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HEWLETT-PACKARD
JOURNAL
TECHNICAL INFORMATION FROM THE -h p- LABORATORIES
VOL. 4 No. 5-6
PUBLISHED BY THE HEWLETT-PACKARD COMPANY, 395 PAGE MILL ROAD, PALO ALTO, CALIFORNIA JAN. -FEB., 1953
More About the -hp- Precision Directional Couplers
AV earlier issue1 described the design of incident on any device connected at the end
the -hp- 10 and 20 db precision multi- of the guide. The other part of the power is
hole directional couplers. These couplers are coupled into the auxiliary guide. It is a prop
distinguished by a relatively constant coup erty of directional couplers that the power
ling over a wave guide range of frequencies coupled into the auxiliary guide flows essen
and by an unusually high directivity of more tially in only one direction. In the -hp- coup
than 40 db, even for coupling values as tight ler, this power flow is in the same direction
aslOdb. as the power in the primary guide.
The multi-hole coupler design has now In the ideal condition all of the power
been extended to a 3 db coupler, that is, a coupled to the auxiliary guide should flow in
coupler in which half the power entering the the same direction. Practically, however, a
main guide is coupled into the auxiliary portion of the auxiliary guide power flows
guide. This coupler has the same constancy in the reverse direction. The ratio of auxil
of coupling and high directivity as the 10 and iary guide power flowing in the desired di
20 db values. In addition, specifications have rection to that flowing in the reversed direc
been established for all couplers on the basis tion is termed the directivity of the coupler.
of production experience. In the past the use of directional couplers has
The -hp- multi-hole couplers consist of been limited by lack of high directivity over
two sections of wave guide mutually coupled a full wave guide frequency range. It is this
by two rows of coupling holes (Fig. 2). feature of high directivity over a broad range
Power entering the input arm of the coupler that has received the attention of designers
flows down the main guide and divides at the in recent years and it is in this feature that
coupling mechanism. Part of the power con the -hp- multi-hole couplers are distinctive.
tinues down the main guide where it will be To a first order effect, the lengths of the
rows of coupling holes shown in
Fig. 2 are chosen to obtain very-
high directivity for the coupling
mechanism itself. The voltage
coefficients of coupling of the in
dividual holes are separately
chosen to obtain the desired cou
pling value and at the same time
to obtain the desired type of re
verse radiation spectrum. The
reverse radiation is designed to
Fig. 1. Tu'o -hp- multi-hole directional couplers in a reflectometer arrange
ment for measuring reflection coefficient magnitude. In background are an 'E. F. Harriett and J. K. Hunton, "A Precision
-hp- 7 -hp- A klystron pou'er supply to pouer signal source and an -hp- 41 5 A Directional Coupler Using Multi-Hole Coup
ling," Hewlett-Packard Journal, Vol. 3, No. 7-8,
standing-wave indicator to read output of detector. March-April, 19