Low noise, high efficiency GaAs IMPATT diodes at 30 GHz

Low noise, very high efficiency IMPATT diodes provide an attractive alternative to Gunn diodes for many millimetre-wave applications. GaAs hi-lo single-drift IMPATT diodes are demonstrated. The diodes are fabricated using molecular beam epitaxy and (at approximately 30 GHz) exhibit exceptional efficiencies (>20%), very low FM noise (-88 dBc/Hz at 100 kHz off-carrier) and simultaneous CW power levels in excess of 300 mW.<>     

Experimental Evaluation of Noise Parameters in Gunn and Avalanche Oscillators

Equations are presented that express noise-to-carrier ratio and rms frequency deviation of a negative-resistance oscillator with a multiple-resonant circuit in terms of effective available noise power densities of both 1/f and white-noise sources, an effective saturation factor, and an appropriate Q/sub L/ of the oscillator. Experimental evaluation of the noise parameters in Gunn and avalanche oscillators by use of these equations is described. AM and FM noise measurements have been made on X-band Gunn oscillators and Si and GaAs avalanche oscillators for frequency off carriers extending from 1 kHz to 10 MHz. Both 1/f and white noise have been observed in these oscillators. The validity of the above equations has been verified for Gunn oscillators from the dependence of the noise spectra on Q/sub L/. For Gunn oscillators and Si and GaAs avalanche oscillators, the effective noise-temperature ratio for white noise, N/kT/sub 0/, has been found to be 23~29, 41~51, and 38~44 dB, and the effective saturation factor to be 2~2.9, 0.5~2.4, and 2, respectively. An increase of N/kT/sub 0/ with the RF voltage across the diode has been observed in Si avalanche oscillators. Parameters for 1/f noise have also been evaluated approximately.     

Intrinsic FM noise of Gunn oscillators

It has been experimentally shown that the product of the mean frequency deviation of FM noise and the external quality factor varies inversely proportional to the power output of Gunn oscillators. This behavior of FM noise of Gunn oscillators with power output is in very good agreement with theoretical predictions of large-signal diffusion noise in GaAs devices. At optimum power output, the calculated and experimentally determined noise measure ranges between 17 and 22 dB.     

Design and Performance of X-Band Oscillators with GaAs Schottky-Gate Field-Effect Transistors

The circuit construction and design of an X-band oscillator with a GaAs Schottky-gate FET have been studied. The oscillation characteristics including stability and noise performance have been examined in order to clarify the position of a GaAs FET as a microwave solid-state oscillator device. The experiments have revealed that 1) the GaAs FET simultaneously possesses the most desirable features of both Gunn and IMPATT oscillators, i.e., low bias voltage operation and fairly high efficiency, and 2) it is situated between Gunn and GaAs IMPATT oscillators with respect to noise properties. The results indicate that the GaAs FET oscillator will soon be joining the family of microwave solid-state oscillators as a promising new member.     

低相噪体效应二极管的研制

体效应振荡器相位噪声主要取决于体效应管的噪声.文中介绍了低相噪体效应管的设计与工艺实现,制作出了一种与设计基本一致的Ku波段低相噪体效应二极管.该器件在Ku波段高端输出功率大于1 50mW、转换效率大于5%.将其安装于低相噪介质振荡器中,在保证一定的输出功率的情况下,相位噪声小于-98dBc/Hz/5kHz,-10dB谱线宽度小于200Hz.     

Q-dependence of Gunn Oscillator FM Noise (Short Papers)

Measurements of FM noise and the external quality factor Q/sub ex/ of X-band Gunn oscillators are reported which show that both unconverted and intrinsic FM noise vary inversely as Q/sub ex/, if bias voltage, RF power, and frequency are kept constant.     

Noise in Single-Frequlency Oscillators and Amplifiers

A generalization of previous oscillator noise analyses has been developed to permit reliable noise characterization of active nonlinear devices. Effects due to sideband correlation in the equivalent noise source are included. A rotating wave approximation (RWA) developed by Lax is used in obtaining the amplitude and phase noise spectra. Conditions are given for phase stabilization of free-running oscillators and for minimum phase noise in phase-Iocked oscillators and amplifiers. Stability criteria, discussion of spurious sidetones, and effects of a noisy synchronizing signal are given. The noise measure is used to obtain alternative expressions for the noise spectra and the carrier-to-noise ratios of locked oscillators and amplifiers. It is shown that the noise power gain of AM fluctuations is usually much lower than the corresponding gain for FM noise. The theory should be useful in optimizing the noise performance of nonlinear RF generators, such as IMPATT, BARITT, and Gunn diode oscillators.     

Parallel-fed c.w. Gunn oscillators cascaded in X band waveguide for higher microwave power

Waveguide devices containing several GaAs Gunn diodes, synchronised to operate at single frequency, have been constructed. Four diodes, cascaded in a waveguide and biased at the same voltage, delivered 300 mW at 9 GHz. These parallel-fed arrays of Gunn oscillators can be tuned to be highly directional. Directivity of 20 dB was observed.     

Performance of P-type epitaxial silicon millimeter-wave IMPATT diodes

A series of p-type IMPATT diodes (p⁺pn⁺) have been fabricated from epitaxially grown silicon for operation as oscillators at Ka-band frequencies. A maximum CW output power level of 700 mW at 29.6 GHz, a maximum conversion efficiency of 10.9 percent, and a minimum FM noise parameter, M, of 25 dB have been measured on this series of p-type diodes. A diode oscillating in a variable height radial disk cavity was frequency tuned from 27.5 to 40 GHz, covering the entire Ka-band, with a 1.4 dB power variation over the tuning range. The minimum CW output power of this tunable oscillator was 360 mW at 6.5 percent efficiency.     

FM noise in a Gunn-effect oscillator

FM noise in a cavity-controlled Gunn oscillator is investigated both theoretically and experimentally. The susceptance of a GaAs Gunn diode fluctuates following velocity fluctuations of high field domains. This results in FM noise. The fluctuations of the velocity are considered to be due mainly to those of carrier concentration fluctuations. Measured FM noise is in good agreement with the model, verifying that fluctuations of carrier concentration result in FM noise in the oscillator. When the quality factor Qexof the resonant cavity used becomes large, the FM noise characteristic deviates from the theoretical one based on the fluctuations of carrier concentration. The fluctuations of the voltage across the diode in the resonant cavity also influence the domain dynamics and hence the diode susceptance. These seem to be causes of the deviation.     

Experiments on integrated gallium-arsenide f.e.t. oscillators at X band

Experimental results obtained with GaAs f.e.t. oscillators at X band are described. It is demonstrated that the output power of f.e.t. oscillators is sufficient to drive X band mixers. The noise measure of these oscillators is competitive with Gunn devices, and can be reduced further.     

A Two-Stage IMPATT-Diode Amplifier

The system aspects and packaging of a two-stage FM IMPATT-diode amplifier are described. The amplifier combines the output power of 4 IMPATT diodes in the final stage to provide an output power of greater than 4 W at 6 GHz. The system has a locking bandwidth of greater than 200 MHz with a 16-dB gain and a noise figure of less than 50 dB. Both the design and the experimental performance of the amplifier and each of its stages are discussed. The noise characterization of IMPATT-diode amplifiers, operating as injection-locked oscillators or stable amplifiers, determined the mode of operation for each stage. Included in the paper are experimental results of large-signal noise characterization of both Si and GaAs IMPATT diodes, as are the noise characteristics related to the output power and gain.     

Transmission-Type Injection Locking of GaAs Schottky-Barrier FET Oscillators

Transmission-type injection-locked oscillators equipped with both signal-input and power-output ports are studied. A comparison with traditional reflection-type injection-locked oscillators, in which a signal is injected into the output port of the oscillator, is presented theoretically. It is shown that the Iocking range of transmission types always differs from the reflection type by a factor of G/sub s// G/sub p/ where G/sub s/ represents the maximum stable gain of the two-port oscillator and G/sub p/ represents the square root of the output power ratio of the two ports. Experiments on common-source injection-locked oscillators using GaAs FET chips are described and show that, with transmission types, a 1.8 times wider Iocking range can be obtained than with reflection types. Furthermore, investigation of FM noise for both types of injection revealed lower off-carrier FM noise for transmission types than reflection types, even though the Iocking gain of the transmission types was kept the same as that of reflection types. Thus overall features of transmission-type injection locking were found to be advantageous for FM signal amplification even though there is a minimal power loss at the signal input port.     

A resonant-cap power combiner for two-terminal millimeter-wavedevices

A power combiner for three active two-terminal devices located under a common resonant cap is presented. An equivalent circuit with lumped elements describing the coupling between the devices is derived from a numerical finite-element simulation of the resonator. The applied monolithically integrated mounting technique for the active devices minimizes parasitic elements and gains high reproducibility and symmetry. Experimental results with GaAs IMPATT diodes on diamond heatsink of up to 500 mW at 91 GHz with a dc to RF conversion efficiency of 9.0% and excellent combining efficiency demonstrate the capability for power generation in the mm-wave region     

High-performance second-harmonic operation W-band GaAsGunn diodes

High output power performance and DC-to-RF conversion efficiency of second-harmonic-operation W-band (75-110 GHz) GaAs Gunn diodes is reported. Output powers of 96 and 48 mW at 94 and 103 GHz, respectively, with a DC-to-Rf conversion efficiency of 2.7 and 2.3 percent, have been achieved using single-diode GaAs Gunn oscillators. The operation of these diodes requires 2 to 4 W of DC power consumption     

Power-noise characterization of phase-locked IMPATT Oscillators

IMPATT diode characterization on the basis of output power and the corresponding FM noise figure over a range of operating conditions is presented. The characterization consists of families of power noise curves obtained for a phase-locked IMPATT oscillator where the supply current, load conductance, and the operating frequency are parameters. It is shown that the maximum output power and minimum FM noise are not achieved concurrently. In particular FM transmitter application, it is shown that the best performance for each type of diode was obtained when operated at less than maximum power (and at reduced efficiency) where the system benefits from the attending lower noise. Better system performance, this application, was obtained with the GaAs IMPATT diode. The power-noise characterization defines the optimum operating conditions for an IMPATT diode and provides a valid basis for the comparison of diodes for specific applications.     

Factors Limiting the Signal-to-Noise Ratio of Negative-Conductance Amplifiers and Oscillators in FM/FDM Communications Systems (Short Papers)

A derivation is presented for the signal-to-noise ratio of negative-conductance amplifiers and oscillators in FM/frequency division multiplexing (FDM) communications applications. Results indicate the limiting value of signal-to-noise ratio depends on the semiconductor properties and channel loading only. This means circuit adjustments, such as Q, cannot increase the signal-to-noise ratio without bounds. Typical specifications are given. Limiting values of signal-to-noise ratio for Gunn and Si IMPATT devices are given in typical applications. Results indicate that Gunn devices have a clear advantage over Si IMPATT'S in a signal-to-noise sense.     

Traveling-Wave IMPATT Amplifiers and Oscillators

Traveling-wave IMPATT oscillators and amplifiers are analyzed using a Iarge-signal transmission-line model. A specific case for a GaAs structure at 33.7 GHz is examined in detail. General equations relating to the design and expected power output from these devices are also developed. It is concluded that more RF power can he generated by traveling-wave structures than is obtainable from discrete IMPATT devices.     

Noise characteristics of GaAs and Si IMPATT diodes for 50-GHz range operation

Direct comparison of noise behaviors between GaAs Schottky-barrier junction and Si diffused p⁺-n junction diodes operating in the 50-GHz range is reported by using the same circuitry. In the oscillator operation, the GaAs diode exhibits excess "1/f^m" noise near carrier, whereas the Si diode shows flat spectrum. Far from the carrier, and AM-DSB-NSR of -133 dB in a 100-Hz bandwidth and an FM noise measure of 27.1 dB are observed for GaAs diodes. Corresponding values obtained for Si diodes are -125 and 36.2 dB, respectively. As a reflection amplifier, minimum noise figures of 27.5 and 38 dB are achieved for the GaAs and Si devices, respectively. These results indicate that the GaAs IMPATT is superior in noise behavior to the Si diode also in the 50-GHz frequency range by about 10 dB. It is emphasized that the noise induced in the bias circuit of the IMPATT oscillator is a replica of the sideband noise of the output power and can be used as an indicator to obtain a low-noise tuning condition of the oscillator.     

Design of Stable, Very Low Noise, Cavity-Stabilized IMPATT Oscillators for C Band

Two types of C-band IMPATT oscillators, which easily meet the noise and stability requirements for use as local oscillators in microwave FM communications equipment, are described. Both types use a transmission cavity-stabilization circuit as proposed by Kurokawa. In one of them a TE/sub 103/ mode rectangular invar cavity is used for stabilization, while in the other the coupling is made via a high-Q cylindrical TE/sub 011/, mode cavity. Although the Si IMPATT diode is inherently noisy, it is shown that a proper choice of circuit parameters and diode characteristics leads to measured FM noise levels of less than 0.2 Hz in a 100-Hz band. With respect to frequency stability, special attention is paid to hysteresis-free compensation of temperature effects and to the influence of changes with time and ambient temperature of the diode and of the internal atmosphere of the cavity. By careful processing and sealing, an average temperature stability of better than -0.4 ppm//spl deg/C was realized with temperature cycling between 26 and 51/spl deg/C over a period of 450 h.