polarized waves, and therefore also in circularly polarized waves. Therefore, in the microwave barrier device, the ground reflection component erases the linear component at a certain distance and a certain installation height, which is a big problem.

A practical microwave antenna focuses radiated radio waves into a single beam. The magnitude of the ground reflection signal is
Affected by antenna beam width. As the beam width increases, the ground reflection signal also increases.

Figure 3 shows an opening of 20cm and an installation height of 100cm above ground.
This figure shows the ground reflection effect for a vertical antenna. This figure shows the relationship between the received signal level and the distance between the transmitter and receiver. The vertical axis has a logarithmic scale of the received signal level. The distance between the transmitter and receiver is also plotted on a logarithmic scale on the horizontal axis.
From this figure, it can be seen that at a certain distance, especially 68 m, the received signal is significantly attenuated. The reason for this is that the ground reflection component is in opposite phase to the direct component at these points. The beamwidth of the antenna can prevent these effects from occurring over very short distances. In the example shown in Figure 1, the beam does not hit the ground until a distance of 12 m from both ends (24 m in total).

The dashed curve in Figure 3 shows the effect of lowering the antenna mounting height by 10 cm. The overall shape of the curves is similar, but the minimum position has changed. Therefore, in actual cases, changes in the effective mounting height due to plant growth or snow accumulation pose a problem.
If the effective mounting height is lowered in this way, the minimum position of the received signal will be too low and the reliability of the function will be compromised. As a result, false alarms and other operational problems occur.

One solution to this problem is to reduce the beamwidth of the antenna to reduce ground reflections. However, if the antenna beam width is narrowed, it is not possible to sufficiently monitor intruders passing through or jumping over the microwave barrier. If we were to use a very large antenna with an aperture of 2 m, sufficient protection would be possible from the ground and at a height of 2 m. However, the large antenna aperture complicates the very narrow (approximately 0.86°) antenna beam alignment and mechanical mounting required to ensure stability in high wind conditions.

Another solution to the above-mentioned problem is to ensure that the ground reflected component never completely cancels out the direct component within the installation range of 10 to 200 m. For this purpose, the installation height of the antenna must be lowered. The solid line in Figure 4 indicates the installation height is 30
The characteristics for a cm antenna are shown. Comparing this with Figure 3, it can be seen that the relative received signal amplitude continuously decreases as the distance between the transmitter and receiver increases, and that the cancellation effect shown in Figure 3 does not occur within the required distance range. Is recognized. Reducing the mounting height of the antenna will increase the ground reflected signal compared to the situation in FIG. 3, but a complete phase reversal with respect to the direct signal can be avoided. In reality, the first cancellation effect is
This occurs due to the distance between the receivers, but this distance is not practically necessary.

The broken line curve in Figure 4 shows the characteristics when the installation height is 20 cm. Again, the relative received signal amplitude gradually decreases with increasing distance, and no direct signal cancellation occurs over the distance range shown.

However, the main drawbacks of these configurations are that they reduce the mounting height, resulting in insufficient protection at height;
There is a danger that an intruder may jump over the microwave barrier device.

[Purpose of the invention]

It is therefore an object of the present invention to avoid the above-mentioned disadvantages and ensure sufficient protection both on the ground and at heights, and also to avoid the disadvantage that the direct component is largely erased by the ground reflected component in a relatively The object is to obtain a microwave barrier device which can be implemented with antennas of small dimensions, in particular with small antenna apertures.

[Summary of the invention]

In order to achieve the above object, in the present invention,
At least two antenna beams were provided, one extending to the ground to form a protected zone and the other inclined upwards with respect to the horizon by an angle greater than half the width of this beam.

In the present invention, the transmitter and receiver are provided with one or more antennas located close enough to the ground that canceling effects due to ground reflections do not occur.
This ensures that sufficient device signal levels are available under all ground conditions. Additionally, the invention provides at least one more antenna beam that is radiated upwardly at an angle such that the majority of the beam does not strike the ground. Under these conditions, no ground reflected signal occurs for this upwardly directed beam. Therefore, the change in signal level due to the distance between the transmitter and receiver is smooth, and no cancellation effect occurs.

However, any movement that occurs within this or these upper beams will appear as a change in signal level at the receiver. This is a significant improvement to the height of the device. FIG. 5 is a basic diagram of the dual beam system according to the invention. In the example shown, aperture 20
Only one transmitting and receiving antenna of cm is provided,
Two antenna beams with a beam width of 8.6° are created. The beam axis of the lower antenna beam is
parallel to the ground. The beam axis of the upper antenna beam is tilted upward by 8.6° with respect to the horizon.

If the mounting height is 30 cm and the transmitter-receiver distance is 100 m, the lower antenna beam will strike the ground at a distance of 4 m from either end of the surveillance area and reach a height of 2 m at a distance of 21 m from said ends. Since the upper antenna beam does not strike the ground, there are no changes in the received signal level due to ground reflections. The upper antenna beam reaches a height of 2 m at a distance of 7 m from the ends.

If desired, further antenna beams can be provided to increase the degree of protection. The receiver has
Circuitry is provided to provide an alarm when one or more antenna beams are completely or partially obstructed.

Hereinafter, the present invention will be specifically explained with reference to illustrated embodiments.

〔Example〕

FIG. 6 is a block diagram showing a complete embodiment of a microwave barrier device according to the present invention. The device has a separate microwave transmitter and microwave receiver, both located on a metal substrate.

Microwave transmitters include microwave oscillators that use Ga-As field effect transistors. When the oscillator 1 receives a current from the exciter 2, it generates oscillation at a desired microwave frequency. The generated microwave signal is sent to two antennas 4, 5 via a splitter 3. The lower antenna 5 is aimed directly at the receiver, while the upper antenna 4 is radiated upward at an angle such that the majority of the beam does not touch the ground. Thus, the microwave transmitter has two relatively small antennas with mutually independent beam directions.

A receiver is placed at the other end of the surveillance area. The radiated incoming microwaves are received by two antennas 6 and 7. Of these, the lower antenna 7 is placed close to the ground so that ground reflected beams do not erase the beam coming directly from the transmitter. The upper antenna 6 is arranged so that its axis of maximum sensitivity is tilted upward, and has extremely low sensitivity to ground reflected signals. With these two separate transmit and receive beams, good monitoring of high altitudes can be achieved while avoiding complete ground reflection effects. The signals received by antennas 6 and 7 are mixed in a microwave mixer 8. Mixer 8 provides an output signal corresponding to the vector sum of the input signals provided by the two antennas.

The total combined signal is rectified in a microwave detector 9, which consists of, for example, a Schottky barrier detection diode. This circuit provides a small output voltage that is proportional to the total signal magnitude.

The rectified signal is amplified by an amplifier. The amplification factor is variable and automatically adjusted by the circuit 10 with automatic amplification control. This circuit 10
Gently adjusts the amplification to compensate for changes in the effective range of the equipment and for long-term phenomena such as environmental changes due to plant growth or snowfall. For short-term changes, such as those caused by an intruder, circuit 10
does not change the amplification factor. Such received signal level changes are sent to the monitor hold circuit 11.

The transmitter is configured to transmit microwave impulses to save power consumption. The signal received by the receiver is therefore also in the form of an impulse. Control signals for operating the transmitter are transmitted to the transmitter via a connection line by a trigger generator 14 in the receiver. This trigger signal also
The monitor hold circuit 11 in the receiver is operated. This circuit converts the impulse output of circuit 10 into a continuous signal that is proportional to the magnitude of the output impulse. When an intruder enters the effective range of the microwave barrier device, a low frequency change occurs in the output signal of the monitor and hold circuit. Threshold detector 12
processes this low-frequency signal to determine the size and speed of the intruder. When the amplitude change exceeds a predetermined threshold, the alarm output means 13 is activated. The operation of the device differs depending on where the intrusion is attempted.

An intruder crawling on the ground causes a change in the signal received by the lower antenna 7. An intruder attempting to jump the microwave barrier near the transmitter may
The beam transmitted by the upper antenna 4 is blocked. As a result, a portion of this signal is reflected towards the receiver and is detected by either the upper or lower antenna 6 or 7, depending on the relative position of the intruder. An intruder attempting to jump the microwave barrier near the receiver will reflect a portion of the transmitted signal towards the upper receiving antenna 6, causing a change in the signal.

In either case, an intruder's attempt causes a change in the received signal at one or both receive antennas. Changes in this signal are processed by associated circuitry.

Figures 7 and 8 show the transmitter and receiver. The antennas 4, 5, 6 and 7 are made in a planar shape. Although antennas 4 and 6 have the same beam pointing angle, this is a different beam pointing angle than antennas 5 and 7 (which are identical to each other). The oscillator 1, the divider 3 and the exciter 2 are arranged on a substrate 15a which together with the mechanical mountings forms the conductive plate (earth) necessary for the operation of the microwave circuit.

In the receiver, all components are similarly placed on the conductive substrate 15b. Antennas 6 and 7 are mounted in the same way as for the transmitter. The functions of the mixer 8 and the detector 9 are the same as those of the microwave receiving module 3.
Built into 0. The output of this receiving module 30 is connected to the input of a receiving circuit 31 which functions as the automatic amplification control circuit 10, the monitor hold circuit 11, the threshold detector 12, the alarm output means 13, and the trigger generator 14.

The action of the planar antenna will be discussed later, but
In the present invention, basically the directional antenna
Any antenna may be used as long as it generates a beam.

FIG. 9 is a perspective view showing details of the planar antenna. The planar antenna is formed with a pattern of metal strips 19 etched onto an insulating dielectric substrate 16. These strips19
are arranged at a constant distance from the conductive metal substrate 17. The pattern of metal strips 19 has a plurality of dipoles 18 (half wavelengths) connected to the supply lines. The microwave signal is fed to an input connection line 20 and distributed to eight strips 19 forming a supply line. The microwave signals distributed on these feed lines reach the end 21 along the strip and excite the dipole 18. Each dipole radiates a microwave signal into the space above the planar antenna. By selecting the spacing of each dipole, the magnitude and phase of each beam from each dipole can be combined to create a constant beam with a particular pointing angle. FIG. 10 shows the supply line 19 and the dipole 18 attached thereto.

In FIG. 9, in the horizontal direction, the microwave signal has the same magnitude and phase at every instant. This means that the maximum beam direction is aligned with the horizontal axis of the substrate.
Make sure to form a 90° angle.

In the vertical plane, the distance of the dipoles 18 is selected to obtain the desired beam pointing direction. This can be determined by the following equation.

α=sin ^-1 (√−λ/D) where, α=beam direction perpendicular to the substrate surface, εr=effective relative dielectric constant of the substrate material, λ=wavelength of microwave signal D=same supply line distance between adjacent dipoles on the sides (see Figure 10).

FIG. 11 shows the maximum beam pointing direction relative to the substrate plane.

The following relationship exists between the beam width θ of each antenna, the geometrical dimension of the radiation aperture, and the beam direction according to the formula given above.

θλ/a however, λ = wavelength of microwave signal, a = effective aperture in the direction of beam propagation.

For a planar antenna with a beam at an α angle, the effective size of the aperture is equal to a·cosα.

Most of the energy radiated by the antenna is within the angular range α±θ/2. To ensure that the upper beam does not experience significant ground reflections, the angle α must slope upward and be greater than half the beam width (θ/2) of the upper antenna. That is, the following formula is applied.

α>θ/2 The lower antennas 5 and 7 are dimensioned to provide the maximum signal to the receiver. The beam angle of these two antenna beams should be zero for this purpose. FIG. 12 shows an arrangement that takes these points into consideration.

The upper antenna used has a vertical radiating aperture of 34.5 cm and the lower antenna has one of 32.5 cm.
Therefore, the beamwidth of the upper antenna beam is
5.0°, and the beam width of the lower antenna beam is 5.3°. The upper antenna produces a beam that propagates upward at a 5.0° angle. The antenna is placed on a rigid substrate that maintains its precise relative position and forms a conductive metal platform and a mounting plate for the electronic components. The ground mounting height of the antenna in the above embodiment is shown in FIG.

In this arrangement, the lower antenna beam hits the ground at a distance of 4 m. The upper antenna beam reaches an altitude of 2 m at a distance of 6 m. Such an arrangement, on the one hand, provides good monitoring of the ground and, on the other hand, prevents the microwave barrier from being bypassed.

Although in the embodiments described above the antennas used to generate the two antenna beams are arranged vertically relative to each other, the antennas may be arranged horizontally adjacent to each other as shown in FIGS. 14 and 15.

The transmitter shown in FIG. 14 has a substrate 40 on which other parts of the transmitter are placed. The oscillator 43, the divider 44 and the exciter 45 are arranged between the antennas 41 and 42 which are arranged horizontally to each other. The antenna is configured as a planar antenna. antenna 4
1 is a downward antenna with a beam axis tilted at 0°.
Generates a beam. Antenna 42 produces an upwardly directed antenna beam that makes no contact with the ground.

The receiver shown in FIG. 15 has two planar antennas 46, 47, a receiving module 48 and a receiving circuit 50 similar to that of the transmitter. These components are provided on a metal substrate 49. antenna 4
6 produces a downward antenna beam whose maximum sensitivity is at an angle of zero to the horizon, and antenna 47 produces an upwardly directed antenna beam which is virtually free from ground reflections.

The operation of this embodiment is the same as for antennas arranged perpendicular to each other. Also in this case, the output signals of the two receiving antennas are vectorially combined and rectified by the receiving module. If the lower or upper antenna beam is obstructed, an alarm signal is generated.

The configuration of the antenna in this example is slightly different from the previous configuration. FIG. 16 shows the arrangement of the antennas that create the downward antenna beam. Divider output 51
The signals coming from are distributed to eight transmission lines 52. The plurality of half-wavelength dipoles 54 are connected to the transmission line 52.
excited by microwaves passing along the The arrangement is such that the signal on transmission line 52 is equal in phase and magnitude at each corresponding point (eg, along line 55) at any given time. Dipole 54 is positioned such that the combined beam is a primarily vertically polarized antenna beam with a beam axis at zero angle to the horizontal. The antenna arrangement is formed on a substrate 53 of insulating material, similar to the embodiments described above.

Its beam characteristics are shown in FIG. Antenna 53 is placed near the ground 56. The beam axis has an elevation angle of 0°. The structure and operation of the downward antenna and beam antenna on the receiving side are also as follows:
essentially the same.

FIG. 18 shows the configuration of the upper antenna beam antenna. This is generally the same as the lower antenna beam antenna shown in FIG. 16, but the transmission lines 57 are arranged to produce a different phase with respect to the dipoles 58 connected to each transmission line 57. The phase of each transmission line relative to the dipole is chosen by choosing the path length between the input 59 and the first dipole of the associated transmission line 57. FIG. 19 shows the beam characteristics.

The inclination angle α of the beam axis (ie, the maximum beam intensity direction) is determined by the following equation.

α=sin ⁻¹ (l√/d) where l and d are the dimensions shown in FIG. 18, and εr is the effective relative dielectric constant of the substrate.

In the horizontal plane, antennas 41 , 42 , 46 and 47 have their maximum in a direction perpendicular to the plane of substrate 49 . This is accomplished by choosing the distances of the individual dipoles on the same transmitter 57 to be exactly in phase. Therefore, the distance D is determined by the following equation (see FIG. 10).

D=λ/√ however, λ = wavelength εr = effective relative permittivity of the substrate.

Figures 20 and 21 illustrate another embodiment of the invention in which the antenna generating (or receiving) the upper and lower antenna beams comprises a single composite antenna.

The transmitter shown in Figure 20 has one planar antenna 60 that generates two separate antenna beams. It is excited by an oscillator 61 supplied by an exciter 62. The entire device is placed on a conductive substrate 63.

Similarly, the receiver shown in FIG.
It has a planar antenna 64 having the same configuration as that of 0. The output signal from the antenna is supplied to a microwave receiving module 65 and demodulated there. Amplification and subsequent processing of the resulting low frequency signal takes place in print receiver circuit 66. This circuit 66 provides an alarm signal in the presence of an intruder.

The configuration of the two antennas 60 and 64 is
As shown in the figure. The antenna is placed on a substrate 68 of insulating material, and a pattern of conductive strips is formed by etching techniques. The eight strip antenna elements 70, 71 excite the plurality of dipoles 69 so as to obtain desired beam characteristics.

The antenna element 70 is an antenna in which the radiation portions from the dipoles of these antenna elements are combined and the maximum thereof is in a direction perpendicular to the plane of the substrate 68.
Dimensions should be such as to create a beam.

On the other hand, the antenna elements 71 are dimensioned so that the radiation waves from each dipole form an upwardly propagating antenna beam, with a large portion of the antenna beam not touching the ground.

Splitting circuit 72 splits the signal entering the transmitter into eight equal parts that excite antenna elements 70 and 71. In the receiver, 72 is a coupling circuit that creates a vector sum of the signals supplied from the antenna elements 70 and 71. That is, circuit 72 sums the two antenna beam signals at the receiver.

FIG. 23 shows the composite antenna characteristics. Antenna device 73 is placed close to ground 74. Lower antenna beam 75 is propagated at zero elevation (ie, beam axis parallel to the ground). the result,
Any movement of the intruder near the ground will result in a change in the received signal on this lower antenna beam.

Upper antenna beam 76 is propagated at a large elevation angle, greater than half the beam width. the result,
This upper antenna beam does not touch the ground.
Since it is not subject to significant ground reflections, the strength of the received signal varies smoothly and continuously with distance.

Figures 24 and 24a show still another embodiment of the invention. In this example, a passive reflector is used to deflect a portion of the lower antenna beam upward, producing an upper antenna beam.

The transmitter and receiver are respectively planar antennas,
Microwave antenna 77 configured as a parabolic antenna or other antenna and producing an antenna beam 78 that is propagated in the direction of the receiving antenna.
has. The passive reflection plate 79 made of metal material is
An antenna that is placed in a portion of the beam path and reflects a portion of the antenna beam upward and is directed upward.
A beam 80 is generated. If an intruder passes through either the lower antenna beam 78 or the upper antenna beam 80, this will cause a change in the received signal and cause an alarm.

25 and 26 show a modification of the above in which a microwave prism is provided in the beam path. Prism 81 is made of dielectric insulating material. Its dimensions are chosen such that when the microwave beam is interrupted, the direction of propagation is deflected upwards within the prism. As shown in FIG. 25, prism 81 is placed in front of transmitting antenna 82 whose beam axis points in the direction of the corresponding receiving antenna.
The radiated waves incident on prism 81 are deflected upward to produce an upper antenna beam that does not strike the ground, while lower antenna beam 84 strikes ground 85 as described above.

FIG. 26 clearly shows the action of prism 81. The radiation wave 86 from the transmitting antenna is deflected upward by a refraction angle α by the prism 81 into an upper antenna beam 87 .

A possible means of creating one or more upper antenna beams is to use a Fresnel lens in the lower antenna beam. A Fresnel lens has multiple steps in an insulating medium. As the incoming micros pass through this Fresnel lens, they are radiated at many different angles. This angle is determined by the interference pattern between the waves passing through the slotted portion and the waves passing through the main area without slots.

As shown in FIG. 27, a Fresnel lens 88
is located within the main beam 91 of the transmitting antenna 89. Lens 88 produces a plurality of upwardly directed antenna beams 90, forming an additional height protection zone of the microwave barrier device according to the invention.

Fresnel lens 88 is shown in detail in FIG. It consists of a block of dielectric insulating material having a plurality of slots 92. slot 9
The depth of the slot 2, the relative permittivity of the dielectric material, and the spacing of the slots determine the propagation angle of the radiation waves emanating from it for a given frequency. Lens 88 has a wedge-like structure such that the incoming radiation wave is first refracted upwardly before passing through slot 92. As a result, the antenna beam radiated from the Fresnel lens is
It is definitely propagated upwards at an angle.

Finally, FIG. 29 shows an example of using a diffractive screen to create multiple antenna beams at different angles from a single incoming antenna beam. Its principle is essentially the same as the Fresnel lens described above. A diffractive screen is placed in front of the antenna that transmits or receives the lower antenna beam. The incoming radiated waves are split into multiple antenna beams and propagate primarily upwards at an angle, improving protection at heights.

The diffraction screen shown in FIG. 29 has a block 93 of dielectric insulating material on which a plurality of metallized strips 94 are provided. The position and width of these strips determine the direction of the outgoing antenna beam. The diffractive screen is made wedge-shaped so that the incoming radiation wave is first refracted upwards before being dispersed onto the metal strip 94.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to prevent the direct component from being erased by the ground reflection component with an antenna of relatively small size, and to ensure good monitoring both on the ground and in high places, and to ensure sufficient protection. A microwave barrier device can be obtained.

[Brief explanation of drawings]

Figure 1 is a diagram showing the usual antenna arrangement and antenna beam, Figure 2 is a diagram showing the relationship between direct signal and reflected signal, Figure 3 is a curve diagram showing an example of ground reflection effect, and Figure 4 is a diagram showing the antenna beam. A curve diagram showing that the ground reflection effect does not occur when the installation height is lowered, Figure 5 is a basic diagram of the double beam system according to the present invention, and Figure 6 is a complete embodiment of the microwave barrier device of the present invention. 7 is a front view showing an example of a transmitter, FIG. 8 is a front view showing an example of a receiver, FIG. 9 is a perspective view showing details of a planar antenna, and FIG. 10 is a front view showing an example of a transmitter. Figure 11 shows the attached dipole, Figure 11 shows the maximum beam direction with respect to the substrate surface, Figure 12 shows the relationship between beam width θ and beam angle α, and Figure 13 shows the antenna installation in the above embodiment. Fig. 14 is a front view showing another example of the transmitter, Fig. 15 is a front view showing another example of the receiver, and Fig. 16 shows the antenna arrangement for creating a downward antenna beam. Figure 17 is a diagram showing the beam characteristics, and Figure 18 is a diagram showing the upper antenna.
Figure 19 shows the configuration of the beam antenna, Figure 19 shows its beam characteristics, Figures 20 and 21 generate (or receive) the upper and lower antenna beams.
22 is a diagram showing the configuration of the antenna, FIG. 23 is a diagram showing the composite antenna characteristics, and FIG. 24 is a diagram showing the composite antenna characteristics. 24a is a diagram showing a reflection plate thereof, FIG. 25 is a diagram showing a modification using a prism, FIG. 26 is a diagram showing the action of the prism, and FIG. 27 is a diagram showing still another embodiment of the present invention.
The figure shows a modification using a Fresnel lens.
FIG. 28 is a perspective view showing details of the Fresnel lens, and FIG. 29 is a view showing a modification using a diffraction screen. 1-5...Microwave transmitter, 4,5...Transmission antenna device, 6-14...Microwave receiver,
6, 7...Receiving antenna device, 11, 12, 13
...A circuit that responds to changes in the received signal.

Claims (1)

[Claims] 1. A microwave transmitter having a transmitting antenna device and a microwave receiver having a receiving antenna device, these transmitters and receivers are arranged at both ends of a monitoring area, and the receiver is arranged at both ends of a monitoring area. In a microwave barrier device having circuitry responsive to changes in the received signal caused by an intruder, at least two antennas
Microwave barrier device, characterized in that beams are formed, one of which extends towards the ground and forms a protected area, the other of which is inclined upwardly with respect to the horizontal by an angle greater than half the width of this beam. . 2. The microwave barrier device of claim 1, wherein two separate antennas are provided to form two mutually independent antenna beams. 3. The microwave barrier device according to claim 2, wherein the two antennas are vertically shifted from each other. 4. The microwave barrier device according to claim 2, wherein the two antennas are shifted from each other in the horizontal direction. 5. The microwave barrier device according to claim 1, further comprising one antenna and a device for splitting the antenna beam to form two antenna beams. 6. The microwave barrier device according to claim 5, wherein the device for splitting the antenna beam comprises a reflector. 7. The microwave barrier device according to claim 5, wherein the device for splitting the antenna beam comprises a prism. 8. The microwave barrier device according to claim 5, wherein the device for splitting the antenna beam comprises a Fresnel lens. 9. The microwave barrier device of claim 5, wherein the device for splitting the antenna beam comprises a diffraction screen. 10. The microwave barrier device according to claim 1, wherein one composite antenna is provided for forming two antenna beams. 11. The microwave barrier device according to claim 2, wherein the two antennas are connected to the same microwave oscillator via a splitter. 12. The microwave barrier device according to claim 1, comprising a circuit for vector-adding signals extracted from two antenna beams. 13. The microwave barrier device of claim 1, wherein the circuit provided on the receiving side is responsive to intruder-induced changes in the signals produced by the two antenna beams.