Nonlinear transmission line frequency comb generator based on step capacitor and application thereof

Abstract

The invention discloses a non-linear transmission line frequency comb generator based on a step capacitor and application of the non-linear transmission line frequency comb generator. The non-linear transmission line frequency comb generator comprises a transmission line and a selected capacitor device, the selected capacitor device is periodically loaded in a transmission path of the transmission line, and the selected capacitor device has a step capacitance characteristic. The nonlinear transmission line frequency comb generator based on the step or quasi-step capacitor provided by the invention can keep stable frequency multiplication efficiency under high input power, and can continuously increase the power of an output frequency comb by increasing the power of an input fundamental wave; the problems that the frequency multiplication efficiency of a traditional * DV nonlinear transmission line frequency comb generator is reduced along with the increase of the input power, and a high-power output frequency comb is difficult to obtain are solved.

Description

Technical Field

[0001] The present invention relates to the technical fields of signal generators and micro-nano manufacturing technologies, and in particular, to a nonlinear transmission line frequency comb generator based on step capacitors and its applications. Background Art

[0002] A nonlinear transmission line (NLTL) frequency comb generator is a device composed of a transmission line and periodically loaded nonlinear elements thereon. By nonlinearly regulating the electromagnetic waves propagating on the NLTL, the waveform thereof is distorted, thereby generating a series of harmonics with equal frequency intervals. Since the frequency comb contains rich frequency information, it has significant advantages in fields such as broadband spectral analysis. In the microwave and terahertz bands, NLTL frequency comb generators are mainly fabricated based on GaAs Schottky Barrier Diodes (SBDs). Since the cut-off frequency of GaAs SBDs can reach the terahertz level, such nonlinear transmission lines usually have low losses and can output frequency combs with frequencies up to 600 GHz.

[0003] Currently, the main challenge faced by frequency comb generators is relatively low output power. Although GaAs NLTL frequency comb generators have shown low losses at low input powers, methods for significantly increasing the frequency comb power by further reducing losses or improving efficiency have approached their limits. Therefore, increasing the input power seems to be the only way to achieve higher-power frequency combs. However, affected by the nonlinear capacitance characteristics of GaAs SBDs, the frequency doubling efficiency of GaAs NLTLs often decreases at high input powers, which limits the possibility of increasing the output frequency comb power by increasing the input power. Therefore, the present invention aims to propose a novel frequency comb generator that not only has a high frequency doubling efficiency but also can maintain a stable frequency doubling efficiency at high input powers, thereby effectively solving the limitations in the prior art. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a nonlinear transmission line frequency comb generator based on step capacitors and its applications.

[0005] To achieve the foregoing invention purpose, the technical solutions adopted by the present invention include:

[0006] In a first aspect, the present invention provides a nonlinear transmission line frequency comb generator based on step capacitors, which includes a transmission line and a selected capacitor device. The selected capacitor device is periodically loaded in the transmission path of the transmission line, and the selected capacitor device has step capacitance characteristics.

[0007] In a second aspect, the present invention also provides an application of the above-mentioned nonlinear transmission line frequency comb generator in the fields of broadband spectral analysis, industrial non-destructive testing, 6G communication, and microwave-terahertz test equipment.

[0008] Based on the above technical solutions, compared with the prior art, the beneficial effects of the present invention at least include:

[0009] The nonlinear transmission line frequency comb generator based on step or quasi-step capacitors provided by the present invention can maintain a stable frequency doubling efficiency at high input powers, and can continuously increase the power of the output frequency comb by increasing the power of the input fundamental wave, solving the problem that the frequency doubling efficiency of traditional GaAs nonlinear transmission line frequency comb generators decreases with the increase of input power, and it is difficult to obtain a high-power output frequency comb.

[0010] The above description is only an overview of the technical solutions of the present invention. In order to enable those skilled in the art to more clearly understand the technical means of the present application and implement it in accordance with the content of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the detailed drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 FIG. is a schematic diagram of the structure and equivalent circuit of a nonlinear transmission line frequency comb generator provided by a typical embodiment of the present invention;

[0012] Figure 2 FIG. is a schematic diagram of the step capacitor characteristics of a nonlinear transmission line frequency comb generator provided by a typical embodiment of the present invention;

[0013] Figure 3 FIG. is a schematic diagram of the waveform distortion process of a nonlinear transmission line frequency comb generator provided by a typical embodiment of the present invention;

[0014] Figure 4 FIG. is a graph showing the variation trend of the frequency doubling efficiency of a nonlinear transmission line frequency comb generator provided by a typical embodiment of the present invention with the input power;

[0015] Figure 5 FIG. is a schematic diagram of the capacitance characteristics of a capacitor device in a nonlinear transmission line frequency comb generator provided by a typical comparative example of the present invention;

[0016] Figure 6 FIG. is a graph showing the variation trend of the frequency doubling efficiency of a nonlinear transmission line frequency comb generator provided by a typical comparative example of the present invention with the input power. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] In view of the deficiencies in the prior art, the inventors of this case have proposed the technical solutions of the present invention through long-term research and a large number of practices. The following will further explain the technical solutions, their implementation processes, principles, etc.

[0018] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be practiced in other ways than those specifically described herein, and thus, the scope of protection of the present invention is not limited by the specific embodiments disclosed below.

[0019] Moreover, relational terms such as "first" and "second" are only used to distinguish one component or method step with the same name from another, and do not necessarily require or imply any actual relationship or order between these components or method steps.

[0020] See Figure 1 As shown, an embodiment of the present invention provides a nonlinear transmission line frequency comb generator based on a step capacitor, which includes a transmission line and a selected capacitor device. The selected capacitor device is periodically loaded in the transmission path of the transmission line, and the selected capacitor device has a step capacitor characteristic.

[0021] The present invention proposes a novel NLTL frequency comb generator, which is realized by periodically loading SBDs with a quasi-step form capacitance on the transmission line. The structure and equivalent circuit of each NLTL period unit are respectively as shown in the left and right small figures in Figure 1 . In the analysis of microwave and millimeter-wave circuits, the transmission line is usually equivalent to an LC circuit network. The SBD operates under reverse bias, and its capacitance characteristic is as shown in Figure 2 : when the reverse bias is greater than the threshold voltage (V th ), the capacitance value approaches zero; while when the reverse bias is less than the threshold voltage, the capacitance value is a constant value C B .

[0022] In some embodiments, the step capacitor characteristic means that the capacitance value of the selected capacitor device has a sudden change characteristic with the change of the reverse bias.

[0023] More specifically, in some embodiments, the step capacitor characteristic is specifically manifested as:

[0024] When the reverse bias applied to the selected capacitor device is greater than the threshold voltage, the capacitance value of the selected capacitor device is equal to or approaches zero; when the reverse bias is less than the threshold voltage, the capacitance value is equal to or approaches a constant value.

[0025] The periodic structure of the NLTL endows it with a low-pass characteristic. In some embodiments, the cut-off frequency of the nonlinear transmission line frequency comb generator is:

[0026]

[0027] where f Brag represents the cut-off frequency, and L TLrepresents the inductance value of the transmission line within one period, C TL represents the capacitance value of the transmission line within one period, C SBD represents the capacitance value of the selected capacitor device within one period.

[0028] For an input signal with a frequency of f0, after being multiplied in frequency by this NLTL, to ensure that the frequency multiplication efficiency of the frequency comb is not limited by the cutoff frequency of the NLTL, all harmonics should be within the lowest cutoff frequency range, that is: In some embodiments, the limiting condition of the nonlinear transmission line frequency comb generator is expressed as:

[0029]

[0030] where n is a natural number, f0 represents the harmonic number of the nonlinear transmission line frequency comb generator, represents the frequency of the input signal, C B represents the constant value.

[0031] In some embodiments, when the input signal propagates in the nonlinear transmission line frequency comb generator, the part of the input signal with a voltage lower than the threshold voltage has a first propagation speed, and the part of the input signal with a voltage higher than the threshold voltage has a second propagation speed, and the first propagation speed is faster than the second propagation speed.

[0032] In some embodiments, the propagation speed of the part of the input signal with a voltage lower than the threshold voltage is expressed as:

[0033]

[0034] The propagation speed of the part of the input signal with a voltage higher than the threshold voltage is expressed as:

[0035]

[0036] where v p represents the propagation speed, and d represents the physical length of the transmission line for each period.

[0037] As a typical example, the working principle of the nonlinear transmission line frequency comb generator provided by the present invention is: Refer to Figure 3 shown, the distortion process of the waveform of the electromagnetic wave in this NLTL. When the bias voltage is V th , sine waves with different powers will all be in two propagation states. The part of the waveform with a voltage lower than V th propagates at a relatively fast phase speed, while the part of the waveform with a voltage higher than V th propagates at a relatively slow phase speed. This phase speed difference causes the waveform of the electromagnetic wave propagating in the NLTL to be distorted, the rising edge to be stretched, and the falling edge to be shortened, and finally form as shown in Figure 3The sawtooth wave shown. Since this phase velocity difference is not affected by power changes at high power, increasing the amplitude of the input signal will cause the amplitude of the output waveform to increase linearly, ensuring the stability of the frequency comb doubling efficiency at high input power.

[0038] In practical applications, it is difficult to obtain an ideal step capacitor to fabricate the above NLTL frequency comb generator. However, the same purpose can be achieved through a quasi-step capacitor, that is, a certain bias voltage change is required to achieve a capacitance mutation. At this time, the input power needs to reach a threshold value so that the amplitude of the input signal is much larger than the voltage value required to cause the capacitance mutation, so as to make the efficiency of the NLTL reach stability, but this does not affect its doubling efficiency at high input power.

[0039] The SBDs based on GaN heterojunctions and GaAs heterojunctions both have a non-linear capacitance in the quasi-step form. Considering the high input power that the NLTL frequency comb generator can withstand, AlGaN / GaN SBD is currently the first choice for fabricating such NLTL frequency comb generators. That is: in some embodiments, the selected capacitor device is a Schottky barrier diode, and the Schottky barrier diode includes a Schottky barrier diode based on a GaN heterojunction and / or a Schottky barrier diode based on a GaAs heterojunction.

[0040] The second aspect of the embodiments of the present invention also provides an application of the non-linear transmission line frequency comb generator provided in any of the above embodiments in the fields of broadband spectral analysis, industrial non-destructive testing, 6G communication, microwave-terahertz test equipment, etc.

[0041] The technical solutions of the present invention will be further described in detail below through several embodiments in conjunction with the drawings. However, the selected embodiments are only used to illustrate the present invention and do not limit the scope of the present invention.

[0042] Example 1

[0043] Based on the above technical solutions, an embodiment of the present invention constructs an NLTL frequency comb generator based on a quasi-step capacitor. A quasi-step capacitor means that its capacitance value will not drop suddenly compared with a step capacitor, but some voltage changes are required.

[0044] Because it is not an ideal step capacitor, the efficiency will only be stable after the input power increases to a threshold value. Its frequency comb characteristics can be seen Figure 6 as shown. Taking AlGaN / GaN NLTL as an example, the stable input power is about 9 dBm.

[0045] Its key characteristic is that the efficiency is stable at high power, and the advantage is that increasing the input power will cause the output power to increase linearly.

[0046] Comparative Example 1

[0047] This comparative example uses a commercial GaAs NLTL (6273SM) frequency comb generator from Marki as a control. Figure 5 The capacitance of the conventional GaAs SBD shown in FIG. 1 changes continuously with voltage; the frequency doubling efficiency of the device changes with input power, as shown in FIG. Figure 6 As shown, the input power range given in its product manual is 16-26dBm, and the efficiency decreases as the power increases.

[0048] In addition, the inventors of the present invention also adjusted various parameters of the device in Example 1 and replaced them with capacitor devices made of other materials with equivalent characteristics, and observed the same frequency comb efficiency performance.

[0049] Based on the above embodiments and comparative examples, it can be clearly seen that the nonlinear transmission line frequency comb generator based on step or quasi-step capacitance provided in the embodiments of the present invention can maintain a stable frequency doubling efficiency under high input power, and can continuously increase the power of the output frequency comb by increasing the power of the input fundamental wave, thereby solving the problem that the frequency doubling efficiency of the traditional GaAs nonlinear transmission line frequency comb generator decreases with the increase of input power, making it difficult to obtain a high-power output frequency comb.

[0050] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A nonlinear transmission line frequency comb generator based on step capacitors, characterized in that It includes a transmission line and a selected capacitor device, the selected capacitor device is periodically loaded in the transmission path of the transmission line, and the selected capacitor device has a step capacitance characteristic.

2. The nonlinear transmission line frequency comb generator according to the claim, characterized in that The step capacitance characteristic means that the capacitance value of the selected capacitor device has a sudden change characteristic with the change of the reverse bias voltage.

3. The non-linear transmission line frequency comb generator according to the claim, characterized in that, The step capacitance characteristic is specifically manifested in: When the reverse bias voltage applied to the selected capacitor device is greater than the threshold voltage, the capacitance value of the selected capacitor device is equal to or approaches zero; when the reverse bias voltage is less than the threshold voltage, the capacitance value is equal to or approaches a constant value.

4. The nonlinear transmission line frequency comb generator according to the claim, characterized in that, The cut-off frequency of the non-linear transmission line frequency comb generator is: where, I ％UDJJ represents the cut-off frequency, / 7 / represents the inductance value of the transmission line within one period, & 7 / represents the capacitance value of the transmission line within one period, & 6％' represents the capacitance value of the selected capacitor within one period.

5. The non-linear transmission line frequency comb generator according to the claim, characterized in that, The limiting condition of the non-linear transmission line frequency comb generator is expressed as: Where Q is a natural number, I represents the harmonic number of the non-linear transmission line frequency comb generator, represents the frequency of the input signal, and & ％ represents the constant value.

6. The nonlinear transmission line frequency comb generator according to the claim, characterized in that, When the input signal propagates in the non-linear transmission line frequency comb generator, the part of the input signal with a voltage lower than the threshold voltage has a first propagation speed, and the part of the input signal with a voltage higher than the threshold voltage has a second propagation speed, and the first propagation speed is faster than the second propagation speed.

7. The nonlinear transmission line frequency comb generator according to the claim, characterized in that, The propagation speed of the part of the input signal with a voltage lower than the threshold voltage is expressed as: The propagation speed of the part of the input signal with a voltage higher than the threshold voltage is expressed as: Among them, Y S represents the propagation speed, and G represents the physical length of the transmission line per period.

8. The nonlinear transmission line frequency comb generator according to any one of claims 1-7, characterized in that, The selected capacitor device is a Schottky barrier diode.

9. The Schottky barrier diode includes a Schottky barrier diode based on the *D1 heterojunction and / or a Schottky barrier diode based on the *D$V heterojunction.

10. Application of the non-linear transmission line frequency comb generator according to any one of claims 1-9 in the fields of broadband spectral analysis, industrial non-destructive testing, *communication, microwave terahertz test equipment.

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