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cally 6X10-*, 2X and A/cm2 re- spectively, in comparison with i\/cm2 for a typical collector-base diffused junc- tion.

Integrated TTL circuits incorporating aluminum-silicon diodes were fabricated. The circuits exhibited turn-on and turn-off propagation delays of 2.5 ns and 3.5 ns, respectively, with 5 volts supply, 3.5 volts signal and 20 mW power dissipation. A con- siderable part of the propagation delay can be attributed to circuit RC time constants. Initial Schottky diode characteristics have remained stable after high-temperature for- ward and reverse bias stressing.

Session 9-Electron Tubes I1 : Traveling Wave Tubes (A) Chairman: J. Mendel Organizer: B. Pallakoff

1) Recent Developments in Ultra-Low- Noise Broad-Band TWT Amplifiers1-I,. Dombro and E . Dornseq, Watkins- Johnson Co., Palo Alto, Calif. A low-noise traveling wave tube amplifier

operating over the double band 8-18 GHz with a maximum noise figure of 8.5 dB has recently been developed. This amplifier has a nominal small-signal gain of 30 dB, a gain variation of less than 6 dB, and a saturated power output of +5 to + l o dBm. The low- noise figure and power output performance exceed that of presently available Ku-band amplifiers, and are comparable to presently available X-band amplifiers as well. The amplifier package, consisting of tube, mag- net, and integral power supply, weighs 18 lb, has a maximum height of 4.75 inches, and is 12 inches long.

State-of-the-art K and &-band low- noise PM-focused TWTAs covering the 18-40 GHz frequency range will also be de- scribed. Each unit is integrally packaged with an all solid-state power supply which operates off 115 k 10 volts ac, 48420 Hz pri- mary power source.

The K-band amplifier exhibits a maxi- mum noise figure of 11 dB with small-signal gain greater than 25 dB and saturation power output greater than 0 dBm over the frequency range 18.0-26.5 GHz. Typical performance is 10.2 dB, 26 dB, and 3 dBm, respectively. Over the partial band range from 19-23 GHz, one developmental model exhibits a noise figure of less than 8.3 dB. The unit weighs less than 18 lb, is 4.75 inches in cross section, and 12 inches long, exclud- ing connectors, and meets the temperature, vibration, and shock requirements of MIL- E-5400 Class 2.

The &-band unit exhibits a ndse figure of less than 14 dB with small signal gain greater than 25 dB and saturation power output greater than 5 dBm over the fre- quency range 26.5-40.0 GHz. A noise figure of less than 13 dB with a minimum value as low as 12.2 dB has been measured over the K,-band range for an early developmental model. Package size is 5.1 by 7 . 5 inches in

Marshall Space Flight Center and in part by the Re- I This work mas sponsored in part by the NASA

search & Technology Division. Air Force Systems

AFB, Rome, X. Y. Command, Rome Air Development Center, Griffiss

cross section, and 12.2 inches long, excluding connectors, and weighs approximately 25 Ib.

2) 50 Percent Efficiency Traveling Wave Amplifiers with Voltage Jumpsl--T. B . Brown, J . C. Dixon, 0. Sauseng, and E . N . Sosa, Hughes Aircraft Co., Electron Dymanics Division, TorranLe, Calif. A C-band broad-band coupled cavity

T\VT and an S-band PPM focused helix TW'T will be described along with the experi- mental results of more than 50 percent effi- ciency. The high efficiency is in part achieved with the voltage elevation of the last few cavities of the circuit or the last few turns of the helix. Further efficiency improvement is obtained with a double stage collector in which only the second stage is biased.

The helix tube operates at the 30-watt C\V level and is adjusted to yield low inter- modulation distortion along with low A M to PM conversion. This performance was achieved by the use of an advanced large signal computer program which allows for the effect of the gap drift length in the volt- age jump region.

The coupled cavity T\VT delivers 10 kiV of Cb' power with a gain of more than 12 dB. The tube and solenoid are cooled by a closed cycle vapor-phase cooling system which requires no coolant pump. This device was developed for use as a low-gain high- power troposcatter-communication ampli- fier.

Army Electronics Command, Fort Monmouth. X. J. 1 This work was in part supported by the U. S.

3) Centipede Twystron@ Amplifiers and Traveling Wave Tubes for Broad-Band High-Efficiency Super-power Amplifica- tion'-T. Roumbanis, Varian Associates, Palo Alto, Calif. Experimental results are presented for

several types of superpower amplifiers using centipede and hybrid Twystron circuits.

The centipede slow-wave circuit element uses a loop type of coupling from cavity to cavity. The fundamental mode is a forward wave because of the negative mutual-induc- tance type of coupling created by reversed loops.

The frequency separation from unwanted modes is far greater than for the more con- ventional cloverleaf type of circuit element for a given fundamental bandwidth; the cold-circuit bandwidth capability is approxi- mately 40 percent making a 20 percent hot bandwidth feasible. The tubes described here were designed for only 15 percent elec- tronically tuned bandwidth.

In the preliminary amplifiers bandwidths in excess of 15 percent were obtained, limited by the mechanical-tuning range of the klystron input-section which was de- signed to complement a TWT ou tpu t section of only 8 percent bandwidth. With an un- tapered output section, 25 percent peak efficiency was obtained, whereas 40.2 percent was obtained with taper. The saturated power output was measured from the pi-

1 This project was sponsored by Rome Air Devel- opment Center. Griffiss AFB, Rome. N. Y.. Contract AF 30 (602)-4351, Project 4506, Task 450601.

mode voltage region to full operatine vol ta.ge without any instability or apprecia'2le 5ne. grain variation.

Data will be presented on an operatit2naI traveling wave tube, and on an 0perati~ma1 Twystron amplifier which has produced approximately 10 mW of peak output power with 37 percent efficiency over a 15 percent frequency bandwidth.

4) Harmonic Generation in Octave Band.. width TWTs, N. Dionne, Raytheon Co., Waltham, Mass. In octave bandwidth TWTs the genera-

tion of power a t harmonic frequencies can result in seriously degraded tube and system performance. Efficiency degradation and relatively high second harmonic power con.. tent lie at the root of the encountered tliffi. culties.

Insight to harmonic generation phenom- ena and its consequences has been gained by use of a large-signal analysis which ha:j been incorporated into a new, digital com- puter program. Included in the programmed analysis are severs, tapers, distributed loss, space charge forces, and simultaneous active coupling between the beam and circuit field; at the fundamental and harmonic frequen- cies. Application of the program to known T W T designs has afforded good agreement between predicted and experimental data.

Efficiency degradation at the low end of the octave band depends upon several fac- tors. Circuit dispersion and the harmonic to fundamental beam coupling impedance rati'o are primary influences. I t is seen that funda- mental electronic efficiency decreases to levels substantially below that for funda- mental signal alone (no active coupling to second harmonic) as the cold circuit phase velocity ratio v,/v, decreases from 1.05 to 0.95. For sufficiently dispersive circuits, efficiency degradation tends to disappear rapidly.

For any given set of small signal pararn- eter specifications, harmonic generation in TWTs is somewhat dependent upon the fundamental saturation gain level. I n addi- tion, when the tube input signal contains second harmonic power less than approxi- mately 25 dB down the fundamental, con- structive as well as destructive interference with the fundamental signal saturation pro- cess can occur depending upon the relative phase difference between the input signal components. Curves illustrating the gain level, the relative input power level, and the relative phase dependencies will be pre- sented.

Means for suppression of harmonik power content and efficiency improvement will be given consideration.

5) Development of a 13.5-dB Noise Figure 5-Watt C-Band Traveling Wave Tube- G. W. Petty, Microwave Electronics, Palo Alto, Calif.

noise T W T has been developed for the 4 to A medium-power PPM-focused low-

8 GHz bandwidth. Through special cathode shaping techniques and beam velocity pro- file in the gun region, a noise figure of 13.5 dB maximum has been attained over the entire band. This achievement in itself is not particularly startling, but when coupled