Ultra-wideband odd-harmonic mixer for spread spectrum and frequency spectrometer

Abstract

The application discloses an ultra-wideband odd harmonic frequency mixer for frequency spreading, and belongs to the technical field of planar harmonic frequency mixing, and comprises a first microstrip line, a Marchand balun, a first Schottky diode, a second Schottky diode, a matching circuit and a second microstrip line; the first microstrip line is located at a radio frequency input end and is connected with a non-balanced end of the Marchand balun, two balanced ends A and B of the Marchand balun are respectively connected with an anode of the first Schottky diode and a cathode of the second Schottky diode, the cathode of the first Schottky diode and the anode of the second Schottky diode are connected in sequence and are connected with the matching circuit and the second microstrip line in sequence, and the second microstrip line is connected with a local oscillator / intermediate frequency port. The harmonic frequency mixer can be directly used for frequency expansion of an existing mainstream frequency spectrometer, and the expansion range can cover the bandwidth of two to three standard waveguide frequency bands.

Description

Technical Field

[0001] This invention relates to the field of planar harmonic mixing technology, and more specifically to an ultra-wideband odd harmonic mixer for spread spectrum. Background Technology

[0002] As a crucial instrument for signal measurement, the spectrum analyzer plays an irreplaceable role in the microwave field. Keysight Technologies and Rohde & Schwarz are currently the major international suppliers of spectrum analyzers. The highest analysis frequency of the mainstream spectrum analyzers offered by these two companies is 50 GHz. The higher the operating frequency of the spectrum analyzer, the more expensive it is.

[0003] To meet users' needs for millimeter-wave and terahertz frequency band measurements, spectrum analyzers typically provide local oscillator (LO) and intermediate frequency (IF) interfaces for connecting external spread spectrum equipment (harmonic mixers) to extend the measurement frequency range of the spectrum analyzer. For example, Keysight Technologies' PXA series and Rohde & Schwarz's FSW series both provide a shared LO / IF spread spectrum SMA interface, compatible with dual-port harmonic mixers, providing 3.75–14.1 GHz and 7.65–17.45 GHz LO signals for spectrum spreading, respectively, while simultaneously receiving the IF signal output from the spread mixer. The RF signal input of spread spectrum equipment is generally a waveguide interface, and its operating frequency band is typically a standard waveguide band. For example, the WR-15 waveguide operates at 50–75 GHz, and the WR10 interface operates at 75–110 GHz, etc.

[0004] In the millimeter-wave band, the operating frequency of some microwave devices under test may span two standard waveguide bands, such as 55–85 GHz, or even exceed the bandwidth of one standard waveguide band, such as 50–90 GHz. In this case, traditional spectrum spreading devices cannot achieve ultra-wideband measurement on their own. Multiple spread spectrum devices with different frequency bands need to be used to measure the data in the corresponding frequency bands separately and then combine them, which greatly increases the complexity of the testing process.

[0005] In related technologies, Chinese invention patent application CN109818579A discloses a high-efficiency ultra-wideband frequency multiplier with harmonic mixing and amplification. It includes: a harmonic generator that receives a fundamental frequency signal and, according to the frequency band requirements of the frequency source, adjusts its operating region using an externally input regulating voltage to generate the maximum second, third, and fourth harmonics respectively; first to fourth filters connected to the output of the harmonic generator; a first RF switch and a first power amplifier connected in sequence; a first mixer; a second RF switch; a third RF switch and a second power amplifier connected in sequence; a fourth RF switch and a second mixer connected in sequence; and a fifth RF switch and a third power amplifier connected in sequence. By using active devices operating in the nonlinear region to generate harmonics, and employing multiple RF switches to amplify or mix each harmonic before synthesizing signals of the same frequency, high-efficiency wideband signal output is achieved. However, it can only achieve a maximum of the fourth harmonic.

[0006] Chinese utility model patent CN209472602U discloses a planar ultra-wideband dual-balanced diode mixer, comprising two baluns and a bridge mixer unit. The bridge mixer unit employs a low-barrier cross-ring diode bridge. The two baluns are a local oscillator balun and a radio frequency balun, respectively. The input and output terminals of the local oscillator balun and the radio frequency balun are connected to the input terminal of the bridge mixer unit. The output terminal of the bridge mixer unit is an intermediate frequency (IF) output terminal formed by converting the local oscillator microstrip balun. The IF output terminal is led out through a jumper with an isolation inductor. It achieves bandwidths of multiple harmonics without the need for a high-frequency shorting line. It utilizes a bridge composed of four Schottky diodes to achieve isolation between the signal terminal and the local oscillator terminal; and the diode bridge provides high and low frequency DC paths for the diodes, eliminating the need for a separate high-frequency shorting line and an IF ground line to achieve bandwidths of multiple harmonics. Summary of the Invention

[0007] The technical problem to be solved by this invention is how to provide an ultra-wideband odd harmonic mixer for spread spectrum with bandwidth covering multiple waveguide frequency bands.

[0008] The present invention solves the above-mentioned technical problems through the following technical means:

[0009] This invention proposes an ultrawideband odd harmonic mixer for spread spectrum, comprising: a first microstrip line, a Marchand balun, a first Schottky diode, a second Schottky diode, a matching circuit, and a second microstrip line;

[0010] The first microstrip line is located at the RF input terminal and connected to the unbalanced terminal of the Marchand balun. The balanced terminals A and B of the Marchand balun are connected to the anode of the first Schottky diode and the cathode of the second Schottky diode, respectively. The cathode of the first Schottky diode and the anode of the second Schottky diode are connected in series with the matching circuit and the second microstrip line. The second microstrip line is connected to the local oscillator / intermediate frequency port.

[0011] In this invention, the harmonic mixer employs a Marchand balun to achieve a single-balanced structure, providing an ultra-wide RF input bandwidth while offering a broadband grounding loop for the local oscillator and intermediate frequency (IF) signals. This harmonic mixer has only two ports: an RF port and a shared port for the RF / IF signals, requiring no other auxiliary equipment. By utilizing higher odd harmonics for spread spectrum, it can be directly used for frequency extension in existing mainstream spectrum analyzers, covering the bandwidth of two to three standard waveguide bands. Furthermore, both the first and second microstrip lines are 50-ohm microstrip lines.

[0012] Furthermore, the cathode of the first Schottky diode and the anode of the second Schottky diode are both connected to point C via microstrip pads to form a radio frequency virtual ground at point C.

[0013] Furthermore, the matching circuit includes multiple microstrip transmission lines connected in sequence, each with a different linewidth and length.

[0014] Furthermore, the Marchand balun employs a dual-wire coupled microstrip balun.

[0015] Furthermore, the first microstrip line, the Marchand balun, the first Schottky diode, the second Schottky diode, the matching circuit, and the second microstrip line are all planar microstrip line structures.

[0016] Furthermore, the present invention also proposes a spectrum analyzer, comprising a spectrum analyzer and an ultra-wideband odd harmonic mixer for spread spectrum as described above, wherein the local oscillator / intermediate frequency port of the mixer is connected to the spread spectrum port of the spectrum analyzer, and the RF terminal of the mixer receives a signal to be measured.

[0017] The advantages of this invention are:

[0018] (1) The harmonic mixer adopts the Marchand balun to achieve a single balanced structure, which provides an ultra-wide RF input bandwidth while providing a broadband grounding loop for the local oscillator and intermediate frequency signals. The harmonic mixer has only two ports, namely the RF port and the local oscillator / intermediate frequency shared port, without the need for other equipment assistance. By utilizing higher odd harmonics to achieve spread spectrum, it can be directly used for frequency extension of existing mainstream spectrum instruments, and the extension range can cover the bandwidth of two to three standard waveguide frequency bands.

[0019] (2) The odd harmonic mixer has the advantages of simple structure, large bandwidth, excellent frequency conversion performance, easy assembly of pure planar circuit and high-density integration with other circuits.

[0020] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of an ultra-wideband odd harmonic mixer for spread spectrum proposed in one embodiment of the present invention;

[0022] Figure 2 This is a diagram showing the Marchand Baron model and simulation results in one embodiment of the present invention, wherein... Figure 2 -(a) is the diagram of the Marchand Baron model. Figure 2 -(b) is a schematic diagram of the Balun S-parameter simulation. Figure 2 -(c) is a schematic diagram of the balun amplitude-phase simulation;

[0023] Figure 3 This is a simulation result diagram of the frequency conversion loss of a 50-110GHz planar dual-port ultrawideband odd harmonic mixer in one embodiment of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] like Figure 1 As shown, the first embodiment of the present invention proposes an ultra-wideband odd harmonic mixer for spread spectrum, comprising: a first microstrip line 1, a Marchand balun 2, a first Schottky diode 3, a second Schottky diode 4, a matching circuit 5, and a second microstrip line 6;

[0026] The first microstrip line 1 is located at the RF input terminal and is connected to the unbalanced terminal of the Marchand balun 2. The balanced terminals A and B of the Marchand balun 2 are connected to the anode of the first Schottky diode 3 and the cathode of the second Schottky diode 4, respectively. After the cathode of the first Schottky diode 3 and the anode of the second Schottky diode 4 are connected, the matching circuit 5 and the second microstrip line 6 are connected in series. The second microstrip line 6 is connected to the local oscillator / intermediate frequency port.

[0027] It should be noted that the radio frequency signal enters the balun through the first microstrip line, and the balun generates a signal with a 180° phase difference. The even harmonics generated by the mixing of the first Schottky diode and the second Schottky diode connected in reverse parallel cancel each other out, and the odd harmonics are superimposed, thereby outputting odd harmonics at the local oscillator / intermediate frequency port.

[0028] The harmonic mixer in this embodiment uses the Marchand balun 2 to achieve a single-balanced structure, providing an ultra-wide RF input bandwidth while providing a broadband grounding loop for the local oscillator and intermediate frequency signals. This harmonic mixer has only two ports, namely the RF port and the local oscillator / intermediate frequency shared port, requiring no other auxiliary equipment. By utilizing higher odd harmonics to achieve spread spectrum, it can be directly used for frequency extension of existing mainstream spectrum analyzers (such as Keysight Technologies' PXA series and Rohde & Schwarz's FSW series), and the extension range can cover the bandwidth of two to three standard waveguide frequency bands.

[0029] In one embodiment, both the first microstrip line 1 and the second microstrip line 6 are 50-ohm microstrip lines.

[0030] In one embodiment, the cathode of the first Schottky diode 3 and the anode of the second Schottky diode 4 are both connected to point C via microstrip pads to form a radio frequency virtual ground at point C.

[0031] In this embodiment, the first Schottky diode 3 and the second Schottky diode 4 are nonlinear elements of the odd harmonic mixer. The first Schottky diode 3 and the second Schottky diode 4 are connected in parallel in reverse order, with one end connected to the balanced terminals A and B of the Marchand balun 2, respectively. The other end is connected to point C via a shared microstrip pad, and then output through the matching circuit 5 and the second microstrip line 6. Simultaneously, due to the 180° phase difference introduced by the Marchand balun 2, an RF "virtual ground" is formed at point C after passing through the first Schottky diode 3 and the second Schottky diode 4, providing a grounding loop for the RF signal.

[0032] In one embodiment, the matching circuit 5 includes multiple microstrip transmission lines connected in sequence, each microstrip transmission line having a different linewidth and length.

[0033] It should be noted that the matching circuit 5 is located between the Schottky diode and the second microstrip line 6, and is used to match the input local oscillator signal and the output intermediate frequency signal to achieve low-loss frequency conversion. Specifically, the frequency conversion loss of the mixer can be optimized by adjusting the linewidth and length of the microstrip line.

[0034] In one embodiment, the Marchand balun 2 is a dual-wire coupled microstrip balun.

[0035] It should be noted that the Marchand balun 2 consists of two symmetrical microstrip coupled lines, splitting the input RF signal into two output ports, A and B. The two RF signals, A and B, are equal in magnitude but 180° out of phase, achieving unbalanced to balanced RF signal conversion. The application of dual-line coupled microstrip baluns provides a wide practical frequency range, enabling unbalanced to balanced conversion of ultra-wideband RF signals. The grounding structure in the coupled lines has high-pass characteristics, allowing only RF signals to pass while suppressing local oscillator and intermediate frequency signals, thus improving the isolation performance between the mixer's local oscillator / intermediate frequency port and the RF port.

[0036] Furthermore, the grounding structure of the Marchand balun 2 dual-coupled line provides a grounding loop for the local oscillator and intermediate frequency signals, and provides DC grounding for the diode.

[0037] The harmonic mixer uses a Marchand balun 2 to achieve a single-balanced structure. The spurious signals related to the local oscillator or radio frequency even harmonics generated by the two Schottky diodes cancel each other out. Therefore, the mixer has the characteristic of suppressing certain spurious responses related to the local oscillator or radio frequency even harmonics.

[0038] In one embodiment, the first microstrip line 1, the Marchand balun 2, the first Schottky diode 3, the second Schottky diode 4, the matching circuit 5, and the second microstrip line 6 are all planar microstrip line structures.

[0039] It should be noted that all the functional circuits of the mixer are planar microstrip structures, which makes it easy to integrate this circuit into other devices or circuits (such as low-noise amplifiers) at high density.

[0040] The ultra-wideband odd harmonic mixer designed in this embodiment for spread spectrum can achieve a maximum bandwidth of 50–110 GHz. The operating frequency of the 50–110 GHz planar dual-port ultra-wideband odd harmonic mixer covers three complete bands: WR-15 (V-band, frequency range 50–75 GHz), WR-12 (E-band, frequency range 60–90 GHz), and WR-10 (W-band, frequency range 75–110 GHz). It can be used with Keysight PXA or newer series spectrum analyzers and Rohde & Schwarz FSW series spectrum analyzers for frequency extension.

[0041] The PXA series provides local oscillator signals from 3.75 to 14.1 GHz for spectrum spreading, while the FSW series provides local oscillator signals from 7.65 to 17.45 GHz. The instrument receives an intermediate frequency (IF) of approximately 300 MHz. Since the local oscillator frequency range for spread spectrum is fixed, higher harmonic orders can be used to achieve ultra-wide bandwidth during spread spectrum operation. The harmonic orders of the harmonic mixer can be determined based on the IF and local oscillator frequency ranges of the spectrum analyzer.

[0042] Taking the PXA series spectrum analyzer as an example, based on the design of the PXA series spectrum analyzer for extending the 50-110GHz odd harmonic mixer, assuming the required harmonic order is 9, the corresponding local oscillator frequency range can be calculated as follows:

[0043] The upper limit of the local oscillator frequency = (110 - 0.3) ÷ 9 = 12.19 GHz;

[0044] The lower limit of the local oscillator frequency = (50-0.3)÷9 = 5.52GHz.

[0045] The corresponding local oscillator frequency range is 5.52–12.19 GHz, which is within the local oscillator frequency range (3.75–14.1 GHz) provided by the PXA series spread spectrum interface. Therefore, the mixer can be optimized using the ninth harmonic.

[0046] If an extended 50–110 GHz odd harmonic mixer is designed based on the FSW series spectrum analyzer, the 50–110 GHz range needs to be divided into two segments, and the mixer needs to be optimized using the fifth and seventh harmonics respectively. This will not be elaborated here.

[0047] The Marchand balun 2 employs microstrip dual-wire coupling, which has advantages such as a wide practical frequency range and simple structure. It can realize the conversion of broadband radio frequency signals from unbalanced to balanced and is suitable for broadband single-balanced mixing. Figure 2 The three-dimensional electromagnetic field simulation model and simulation results of the Marchand balun 2 are presented. The simulation results show that the bandwidth of the Marchand balun 2 can meet the requirements of transmission loss within 4dB at output ports A and B in the radio frequency range, i.e., within 50 to 110 GHz, and return loss at the input end within the band is better than 10dB. It also has good suppression effect in the local oscillator and intermediate frequency bands. The amplitude imbalance of the balun is better than 0.4dB and the phase imbalance is within ±3° in the 50 to 110 GHz range.

[0048] Furthermore, Figure 3 The simulation results of the final conversion loss of the ninth harmonic mixer are shown. In the RF frequency range of 50–110 GHz, the conversion loss of the ninth harmonic mixer is better than 20 dB, and the in-band flatness is better than 2.5 dB. Furthermore, Figure 3 The results of fifth-harmonic mixing and seventh-harmonic mixing with the same harmonic mixer are also shown. Generally, the lower the harmonic order of the harmonic mixer, the lower the conversion loss. Therefore, when using this mixer as a spread spectrum device to measure a lower frequency range, such as 50–70 GHz, the fifth-harmonic mixing setting can be used on the spectrum analyzer. This results in lower conversion loss and a higher dynamic range for spread spectrum compared to the ninth-harmonic mixing setting.

[0049] It should be noted that in mixer design, the mixer includes linear and nonlinear parts. The linear part includes the first Schottky diode 3 and the second Schottky diode 4. The part of the mixer structure other than the first Schottky diode 3 and the second Schottky diode 4 is the linear part. The S-parameters of the Marchand balun, the first Schottky diode 3, and the second Schottky diode 4 can be obtained using three-dimensional electromagnetic field simulation software. The S-parameters are then imported into circuit simulation software (e.g., Keysight Technologies' ADS). The matching circuit 5 in ADS consists of multiple microstrip transmission lines. By adjusting the linewidth and length of the microstrip lines, the frequency conversion loss of the mixer is optimized, thereby obtaining all the final circuit parameters, and then the mixer design is performed.

[0050] Furthermore, the first Schottky diode 33 and the second Schottky diode 44 are modeled. Generally, it is more accurate to combine the three-dimensional electromagnetic field model with the diode SPICE parameters.

[0051] The planar dual-port ultrawideband odd harmonic mixer provided in this embodiment has the advantages of simple structure, large bandwidth, excellent frequency conversion performance, easy assembly of pure planar circuit and high-density integration with other circuits. It can be used for frequency extension of existing mainstream spectrum analyzers, and the extension range can cover the bandwidth of two to three standard waveguide frequency bands.

[0052] Furthermore, one embodiment of the present invention also proposes a spectrum analyzer, including a spectrum analyzer and an ultra-wideband odd harmonic mixer for spread spectrum as described above, wherein the local oscillator / intermediate frequency port of the mixer is connected to the spread spectrum port of the spectrum analyzer, and the RF terminal of the mixer receives a signal to be measured.

[0053] It should be noted that by connecting the local oscillator / intermediate frequency port of the mixer to the spread spectrum port of the spectrum analyzer, connecting the RF end to the signal under test, and then setting the harmonic order in the spectrum analyzer, the spectrum corresponding to the RF frequency can be directly displayed.

[0054] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0055] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0056] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. An ultra-wideband odd-harmonic mixer for spread spectrum, characterized in that, include: First microstrip line, Marchand balun, first Schottky diode, second Schottky diode, matching circuit, and second microstrip line; The first microstrip line is located at the RF input terminal and connected to the unbalanced terminal of the Marchand balun. The balanced terminals A and B of the Marchand balun are connected to the anode of the first Schottky diode and the cathode of the second Schottky diode, respectively. The cathode of the first Schottky diode and the anode of the second Schottky diode are connected in series with the matching circuit and the second microstrip line. The second microstrip line is connected to the local oscillator / intermediate frequency port.

2. The ultra-wideband odd harmonic mixer for spread spectrum as described in claim 1, characterized in that, Both the first microstrip line and the second microstrip line are 50-ohm microstrip lines.

3. The ultra-wideband odd harmonic mixer for spread spectrum as described in claim 1, characterized in that, The cathode of the first Schottky diode and the anode of the second Schottky diode are both connected to point C via microstrip pads to form a radio frequency virtual ground at point C.

4. The ultra-wideband odd harmonic mixer for spread spectrum as described in claim 1, characterized in that, The matching circuit includes multiple microstrip transmission lines connected in sequence, each with a different linewidth and length.

5. The ultra-wideband odd harmonic mixer for spread spectrum as described in claim 1, characterized in that, The Marchand balun is a dual-wire coupled microstrip balun.

6. The ultra-wideband odd harmonic mixer for spread spectrum as described in any one of claims 1-5, characterized in that, The first microstrip line, the Marchand balun, the first Schottky diode, the second Schottky diode, the matching circuit, and the second microstrip line are all planar microstrip line structures.

7. A spectrum analyzer, characterized in that, The device includes a spectrum analyzer and an ultra-wideband odd harmonic mixer for spread spectrum as described in any one of claims 1-6, wherein the local oscillator / intermediate frequency port of the mixer is connected to the spread spectrum port of the spectrum analyzer, and the RF input of the mixer receives a signal to be measured.

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