A microwave oscillator based on BGA-GWG resonant cavity

Abstract

The present invention discloses a microwave oscillator based on a BGA-GWG resonant cavity, comprising an oscillation circuit, a BGA-GWG resonant cavity, and a source microstrip line. The oscillation circuit uses a field-effect transistor as an active device, and the gate of the field-effect transistor is connected in series with an ohmic microstrip line. The drain electrode is connected to one end of a first series microstrip line and a parallel open microstrip line, and the other end of the first series microstrip line and the parallel open microstrip line serves as the oscillator output end. The source electrode is connected to one end of a second series microstrip line and a parallel open microstrip line, and the other end of the second series microstrip line and the parallel open microstrip line serves as the oscillator source end and is connected to the source microstrip line. The BGA-GWG cavity is a GWG cavity based on BGA flip-chip technology, which is coupled next to the source microstrip line. The oscillator of the present invention has ultra-high stability of the output frequency and ultra-low phase noise, and is lightweight and compact.

Description

Technical Field

[0001] The invention belongs to the field of electromagnetic field and microwave technology, and particularly relates to a microwave oscillator based on a BGA-GWG resonant cavity. Background Art

[0002] Modern radar and communication systems are developing rapidly, carrying ever-increasing amounts of data and transmitting at ever-increasing speeds. Consequently, RF hardware systems require increasingly high-performance microwave frequency sources. The microwave frequency source is arguably the heart of modern communication systems, and its development, in turn, relies on underlying oscillators. Therefore, the performance of the oscillator directly and significantly impacts the performance of the frequency source, and thus the entire communication system. Phase noise is the most critical performance parameter of an oscillator, determining the overall performance of the communication system. To achieve low-phase-noise oscillators, high-quality frequency-stabilizing components are required. These components primarily employ various resonant structures, including dielectric resonators, substrate-integrated waveguide (SIW) resonators, and other high-Q resonant devices.

[0003] In recent years, research on oscillators has primarily focused on resonators with high frequency selectivity. Some researchers have proposed substrate-integrated waveguide technology, which offers advantages such as small size, high integration density, and high stability, using LTCC and PCB processes. The planar structure of the substrate-integrated waveguide cavity facilitates connection to external circuits, making its application in oscillator design of great practical significance. In 2009, Professor P.-S. Kildal of Sweden proposed gapped substrate-integrated groove waveguide (GWG) transmission line technology. Gap-substrate-integrated groove waveguides are classified into three types: ridge-gap substrate-integrated groove waveguide (Ridge GWG), groove-gap substrate-integrated groove waveguide (Groove GWG), and microstrip-gap substrate-integrated groove waveguide. These three GWG structures can be constructed entirely of metal or a combination of metal and printed circuit boards (PCBs).

[0004] Resonators based on GWG structures exhibit extremely high Q and extremely low loss. They can be used as frequency stabilizers to significantly improve the output frequency stability of oscillators and significantly reduce the phase noise of microwave oscillators. A typical ridge GWG design utilizes a spike unit, where a ridge is surrounded by periodic spikes in the non-propagation direction. This is typically fabricated by machining. Ridge GWGs or microstrip GWGs can also be integrated on printed circuit boards (PCBs) or low-temperature co-fired ceramic (LTCC) substrates. LTCC or PCB substrates are supported by a substrate frame based on a metal base to maintain the air gap and low transmission loss. However, this machining method makes it difficult to maintain a constant air gap height over large dimensions and may even collapse upon exposure to even small pressures or impacts. This can lead to performance degradation or instability in the resonant cavity based on conventional GWGs, and consequently, unstable performance in microwave oscillators based on conventional GWGs. To address these issues, microwave oscillators using novel GWG resonant cavity structures are needed. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned prior art and provide a microwave oscillator based on a BGA-GWG resonant cavity, whose phase noise can reach -105.1dBc / Hz@100kHz and -125.1dBc / Hz@1MHz; at the same time, the oscillator achieves the characteristics of lightweight and small size.

[0006] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0007] A microwave oscillator based on a BGA-GWG resonant cavity comprises an oscillation circuit, a BGA-GWG resonant cavity and a source-end microstrip line;

[0008] The oscillation circuit uses a field effect transistor as an active device, wherein the gate of the field effect transistor is connected in series with an ohmic microstrip line; the drain is connected to one end of the first series microstrip line and the parallel open microstrip line, and the other end of the first series microstrip line and the parallel open microstrip line is the oscillator output end; the source is connected to one end of the second series microstrip line and the parallel open microstrip line, and the other end of the second series microstrip line and the parallel open microstrip line is the oscillator source end, which is connected to the source end microstrip line;

[0009] The BGA-GWG cavity is a GWG cavity based on BGA flip-chip technology, which is coupled next to the source end microstrip line;

[0010] The source end and the output end of the oscillator realize impedance transformation through a first series microstrip line and a parallel open microstrip line and a second series microstrip line and a parallel open microstrip line.

[0011] To optimize the above technical solutions, specific measures taken also include:

[0012] The field effect transistor mentioned above adopts a gallium arsenide field effect transistor.

[0013] The source and drain of the field effect transistor are connected to a DC voltage to provide a static operating point of the field effect transistor.

[0014] The above-mentioned microstrip lines are all 50-ohm microstrip lines.

[0015] The above-mentioned BGA-GWG resonant cavity includes a T-substrate, a B-substrate and BGA solder balls between the T-substrate and the B-substrate, and the T-substrate is assembled on top of the B-substrate through flip-chip technology. The BGA solder balls support the T-substrate and the B-substrate to form an air gap layer.

[0016] In the above-mentioned BGA-GWG resonant cavity, each BGA solder ball, the T-substrate portion directly above it, the B-substrate portion directly below it, and the air gap layer portion constitute a BGA periodic unit.

[0017] The central part of the BGA-GWG resonant cavity is the resonant region, and a 4×4 BGA period unit is removed near the source end of the oscillator for electromagnetic coupling between the resonant cavity and the source end microstrip line.

[0018] The lower surfaces of the T-substrate and the B-substrate are covered with metal.

[0019] The present invention has the following beneficial effects:

[0020] The oscillator of the present invention uses a gallium arsenide field-effect transistor (GaAs) as the active device. A common-gate structure allows the GaAs to operate in an unstable state that allows oscillation. A high-Q BGA-GWG resonant cavity stabilizes the output frequency and reduces phase noise. Due to the resonator's higher Q and lower loss, the BGA-GWG resonator is electromagnetically coupled to the oscillator's source microstrip line. The oscillator selects its frequency using this high-Q, low-loss resonator, achieving ultra-high output frequency stability and ultra-low phase noise. The resonant cavity is implemented using a GWG based on BGA flip-chip technology, lacking metal vias, resulting in a lightweight and low-profile design. The BGA-GWG's underlying substrate can be shared with the rest of the oscillator, reducing processing complexity and production costs. The impedance transformation network at the oscillator's source and output ends is implemented using a series 50-ohm microstrip line and a parallel open-circuit 50-ohm microstrip line. The oscillator circuit and BGA-GWG cavity can be constructed using a double-sided PCB. In practical applications, the oscillator of the present invention can be directly applied to demodulation applications of receivers and modulation applications of transmitters; at the same time, it can also be combined with direct digital frequency synthesis technology and phase-locked loop frequency synthesis technology to generate flexible and variable low phase noise frequency sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of a microwave oscillator of the present invention;

[0022] The accompanying drawings are marked as follows: 1-source end microstrip line, 2-BGA solder ball, 3-second series microstrip line and parallel open microstrip line, 4-ohm microstrip line, 5-first series microstrip line and parallel open microstrip line, 6-T-substrate, 7-B-substrate, 8-air gap layer;

[0023] Figure 2 Schematic diagram of the coupling between the BGA-GWG resonant cavity and the source end microstrip line in the microwave oscillator of the present invention and its dimensions.

[0024] Figure 3 14 GHz microwave oscillator output spectrum simulation results according to an embodiment of the present invention;

[0025] Figure 4 14 GHz microwave oscillator output signal phase noise simulation results in the embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0027] Although the steps in the present invention are arranged with numbers, they are not intended to limit the order of the steps. Unless the order of the steps is clearly stated or the execution of a step requires other steps as a basis, the relative order of the steps can be adjusted. It is understood that the term "and / or" used herein refers to and covers any and all possible combinations of one or more of the associated listed items.

[0028] like Figure 1 As shown, the present invention provides a microwave oscillator based on a BGA-GWG resonant cavity (based on a ball grid array flip-chip semi-air-filled substrate integrated groove gap waveguide cavity), such as a 14 GHz microwave oscillator, comprising an oscillation circuit, a BGA-GWG resonant cavity and a source-end microstrip line 1;

[0029] The oscillation circuit uses a GaAs field-effect transistor as an active device, and uses a common-gate structure to make the field-effect transistor work in an unstable state that can generate oscillation. Specifically:

[0030] The gate of the field effect transistor is connected in series with an ohmic microstrip line 4, specifically a 50-ohm microstrip line, to reduce the stability of the field effect transistor and make it more prone to oscillation;

[0031] The drain is connected to one end of the first series microstrip line and the parallel open microstrip line 5, and the other end of the first series microstrip line and the parallel open microstrip line 5 is the output end of the oscillator; the source is connected to one end of the second series microstrip line and the parallel open microstrip line 3, and the other end of the second series microstrip line and the parallel open microstrip line 3 is the source end of the oscillator, which is connected to the source end microstrip line 1;

[0032] Connect a DC voltage V to the source and drain of the field effect transistor. s With V d , used to provide the static operating point of the field effect transistor;

[0033] A BGA-GWG resonant cavity with the same resonant frequency of 14 GHz is placed next to the source end microstrip line 1. The BGA-GWG cavity is a semi-air-filled substrate integrated gap waveguide based on the Ball Grid Array (BGA flip-chip) technology. It uses flip-chip technology, has no metal through-holes, is light in weight, and has a low profile. It is coupled next to the source end microstrip line 1.

[0034] The source end and the output end of the oscillator realize impedance transformation through the first series microstrip line and the parallel open microstrip line 5 and the second series microstrip line and the parallel open microstrip line 3.

[0035] That is, the drain uses an open microstrip line and a series microstrip line for impedance matching; the GWG cavity is coupled next to the source microstrip line 1, and a microstrip line is connected in series with a small open microstrip line in parallel for impedance transformation;

[0036] The high-Q BGA-GWG resonant cavity stabilizes the output frequency and reduces phase noise.

[0037] The oscillation circuit and BGA-GWG cavity can be realized through a double-sided PCB board.

[0038] The BGA-GWG resonant cavity used in the present invention is composed of multiple groups of 4×4 BGA periodic units. Specifically:

[0039] The BGA-GWG resonant cavity includes a T-substrate 6, a B-substrate 7 and a BGA solder ball 2 between the T-substrate 6 and the B-substrate 7, with the T-substrate 6 on the top and the B-substrate 7 on the bottom. The BGA solder ball 2 supports the T-substrate 6 and the B-substrate 7 to form an air gap layer 8.

[0040] In the BGA-GWG resonant cavity, each BGA solder ball 2, the T-substrate 6 portion directly above it, the B-substrate 7 portion directly below it, and the air gap layer 8 portion constitute a BGA periodic unit.

[0041] The lower B-substrate 7 of the BGA-GWG resonant cavity shares a common substrate with the rest of the oscillator circuit. The portion of the BGA-GWG resonant cavity near the microstrip line requires a portion of the BGA periodic unit to be removed to facilitate electromagnetic coupling between the resonant cavity and the microstrip line. Specifically, the central portion of the BGA-GWG resonant cavity serves as the resonant region, while a 4×4 BGA periodic unit is removed near the oscillator source to facilitate electromagnetic coupling between the resonant cavity and the source microstrip line 1.

[0042] The lower surfaces of the T-substrate 6 and the B-substrate 7 are both covered with metal.

[0043] Example

[0044] like Figure 1 The figure shows a schematic diagram of a 14GHz microwave oscillator based on a BGA-GWG resonator. The microwave oscillator is made using printed circuit board technology. Its double-sided substrate medium is Rogers4350 with a relative dielectric constant of ε r It is 3.48.

[0045] The field effect transistor used is ATF-13100, and the source and drain of the field effect transistor are connected to a DC voltage V s With V d 0.65V and 0.3V respectively, used to provide the static operating current of the transistor;

[0046] A 50-ohm microstrip line 4 with an electrical length of 49° is connected in series to the gate of the field effect transistor to improve the instability of the field effect transistor;

[0047] The BGA-GWG resonant cavity includes a T-substrate 6, a B-substrate 7 and a BGA solder ball 2 between the T-substrate 6 and the B-substrate 7, with the T-substrate 6 on the top and the B-substrate 7 on the bottom. The BGA solder ball 2 supports the T-substrate 6 and the B-substrate 7 to form an air gap layer 8.

[0048] like Figure 2 Figure 1 shows the coupling diagram of the BGA-GWG resonant cavity and the source end microstrip line in the 14 GHz microwave oscillator. The specific structural dimensions are: L1 = 35 mm, d1 = 0.5 mm, d2 = 4.7 mm.

[0049] Figure 3 and Figure 4 This is the output spectrum and output phase noise simulation result diagram of the microwave oscillator of the present invention. It can be observed that the output frequency can reach 13.98 GHz. When the output frequency is 14 GHz, the phase noise is -105.1 dBc / Hz at the offset frequency of 100 kHz, and the phase noise is -125.1 dBc / Hz at the offset frequency of 100 kHz.

[0050] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0051] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A microwave oscillator based on a BGA-GWG resonant cavity, characterized in that: It includes an oscillating circuit, a BGA-GWG resonant cavity and a source-end microstrip line (1); The oscillation circuit uses a field effect transistor as an active device, wherein the gate of the field effect transistor is connected in series with an ohmic microstrip line (4); the drain is connected to one end of a first series microstrip line and a parallel open microstrip line (5), and the other end of the first series microstrip line and the parallel open microstrip line (5) is an oscillator output end; the source is connected to one end of a second series microstrip line and a parallel open microstrip line (3), and the other end of the second series microstrip line and the parallel open microstrip line (3) is an oscillator source end, which is connected to the source end microstrip line (1); the source and drain of the field effect transistor are connected to a DC voltage to provide a static operating point of the field effect transistor; The BGA-GWG cavity is a GWG cavity based on BGA flip-chip technology, which is coupled next to the source end microstrip line (1); The source end and the output end of the oscillator realize impedance transformation through a first series microstrip line and a parallel open microstrip line (5) and a second series microstrip line and a parallel open microstrip line (3); The BGA-GWG resonant cavity comprises a T-substrate (6), a B-substrate (7), and a BGA solder ball (2) between the T-substrate (6) and the B-substrate (7), and the T-substrate (6) is assembled on the B-substrate (7) by a flip-chip technology, and the BGA solder ball (2) supports the T-substrate (6) and the B-substrate (7) to form an air gap layer (8). In the BGA-GWG resonant cavity, each BGA solder ball (2), the T-substrate (6) portion directly above it, the B-substrate (7) portion directly below it, and the air gap layer (8) portion constitute a BGA periodic unit. The central part of the BGA-GWG resonant cavity is a resonant region, and a 4×4 BGA periodic unit is removed near the oscillator source end for electromagnetic coupling between the resonant cavity and the source end microstrip line (1).

2. The microwave oscillator based on the BGA-GWG resonant cavity according to claim 1, characterized in that: The field effect transistor is a gallium arsenide field effect transistor.

3. The microwave oscillator based on the BGA-GWG resonant cavity according to claim 1, characterized in that: The microstrip lines are all 50-ohm microstrip lines.

4. The microwave oscillator based on the BGA-GWG resonant cavity according to claim 3, characterized in that: The lower surfaces of the T-substrate (6) and the B-substrate (7) are both covered with metal.

Images