Double-layer cascade dual-polarization broadband band-absorption type frequency selection surface
Technical Field
The invention belongs to the technical field of microwaves, and relates to a dual-polarization broadband band-absorption type low-pass frequency selection surface which can be used as a stealth antenna housing of a low frequency band (VHF/UHF) antenna, wherein potential application scenes of the surface comprise a comprehensive communication mast of a warship and the like.
Background
In current military application, a frequency selective surface and a frequency selective structure are used as an antenna housing, which is one of effective modes for reducing a radar scattering cross section.
The frequency selective surface is substantially a spatial filter, which can only screen electromagnetic waves of a specific frequency band, polarization mode, incident angle, and the like, and cannot absorb the electromagnetic waves. Therefore, for a radome developed based on a frequency selective surface, only the probe wave can be reflected, deviating from its incident path to reduce RCS. However, this method can only work for a single station, and for a two-station or even multi-station detection system, the stealth purpose can only be achieved by absorbing incident waves. The concept of a wave-absorbing frequency selective structure/surface is thus led out, and such an ideal radome exhibits the following characteristics: in the pass band, the antenna housing is invisible to incident electromagnetic waves, and therefore the electromagnetic waves can be transmitted without damage completely; and outside the working frequency band, the invisible electromagnetic wave shielding cover can effectively absorb incident electromagnetic waves, so that the purpose of stealth is achieved.
The currently reported wave absorption frequency selective structures are all band-pass types, and the band-absorption type is not reported yet. In fact, in many low-frequency-band systems, such as a comprehensive mast on a warship, and various detection systems for communication signals, antennas thereof mostly operate in VHF and UHF frequency bands, and therefore there is an urgent need for a low-frequency-band transmissive antenna cover for absorbing high-frequency (radar frequency) waves.
Disclosure of Invention
The invention aims to provide a broadband wave-absorbing frequency selection surface based on two-dimensional plane cascade, which adopts a mode of combining a band-stop reflection wave-absorbing surface with a wave-absorbing surface structure to build a dual-polarization broadband band-absorbing type low-pass frequency selection surface, can generate an extremely wide wave-absorbing band at a high frequency and realize the low-insertion loss low-pass characteristic at a low frequency band. The structure is thin in thickness, simple in structure, easy to design, convenient to process and low in cost, and has the potential of being designed into a curved surface frequency selection surface.
The double-layer cascade dual-polarization broadband band-absorption type low-pass frequency selection surface is of a periodic structure, and each structural unit comprises a band-stop reflection wave absorption surface and a wave absorption surface.
The wave absorption surface is a periodically distributed structural unit, each unit is arranged in a seamless mode and comprises a first medium substrate and a first metal ring plated on the first incidence surface (namely the left surface) of electromagnetic waves of the first medium substrate; the first metal ring is of a closed annular structure, the side length of the first metal ring is smaller than the length of two shafts of the first medium substrate, and four radio-frequency resistors are welded at the centers of four sides of the metal ring.
The radio frequency resistors have the same resistance value, and the resistance values of the radio frequency resistors need specific analysis according to specific conditions.
The band-stop reflection wave absorption surface is a periodic distribution structure unit which is vertically arranged, each unit is seamlessly arranged and comprises a second medium substrate, a second metal ring plated on the first incident surface (namely the left surface) of electromagnetic waves of the second medium substrate, a third metal ring plated on the other surface (namely the right surface) of the second medium substrate, and a fourth metal ring plated on the other surface (namely the right surface) of the second medium substrate; the second, third and fourth metal rings are of closed ring structures, and the side lengths of the second, third and fourth metal rings are all smaller than the lengths of two shafts of the second dielectric substrate; four radio frequency resistors are welded at the centers of the four sides of the second metal ring.
The first dielectric substrate and the second dielectric substrate have the same size.
The first, second, third and fourth metal rings are overlapped with the centers of the first and second dielectric substrates.
The two-axis lengths of the first and second dielectric substrates refer to two side lengths of the first and second dielectric substrates in the x-axis and y-axis directions.
The wave absorbing surface and the band-stop reflection wave absorbing surface are arranged in parallel, and a straight line where the centers of the wave absorbing surface and the band-stop reflection wave absorbing surface are located is parallel to the Z axis; and the wave absorbing surface and the band elimination reflection wave absorbing surface are provided with an interval, the size of the interval needs to be specifically analyzed according to specific conditions, and the size of the interval can influence the wave absorbing effect and the effect of a low-frequency pass band.
The invention can also be realized by changing the side length d of each metal ring1、d2、d3And d4Width w1、w2、w3And w4Depth d of recess of fourth metal ringdAnd width wdResistance value R of radio frequency resistor1And R2Height h of air path between wave absorbing surface and reflection-resisting wave absorbing surfaceaThe low-frequency wave-transmitting performance and the high-frequency wave-absorbing performance are comprehensively regulated and controlled by the structural parameters.
The specific working principle is as follows: the electromagnetic waves are emitted into the surface of the structure, directly penetrate through the wave absorbing surface and are emitted to the band elimination reflecting surface, the second metal ring loaded with the radio frequency resistor on the left surface of the band elimination reflecting wave absorbing surface absorbs a part of the electromagnetic waves near the resonance frequency point of the second metal ring and reflects a part of the electromagnetic waves, and the rest electromagnetic waves directly penetrate through the second metal ring. The electromagnetic waves reflected by the second, third and fourth metal rings pass through the wave absorption surface again and are absorbed. Since the structure is completely the same in the x-axis direction and the y-axis direction, the filter characteristics generated for the incident TE wave and TM wave are completely the same, and thus the structure has dual polarization characteristics.
The TE wave represents an electromagnetic wave incident in a negative z-axis direction and having an electric field direction parallel to the y-axis; the TM wave represents an electromagnetic wave incident in a negative z-axis direction and having an electric field direction parallel to the x-axis. The invention aims to provide the dual-polarized broadband absorption type low-pass frequency selection surface which is applied to a stealth antenna housing of a low frequency band (VHF/UHF) antenna.
The dual-polarized broadband absorption type low-pass frequency selection surface has the following advantages:
(1) the dual-polarized broadband absorption type low-pass frequency selection surface is represented as a wave absorber in a high frequency band, and can better absorb incident electromagnetic waves; in a low frequency band, the optical fiber is almost transparent to electromagnetic waves, and both incident waves and emergent waves can be transmitted with low insertion loss or even without insertion loss. The characteristics can reduce RCS and hardly reduce the gain of the antenna when the antenna housing can be used as a radome of a low frequency (VHF, UHF) antenna.
(2) The dual-polarized broadband absorption type low-pass frequency selection surface adopts the traditional two-dimensional plane stacking, and the wave absorption ring is added on the reflecting surface, so that an extremely wide absorption band is realized at a high frequency.
(3) The dual-polarized broadband absorption type low-pass frequency selection surface is simple to manufacture, the whole structure can be realized by using a common PCB (printed circuit board) process, and the wave-absorbing surface element device only needs to be welded with a resistor, so that the manufacturing is simple and the cost is low.
Drawings
FIG. 1 is a schematic diagram of a three-dimensional cell structure of the present invention;
FIG. 2 is a schematic structural view of a wave-absorbing surface of the present invention;
FIG. 3 is a schematic diagram of the structure of the left surface of the wave absorbing surface with the reflection resistance of the invention;
FIG. 4 is a schematic diagram of the structure of the right surface of the wave absorbing surface with the reflection resistance of the invention;
FIG. 5 is a simulation diagram of the S-parameters of the present invention;
FIG. 6 is a simulation diagram of the wave absorption rate of the present invention.
Detailed Description
The present invention is further analyzed with reference to the following specific examples.
As shown in fig. 1, the dual-polarized broadband absorption-type frequency selective surface is a periodic structural unit which is vertically arranged, and each structural unit is seamlessly arranged and comprises a wave absorption surface and a band-stop reflection wave absorption surface;
as shown in fig. 2, the wave absorbing surface comprises a first Rogers5880 medium substrate 1 with the thickness of 0.508 mm, a first metal ring 3 is plated on the left surface of the medium substrate 1, the metal ring 3 is overlapped with the center of the medium substrate 1, and four radio frequency resistors 2 with the same resistance are welded at the centers of four sides of the metal ring 3.
As shown in fig. 3 and 4, the band-stop reflection wave-absorbing surface comprises a second medium substrate 6 of Rogers5880 with the thickness of 0.508 mm, a second metal ring 4 is plated on the left surface of the medium substrate 6, the metal ring 4 is overlapped with the center of the medium substrate 2, four radio-frequency resistors 5 with the same resistance are welded at the centers of four sides of the metal ring 4, a third metal ring 7 and a fourth metal ring 8 are plated on the right surface of the medium substrate 6, and the metal ring 3, the metal ring 4, the metal ring 7 and the metal ring 8 are overlapped with the center of the medium substrate 6.
As shown in fig. 1, the wave absorption surface and the band-stop reflection wave absorption surface are arranged in parallel, and a straight line where the centers of the wave absorption surface and the band-stop reflection wave absorption surface are located is parallel to a Z axis;
the first dielectric substrate 1 and the second dielectric substrate 4 are both square.
The first metal ring 3, the second metal ring 4, the third metal ring 7 and the fourth metal ring 8 are all closed ring structures.
The specific structural geometric parameters are as follows:
wherein p is the width period of the unit structure in the x-axis direction and the length period in the y-axis direction (i.e. the period lengths of the Rogers5880 first dielectric substrate 1 and the second dielectric substrate 6 in the x-y two-axis directions), d1And w1Length of side and width, d, of the first metal ring 3, respectively2And w2Side length and width, d, of the second metal ring 4, respectively3And w3Length of side and width, d, of third metal ring 7, respectively4And w4Are respectively a fourth metalSide length and width of the ring 8, ddIs the concave depth of the middle part of the fourth metal ring, wdIs the width of the concave portion in the middle of the fourth metal ring, lRIs the length of the radio frequency resistor, R1And R2The resistance values, t, of the radio frequency resistor 1 and the radio frequency resistor 2 respectivelysIs the dielectric thickness, h, of the first dielectric substrate 1 and the second dielectric substrate 6aIs the height of the air path between the wave absorbing surface and the band-stop reflecting surface.
Fig. 5 and 6 are simulation results of the double-layer cascaded dual-polarized broadband band-absorption type low-pass frequency selection surface. The simulation result of fig. 5 shows that the passband of the structure shows a low-pass filtering characteristic, and the insertion loss is lower than 0.5dB in the frequency band with the frequency lower than 0.5 GHz. Meanwhile, an absorption band with the frequency band of 4-11.7 GHz is formed at a high frequency, the absorption band covers a C band and a part of X bands, and the relative bandwidth reaches 91.1%. The simulation result of fig. 6 shows that the low-pass band absorption type frequency selective structure has the wave absorption efficiency of about 90% in the wave absorption band and has excellent wave absorption effect.