HP 416A - Application; Reflectometer Systems

APPLICATION
Reflectometer Systems --
General - In the measurement of reflection coefficients, an assembly of
devices based upon the use of directional couplers is referred to as a reflectom-
eter. Directional couplers permit the incident and reflected voltage vectors to
be separated out with a high degree of discrimination from a tran smission line.
A microwave reflectometer permits rapid measurement of the magnitude of the
reflection coefficient of an unknown load
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NOTE : The frequency ranges in which a refle c torne ter m ay be operated
are de ter mined by the bandwidth limits of the ty pes of dire cti onal
couplers now available . So far as the Model 416A Ratio Meter
is concerned, provided the voltage at its inputs has a frequency
of 1, 000 ( ± 40 ) cycles and a level within specified limits, the only
frequency li mitation s on the use of the Model 416A are t hose which
exist be ca use of limitations in the other eq ui pm ents used to build
the reflectometer systemo
Equipment -
A
typical arrangement of equipment assembled as a miyrowave
reflectometer is shown in block di agra m form i n F ig. 7 , a nd inc lud es :
A
sour c e (with modulating capabilities) of signals in the frequency range
in which reflection coe ff icie nts are to be me asure d
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To m inim ize re -
flections , the signal so u rce should present a reas onable m a tch to the im-
ped a nce of the t ransm i ssion system o (For signals in the 7 - kmc to lO = kmc
range , an oscill at or suc h as the Hewle tt- P ackar d Model 670H r or HM 7
is suitable o The maximum output of the Model 670 rap prox i rnately ± 10 dbm 7
is sufficiently high to pe rmit i nsert i on of a 6 - 10 db pa d to isolate the im= --
pedance of the sign a l source,)
A po wer su pply an d a supply of modul ati ng voltage ( 1-kc square-wave) for
t he signal sour ce
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(A po wer s upply suc h as t he H ew lett - P ac k ar d Model
717A Klystron Po wer Supply in cludes a sour ce of 1 =k c square=wave voltageo)
Two dir ecti onal c oupl erso In the 2, 6 = kmc to 18 0 0 - km c range, c ouplers
s uch as the He wlett- Pack ar d Model 752 Dir ectional Coupler s may be used o
Two square-law dectectors , Hewle tt- Packard Models 421 an d 485 Wave -
guide Reflectomete r Detector Mounts are av ai lable in six c ommonly used
waveguide sizes c overing t he 20 6 to 18 . 0 KMC frequency ran ge .
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For a discussion of coaxial sy stems see the Hewl ett= P ackar d Journal, VoL 7,
No. 2, "High = Directivity Coaxial D ir ectional Coupler s an d Refl ect ometers
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