AM-PM Conversion Research Articles

Calculation of Intermodulation from a Single Carrier Amplitude Characteristic

The intermodulation analysis presented in this paper is based on the important observation that any output component of a memoryless nonlinear device can be expressed as an integral of the product of two functions, one being the single carrier amplitude characteristic of the nonlinear device and the other being a function of the statistical parameters of the input signal. The analysis can also be extended to nonlinear devices with AM-PM conversion by expressing the amplitude characteristic as a complex function. The signal-dependent function is given analytically for two simple but important types of signals, for two sinusoidal carriers of equal level, and for Gaussian noise, and it is demonstrated that good agreement has been obtained when the method has been applied to microwave devices like high power <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</tex> -band klystrons and traveling wave tubes. It is also shown that the method is convenient for analysis of intermodulation in cascaded nonlinear elements for which the individual single carrier amplitude characteristics are known.

A Volterra Series Description of Crosstalk Interference in Communications Systems

This paper studies a general description of interchannel and intra-channel crosstalk interference created in a communications system. This description is in the form of a Volterra series expansion of the interference signal in terms of the signal which produced the interference. From it we are able to precisely define the “intelligible” part of the crosstalk. This description also provides us with quantitative measures of the amount of crosstalk created in some communications channel by signals in another channel, as well as a measure (intelligible crosstalk ratio) of the amount of intelligible crosstalk produced. We then consider a particular model for the generation of intelligible crosstalk [or direct adjacent channel interference (DACI)] between two neighboring angle-modulated channels in which the signal in one channel adds to the signal of the second channel, the sum is filtered, and the filter output then passes through an AM-PM conversion device. Using our definition, a simple expression for the intelligible crosstalk ratio for this model is derived in terms of the filter characteristic. We observe that this crosstalk ratio exhibits a number of properties usually associated with DACI.

Intelligible Crosstalk in Multiple-Carrier FM Systems with Amplitude Limiting and AM-PM Conversion

Intelligible crosstalk will occur in a multiple-carrier FM system when a gain slope versus frequency characteristic is followed by AM-PM conversion. This phenomenon can be particularly serious in a communication satellite repeater that utilizes a traveling-wave tube for output power amplification. A model that includes both amplitude saturation and AM-PM conversion is developed and the two-carrier intelligible crosstalk is calculated.

The Effects of Quadratic AM-PM Conversion in Frequency-Division Multiplexed Multiple-Access Communication Satellite Systems

A traveling-wave tube amplifier such as those employed in frequency-division multiplexed multiple-access communication-satellite repeaters is considered. The amplifier nonlinearity is assumed to follow an error-function characteristic, and the AM-PM conversion is taken to be a quadratic function of the envelope of the input signal. An exact expression allowing for both arbitrary amounts of amplifier saturation and AM-PM conversion is derived for the autocorrelation function of the amplifier output when the input is a Gaussian bandpass process. Distortion spectra are calculated for the parameters of a typical travelingwave tube transmitter.

Effects of intermodulation, AM-PM conversion, and additive noise in multicarrier TWT systems

The intermodulation due to the traveling-wave tube (TWT) is analyzed for the case where arbitrarily modulated carriers and Gaussian noise are amplified through the TWT. Both AM-PM conversion effects and nonlinear amplification in the TWT are considered. The possibility of reducing intermodulation for system improvement is also discussed.

A new method of AM-PM conversion by using a locking oscillator

Phase modulated output can be obtained from an injection locked oscillator which has an amplitude modulated external force. The principle of AM-PM conversion and its experimental results are shown.

Proposal of QAM-OFDM System with IDAR Method Designed for Satellite Channel

The future satellite communication systems are required to support the higher transmission data rate for providing multimedia services by employing the efficient modulation method such as multilevel QAM. However, the employment of conventional single carrier transmission method with multi-level QAM which has larger PAPR (Peak to Averaged Power Ratio) would cause the fatal degradation of signal quality due to the non-linear amplifiers located at the earth station and satellite. To overcome this problem, this paper proposes broadband satellite communication systems by using the multilevel QAM-OFDM technique with IDAR (Improved Decision Aided Reconstruction) method, which is designed for satellite channel. In the IDAR method, the characteristics of non-linear amplifiers are required to be known at the receiver for mitigating the intermodulation noise. This paper also proposes the estimation method for AM-AM and AM-PM conversion characteristics of non-linear amplifiers by using low PAPR preamble symbols. The various computer simulations are conducted in this paper to verify the effectiveness of proposed system in the non-linear satellite channel.

Gain- and phase-matched low-noise TWT amplifiers

This paper will be presented in two parts. The first presents the latest advances in precision gain and phase-matched amplifiers. A set of three C-Band low-noise traveling-wave amplifiers has been gain and phase matched to stringent combination of electrical and environmental speeifications for a new mono-pulse radar system. No previous C-Band amplifiers of any kind have attained such a low noise figure (about 5 db at room temperature) with a power output of 20 milliwatts. In addition, these units are required to remain extremely gain and phase stable over a wide temperature range, to be gain and phase matched, and meet numerous other specifications sueh as low VSWR, fine grain, spurious PM, tube-to-tube interaction, and low AM-PM conversion. These results, which are important for designers of sensitive mono-pulse and phase array radar receivers with wide dynamic range, are a significant advance with respect to those reported by the author two years ago. At that time, the best gain stability achivable over a wide temperature range was ±1 db. The best phase stability consistently achieved was ±15°.

The effects of limiting on angle- and amplitude-modulated signal

The AM compression, AM-PM and PM-AM conversion of a limiter is determined from its describing function.

TD-3 System: Active IF Units for the Transmitter and Receiver

TD-3 IF circuits are designed to operate with a carrier frequency of 70 MHz with extremely flat transmission characteristics over the 60–80 MHz band. The automatic gain control of the IF main amplifier and the excess gain of the limiter together provide an effective AGC range of more than 40 dB. The units are designed to provide low noise figures and low AM-PM conversion.

Measurements of AM-PM conversion in low-noise TWT's, TDA's, and parametric amplifiers

Experiments have been carried out to determine the AM-PM conversion coefficients of traveling-wave tubes, tunnel diode amplifiers, and parametric amplifiers. Phase-input power characteristics have been measured by a precision phase bridge, and formulas are quoted for the calculation of both intelligible and unintelligible cross-talk coupling when the device handles multiple FM carriers.

Distortion of SSB Transmission Due to AM-PM Conversion

It appears not to have been widely recognized that intermodulation distortion of a SSB-AM signal will be generated by AM-PM conversion effects present in amplifiers (such as traveling wave tubes), as well as by output-input nonlinearity. When the SSB-AM signal is carrying multichannel telephony this can be an important source of distortion. In the present paper, a formula is developed relating intermodulation distortion to AM-PM conversion level. The theory is also applied to two-tone testing, in order to allow comparison with experiment. The experimental results are found to be in satisfactory agreement with theoretical predictions.

Intelligible Crosstalk Between Frequency Modulated Carrers Through AM-PM Conversion

When two or more frequency modulated signals are transmitted simultaneously through a nonlinear device, intelligible crosstalk from one signal to another is a potential problem. Such a situation arises in connection with the multicarrier use of satellite transponders. In this paper, intelligible crosstalk arising from transmission vs frequency deviations followed by amplitude-to-phase (AM-PM) conversion is considered. The AM-PM conversion characteristics of the transponder are represented by a single constant coefficient determined through a simple measurement technique. Crosstalk ratios for an arbitrary <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> carrier system are derived and experimental verification is presented for the two-carrier case.