A negative resistance voltage-controlled oscillator based on a tunable quarter-mode waveguide resonator

Abstract

The present application relates to the technical fields of microwave and millimeter wave devices, and discloses a negative resistance voltage-controlled oscillator based on a frequency-adjustable quarter-mode resonant module, comprising a frequency-adjustable quarter-mode resonant module, a phase-shifting microstrip line, a negative resistance unit and an output microstrip line; the resonant unit adopts the frequency-adjustable quarter-mode resonant module, which is obtained by dividing an original complete substrate integrated waveguide resonant cavity into four equal parts along the vertical direction of two adjacent sides; a shielding via array is arranged on the open edge of the resonant cavity, and a slot is designed on the inner side of the resonant cavity to reduce electromagnetic leakage and optimize the quality factor; the negative resistance unit is connected with the resonant unit through the phase-shifting microstrip line, and signal output is realized through the output microstrip line. The present application has excellent phase noise characteristics and high frequency tuning capability while realizing the miniaturization of the oscillator, and takes into account the high frequency stability and low phase noise performance, and is suitable for high-performance wireless communication systems and related applications in the fields of microwave and millimeter wave.

Description

Technical Field

[0001] This invention relates to the field of microwave and millimeter-wave device technology, specifically to a negative resistance voltage-controlled oscillator based on an adjustable quarter-mode waveguide resonant cavity. Background Technology

[0002] With the rapid development of modern communication technology, frequency sources are increasingly widely used in wireless communication, radar detection, precision measurement, and other fields. Among them, the voltage-controlled oscillator (VCO), as the core component of the frequency source, directly affects the frequency stability, phase noise, and tuning capability of the entire system. In high-frequency communication and millimeter-wave applications, low phase noise, miniaturization, and a wide frequency tuning range are the main technological development directions for VCOs. However, traditional VCOs still face many challenges in balancing performance and size.

[0003] Substrate integrated waveguide (SIWB) technology has garnered significant attention in microwave and millimeter-wave circuit design in recent years. Its superior transmission characteristics, high quality factor, and compatibility with planar integrated circuit processes provide an ideal solution for miniaturization and high performance of high-frequency devices. However, the size of the original, fully integrated SIWB resonant cavity is typically large, limiting its applicability in extremely compact applications. To address this issue, quarter-mode SIWB technology significantly reduces device size by dividing the fully integrated resonant cavity into quarters, while retaining the high quality factor advantage of SIWB. This technology has been widely used in the design of miniaturized resonators and filters, but its application in voltage-controlled oscillators (VCOs) remains limited. On the other hand, negative resistance oscillators have been widely used in the high-frequency domain due to their simple structure, low power consumption, and excellent phase noise characteristics. However, the resonators used in traditional negative resistance oscillator designs are mostly based on microstrip lines, cavity resonators, or fully integrated SIWB structures, which have limitations in terms of miniaturization and frequency tunability.

[0004] To further meet the demands of modern communication and radar systems for oscillators with miniaturization, low phase noise, and flexible frequency control, a negative resistance voltage-controlled oscillator based on a frequency-tunable quarter-mode resonant module is proposed. This oscillator significantly improves miniaturization by combining quarter-mode substrate integrated waveguide technology and a negative resistance circuit structure, while achieving precise frequency control through varactor diode tuning. Compared to traditional designs, this invention achieves a good balance between miniaturization, low phase noise, and high-frequency tunability, providing a new technical solution for the design of high-performance oscillators. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a negative resistance voltage-controlled oscillator based on a frequency-adjustable quarter-mode resonant module with miniaturization advantages.

[0006] Technical solution: To achieve this objective, the present invention adopts the following technical solution:

[0007] A negative resistance voltage-controlled oscillator (VCO) based on an adjustable quarter-mode waveguide resonator is disclosed. The VCO includes an adjustable quarter-mode resonant module, a phase-shifted microstrip line, a negative resistance unit, and an output microstrip line. The adjustable quarter-mode resonant module serves as a frequency selection network, and its output port is coupled to the input of the negative resistance unit via the phase-shifted microstrip line. The phase-shifted microstrip line is used to adjust the phase shift of the closed-loop circuit to meet the oscillation equilibrium condition. The negative resistance unit uses an active device to generate an equivalent negative resistance to offset the energy loss of the adjustable quarter-mode resonant module, thereby maintaining controlled electromagnetic oscillation. The output of the negative resistance unit is connected to the output microstrip line to achieve signal output. This oscillator achieves a microwave frequency signal output with low phase noise and wide tuning capability by dividing the original complete substrate-integrated waveguide resonator into four equal parts along the central axis of adjacent sides, forming a quarter-mode structure with open edges, and loading varactor diodes and shielding suppression structures on these open edges. This significantly reduces the circuit size while maintaining the high quality factor of the resonator.

[0008] Preferably, the frequency-tunable quarter-mode resonant module includes a quarter-mode substrate integrated waveguide body, a metallized via array, a shielded via array, a varactor diode, a bias circuit, and an output port; the metallized via array is distributed circumferentially on the dielectric substrate to form an electric wall structure that defines the boundary of the electromagnetic wave.

[0009] Preferably, the quarter-mode substrate integrated waveguide body is obtained by dividing a complete original substrate integrated waveguide resonant cavity into four mutually perpendicular sections along the geometric center lines of two adjacent sides, so that the resonant cavity maintains the same fundamental mode resonant frequency as the original cavity while reducing its volume to one-quarter of the original size.

[0010] Preferably, the shielding via array is disposed on the open edge of the quarter-mode substrate integrated waveguide body, and a slot is provided on the inner side of the shielding via array. The energy radiation of the open edge is suppressed by the synergistic effect of the shielding via array and the slot, thereby reducing electromagnetic leakage.

[0011] Preferably, the varactor diode is loaded at the apex of the open section of the quarter-mode substrate integrated waveguide body, and achieves deep coupling with the cavity resonant mode through the capacitive load effect at the point of strongest electric field.

[0012] Preferably, the bias circuit is electrically connected to the varactor diode and is used to apply an adjustable reverse bias voltage to the varactor diode. By changing the equivalent junction capacitance of the varactor diode, the resonant frequency of the entire resonant circuit is changed, thereby realizing the voltage-controlled tuning function.

[0013] Preferably, the characteristic impedance of both the phase-shifted microstrip line and the output microstrip line is 50 ohms, and the length of the phase-shifted microstrip line is configured such that the magnitude of the input reflection coefficient of the negative resistance unit at the resonant point is greater than 1 and the phase meets the oscillation requirement.

[0014] Preferably, the negative resistance unit includes a three-terminal active device and an external feedback branch. By adding a positive feedback loop to a specific pin of the three-terminal active device, the active device is made to generate negative resistance characteristics in the unstable region, thereby providing negative gain for the frequency-adjustable quarter-mode resonant module.

[0015] Preferably, the frequency-adjustable quarter-mode resonant module consists of a dielectric substrate and metal layers laid on the upper and lower surfaces of the dielectric substrate. The dielectric substrate has a relative permittivity of 2.2 and a thickness of 0.508 mm.

[0016] Preferably, the end of the output microstrip line is connected to the load via electrical interconnection, and the output microstrip line serves as an impedance matching branch to maximize the transmission of the radio frequency energy generated by the negative resistance unit to the external load.

[0017] This invention provides a negative resistance voltage-controlled oscillator based on an adjustable quarter-mode waveguide resonator. It has the following advantages:

[0018] This invention discloses a negative resistance voltage-controlled oscillator based on a frequency-tunable quarter-mode resonant module. Compared with traditional oscillators using a complete, original, fully integrated substrate waveguide resonator design, this invention significantly reduces the size of the resonator by introducing a quarter-mode design, thereby greatly reducing the overall volume of the oscillator. Furthermore, thanks to the negative resistance oscillator architecture, it eliminates the need for a long feedback microstrip line, further optimizing the circuit layout and compressing the oscillator's space requirements. Simultaneously, this invention utilizes a high-quality quarter-mode substrate integrated waveguide body, effectively coupled with the negative resistance unit, ensuring that the oscillator maintains excellent phase noise performance while achieving miniaturization. This invention achieves a good balance between miniaturization, low phase noise, and high tuning capability, exhibiting significant technical and application advantages. Attached Figure Description

[0019] Figure 1 This is a structural diagram of the negative resistance oscillator in a specific embodiment of the present invention;

[0020] Figure 2This is a structural diagram of the original complete substrate-integrated waveguide resonator in a specific embodiment of the present invention;

[0021] Figure 3 This is a test diagram of the output power of the negative resistance oscillator in a specific embodiment of the present invention;

[0022] Figure 4 This is a phase noise test diagram of a negative resistance oscillator in a specific embodiment of the present invention.

[0023] Among them, 1. Frequency-adjustable quarter-mode resonant module; 2. Phase-shifting microstrip line; 3. Negative resistance unit; 4. Output microstrip line; 5. Shielded via array; 6. Quarter-mode substrate integrated waveguide body; 7. Metallized via array; 8. Slot; 9. Output port; 10. Varactor diode; 11. Bias circuit; 12. Original complete substrate integrated waveguide resonant cavity. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Please see the appendix Figure 1 - Appendix Figure 4 This invention provides a negative resistance voltage-controlled oscillator based on an adjustable quarter-mode waveguide resonant cavity, which mainly consists of an adjustable quarter-mode resonant module 1, a phase-shifting microstrip line 2, a negative resistance unit 3, and an output microstrip line 4. The negative resistance voltage-controlled oscillator uses the adjustable quarter-mode resonant module 1 as the frequency selection network. Its output port 9 is coupled to the input terminal of the negative resistance unit 3 through the phase-shifting microstrip line 2. The phase-shifting microstrip line 2 is used to adjust the phase shift of the closed-loop circuit to meet the oscillation balance condition. The negative resistance unit 3 uses the equivalent negative resistance generated by the active device to offset the energy loss of the adjustable quarter-mode resonant module 1, thereby maintaining controlled electromagnetic oscillation. The negative resistance unit 3 includes a three-terminal active device and an external feedback branch. By adding a positive feedback loop to a specific pin of the three-terminal active device, the active device is placed in an unstable region to generate negative resistance characteristics. The output terminal of the negative resistance unit 3 is connected to the output microstrip line 4 with a characteristic impedance of 50 ohms and is finally connected to the load through electrical interconnection.

[0026] Specifically, the negative resistance unit 3 provides positive feedback to the transistor, causing it to be in an unstable negative resistance state. This counteracts the energy loss generated by the frequency-adjustable quarter-mode resonant module 1, enabling continuous signal output from the oscillation circuit. Both the phase-shifting microstrip line 2 and the output microstrip line 4 use 50-ohm feed resistors. The length of the phase-shifting microstrip line 2 is precisely configured to ensure that the input reflection coefficient modulus of the negative resistance unit 3 at the resonant point is greater than 1. This ensures that the circuit meets the specific frequency start-up requirements after the circuit is closed, maximizing the transfer of the generated radio frequency energy to the external load.

[0027] The frequency-tunable quarter-mode resonant module 1 includes a quarter-mode substrate integrated waveguide body 6, a metallized via array 7, and an output port 9. The quarter-mode substrate integrated waveguide body 6 is obtained by dividing a complete original substrate integrated waveguide resonant cavity 12 into four mutually perpendicular sections along the geometric center lines of two adjacent sides, so that the resonant cavity maintains the same fundamental mode resonant frequency as the original cavity while reducing its volume to one-quarter of the original size; the metallized via array 7 is distributed circumferentially on the dielectric substrate to form an electric wall structure that defines the boundary of the electromagnetic wave.

[0028] Specifically, the structure is created by dividing the substrate integrated waveguide into four equal parts along two adjacent perpendicular directions, forming a quarter-mode structure with open edges. This division method achieves oscillator miniaturization while retaining the high quality factor of the substrate integrated waveguide. Compared to the traditional design using a complete original substrate integrated waveguide resonant cavity, this implementation significantly reduces the physical size of the resonant cavity and substantially lowers the overall volume of the oscillator by introducing a quarter-mode design.

[0029] The frequency-tunable quarter-mode resonant module 1 also integrates a varactor diode 10 and a bias circuit 11. The varactor diode 10 is applied at the apex of the open section of the quarter-mode substrate integrated waveguide body 6, achieving deep coupling with the cavity resonant mode through the capacitive load effect at the point of strongest electric field. The bias circuit 11 is electrically connected to the varactor diode 10 and is used to apply an adjustable reverse bias voltage to the varactor diode 10. By changing the equivalent junction capacitance of the varactor diode 10, the resonant frequency of the entire resonant circuit is changed, thereby realizing the voltage-controlled tuning function.

[0030] Specifically, the varactor diode 10 is coupled by being loaded at the apex of the open portion of the quarter-mode substrate integrated waveguide body 6, and reverse biased by the bias circuit 11 to achieve capacitance variation. In this embodiment, the frequency tuning range of the voltage-controlled oscillator is 10.10 GHz–10.74 GHz. Throughout the tuning range, the phase noise at a 1 MHz offset from the center frequency is stabilized at around -115 dBc / Hz, and the output power is maintained at around 5 dBm, achieving a balance between high-frequency stability and low phase noise performance.

[0031] The frequency-tunable quarter-mode resonant module 1 has a shielded via array 5 on the open edge of the quarter-mode substrate integrated waveguide body 6, and a slot 8 is provided inside the shielded via array 5. The energy radiation from the open edge is suppressed through the synergistic effect of the shielded via array 5 and the slot 8. The oscillator is built entirely on a dielectric substrate. The dielectric substrate and the metal layers laid on the upper and lower surfaces of the dielectric substrate form the resonant cavity. The dielectric substrate has a relative permittivity of 2.2 and a thickness of 0.508 mm.

[0032] Specifically, the shielded via array 5 is used to reduce electromagnetic leakage caused by the open cavity structure. Combined with the inner slot design 8, it effectively increases the Q value (quality factor) of the resonant cavity. In this embodiment, the overall circuit size of the oscillator is controlled to approximately 25mm*40mm. This structure not only effectively avoids dependence on long feedback microstrip lines, but also ensures excellent phase noise characteristics while significantly reducing size through the shielding suppression structure, making it suitable for microwave and millimeter-wave applications.

[0033] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A negative resistance voltage-controlled oscillator based on an adjustable quarter-mode waveguide resonant cavity, characterized in that: The negative resistance voltage-controlled oscillator includes a frequency-tunable quarter-mode resonant module (1), a phase-shifting microstrip line (2), a negative resistance unit (3), and an output microstrip line (4); the output port (9) of the frequency-tunable quarter-mode resonant module (1) is coupled to the input terminal of the negative resistance unit (3) through the phase-shifting microstrip line (2); the negative resistance unit (3) contains an active device that generates an equivalent negative resistance; the output terminal of the negative resistance unit (3) is connected to the output microstrip line (4); the frequency-tunable quarter-mode resonant module (1) is a quarter-mode structure with an open edge formed by cutting the original complete substrate integrated waveguide resonant cavity (12) into four equal parts along the central axis of two adjacent sides, and a varactor diode (10) and a shielding suppression structure are loaded on the open edge.

2. The negative resistance voltage-controlled oscillator based on an adjustable quarter-mode waveguide resonant cavity according to claim 1, characterized in that: The frequency-tunable quarter-mode resonant module (1) includes a quarter-mode substrate integrated waveguide body (6), a metallized via array (7), a shielded via array (5), a varactor diode (10), a bias circuit (11), and an output port (9); the metallized via array (7) is distributed circumferentially on the dielectric substrate.

3. A negative resistance voltage-controlled oscillator based on an adjustable quarter-mode waveguide resonant cavity according to claim 2, characterized in that: The quarter-mode substrate integrated waveguide body (6) is obtained by dividing a complete original substrate integrated waveguide resonant cavity (12) into four mutually perpendicular sections along the geometric center lines of two adjacent sides.

4. A negative resistance voltage-controlled oscillator based on an adjustable quarter-mode waveguide resonant cavity according to claim 2, characterized in that: The shielding via array (5) is disposed on the open side of the quarter-mode substrate integrated waveguide body (6), and a slot (8) is provided on the inner side of the shielding via array (5).

5. A negative resistance voltage-controlled oscillator based on an adjustable quarter-mode waveguide resonant cavity according to claim 2, characterized in that: The varactor diode (10) is loaded at the apex of the open portion of the quarter-mode substrate integrated waveguide body (6).

6. A negative resistance voltage-controlled oscillator based on an adjustable quarter-mode waveguide resonant cavity according to claim 2, characterized in that: The bias circuit (11) is electrically connected to the varactor diode (10) and configured to apply an adjustable reverse bias voltage to the varactor diode (10).

7. A negative resistance voltage-controlled oscillator based on an adjustable quarter-mode waveguide resonant cavity according to claim 1, characterized in that: The characteristic impedance of both the phase-shifting microstrip line (2) and the output microstrip line (4) is 50 ohms.

8. A negative resistance voltage-controlled oscillator based on an adjustable quarter-mode waveguide resonant cavity according to claim 1, characterized in that: The negative resistance unit (3) includes a three-terminal active device and an external feedback branch. The external feedback branch is connected to the pins of the three-terminal active device to form a positive feedback loop.

9. A negative resistance voltage-controlled oscillator based on an adjustable quarter-mode waveguide resonant cavity according to claim 1, characterized in that: The frequency-adjustable quarter-mode resonant module (1) consists of a dielectric substrate and metal layers laid on the upper and lower surfaces of the dielectric substrate. The dielectric substrate has a relative permittivity of 2.2 and a thickness of 0.508 mm.

10. A negative resistance voltage-controlled oscillator based on an adjustable quarter-mode waveguide resonant cavity according to claim 1, characterized in that: The output microstrip line (4) is an impedance matching branch, and its end is connected to the load through electrical interconnection.

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