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HEWLETT-PACKARD

JOURNAL
T E C H N I C A L I N F O R M A T I O N F R O M T H E - h p - L A B O R A T O R I E S
VOL. 3 No. 7-8



UBLISHED 1952 THE HEWLETT-PACKARD COMPANY, 395 PAGE MILL ROAD, PALO ALTO, CALIFORNIA MARCH-APRIL, 1952




A Precision Directional Coupler Using
Multi-Hole Coupling
DIRECTIONAL couplers have been used auxiliary guide is termed the "directivity"
widely in wave guide applications for of the coupler.
such purposes as monitoring power, meas The property of dividing power leads to
uring reflections, mixing, and for isolation the use of directional couplers in monitoring
of signal sources. All of these applications power levels that are greater than the range
make use of the property that power flowing of convenient power-measuring equipment.
in one direction in the main branch of the For many applications and for measurement
coupler induces a power flow in only one work especially, it is desirable that the power
direction in the auxiliary circuit. division or "coupling" be constant with fre
A common type of directional coupler con quency in order to reduce measurement
sists of two sections of waveguide bonded error.
together physically and electrically coupled Directional couplers can be divided into
by one or more apertures common to both two classes, depending upon whether they
guides. Power entering the input arm of the are to be used for monitoring power or for
coupler flows down the primary guide and measuring the amplitude of small reflections.
divides at the coupling mechanism. The lar Power monitoring usually requires a cou
ger portion continues down the primary pling not tighter than 20 db and a directivity
guide; the smaller portion is coupled into the of only moderate value.
auxiliary guide. Ideally, a uni-directional Couplers used for measuring reflections
flow of power in the primary guide should require tighter coupling and higher directiv
couple into the auxiliary guide a flow of ity than those used for power monitoring.
power that is also uni-directional. As a prac Usually, a coupling tighter than 20 db and
tical matter, some of the coupled power or a directivity greater than 30 db are desirable.
dinarily flows in the reverse direction. The If small reflections are to be measured, even
ratio of this forward to reverse power in the higher directivity is required. Heretofore,
such high directivity has not
generally been obtainable over
a wide band when the coupling
is tighter than 30 or 40 db be
cause of imperfections in cou
pling mechanisms.
Two new couplers in 10 and
20 db values have been designed
in the 8,200 to 12,400 megacycle
Fig. 1. -hp- Multi-hole directional coupler. range to provide constant cou-
P R I N T E D I N U . S . A . C O P Y R I G H T 1 9 5 2 H E W L E T T - P A C K A R D C O .