JP2759346B2 - Method for receiving microwave signal using light beam forming network - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for receiving a Myroku wave signal using an optical beam forming network for converting a plurality of microwave signals into corresponding optical signals.

[Related Art] In recent years, it has become important to generate a radiation pattern by using a phase-controlled active antenna. For example, U.S. Pat. No. 3,878,520 discloses an optical network capable of transmitting on multiple channels simultaneously. Publication, Koepf, GA: Optical Processor for Phased Arra
y Antenna Beam Formation, SPIE, Vol.477, Optical Tech
nology for Microwave Application (1984), pp.74-8
An optical network of a receiver suitable only for individual radiation patterns is also known from 1,1984. This publication is described further below.

[Problems of the Invention] It is an object of the present invention to provide a method in which a plurality of microwave signals coming from different directions can be simultaneously received by a single light beam forming circuit.

Means for Solving the Problems The object of the present invention is to provide a receiving method of the type mentioned at the outset, in which the optical signal of each antenna element modulated by microwaves is coherent to the other laser. Amplify with each one laser, radiate the amplified signal through each one pinhole, and direct it to one detector array with a common Fourier transform lens, and the laser beam in the plane of this detector Interfering with each other, signals in different receive directions are resolved by being incident on different areas of the detector array.

Other advantageous embodiments of the invention are set out in the dependent claims.

Embodiment The present invention will be described in more detail with reference to the drawings showing two embodiments.

In a typical lightning system, a signal is multiplexed and distributed between a microwave channel and an antenna element using a fiber optic for a phase shifter and an amplitude adjuster. However, control of the antenna is performed by a computer. Distribution of the signal from the antenna controller to the phase shifter is also performed via fiber optics.

Since the design calculation of the aperture of the antenna element by the phase and the amplitude is a Fourier transform, it is immediately possible to perform the Fourier transform using the Fourier optical system. In a beam forming system using Fourier optics, not only a distribution network but also an antenna control unit can be formed optically in principle. Such systems are well known in principle and have already been mentioned at the beginning of the publication, Koepf, GAOptical Processor for phased Array Ant.
enna Beam Formation, SPIE, Vol. 477, pp. 74-81, 1984.

The method disclosed in this publication utilizes a fiber optics distribution network only for the transmission system. For reception, it is necessary to perform distribution and addition of a microwave component signal.

Known schemes do not offer the advantage of transmitting the microwave signal of the receiving system over fiber optics to reduce weight and occupied space, since the receiving distribution network must be composed of microwave components. In addition, this method can only be used to form individual radiation patterns (for transmission or reception).

Although the present invention overcomes two difficulties, the advantages and possibilities of the present invention are described below.

What is essential for a compact and lightweight beamforming system is that all beamforming is performed not only in the transmission system but also in the reception system using a single optical beamforming network, and signal distribution is performed via optical fibers. is there. This is not possible with the method described in the above publication. Using the novel method proposed here, a large number of radiation patterns can be generated that can be controlled in real time, and a large number of channels can be received from the same or different directions using a phase-controlled active antenna. You can send in the direction.

In order to generate a number of radiation patterns for the receiving operation according to FIG. 1, the microwave-modulated optical signal of the optical fiber of each antenna element is amplified by one laser each. It is important that the "fundamental wavelengths" of the individual lasers are tied together. As coherence of the laser beam is essential in the "pinhole" plane, it is recommended not to use an optical fiber after the laser, as can be considered. If there is a temperature drop in the glass fibers, these fibers will exhibit different elongations, disrupting the coherence of the optical signal.

Instead, the laser emits through a "pinhole" at the focal plane. After the Fleier optics, the signals of one microwave channel with an associated radiation pattern are each detected by one detector. In order to tilt the beam, it is in principle possible to move the detector in the same way as a laser, but all possible microwave channels or radiation patterns are detected using one group of detectors and then one. It is easier to select the desired microwave channel or radiation pattern with one multiplexer. Since the laser beams interfere with each other in the plane of the detector, it is not necessary to additionally provide, for example, a reference beam of the local oscillator LO, but it can be employed to detect the modulated optical signal with high sensitivity.

If one wants to use the same beam forming system for the transmitting system and the receiving system, a bundle of fibers can be used before and after the Fourier transform lens according to FIG. In the transmission system, an amplitude-modulated laser signal is extracted from an optical fiber having a fiber end shifted laterally. Take the Fourier transformed signal into a bundle of fibers. However, here the mixing with the local oscillator LO is 3 dB in the fiber.
This takes place in the combiner.

In reception, the local oscillator LO and the laser switch, acting as a laser amplifier for the optical signal from the antenna element. These signals are Fourier transformed and are incident on the pigtail of FIG. 2 and are detected by one detector. Again, as above, the diameter of the inlet and outlet openings is important for the half-width of the radiation pattern.

The profile of the main lobe of the radiation pattern of the transmission system can be adjusted with an aperture in the focal plane of the modulated laser. In this case, these apertures have been replaced by "pinholes".
The contour can be changed by changing the aperture. The aperture can be made mechanically or formed of electro-optic components such as an LCD matrix.

Another possibility for determining the contour is to combine a large number of individual patterns.

The contour of the main lobe of the radiation pattern of the receiving system can likewise be adjusted with an aperture in the focal plane of the detector. Even in this case, the contour can be changed by changing the aperture. This aperture can also be made mechanically or formed from electro-optic components such as an LCD matrix.

According to the present invention, a new method for generating a large number of antenna lobes that can be controlled in real time is presented. Due to the control of the radiation pattern, which allows a large number of channels to be operated simultaneously, and the efficient injection of the local oscillator LO through the holographic plate, this method is fundamentally different from the ideas of the detailed publications. Not only the transmission system according to the present invention but also the reception system in particular is not constituted by microwave components but is constituted by an optical system and an electro-optical system. Therefore, this method is fundamentally different from the concept of the above publication. The method proposed here merely uses an optical system and an electro-optical system to form a beam from a large number of radiation patterns that can be controlled in real time. Therefore, it is more advanced than all existing systems in terms of compactness and lightness.

[Brief description of the drawings]

FIG. 1, a schematic diagram of a beam forming network for receiving a number of microwave channels, FIG. 2, a schematic diagram of a beam forming network for transmitting and receiving a number of microwave channels.

Claims (3)

(57) [Claims] 1. A method for receiving a Myroku wave signal using an optical beam forming network for converting a plurality of microwave signals into a corresponding optical signal, comprising the steps of: converting an optical signal of each antenna element modulated by microwave into another laser; Amplified by one laser each, which is coherent to each other, emits the amplified signal through one pinhole, and directs it to one detector array with a common Fourier transform lens, A method wherein the laser beams interfere with each other in the plane so that signals in different receive directions are incident on different areas of the detector array. 2. The method according to claim 1, wherein the directivity of the different radiation patterns is adjusted with an aperture in the focal plane of the detector. 3. The method according to claim 2, wherein the lateral movement of a detector or a group of detectors tilts the individual radiation patterns.