Microwave Frequency Measurement Research Articles

High-Precision Photonics-Assisted Two-Step Microwave Frequency Measurement Combining Time and Power Mapping Method

High-Precision Photonics-Assisted Two-Step Microwave Frequency Measurement Combining Time and Power Mapping Method

Broadband Instantaneous Frequency Measurement Using Frequency-to-Time Mapping and Channelization

A photonic instantaneous microwave frequency measurement scheme based on frequency-to-time mapping and channelization is proposed. An unknown signal is divided into four channels and mixed with a broadband linear frequency-modulated signal. The frequency information is converted to the time domain, and the frequency measurement range has been expanded due to channelization. A simulation system has been constructed to demonstrate the effectiveness of the proposed method. A proof-of-concept experimental result shows that the frequency measurement errors can be kept in 20 MHz with a 10 MHz resolution, and the frequency measurement range is 1 GHz to 39 GHz.

Photonic-assisted wideband microwave frequency measurement based on optical heterodyne detection

A photonic-assisted microwave frequency measurement (MFM) method based on optical heterodyne detection is proposed and experimentally demonstrated. In the proposed MFM system, a linearly chirped optical waveform (LCOW) from a three-electrode distributed Bragg reflector laser diode (DBR-LD) and a multi-wavelength signal from a Mach-Zehnder modulator (MZM), where the signal under test (SUT) is modulated on an optical carrier from a distributed feedback laser diode (DFB-LD), are heterodyne detected by the photodetector (PD). A bandpass filter then filters the detected signal, and the envelope is detected by an oscilloscope. Then, frequency-to-time mapping is realized, and the signal frequency is measured. Thanks to the fast tuning rate and large tuning range of the DBR-LD, the proposed MFM system has a high measurement speed and a broad instantaneous measurement bandwidth. In the experimental demonstration, a measurement error below 39.1 MHz is achieved at an instantaneous bandwidth of 20 GHz and a measurement speed of 1.12 GHz/µs. The MFM of a frequency-hopping signal is also experimentally demonstrated. The successful demonstration of the MFM system with a simple structure provides a new optical solution for realizing broadband and fast microwave frequency measurements.

Frequency-Phase-Mapping Method in Microwave Frequency Measurement With Single Optical Frequency Comb

Frequency-Phase-Mapping Method in Microwave Frequency Measurement With Single Optical Frequency Comb

Microwave photonics frequency measurement with improved accuracy based on an artificial neural network.

Photonics-assisted techniques for microwave frequency measurement (MFM) show great potential for overcoming electronic bottlenecks, with wild applications in radar and communication. The MFM system based on the stimulated Brillouin scattering (SBS) effect can measure the frequency of multiple high-frequency and wide-band signals. However, the accuracy of the MFM system in multi-tone frequency measurement is constrained by the SBS bandwidth and the nonlinearity of the system. To resolve this problem, a method based on an artificial neural network (ANN) is suggested, which can establish a nonlinear mapping between the measured two-tone signal spectra and the theoretical frequencies. Through simulation verification, the ANN optimized frequencies within the range of (0.5, 27) GHz of the MFM system show 79%, 76%, 70%, 44% reduction in errors separately under four spectral signal-to-noise ratios (SNR) conditions, 20dB, 15dB, 10dB, 0dB, and the frequency resolution is improved from 30MHz to 10MHz.

Continuous broadband microwave electric field measurement in Rydberg atoms based on the DC Stark effect

We demonstrate a method for broadband tunable continuous frequency electric field measurement based on the DC Stark effect in Rydberg atoms. In our experiment, we place a pair of parallel electrode plates inside the atomic vapor cell, utilizing the DC Stark effect to induce splitting and shifting of the Rydberg energy levels, thereby altering the resonance frequency of the Stark subpeaks. By employing the 52D5/2 Rydberg state, we achieve electric field measurements in the frequency range of 5.083–14.470 GHz. At an EDC of 3.45 V/cm and a resonant microwave frequency of 14.470 GHz, using heterodyne technology, the microwave electric field sensitivity is 538.89 μV/cm/√Hz, with a linear dynamic range of 23 dB. In comparison, a Rydberg heterodyne receiver with an EDC of 0 V/cm and a resonant microwave frequency of 5.083 GHz has a sensitivity of 5.43 μV/cm/√Hz and a linear dynamic range of 51 dB. This work will promote the study of atomic microwave receivers in continuous microwave frequency measurement.

Photonic instantaneous microwave frequency measurement based on frequency-phase mapping with high precision

This paper presents an instantaneous microwave frequency measurement scheme based on a frequency-phase mapping technique. In our scheme, a low-frequency (LF) reference signal and two microwave signals with a relative time delay are modulated on the optical carriers via two dual-parallel Mach–Zehnder modulators. The generated electrical signal has the same frequency as that of the LF reference signal, but with a phase shift, which depends on the microwave signal frequency and the time delay. Therefore, a linear frequency-phase mapping function with a high slope is constructed, which improves the accuracy of the whole frequency measurement range. The scheme has a compact structure without an optical filter and polarization devices, which enhances the long-term stability of the system. The simulation shows that our scheme has a 4.1–40 GHz frequency measurement range with errors less than ±0.04 GHz.

Photonics-assisted joint radar detection and frequency measurement system

A photonics-assisted joint radar detection and microwave frequency measurement system is proposed. A broadband dual-chirp linear frequency-modulated (LFM) signal is generated based on an optically injected semiconductor laser, which is later shared by two functional modules. Thanks to the photonics-assisted broadband signal generation method, both radar detection with high resolution and microwave frequency measurement with high accuracy can be realized without using high-speed electronic devices. In the experiment, a two-dimensional resolution of 1.25 cm × 1.33 cm and a measurement error within ±50 MHz are achieved in radar detection and frequency measurement, respectively.

Spatial Microwave Field Frequency Measurement through Two‐Level Resonance of Nitrogen‐Vacancy Color Center in Diamond

This article presents a frequency measurement method for spatial microwave signals with solid‐state atom resonance, performing measurements based on the burnt hole in spectrum with two microwave fields acting on nitrogen vacancies (NVs) simultaneously. The population on |0⟩ of the NV color center in the ground state affected by the resonance of two microwave fields with similar frequencies responds excellently to external microwave frequencies, and a phenomenon named hole burning occurs. The full width at half maximum (FWHM) of the resonant peak at the hole is 18.9 kHz. When microwaves of different frequencies are applied, the resonant peak precisely follows the signal frequency in the experiment. Subsequently, the resonant peak is processed using the differential method to obtain a frequency measurement error on the order of 100 Hz. The spatial resolution of this method is within the millimeter scale. This study can provide technical support for applications in microwave frequency measurement and spatial mapping with quantum precision measurement.

Improving the Accuracy and Resolution of Filter- and Frequency-to-Time Mapping-Based Time and Frequency Acquisition Methods by Broadening the Filter Bandwidth

In this article, a method for improving the accuracy and resolution of the filter-and frequency-to-time mapping (FTTM)-based time and frequency acquisition system in the fast sweep scenario is proposed by broadening the filter bandwidth. It is found that the width of the generated pulse via FTTM is mainly determined by the impulse response of the filter when the sweep rate is very fast. Therefore, appropriately increasing the filter bandwidth can significantly reduce the pulsewidth, so as to improve the measurement accuracy and resolution. To verify the validity, short-time Fourier transform (STFT) and microwave frequency measurement (MFM) systems employing the stimulated Brillouin scattering (SBS)-based FTTM are further investigated by inserting a frequency-sweep pump wave for SBS gain bandwidth broadening. The improvement of accuracy and frequency resolution is well confirmed by comparing the measurement results with and without SBS gain spectrum broadening. The MFM accuracy is improved by more than ten times compared with other reported works under a similar fast sweep rate, and the frequency resolution of the STFT is also much improved compared with our former results.

Photonic-Assisted Microwave Frequency Measurement Using High Q-Factor Microdisk with High Accuracy

Frequency measurement plays a crucial role in radar, communication, and various applications. The photonic-assisted frequency measurement method offers several advantages, including resistance to electromagnetic interference, broad bandwidth, and low power consumption. Notably, frequency-to-time mapping enables the measurement of various microwave signal types, such as single-frequency, multiple-frequency, frequency hopping, and chirped signals. However, the accuracy of this method is currently limited due to the absence of resonant devices with high-quality factors, which are essential for achieving higher-precision measurements. In this work, a frequency measurement method based on an ultrahigh-quality-factor microdisk is proposed. By establishing a correlation between the time difference and the frequency to be measured, a reduction in measurement error to below 10 MHz within a frequency measurement range of 3 GHz is realized. Our work introduces a new approach to frequency measurement using optical devices, opening new possibilities in this field.

Photonics-assisted two-step microwave frequency measurement based on frequency-to-time mapping

Photonics-assisted two-step microwave frequency measurement based on frequency-to-time mapping

High-performance transient SBS-based microwave measurement using high-chirp-rate modulation and advanced algorithms.

The transient stimulated Brillouin scattering (SBS) effect, enabled by optical chirp chain (OCC) technology, has already been proposed and demonstrated for microwave frequency identification with high temporal resolution. Through increasing the OCC chirp rate, the instantaneous bandwidth can be effectively extended without loss of the temporal resolution. However, the higher chirp rate results in more asymmetric transient Brillouin spectra, which worsens the demodulation accuracy when using the traditional fitting method. In this Letter, advanced algorithms, including image processing and artificial neural network, are employed to improve the measurement accuracy and demodulation efficiency. A microwave frequency measurement scheme is implemented with 4 GHz instantaneous bandwidth and 100 ns temporal resolution. Through the proposed algorithms, the demodulation accuracy of transient Brillouin spectra under 50 MHz/ns high chirp rate is improved from 9.85 MHz to 1.17 MHz. Moreover, owing to the matrix computations of the proposed algorithm, the time consumption is reduced by two orders of magnitude compared with the fitting method. The proposed method allows a high-performance OCC transient SBS-based microwave measurement, which provides new possibilities to realize real-time microwave tracking for diverse application fields.

Instantaneous Frequency Measurement Using Photonics-Assisted Broadband Signal Generation and Processing

A photonics-based instantaneous microwave frequency measurement with broadband signal generation and processing is proposed and demonstrated. In this scheme, a broadband triangular linear frequency-modulated (LFM) signal is first optically generated, and photonic mixing of the LFM signal with a signal under test (SUT) is implemented before extracting the frequency information in the oscilloscope. In the experiment, both accurate single-frequency and multifrequency measurements are successfully realized using low-speed electronic devices. The experimental results confirm a measurement accuracy of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt;$</tex-math> </inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula> 50 MHz within a frequency range from 1 to 39 GHz.

Toward the realization of a primary low-pressure standard using a superconducting microwave resonator.

We describe a primary gas pressure standard based on the measurement of the refractive index of helium gas using a microwave resonant cavity in the range between 500Pa and 20kPa. To operate in this range, the sensitivity of the microwave refractive gas manometer (MRGM) to low-pressure variations is substantially enhanced by a niobium coating of the resonator surface, which becomes superconducting at temperatures below 9K, allowing one to achieve a frequency resolution of about 0.3Hz at 5.2GHz, corresponding to a pressure resolution below 3 mPa at 20Pa. The determination of helium pressure requires precise thermometry but is favored by the remarkable accuracy achieved by ab initio calculations of the thermodynamic and electromagnetic properties of the gas. The overall standard uncertainty of the MRGM is estimated to be of the order of 0.04%, corresponding to 0.2Pa at 500 and 8.1Pa at 20kPa, with major contributions from thermometry and the repeatability of microwave frequency measurements. A direct comparison of the pressures realized by the MRGM with the reference provided by a traceable quartz transducer shows relative pressure differences between 0.025% at 20kPa and -1.4% at 500Pa.

Photonic-assisted multiple microwave frequency measurement with improved robustness.

A multiple microwave frequency measurement approach based on frequency-to-time mapping (FTTM) is reported. The FTTM is constructed by optical sideband sweeping and electric-domain intermediate frequency envelope monitoring. Two optimized operations are implemented. First, the use of balanced photodetection cancels out the beat components generated by the signals under test (SUT) themselves, so as to exclude frequency misjudgment. Second, a reference signal is introduced to map the SUT frequency to a relative time difference instead of an absolute time value, avoiding the measuring bias caused by time synchronization. As a result, the proposed scheme with improved robustness could be attractive for future practical applications. An experiment is performed. Microwave frequency measurement from 16 to 26 GHz is demonstrated, with an average error of 7.53 MHz.

Photonic Multiple Microwave Frequency Measurement System with Single-Branch Detection Based on Polarization Interference

A photonic microwave frequency measurement system with single-branch detection based on polarization interference is proposed. In this scheme, a 15-line non-flat optical frequency comb (OFC) based on sawtooth signal modulation via a Mach–Zehnder modulator is generated. The intercepted microwave signal with multiple-frequency components can be measured by frequency down-conversion with this simple structure. This system can measure the multi-tone microwave signals in real time. The single-branch detection makes the system a simple and compact structure and avoids the unbalanced variation, as in a two-branches scheme. The blind area of the system can be solved by adjusting the comb-line spacing of the OFC. A simulation is carried out and related discussion is given. The result reveals that it can measure multi-tone microwave signals with a resolution of less than 2 MHz over 0.1–12 GHz.

Microwave Frequency Measurement System Using Fixed Low Frequency Detection Based on Photonic Assisted Brillouin Technique

Microwave frequency measurement system is the chief component of the receiver, which is of indispensable significance in electronic warfare and modern radar. In this work, a simple and novel frequency measurement system that detects at fixed low-frequency point is established, which is implemented by introducing a frequency down-conversion, in conjunction with Brillouin Technique. A swept frequency signal is applied for the purpose of carrying the sideband of unknown signal. The frequency-shifted carrier is realized through the all-optical Brillouin frequency shifting process, which is used to downconvert unknown signals. Eventually, the unknown signal can be obtained by recording the frequency of the sweep signal when the beat signal occurs at a preset fixed frequency of 828 MHz. The proposed approach does not require broadband electronic monitoring equipment, which reduces the pressure of subsequent processing and acquisition. An experiment has been performed to vindicate the feasibility of the measurement system, which shows that a measurement ranges from 1 to 9.5 GHz. Meanwhile, the savitzky-golay algorithm is utilized to improve the frequency resolution to 15 MHz. Furthermore, a large bandwidth measurement range and the expanded uncertainty (95.45% coverage) of 3.604 MHz in the system are also discussed and verified.

Multiple microwave frequency measurement system based on a sawtooth-wave-modulated non-flat optical frequency comb.

A photonic-assisted instantaneous microwave measurement system, capable of measuring multiple frequency signals, is demonstrated and analyzed. The principle lies in the combination of a channelizer and frequency-to-power mapping. An effective generation method of a non-flat optical frequency comb is proposed based on sawtooth wave modulation, which has more comb lines and adjustable comb spacing. Under this method, two low-speed post-processing devices are utilized to realize frequency measurements up to 32GHz. The scheme is verified by simulation, and factors affecting system performance are also studied.

Photonics-Based Instantaneous Microwave Frequency Measurement System With Improved Resolution and Robust Performance

This paper presents a photonics-based instantaneous microwave frequency measurement system. The system operates based on the frequency-to-power mapping technique. The trade-off between frequency measurement range and resolution, which is present in the reported frequency-to-power-mapping based frequency measurement systems, is addressed by designing the system to produce two amplitude comparison functions (ACFs). Using two ACFs enables an RF signal frequency in a specified range to be determined while having an improved resolution and smaller errors compared to using only one ACF for frequency measurement. The proposed frequency measurement system is designed to have a simple structure and robust performance suitable for use in real world applications. The effect of the higher order sidebands and harmonics on the system performance are investigated. Proof-of-concept experiments are carried out with results showing frequency measurement errors can be reduced by using the proposed system that generates two ACFs for frequency measurement.