Frequency Of Radio Frequency Signal Research Articles

Maintenance-free wireless multi-functional sensing enabled by electrostatic generator

Conventional self-powered sensor nodes rely on commercial sensing and wireless modules, making it difficult to achieve both long-range and real-time sensing, due to the limited energy harvested from the environment and the module’s high-power consumption. To solve this problem, a universal paradigm for self-powered sensor nodes with real-time, long-range and multi-functional sensing capability was proposed, which is achieved by low-power signal modulation using an electrostatic generator and a surface acoustic wave resonator (SAWR)-based transmitter. Once the sensor node is mechanically stimulated, the generator triggers the transmitter to generate radio frequency (RF) signals, containing both the generator’s motion status which encodes the RF signal amplitude to binarized 1/0 and the information sensed by SAWR which modulates the RF signal frequency. Based on the paradigm, we demonstrated simultaneous and continuous monitoring of wind speed and temperature from two sensor nodes located over 100 m, opening up new possibilities for maintenance-free wireless sensing.

Microwave frequency measurement based on a frequency-to-phase mapping technique.

A new frequency-to-phase mapping technique for measuring a radio-frequency (RF) signal frequency is presented. The concept is based on generating two low-frequency signals where their phase difference is dependent on the input RF signal frequency. Hence, the input RF signal frequency can be determined by using a low-cost low-frequency electronic phase detector to measure the phase difference between the two low-frequency signals. The technique can measure the frequency of an RF signal instantaneously and has a wide frequency measurement range. The proposed frequency-to-phase-mapping-based instantaneous frequency measurement system is experimentally verified over the 5 to 20 GHz frequency measurement range with errors of less than ±0.2 GHz.

A tunable ultra‐wideband superheterodyne radio frequency receiver with high‐image‐rejection levels

This article presents the superheterodyne radio frequency (RF) receiver composed of two receiving channels, which can realize an ultra-wide receiving frequency band. The RF signal can be received and demodulated in a variable frequency band by controlling the voltage of RF switches, which makes the RF signal enter the appropriate frequency conversion channel and tuning the local oscillator frequency according to the RF signal frequency. Therefore, the receiver realizes the adjustable working frequency band and an ultra-wide receiving frequency band. The designed superheterodyne RF receiver is simulated, manufactured, and measured. Finally, the article achieves a tunable ultra-wideband superheterodyne RF receiver with an image-rejection architecture that can provide rejection of more than 29.0 dB. The receiving frequency band of the receiver is 2.5 GHz –12 GHz. When the proposed receiver link receives multiple types of quadrature signals with a symbol rate of 50 M Baud, the error vector magnitude is less than 1.90%.

Optical injection locking assisted all-optical microwave oscillator

This paper reports an optical injection locking (OIL) assisted all-optical microwave oscillator (AOMO) scheme for the photonic generation of a microwave (MW) signal and demonstrates a 40th harmonic single-mode signal generation with an external low-frequency radio-frequency (RF) signal. In this all-optical single-loop oscillator that only depends on optical devices, the stimulated Brillouin scattering (SBS) effect of a coil of single-mode fiber (SMF) and a semiconductor optical amplifier (SOA) are used to select the oscillation frequency and modulate the optical feedback signal, respectively. The OIL effect in a distributed feedback (DFB) laser multiplies the frequency of the external RF signal. Thanks to the OIL module, it only requires an optical loop to acquire a single-mode oscillation and the oscillation signal is phase-related to the low-frequency RF source. The experiment demonstrates the generation of a single-mode MW signal of 10.71 GHz with an external RF signal of 267.8 MHz, with a frequency multiplication factor of 40. Mode-hopping is not evident in the output signal, and a moderately low-quality OIL signal is acceptable since unwanted harmonics and the phase noise floor of the OIL signal have little impact on the generated MW signal.

Rydberg RF Receiver Operation to Track RF Signal Fading and Frequency Drift

Significant progress has been made in recent years demonstrating an all-optical high sensitivity Radio Frequency (RF) sensor exploiting the Electromagnetically Induced Transparency (EIT) effect in an atomic vapor. Rydberg RF sensors have previously been shown to exhibit excellent lab-based performance in measuring electric field properties. As a commercial network operator we wish to exploit these capabilities to produce a rugged high-sensitivity receiver for 5G signals, so we seek simple planning rules applicable to readily available low cost components. We present a simple analytic model for the operation of a sensitive Rydberg RF receiver to predict the optical modulation in response to an RF signal. We focus on maximizing the contrast in the optical response to a modulated RF signal rather than to a constant RF field. We show that the optical modulation depth can be maximized using an optimum coupling intensity. The optical modulation depth drops off rapidly as the RF source is detuned away from resonance. By detuning the coupling frequency to compensate for the RF detuning we demonstrate that the useful RF bandwidth of the receiver can be significantly extended. We measure this variation in optical response using a Rubidium vapor at a 15 GHz RF carrier frequency. Using readily available optical components we obtain good agreement with our model. This convenient analytic approach will simplify the design and operation of Rydberg RF receivers as sensitive components in future 5G mobile communications, particularly for the power-limited uplink from mobile device to base-station.

Instantaneous frequency measurement using two parallel I/Q modulators based on optical power monitoring

A scheme for instantaneous frequency measurement (IFM) using two parallel I/Q modulators based on optical power monitoring is proposed. The amplitude comparison function (ACF) can be constructed to establish the relationship between the frequency of radio frequency (RF) signal and the power ratio of two optical signals output by two I/Q modulators. The frequency of RF signal can be derived by measuring the optical power of the optical signals output by two I/Q modulators. The measurement range and measurement error can be adjusted by controlling the delay amount of the electrical delay line. The feasibility of the scheme is verified, and the corresponding measurement range and measurement error of the system under different delay amounts of the electrical delay line are given. Compared with previous IFM schemes, the structure of this scheme is simple. Polarization devices, a photodetector and an electrical power meter are not used, which reduces the impact of the environmental disturbance on the system and the cost of the system. In simulation, the measurement range can reach 0 GHz–24.5 GHz by adjusting the delay amount of the electrical delay line τ = 20 ps. The measurement error of the scheme is better at low frequency, and the measurement error of low frequency 0 GHz–9.6 GHz can reach –0.1 GHz to +0.05 GHz.

Sub-nanosecond-speed frequency-reconfigurable photonic radio frequency switch using a silicon modulator

Radio frequency (RF) switches are essential for implementing routing of RF signals. However, the increasing demand for RF signal frequency and bandwidth is posing a challenge of switching speed to the conventional solutions, i.e., the capability of operating at a sub-nanosecond speed or faster. In addition, signal frequency reconfigurability is also a desirable feature to facilitate new innovations of flexible system functions. Utilizing microwave photonics as an alternative path, we present here a photonic implementation of an RF switch providing not only the capability of switching at a sub-nanosecond speed but also options of frequency doubling of the input RF signals, allowing for flexible output waveforms. The core device is a traveling-wave silicon modulator with a device size of 0.2 mm × 1.8 mm and a modulation bandwidth of 10 GHz. Using microwave frequencies, i.e., 15 GHz and 20 GHz, as two simultaneous RF input signals, we experimentally demonstrated their amplitude and frequency switching as well as that of the doubled frequencies, i.e., 30 GHz and 40 GHz, at a switching frequency of 5 GHz. The results of this work point to a solution for creating high-speed RF switches with high compactness and flexibility.

Highly sensitive, broadband microwave frequency identification using a chip-based Brillouin optoelectronic oscillator.

Detection and frequency estimation of radio frequency (RF) signals are critical in modern RF systems, including wireless communication and radar. Photonic techniques have made huge progress in solving the problem imposed by the fundamental trade-off between detection range and accuracy. However, neither fiber-based nor integrated photonic RF signal detection and frequency estimation systems have achieved wide range and low error with high sensitivity simultaneously in a single system. In this paper, we demonstrate the first Brillouin opto-electronic oscillator (B-OEO) based on on-chip stimulated Brillouin scattering (SBS) to achieve RF signal detection. The broad tunability and narrowband amplification of on-chip SBS allow for the wide-range and high-accuracy detection. Feeding the unknown RF signal into the B-OEO cavity amplifies the signal which is matched with the oscillation mode to detect low-power RF signals. We are able to detect RF signals from 1.5 to 40 GHz with power levels as low as -67 dBm and a frequency accuracy of ± 3.4 MHz. This result paves the way to compact, fully integrated RF detection and channelization.

Channelized amplification of RF signal based on actively mode locked fiber laser

A new approach for implementing channelized radio frequency (RF) signals amplification based on actively mode locked laser (MLL) is proposed and demonstrated. The channelized amplification (CA) is based on the mode-locking gain of the fiber ring laser while the frequency of RF signal applied to Mach–Zehnder modulator (MZM) in the fiber laser matching the fundamental or harmonic of the laser cavity mode. The experimental results show that high RF regenerative gain with a maximum 44 dB and high Q factor normally greater than 105 can be achieved with this approach of CA. By electrically tuning the fiber delay line incorporated in the ring laser so as to scan the center frequency of the channelized amplifier, spectrum recognition of quadrature phase shift keying (QPSK) modulated electro-magnetic signal with low power density is successfully implemented. The limit of input power and linear operating dynamic range is also measured and discussed.

RF signal detection by a tunable optoelectronic oscillator based on a PS-FBG.

Low-power radio frequency (RF) signal detection is highly desirable for many applications, ranging from wireless communication to radar systems. A tunable optoelectronic oscillator (OEO) based on a phase-shifted fiber Bragg grating for detecting low-power RF signals is proposed and experimentally demonstrated. When the frequency of the input RF signal is matched with the potential oscillation mode of the OEO, it is detected and amplified. The frequency of the RF signal under detection can be estimated simultaneously by scanning the wavelength of the laser source. The RF signals from 1.5 to 5GHz as low as -91 dBm are detected with a gain of about 10dB, and the frequency is estimated with an error of ±100 MHz. The performance of the OEO system for detecting an RF signal with different modulation rates is also investigated.

An Approach for Noninvasive Blood Glucose Monitoring Based on Bioimpedance Difference Considering Blood Volume Pulsation

Noninvasive blood glucose monitoring (NBGM) provides a promising solution for patients with diabetes with the advantages of painless and continuous monitoring. To better characterize the response of glucose to radio-frequency (RF) signals at low frequencies, the conductivity and relative permittivity of aqueous solutions with different glucose concentrations were obtained by the use of an impedance analyzer in the frequency range of 1 kHz to 1 MHz. Furthermore, considering the blood volume pulsation in cardiac cycle, a new approach based on measuring bioimpedance was presented for NBGM in this paper. For this purpose, an inhomogeneous arm model, which consists of three tissue layers (i.e., blood, blood vessel, and other relevant tissues), was proposed to validate the aforementioned approach. Furthermore, the measurements were carried out by means of in vitro experiment and in vivo studies, respectively. The results showed that as the glucose concentration increased, the conductivity of aqueous solutions decreased when the frequency of RF signal was below 1 MHz. However, the relative permittivity was almost insensitive to glucose concentration. The simulation result of the arm model showed that as the glucose concentration increased, the bioimpedance difference of blood volume decreased. This was supported by both in vitro and in vivo experiments. We therefore suggest that the proposed approach for NBGM has potentials in practical applications.

Microwave Frequency Quadrupling Based on Distributed Feedback Laser and a Single Intensity Modulator

ABSTRACTIn this article, we have proposed and experimentally demonstrated a directly modulated distributed feedback laser (DFB-LD) to generate microwave and millimeter-wave signals. The proposed scheme uses DFB-LD and intensity modulator (IM) biased at null point. A radio frequency (RF) signal from a signal generator is split into two branches and one branch directly modulates the DFB-LD, while the other branch drives the IM. Two second-order sidebands separated by four times the frequency of the input RF signal are generated. Experimental results indicated that we can generate a four-fold microwave signal with a good optical signal to noise ratio.

Linearization of microwave photonic link based on nonlinearity of distributed feedback laser

A microwave photonic link (MPL) with spurious-free dynamic range (SFDR) improvement utilizing the nonlinearity of a distributed feedback (DFB) laser is proposed and demonstrated. First, the relationship between the bias current and nonlinearity of a semiconductor DFB laser is experimentally studied. On this basis, the proposed linear optimization of MPL is realized by the combination of the external intensity Mach–Zehnder modulator (MZM) modulation MPL and the direct modulation MPL with the nonlinear operation of the DFB laser. In the external modulation MPL, the MZM is biased at the linear point to achieve the radio frequency (RF) signal transmission. In the direct modulation MPL, the third-order intermodulation (IMD3) components are generated for enhancing the SFDR of the external modulation MPL. When the center frequency of the input RF signal is 5 GHz and the two-tone signal interval is 10 kHz, the experimental results show that IMD3 of the system is effectively suppressed by 29.3 dB and the SFDR is increased by 7.7 dB.

A Reconfigurable Direct RF Receiver With Jitter Analysis and Applications

In typical direct radio frequency (RF) sampling receivers, the sample clock jitter results in SNR degradation on received signals that increases log linearly with RF signal frequency. De-jittering received signals is computationally expensive, especially for wideband communications signals, because the induced jitter on received signals varies as a function of RF signal frequency. This paper considers a reconfigurable direct RF receiver (RDRFR) that has a stair-step jitter pattern as a function of RF signal frequency. The RDRFR uses a two-stage sampling circuit. In the first stage, the RF input is bandpass filtered and pulse sampled without quantizing the signal. The discrete-time analog signal is then interpolated with a continuous time low-pass filter, then sampled and quantized by a traditional analog-to-digital converter. With this two-stage sampling circuit, the induced signal jitter from the RF sampling is identical for all in-band signals and is the same to within an integer scale factor for all signals, in-band or out-of-band. This key circuit property means that it is possible to remove jitter with very low computational complexity in the RDRFR. Furthermore, this result can be exploited to improve system performance with non-ideal anti-alias filters by identifying non-desired signals caused by out-of-band leakage.

A tunable photonic microwave notch filter based on all-optical mixing

A novel photonic microwave notch filter based on all-optical mixing using a single narrow-linewidth optical source is proposed. In the proposed filter, the optical carrier emitted from a laser source is externally intensity modulated by a subcarrier signal and then applied to a second intensity modulator, which is driven by a local radio-frequency (RF) source with a dc bias to suppress the even-order sidebands. Since the higher odd-order sidebands have a much lower power than the first-order sidebands, only two first-order sidebands are considered with the subcarrier signal transferred to the two sidebands via optical mixing. By using a linearly chirped fiber Bragg grating as a dispersive device to introduce time delays, a two-tap photonic microwave notch filter is realized. The tunability of the proposed filter is achieved by adjusting the frequency of the local RF signal. Based on the proposed architecture, a two-tap microwave notch filter with a free spectral range tunable from 2.1 to 4.2 GHz is experimentally demonstrated.