Continuous-wave Microwave Signal Research Articles

Speed Calibration and Traceability for Train-Borne 24 GHz Continuous-Wave Doppler Radar Sensor

The 24 GHz continuous-wave (CW) Doppler radar sensor (DRS) is widely used for measuring the instantaneous speed of moving objects by using a non-contact approach, and has begun to be used in train-borne movable speed measurements in recent years in China because of its advanced performance. The architecture and working principle of train-borne DRSs with different structures including single-channel DRSs used for freight train speed measurements in railway freight dedicated lines and dual-channel DRSs used for speed measurements of high-speed and urban rail trains in railway passenger dedicated lines, are first introduced. Then, the disadvantages of two traditional speed calibration methods for train-borne DRS are described, and a new speed calibration method based on the Doppler shift signal simulation by imposing a signal modulation on the incident CW microwave signal is proposed. A 24 GHz CW radar target simulation system for a train-borne DRS was specifically realized to verify the proposed speed calibration method for a train-borne DRS, and traceability and performance evaluation on simulated speed were taken into account. The simulated speed range of the simulation system was up to (5~500) km/h when the simulated incident angle range was within the range of (45 ± 8)°, and the maximum permissible error (MPE) of the simulated speed was ±0.05 km/h. Finally, the calibration and uncertainty evaluation results of two typical train-borne dual-channel DRS samples validated the effectiveness and feasibility of the proposed speed calibration approach for a train-borne DRS with full range in the laboratory as well as in the field.

A Single-Chip Electron Paramagnetic Resonance Transceiver in 0.13-<formula formulatype="inline"><tex Notation="TeX">$\mu$</tex> </formula>m SiGe BiCMOS

We report the first absorption-based single-chip transceiver for electron paramagnetic resonance (EPR) spectroscopy in silicon. The chip is implemented in a 0.13- $\mu$ m SiGe BiCMOS process technology. The transmitter generates and delivers a continuous-wave microwave signal with a frequency range from 895 to 979 MHz and the receiver adopts a direct-conversion architecture. Based on the single-chip transceiver and a printed-circuit-board-based planar resonator, an EPR spectrometer is assembled and tested. The spectrometer successfully measures the EPR response from samples including 2,2-Diphenyl-1-Picrylhydrazyl powder, Fe $_{3}$ O $_{4}$ nanoparticles, and Fe $_{2}$ O $_{3}$ nanoparticles.

First Trials for a Microwave Reflectometric Tool to Survey Decay in Historic Timber Structures

Timber structures can be degraded during their life both by structural problems and by biological degradation factors like fungi, and insects. The occurrence of those biodegradation agents could lead to a loss of their structural integrity, in the absence of appropriate maintenance. An early assessment of the decay is even more important when the wooden structures are part of historical buildings, in the interest of conservation of cultural heritage. This work presents an application of microwave reflectometry for the in situ evaluation of timber structures. The measurement system allows detecting anomalies inside the material in a non-destructive and non-invasive manner. The reflection coefficient is measured by means of a vector network analyzer (VNA) using a double-ridge antenna, which transmits the continuous-wave microwave signal and receives the signal reflected by the material under investigation. Measurements on laboratory models demonstrated the feasibility of the method. Results obtained on timber beam sections, compared with the findings of traditional investigation methodologies, demonstrate the potentiality of microwave reflectometry, suggesting its possible usefulness during the diagnostic phase as a non-invasive tool for preliminary screening.

Photonic Generation of Phase Coded Microwave Pulses Using Cascaded Polarization Modulators

We demonstrate a technique of generating a binary phase coded microwave pulse based on two cascaded polarization modulators (PolMs). The first PolM (PolM1) followed by an optical band-pass filter is used to generate two phase-locked and polarization orthogonal optical frequencies. The second PolM (PolM2) aims to change their polarization states. A polarizer attached to the output of PolM2 allows only one of the two optical frequencies passing, or combines them with positive/negative phase difference. By changing the voltage level of the electrical modulation signal applied to PolM2, a series of binary phase coded microwave pulses is directly generated from a continuous wave microwave signal in the optical domain. In the proposed system, the precise amplitude control or amplification of the modulation signal are avoided. The waveform of the generated pulse is very stable. For a proof-of-concept experiment, a series of 25-GHz pulses with ${\sim}{\rm 2.08}$ -ns pulse duration and ${\sim}{\rm 10.24}$ -ns repetition time is generated. The pulses are phase coded by a 13-bit Barker code.

Photonic Frequency Measurement and Signal Separation for Pulsed/CW Microwave Signals

A novel photonic approach to simultaneously implement frequency measurement and signal separation is proposed and experimentally demonstrated for pulsed and continuous-wave (CW) microwave signals. In this approach, a light wave is externally modulated with carrier suppressed by a pulsed or CW microwave signal to be measured, and then sent to two optical complementary filters to perform frequency-to-amplitude mapping. The outputs of the two filters are detected by low-speed photodetectors, low-frequency alternating currency (AC) electronic component and direct current (DC) one being generated. The carrier frequency of the pulsed microwave signal can be estimated by monitoring the power of the AC component, while the frequency of the CW microwave signal is discriminated from the power of the DC component, with the frequency measurement and the signal separation simultaneously realized. In proof-of-concept experiments, within the frequency range from 5 to 20 GHz, measurement errors less than ±0.1, ±0.11 , or ±0.13 GHz are achieved for a pulsed signal with pulse repetition frequency of 0.25, 0.5, or 1 MHz, whereas the errors less than ±0.08 GHz are derived for a CW signal.

Instantaneous Microwave Frequency Measurement Based on Amplified Fiber-Optic Recirculating Delay Loop and BroadBand Incoherent Light Source

A novel approach to implementing instantaneous frequency measurement (IFM) based on an amplified fiber-optic recirculating delay loop and a broadband incoherent light source (ILS) is proposed, analyzed, and experimentally demonstrated. Since the semiconductor optical amplifier-based fiber-optic delay loop has an infinite impulse response that varies from a large positive value to negative infinity on a log scale, a unique relationship between the output power, and the frequency of the input continuous-wave (CW) microwave signal is established. Meanwhile, it is experimentally shown that the use of the ILS can greatly improve the stability of the proposed IFM system. When the input power of CW microwave signal is within the range of -7 dBm to -16 dBm, the measured errors remain within ±400 KHz over a frequency range of 6.94-6.958 GHz. The measurement error, the complexity and cost of the proposed IFM system can be considerably reduced by only using one ILS, one modulator, and one photodetector. Since the proposed IFM system has a capability of optical integration, it is theoretically estimated that the measurement range can be extended to 20 GHz with a measurement resolution of 1.36 dB/GHz.

Instantaneous Microwave Frequency Measurement Using Programmable Differential Group Delay (DGD) Modules

We propose and experimentally demonstrate a photonic approach for the measurement of microwave frequencies with adjustable measurement range and resolution. After an unknown microwave signal is modulated onto an optical carrier by a Mach-Zehnder modulator (MZM), the optical output of the MZM is sent to two programmable differential group delay (DGD) modules to introduce different microwave power fading effects, respectively. When the microwave powers of the two channels are measured with two photodetectors separately, a fixed relationship between the microwave power ratio and the microwave frequency is established. The frequency measurement range and resolution can be tuned by electrically varying the DGD values. Frequency measurement with good accuracy for the microwave signals is experimentally realized. When the input power of a continuous-wave microwave signal is within the range of 15 to 3 dBm, the measured errors remain within 0.04 GHz for a measurement range of 4.5-6.5 GHz.

Instantaneous Microwave Frequency Measurement With Improved Measurement Range and Resolution Based on Simultaneous Phase Modulation and Intensity Modulation

A novel approach to implementing instantaneous microwave frequency measurement based on simultaneous optical phase modulation and intensity modulation with improved measurement range and resolution is proposed and experimentally demonstrated. The simultaneous optical phase modulation and intensity modulation are implemented using a polarization modulator (PolM) in conjunction with an optical polarizer. The phase- and intensity-modulated optical signals are then sent to a dispersive element, to introduce chromatic dispersions, which results in two complementary dispersion-induced power penalty functions. The ratio between the two power penalty functions has a unique relationship with the microwave frequency. Therefore, by measuring the microwave powers and calculating the power ratio, the microwave frequency can be estimated. Thanks to the complementary nature of the power penalty functions, a power ratio having a faster change rate versus the input frequency, i.e., a greater first-order derivative, is resulted, which ensures an improved measurement range and resolution. The proposed approach for microwave frequency measurement of a continuous-wave and a pulsed microwave signal is experimentally investigated. A frequency measurement range as large as 17 GHz with a measurement resolution of plusmn 0.2 GHz for a continuous-wave microwave signal and plusmn0.5 GHz for a pulsed microwave signal is achieved.