Theoretical Study of Millimeter Wave Harmonic Oscillator Stabilized with a Transmission Cavity

An equivalent circuit model of millimeter wave second harmonic oscillator stabilized with a transmission cavity has been proposed for constructing analytical formulations between performance parameters of the oscillator and parameters of the circuit. The model consists of an equivalent circuit of fundamental wave and that of second harmonic wave. Each of the circuits comprises circuit models of main cavity, transmission waveguide, and transmission cavity. Absorbing material placed between the transmission waveguide and the transmission cavity can suppress additional resonances originated from transmission cavity. The behavior of the second harmonic oscillator can be effectively described by the circuit model. Furthermore, based on this model, mechanical tuning characteristics have been studied at first, and then analytical formulas for quality factor and efficiency depending on circuit parameters have been derived. The circuit parameters can be conveniently extracted by electromagnetic field simulation. Hence the formulas exhibit both compact form and enough accuracy. Thereafter, general rules of performance parameters varying with circuit parameters have been deduced for the harmonic oscillators. Then some design considerations have been derived according to the corresponding analysis. The equivalent circuit model is useful for designing and adjusting millimeter wave second harmonic stabilizing oscillator with a transmission cavity.     

Impedance Characteristics of Two Coplanar RLTs in Millimeter Wave VCO Waveguide Cavities

Impedance characteristics of two coplanar radial line transformers (RLTs) placed in millimeter wave voltage control oscillators (VCOs) waveguide cavities have been studied in this paper. Mode matching methods are employed to calculate self impedance of the RLT mounted on active device and mutual impedance of the two coplanar RLTs. Some general rules concerning impedance characteristics of two coplanar RLTs configuration influenced by the parameters of the structure have been deduced. In addition, an equivalent network is presented based upon the impedance matrix of the coplanar RLTs; the load impedance looking outward from the active device has been derived in virtue of the equivalent network and the impedance of varactor diode. The equivalent network which describes the relationships between the load impedance and the impedance of varactor diode is helpful for developing millimeter wave varactor-tuned VCO of this structure.     

Varactor Controlled Gunn Oscillator at W-Band

This paper describes the experimental circuit and measured performance of varactor tuned Gunn oscillator at W-band. The power output of 12.5 dBm has been achieved when packaged GaAs Gunn diode is used. Linear frequency excursion of 150 MHz with power variation of 1 dB has been observed when varactor was given reverse bias from 0 to 20 volts. GaAs hyperabrupt varactor is used in parallel to gunn diode at a distance of odd multiple of g/2 in waveguide channel.     

Injection locking of a diode laser locked to a Zeeman frequency stabilized laser oscillator

We describe the design and performance of an injection-locked diode laser locked to a stabilized, single frequency, unmodulated diode laser. The master oscillator is a grating-tuned, external cavity diode laser which is stabilized on a Doppler free alkali metal resonance transition frequency via Zeeman locking. The master oscillator frequency is shifted by an acousto-optic modulator, which provides optical isolation of the master oscillator laser while tuning of the acousto-optic modulation frequency can also provide frequency offset tuning. The slave laser is a free running diode which is injection-locked by a small fraction of the frequency shifted master oscillator light. Good long- and short-time frequency stability are observed for both the Zeeman-locked master oscillator and the injection-locked slave laser.     

Millimeter wave monolithic high electron mobility (HEM) varactor diode-grid frequency tripler arrays

High Electron Mobility (HEM) varactor structures have been studied for millimeter-wave monolithic diode-grid frequency tripler array applications. The improved HEM varactor diode structures provide a highly nonlinear C-V characteristic (i.e., a steep slope of the C-V curve and a large capacitance ratio) which produces high harmonic generation efficiency and reduce the power requirement for efficiently pumping each device. The effects of the light illumination on the C-V characteristics of the Barrier-Intrinsic-N⁺ (BIN) varactor diode have also been studied and the results will be discussed in this paper. In the development of a monolithic diode-grid frequency multiplier array, the low-loss quasioptical configuration is used for the construction of the multiplier circuit. The study of the effects of the light illumination on the C-V characteristics of varactor diode is important in understanding the potential applications of the quasi-optical varactor diode-grid frequency multiplier array circuit.     

Development of Broad Band VCO at Ka-Band

A broad band VCO has been developed at Ka-band for FMCW Radar applications. To achieve a wide range of frequency variation, VCO has been designed in series configuration. Design steps have been presented. VCO exhibits a tuning range of 600 MHz with the power output of 50 mw, when the controlled varactor voltage varies from 7.5 volts to 15 volts. Frequency drift with temperature has been contained within 30 MHz using a proportionally controlled DC heater module over the temperature range of 0°C to +55°C. Phase Noise of the oscillator measured at the mid and extreme frequencies is about -70 dBc/kHz at 10 kHz away from the carrier. The experimental circuit and measured performance is also presented.     

Integrated image-line steerable active antennas

This paper reports a varactor-tuned Gunn oscillator constructed in an image-line circuit and integrated with a grating antenna. The combined circuit exhibited a 2 percent electronic tuning range corresponding to a frequency steerable range of 4 degrees. The active antenna demonstrated a clean spectrum with low side lobes. The beam angles agree very well with the prediction. The circuit can be produced at low cost and should have many applications at millimeter-wave frequencies     

Nonlinear Frequency-Modulation Distortion Analysis for VCO Based on Harmonic Balance Method

The analysis methods for the steady-state responses of the voltage tuning negative resistance oscillator (voltage-controlling oscillator, VCO) by the microwave nonlinear autonomous circuit harmonic balance method in millimeter-wave bands are studied in the paper. Firstly, the quasi-periodic characteristic of the steady-state response of the VCO modulated by a periodic signal is proved. Then, on the bases of the harmonic balance analysis and the inter-modulation balance analysis, a novel method for obtaining the steady-state tuning performance and the nonlinear frequency-modulation distortion characteristic of the VCO is presented. The total analysis process is aimed to a kind of NRD-guide Gunn diode VCO. The large-signal lumped equivalent circuit model of the millimeter-wave P⁺N-junction varactor is also given for explaining the algorithm and the principle of the NRD-guide VCO.     

A 345 GHZ heterodyne receiver for the James Clerk Maxwell Telescope

In this paper we describe the design and performance of a low-noise 345 GHz heterodyne receiver. The mixer uses a lead alloy SIS tunnel junction mounted in reduced height rectangular waveguide and is tuned with a single backshort. Local oscillator power is provided by a broad-band Gunn oscillator which drives a frequency quadrupler. The heterodyne performance has been verified in the laboratory using a gas absorption cell. In November 1991 this receiver was successfully commissioned and by direct comparison with a Schottky diode receiver we confirm a best receiver noise temperature of 150K (DSB) at 355 GHz and a tuning range of 300 to 380 GHz. The receiver is now available as a JCMT facility instrument.     

A Gunn-Diode Active Leaky-Wave Frequency Scanning Antenna

A frequency tunable active leaky-wave scanning antenna using Gunn-diode voltage control oscillator (VCO) as source is developed. The frequency tuning controlled by changing either the varactor diode dc bias or the Gunn diode dc bias is demonstrated. The measured scanning angle of active antenna is close to 15 degree as the Gunn VCO frequency tuned from 12.58GHz to 12.98GHz. To excite the first higher order mode of the microstrip leaky-wave antenna is fed asymmetrically. The dominant mode excitation has been successfully suppressed by adding a sequence of covered wire in the middle line of the microstrip leaky wave antenna. This is a prototype of frequency scanning antenna using two terminal device, which can be easily scaled up to millimeter wave frequency region.     

Varactor-tuned gunn diode voltage controlled oscillator antenna array

A simple varactor tuned X-band Gunn diode VCO antenna array which is strongly coupled has been demonstrated. These arrays have the advantages of simple biasing circuit, no resistors required to eliminate multimode problem and suitable for monolithic integration circuit. Preliminary results show a maximum tuning range of 47MHz for 1×1 array and 170MHz for 2×2 array. In order to solve power combining heating problem, we move the backside metal forward and it becomes a microstrip form. The measured frequency and radiation patterns of these grid arrays agree very well with theoretical calculations.     

Electronically tunable surface-coil-type resonator for L-band EPR spectroscopy

The automatic frequency control (AFC) circuit in conventional electron paramagnetic resonance (EPR) spectrometers automatically tunes the microwave source to the resonance frequency of the resonator. The circuit works satisfactorily for samples stable enough that the geometric relations in the resonance structure do not change in a significant way. When EPR signals are measured during in vivo experiments with small rodents, however, the distance between the signal source and the surface-coil detector can change rapidly. When a conventional AFC circuit keeps the oscillator tuned to the resonator under those conditions, the resultant frequency change may exceed +/-5 MHz and markedly shift the position of the EPR signal. Such a shift results in unacceptable effects on the spectra, especially when the experimenter is dealing with narrow EPR lines. The animal movement also causes a mismatching of the resonator and the 50-ohm transmission line. Direct results of this mismatching are increased noise; shifts in the position of the baseline; and a high probability of overdriving the signal preamplifier with consequent loss of the EPR signal. We therefore designed, built, and tested a new surface-coil resonator using varactor diodes for tuning the resonance frequency to the fixed frequency oscillator and for capacitive matching of the resonator to the 50-ohm transmission line. The performance of the automatic matching system was tested in vivo by measuring EPR spectra of lithium phthalocyanine implanted in rats. Stability and sensitivity of the spectrometer were evaluated by measuring EPR spectra with and without the use of the automatic matching system. The overall experimental performance of the spectrometer was found to significantly improve during in vivo experiments using the automatic matching system. Excellent matching between the 50-ohm transmission line and the resonator was maintained under all experimental circumstances that were tested. This should allow us now to carry out experiments that previously were not possible.     

A GaAs planar Schottky varactor diode for left-handed nonlinear transmission line applications

The left-handed nonlinear transmission line(LH-NLTL) based on monolithic microwave integrated circuit(MMIC) technology possesses significant advantages such as wide frequency band,high operating frequency,high conversion efficiency,and applications in millimeter and submillimeter wave frequency multiplier.The planar Schottky varactor diode(PSVD) is a major limitation to the performance of the LH-NLTL frequency multiplier as a nonlinear component.The design and the fabrication of the diode for such an application are presented.An accurate large-signal model of the diode is proposed.A 16 GHz-39.6 GHz LH-NLTL frequency doubler using our large-signal model is reported for the first time.The measured maximum output powers of the 2nd harmonic are up to 8 dBm at 26.4 GHz,and above 0 dBm from 16 GHz to 39.6 GHz when the input power is 20 dBm.The application of the LH-NLTL frequency doubler furthermore validates the accuracy of the large-signal model of the PSVD.     

ACTIVE-PASSIVE PIEZOELECTRIC ABSORBERS FOR SYSTEMS UNDER MULTIPLE NON-STATIONARY HARMONIC EXCITATIONS

Previous research has shown that piezoelectric materials can be shunted with electrical networks to form devices that operate similarly to a mechanical vibration absorber. These systems can be tuned to provide modal damping (modal tuning) or to attenuate a harmonic disturbance (tonal tuning). Semi-active piezoelectric absorbers have also been proposed for suppressing harmonic excitations with varying frequency, a scenario that cannot be easily controlled using passive devices. However, these semi-active systems have limitations that restrict their applications. In a previous study, the authors have developed a high performance active-passive alternative to the semi-active absorber that uses a combination of a passive electrical circuit and active control actions. The active control consists of three parts: an adaptive inductor tuning action, a negative resistance action, and a coupling enhancement action. This new device has been shown, both analytically and experimentally, to be very effective for the suppression of harmonic disturbances with time-varying frequency. In the present paper, the adaptive active-passive piezoelectric absorber configuration is extended so that it can track and suppress multiple harmonic excitations. A new optimal tuning law is derived, and the stability conditions of the system are investigated. The effectiveness of this new multi-frequency absorber design is demonstrated by comparing its performance and control power requirement to the popular Filtered-x adaptive feedforward control algorithm.     

Demonstration of a transportable 1 Hz-linewidth laser

We present the setup and test of a transportable clock laser at 698 nm for a strontium lattice clock. A master-slave diode laser system is stabilized to a rigidly mounted optical reference cavity. The setup was transported by truck over 400 km from Braunschweig to Düsseldorf, where the cavity-stabilized laser was compared to a stationary clock laser for the interrogation of ytterbium (578 nm). Only minor realignments were necessary after the transport. The lasers were compared using a Ti:Sapphire frequency comb as a transfer oscillator. The generated virtual beat showed a combined linewidth below 1 Hz (at 1156 nm). The transport back to Braunschweig did not degrade the laser performance, as was shown by interrogating the strontium clock transition.     

同轴虚阴极谐振效应研究

中国工程物理研究院应用电子学研究所的一些实验表明由阳极反射板、阳极网和阴极发射的电子束形成的环状虚阴极围成的准谐振腔是决定同轴虚阴极输出微波功率和传输模式的关键所在. 在二极管电压350kV，电流23kA条件下，获得了500MW的微波输出功率，能量转换效率约6.2％，工作频率3.3GHz，输出微波主要由TM₀₁模式和TE₁₁模式组成. 对同轴虚阴极的谐振效应进行了分析. 关键词： 高功率微波 同轴虚阴极 谐振腔 模式竞争     

Nonlinear resonant tunneling diode (RTD) circuits for microwave A/D conversion

Short-duration electrical pulses play important roles in ultrafast time-domain metrology: they are used to sample rapidly varying signals or as probe signals in ranging radars, time-domain reflectometry and in communication. In this work, we design a nonlinear transmission, which is loaded with resonant tunneling diode to be suitable for microwave A/D conversion. A resonant tunneling diode (RTD) has a negative differential resistance that means when the voltage increases the current decreases. The equivalent circuit of monostable line is given. The simulation is performed by using OrCad program. Results show that a spike is produced and after a charging time constant, another switching occurs. Hence – similar to a relaxation oscillator – the spiking period is determined by the amplitude and frequency of the input current. The transmission line itself ensures the generation and propagation of identical spikes, such as solitons formed after few diodes.     

A high efficiency 46 to 92 GHz all microstrip frequency doubler

Using packaged GaAs varactor diodes, a high efficiency 46 to 92 GHz frequency doubler has been developed. Microstrip circuits have been used to match the input and output impedances presented by the diode. A conversion loss of 8 to 10 dB was measured. This doubler circuit is useful for W-band (75 to 110 GHz) integrated circuit receivers and transceivers. The use of microstrip circuit can drastically reduce the fabrication cost in addition to size and weight.     

Investigations on optically controlled millimeter wave Gunn oscillators

There is a growing interest in optically controlled millimeter wave oscillators. In this paper, we have investigated the external-circuit impedances of an optically controlled millimeter wave subharmonic Gunn diode oscillator, which is illuminated by GaAs/GaAlAs laser beam. The variation of the external-circuit impedances looking outward from the Gunn diode with respect to the optical injection plasma density are calculated based on a field analysis method. The results give some useful conclusions for optically controlled millimeter wave Gunn diode oscillator design. Experimentally an optical tuning frequency shift of 7MHz is achieved at W-band.     

Frequency-locked tunable LD laser with a broad bandwidth

Using lock-in amplifer and proportional, integral, and derivative (PID) electric circuit, the frequency of diode laser is stabilized on a highly mechanical stable Fabry-Perot (FP) cavity transmission peak. When the frequency locking system is on, the frequency tunable range of the laser is about 4 GHz around the D1 transition of Rb. The laser frequency tuning is implemented by scanning the FP cavity length. The fluctuation of frequency of the output laser is less than 1 MHz, and the drift of the center frequency is less than 1.5 MHz in 1.5 min. This system has great potential of the application in the experimental investigation of the interaction between light and atoms, especially, for the case of far off the atomic resonance.