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The PTGMTT SYMPOSIUM DIGEST serves as a convenient, timely record of the disclosures of the most recent advances in the microwave art at the 1963 PTGMTT NATIONAL SYMPOSIUM.

Digital satellite communications is conducted in a bandwidth and power limited system of noise contributors, filters, nonlinear amplifiers, and adjacent channel interference. This paper will discuss the overall system architecture, identifying all types of filters, amplifiers, and modulation techniques in a system involving a transmitting earth terminal and up-link, a satellite transponder, and a down-link and receiving earth terminal which includes the receivers. The parameters relating to overall link performance will be discussed for a wide variety of modulation techniques and for various bandwidth efficiencies.

Quadriphase modulation of microwave or mm-wave carriers involves the rapid shifting of the phase of the carrier between one of four orthogonal positions by binary data included on two parallel data streams. The received quadriphase (QPSK) carrier can be demodulated by mixing this carrier with an appropriately phased local oscillator signal in a doubly-balanced mixer. One of the problems in demodulation of quadriphase carriers is the generation of the local oscillator having carrier frequency and phase information. This can be accomplished either at RF from the incoming QPSK carrier or at baseband by comparing the crosstalk associated with the two demodulated data streams, This paper will describe the applicable microwave technologies utilizing special quadruple frequency multipliers which provide microwave carrier reconstruction which facilitates the demodulation of data information from the carrier.

The basic QPSK modulator of the 1970-75 era in worldwide telecomnunications has yielded new modulation techniques of BPSK, SQPSK, 8-QPSK, and FFSK which use the basic PSK device technologies. The PSK modulators must today, meet many new requirements which were not of importance only a few years ago; i.e., the ability to switch phase at subnanosecond rates, the ability to produce PSK and QPSK carriers at data rates from 50 Mbps to in excess of one gigabit, the ability to produce modulated carriers at power levels in excess of one watt, and the ability to produce QPSK carriers at millimeter wave frequencies up to 100 GHz. This paper will review the original technologies employed during the 1960's and 1970's for low data rate carriers at lower microwave frequencies and will address new advances in switching speeds using dual gate FET's, higher power modulators using special driver circuits, and the use of multipliers to develop PSK carriers well into the millimeter frequencies above 50 GHz.

Time division use of the radio spectrum has created new multiple access techniques involving transmission of bursts of digitally modulated carriers using phase shift keyed modulation. Such systems are known as TDMA and involve burst carriers incorporating data rates from kilobits to gigabits per second. In order for these digitally modulated bursts to be demodulated at a terminal remote from the transmitter or source, it is necessary to provide a means to "recover" carrier frequency and phase from the received burst in order to be able to operate a coherent receiver. This paper will discuss the types of carrier burst synchronization techniques now in use, including the use of preambles to each burst which contain modulation by unique bit words which can be used to phase synchronize the receiver demodulator oscillator on a burst-to-burst basis. This paper will discuss the new microwave techniques of multipliers, tracking filters, anti-hangup resonators, which can be used to accomplish this synchronization for data rates from 40 Mbps to 1.6 Gbps.

The general usage of multibeam antennas in satellite communication system is reviewed, and design constraints for a six-beam reconfigurable satellite antenna system are considered. These show that losses in the variable beam-forming network (BFN) Iimit performance achievable with a conventional common-power-amplifier/receiver system. An alternative design for an active BFN is presented, and relative performance predicted at 4/6, 11/14, and 20/30 GHz.

The method of Smith and Shulman has been used for the frequency modulation of a 1-kilowatt continuous-wave magnetron. This tube is of the "vane" type, having twelve resonant cavities, and it is mechanically tunable over a range from about 720 to 900 megacycles by a cylindrical element which varies the interstrap capacitance. At the applied magnetic field required for frequency modulation without change in amplitude, 1 kilowatt output at 900 megacycles is obtained with an anode voltage of 2.5 kilovolts and an efficiency of about 55 per cent; the efficiency rises with decreasing frequency or with increasing magnetic field. At 900 megacycles, electron beams in nine of the magnetron resonant cavities give a frequency deviation of 3.5 megacycles (a total frequency swing of 7 megacycles) at an output of 1 kilowatt, rising to 4 megacycles at an output of 750 watts. The frequency deviation is reduced when the tube is tuned to lower frequencies. The modulator power required would be very low, since the grid-cathode capacitance of the frequency-modulation guns is small and the grids draw no current. It would be practicable to increase the frequency deviation of this tube by about 15 per cent through an increase in beam current, and by an additional 20 per cent through the use of eleven beams. A change in the type of beam cathode would effect an even greater deviation.

This paper presents a technical survey and status report of the microwave subsystems presently in use in the RF portion of modern high-speed phase-shift-keying communication systems, operating at data rates up to one gigabit per second.The principal subsystems reviewed will include four-phase phase-shift modulators of both the direct-frequency type plus up-converter; the four-phase demodulators; and the microwave circuits used to derive both carrier frequency (clock) and reference phase information from a received QPSK modulated carrier. The circuits and subsystems reviewed will be discussed at the level of the technology of the associated microwave components including details of the switching diodes, high FT transistors, video amplifiers, VCO's and special frequency multipliers involved.

An 800 mc continuous-wave magnetron will be described which utilizes a cathode-grid structure on which a standing wave may be set up around the cathode close to the source of the emission to introduce a locking wave in the electron stream. An experimental magnetron has been locked in frequency over a range up to and exceeding 10 mcs. The frequency locking range varies as a function of the locking power and also of the reciprocal of the output power. The output power of the experimental magnetron has been anode-voltage modulated from virtually zero power to several hundred watts without attendant frequency modulation and with negligible phase modulation. However, load conditions, especially in the case of phase modulation, are critical. The locking power is from 5 to 30% of the output power depending upon the percent modulation and the frequency locking range. The efficiency of the magnetron, utilizing the cathode-grid structure, was found to be slightly less than that of a magnetron having a normal cathode.

Gigabit-rate communications will use high speed logic systems which will use gigahertz-rate hi-stable devices for various logic functions including waveform generation. The chief requirement of such devices is the generation of square-wave end steep-rise-front voltage, current, and power functions. This paper will review the long art of bi-stable devices and will compare the features of each including consideration of speed and developed voltage. The impact of new transistors with high F/sub T/'s will be discussed, and experimental counter logic devices will be discussed which count at speeds at one gigahertz, and will include a discussion of experimental signal sources developing waveforms such as square waves, and pseudo random codes at gigahertz rates.

This paper describes a new type of magnetron in which reflex action of portions of the space-charge spokes controls the operating frequency as a function of the magnetron current. In this reflex magnetron, the resonant structure and the cathode are concentrically positioned and have different potentials. A magnet field is provided parallel to the axes of the cathode to produce magnetron action. An electrode positioned in the space outside the vane tips of the magnetron causes portions of the space-charge spokes to pass into this outer space and then return, or be reflexed, to the vane tips where they are collected. The electrons which enter the outer space change angular velocity with respect to the angular velocity of the electrons in the spokes. Consequently, when these electrons return to the vane tips, they change or control the frequency of the oscillations.

Many papers have been written concerning the theory, design, techniques, and measurements relating to power sources consisting of chains of transistor oscillators and simplifiers and varactor multipliers. In general, these papers have emphasized circuit design and in particular, have made an emormous point of designing for optimum power conversion efficiency. However, attractive high efficiency may be from the device standpoint, power stability and low noise output are far more important parameters from the system standpoint in which the chain is used, to assure continuous spurious and noise free circuit operation, even at the sacrifice of output power.