Dual-transmission-band tunable absorbing and transmitting integrated frequency selective surface

Abstract

The application provides a dual-transmission-band adjustable absorbing and transmitting integrated frequency selective surface, which comprises periodically arranged frequency selective surface units composed of a lossy layer and a lossless layer, the lossy layer comprises a first resonant structure and a first bias circuit, the lossless layer comprises a second resonant structure and a second bias circuit, the transmission of metal traces in the two bias circuits to different direct currents enables four groups of variable capacitance diodes in the two resonant structures to generate different capacitance values, thereby realizing continuous adjustment of one of the two transmission bands while keeping the other transmission band stable, absorbing electromagnetic wave energy in a specific frequency range, avoiding the defects that the existing technology causes interference to communication electromagnetic waves when other electromagnetic wave frequencies in the external environment are close to the communication electromagnetic wave frequencies due to the fixed two passband frequency bands or the fixed one of the two passband frequency bands, effectively improving the wireless communication quality, and improving the absorption capacity of the two specific electromagnetic frequency bands.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of antenna microwave technology and relates to a frequency selective surface, in particular to a dual-transmission frequency band adjustable absorbing and transmitting integrated frequency selective surface. BACKGROUND

[0002] The dual-band bandpass frequency selective surface is a two-dimensional periodic array with specific bandpass frequency selection characteristics in two different frequency bands, which can realize frequency band separation, interference suppression and other functions, including a dual-band bandpass frequency selective surface, a dual-transmission frequency band absorbing and transmitting integrated frequency selective surface and a single-transmission frequency band adjustable dual-band absorbing and transmitting integrated adjustable frequency selective surface loaded with active devices. The absorbing and transmitting integrated frequency selective surface adds the absorbing function to the dual-band bandpass frequency selective surface, that is, it absorbs electromagnetic wave energy in a specific frequency range instead of completely reflecting or transmitting the electromagnetic wave. The absorbing and transmitting integrated adjustable frequency selective surface loaded with active devices can change the equivalent circuit characteristics of the structural unit by adjusting the parameters of the active devices, such as the values of capacitance or inductance, so as to change the frequency selection range or the center frequency. For example, the patent application with the application number 202410648405 and the name "a single-transmission frequency band adjustable dual-band absorbing and transmitting integrated frequency selective surface" discloses a single-transmission frequency band adjustable dual-band absorbing and transmitting integrated frequency selective surface, which includes a frequency selective surface unit composed of a lossy layer and a lossless layer arranged periodically. The lossy layer includes a first resonant structure and a first bias circuit, and the lossless layer includes a second resonant structure and a second bias circuit. The transmission of the two bias circuits to different direct currents makes the varactor diodes in the two resonant structures produce different capacitance values, thereby realizing continuous adjustment of the low-frequency transmission band while maintaining the stability of the high-frequency transmission band in the dual-frequency transmission band and absorbing electromagnetic wave energy in a specific frequency range. However, as shown in the first resonant structure, a group of varactor diodes 25 are arranged between the first square patch 21 and the first square metal ring 22, and as shown in the second resonant structure, a group of varactor diodes 54 are arranged between the second square patch 52 and the second square metal ring 51, which causes interference to the communication electromagnetic wave when the frequency of the external other electromagnetic wave is close to the frequency of the communication electromagnetic wave in the fixed transmission frequency band, thereby having certain limitations. Figure 1 Figure 2 The same group of varactor diodes 54 are arranged between the second square patch 52 and the second square metal ring 51 of the second resonant structure, which causes interference to the communication electromagnetic wave when the frequency of the external other electromagnetic wave is close to the frequency of the communication electromagnetic wave in the fixed transmission frequency band, thereby having certain limitations. SUMMARY

[0003] The purpose of the present application is to provide a dual-transmission frequency band adjustable absorbing and transmitting integrated frequency selective surface to reduce the interference of the frequency of the external other electromagnetic wave to the two communication electromagnetic waves and improve the quality of wireless communication.

[0004] ​To achieve the above objectives, the technical solution adopted by the present invention includes a frequency selective surface unit composed of multiple lossy and lossless layer structures arranged vertically and without contact. The lossy layer structure includes a first dielectric substrate 1 and a first resonant structure 2 printed on its upper surface; the lossless structure layer includes a second dielectric substrate 4 and a second resonant structure 5 printed on its upper surface; the first resonant structure 2 includes a first square metal ring 22 and a first square patch 21 nested within the ring. A first varactor diode 25 is disposed between the left and right opposite sides of the first square patch 21 and the first square metal ring 22. A first metal strip 24 is connected to each side of the first square metal ring 22, and a resistor 26 is disposed on the metal strip connected to the first varactor diode 25.

[0005] A second metal strip 23 and a third metal strip 27 perpendicularly intersecting the first metal strip 24 are provided on the first metal strip 24 connected to the left and right sides of the first square metal ring 22. A second varactor diode 28 is provided between the two metal strips. The resistor 26 is located between the second metal strip 23 and the first square metal ring 22.

[0006] The second resonant structure 5 includes two first rectangular metal rings 51 and two second rectangular metal rings 52 arranged side by side. Each first rectangular metal ring 51 is provided with a first rectangular patch 53 and a third varactor diode 55 connected to its left and right opposite sides. Each second rectangular metal ring 52 is provided with a second rectangular patch 54 and a fourth varactor diode 56 connected to its left and right opposite sides.

[0007] The first dielectric substrate 1 and the second dielectric substrate 4 are both square in shape, and the two dielectric substrates have the same relative permittivity.

[0008] The second metal strip 23 has a length equal to the side length of the first dielectric substrate 1.

[0009] The length of the third metal strip 27 is less than the length of the second metal strip 23.

[0010] The distance between the third metal strip 27 and the second metal strip 23 is greater than the length of the second varactor diode.

[0011] The frequency selective surface unit, its lossy layer structure further includes a first bias circuit. The first bias circuit includes three first metal traces 3 printed on the lower surface of the first dielectric substrate 1, located at the projection positions of the first metal strips 24 connected to the upper and lower opposite sides of the first square metal ring 22, and outside the projection positions of the two third metal strips 27. The first metal traces 3 at the projection positions of the first metal strips 24 on the upper and lower opposite sides of the square metal ring 22 are connected to the first square patch 21, and the first metal traces 3 located outside the projection positions of the third metal strips 27 are connected to the first metal strips 24 connected to the left and right opposite sides of the first square metal ring 22, respectively, and are connected through metallized vias.

[0012] The frequency selective surface unit further includes a second bias circuit in its lossless layer structure. The second bias circuit includes two second metal traces 6 printed on the lower surface of the second dielectric substrate 1 at the projection positions of the first rectangular patch 53 and the second rectangular patch 54, respectively. The traces 6 are connected to the first rectangular patch 53 and the second rectangular patch 54 through metallized vias.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] 1. In this invention, when only one set of varactor diodes in the lossy and lossless layers receives a different DC voltage while the other set remains at a constant DC voltage, only the transmission frequency band corresponding to the set receiving the changing voltage will be adjusted, while the transmission frequency band corresponding to the other set will remain unaffected. Simultaneously, it absorbs electromagnetic wave energy within a specific frequency range, avoiding the defect in existing technologies where external electromagnetic wave frequencies approaching the fixed transmission frequency band in a dual-transmission band can interfere with communication electromagnetic waves within that fixed transmission frequency band. This invention can respond to environmental changes and adjust the frequency band in real time to adapt to different communication requirements.

[0015] 2. This invention, through two sets of components in the first resonant structure, each containing two metal strips and a varactor diode, and two sets of rectangular metal rings, rectangular patches, and varactor diodes arranged side-by-side in the second resonant structure, optimizes the absorption capability of two specific electromagnetic frequency bands, 3.52-4.68GHz and 7.23-9.38GHz, while achieving tunable characteristics in both transmission bands. This reduces radar wave reflection, effectively lowers the strength of radar interception signals, and consequently reduces the likelihood of communication equipment being detected by radar systems in these two frequency bands. Attached Figure Description

[0016] Figure 1 This is a top view of the first resonant structure in the prior art.

[0017] Figure 2 This is a top view of the existing second resonant structure.

[0018] Figure 3 This is a schematic diagram of the overall structure of the present invention.

[0019] Figure 4 This is a top view of the first resonant structure of the present invention.

[0020] Figure 5 This is a top view of the second resonant structure of the present invention.

[0021] Figure 6 This is a schematic diagram of the adjustable S-parameter characteristics of the S-band of the present invention.

[0022] Figure 7 for Figure 6 The local characteristic diagram.

[0023] Figure 8 This is a schematic diagram of the adjustable S-parameter characteristics of the C-band transmission band of the present invention.

[0024] Figure 9 for Figure 8 The local characteristic diagram. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0026] Reference Figure 3 The present invention includes a plurality of frequency selective surface units composed of lossy layer structures and lossless layer structures arranged in a periodic manner and arranged vertically and not in contact. The lossy layer includes a first dielectric substrate 1 and a first resonant structure 2 printed on its upper surface. The lossless structure layer includes a second dielectric substrate 4 and a second resonant structure 5 printed on its upper surface.

[0027] The lossy layer includes a first dielectric substrate 1 and a first resonant structure 2 printed on its upper surface; the structure of the first dielectric substrate 1 is as follows: Figure 3 As shown, F4B, with its excellent electrical insulation properties, is used as the dielectric substrate. It has a dielectric constant of 2.65, a loss angle of only 0.0013, and a thickness of 0.5 mm. F4B effectively isolates the metal resonant structure from other circuit components, avoiding the risk of short circuits and providing a solid support base for the metal resonant structure. This ensures that the resonant structure can be stably arranged and operated without shifting or deforming due to mechanical stress.

[0028] The structure of the first resonant structure 2 is as follows: Figure 4As shown, the device includes a first square metal ring 22 and a first square patch 21 nested within the ring, with a side length of 5.4 mm. A first varactor diode 25 is disposed between each of the left and right opposite sides of the first square patch 21 and the first square metal ring 22. The first varactor diode 25 is an SMV1405-040LF, and its capacitance value can change uniformly with the supplied voltage. The capacitance value ranges from a minimum capacitance of 0.63 pF when the supplied voltage is 30 V to 0 V. The maximum capacitance is 2.67pF. Its equivalent circuit consists of a resistor with a resistance of approximately 0.8Ω, an inductor with an inductance of 0.7nH, and a variable capacitor connected in series. The outer side length of the first square metal ring 22 is 10mm, and the inner side length is 8.6mm. Each side of the first square metal ring 22 is connected to a metal strip 24, which is 1mm wide and 12mm long. A resistor 26 with a resistance of 200Ω is also provided on the first metal strip, and the first resonant junction is embedded therein. The resistor 26 in the structure converts the current at the resonance point into heat energy, thereby absorbing electromagnetic waves. A second metal strip 23 and a third metal strip 27 are arranged intersecting the left and right sides of the first metal strip, with a 1.9mm gap between the second metal strip 23 and the third metal strip 27. The gap between the second metal strip and the third metal strip generates an equivalent capacitance. The length of the gap affects the capacitance value of the equivalent capacitance, thus generating another wave-transparent band under the condition that there is already a wave-transparent band. The length of the second metal strip 23 must be equal to the period length of the unit array to be used as the grounded cathode for power supply of the varactor diode. A second varactor diode 28 is set on the first metal strip between the second metal strip 23 and the third metal strip 27. This second varactor diode 28 adopts MA46H120, and its capacitance value can change uniformly with the supply voltage. The capacitance value changes from a minimum capacitance value of 0.1pF when the supply voltage is 16V to a maximum capacitance value of 1.1pF when the supply voltage is 0V.

[0029] The damaged layer structure also includes a first bias circuit composed of a first metal trace printed on the lower surface of the first dielectric substrate 1, a second metal trace, and metallized vias of the metal traces; the metallized vias have a height of 0.5 mm and a radius of 0.2 mm. The first and second metal traces are made of copper and serve as conductors for current transmission, allowing the positive voltage of the external power supply to pass through the metallized vias to the first square patch 21. The voltage transmitted by the first metal trace is used to control the capacitance value of the varactor diode 28, and the voltage transmitted by the second metal trace is used to control the capacitance value of the varactor diode 28. The cathode corresponding to the first metal trace is a vertical first metal strip 24, and the cathode corresponding to the second metal trace is a vertical second metal strip 23, ensuring that the first and second metal traces are in parallel and do not affect each other's voltage values.

[0030] The lossless layer includes a second dielectric substrate 4 and a second resonant structure 5 printed on its upper surface; the structure of the second dielectric substrate 4 is as follows: Figure 3 As shown, both the first dielectric substrate and the first dielectric substrate are F4B dielectric boards with a dielectric constant of 2.65, a loss angle of 0.0013, and a thickness of 0.5 mm.

[0031] The second resonant structure 5 includes two sets of 2×2 first rectangular metal rings 51 and second rectangular metal rings 52. Each set of metal rings contains a first rectangular patch 53 and a second rectangular patch 54. The outer ring of the first rectangular metal ring has a side length of 12mm, the inner ring width is 3mm, and the length is 11.5mm. The first rectangular patch is 5mm long and 2.18mm wide. The outer ring of the second rectangular metal ring has a side length of 12mm, the inner ring width is 5.2mm, and the length is 11.5mm. The second rectangular metal ring is 5mm long and 3.6mm wide. A third varactor diode 55 is positioned between the left and right opposite sides of the first rectangular patch 53 and the first rectangular metal ring 51. This varactor diode 55, like the first varactor diode 55, is an SMV1405-040LF. A fourth varactor diode 56 is disposed between the left and right opposite sides of the square patch 54 and the second rectangular metal ring 52. Like the second varactor diode 28, it is an MA46H120. The two sets of 2×2 first rectangular metal rings 51 and second rectangular metal rings 52 each contain a first rectangular patch 53 and a second rectangular patch 54. Each set of four metal rings and four square patches is symmetrical vertically and horizontally, and the outer side length of each set of metal rings is half that of the periodic array. The lossless layer structure also includes a second bias circuit composed of a third metal trace, a fourth metal trace, and metallized vias of the metal traces printed on the lower surface of the second dielectric substrate 1. The third and fourth metal traces are made of copper and serve as conductors for current transmission.

[0032] The third metal trace transmits the positive voltage of the external power supply to the first rectangular patch 53 through a metallized via, and the fourth metal trace transmits the positive voltage of the external power supply to the second rectangular patch 54 through a metallized via. The voltage transmitted by the third metal trace is used to control the capacitance value of the third varactor diode 55, and the voltage transmitted by the fourth metal trace is used to control the capacitance value of the fourth varactor diode 56. The cathode corresponding to the third metal trace is the first rectangular patch 53, and the cathode corresponding to the fourth metal trace is the vertically oriented second rectangular patch 54, ensuring that the third and fourth metal traces are in parallel and do not affect each other's voltage values.

[0033] The working principle of this invention is as follows: This invention relates to a frequency selective surface unit, which includes multiple periodically arranged lossy layer structures and lossless layer structures. The lossy layer consists of a first resonant structure and a first bias circuit arranged vertically and not in contact, while the lossless layer consists of a second resonant structure and a second bias circuit. When the frequency selective surface unit is irradiated by electromagnetic waves in both the S-band and C-band, and the S-band communication electromagnetic waves are interfered with by electromagnetic waves of similar frequency, the transmission of different DC voltages through the first and third metal traces in the two bias circuits causes the first and third varactor diodes in the two resonant structures to generate different capacitance values. This allows for continuous adjustment of the low-frequency transmission band while maintaining stability in the high-frequency transmission band. Similarly, when the C-band communication electromagnetic waves are interfered with by electromagnetic waves of similar frequency, the transmission of different DC voltages through the second and fourth metal traces in the two bias circuits causes the second and fourth varactor diodes in the two resonant structures to generate different capacitance values. This also allows for continuous adjustment of the high-frequency transmission band while maintaining stability in the low-frequency transmission band. This design avoids the defects of existing technologies where interference occurs when the frequencies of other external electromagnetic waves are close to the communication electromagnetic wave frequencies due to the fixed two or one passband frequency bands. Furthermore, it can absorb electromagnetic wave energy within a specific frequency range, achieving electromagnetic stealth and thus effectively improving the quality of wireless communication.

[0034] The technical effects of the present invention will be explained below with reference to simulation experiments:

[0035] 1. Simulation content:

[0036] By establishing the Floquet port excitation and master-slave boundary in the simulation software ANSYS Electronics Desktop v.19.2, the S-parameter characteristics of the two transmission bands of this invention were simulated respectively, and the results are as follows. Figures 6 to 9 As shown.

[0037] 2. Simulation Result Analysis:

[0038] Reference Figure 6 and Figure 7When the capacitance value c1 of the first varactor diode 25 in the lossy layer changes to 0.7pF according to the supply voltage, and the capacitance value c2 of the third varactor diode 55 in the lossless layer changes to 0.7pF, the frequency selection surface shows that the transmission band frequencies with a transmission coefficient above -2dB are approximately 2.84-2.94GHz and 5.73-6.08GHz, while the absorption band frequencies with an absorption coefficient below -10dB are approximately 3.50-4.71GHz and 7.23-9.38GHz. When the capacitance value c1 of the first varactor diode 25 in the lossy layer changes to 0.78pF according to the supply voltage, and the capacitance value c2 of the third varactor diode 55 in the lossless layer changes to 0.78pF, the frequency selection surface shows that the transmission band frequencies with a transmission coefficient above -2dB are approximately 2.72-2.80GHz and 5.73-6.08GHz, while the absorption band frequencies with an absorption coefficient below -10dB are approximately 3.50-4.71GHz and 7.23-9.38GHz. When the capacitance value c1 of the first varactor diode 25 in the lossy layer changes to 0.84pF according to the supply voltage, and the capacitance value c2 of the third varactor diode 55 in the lossless layer changes to 0.86pF, the frequency selection surface shows that the transmission band frequencies with a transmission coefficient above -2dB are approximately 2.63-2.69GHz and 5.73-6.08GHz, while the absorption band frequencies with an absorption coefficient below -10dB are approximately 3.50-4.71GHz and 7.23-9.38GHz. When the capacitance value c1 of the first varactor diode 25 in the lossy layer changes to 0.94pF according to the supply voltage, and the capacitance value c2 of the third varactor diode 55 in the lossless layer changes to 0.96pF, the frequency selection surface shows that the transmission band frequencies with a transmission coefficient above -2dB are approximately 2.51-2.54GHz and 5.73-6.08GHz, while the absorption band frequencies with an absorption coefficient below -10dB are approximately 3.50-4.71GHz and 7.23-9.38GHz.

[0039] Reference Figure 8 and Figure 9When the capacitance value c1 of the second varactor diode 28 in the lossy layer changes to 0.8pF according to the supply voltage, and the capacitance value c2 of the fourth varactor diode 56 in the lossless layer changes to 0.2pF, the frequency selectivity surface shows that the transmission band frequencies with a transmission coefficient above -2dB are approximately 2.84-2.93GHz and 5.71-6.13GHz, while the absorption band frequencies with an absorption coefficient below -10dB are approximately 3.50-4.43GHz and 7.23-9.38GHz. When the capacitance value c1 of the second varactor diode 28 in the lossy layer changes to 0.5pF according to the supply voltage, and the capacitance value c2 of the fourth varactor diode 56 in the lossless layer changes to 0.17pF, the frequency selectivity surface shows that the transmission coefficient is above -2dB. The transmission band frequencies are approximately 2.84-2.93 GHz and 5.47-5.93 GHz, while the absorption bands with absorption coefficients below -10 dB are 3.50-4.43 GHz and 7.23-9.38 GHz. When the capacitance value c1 of the second varactor diode 28 in the lossy layer changes to 1.15 pF according to the supply voltage, and the capacitance value c2 of the fourth varactor diode 56 in the lossless layer changes to 0.25 pF, the frequency selection surface shows that the transmission band frequencies with transmission coefficients above -2 dB are approximately 2.84-2.93 GHz and 5.25-5.65 GHz, while the absorption bands with absorption coefficients below -10 dB are 3.50-4.23 GHz and 7.23-9.38 GHz.

[0040] Reference Figures 6 to 9 This frequency selective surface features multiple adjustable transmission bands with transmission coefficients above -2dB. The center frequency of its low-frequency transmission band can be continuously adjusted by changing the capacitance of the varactor diode, covering the following frequency bands: 2.63 GHz to 2.69 GHz, 2.72 GHz to 2.80 GHz, 2.72 GHz to 2.80 GHz, and 2.84 GHz to 2.94 GHz. Since the capacitance of the varactor diode changes linearly and continuously, the center frequency of the low-frequency transmission band of this frequency selective surface can be continuously adjusted within the range of 2.63 GHz to 2.94 GHz. Similarly, the center frequency of its high-frequency transmission band can also be continuously adjusted by changing the capacitance of the varactor diode, covering the following frequency bands: 5.71 to 6.13 GHz, 5.47 to 5.93 GHz, and 5.25-5.65 GHz. The center frequency of the high-frequency transmission band can be continuously adjusted within the range of 5.25 GHz to 6.13 GHz. By changing the capacitance value of the varactor diode, the frequency of the low-frequency transmission band can be continuously adjusted between 2.63 GHz to 2.94 GHz and the frequency of the high-frequency transmission band between 5.25 GHz to 6.13 GHz. The transmission coefficient of both the high-frequency and low-frequency transmission bands is always kept above -2dB, ensuring good transmission performance.

[0041] from Figure 6 and Figure 8 It can be seen that while maintaining the continuous adjustability of the low-frequency and high-frequency transmission bands, the frequency selective surface also has the ability to absorb electromagnetic waves in the range of 3.52-4.68GHz and 7.23-9.38GHz.

Claims

1. A dual-transmissive-band independently adjustable frequency selective surface, comprising a plurality of frequency selective surface units composed of lossy and lossless layer structures arranged vertically and not in contact, wherein the lossy layer structure comprises a first dielectric substrate (1) and a first resonant structure (2) printed on its upper surface; the lossless layer structure comprises a second dielectric substrate (4) and a second resonant structure (5) printed on its upper surface; the first resonant structure (2) comprises a first square metal ring (22) and a first square patch (21) nested within the ring, wherein a first varactor diode (25) is disposed between the left and right opposite sides of the first square patch (21) and the first square metal ring (22), and a first metal strip (24) is connected to each side of the first square metal ring (22), and a resistor (26) is disposed on the metal strip connected to the first varactor diode (25); characterized in that: A second metal strip (23) and a third metal strip (27) perpendicularly intersecting the first metal strip (24) connected to the left and right sides of the first square metal ring (22) are provided on the first metal strip (24). A second varactor diode (28) is provided between the two metal strips. The resistor (26) is located between the second metal strip (23) and the first square metal ring (22). The second resonant structure (5) includes two × two first rectangular metal rings (51) and two × two second rectangular metal rings (52) arranged side by side. Each first rectangular metal ring (51) contains a first rectangular patch (53) and a third varactor diode (55) connected to its left and right opposite sides. Each second rectangular metal ring (52) contains a second rectangular patch (54) and a fourth varactor diode (56) connected to its left and right opposite sides.

2. The frequency selective surface according to claim 1, characterized in that, The first dielectric substrate (1) and the second dielectric substrate (4) are both square in shape, and the two dielectric substrates have the same relative permittivity.

3. The frequency selective surface according to claim 1, characterized in that, The second metal strip (23) has a length equal to the side length of the first dielectric substrate (1).

4. The frequency selective surface according to claim 3, characterized in that, The length of the third metal strip (27) is less than that of the second metal strip (23).

5. The frequency selective surface according to claim 4, characterized in that, The distance between the third metal strip (27) and the second metal strip (23) is greater than the length of the second varactor diode.

6. The frequency selective surface according to claim 1, characterized in that, The frequency selective surface unit, its lossy layer structure further includes a first bias circuit. The first bias circuit includes three first metal traces (3) printed on the lower surface of the first dielectric substrate (1) at the projection positions of the first metal strips (24) connected to the upper and lower opposite sides of the first square metal ring (22) and outside the projection positions of the two third metal strips (27). The first metal traces (3) at the projection positions of the first metal strips (24) on the upper and lower opposite sides of the square metal ring (22) are connected to the first square patch (21), and the first metal traces (3) located outside the projection positions of the third metal strips (27) are connected to the first metal strips (24) connected to the left and right opposite sides of the first square metal ring (22) are connected through metallized vias.

7. The frequency selective surface according to claim 1, characterized in that, The frequency selective surface unit further includes a second bias circuit in its lossless layer structure. The second bias circuit includes two second metal traces (6) printed on the lower surface of the second dielectric substrate (4) at the projection positions of the first rectangular patch (53) and the second rectangular patch (54), respectively. The traces are connected to the first rectangular patch (53) and the second rectangular patch (54) through metallized vias.

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