W-band bi-directional coupler applied to spread spectrum system of vector network analyzer

Abstract

The invention discloses a W-band bi-directional coupler applied to a vector network analyzer spread spectrum system. The W-band bi-directional coupler comprises a bi-directional coupler assembly, a receiver unit, a radio frequency signal transmitting unit and a local oscillator signal power dividing unit. The bi-directional coupler assembly comprises a first coupler and a second coupler, and the first coupler and the second coupler share a rectangular waveguide as a main transmission line and are distributed in a mirror image mode with the vertical center axis of the rectangular waveguide as the symmetry axis. Both the first coupler and the second coupler comprise substrate integrated waveguides which are formed by metalized through holes and serve as auxiliary transmission lines; the device is high in integration level, small in size, low in cost and suitable for high-frequency and low-frequency scenes.

Description

Technical Field

[0001] The present invention belongs to the field of microwave and radio frequency, and particularly relates to a W-band dual directional coupler applied to a spread-spectrum system of a vector network analyzer. Background Art

[0002] As a key device in the field of radio frequency and microwave measurement, a vector network analyzer (VNA) is widely used in fields such as electronic communication, radar systems, satellite communication, and high-frequency integrated circuits. With the rapid development of 5G communication, millimeter-wave radar, and terahertz technology, the demand for high-frequency, high-precision, and high-dynamic-range testing is increasing day by day. By measuring S-parameters, a vector network analyzer can comprehensively evaluate the transmission and reflection characteristics of devices and systems, providing important support for R & D and production. The core spread-spectrum system depends on the coordinated work of a signal source, a signal separation device, a receiver, and a data processing unit, among which the performance of the signal separation device directly affects the test accuracy and efficiency.

[0003] Currently, signal separation in vector network analyzers mainly relies on directional couplers. In the low-frequency band (such as the microwave band), microstrip directional couplers are widely used because of their simple structure and easy integration, and are usually built into the instrument. In the high-frequency band (such as the W-band and above), due to the significant increase in microstrip line losses, waveguide directional couplers have become the mainstream solution. The waveguide structure utilizes the electromagnetic waveguide characteristics of the metal cavity to achieve low insertion loss, high directivity, and wideband performance, meeting the requirements of high-frequency testing.

[0004] However, although microstrip directional couplers perform well in the low-frequency band, as the frequency increases, their insertion loss increases sharply, resulting in serious signal attenuation and making it difficult to meet the test requirements of the W-band and higher frequency bands. Although waveguide directional couplers have excellent performance in the high-frequency band, they are large in size, difficult to integrate, and have high manufacturing costs, which hinder the development of vector network analyzers towards miniaturization and low cost. Summary of the Invention

[0005] Object of the Invention: The object of the present invention is to provide a W-band dual directional coupler with high integration, small size, low cost, and suitable for both high and low frequencies, which is applied to the spread-spectrum system of a vector network analyzer.

[0006] Technical Solution: The dual directional coupler described in the present invention includes a dual directional coupler assembly, a receiver unit, a radio frequency signal transmitting unit, and a local oscillator signal power splitting unit; the dual directional coupler assembly includes a first coupler and a second coupler, the first coupler and the second coupler share a rectangular waveguide as the main transmission line, and are mirror-symmetrically distributed with the vertical central axis of the rectangular waveguide as the symmetry axis; both the first coupler and the second coupler include a substrate integrated waveguide formed by metallized vias as the secondary transmission line.

[0007] The design of this solution uses a rectangular waveguide as the main transmission line, which can support the transmission of high-frequency signals, has low loss, high power capacity, and good electromagnetic shielding performance. The first coupler and the second coupler share the same main waveguide and are symmetrically distributed with respect to the vertical center axis, making the structure more compact. At the same time, signal crosstalk is reduced, and the symmetry and consistency of the directional coupler are improved. The secondary transmission line uses a substrate integrated waveguide (SIW) composed of metallized vias, which combines the low-loss characteristics of traditional waveguides and the easy integration advantages of planar circuits. It can be compatible with PCB or chip processes, reducing manufacturing costs. The closed structure of the SIW can effectively suppress electromagnetic leakage, improve the coupling accuracy, and its symmetric layout helps to enhance the directivity and port isolation of the double directional coupler. Combining the collaborative work of the receiver unit, the RF signal transmitting unit, and the local oscillator signal power splitting unit improves the signal processing ability and frequency stability of the overall system.

[0008] Preferably, both the first coupler (11) and the second coupler (12) include a RF input end, a RF output end, a coupling end, and an isolation end. The first coupler (11) couples the incident signal propagating forward to the first coupling end. The second coupler (12) couples the reflected signal propagating backward to the second coupling end. This design realizes the efficient discrimination and independent detection of the signal transmission direction, improves the directivity, isolation degree, and measurement accuracy of the reflected signal of the double directional coupler, making it have more stable signal transmission and higher coupling accuracy when operating in the W band, and is suitable for high-frequency systems that need to monitor incident and reflected waves simultaneously.

[0009] Preferably, the isolation end realizes the matching of the RF signal through a chip resistor, which can further improve the integration, effectively absorb the residual signal energy and suppress reflection, thereby significantly improving the isolation degree between ports, saving costs, reducing signal crosstalk, and optimizing the voltage standing wave ratio (VSWR) at the same time, ensuring that the double directional coupler maintains stable directional performance and signal detection accuracy in a wide frequency band range.

[0010] Preferably, the first coupler includes metallized vias, coupling circular holes, and microstrip lines. The metallized vias are used to achieve electromagnetic shielding and signal isolation between the rectangular waveguide and the microstrip line. The coupling circular holes are used to couple the electromagnetic field energy in the rectangular waveguide to achieve directional signal transmission. The microstrip line is used to transmit the signal extracted by the coupling circular holes to the receiver unit. Using metallized vias to achieve electromagnetic shielding and signal isolation between the rectangular waveguide and the microstrip line can effectively reduce interference. The coupling circular holes accurately couple the electromagnetic field energy in the rectangular waveguide to ensure the efficient transmission of directional signals. The microstrip line is responsible for transmitting the coupled signal to the receiver unit with low loss, thereby improving the signal transmission efficiency, directivity, and detection sensitivity of the overall system, while maintaining a compact structure and easy integration.

[0011] Preferably, the metallized through-holes include a first through-hole column and a second through-hole column arranged along the edge of the first coupler, and the first through-hole column and the second through-hole column cooperate with the top and bottom metal layers of the printed circuit board to form a substrate integrated waveguide, and the substrate integrated waveguide serves as a secondary transmission line and is responsible for receiving the radio frequency signal coupled from the rectangular waveguide; this design not only realizes the efficient coupling and transmission of the radio frequency signal in the rectangular waveguide, but also has the low loss characteristics of the traditional waveguide and the compact advantages of the planar circuit, significantly improving the stability and directionality of the signal transmission, while reducing the manufacturing cost and assembly complexity, and is suitable for the integrated design requirements of high-frequency millimeter wave systems.

[0012] Preferably, the coupling circular hole is located between the first through-hole column and the second through-hole column, and is composed of several rows of corroded circular holes in the top metal layer of the printed circuit board, and is axisymmetric in the horizontal direction and the vertical direction corresponding to the transmission direction of the RF signal. This design realizes the efficient coupling and balanced transmission of the conductive magnetic field energy of the rectangular waveguide. This symmetrical design not only enhances the stability and consistency of signal coupling, but also reduces the directional deviation, while optimizing the electromagnetic field distribution, significantly improving the frequency response flatness and signal transmission accuracy of the dual directional coupler, and is suitable for precise signal monitoring and control of high-performance RF systems.

[0013] Preferably, the coupling circular holes are distributed in multiple rows, with two rows of larger circular holes in the middle, and several rows of smaller circular holes on both sides of the larger circular holes, and are symmetrically distributed, and the size of the circular holes tends to decrease from the center of the coupling circular holes to both ends; this design realizes the gradient coupling and optimal matching of the conductive magnetic field energy of the rectangular waveguide. This gradual aperture design effectively broadens the working bandwidth, improves the frequency response characteristics, and enhances the coupling efficiency and directivity, so that the dual-directional coupler maintains stable signal transmission performance and higher power capacity within a wide bandwidth, which is suitable for the precise signal monitoring and control needs of high-frequency millimeter-wave systems.

[0014] Preferably, the microstrip line includes a microstrip line transition structure and a microstrip transmission line connected to the microstrip line transition structure; the first coupler and the second coupler of the dual directional coupler assembly are linearly connected to the receiver unit via the microstrip line transition structure; by adopting the connection method of the microstrip line transition structure and the microstrip transmission line, a difference from the waveguide connection method adopted by the traditional W-band coupler is achieved. The traditional waveguide connection has the problems of large space occupancy and high-frequency signal leakage, while the direct connection method of the microstrip line adopted in the present invention can effectively reduce the volume and realize integrated design; at the same time, due to the efficient transmission characteristics of the microstrip line, the leakage of high-frequency signals can be effectively reduced, and the isolation of the system can be significantly improved, thereby improving the overall performance, reducing unnecessary losses in traditional couplers, and optimizing transmission efficiency.

[0015] Preferably, one wide wall of the rectangular waveguide is the top metal layer of the printed circuit board, and the rectangular waveguide cavity is pressed above the coupling round hole. By designing one wide wall of the rectangular waveguide as the top metal layer of the printed circuit board, the structure of the printed circuit board itself can be effectively utilized to construct the waveguide, simplifying the overall design and manufacturing process. At the same time, the rectangular waveguide cavity is pressed above the coupling round hole, ensuring efficient coupling and signal transmission between the waveguide and other components. This design not only saves space but also enhances the signal transmission stability and transfer efficiency, reducing the losses and unnecessary complexities that may occur in traditional waveguide designs, thereby improving the overall performance and integration level.

[0016] Preferably, the output end of the radio frequency signal transmitting unit is connected to the input end of the rectangular waveguide for transmitting radio frequency signals. The first coupler and the second coupler of the dual-directional coupler assembly are respectively connected to the input end of the receiver unit for coupling and transmitting signals. The output end of the local oscillator signal power splitting unit is connected to the local oscillator port of the receiver unit for providing local oscillator signals. The receiver unit includes a low-noise amplifier, a mixer, and a low-pass filter connected in sequence. The low-noise amplifier is used to amplify the coupled signals transmitted by the first coupler and the second coupler. The mixer is used to mix the amplified coupled signals with the local oscillator signals provided by the local oscillator signal power splitting unit. The low-pass filter is used to extract the difference frequency signals after mixing. By optimizing the collaborative work of the radio frequency signal transmitting unit, the dual-directional coupler assembly, and the receiver unit, the receiving sensitivity and signal processing ability of the system are significantly improved. The low-noise amplifier effectively amplifies the coupled signals. The mixer realizes the precise analysis and processing of signals through the mixing operation with the local oscillator signals, and the low-pass filter further extracts the required difference frequency signals, improving the signal quality and stability. The entire design can not only efficiently and accurately detect incident and reflected radio frequency signals but also effectively reduce the system noise, enhance the anti-interference ability and signal processing stability, ensuring the high-performance performance of the system in complex environments.

[0017] Advantages: Compared with the prior art, the present invention has the following remarkable advantages: 1. High integration, small size, low cost, and applicable to high and low frequency scenarios; 2. Combining the advantages of waveguide structures and substrate integrated waveguide structures, while reducing the insertion loss, it can be directly integrated with the planar circuit system, reducing the device size and production cost; 3. Through this integrated design connected by microstrip lines, the leakage of high-frequency signals can be reduced and the isolation degree can be improved; 4. The use of chip resistors can further improve the integration level and reduce the cost. Description of the Drawings

[0018] Figure 1 is the principle block diagram of the present invention; Figure 2 is the structural schematic diagram of the dual-directional coupler assembly of the present invention; Figure 3 It is a top view of the dual-directional coupler component of the present invention; Figure 4 It is a schematic diagram of the internal structure of the first coupler of the present invention; Figure 5 and Figure 6 It is an S-parameter result diagram of the present invention. Specific Embodiments

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0020] As Figure 1 shown, the dual-directional coupler of the present invention includes: a dual-directional coupler component 1, a receiver unit 2, a radio frequency signal transmitting unit 3, and a local oscillator signal power splitting unit 4; the dual-directional coupler component 1 is composed of a rectangular waveguide structure and a substrate integrated waveguide structure. The rectangular waveguide 13 is responsible for transmitting radio frequency signals, and the substrate integrated waveguide is responsible for receiving the signals coupled from the rectangular waveguide. The design of the substrate integrated waveguide structure is beneficial to integrating the dual-directional coupler component 1 into the spread-spectrum system of the vector network analyzer.

[0021] Specifically, the dual-directional coupler component 1 includes a first coupler 11 and a second coupler 12. The two couplers share a rectangular waveguide 13 as the main transmission line, and the two sub-transmission lines are both substrate integrated waveguide structures, and the two couplers are symmetrical to each other; the first coupler 11 is mainly responsible for receiving the incident radio frequency signal, and the second coupler 12 is mainly responsible for receiving the reflected radio frequency signal. The combined use of the two couplers ensures the effective extraction and separation of the incident signal and the reflected signal, thereby providing reliable data support for the vector network analyzer to evaluate the performance of high-frequency devices and systems.

[0022] Specifically, as Figure 2 and Figure 3 shown, both the first coupler 11 and the second coupler 12 include a radio frequency input end, a radio frequency output end, a coupling end, and an isolation end. The isolation end is connected to a chip matching resistor; the matching load is a chip matching resistor. Connecting the matching load can absorb the signals leaked from the isolation end, prevent them from being reflected to other ports, improve the isolation degree of the dual-directional coupler, and thus improve the signal-to-noise ratio and measurement accuracy of the spread-spectrum system of the vector network analyzer. The integrated design of the chip matching load not only saves the circuit board space, but also reduces the influence of external parasitic parameters. At the same time, the matching accuracy is improved through process consistency, which is beneficial to realizing the miniaturization of the system and optimizing the high-frequency performance.

[0023] Specifically, taking the first coupler 11 as an example, the first coupler 11 includes metallized vias 111, coupling round holes 112, microstrip lines 113, and a rectangular waveguide 13. The metallized vias 111 consist of two rows of metallized vias, which cooperate with the top and bottom metal layers of the printed circuit board to form a substrate integrated waveguide structure; the coupling round holes 112 are composed of multiple rows of etched round holes in the top metal layer of the printed circuit board, located in the middle of the two rows of metallized vias. The coupling round holes 112 are axisymmetric both in the horizontal direction and the vertical direction along the RF signal transmission direction, and are composed of a series of etched round holes, which are distributed in multiple rows. Among them, there are two rows of larger round holes in the middle position, surrounded by multiple rows of smaller round holes. Some of the smaller round holes are symmetrically distributed on both sides of the larger round holes, and from the center to both ends, the size of the round holes gradually decreases; the microstrip line 113 includes a microstrip line transition structure and a 50-ohm microstrip line; the rectangular waveguide 13 uses the top metal layer of the printed circuit board as one side wide wall, and the waveguide cavity is pressed above the coupling round holes 112. Similarly, the structure of the second coupler 12 is the same as that of the first coupler 11.

[0024] Specifically, as Figure 4 shown, the diameter and hole pitch of the two rows of metallized vias constituting the metallized vias 111 need to be in accordance with the via diameter r1 = 0.1 mm in order to confine the electromagnetic wave in the rectangular cavity formed by the two rows of metallized vias and the top and bottom metal layers of the printed circuit board. The distance between the two rows of metallized vias affects the operating frequency of the double directional coupler. The rectangular waveguide 13 is a W-band standard rectangular waveguide WR-10. The length of the wide side affects the operating frequency, and the length of the narrow side affects the coupling degree. The RF signal transmitted in the rectangular waveguide 13 enters the substrate integrated waveguide structure through the coupling round holes 112, which is beneficial for the integration of the double directional coupler component 1 with the planar circuit and then with the vector network analyzer frequency extension system. The coupling round holes 112 are composed of two rows of etched round holes, and each row has 8 etched round holes of different sizes. Taking the two rows of round holes on the vertical symmetry right side of the coupling round holes as an example, the number of coupling holes affects the operating bandwidth, the diameter affects the coupling degree, and the diameters of the coupling holes from the center outwards are approximately 0.5 mm, 0.3 mm, 0.22 mm, and 0.2 mm; the distance between adjacent etched round holes parallel to the RF signal transmission direction affects the center frequency point; the position of the etched round holes perpendicular to the RF signal transmission direction affects the directivity, and its position affects the magnitude and position of the directivity. The lateral spacing from the center outwards is approximately 0.7 mm, 2 mm, 3.5 mm, and 5 mm, and the longitudinal spacing from the center outwards is approximately 1.7 mm, 0.8 mm, 1.2 mm, and 1.3 mm in sequence.

[0025] Specifically, the incident RF signal received by the receiver unit 2 from the coupling end of the first coupler 11 is mixed with the local oscillator signal through a low noise amplifier to obtain a reference intermediate frequency signal, which is then output after passing through a low pass filter; the reflected RF signal received by the receiver unit 2 from the coupling end of the second coupler 12 is mixed with the local oscillator signal through a low noise amplifier to obtain a measurement intermediate frequency signal, which is then output after passing through a low pass filter. The low noise amplifier helps to increase the RF signal and improve the receiver sensitivity, and the low pass filter can filter out unnecessary frequency components, improve measurement accuracy, and thus improve the performance of the vector network analyzer spread spectrum system.

[0026] Specifically, the RF signal transmitting unit 3 performs frequency doubling, amplification, attenuation, filtering and other operations on the input RF signal, and then transmits the RF signal to the dual directional coupler component 1; since the frequency of the input RF signal is relatively low, it is firstly increased in frequency by a sextuple frequency multiplier to ensure that it is suitable for W-band application scenarios. At the same time, in view of the low input power of the signal, it is not enough to meet the working requirements of the vector network analyzer spread spectrum system, so it is necessary to further enhance the signal power through an amplifier. In order to prevent the harmonics and stray signals that may be generated in the above processing process from interfering with the final effect, the signal needs to be filtered before entering the mixer.

[0027] Specifically, the local oscillator signal power division unit 4 is used to perform frequency multiplication, amplification, filtering, power division and other operations on the input local oscillator signal, and then transmit the local oscillator signal to the receiver unit 2. The input local oscillator signal is first processed by a sextuple frequency multiplier due to its low frequency to ensure that it is suitable for W-band application scenarios. At the same time, in view of the insufficient power of the input signal, it is impossible to directly meet the working requirements of the mixer, so it is necessary to further enhance the signal strength through an amplifier. In order to prevent harmonics and stray interference that may be generated during the above processing, the signal also needs to be filtered, and finally the local oscillator signal is evenly distributed to the receiver unit 2 with the help of a power divider.

[0028] A method for using the dual directional coupler corresponding to the dual directional coupler of the present invention comprises the following steps: (1) The RF signal transmitting unit 3 generates and amplifies the W-band RF signal and inputs it into the main transmission line of the rectangular waveguide 13; (2) The dual directional coupler component 1 couples the incident signal and the reflected signal from the rectangular waveguide 13 through its symmetrically distributed substrate integrated waveguides, wherein the first coupler 11 couples the incident signal transmitted in the forward direction to the first coupling end; and the second coupler 12 couples the reflected signal transmitted in the reverse direction to the second coupling end; (3) The dual directional coupler component 1 converts the signals at the first coupling end and the second coupling end into matching microstrip line signals through the microstrip line transfer structure; (4)The receiver unit 2 amplifies the two converted microstrip line signals with low noise, and mixes them with the local oscillator signal provided by the local oscillator signal power splitting unit 4 to generate an intermediate frequency signal; (5)The receiver unit 2 performs low-pass filtering on the mixed intermediate frequency signal and outputs it.

[0029] In order to verify the feasibility of the dual-directional coupler component 1 in the present invention, the designed structure was verified for parameters using the S parameters characterizing the microwave transmission performance. Figure 5 and Figure 6 The corresponding results are given. The results show that the dual-directional coupler component 1 proposed in the present invention can achieve stable transmission of W-band (75 - 110 GHz) signals, with a directivity > 19 dB, an in-band coupling degree of 30 dB, an in-band flatness < 1.5 dB, and a return loss < -15 dB within its operating frequency band.

Claims

1. A W-band dual directional coupler for a vector network analyzer spread spectrum system, characterized in that: The invention comprises a dual directional coupler component (1), a receiver unit (2), a radio frequency signal transmitting unit (3) and a local oscillator signal power division unit (4); the dual directional coupler component (1) comprises a first coupler (11) and a second coupler (12); the first coupler and the second coupler share a rectangular waveguide (13) as a main transmission line and are mirror-distributed with the vertical central axis of the rectangular waveguide as a symmetry axis; the first coupler (11) and the second coupler (12) both comprise a substrate integrated waveguide composed of a metallized through hole (111) as a secondary transmission line.

2. The dual directional coupler according to claim 1, characterized in that: The first coupler (11) and the second coupler (12) both comprise a radio frequency input end, a radio frequency output end, a coupling end and an isolation end; the first coupler (11) couples a forwardly transmitted incident signal to the first coupling end; and the second coupler (12) couples a reversely transmitted reflected signal to the second coupling end.

3. The dual directional coupler according to claim 2, characterized in that: The isolation end achieves matching of the radio frequency signal through chip resistance.

4. The dual directional coupler according to claim 1, characterized in that: The first coupler (11) comprises a metallized through hole (111), a coupling circular hole (112) and a microstrip line (113); the metallized through hole (111) is used to achieve electromagnetic shielding and signal isolation between the rectangular waveguide (13) and the microstrip line (113); the coupling circular hole (112) is used to couple electromagnetic field energy in the rectangular waveguide (13) to achieve directional signal transmission; and the microstrip line (113) is used to transmit the signal extracted by the coupling circular hole (112) to the receiver unit (2).

5. The dual directional coupler according to claim 4, characterized in that: The metallized through hole (111) comprises a first through hole column and a second through hole column arranged along the edge of the first coupler (11); the first through hole column and the second through hole column cooperate with the top and bottom metal layers of the printed circuit board to form a substrate integrated waveguide; the substrate integrated waveguide serves as a secondary transmission line and is responsible for receiving a radio frequency signal coupled from the rectangular waveguide (13).

6. The dual directional coupler according to claim 4, characterized in that: The coupling circular hole (112) is located between the first through hole column and the second through hole column, is composed of a plurality of rows of etched circular holes in the metal layer on the top of the printed board, and is axisymmetric in the horizontal direction and the vertical direction corresponding to the radio frequency signal transmission direction.

7. The dual directional coupler according to claim 4, characterized in that: The coupling circular holes (112) are distributed in multiple rows, wherein two rows of larger circular holes are located in the middle, and a plurality of rows of smaller circular holes are distributed on both sides of the larger circular holes in a symmetrical distribution, and the size of the circular holes tends to decrease from the center of the coupling circular hole (112) toward both ends.

8. The dual directional coupler according to claim 4, characterized in that: The microstrip line (113) comprises a microstrip line transition structure and a microstrip transmission line connected to the microstrip line transition structure; the first coupler (11) and the second coupler (12) of the dual directional coupler assembly (1) are linearly connected to the receiver unit (2) via the microstrip line transition structure.

9. The dual directional coupler according to claim 1, characterized in that: The rectangular waveguide (13) uses the top metal layer of the printed circuit board as a wide wall on one side, and the rectangular waveguide cavity is pressed onto the top of the coupling circular hole (112).

10. The dual directional coupler according to claim 1, characterized in that: The output end of the radio frequency signal transmitting unit (3) is connected to the input end of the rectangular waveguide (13) for transmitting radio frequency signals; the first coupler (11) and the second coupler (12) of the dual directional coupler assembly (1) are respectively connected to the input end of the receiver unit (2) for coupling and transmitting signals; the output end of the local oscillator signal power splitter unit (4) is connected to the local oscillator port of the receiver unit (2) for providing a local oscillator signal; the receiver unit (2) comprises a low noise amplifier, a mixer and a low pass filter connected in sequence; the low noise amplifier is used to amplify the coupled signals transmitted by the first coupler (11) and the second coupler (12); the mixer is used to mix the amplified coupled signal with the local oscillator signal provided by the local oscillator signal power splitter unit (4); and the low pass filter is used to extract the difference frequency signal after mixing.

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