CN100433448C - Super thin one side steep filter property frequency selecting surface - Google Patents

Abstract

The ultra-thin unilateral steep drop filter characteristic frequency selective surface can be used as a frequency band multiplexer for multi-frequency antennas in communication systems such as satellites and radars. This structure is formed by laminating two layers of microwave plates with three layers of metal surfaces and two layers of dielectric. Layers are fabricated on multilayer substrates. Among them, the metal surface (1) on the upper and lower surfaces is engraved with periodic generous annular gaps (3) of the same size, and another size that coincides with the center position of the annular gap above the upper and lower surfaces is engraved on the middle metal surface (2) Periodic small square ring-shaped gaps (4), the middle of the three-layer metal surface is filled with two layers of medium (5), on the laminated multi-layer substrate around each periodic square ring gap unit is set at a uniform interval A series of metallized through holes (6) form a substrate-integrated waveguide cavity equivalent to a conventional metal cavity. The selection characteristic of the single sideband of the selective surface is greatly improved, its thickness is only one-sixth of the traditional cascaded structure, and it has stable passband and selection characteristics for the change of the angle and polarity of the incident wave.

Description

Ultra-thin unilateral steep-descent filter characteristic frequency selective surface

technical field

The invention is an ultra-thin frequency selective surface with unilateral steep drop filter characteristics based on substrate integrated waveguide cavity cascading, which can be used as a frequency band multiplexer and applied to multi-frequency antennas of communication systems such as satellites and radars, belonging to microwave technology field.

Background technique

Frequency selective surfaces (FSS) are widely used in engineering applications. FSS has good selectivity for the transmission and reflection of electromagnetic waves. It has all-pass characteristics for electromagnetic waves in its passband, and total reflection characteristics for electromagnetic waves in its stopband. It has a spatial filtering function. In the microwave field, FSS can be used in the frequency band multiplexer of the communication satellite system, and the communication capacity can be expanded by using multi-feed configuration. Another main use is to make radomes for shielding and stealth of radar antennas in aerospace. High performance waveguide filters can also be fabricated as monolithically integrated inserts. The main performance of FSS is the frequency selection characteristic, the sensitivity to the incident direction and polarization of the excitation source, and the stability of the bandwidth. Traditional FSSs formed by periodic patch or slit arrays are poor in selectivity. In order to improve the frequency selection characteristics of FSS, the most common method in the world is to cascade multi-screen FSS to obtain better selection characteristics, but most of them are Chebyshev response characteristics, and the selection characteristics are not high enough. At the same time, a dielectric layer used as an impedance transformer is filled between the cascaded multi-layer FSS. The thickness of the dielectric layer is about a quarter of the wavelength corresponding to the center frequency of the working frequency band, which makes the thickness of the entire FSS structure very large, which limits It is used in many practical applications.

Contents of the invention

Technical problem: The purpose of the present invention is to provide a frequency selective surface with ultra-thin unilateral steep drop filter characteristics based on the cascaded formation of substrate integrated waveguide cavities. This frequency selective surface has good performance stability in the working frequency band and has a large thickness. Reduced, easy to process, simple in structure and low in cost. Compared with the existing multi-layer cascaded frequency selective surface, the frequency selective surface has better performance stability and greatly reduced volume.

Technical solution: The ultra-thin unilateral steep drop filter characteristic frequency selective surface of the present invention is manufactured by laminating two layers of microwave plates. The substrate includes metal surfaces on the upper and lower surfaces and a metal surface in the middle layer. Between the three layers of metal surfaces Filled with upper and lower dielectric layers; at the same time, open a large square annular slot of the same size on the metal surface of the upper and lower surfaces, and engrave a small square of another size on the middle metal surface whose center position coincides with the square annular slot on the upper and lower surfaces. Ring-shaped slots; finally, on the laminated substrate, a series of metallized through-holes are arranged at uniform intervals around each periodic generous ring-shaped slot unit, forming a substrate-integrated waveguide equivalent to a traditional metal cavity cavity.

The selection surface is used to couple the plane wave to the cavity, and the large square ring-shaped slot groove etched on the upper and lower metal surfaces is a "□"-shaped slot that is completely symmetrical about the length and width directions; it is used to couple the electromagnetic wave in a cavity The small square ring-shaped slot etched on the metal surface of the middle layer to another cavity is a "□"-shaped slot that is completely symmetrical about the two directions of length and width.

When the center frequency of the selected surface is 30GHz in the Ka frequency band, the side length of the large square annular slot on the upper and lower metal surfaces is 2.52 mm, and the width is 0.21 mm. The side length of the small square annular slot on the metal surface of the middle layer is 1.35 mm, and the width is 0.13 mm; the dielectric substrate used is Rogers5880 material with a dielectric constant of 2.2, and its thickness is 0.254 mm.

The diameter of the metallized through hole is 0.4 mm, the center-to-center distance of two adjacent metallized through-holes between the metallized through-hole arrays is 0.6 mm, and the ratio of the metallized through-hole diameter to the hole-center distance is greater than 0.5.

This frequency selective surface combines the transmission properties and field distribution of conventional periodic structures and common cavity structures. During operation, the periodic gap on the surface couples the plane wave within a certain frequency range into the cavity, and then couples the energy of the double-mode resonance in the cavity to the next cavity through the coupling gap in the middle. The secondary filtering function couples waves of a narrower frequency range out through the slot on the other side, thereby completing the highly selective transmission of spatial plane waves.

The working principle is: after the plane wave is incident on the frequency selective surface, the periodic square ring gap couples the plane wave of the working frequency band into the cavity, and then through the coupling of two different modes in the cavity and the coupling between the cavities, through another Slits on one side of the surface couple electromagnetic waves into space. The spatial plane wave passes through the upper and lower surface gaps and the selective transmission of the two middle cavities, and finally achieves a filtering effect with unilateral steep drop filtering characteristics.

Beneficial effects: The ultra-thin new frequency selective surface based on the unilateral steep drop filter characteristic formed by the substrate integrated waveguide technology has the following advantages:

a Compared with the previous multi-screen cascaded frequency selective surface, this new type of frequency selective surface has greatly improved the selection characteristics of SSB, and its volume is greatly reduced. one-sixth.

b This new type of frequency selective surface has stable performance, low insertion loss and high selectivity in the working frequency band. Moreover, its high selectivity and bandwidth stability do not change with the incident angle and polarization state of the incident wave.

c This new type of frequency selective surface structure is simple, and the entire structure can be realized on a common dielectric substrate covered with metal on the upper and lower surfaces. In the design process, it is only necessary to adjust the shape and size of the square ring gap and the periodic size of the metal through hole to obtain the required performance. Few structural parameters greatly save the time for design optimization.

d This new type of frequency selective surface is simple and convenient to manufacture, and can be realized with ordinary laminated PCB technology, and the cost is low.

Description of drawings

Fig. 1 is a structural top view of a schematic partial unit of the present invention. P is the period length and width of a periodic unit, C is the length and width of the substrate integrated waveguide cavity formed by metallized through holes in a periodic unit, L is the side length of the square ring gap on the upper and lower metal surfaces, L _m is the side length of the coupling square ring gap on the middle metal layer, W is the width of the square ring gap on the upper and lower metal surfaces, W _m is the width of the coupling square ring gap on the middle metal layer, d is the diameter of the through hole, d _p is the center-to-center distance between two adjacent through holes, h is the thickness of the dielectric layer, and mh is the thickness of the metal layer.

Fig. 2 is a structural side view of a schematic partial unit of the present invention.

Figure 3 is a perspective view of a schematic partial unit of the present invention. In the figure, there are: upper and lower metal surfaces 1 , metal surface 2 of the middle layer, large square annular slot 3 , small square annular slot 4 , intermediate dielectric layer 5 , and metallized through hole 6 .

Fig. 4 is a schematic diagram of the overall structure of the present invention applied to the Ka band.

Fig. 5 is a comparison between the present invention and the frequency selective surface based on the substrate integrated waveguide single cavity when the plane wave is vertically incident.

Fig. 6 is a comparison between the results of the present invention and the common multi-screen cascaded Chebyshev response frequency selective surface when the plane wave is vertically incident.

Detailed ways

The ultra-thin new frequency selective surface based on the unilateral steep drop filter characteristics of the substrate integrated waveguide technology firstly introduces the high quality factor resonance of the cavity to improve the frequency selective characteristics of the FSS, and enhance its invariance to the incident angle and polarization of the excitation source Sensitivity and bandwidth stability in various environments, and secondly use the traditional cascaded cavity filter theory to design multilayer substrate integrated waveguide cavity cascaded FSS. In terms of structure, the ultra-thin single-side steep drop filter characteristic frequency selective surface is made of two layers of microwave boards laminated by multi-layer printed circuit board technology. Its upper and lower surfaces and the middle layer are metal surfaces, and the middle of the three layers of metal is composed of dielectric filling. On the upper and lower metal surfaces, there are periodic square annular gap units with the same position, size and period length, and the middle layer metal surface is engraved with periodic square annular gap units with different sizes from the upper and lower metal surface gaps, but the center positions coincide and the period length is the same. Ring gap unit. On the multi-layer substrate made of three-layer metal surface and two-layer dielectric lamination, a series of metallized through-holes are arranged around each square ring-shaped gap unit at uniform intervals, forming an upper and lower structure equivalent to a traditional metal cavity. Cascaded substrate-integrated waveguide cavities. The square ring-shaped slits etched on the upper and lower metal surfaces are "□"-shaped slits that are completely symmetrical about the two directions of length and width. When the central frequency of the Ka frequency band is 30GHz, the side length of the upper and lower surface square annular slots is 2.52 mm, and the width is 0.21 mm. The side length of the square annular slot in the middle layer is 1.35 mm, and the width is 0.13 mm. The board is Rogers5880 material with a dielectric constant of 2.2, the thickness of the dielectric layer is 0.254 mm, and the thickness of the metal layer is 0.018 mm. The diameter of the metallized through hole is 0.4 mm, the center-to-center distance of two adjacent metallized through-holes between the metallized through-hole arrays is 0.6 mm, and the ratio of the metallized through-hole diameter to the hole-center distance is greater than 0.5.

The manufacturing process of the present invention is as follows: at first select two dielectric substrates, open square ring-shaped slit grooves whose dimensions correspond to the outer surface and the middle layer respectively on the upper and lower two metal surfaces of one of the substrates, The opening size of the metal surface on one side corresponds to the square ring-shaped slot on the outer surface, and the metal surface on the other side is completely erased. Then stack the side of the first substrate with a square annular slit groove corresponding to the size of the middle layer and the side of the second substrate without the metal layer for lamination. Finally, on the laminated substrate, a series of metallized through-holes are drilled at uniform intervals around each periodic square-ring slot unit to form a substrate-integrated waveguide cavity equivalent to a traditional metal cavity. Choose an appropriate hole diameter and hole spacing to avoid energy leakage between cavities. This frequency selective surface combines the transmission properties and field distribution of conventional periodic structures and common cavity structures. Since the thickness of the single-layer substrate is much smaller than the broadside of the cavity formed by the substrate-integrated waveguide, it has little effect on the resonance of the cavity, so choosing an ultra-thin substrate can greatly reduce the thickness of the entire frequency selective surface. Selecting an appropriate size of the coupling square ring gap in the middle layer can adjust the coupling amount of the upper and lower cavities, thereby forming a frequency selective surface with unilateral steep drop filter characteristics. The entire frequency selective surface is completely realized by ordinary PCB technology. The cavity structure is realized by a metallized through-hole array, which is simple to manufacture and low in cost.

We have realized the ultra-thin frequency-selective surface based on the substrate integrated waveguide technology introduced above in the Ka-band with unilateral transmission zero, the relative permittivity ε _r of the dielectric substrate and the structural geometric parameters (see Figures 1, 2, and 3 )as follows:

Claims (3)

1. A kind of ultra-thin unilateral steep filter characteristic frequency selective surface, it is characterized in that it is made by laminating with two layers of microwave plates, and multilayer substrate comprises the metal face (1) of upper and lower surface and the middle layer metal face (2) ), two upper and lower dielectric layers (5) are filled between the three layers of metal surfaces; periodical generous ring-shaped slots with exactly the same position, size and period length are engraved on the metal surface (1) of the upper and lower metal surfaces (3), the metal surface (2) of the middle layer is engraved with periodic small square ring-shaped gap grooves (4) that are different in size from the upper and lower metal surface gaps but coincide with the center position and have the same period length; finally, the laminated multi-layer A series of metallized through-holes (6) are arranged at uniform intervals around each periodical generous annular slot (3) unit on the substrate to form a substrate-integrated waveguide cavity equivalent to a traditional metal cavity; this option The surface is used to couple the plane wave to the cavity, and the generous ring-shaped slot (3) etched on the upper and lower metal surfaces (1) is a "□"-shaped slot that is completely symmetrical about the two directions of length and width; The electromagnetic wave is coupled to another cavity, and the small square ring-shaped slot (4) etched on the metal surface (2) of the middle layer is a "□"-shaped slot that is completely symmetrical about the two directions of length and width. 2. The ultra-thin unilateral steep drop filter characteristic frequency selection surface according to claim 1, characterized in that the selection surface is a generous annular slot (3) on the upper and lower metal surfaces (1) when the central frequency of the Ka frequency band is 30GHz The side length is 2.52 millimeters, and the width is 0.21 millimeters, and the side length of the small square annular slot (4) on the metal surface (2) of the middle layer is 1.35 millimeters, and the width is 0.13 millimeters; the dielectric substrate used is a dielectric constant of 2.2 Rogers5880 material, its thickness is 0.254 mm. 3. The ultra-thin unilateral steep drop filter characteristic frequency selective surface according to claim 1, characterized in that the diameter of the metallized through hole (6) is 0.4 mm, two adjacent metallized through holes (6) arrays The center-to-center distance of the metallized through-hole (6) is 0.6 mm, and the ratio of the diameter of the metallized through-hole (6) to the center-to-hole distance is greater than 0.5.

Images