A compact ultra-wideband artificial surface plasmon polariton circulator

Abstract

The application discloses a compact ultra-wideband artificial surface plasmon circulator, comprising first to third power dividers with the same structure and first to third SSPP waveguides with the same structure, wherein the first and second output ports of the first power divider are connected with the first end of the first SSPP waveguide and the second end of the third SSPP waveguide respectively, the first and second output ports of the second power divider are connected with the first end of the second SSPP waveguide and the second end of the first SSPP waveguide respectively, and the first and second output ports of the third power divider are connected with the first end of the third SSPP waveguide and the second end of the second SSPP waveguide respectively; the output ports of each power divider are loaded with first and second patch resistors, each SSPP waveguide is loaded with a low-noise amplifier, and the adjacent included angles of the three low-noise amplifiers are all 120 degrees. The application realizes wideband operation, thin structure, good isolation and planar integration capability without ferrite and an external magnetic field.

Description

Technical Field

[0001] This invention belongs to the field of microwave and millimeter-wave radio frequency device technology, and specifically relates to a compact ultrawideband artificial surface plasmon polariton (SSPP) circulator. Background Technology

[0002] A circulator is a three-port microwave device used to transmit non-reciprocal signals, and it is widely used in systems such as radar, base stations, and transceiver front-ends. Traditional ferrite circulators utilize the gyromagnetic effect under an applied magnetic field to achieve unidirectional transmission, offering advantages such as high isolation and low insertion loss. However, they have the following inherent drawbacks:

[0003] (1) It requires ferrite materials and permanent magnets, which are large in size and heavy in weight, making them difficult to integrate;

[0004] (2) Incompatible with standard semiconductor processes, making it impossible to implement a system-on-a-chip;

[0005] (3) The operating bandwidth is relatively narrow, usually narrowband or limited octave.

[0006] To overcome the aforementioned problems, researchers have proposed magnetization-free schemes such as active quasi-circuits, time-modulated circuits, and nonlinear circuits. However, these schemes suffer from problems such as poor noise figure, high power consumption, poor linearity, complex control circuits, or power sensitivity. On the other hand, SSPP waveguides have advantages such as subwavelength field confinement, low crosstalk, and tunable dispersion, but existing SSPP-based circuits still rely on ferrites to achieve non-reciprocity, failing to fully utilize the integrated advantages of SSPP. Summary of the Invention

[0007] The purpose of this invention is to provide a compact, ultrawideband artificial surface plasmon circulator that does not require ferrite or an external magnetic field, while achieving broadband operation, a thin structure, good isolation, and planar integration capability.

[0008] To achieve the above objectives, the solution of the present invention is:

[0009] A compact ultrawideband artificial surface plasmon circulator includes first to third power dividers and first to third SSPP waveguides with identical structures. The first and second output ports of the first power divider are respectively connected to the first end of the first SSPP waveguide and the second end of the third SSPP waveguide. The first and second output ports of the second power divider are respectively connected to the first end of the second SSPP waveguide and the second end of the first SSPP waveguide. The first and second output ports of the third power divider are respectively connected to the first end of the third SSPP waveguide and the second end of the second SSPP waveguide.

[0010] Each of the power dividers has a first patch resistor and a second patch resistor loaded at its output port, and each of the SSPP waveguides has a low-noise amplifier loaded thereon, with the angle between adjacent low-noise amplifiers being 120 degrees.

[0011] Each of the SSPP waveguides adopts a blade-shaped metal structure with periodically arranged metal grooves formed on its outer side.

[0012] In the SSPP waveguide, the dispersion characteristics and cutoff frequency are controlled by adjusting the groove depth, width, and / or period parameters.

[0013] Each of the power dividers is a Wilkinson power divider, with its input ports connected to the two input terminals of the first impedance transformation stub, the two output terminals of the first impedance transformation stub connected to the two input terminals of the second impedance transformation stub, and the two output terminals of the second impedance transformation stub connected to the first and second output ports, which extend in different directions and are respectively connected to the ports of the corresponding SSPP waveguides; the two output terminals of the first and second impedance transformation stubs are respectively connected to first and second patch resistors with different resistance values.

[0014] The first to third SSPP waveguides are all printed with pads for soldering low-noise amplifiers. The input and output ports of the low-noise amplifiers are connected to the corresponding SSPP waveguides by gold wire bonding.

[0015] Among them, each of the power dividers is a Wilkinson power divider.

[0016] The operating frequency band of each SSPP waveguide covers 2-20GHz, with a small signal gain ≥11.6dB. Its bias circuit is powered uniformly through jumpers or copper wires printed on the edge of the dielectric substrate.

[0017] The circulator is fabricated on an FR4 dielectric substrate with a thickness of 0.787 mm and a relative permittivity ε. r =2.2, the top layer is a copper metal graphic.

[0018] By adopting the above scheme, this invention provides a magnetless ultrawideband circulator that utilizes the unidirectional amplification characteristics of a low-noise amplifier (LNA) to achieve non-reciprocal transmission. It requires no ferrite materials or external bias magnetic field, has a thickness of only 1.787 mm, and is suitable for planar integration. Actual measurements show that this circulator operates with a bandwidth of 5-13 GHz (approximately 88% of the relative bandwidth), classifying it as an ultrawideband device. It exhibits isolation >10 dB, return loss >10 dB, and insertion loss of approximately 2 dB. Furthermore, it can be further extended to higher frequency bands using the dispersion modulation capabilities of SSPP waveguides. This invention combines the advantages of ultrawideband, low profile, magnetization-free operation, and easy planar integration, providing a compact and wideband solution for modern radio frequency systems. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of the circulator of the present invention;

[0020] Figure 2 This is a magnified view of a portion of the circulator's structure;

[0021] (a) is a schematic diagram of the waveguide unit structure, and (b) is a schematic diagram of the output branch of the power divider.

[0022] Figure 3 This is a schematic diagram of the transmission performance of the power divider and SSPP waveguide;

[0023] Figure 4 This is an experimental schematic diagram of the circulator of the present invention. Detailed Implementation

[0024] This invention provides a compact ultrawideband artificial surface plasmon circulator, comprising three power dividers and three SSPP waveguides. Each power divider achieves equal power distribution within the 0-20 GHz range, and each SSPP waveguide is loaded with a low-noise amplifier (LNA). The three power dividers and three SSPP waveguides are alternately connected to form a closed loop. The power dividers split the input signal into two equal paths. The clockwise signal is amplified by the LNA and then transmitted; the counterclockwise signal is blocked by the reverse isolation characteristic of the LNA, thereby achieving clockwise unidirectional transmission. Through microwave network analysis, the overall S-parameter matrix approximates that of an ideal circulator.

[0025] The SSPP waveguide employs a blade-shaped metal structure, with its unit structure comprising periodically arranged metal grooves. Dispersion characteristics and cutoff frequency are controlled by adjusting the groove depth, width, and period parameters. Increasing the groove depth (h) increases the equivalent inductance, thereby enhancing the confinement of electromagnetic waves, resulting in a lower cutoff frequency, enhanced diffuse wave characteristics, and a steeper dispersion curve. Increasing the period (s+d) makes the delay effect of the structure on the wave within a unit period more pronounced, also lowering the cutoff frequency and enhancing diffuse wave characteristics. Increasing the period duty cycle (s / (s+d)) can extend the operating frequency range and mitigate the dispersion curve's tendency at higher frequencies. Increasing the width of the lower microstrip line (w) increases the capacitance to ground, enhancing surface wave confinement, lowering the cutoff frequency of the dispersion curve, enhancing diffuse wave characteristics, and making the curve steeper near the cutoff frequency.

[0026] The power divider is a Wilkinson power divider, whose output branch adopts a T-type open circuit structure to support SSPP mode transmission, and different surface mount resistors are loaded at the two output ports to achieve output balance.

[0027] The LNA operates in the 2-20GHz frequency band and has a small signal gain of ≥11.6dB. Its bias circuit is powered by jumpers or copper wires printed on the edge of the dielectric substrate.

[0028] The circulator's overall structure is fabricated on a 0.787mm thick FR4 dielectric substrate with a relative permittivity εr=2.2. The top layer is a copper metal pattern, requiring no ferrite materials or permanent magnets. The circulator operates in the 5-13GHz frequency band, with a return loss >10dB, isolation >10dB, and clockwise insertion loss ≤2dB within this band.

[0029] With the above structure, the overall thickness of the circulator is 1.787 mm, achieving a thin and compact structure.

[0030] The technical solution and beneficial effects of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] Example 1: Design of a compact ultrawideband artificial surface plasmon circulator

[0032] This embodiment fabricated a three-port circulator prototype. The dielectric substrate is FR4, 0.787 mm thick, with εr = 2.2. The top copper layer is... Figure 1 Structural etching: Three Wilkinson power dividers (e.g.) Figure 2 (b) As shown, the signal is input from the right port and outputs in the upper left and lower left directions after passing through two impedance matching stubs. Following the design method of a dual-stub power divider, the characteristic impedances of the transmission lines of the two impedance matching stubs are 143.77 Ohms and 100 Ohms, respectively. 100Ω and 150Ω patch resistors are connected across the two symmetrical branches of each impedance matching stub to absorb reflected signals caused by mismatch between the two output ports, thus ensuring high isolation between the two output ports. Simultaneously, to match the structure of the SSPP waveguide, the microstrip line of the impedance matching stub is equivalently transformed into a T-shaped structure with a shorted open stub connected in parallel between the two transmission lines, as shown below. Figure 2 As shown in (b), the parameters are w1=1.5mm, a1=0.2mm, a2=0.33mm, d2=1mm, d1=0.75mm, s1=0.65mm, s2=0.4mm, h1=0.8mm, h2=1mm, l1=4.2mm, and l2=4.2mm. Three SSPP waveguides (unit structure as shown) Figure 2As shown in (a), with parameters d=0.6mm, s=0.4mm, w=1.5mm, h=1mm, pads are printed in the middle to solder the HMC-ALH102 type LNA chip. This chip operates in the 2-20GHz frequency band with a gain ≥11.6dB. The LNA bias is provided by an external DC power supply through jumpers (in integrated implementation, the bias line can be printed on the edge of the substrate for unified power supply). The connection between the chip and the SSPP waveguide meets the clockwise amplification direction according to the requirements of the clockwise ring function. The input and output ports of the chip are connected to the SSPP waveguides at both ends by gold wire bonding. The power divider and the SSPP waveguide achieve transition matching through a gradient structure, with the upper tooth height gradually increasing to h in steps of 0.1h.

[0033] In this design, a power divider with a power distribution ratio of 0.5 was employed. While a higher distribution ratio theoretically improves the isolation of the circulator, this would require narrower impedance matching circuit breakers. Given that the current minimum circuit breaker width is 0.2 mm, which is close to the tolerance limit of the manufacturing process, an equal-split configuration (ratio of 0.5) was chosen to ensure manufacturability. The transmission characteristics of the power divider and SSPP waveguide were obtained using the 3D full-wave electromagnetic simulation software CST Microwave Studio. Figure 3 The simulated return loss and insertion loss are shown. In the 0–20 GHz range, the return loss is consistently above 10 dB, and the insertion loss is below 5 dB. The cutoff frequency of the SSPP unit exceeds 40 GHz, covering the entire operating bandwidth of the power divider. Simulation results for the SSPP waveguide also show excellent transmission performance in the 0–20 GHz range, with an insertion loss of less than 0.5 dB. To achieve such a broadband power divider, the quarter-wavelength impedance transformer in the output section is equivalently converted into a T-shaped open-circuit short-circuit structure that supports SSPP mode. Furthermore, the number of these T-shaped units is tripled to obtain a broadband frequency response.

[0034] Example 2: Performance Testing

[0035] Figure 4 (a) An experimental setup for an active quasi-circuit based on SSPP is shown. In the experiment, the fabricated three-port prototype device was connected to a vector network analyzer (blue line) for S-parameter measurements. The red dashed lines represent the three DC power supplies providing the required bias for the LNA. The inset in the figure shows the analyzer interface during measurements.

[0036] The measured reflection coefficient is as follows Figure 4 As shown in (b), the device maintains a return loss of over 10 dB in the 5-13 GHz band. The three measured S-parameter curves (S... 11 ,S 22 ,S 33They exhibit nearly identical frequency responses, with no parasitic resonances or abrupt impedance mismatches. This indicates that the transition between the power divider and the SSPP waveguide has been optimized to minimize reflections. Therefore, stable and efficient signal coupling is achieved across the entire bandwidth.

[0037] Figure 4 (c) Clockwise and counterclockwise transmission were compared. In the forward direction (clockwise), the transmission coefficient (e.g., S) 21 The difference is approximately -2 dB. This near-uniform transmission is achieved thanks to the integrated low-noise amplifier (LNA), which compensates for the inherent losses of the SSPP waveguide. The significant difference between forward and reverse transmission confirms nonmagnetic nonreciprocity, demonstrating that the proposed quasi-circuit breaks Lorentz reciprocity without bulky magnetic components.

[0038] Figure 4 (d) demonstrates the isolation performance. The isolation level remained above 10 dB across the entire frequency band without a significant decrease in frequency dependence. This level of isolation not only reduces crosstalk between the transmit and receive paths but also protects the source from load reflections, which is crucial for protecting sensitive receiver front-ends in high-power RF environments. The final test results are summarized below:

[0039] 1. Operating frequency band: 5-13GHz;

[0040] 2. Return loss: >10dB (full bandwidth)

[0041] 3. Clockwise insertion loss: approximately 2dB;

[0042] 4. Counterclockwise isolation: >10dB (full bandwidth);

[0043] 5. Overall thickness: 1.787mm.

[0044] This embodiment requires no ferrite materials or permanent magnets, achieving a thin, ultra-wideband, non-magnetic circulator.

[0045] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0046] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A compact, ultrawideband artificial surface plasmon circulator, characterized in that: It includes first to third power dividers with identical structures and first to third SSPP waveguides with identical structures. The first and second output ports of the first power divider are respectively connected to the first end of the first SSPP waveguide and the second end of the third SSPP waveguide. The first and second output ports of the second power divider are respectively connected to the first end of the second SSPP waveguide and the second end of the first SSPP waveguide. The first and second output ports of the third power divider are respectively connected to the first end of the third SSPP waveguide and the second end of the second SSPP waveguide. Each of the power dividers has a first patch resistor and a second patch resistor loaded at its output port, and each of the SSPP waveguides has a low-noise amplifier loaded thereon, with the angle between adjacent low-noise amplifiers being 120 degrees.

2. The circulator as described in claim 1, characterized in that: Each of the SSPP waveguides adopts a blade-shaped metal structure with periodically arranged metal grooves formed on its outer side.

3. The circulator as described in claim 1, characterized in that: In the SSPP waveguide, the dispersion characteristics and cutoff frequency are controlled by adjusting the groove depth, width, and / or period parameters.

4. The circulator as described in claim 1, characterized in that: Each of the power dividers is a Wilkinson power divider, with its input ports connected to the two input terminals of the first impedance transformation stub, the two output terminals of the first impedance transformation stub connected to the two input terminals of the second impedance transformation stub, and the two output terminals of the second impedance transformation stub connected to the first and second output ports, which extend in different directions and are respectively connected to the ports of the corresponding SSPP waveguides; the two output terminals of the first and second impedance transformation stubs are respectively connected to first and second patch resistors with different resistance values.

5. The circulator as described in claim 1, characterized in that: The first to third SSPP waveguides are all printed with pads for soldering low-noise amplifiers. The input and output ports of the low-noise amplifiers are connected to the corresponding SSPP waveguides by gold wire bonding.

6. The circulator as claimed in claim 1, characterized in that: Each of the SSPP waveguides operates in the frequency band of 2-20GHz, with a small signal gain ≥11.6dB. Its bias circuit is powered uniformly through jumpers or copper wires printed on the edge of the dielectric substrate.

7. The circulator as claimed in claim 1, characterized in that: The circulator is fabricated on an FR4 dielectric substrate with a thickness of 0.787 mm and a relative permittivity ε. r =2.2, the top layer is a copper metal graphic.

Images