Analysis of Millimeter Wave Varactor-Tuned Gunn Oscillator Stabilized with a Transmission Cavity

A novel circuit architecture which describes millimeter wave varactor-tuned Gunn oscillator stabilized with a transmission cavity has been proposed in this paper. A corresponding equivalent circuit model has been presented in order to study its performance characteristics. The circuit model consists of four parts which are varactor cavity, main cavity, transmission waveguide and transmission cavity. Based upon this model, electrical tuning characteristics have been studied at first. Mode jumping problems during electrical tuning process have been analyzed qualitatively. Moreover, quality factor and efficiency of the circuit model have been derived by virtue of relevant circuit parameters. The effects of some important circuit parameters affecting circuit performance parameters have been discussed. The circuit model can describe the circuit architecture accurately and effectively. This circuit architecture, which can generate signals exhibiting low frequency modulation noise, high frequency stabilization and electrical tunable characteristics, is applicable to various practical situations.     

Novel varactor-tuned millimetre-wave Gunn oscillator

A novel design of varactor-tuned millimetre-wave second-harmonic Gunn oscillator is reported in which a varactor is mounted in a secondary cavity resonant at the fundamental frequency of the Gunn diode. This has the advantage that the varactor does not significantly load the Gunn diode at the output second-harmonic frequency, and enables the oscillator to produce the maximum possible output power from the diode while still offering varactor tuning and high Q.     

Wide-Band Varactor-tuned Coaxial Oscillators

An experimental investigation into the effects of package and circuit reactances on wide-band varactor-tuned oscillators is described. The results are used to design an X-band Gunn coaxial oscillator with a tuning range in excess of 3 GHz. It is shown that the stray reactance, junction capacitance, and bond-wire inductance affect the varactor tuning characteristics. The characteristics are conveniently displayed by the reflection phase variation with tuning voltage and frequency. A general theory for wide-band varactor-tuned oscillators is presented which is related to the impedance characteristics. These results are used to design three coaxial varactor-tuned oscillators. The first two oscillators are series arrangements while the third oscillator is a parallel arrangement. A simple circuit technique is used to improve the tuning range of each arrangement. This technique is shown to increase the coupling to the varactor diode and decrease the oscillator Q by reactance compensation.     

Varactor-tuned integrated Gunn oscillators

Electronic tuning of Gunn diodes in hybrid integrated circuits has been studied. Microstrip transmission lines were used to form resonant circuits into which a Gunn diode and a varactor diode were mounted to provide the microwave power and frequency tuning, respectively. Basically, two types of circuits have been investigated. The first is a half-wavelength open-circuited microstrip `cavity' with this transmission line and the varactor diode attached between the end of the cavity and an RF ground. The second is a lumped LC circuit in which the inductance of a short high-impedance microstrip line is resonated with the lumped capacitance of the varactor diode. The latter circuit provides a tuning range of over 10 percent at 7.5 GHz. The power output varies within 2 dB in the tuning range.     

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.     

Microwave voltage tuned microstrip ring resonator oscillator

A microwave oscillator incorporating a varactor-tuned microstrip ring resonator was developed using a single packaged varactor diode which together with other required components was mounted inside the ring structure. A tuning bandwidth of ~30% was achieved with forward and reverse biasing of the varactor diode. The measured phase noise of the new oscillator was found to be better than -90 dBc kHz from the carrier     

Varactor-tuned X band Gunn oscillator using lumped thin-film circuits

The operation of a varactor-tuned oscillator using an unen-capsulated Gunn and varactor diode is described, where the associated circuit consists of lumped elements fabricated using thin-film techniques. Depending on the GaAs material, the oscillator provides output powers greater than 10 mW and a tunable 3 dB bandwidth in excess of 1 GHz. At zero varactor bias, the frequency can be set in the 7?12 GHz range. Satisfactory correlation with the theory is demonstrated.     

Varactor diode for tuning high-power solid-state microwave oscillators

A novel varactor diode has been developed for tuning high-power microwave solid-state oscillators. The resulting output power against frequency remains much flatter than conventional high-power varactor-tuned oscillators.     

Wide-Range Varactor-Tuned Terahertz Oscillator Using Resonant Tunneling Diode

We propose a wide-range varactor-tuned terahertz oscillator using a resonant tunneling diode (RTD) and estimate the tuning range. In a slot antenna, a varactor diode is placed in parallel with an RTD and can be operated with different bias voltages. Frequency tuning is possible by changing the varactor-diode capacitance with the bias voltage. A wide frequency tuning range >200 GHz (500 to 740 GHz) is obtained with an oscillator with a 20-μm-long antenna, 1.3-μm² RTD mesa, and 16-μm² varactor-diode mesa by electromagnetic-field analysis including a varactor-diode model.     

Q Degradation in Varactor-Tuned Oscillators (Short Papers)

A general analysis of varactor-tuned negative-resistance oscillators is presented to show the varactor loading effect on the oscillator Q. The external Q of the varactor loaded circuit normalized with respect to the unperturbed external Q is plotted as a function of the tuning range for several values of the varactor Q and the capacitance ratio.     

An integrated wide-band varactor-tuned Gunn oscillator

A report is made of a thin-film varactor-tuned Gunn effect oscillator in X band employing unencapsulated diodes. The Gunn device, which is an inverted mesa type, is mounted off the substrate on a copper header and this arrangement can dissipate 7 W without the Gunn device suffering thermal damage. The varactor is a beam-lead silicon p⁺nn⁺IMPATT diode connected in series with the Gunn device. A circulator is integrated with the oscillator to provide load isolation, and tuning ranges in excess of 2 GHz are reported. Good agreement exists between calculated and measured values of oscillator tuning range.     

A 50-GHz silicon IMPATT diode oscillator and amplifier

Recent experimental observations on a silicon impact avalanche transit-time diode oscillator and amplifier CW-operated at 50 GHz are presented. 1) CW oscillation power of 100 mW was obtained at an overall efficiency of 2 percent. The oscillation frequency was continuously tunable over a 1.3-GHz range by a sliding short. 2) Phase-locking has been achieved with a maximum normalized gain-bandwidth product of 0.1. The minimum locking signal power required for a 500-MHz locking bandwidth was 20 dB below the oscillator output. 3) Electronic tuning of the oscillator frequency was demonstrated by placing a millimeter-wave varactor diode in the tuning circuit. The output frequency versus the bias voltage on the varactor diode was linear with maximum frequency deviation of 300 MHz. Frequency modulation of the oscillator by driving the varactor with a sinusoidal source was obtained at a modulation frequency of 50 MHz. 4) Stable amplification with 13-dB gain was obtained, centered at 52.885 GHz with a 3-dB bandwidth of 1 GHz. The maximum output power obtained was 16 mW. Higher gain of about 17 dB was obtained at a reduced bandwidth. The noise figure of the amplifier was 36 dB. Equivalent circuits for the oscillator and the amplifier are derived. The calculated results agree reasonably well with the experimental observations.     

Selection and modeling of integrated RF varactors on a 0.35-/spl mu/m BiCMOS technology

Integrated varactors are becoming a common feature for many RF designs and in particular RF voltage controlled oscillators (VCOs). Optimization of the quality of both the inductor and the varactor from the VCO core is essential. This work details the characterization and optimization of a number of varactor types available on a typical submicron BiCMOS process. Engineering of the bottom plate of the varactor was used to optimize the quality factor of the varactor. No additional mask layers or processing steps were required to achieve this. Integrated isolated diode varactors with quality factors of 30 at 2 GHz have been demonstrated with tuning capacitance ranges of 2.5. Integrated MOS capacitor varactors with quality factors of 50 at 2 GHz have been demonstrated with tuning capacitance range of 5. A spice model for one of the varactor types is further developed in this paper. Accurate prediction of varactor performance over voltage bias and frequency was achieved.     

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 λg/2 in waveguide channel.     

Varactor Tuning Diodes as a Source of Intermodulation in RF Amplifiers

In RF amplifiers used in the front ends of VHF receivers which are to be tuned over a wide frequency range, varactor diodes are often used to accomplish the necessary change in tuning capacitance. nce. The variation of capacitance with dc voltage which enables the tuning function to be accomplished results in a nonlinear characteristic stic which, in turn, introduces harmonic and intermodulation dtion.storon. This paper is concerned with the determination of tef12f 1-J2) intermodulation distortion product generated by the varactor diodes and modified by the characteristics of the input tuned circuit. Both third-order and "distortion-on-distortion" second-order intermodulation mechanisms are included in the calculation. An expression is presented for the magnitude of the (2f1-f2) intermodulation intercept which includes the effects of the characteristics of the tuned circuit and the various parameters used to characterize the varactor diode. Design considerations combining both the linear and the intermodulation ation performance of the input circuit are discussed, including design tradeoffs and interrelationships among the circuit parameters and performance variables. Illustrative calculations are given based on the characteristics of the MV3102 varactor diode.     

Broad-Band Varactor-Tuned Impatt-Diode Oscillator (Short Papers)

A varactor-tuned IMPATT-diode oscillator with a continuous and monotonic tuning bandwidth of 27 percent and a potential tuning range in excess of 40 percent is described. The results of a computer program which optimizes the tuning bandwidth of the equivalent circuit of the voltage-controlled oscillator (VCO) are presented. The VCO consists of two varactors located symmetrically on each side of an IMPATT diode all mounted in a ridged waveguide with two matched outputs into 50-Omega coaxial. Experimental results on bandwidth, power output, frequency linearity, and FM noise are presented.     

U-band shield suspended-stripline Gunn DRO and VCO

A millimeter-wave IC dielectric resonator oscillator (DRO) is proposed. Equations that give the resonant frequency of the dielectric resonator DR in suspended stripline (SSL) are derived. A U-band voltage-controlled oscillator (VCO) with varactor tuning also has been developed. The Gunn diode and varactor used in both of the oscillators are commercially available packaged devices. Restrictions on the performance of the oscillators imposed by packaged and mounted networks and the self-characteristics of the solid-state devices have been analyzed. An electronic tuning range greater than 1000 MHz with an output power exceeding 15 dBm across the bandwidth in the 53-GHz region has been realized for the SSL VCO. An SSL DRO with an output power of more than 17 dBm and a mechanical tuning range of 1.5 GHz in the 54-GHz region has been achieved     

X-band varactor tuned monolithic GaAs FET oscillators†

The design, fabrication and performance of X-band varactor-tuned monolithic GaAs FET oscillators is described. The design is based on small and large signal device characteristics. A manufacturable process is used in order to realize the oscillators. The experimental performance agrees with the theoretical expectations within 0·2% for the oscillation frequency and 4% for the tuning bandwidth. Best tuning bandwidth and output power values exceeded 2 GHz and 28 mW. Wafer dispersion depends on oscillator characteristics and varies between ±1% and ±7·7% for oscillators with a varactor in the FET source. The rf wafer yield is 65%. Finally, noise and temperature characteristics are given.     

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.     

High-performance millimetre-wave suspended stripline Gunn VCO

A novel millimetre-wave integrated circuit Gunn voltagecontrolled oscillator (VCO) has been developed with high output power using suspended stripline. An output power of 100 to 150mW has been achieved at frequencies between 33 and 42 GHz. A varactor diode was mounted in alignment and in close proximity to the Gunn diode to achieve an electronic tuning range of 300 MHz