RU2810828C1 - Method for reducing radar signature of aircraft antennas - Google Patents

Abstract

FIELD: aviation.

SUBSTANCE: method for reducing the radar signature of aircraft antennas. The method consists in selecting an element of the aircraft that can be isolated from the body of the aircraft without changing its theoretical contour, material and design, calculating the impedance in relation to the element of the aircraft, isolating the element of the aircraft from the body of the aircraft, for which purpose it is installed between the element and the aircraft body dielectric bearings or dielectric spacers, and use the element as an aircraft antenna.

EFFECT: reducing the radar signature of an aircraft.

4 cl, 10 dwg

Description

The invention relates to the field of aviation, in particular to a method for reducing the radar signature of aircraft antennas, and can be used to reduce the radar signature of aircraft antennas, in particular kilometer wave (KWW) and decameter wave (DKMV) antennas.

Reducing the radar signature of aircraft is one of the most important factors in the effectiveness of the use of aircraft. The use of aircraft with a low effective dispersion area (RCS) ensures successful penetration of the air defense system. EPR is the main characteristic that determines the properties of an aircraft as a reflector of electromagnetic radiation from an object. The ESR value characterizes the ability of a scattering body to convert an electromagnetic wave incident on it into a scattered wave of a certain polarization, propagating in the direction of the receiver.

The following designs are known from the prior art: antennas with capacitive coupling, so-called cap or with an insulated part of the aircraft body, antennas with inductive coupling, antennas with conductive coupling or loop antennas, antennas with diffraction coupling or slot antennas.

The main disadvantage of using such structures on modern aircraft, which are subject to low radar signature requirements, is the presence of structural elements that extend onto the theoretical contour of the aircraft and a high level of ESR.

From patent RU 2565158 C1, published. 10.20.2015, there is a known method for reducing the radar signature of aircraft, which consists of placing the antenna in a sealed cavity of a radio-transparent fairing, filling the cavity with a plasma-forming gas mixture and introducing an electron beam into the mixture. However, plasma formation and the efficiency of absorption of radio waves by plasma depend on the parameters of the gas mixture, both during storage and during flight, and are not stable. In general, this method is difficult to implement and cost the aircraft, reduces the reliability of the aircraft and does not provide a significant reduction in the ESR.

The disadvantages of aircraft known from the prior art and methods for reducing the radar signature of aircraft include the insufficient effective reduction of the radar signature of antennas, as a result of increased ESR of aircraft, the need to use additional special measures to reduce the ESR of aircraft, causing an increase in the weight of the aircraft.

The objective of the invention is to reduce the radar signature of aircraft.

The technical result of the claimed invention is to ensure the absence of antenna elements extending onto the theoretical contour of the aircraft, reducing the effective dispersion area of the antenna and reducing the radar signature of the aircraft.

The technical result is achieved by a method consisting in selecting an element of the aircraft that can be isolated from the body of the aircraft without changing its theoretical contour, material and design, calculating the impedance in relation to the element of the aircraft, isolating the element of the aircraft from the body of the aircraft, for which purpose dielectric bearings or dielectric spacers are installed between the element and the aircraft body, and the element is used as an antenna of the aircraft.

As an element of the aircraft, control surfaces, aircraft fins, horizontal tail, vertical tail, ailerons, flaperons, elevons, spoilers, and rotary beads are selected.

Elements of the aircraft can be used as antennas, in particular in the ranges of kilometer waves (KWW) and decameter waves (DKW), hectometer waves (HCW) and myriameter waves (MRW).

Brief description of drawings

fig. 1 - aircraft with a capacitively coupled antenna;

fig. 2 - aircraft with an inductively coupled antenna;

fig. 3 - aircraft with a conductive antenna (loop antenna);

fig. 4 - aircraft with a diffraction-coupled antenna (slot antenna;

fig. 5 - keel of the aircraft;

fig. 6 - keel of the aircraft with a slot-type antenna;

fig. 7 - keel of the aircraft, used as an antenna of the aircraft;

fig. 8 - active part of the antenna impedance;

Fig.9 - reactive part of the antenna impedance.

fig. 10 - backscatter diagrams (BSD) of the keel and keel from a slot-type antenna;

Fig. 1-4 show aircraft with antennas known from the prior art.

In fig. 8 the following notations are used:

1 - keel of the aircraft;

2 - dielectric bearing.

In fig. 7 shows the fin of the aircraft 1, which is isolated from the body of the aircraft by dielectric bearings 2, and is used as an antenna.

A way to reduce the radar signature of aircraft antennas is to use existing elements of the aircraft as antennas without changing their theoretical contour, materials and design as a whole. In this case, the contribution to the EPR will be zero. The implementation of the claimed method occurs as follows.

To use as an antenna, select a structural element of the aircraft that can be isolated from the body of the aircraft without changing its theoretical contour, materials and design as a whole. Such elements are: ailerons, flaperons, elevons, spoilers, horizontal and vertical tails, rotary beads, etc.

In relation to the selected element, the impedance is calculated as an antenna-feeder device, i.e. antennas. The electrical characteristics of antenna-feeder devices installed on the aircraft must comply with the requirements of GOST R 50860-2009.

Impedance calculation is carried out by mathematical modeling by the method of moments - an exact method for solving Maxwell's integral equations in the frequency domain through a system of linear algebraic equations. The accuracy of the method depends on the quality of the surface approximation by the finite element mesh, since the exact solution is achieved at the nodal points of the elements, called basis functions. The numerical determination of the field is based on the analytical solution of the problem of excitation of the structure by an elementary current source. In mathematics, such a solution is called the Green's function. The moment modeling method is effective if the Green's function is written analytically in a simple form.

The surface of the aircraft is subjected to sampling, with the metal elements of the analyzed structure being replaced by equivalent electrical surface currents. To approximate the current within elementary areas, constant, linear and triangular basis functions are used. Thus, the boundary conditions on the metal surface in the mathematical modeling method are satisfied approximately, namely at several points within each elementary area.

As a result of specifying boundary conditions at discrete points, a system of linear algebraic equations is obtained for the coefficients of the basis functions, which have the meaning of the amplitudes of currents flowing within the elementary area. This system of linear algebraic equations is solved using the well-known Gaussian elimination method.

Next, the antenna parameters are calculated, in particular the impedance, for which the antenna is represented in the form of a microwave radiating multiport network (S,Y,Z matrix). Moreover, the multi-port network has outputs (ports) in the form of transmission lines, most often single-wave transmission lines. In this transmission line, a certain section is established, called a reference plane, in which the amplitudes of the incident and reflected waves, currents and voltages, etc. are determined. These parameters allow you to further find the Y, Z or S matrices of the multiport network.

It is assumed that outside the multiport network in the transmission line, fields can only exist in the form of incident and reflected waves. However, in a transmission line, there are always higher types of waves that are attenuated along the transmission line. These waves are excited in a multiport network and always create a finite field in any section of the output transmission line. But, since the reference plane is located at a sufficient distance from the place of excitation of reactive waves, their amplitude in this place will be negligible.

To determine, for example, the scattering matrix of a multiport network, it is necessary to perform N experiments, consisting of connecting an ideal generator to one of the ports of the device, and connecting ideal matched loads to the others, and then measuring the amplitudes of the waves reflected from the multiport network. An ideally matched load can be an endless transmission line in which there are no sources of reflection or some hypothetical matched load. Thus, the problem arises of how to create an infinite transmission line model. It is quite difficult to do this using purely electrodynamic methods, since all structures subject to numerical analysis must be finite. Among other things, this model should be logically included in the general scheme for solving the electrodynamic problem, in the scheme for modeling moment methods, ending with ports. In practice, these are most often coaxial connectors to which single-wavelength coaxial cables are connected. Such connectors are not perfectly matched, but the problem is being solved to create a model of an ideal connector that does not cause reflections.

The outermost layer adjacent to the metal wall is used to describe the port. The cell numbers in this layer vary from 1 to N. In the case of an operator equation, which is then applied to moment method modeling based on boundary conditions, these are boundary conditions on the surface of the strip conductor, requiring the tangential electric field to be zero. This boundary condition is valid for all grid cells except those used to describe the port. Let us establish other conditions here, namely, the equality of the electric field at the outermost areas not to zero, but to a certain value determined by the voltage in the gap between the conductor and the wall.

Assuming the cell size is small enough, Ohm's law for gap voltage is:

Where

E ₀ - EMF included in the gap,

Z is the concentrated resistance included in the gap,

J is the total longitudinal current flowing through the conductor.

The relationship is nothing more than Ohm's law for a section of a circuit. This circuit models two processes: absorption of a wave propagating from the circuit to the load and excitation of the circuit by a wave incident from outside. Resistance Z is equal to the characteristic impedance of the stripline transmission line approaching the port.

The total current J is determined through the integral over the cross section of the conductor. Under discrete grid conditions, it is replaced by the sum of the grid element currents.

It is also necessary to take into account that currents have two components, therefore, the basis and test functions are vector functions. The port model described above is not strict. It is based on the assumption that a concentrated load can provide perfect matching to a stripline transmission line. This, strictly speaking, is only true for fairly low frequencies. However, the practice of using such a model has shown that it gives good results in most practically important cases. A similar model in the form of a lumped source is used not only to describe printed circuits, but also in the analysis of dipole and wire antennas, when the real supply transmission line is replaced by a lumped generator with finite internal resistance.

The resulting impedance values of the selected aircraft element are checked for compliance with the requirements of GOST R 50860-2009. To use the selected aircraft element as an aircraft antenna, you must make sure that its characteristics comply with the requirements of GOST R 50860-2009.

Next, the selected element of the aircraft is insulated, for which the insulation of the selected element is studied by selecting dielectric bearings or dielectric bearings of dielectric spacers between the body of the aircraft and the selected element according to the characteristics of strength, service life and electrical capacitance.

A method for reducing the radar signature of aircraft antennas was tested on the Su-57 aircraft. As the antennas of the aircraft in the KLMV and DKMV ranges, namely the top-feed antenna of the pulse-phase radio navigation system (AVP-IFRNS) and the top-feed antenna of decameter waves (AVP-DKMV), a one-piece rotating vertical tail of the aircraft was chosen, i.e. left keel and right keel. The insulation of the aircraft tail elements is carried out using a highly loaded bearing or insulating pads with dielectric fasteners.

Aerodynamic distributed (air) loads in the form of pressure and vacuum forces are perceived by the keel skins and are transmitted through riveted, bolted and adhesive connections to the frame elements of the one-piece rotating vertical tail.

The shearing force along the wall of the tip diaphragm is transmitted through the angle by the cut of the pin to the wall of the end rib, then through the angles along the walls of the spar and along the front wall it is transferred to the cuts of the bolts and rivets securing the angles to the wall of the root rib, and from there by shear and bending to the keel axle axis.

The bending moment by tension-compression of the winglet skin and winglet diaphragm flanges is transmitted to the tip fastening bolts and then through the tension-compression linings of the spar flanges and casings is transferred to the connecting bolts, and from them to the axle shaft flanges and the keel axle shaft itself.

The torque is perceived by the tip contour and then, through the flow of tangential forces along the end rib, the contour between the front wall and the tail profiles of the skins is balanced by the flow of tangential forces on the root rib and is transmitted by a pair of forces to the axle shaft.

Thus, all loads from the solidly rotating vertical tail are transferred to the axle shaft. In this case, the shearing force and bending moment are transmitted to the axle shaft supports in the form of reactions (the axle shaft works for shearing and bending), and the torque is balanced by the moment on the drive bracket. The axle shaft rotates due to torque.

To insulate the keel, single-stage insulation was adopted as the simplest and, at the same time, providing the necessary level of protection. Due to the rather large magnitudes of reactions in the supports, insulation along the outer ring of the bearing was used to reduce the specific pressure.

In fig. Figure 7 shows the design of the aircraft antenna, which serves as the keel of the aircraft.

The vertical tail, including the right keel and the left keel, used as antennas of the aircraft belongs to the Pistolkors plume-vibrator type antennas. In this case, the outer surface of the keel is used as a vibrator, and the braided antenna feeders of the meter wave and decimeter wave ranges, placed in the radio-transparent tip of the keel, are used as loops. The antenna's counterweight is the entire surface of the aircraft's airframe. On the keel, used as an antenna, a matching device, standard with other types of antennas, is installed. At the base of the fin there are ferrite inserts (chokes) used to remove interference induced into the path from antennas in the range of kilometer waves, meter waves and decameter waves.

The impedance value, namely its active and reactive parts, in relation to the vertical tail of the aircraft used as an antenna for the upper supply of decameter waves (AVP-DKMV) of the range, obtained as part of interdepartmental tests (IUT) of this antenna, are shown in Figs. 8, 9 .

Similar characteristics were obtained for the vertical tail of an aircraft used as an antenna for the upper feed of a pulse-phase radio navigation system (APP-IFRNS).

In fig. Figure 10 shows backscatter diagrams (BSD) of the keel and the keel from a slot-type antenna. Graphic data shows that the backscatter diagrams of antennas made from elements of the aircraft do not differ from the own backscatter diagrams of such elements, in particular the left keel and the right keel of the aircraft. For comparison, the graph shows a curve made with a dotted line, characterizing the backscatter diagram of the keel with a slot antenna, and a curve made with a solid line, characterizing the backscatter diagram of the keel used as an antenna. The curves show that the contribution to the EPR of a keel with a slot antenna is quite high, while the backscatter patterns of an antenna made in the form of a keel do not differ from the own backscatter patterns of the keel and do not contribute to the ESR.

In addition, the proposed technical solution provides dielectric isolation and transfers loads from the vertical tail to the aircraft structure. This is achieved by installing dielectric bearings on the vertical tail axis of the aircraft, which transmits shearing forces from the vertical tail axis and bending moment to the aircraft structure, as well as by a dielectric bearing installed between the vertical tail rocker and the vertical tail drive, transmitting torque with the vertical tail axis to the vertical tail drive.

As a result of the manufacture and experimental testing of prototypes, results were achieved confirming the effectiveness of the method for reducing the radar signature of aircraft antennas, namely the complete elimination of the contribution to the aircraft's EPR from antennas of the KLMV and DKMV ranges, electrical insulation of the control surface from the surface of the aircraft, while ensuring a combination of simplicity designs with potential for unification.

It is worth noting that the design of the vertical tail, which is solidly rotatable, is not the determining criterion for choosing an aircraft element as an antenna. Fixed tail surfaces and other elements of the aircraft can be used as an aircraft antenna. In this case, the contribution to the EPR of the aircraft elements used as antennas will be zero.

Thus, the use of aircraft elements as an aircraft antenna ensures the absence of antenna elements extending onto the theoretical contour of the aircraft, reduces the effective dispersion area, and ensures a reduction in the radar signature of the aircraft.

Claims (4)

1. A method for reducing the radar signature of aircraft antennas, characterized by selecting an element of the aircraft that can be isolated from the body of the aircraft without changing its theoretical contour, material and design, calculating the impedance in relation to the element of the aircraft, isolating the element of the aircraft from the body aircraft, for which purpose dielectric bearings or dielectric spacers are installed between the element and the aircraft body, and the element is used as an antenna of the aircraft. 2. The method according to claim 1, in which control surfaces, fins of the aircraft, horizontal tail, vertical tail, ailerons, flaperons, elevons, spoilers, and rotary extensions are selected as an element of the aircraft. 3. The method according to claim 1, in which the aircraft antennas are antennas of the kilometer wave ranges (KWW) and decameter waves (DKWM). 4. The method according to claim 1, in which the aircraft antennas are antennas of the hectometer wave (HCW) and myriameter wave (MMW) ranges.