Radio Frequency Signal Generation Research Articles

Novel Architecture for a Photonics-Assisted Radar Transceiver Based on a Single Mode-Locking Laser

A novel solution for the optical generation of radio-frequency signals for coherent radars is proposed, which exploits the same mode-locking laser of the photonic-assisted radar receiver. The scheme, which is based on the concept of shifting the frequency of a laser mode, exploits a commercial optical in-phase/quadrature modulator to allow using a single mode-locking laser for both the radar transmitter and receiver, making the solution attractive for immediate and practical implementation in photonics-assisted transceivers.

Transmission of Wireless and Wired Services Employing a Simple System Architecture

This letter presents a novel modulation approach for simultaneous generation and transmission of optical radio-frequency (RF) wireless vector signal and baseband (BB) wireline signal using a single-electrode Mach-Zehnder modulator. Based on a double sideband with carrier suppression scheme and properly predistorted driving vector signal, a 2.5-Gb/s quadrature phase-shift keying (QPSK) signal at 60 GHz is generated with a 1.25-Gb/s BB ON-OFF-keying (OOK) signal. The proposed system can carry higher spectral efficiency vector signals and needs no optical filter to separate the BB and RF signals at remote nodes. Moreover, optical RF signal generation with frequency doubling is also achieved to reduce the bandwidth requirement of the transmitter. After transmission over 25-km single-mode fiber, the power penalties of the generated QPSK and OOK signals are about 4 and 0.1 dB, respectively.

Hybrid Access Network Integrated With Wireless Multilevel Vector and Wired Baseband Signals Using Frequency Doubling and No Optical Filtering

This letter experimentally demonstrated a hybrid access network which supports both radio-over-fiber and fiber-to-the-x systems. A 20-GHz radio-frequency (RF) 312.5-MSymbol/s M-ary phase-shift keying (PSK) signal and a baseband (BB) 1.25-Gb/s on-off keying signal are simultaneously generated and transmitted over an identical distributed infrastructure. The wired BB signal is compatible with the existing passive optical network (PON) system, and the wireless RF PSK signal can also share the same distributed infrastructure. The proposed system has no RF fading issue, no narrowband optical filter at remote node to separate the RF and BB signals, and can carry vector signals. Moreover, a frequency doubling for optical RF signal generation is achieved to reduce the bandwidth requirement of the transmitter. After transmission over 25-km standard signal-mode fiber, the receiver sensitivity penalties are less than 0.5 dB for both the RF and BB channels.

A new detection system for laser induced breakdown spectroscopy based on an acousto-optical tunable filter coupled to a photomultiplier: Application for manganese determination in steel

The development of a new detection system for laser induced breakdown spectroscopy (LIBS), based on a collinear quartz acousto-optical tunable filter (AOTF) for the ultraviolet spectral region coupled to a photomultiplier, is described. It was used in conjunction with a 1064 nm, 5 ns pulse duration neodymium-doped yttrium aluminium garnet (Nd:YAG) laser source and also employed a radio-frequency signal generator to control the AOTF and a digital delay generator to delay the start of the detection in relation to the instant of the application of the laser pulse. The detection system was optimized for highest detectivity for the manganese peak at 293.9 nm while analyzing a steel sample by LIBS. The resulting signal to background ratio at the optimal conditions of 2 µs delay time, 40 µs integration time gate and 110 mJ pulse energy was similar to that of a commercial echelle-intensified charge-coupled device (echelle-ICCD) detection system. The new detection system was then employed for manganese determination in steel samples, taking the emission signals at just 15 wavelengths, 5 related to the above mentioned manganese peak, another 5 to background emission around 296.0 nm and the others to the iron peak at 297.3 nm (internal standard). The resulting analytical curve for manganese, obtained using 5 samples in the concentration range of 0.214 to 0.939% w/w, presented a correlation coefficient of 0.979 for an exponential regression function. The relative errors of predicting the manganese concentrations, using the calibration curve, for 2 samples, containing 0.277 and 0.608% w/w, were 20.7 and − 1.9%, respectively.

Parallel Testing of a Phase-Locked Loop Lock Time in Production

Methods to accurately measure a phase-locked loop lock time in a multisite production environment will be presented. These methods are also applicable for testing voltage-controlled oscillators or transceiver frequency settling times and frequency and phase errors after settling for multiple devices under test in parallel using onboard frequency mixers and radio frequency (RF) signal generators or using RF receivers of automated testers. Fast Fourier transform (FFT) techniques are used to measure the lock time in a case when output frequency error exists.

Development of multi-channel radiofrequency (RF) interstitial hyperthermia system compatible with high-dose rate iridium-192 brachytherapy

9694 Background: We have developed a multi-channel RF interstitial hyperthermia system compatible with the high-dose rate Iridium-192 remote after loading system (Ir-192 RALS). The purpose of this presentation is to evaluate the heating characteristics of the system. Methods: The system is composed of eight channel RF signal generators, which can be controlled individually. Each RF generator consists of two types of electrodes: 1) an internal electrode made of stainless steel, which is originally an Ir-192 RALS applicator; and 2) a shared rectangular external electrode made of copper plate. For the computer simulation, we used simulation software (e-m CAD system, MAFIA ver. 3.20, CST, Germany) to calculate RF field distribution, magnetic field distribution and the specific absorption rate (SAR) distribution, in an arrangement using 4 needles inserted in a square-like formation, 2cm in distance from one another. For the experiments using the agar phantom, we generated a 5W 13.56 MHz RF signal for 5 minutes for 4 electrodes in the same square fashion. Results: The results from the computer simulation showed that SAR distribution outside each electrode was elevated, but the area inside the 4 electrodes did not show temperature elevation. The results from the experiments using the agar phantom showed a temperature increase in the center of the area surrounded by the 4 electrodes. Conclusions: Using an independently controlled RF signal, the results from the experiments with the agar phantom showed satisfactory temperature rise. The RF interstitial system we developed can provide greater heating volume compared to using a single internal electrode or multiple electrodes with a single generator. In addition, our system is compatible with the Ir-192 RALS, allowing for less-invasive interstitial hyperthermoradiotherapy by eliminating the trauma of needle re-insertion. No significant financial relationships to disclose.

Development of multi-channel radiofrequency (RF) interstitial hyperthermia system compatible with high-dose rate iridium-192 brachytherapy

9694 Background: We have developed a multi-channel RF interstitial hyperthermia system compatible with the high-dose rate Iridium-192 remote after loading system (Ir-192 RALS). The purpose of this presentation is to evaluate the heating characteristics of the system. Methods: The system is composed of eight channel RF signal generators, which can be controlled individually. Each RF generator consists of two types of electrodes: 1) an internal electrode made of stainless steel, which is originally an Ir-192 RALS applicator; and 2) a shared rectangular external electrode made of copper plate. For the computer simulation, we used simulation software (e-m CAD system, MAFIA ver. 3.20, CST, Germany) to calculate RF field distribution, magnetic field distribution and the specific absorption rate (SAR) distribution, in an arrangement using 4 needles inserted in a square-like formation, 2cm in distance from one another. For the experiments using the agar phantom, we generated a 5W 13.56 MHz RF signal for 5 minutes for 4 electrodes in the same square fashion. Results: The results from the computer simulation showed that SAR distribution outside each electrode was elevated, but the area inside the 4 electrodes did not show temperature elevation. The results from the experiments using the agar phantom showed a temperature increase in the center of the area surrounded by the 4 electrodes. Conclusions: Using an independently controlled RF signal, the results from the experiments with the agar phantom showed satisfactory temperature rise. The RF interstitial system we developed can provide greater heating volume compared to using a single internal electrode or multiple electrodes with a single generator. In addition, our system is compatible with the Ir-192 RALS, allowing for less-invasive interstitial hyperthermoradiotherapy by eliminating the trauma of needle re-insertion. No significant financial relationships to disclose.

A controllable phase coherent pulsed RF signal generator for microwave network analyzer measurements

In this paper, a method is proposed to build a phase coherent modulated radio-frequency (RF) signal with high depth, which can be used as an excitation signal for nonlinear pulsed-RF network analyzer measurements. The source consist of an RF carrier modulated by an arbitrary waveform generator whose sampling clock is phase coherent to the carrier. A software feedback technique is used to eliminate spurious harmonics and to correct the amplitude and phase distortions in the IF signal path. This technique allows to create a modulated excitation signal with a known spectrum (in amplitude and phase). Such a modulation signal is required to fully characterize a device-under-test under noncontinuous wave (modulated or pulsed) test conditions with a sampling downconvertor. The measurement of a controlled pulsed-RF spectrum shows the obtained performance (the bandwidth is limited to 4 MHz at this moment).

Scanning heterodyne optical interferometers

Compact, high performance, scanning heterodyne optical interferometers are introduced for interferometric phase-based measurement applications. The novel, in-line, almost common-path optical interferometer design offers robustness to externally induced phase noise via mechanical vibrations, thermal effects, and other environmental effects. Novel instrument designs are introduced for both transmissive and reflective interferometry. These instruments use acousto-optic devices or Bragg cells to implement rapid (e.g., <50 μs/scan spot) optical scanning of the test medium. Although the read optical beam scans a given test region, the double Bragg diffraction optical design of the instrument makes the final interfering output beams stationary on the two high speed photodetectors used for radio frequency signal generation via heterodyne detection. One photodetector acts as the fixed phase reference, while the other fixed photodetector picks up the test medium phase information as the optical beam scans the test region. The transmissive design instrument is built in the laboratory using flint glass Bragg cells. A typical 120 MHz heterodyne detected signal output had a carrier-to-noise ratio of 108.9 dBc/Hz measured at a +160 kHz offset using a spectrum analyzer resolution bandwidth of 30 kHz. The corresponding single-sideband phase noise was estimated at −101.57 dBc/Hz at 160 kHz offset. The measured instrument radio frequency dynamic range was ∼60 dB or an equivalent of 30 dB optical dynamic range, with a 1/1000 of a fringe cycle phase measurement accuracy. Test medium optical phase mapping was successfully tested with the instrument using a large area, 6 μm thick, birefringent-mode nematic liquid crystal cell. Our instrument allows the use of high continuous wave or peak power, broad spectral linewidth, coherent light sources. The instrument can have a high 50% optical power efficiency. High speed two-dimensional optical scanning of a test medium is possible with our instrument by using a fixed one-dimensional output high speed detector array, or via the use of high speed nonmechanical electro-optic deflectors.

The Design of Radio-Frequency Signal Generators

Certain factors involved in designing signal generators free from stray voltage errors are considered. The importance of accounting for all circuit details, particularly of wiring elements, is stressed. The impedances of certain connections, particularly of the output connections from generator to measured receiver, are shown to be important. Shielding is considered in some detail.