A Comparison of One- and Two-Idler Parametric Amplifiers (Correspondence)

The performance of a two-idler parametric amplifer is compared with that of a single-idler amplifer with a broad-banding resonator at its input. Both circuits contain the same varactor and are pumped at the same frequency. For most of the cases considered the two-idler amplifier gives a somewhat narrower bandwidth, slightly higher noise temperature, but lower sensitivity to variation of m/sub 1/ (the pump modulation rate) than the single-idler amplifier. The comparison is made over a range of pump and varactor cutoff frequencies     

Subharmonic pumping of parametric amplifiers

The purpose of this paper is to present in some detail the operation of a parametric amplifier pumped subharmonically as compared to being directly pumped. As considered here, subharmonic pumping does not involve harmonic pump power generation (external to the varactor) but the utilization of higher-order time-dependent capacitances to yield parametric amplification by employing, basically, only a three-frequency system. The analysis given here is based on an evaluation of the Fourier series representation of the time-dependent capacitance resulting from large-signal ("hard") pumping of varactors. This evaluation indicates that significant values of higher-order time-dependent capacitances suitable for parametric amplification are obtained with relative pump swings in excess of about 90 per cent. Utilizing these higher-order time-dependent capacitances, the amplifier operation for various orders of subharmonic pumping is treated, including such factors as pump power requirements, gain, and noise figure. It is shown that, under certain conditions, less pump power is required to generate the same negative conductance than with direct fundamental pumping. Furthermore, for the same pump power and fundamental pump frequency, it is determined that significant improvements in amplifier noise figure are achieved by employing subharmonic pumping, provided varactor losses are small. From the results obtained by both analysis and experiment, it is concluded that subharmonic pumping, even without harmonic power generation, is not only feasible but can be very useful up to C-band signal frequencies with existing varactors.     

Varactor harmonic-generator chain as a pump source for a parametric amplifier

This letter gives the results of experiments on the pumping of an X band nondegenerate parametric amplifier with a Q band varactor harmonic-generator chain. It is shown that care must be taken to ensure efficient filtering in the first stage of the chain, and methods are given to obviate spurious responses in the tuning range of the parametric amplifier caused by additional harmonics from the solid-state pump source mixing in the varactor diode of the parametric amplifier.     

A parametric amplifier for 46 GHz

A degenerate parametric amplifier for 46 GHz is described. It uses a Schottky barrier varactor packaged in a modified Sharpless wafer. The novel amplifier mount construction, which uses no tuning screws, yields predictable and reproducible results. In good agreement with theory, 14-mW pump power was required and a noise temperature of less than 400°K was measured.     

Low-noise photoparametric up-converter

An analysis is given for a photoparametric up-converter system. The up-converter consists of a single triplate line with one coaxial output connected to a circulator, through which the pump is applied and the signal extracted. The other end of the line is connected to the photo diode via a small coupling capacitor. The light is modulated at frequencies from a few hertz to some upper limit determined by the bandwidth of the triplate circuit. This arrangement is shown to give excellent results and the limit performance, as determined only by the diode parameters may be attained by following the up-converter with a degenerate parametric amplifier using the same pump plus a varactor doubler.     

Design Considerations for an Integrated 1.8-GHz Parametric Amplifier

A hybrid-integrated parametric amplifier has been fabricated in a microstrip transmission-line configuration. General design considerations and their implementation in a microstrip medium are discussed. The amplifier exhibited a power gain of 10 dB and 50-MHz half-power bandwidth with a noise figure of 2.0 dB. It was pumped at X-band frequency and required only 10 mW of pump power. The integrated pump source consisted of the transistor oscillator and a varactor quadrupler stage.     

Design Considerations for an Integrated 1.8-GHz Parametric Amplifier

A hybrid-integrated parametric amplifier has been fabricated in a microstrip transmission-line configuration. General design considerations and their implementation in a microstrip medium are discussed. The amplifier exhibited a power gain of 10 dB and 50-MHz half-power bandwidth with a noise figure of 2.0 dB. It was pumped at X-band frequency and required only 10 mW of pump power.The integrated pump source consisted of the transistor oscillator and a varactor quadruple stage.     

Accurate Determination of Varactor Resistance at UHF and Its Relation to Parametric Amplifier Noise Temperature

A thorough investigation is made on the frequency-dependent properties of a varactor diode loss resistance at UHF. The variation of the losses with frequency in a varactor diode mounted cavity has been theoretically investigated, and it is shown that the previously reported inverse-squared frequency dependence of the varactor loss resistance can be attributed to the distributed cavity losses transformed across the varactor diode. A new measurement technique is introduced in which the circuit losses are first matched to the input line instead of the varactor loss resistance as an application of the relative impedance method. Measurements carried out with this technique for five different varactor diodes showed that the loss resistances of these diodes are not frequency dependent. It is also shown that the choice of the varactor diode capacitance plays an important role on the parametric amplifier noise temperature at UHF. In an experimental parametric amplifier the effect of varactor diode capacitance on the noise temperature has been demonstrated. It has been theoretically and experimentally shown that, generally, varactor diodes having higher capacitances result in better noise temperature at UHF.     

Design considerations for an integrated 1.8GHz parametric amplifier

A hybrid-integrated parametric amplifier has been fabricated in a microstrip transmission-line configuration. General design considerations and their implementation in a microstrip medium are discussed. The amplifier exhibited a power gain of 10 dB and 50-MHz half-power bandwidth with a noise figure of 2.0 dB. It was pumped atX-band frequency and required only 10 mW of pump power. The integrated pump source consisted of the transistor oscillator and a varactor quadrupler stage.     

Large-signal varactor measurements

A simple method of measuring the large-signal parameters of a varactor diode for parametric-amplifier and harmonic-generator applications is described. These large-signal parameters and the conventional small-signal parameters are used to calculate the performance of the diodes in an X-band parametric amplifier. The practical performance of the amplifier shows very good agreement with the large-signal parameters.     

Parametric Amplification (Correspondence)

According to Manley-Rowe power relations the difference of pump and signal frequencies yields the so-called negative resistance parametric amplifier. In this case, infinite gain is possible in contrast to the sum frequency amplifier or up-converter which has a finite gain determined by the pump and signal frequencies.     

Multiple-Idler Parametric Amplifiers

The input resistance and noise performance of multiple-idler parametric amplifiers are examined in this paper. General expressions applicable to any given amplifier are derived. Simplifications resulting from a sinusoidal elastance variation permit writing an expression for the input resistance of an amplifier having any given number of idlers by inspection. These expressions are then applied to examine the properties of an amplifier having two idlers. The conditions required for minimum noise performance are derived, and it is found that high pump frequencies and external resistive loading of one idler are required. When the two-idler amplifier is compared to a conventional single-idler amplifier under those conditions which permit operation of the same diode at the same signal and pump frequencies, it is found that an improvement in noise figure results. However, the single idler amplifier pumped at the optimum frequency is capable of better noise performance, because minimum noise conditions cannot be satisfied for the two-idler device at this pump frequency. When below-signal-frequency pumping is utilized in the two-idler amplifier, the reduction in required pump power is substantial, but the noise figure is degraded by a minimum of approximately 3 dB.     

Stabilization of the Gain versus Frequency Characteristics of Parametric Amplifiers at High Input Signal Levels

Decreasing the negative bias voltage of varactor diodes in a parametric amplifier causes the gain versus frequency characteristic of the amplifier to shift to the higher-frequency side, resulting in a so-called "positive slope" at the signal center frequency. The same happens when the pump power is increased or when the signal power is increased, but in the latter case only when the idler circuit load resistance is below a certain value. The slope of the gain characteristic can be partially or completely compensated by detuning the signal-circuit characteristic relative to the gain versus freqnency characteristic in such a way that the latter is located on a certain point of the left or right slope of the signal-circuit chara-teristic, or by resistive loading of the idler circuit. Complete cancellation was achieved in the range from -30 to -20 dBm signal input power by using both methods simultaneously on a practical model of a parametric amplifier operating at a signal center frequency of 3.95 GHz and a pump frequency of 11.76 GHz. The loading of the idler circuit was done by drawing a little rectified diode current. The necessary increase in pump power, in order to maintain the same gain as with both signal and idler circuits tuned to resonance, was less than 3 dB, the increase in noise figure a few tenths of 1 dB from a typical value of approximately 3 dB.     

Gain stabilisation of parametric amplifiers

A method of stabilising the gain of a parametric amplifier from the pumped conduction current of a varactor diode is described. Long-term stabilities of 0.1dB/week have been achieved on a 13dB-gain amplifier with diode currents of less than 1 ?A.     

A Unilateral Parametric Amplifier

A theoretical investigation of a unilateral parametric amplifier using two varactor diodes indicates an improvement of unilateral stability over already existing types. A circuit is suggested which uses lower sideband idler energy for achieving forward gain and upper side-band energy to obtain substantial reverse loss. The phases of the applied signals and of the pump at the two varactors have to be 90/spl deg/ out of phase to achieve unilateral operation. Numerical evaluation of the theoretical results for a signal frequency at 4.0 GHz and a pump frequency at 12.0 GHz, assuming a diode junction capacitance of C/sub j/ = 0.4 pF and a bulk resistance of R/sub s/ = 2/spl Omega/ was done for several pump power levels. For 14 dB maximum forward gain, the 3 dB bandwidth of the gain versus frequency characteristic of the unilateral amplifier is about 18 percent smaller than that of the reflection type amplifier. The maximum reverse loss for these conditions is 7.3 dB. For lower forward gain the backward loss increases relatively until for very low gain values (about 1 dB) the amplifier is unconditionally stable, i.e., the backward loss is larger than the forward gain. The theoretical noise figure is about 1.95 dB at signal center frequency for 14 dB forward gain and, for /spl plusmn/80 MHz from the center frequency, only 0.1 dB higher than for the reflection type amplifier.     

Intermodulation in parametric amplifiers

Third-order intermodulation products due to the charge-voltage nonlinearity of the varactor diode in a parametric amplifier have been computed. Some experimental data obtained from a two-carrier measurement have been reported. Finally, the noise power density in a telephone channel due to parametric amplifier intermodulation has been calculated as a function of total input power into the amplifier.     

A Ferrimagnetically-Tuned Parametric Amplifier

A parametric amplifier can normally be tuned only over relatively restricted frequency ranges. One of the basic reasons for this tuning difficulty is that more than one frequency range is of importance for, in addition to the signal frequency, a pump frequency and one or more sum or difference frequencies must be considered. In this paper a tunable negative-resistance parametric amplifier is described which uses ferrimagnetically-tuned signal and idler circuits, together with a fixed-frequency pump source. This amplifier is unique in two respects. One is that the amplifier is electrically tuned through the use of yttrium iron garnet (YIG) resonators. Secondly, useful low-noise performance has been achieved over a tuning range of almost one octave, this amplifier thus successfully demonstrates that the technique of magnetic tuning with YIG resonators can be applied to a device as complex as a parametric amplifier in much the same manner as it has been applied in the past to microwave band-pass and band-stop filters.     

Input Conductance of a Four-Frequency Parametric Up-Converter

The limited power gain of a parametric upper sideband up-converter may be enhanced arbitrarily by allowing additional dissipation of energy at the lower sideband. However, the input conductance of such a four-frequency device will be critically dependent upon the amount of lower sideband energy dissipated. In this paper, we shall consider a varactor diode-type four-frequency up-converter employing a single resonant circuit common to both the pump and the sidebands. The input conductance of this configuration is analyzed in terms of the relative deviation of the pump frequency from the resonance frequency of the common circuit. We show that the input conductance also is seriously affected by the presence of second harmonic capacitance variation such as may occur at high-pump levels. Numerical results have been plotted for a wide range of circuit parameters. Also presented in this paper are the experimental results of measurements performed on such an amplifier, showing good agreement with the theory.     

High-dynamic-range low-noise microwave amplifier

The operation of a high-dynamic-range parametric amplifier is described. The varactor is a GaAs p?n junction with an n type layer suitable for operation as a K band transferred-electron oscillator (t.e.o.). A dynamic range of approximately 177 dB/Hz and a noise figure of less than 2 dB were measured at C band. The tests were made to show the feasibility of high-dynamic-range low-noise microwave amplification for radar-receiver applications, and to establish the feasibility of high-performance monolithic multifunction chips from the material standpoint.     

Operation of avalanche diodes as c.w. amplifiers at fractions of the transit frequency

The operation of an avalanche diode as a self-pumped parametric amplifier at low current densities is described. Gains of up to 15 dB are obtained at frequencies of the order of one-quarter of the transit frequency, while the diode is providing its own pump at three-quarters of that frequency. A theory based on utilising a Read-diode approximation to the device is used to calculate the response of such an amplifier, and good agreement is found for both the gain and saturation characteristics of the device.