A compact microwave pulse compression dispersion system with coaxial structure

Abstract

The present invention relates to a compact microwave pulse compression dispersion system with a coaxial structure, comprising: a feeding end for matching the different port cross sections of a pulse signal source and a pulse compression end and obtaining a pulse signal; a pulse compression end for transmitting the pulse signal through a working mode TEM and a high-order mode TE. m,1 The coupling of spatial harmonics forms a special dispersion characteristic, and uses the dispersion characteristic to compress the input pulse signal in the time domain; the output end is used to match the different port cross-sections of the pulse compression end and the load end and output the narrow pulse signal after pulse compression; wherein the feed end, the pulse compression end and the output end all include: an inner conductor, the inner conductor is nested inside the hollow outer conductor, the central axis of the outer conductor overlaps the central axis of the inner conductor, and the inner surface of the outer conductor or the outer surface of the inner conductor is provided with spiral corrugations. The present invention has the advantages of few components, compact structure, and easy system integration, and can be used to achieve high-efficiency microwave frequency band pulse compression.

Description

Technical Field

[0001] The invention relates to the technical field of microwave pulse compressors, and in particular to a compact microwave pulse compression dispersion system with a coaxial structure. Background Art

[0002] Microwave pulse compressor is a very important device in the field of microwave technology. It can compress long microwave pulses with relatively low power and convert them into narrow pulses with relatively high power. The narrow pulse microwave signal obtained by pulse compression has higher time resolution, greater signal energy density and shorter time domain duration, which is of great significance for improving the performance and accuracy of signal processing systems, and enhancing the penetration and anti-interference capabilities of signals. At present, microwave pulse compressors are widely used in radar, wireless communication, accelerator and other systems. For example, in radar systems, microwave pulse compressors can improve the resolution and target detection capabilities of radars, while reducing the observation time of dynamic targets by the system, thereby improving the performance and efficiency of radar systems; in communication systems, microwave pulse compressors can be used to improve the transmission rate and spectrum efficiency of communication signals, while reducing the distortion and attenuation of signals during transmission, thereby improving the reliability and performance of communication systems; in remote sensing applications, microwave pulse compressors can be used to improve the resolution and clarity of remote sensing images, while enhancing the recognition and monitoring capabilities of ground features, thereby improving the monitoring and detection capabilities of remote sensing systems.

[0003] Existing microwave pulse compressors can be divided into two categories, active and passive, based on the way they achieve pulse compression. Among them, active pulse compressors contain tunable elements whose states or parameters change over time, such as switches or phase modulation devices. The advantages of this type of pulse compressor are higher peak power and compression gain, but due to the need for additional tuning control circuits, the structure of the active pulse compression system is relatively complex and the cost is relatively high. In addition, this type of structure is generally suitable for compression of quasi-monochromatic wave signals as input pulses. In contrast, the passive pulse compressor has a simpler structure, and its core is a dispersion system that is not time-dependent. Its working principle is mainly based on the dispersion effect of microwave signals of different frequencies when transmitted in a dispersion structure, that is, microwave signals of different frequencies have different propagation speeds (group velocities) in a dispersion system. Based on this characteristic, a frequency-modulated pulse whose group velocity increases with time can be input into the dispersion system. At this time, from the perspective of the input port of the dispersion system, the group velocity of the signal injected first is small, and the group velocity of the signal injected later is large. Therefore, during the transmission process, the signal injected later will catch up with the signal in front due to its fast propagation speed. Under the conditions that the dispersion structure length and the frequency modulation parameters of the pulse are set appropriately, signals of different frequency components will arrive at the exit of the dispersion structure at the same time, thereby shortening the signal pulse and doubling the power.

[0004] From the principle of passive microwave compressor, we can know that the dispersion structure is the key component to realize passive microwave pulse compression. At present, there are many types of dispersion structures used in passive microwave pulse compressors, such as resonant cavity, quasi-optical cavity, regular waveguide, plasma-loaded waveguide and periodic dielectric-loaded waveguide. These dispersion structures differ in terms of structural complexity. Among them, the dispersion structure using the resonant cavity requires the addition of a mode converter and a polarizer between the input end and the cavity, which not only increases the complexity of the structure, but also has additional coupling losses; the dispersion structure of the quasi-optical cavity requires the precise arrangement of multiple reflective mirrors, and has high requirements for processing and optical path control; the dispersion structure loaded with plasma requires the addition of plasma generation and control mechanisms, which is the most difficult to implement; the periodic dielectric-loaded waveguide requires the addition of a periodically arranged dielectric waveguide, and the structure is also relatively complex; and the regular waveguide (generally a rectangular waveguide or a circular waveguide) is the simplest and easiest way to implement.

[0005] In practical applications, in order to reduce transmission loss and improve pulse compression efficiency, the working point needs to be selected in the strong dispersion region where the group velocity changes rapidly with the working frequency. According to waveguide theory, the strong dispersion region of a regular waveguide is near its cutoff frequency. When the working frequency is higher than the cutoff frequency, the group velocity of the working mode will gradually increase with the increase of frequency, but the change will gradually slow down. In theory, the optimal working area for pulse compression using a regular waveguide should be near the cutoff frequency of the regular waveguide, but when working near the cutoff frequency, there will be a strong reflection problem of the incident wave, resulting in low compression efficiency. Although the reflectivity of the high-frequency region far away from the cutoff is low, the group velocity changes slowly in this region. If this region is selected as the compression working area, a very long regular waveguide is required to obtain a higher compression gain. The resulting high ohmic loss will also lead to a deterioration in compression efficiency. In summary, although the regular waveguide has a simple structure, it is difficult to achieve high-performance microwave pulse compression due to the above-mentioned limitations.

[0006] In order to overcome the strong reflection of regular waveguides near the cutoff frequency, the prior art proposes an improved structure based on circular waveguides to achieve pulse compression. This structure is a spiral corrugated circular waveguide, which is based on a regular metal circular waveguide and is achieved by etching shallow spiral corrugations on the inner wall of the waveguide, such as Figure 1 As shown. In fact, this spiral corrugated circular waveguide belongs to a periodic structure, which is periodic in both the circumferential direction and the axial direction. According to Floquet's theorem, a series of spatial harmonics will be formed when the electromagnetic mode is transmitted in a periodic structure. Under the condition of appropriate working parameter settings, different modes can obtain phase synchronization through each other's spatial harmonics and thereby produce mutual coupling. The new eigenmode formed by coupling can enable the spiral corrugated waveguide to obtain dispersion characteristics different from those of the regular waveguide. Based on this principle, by properly designing the working parameters, the spiral corrugated waveguide can form a strong dispersion zone where the group velocity changes rapidly with the frequency in the working area far away from the cutoff, thereby solving the problem that it is difficult for regular waveguides to have both strong dispersion and low reflection.

[0007] Since the concept of spiral corrugated circular waveguide as a dispersion structure was proposed, research institutions in many countries have studied its application in microwave pulse compressors, focusing mainly on the optimization of working modes and spiral corrugation parameters. The spiral corrugated circular waveguide dispersion structure proposed in the prior art uses the lowest-order TE1,1 mode of the circular waveguide as the incident wave, and couples this mode with the higher-order TE-2,1 mode to form the dispersion curve required for pulse compression. For this purpose, a three-fold spiral corrugation (the number of periods of the spiral corrugation in the circumferential direction is 3) is introduced to match the above-mentioned coupling mode combination. In subsequent actual measurements, it was found that the structure can compress a wide pulse with an average power of 5.6kW and 80ns into a short pulse with an average power of 140kW and 1.5ns, with a compression gain of 25. Due to the small average radius of the structure, the power capacity is relatively small. Then the existing technology improved the original spiral corrugated circular waveguide pulse compressor, using the high-order mode TE3,1 as the incident wave mode, the TE-2,2 mode as the coupling mode, and using a five-fold spiral corrugation to achieve the coupling of the above two modes. Finally, with the help of the above parameter combination, the average radius of the corrugated waveguide was increased to 2.2 times of the initial structure, which also brought a 7-fold increase in power capacity. In China, some research institutions have also conducted relevant research on spiral corrugated circular waveguide pulse compressors. For example, theoretical research and simulation analysis were conducted on spiral corrugated circular waveguide pulse compressors based on three-fold and five-fold.

[0008] Up to now, the spiral corrugated waveguide pulse compressors studied by scholars at home and abroad all adopt the spiral corrugated circular waveguide dispersion structure. Figure 2 (a)- Figure 2(b) is a physical picture of the five-fold spiral corrugated circular waveguide pulse compression system. As can be seen from the figure, a complete pulse compressor system is connected to multiple auxiliary components including polarizers, mode converters, and tapered waveguide transitions in addition to the spiral corrugated circular waveguide. This is because, in order for the spiral corrugated circular waveguide dispersion structure to work properly, it is necessary to inject a circularly polarized TE3,1 mode incident wave into it. This high-order circularly polarized TE3,1 mode cannot be generated directly. It is necessary to first convert the lowest-order linearly polarized TE1,1 mode into a circularly polarized TE1,1 mode. This process is completed by a polarizer composed of an elliptical waveguide segment; and then the circularly polarized TE1,1 mode output by the polarizer needs to be further converted into a circularly polarized TE3,1 mode. This process is completed by a mode converter composed of a spiral waveguide. In order to match the different waveguide radii of the polarizer, mode converter, and dispersion structure, a tapered circular waveguide with a gradually changing radius needs to be added between the polarizer and the mode converter and between the mode converter and the dispersion structure. In addition, in order to reduce the reflection between the spiral corrugated waveguide and the uniform waveguide, it is necessary to add transition sections at both ends of the mode converter and the dispersion structure, in which the structural cross section will smoothly change from a circular cross section to a spiral corrugated cross section. At the same time, in order to effectively output the compressed signal, a set of auxiliary components that are exactly the same as the input section needs to be symmetrically connected to the output section of the dispersion structure.

[0009] The addition of these auxiliary parts not only makes the overall structure of the compressor complicated, but also has the following key issues that affect the compression performance: 1) After all components including the dispersion structure are connected, the compressor will become very long, which not only brings a large ohmic loss to the transmission signal, resulting in a decrease in compression efficiency; and the structure is too long, which will make it difficult to miniaturize the device, greatly limiting the application of the compressor in practice; 2) In order to ensure the purity of the output mode of the spiral corrugated mode converter, only shallow corrugations with smaller amplitudes can be used. In this case, it is necessary to increase the length of the mode converter to improve the efficiency of mode conversion, but this also brings about the problem mentioned in 1). In fact, even if a sufficiently long mode converter is used, its conversion efficiency cannot reach 100% ( Figure 2 The mode conversion efficiency of the converter shown is about 95%), and the non-ideal conversion rate of the mode converter will not only reduce the pulse compression efficiency, but also affect the mode purity of the output signal; 3) Different components in the compressor are independently processed and then assembled. In order to ensure the performance of the overall system, all component size deviations are required to be controlled within a small range, and high processing accuracy is required; in addition, the large number of components also increases the difficulty of assembly, and the non-ideal connection between different component interfaces during assembly will introduce reflections and parasitic mode conversions, which will also affect the compression efficiency and mode purity. Summary of the invention

[0010] In view of the shortcomings of existing spiral corrugated circular waveguide pulse compressors, the present invention proposes a compact microwave pulse compression dispersion system with a coaxial structure. The system has the advantages of few components, compact structure, and easy system integration, and can be used to achieve high-efficiency microwave frequency band pulse compression.

[0011] To achieve the above object, the present invention provides the following solutions:

[0012] A compact microwave pulse compression dispersion system with a coaxial structure, comprising:

[0013] A feeding end, used to match the different port cross-sections of the pulse signal source and the pulse compression end and obtain the pulse signal;

[0014] A pulse compression end, used to form a special dispersion characteristic by coupling the spatial harmonics of the working mode TEM and the high-order mode TEm,1, and to compress the pulse signal in the time domain by using the dispersion characteristic;

[0015] An output end, used for matching the different port cross-sections between the pulse compression end and the load end and for outputting a narrow pulse signal after pulse compression;

[0016] Among them, the feeding end, the pulse compression end and the output end all include: an inner conductor, the inner conductor is nested in a hollow outer conductor, the central axis of the outer conductor overlaps with the central axis of the inner conductor, and the inner surface of the outer conductor or the outer surface of the inner conductor is provided with spiral corrugations.

[0017] Optionally, the inner surface of the outer conductor in the feeding end and the output end or the outer surface of the inner conductor is provided with non-uniform spiral corrugations, and the inner surface of the outer conductor in the pulse compression end or the outer surface of the inner conductor is provided with uniform spiral corrugations with constant amplitude.

[0018] Optionally, the feeding end and the output end are connected to the pulse compression end in a manner of superimposing a tapered waveguide with a gradually varying spiral corrugation.

[0019] Optionally, the spiral corrugation adopts a smooth profile including: sine, cosine, circular or arc.

[0020] Optionally, a dielectric is filled between the inner conductor and the outer conductor.

[0021] Optionally, a central coupling point of the spatial harmonics of the working mode TEM and the higher-order mode TEm,1 is set near the cutoff frequency of the reverse wave of the higher-order mode TEm,1.

[0022] Optionally, the coupling conditions include:

[0023] Coupling condition 1:

[0024] The number of spiral corrugations in the feeding end, the pulse compression end and the output end and the high-order mode TE m,1 The angular mode index satisfies:

[0025] m b =m

[0026] Among them, mb is the number of spiral corrugations, and m is the angular mode index;

[0027] Coupling condition 2:

[0028] Under the condition that the spatial harmonic phases of the working mode TEM and the high-order mode TEm,1 are synchronized, the propagation constant of the working mode TEM wave and the propagation constant of the high-order mode TEm,1 wave satisfy:

[0029] k0(f0)+k1(f0)=k b

[0030] Where k0 is the propagation constant of TEM wave, f0 is the coupling center frequency, k1 is the propagation constant of TEM wave, and k b =2π / p b , p b is the axial period of the spiral corrugation.

[0031] Optionally, the coupling condition also includes:

[0032] Coupling condition 3:

[0033] The ripple amplitude at the pulse compression end is smaller than the average radius of the conductor surface to which the ripple belongs;

[0034] Coupling condition 4:

[0035] The operating frequency of the pulse signal is set to be less than f c In the range of , the coupling center frequency f0 should satisfy:

[0036] f0<1.1f c

[0037] Among them, f c is the cutoff frequency of the higher-order mode TEm,1.

[0038] Optionally, the coupling condition also includes:

[0039] Coupling condition 5:

[0040] Setting the length of the pulse compression end to ensure that different frequency components of the pulse signal arrive at the output end at the same time;

[0041] Coupling condition 6:

[0042] A slope angle threshold is set, and the slope angle of the change of the average radius of the inner and outer conductors in the transition section between the feeding end and the output end is less than the slope angle threshold.

[0043] The beneficial effects of the present invention are:

[0044] The present invention proposes a compact microwave pulse compression dispersion system with a coaxial structure. Compared with the existing passive pulse compression system, the present invention has significant differences in both structure and working mechanism. It is these differences that bring better effects and obvious benefits to the present invention, which are mainly reflected in: 1) Compared with the pulse compression dispersion system based on uniform waveguide, the present invention uses the mode coupling induced by spiral corrugation to form a strong dispersion working area, and uses a tapered waveguide loaded with a transition section of non-uniform spiral corrugation to complete the input and output of the pulse signal, so that the signal can be compressed with a relatively short structure under smaller port reflection conditions. Therefore, the dispersion system proposed by the present invention has lower signal attenuation, which helps to improve the efficiency of pulse compression; 2) Compared with the pulse compression dispersion system based on spiral corrugated circular waveguide, the present invention adopts a coaxial structure The use of spiral corrugated waveguides to form the dispersion characteristics required for pulse compression can obtain two benefits. On the one hand, by using the TEM wave unique to the coaxial waveguide as the working mode, the polarizer, mode converter and tapered waveguide transition section connecting these devices in the circular waveguide dispersion system can be simplified, which greatly simplifies the dispersion system structure, not only reducing the difficulty of the dispersion system implementation and the cost of processing and assembly, but more importantly, reducing the intermediate links such as polarization and conversion of pulse signals that are not related to dispersion, thereby further improving the efficiency of pulse compression; on the other hand, the coaxial waveguide has two inner and outer conductors. In the parameter design process, the lateral size of the structure can be increased and the mode spectrum can be thinned (that is, the interval between the eigenmodes can be increased) by combining the appropriate parameters of the inner and outer conductors. This not only ensures the mode purity of the coupling process, but also gives the dispersion system a larger heat dissipation surface. This characteristic helps to improve the stability of the mode coupling of the dispersion system, and can also effectively improve the power capacity of the pulse compressor. By utilizing the above effects and benefits, the coaxial structure spiral corrugated waveguide dispersion system of the present invention is expected to provide a simpler, more compact and more efficient implementation solution for passive microwave pulse compression, thereby promoting performance improvement and innovative development in high-power microwave application fields such as radar, electronic countermeasures, remote sensing and telemetry, and physical property research. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0046] Figure 1 Schematic diagram of a spiral corrugated circular waveguide according to an embodiment of the present invention;

[0047] Figure 2 This is a physical picture of a five-fold spiral corrugated circular waveguide pulse compression system according to an embodiment of the present invention; wherein: Figure 2 (a) is a physical diagram of the overall connection relationship of the spiral corrugated circular waveguide pulse compressor. Figure 2 (b) is a schematic diagram of the components of the input dispersion system;

[0048] Figure 3 The schematic diagram of the overall structure of the coaxial compact microwave pulse compression dispersion system according to the embodiment of the present invention is shown in FIG. Figure 3 (a) Schematic diagram of the connection relationship between the pulse compression end, the feeding end, and the output end transition section formed by the uniform spiral corrugated coaxial waveguide in the dispersion structure; Figure 3 (b) is a schematic diagram of the longitudinal cross section of the outer conductor of the dispersion structure; Figure 3 (c) is a schematic diagram of the longitudinal cross section of the filler between the inner and outer conductors of the dispersion structure; Figure 3 (d) is a schematic diagram of the longitudinal cross section of the inner conductor of the dispersion structure;

[0049] Figure 4 The schematic diagram of the structure of the feed end transition section and its end surface in the coaxial structure compact microwave pulse compression dispersion system according to the embodiment of the present invention; wherein, Figure 4 (a) is a schematic diagram of the structure of the non-uniform spiral corrugated tapered coaxial waveguide constituting the transition section of the feeding end; Figure 4 (b) is a schematic diagram of the connection surface between the feed end transition section and the feed waveguide or connector; Figure 4 (c) is a schematic diagram of the connection surface of the pulse compression end formed by the feed end transition section and the uniform spiral corrugated coaxial waveguide;

[0050] Figure 5 The structure schematic diagram of the pulse compression end and its end surface composed of a uniform spiral corrugated coaxial waveguide in a coaxial structure compact microwave pulse compression dispersion system according to an embodiment of the present invention; wherein, Figure 5 (a) is a schematic diagram of the overall structure of a uniform spiral corrugated coaxial waveguide, i.e., the pulse compression end; Figure 5 (b) is a schematic diagram of the uniform spiral corrugated coaxial waveguide, i.e., the connecting surface of the transition section between the pulse compression end and the feeding end; Figure 5 (c) is a schematic diagram of the uniform spiral corrugated coaxial waveguide, i.e., the connecting surface of the transition section between the pulse compression end and the output end;

[0051] Figure 6 The structure diagram of the output end transition section and its end surface in the coaxial structure compact microwave pulse compression dispersion system according to the embodiment of the present invention; wherein, Figure 6(a) is a schematic diagram of the structure of the non-uniform spiral corrugated tapered coaxial waveguide constituting the transition section at the output end; Figure 6 (b) is a schematic diagram of the connection surface between the output end transition section and the uniform spiral corrugated coaxial waveguide, i.e., the pulse compression end; Figure 6 (c) is a schematic diagram of the connection surface between the output end transition section and the output end device or load;

[0052] Figure 7 is a schematic diagram of a dispersion curve of a uniform coaxial waveguide according to an embodiment of the present invention;

[0053] Figure 8 A schematic diagram of dispersion characteristics of a coaxial structure compact microwave pulse compression dispersion system according to an embodiment of the present invention;

[0054] Fig. 9 A schematic diagram of a curve showing the relationship between the group velocity of the working mode of the coaxial structure compact microwave pulse compression dispersion system and the frequency variation;

[0055] Among them, 1. feeding end, 2. pulse compression end, 3. output end, 4. outer conductor, 5. filler between inner and outer conductors, 6. inner conductor. DETAILED DESCRIPTION

[0056] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0058] The present invention discloses a compact microwave pulse compression dispersion system with a coaxial structure, comprising: a feeding end 1, used for matching the different port cross-sections of a pulse signal source and a pulse compression end and obtaining a pulse signal; a pulse compression end 2, used for forming a special dispersion characteristic by coupling a working mode TEM with the spatial harmonics of a high-order mode TEm,1, and performing pulse compression on the pulse signal in the time domain by using the dispersion characteristic; an output end 3, used for matching the different port cross-sections of the pulse compression end and a load end and outputting a narrow pulse signal after pulse compression; wherein the feeding end 1, the pulse compression end and the output end all comprise: an inner conductor 6, the inner conductor 6 is nested inside a hollow outer conductor, the central axis of the outer conductor 4 overlaps with the central axis of the inner conductor 6, and the inner surface of the outer conductor 4 or the outer surface of the inner conductor 6 is provided with a spiral corrugation, specifically:

[0059] The coaxial structure compact microwave pulse dispersion system proposed in the present invention is composed of a section of uniform spiral corrugated coaxial waveguide and two sections of non-uniform spiral corrugated tapered coaxial waveguide transition sections, wherein the uniform spiral corrugated coaxial waveguide is the core of the compressor dispersion system, and its two ends are respectively connected to the transition sections of the feed end 1 and the output end 3. The uniform spiral corrugated coaxial waveguide and the two sections of non-uniform spiral corrugated tapered coaxial waveguide transition sections are both coaxial structure waveguides containing inner and outer double conductors, wherein the inner conductor 6 and the outer conductor 4 have the same axial length, the inner conductor 6 is nested inside the hollow outer conductor, the central axis of the outer conductor 4 overlaps with the central axis of the inner conductor 6, and the filler 5 between the inner and outer conductors can be filled with air or other dielectrics.

[0060] The inner surface of the outer conductor 4 or the outer surface of the inner conductor 6 in the feed end 1 and the output end 3 is provided with non-uniform spiral corrugations, and the inner surface of the outer conductor 4 or the outer surface of the inner conductor 6 in the pulse compression end is provided with uniform spiral corrugations with constant amplitude. Specifically, the uniform spiral corrugated coaxial waveguide in the new dispersion system proposed by the present invention has uniform spiral corrugations with constant amplitude on the inner surface of the outer conductor 4 or the outer surface of the inner conductor 6, and these corrugations must have periodicity in two dimensions, the circumferential direction and the axial direction. Theoretically, the contour of the spiral corrugation on the longitudinal section can be any shape, but in order to improve the power capacity of the system and avoid ionization breakdown in high-power occasions, a smooth contour should be used as much as possible, such as sine / cosine, circular or arc-shaped. The transition sections of the feed end 1 and the output end 3 of the new dispersion system are both composed of non-uniform spiral corrugated conical coaxial waveguides, and the spiral corrugation introduction method of the two transition sections should be the same as the corrugation introduction method of the uniform spiral corrugated coaxial waveguide, that is, the inner surface of the outer conductor 4 or the outer surface of the inner conductor 6. In practical applications, the feed end 1 transition section is used to match the connection between the dispersion system and the feed waveguide / connector that provides the input pulse. The cross section of the connection between the feed waveguide / connector and the feed waveguide / connector is the annular cross section of a regular coaxial waveguide, and its size is the same as the transverse cross section size of the feed waveguide / connector. The output end 3 transition section is used to match the connection between the dispersion system and the output end device or load. The cross section of the connection between the output end device or load is also the annular cross section of a regular coaxial waveguide, and its size is the same as the transverse cross section size of the actual device or load connector. After a certain length along the axial direction, the transverse cross section of the feed end 1 and the output end 3 transition sections smoothly changes from the annular cross section of the regular coaxial waveguide at one end to the corrugated profile cross section of the uniform spiral corrugated coaxial waveguide. The gradual change mode can be linear or nonlinear such as a quadratic curve as the axial position changes.

[0061] The feed end 1 and the output end 3 are connected to the pulse compression end by means of a tapered waveguide superimposed with a gradient spiral corrugation. Specifically, the main reason for the lengthy structure of the traditional spiral corrugated circular waveguide dispersion system is the addition of paired polarizers, mode converters, tapered waveguide transitions and other auxiliary components. In fact, the addition of these components is determined by the working mechanism of the spiral corrugated circular waveguide dispersion system. According to the coupled mode theory, the mode coupling induced by the spiral corrugations in the circular waveguide can only be established between the eigenmodes of circular polarization. The eigenmodes of the circular waveguide are only TE modes or TM modes. These modes are generally not directly available and need to be converted through a mode converter (if higher-order modes are required, multiple conversions are required). At the same time, a polarizer is required to obtain the circular polarization state required for coupling.

[0062] In order to overcome the limitations of the working mechanism of the existing spiral corrugated circular waveguide dispersion system, the new dispersion system proposed in the present invention adopts the main mode TEM of the coaxial waveguide as the working mode of the incident wave. The main basis for this parameter setting is: the TEM mode is the lowest-order mode of the coaxial waveguide, which can be transmitted in the coaxial waveguide of any structure, and TEM is also the most common output mode of most microwave signal sources. Therefore, using TEM as the working mode can make the new dispersion system proposed in the present invention directly match the output signal of the microwave signal source, and there is no need to connect a mode converter between the two. At the same time, according to microwave theory, TEM is a circularly symmetric mode and there is no rotation effect, so the new dispersion system proposed in the present invention does not need to be connected to a polarizer. Since the mode converter and polarizer are simplified, the tapered waveguide originally introduced to match the different cross-sections of the ports of these two auxiliary components can also be cut accordingly. Considering that in actual applications, there are still differences between the feeding port for inputting pulse signals to the new dispersion system and the device or load port connected to the output end 3 of the dispersion system and the two lateral end faces of the corrugation profile of the uniform spiral corrugated coaxial waveguide in the new dispersion system. Therefore, the present invention adopts a tapered waveguide superimposed with a gradient spiral corrugation to construct a transition section between the feeding end 1 and the output end 3 of the new dispersion system, thereby reducing the reflection of the input end 1 and the output end 3 of the new dispersion system with a structure that is as short as possible.

[0063] According to the working mechanism of passive microwave pulse compression, the dispersion system must be able to make the incident wave mode produce a group velocity that increases or decreases monotonically with the increase of frequency within the working frequency range. For a regular coaxial waveguide, the phase velocity of the TEM wave when it is transmitted inside it has nothing to do with the frequency, and only depends on the dielectric constant and magnetic permeability of the medium inside the waveguide. Therefore, when the waveguide is filled with a uniform medium, the TEM wave of the regular waveguide has no dispersion effect.

[0064] The novel dispersion system proposed by the present invention has spiral corrugations introduced on the surface of the outer conductor 4 or the inner conductor 6. The two-dimensional periodic boundary formed by the spiral corrugations has two effects on the electromagnetic waves transmitted inside the waveguide: on the one hand, the two-dimensional periodic boundary causes all coaxial waveguide eigenmodes to generate spatial harmonics. Assuming that the axial period length of the spiral corrugations is pb, the propagation constants between different spatial harmonics of the same eigenmode will differ by an integer multiple of kb (=2π / pb); on the other hand, under the influence of the uneven waveguide boundary generated by the spiral corrugations, spatial harmonics of different modes can be mutually coupled under the condition of phase synchronization. Therefore, under the condition of appropriate parameters, the TEM mode can be coupled with the higher-order mode by means of the spiral corrugations, thereby changing the dispersion characteristics of the TEM mode. Based on this principle, the novel dispersion system proposed by the present invention adopts the higher-order mode TEm,1 (TE mode with an angular mode index of m and a radial index of 1) as the coupling mode, and forms the dispersion characteristics required for pulse compression by coupling the working mode TEM with the spatial harmonics of TEm,1. Among the series of spatial harmonics of the working modes TEM and TEm,1, the amplitudes of the 0th and 1st spatial harmonics are the strongest. If the phase velocities of the 0th spatial harmonic of TEM and the 1st spatial harmonic of TEm,1 can be nearly equal, then the two modes can obtain the phase synchronization condition for coupling. At the same time, in order to make the eigenmode generated by coupling form a group velocity that monotonically increases / decreases with frequency, the coupling point should be set at the high-order mode TE m,1 Near the cutoff frequency of the reverse wave.

[0065] According to the above principles, the structure and operating parameters of the novel dispersion system proposed in the present invention should meet the following conditions: 1) In order to match the working modes TEM and TE m,1 The coupling, the uniform spiral corrugated coaxial waveguide in the dispersion structure and the spiral corrugation number m in the transition section connecting the two ends b With high-order mode TE m,1 The angular mode index m should satisfy m b =m, where m is a non-zero integer; 2) At the coupling center frequency f0 that satisfies the phase synchronization condition, the propagation constant k0 of the TEM wave is equal to TE m,1 The wave propagation constant k1 must satisfy k0(f0)+k1(f0)=k b ; 3) The corrugation amplitude of the uniform spiral corrugated coaxial waveguide should be much smaller than the average radius of the conductor surface to which the corrugation belongs, that is, the spiral corrugation amplitude on the inner surface of the outer conductor should be much smaller than the average radius of the inner surface of the outer conductor, and the spiral corrugation on the inner conductor surface should be much smaller than the average radius of the outer surface of the inner conductor; 4) Assume that the high-order mode TE m,1 The cut-off frequency is f c , the coupling center frequency should satisfy f0<1.1f c At the same time, the input pulse signal operating frequency should be set at less than fc 5) The length of the uniform spiral corrugated coaxial waveguide section (the number of spiral corrugation periods included) depends on the input pulse parameters. The design principle is to allow different frequency components of the input pulse to reach the output end 3 of the uniform corrugated waveguide at the same time as much as possible; 6) The slope angle of the average radius change of the inner conductor 6 and the outer conductor 4 in the transition section should be as small as possible. Less than 5° to reduce parasitic mode conversion.

[0066] Figure 3 The figure is a schematic diagram of the overall structure of the coaxial compact microwave pulse compression dispersion system proposed in the present invention. The structure adopts a method of introducing a spiral corrugation on the inner surface of the outer conductor. The number of folds of the introduced spiral corrugation in the circumferential direction is 3, and its longitudinal profile is a cosine shape, wherein: Figure 3 (a) Schematic diagram of the connection relationship between the uniform spiral corrugated coaxial waveguide in the dispersion structure, i.e., the pulse compression end 2 and the feed end 1 and the transition section between the output end 3;

[0067] Figure 3 (b) is a longitudinal cross section of the outer conductor 4 of the dispersion structure; Figure 3 (c) is a longitudinal cross section of the filler 5 between the inner conductor 6 and the outer conductor 4 of the dispersion structure; Figure 3 (d) is a longitudinal cross section of the dispersion structure inner conductor 6.

[0068] Figure 4 It is a schematic structural diagram of a transition section and an end surface of a feed end 1 in a coaxial structure compact microwave pulse compression dispersion system proposed by the present invention, wherein: Figure 4 (a) is a schematic diagram of the structure of the non-uniform spiral corrugated tapered coaxial waveguide constituting the transition section of the feed end 1; Figure 4 (b) is a schematic diagram of the connection surface between the transition section of the feeding end 1 and the feeding waveguide or connector; Figure 4 (c) Schematic diagram of the connection surface between the transition section of the feeding end 1 and the uniform spiral corrugated coaxial waveguide section, i.e., the pulse compression end 2.

[0069] Figure 5 This is a schematic diagram of the structure of the core structure of the coaxial structure compact microwave pulse compression dispersion system proposed by the present invention, namely, the uniform spiral corrugated coaxial waveguide, namely, the pulse compression end 2 and its end face, wherein: Figure 5 (a) is a schematic diagram of the overall structure of the uniform spiral corrugated coaxial waveguide, i.e., the pulse compression end 2; Figure 5 (b) is a schematic diagram of the connection surface of the transition section between the uniform spiral corrugated coaxial waveguide, i.e. the pulse compression end 2 and the feeding end 1; Figure 5 (c) is a schematic diagram of the connection surface of the transition section between the uniform spiral corrugated coaxial waveguide, i.e. the pulse compression end 2 and the output end 3.

[0070] Figure 6The present invention provides a schematic diagram of the structure of the output end 3 transition sections and their end faces in the coaxial structure compact microwave pulse compression dispersion system, wherein: Figure 6 (a) is a schematic diagram of the structure of the non-uniform spiral corrugated tapered coaxial waveguide constituting the 3 transition sections at the output end; Figure 6 (b) is a schematic diagram of the connection surface between the transition section of the output end 3 and the uniform spiral corrugated coaxial waveguide, i.e., the pulse compression end 2; Figure 6 (c) is a schematic diagram of the connection surface between the transition section at the output end 3 and the output end device or load.

[0071] The uniform spiral corrugated waveguide, i.e., the pulse compression end 2, involved in the specific embodiment of the present invention is constructed as follows: Figure 5 As shown. According to the above-mentioned parameter design principle, the parameter scheme of the structure is as follows: the average radius of the inner wall of the outer conductor 4 is 20mm, the longitudinal cross section of the outer conductor 4 surface is etched with a cosine-shaped spiral corrugation, the amplitude of the spiral corrugation is 2mm, the number of folds is 3, the axial period length is 25.17mm, and the rotation direction is right-handed; the inner conductor 6 is a regular cylindrical conductor with a smooth surface and an average outer wall radius of 7mm; in order to reduce the loss, the material of the inner and outer conductors is copper; the filler 5 between the inner and outer conductors is air, and its relative dielectric constant is εr=1.0006, and the relative magnetic permeability μr is about 1; the working mode (incident wave) is TEM, and the coupling mode used to change the dispersion characteristics of the working mode is TE3,1.

[0072] In order to facilitate analysis and comparison, Figure 7 A dispersion curve of a uniform coaxial waveguide with a smooth inner surface is given. The radius of the inner wall of the outer conductor of the uniform waveguide is taken as the average radius of the inner wall of the outer conductor of the uniform spiral corrugated waveguide, i.e., the pulse compression end 2 involved in the embodiment of the present invention (i.e., 20 mm), and the radius of the outer wall of the inner conductor is taken as the average radius of the outer wall of the inner conductor of the uniform spiral corrugated waveguide, i.e., the pulse compression end 2 involved in the embodiment of the present invention (i.e., 7 mm). It can be seen from the figure that in the absence of a spiral corrugated boundary, the TEM and TE3,1 modes are independent of each other and there is no coupling. The dispersion curve of the TEM mode is a straight line with a constant slope and a group velocity close to the speed of light c, indicating that the TEM mode of the uniform coaxial waveguide with a smooth inner surface has no dispersion effect.

[0073] Figure 8It is a dispersion relation curve of a specific embodiment of the coaxial structure compact microwave pulse compression dispersion system of the present invention. The dotted line in the figure is the dispersion curve of the 0th harmonic of TEM and the 1st harmonic of TE3,1 when not coupled, and the solid line is the dispersion curve of the new eigenmode formed by coupling. It can be seen from the figure that: near the cutoff frequency of TE3,1, the 0th harmonic of TEM and the 1st harmonic of TE3,1 obtain phase synchronization conditions to produce strong coupling, and two new eigenmodes are formed by coupling, namely LE located in the low frequency band and HE located in the high frequency band. Among them, the dispersion curve of the LE mode approaches the dispersion curve of the 0th harmonic of TEM when it is not coupled in the low frequency region, and gradually begins to deviate and gradually approaches the dispersion curve of the 1st harmonic of TE3,1 mode when it is not coupled near the coupling center frequency. Near the coupling center frequency, the LE mode dispersion curve is significantly bent, resulting in a large change in the slope, indicating that the specific embodiment of the present invention exhibits a strong dispersion effect at this coupling frequency, and therefore can meet the requirements of microwave pulse compression. Moreover, the strong dispersion region of the LE mode is far away from the cutoff frequency of the HE mode, so the HE mode will not be excited when working in this region, thereby ensuring the stability of the working mode and overcoming the strong reflection problem caused by the regular waveguide dispersion structure when working near the cutoff frequency.

[0074] Fig. 9 A distribution curve of the group velocity of the low-frequency band LE mode near the center coupling frequency of a specific embodiment of the coaxial structure compact microwave pulse compression dispersion system of the present invention is given, and the vertical axis variable group velocity of the curve is normalized with the speed of light c. It can be seen from the figure that when the operating frequency increases from 8.0GHz to 9.84GHz, the group velocity decreases from 0.98c to 0.001c. Therefore, when the frequency of the input wide pulse signal decreases with time, its group velocity will increase with time (that is, from the time domain point of view, the speed of the signal input in front is slow, and the speed of the signal input in the back is fast); after a period of transmission, the signal input in the back will catch up with the signal input in the front, so that the pulse width continues to narrow during the transmission process. Therefore, by selecting a suitable dispersion structure length, high-gain compression can be achieved. It should be pointed out that Fig. 9 The group velocity of the working mode can be continuously changed from close to the speed of light c to approaching 0, and has a larger dynamic range of group velocity change compared to the spiral corrugated circular waveguide dispersion structure. Therefore, under the same conditions, the specific embodiment of the present invention can achieve pulse compression with the same gain with a shorter structure length, thereby improving the efficiency of pulse compression with lower signal attenuation.

[0075] The above embodiments are only descriptions of the preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the protection scope determined by the claims of the present invention.

Claims

1. A compact microwave pulse compression dispersion system with a coaxial structure, characterized in that: include: A feeding end, used to match the different port cross-sections of the pulse signal source and the pulse compression end and obtain the pulse signal; A pulse compression end, used to form a special dispersion characteristic by coupling the spatial harmonics of the working mode TEM and the high-order mode TEm,1, and to compress the pulse signal in the time domain by using the dispersion characteristic; Among them, TEM is the main mode using coaxial waveguide, TEm,1 is the TE mode with angular mode index m and radial index 1, and TE mode is the eigenmode of circular waveguide; An output end, used for matching the different port cross-sections between the pulse compression end and the load end and for outputting a narrow pulse signal after pulse compression; Wherein, the feeding end, the pulse compression end and the output end all include: an inner conductor, the inner conductor is nested inside a hollow outer conductor, the central axis of the outer conductor overlaps with the central axis of the inner conductor, and the inner surface of the outer conductor or the outer surface of the inner conductor is provided with spiral corrugations; The inner surface of the outer conductor in the feeding end and the output end or the outer surface of the inner conductor is provided with non-uniform spiral corrugations, and the inner surface of the outer conductor in the pulse compression end or the outer surface of the inner conductor is provided with uniform spiral corrugations with constant amplitude; The feeding end and the output end are connected to the pulse compression end in a manner of superimposing a tapered waveguide with a gradually changing spiral corrugation.

2. The compact microwave pulse compression dispersion system of coaxial structure according to claim 1, characterized in that: The spiral corrugation adopts a smooth profile including: sine, cosine, circular or arc.

3. The compact microwave pulse compression dispersion system of coaxial structure according to claim 1, characterized in that: A dielectric is filled between the inner conductor and the outer conductor.

4. The compact microwave pulse compression dispersion system of coaxial structure according to claim 1, characterized in that: The central coupling point of the spatial harmonics of the working mode TEM and the high-order mode TEm,1 is set near the cutoff frequency of the reverse wave of the high-order mode TEm,1.

5. The compact microwave pulse compression dispersion system with a coaxial structure according to claim 4, characterized in that: The coupling conditions include: Coupling condition 1: The number of spiral corrugations in the feeding end, the pulse compression end and the output end and the high-order mode TE m,1 The angular mode index satisfies: m b =m Among them, mb is the number of spiral corrugations, and m is the angular mode index; Coupling condition 2: Under the condition that the spatial harmonic phases of the working mode TEM and the high-order mode TEm,1 are synchronized, the propagation constant of the working mode TEM wave and the propagation constant of the high-order mode TEm,1 wave satisfy: k0(f0)+k1(f0)=k b Where k0 is the propagation constant of TEM wave, f0 is the coupling center frequency, k1 is the propagation constant of TEM wave, and k b =2π / p b , p b is the axial period of the spiral corrugation.

6. The compact microwave pulse compression dispersion system of coaxial structure according to claim 5, characterized in that: The coupling conditions also include: Coupling condition 3: The ripple amplitude at the pulse compression end is smaller than the average radius of the conductor surface to which the ripple belongs; Coupling condition 4: The operating frequency of the pulse signal is set to be less than f c In the range of , the coupling center frequency f0 should satisfy: f0<1.1f c Among them, f c is the cutoff frequency of the higher-order mode TEm,1.

7. The compact microwave pulse compression dispersion system with a coaxial structure according to claim 4, characterized in that: The coupling conditions also include: Coupling condition 5: Setting the length of the pulse compression end to ensure that different frequency components of the pulse signal arrive at the output end at the same time; Coupling condition 6: A slope angle threshold is set, and the slope angle of the change of the average radius of the inner and outer conductors in the transition section between the feeding end and the output end is less than the slope angle threshold.

Images