Oscillator consisting of Gunn diode embedded in coaxial circuit has excellent temperature stability and low fabrication costs as compared with automatic-frequency-control crystal oscillators

Dengenford, J. E.

Dickens, L. E.

Maki, D. W.

Newman, B. A.

English

NASA Technical Reports Server

December 1975	 B75-10306 
NASA TECH BRIEF
A	 11 
Marshall Space Flight Center 
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Temperature-Stable Gunn-Diode Oscillator 
.
The problem: 
Many solid-state oscillators are subject to frequency 
shifts in response to temperature changes. This 
problem can be overcome with automatic-frequency-
control (AFC) crystal oscillators. However, the 
crystal-controlled devices are relatively expensive. 
The solution: 
An oscillator consisting of a Gunn diode embedded 
in a coaxial circuit has excellent temperature stability 
and low fabrication costs. 
How it's done: 
In the illustrated oscillator the low impedance of a 
Gunn diode is transformed through a section of radial 
line and low-impedance coaxial cable. This results in 
an even lower impedance and raises the oscillator 
loaded Q factor to 150. A section of high-impedance 
coaxial cable runs the length of the device. 
Only the transformer and center conductor need to 
be made from a low-thermal-expansion material, thus 
reducing manufacturing costs. Initial results indicate 
RF
Output
Variable-Depth 
Coaxial-Cable 
Aluminum	 Probe 
Housing 
Gunn
Low-Impedance	 Kovar 
Transformer	 Center Conductor 
(Kovar)
that the oscillator has a stability of 1 part in 104 over a 
range of 30° C at 9.5 GHz. 
An RF cavity, which includes the transformer and a 
section of the coaxial cable, is terminated by a choke 
short. The cavity length is one-half the oscillator 
wavelength (A/2), and a variable-depth coaxial-cable 
probe at the cavity midpoint serves as the RF output. 
The choke is a hollow brass piece with an exterior 
length equal to A/4 in air and an interior length equal 
to A/4 in rexolite. The choke is followed by a block of 
rexolite that is firmly attached to the center conductor 
cable at a single point. A section of RF absorbing 
material further reduces any leakage out of the bias 
port. 
As the temperature rises the transformer and the 
conductor cable expand. However, the section of 
rexolite, although smaller than the cavity length, also 
expands an equal amount. The thickness of rexolite (a 
material with a high coefficient of thermal expansion 
= 90x10/°C) expands in a direction opposite to the 
cable-and-transformer expansion and maintains a 
constant cavity length. It may also be designed to 
compensate for any residual diode drift. 
	
Lock	 RF Absorbing 
Brass	 Screw	 Material	 Bias 
Choke	 N.,	 I	 Connection 
Rexolite 
Compensators	 Retaining 
Nut 
Temperature-Stable Gunn-Diode Oscillator
(continued overleaf) 
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Reference: B75-10306 
B75-10306
Patent status: 
Inquiries concerning rights for the commercial use 
of this invention should be addressed to: 
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Marshall Space Flight Center 
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Marshall Space Flight Center, Alabama 35812 
Source: J. E. Dengenford, L. E. Dickens, 
D. W. Maki, and B. A. Newman of

Westinghouse Electric Corp. 
(MFS-23242) 
Category: 01 (Electronics - Components

and Circuitry)


Temperature-stable Gunn-diode oscillator

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