Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Distributive type parameters
Reexamination Certificate
1999-09-30
2001-10-02
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Distributive type parameters
C324S629000, C324S637000, C333S248000
Reexamination Certificate
active
06297649
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a harmonic rejection load pull tuner. More particularly, the present invention concerns a RF or microwave tuning device which has the ability to create high reflection factors for frequencies in the MHz and GHz frequency range, in order to improve the measurement of the characteristics and the behaviour of devices under test (hereinafter referred to as “DUT”), such as high power transistors, multiplier diodes and other non-linear devices.
DESCRIPTION OF THE PRIOR ART
RF/microwave tuners are electronic or mechanical devices which modify in a predictable way or not the complex impedance seen by the DUT at a given frequency of operation. When the impedance (and consequently the reflection factor) presented to the DUT changes, so does the capability of the DUT to generate or amplify the signal injected to it. To perform a full characterisation of a DUT, the tuner is adjusted to sequentially and uniformly cover a great number of points all over the Smith chart (see FIG.
1
).
This technique of subjecting DUTs to variable load (or source) impedance conditions, commonly referred to as “load pull”, is used to test DUTs for amplifier, oscillator or frequency multiplier applications.
Load pull testing can be made using manually or automatically operated RF/microwave tuners. These tuners are connected to the input or output side of the DUT and the power or frequency processed by the DUT is measured as a function of the impedance generated by the tuner Appropriate plots (contours) of output power or frequency, or other desirable unit to be measured (see FIG.
2
), then allow design engineers to construct networks that will cause the DUT to perform as expected in a real circuit.
There are a number of automatic and manual tuners in the RF and microwave frequency range presently available, such as the ones used in the measurement shown in
FIGS. 3
a
and
3
b
. Most of these tuners covers a wide frequency range of operation, in general more than one octave (f
max
/f
min
>2). For these commercially available tuners, the impedances at the harmonic frequencies (2f
o
, 3f
o
, etc.) are manipulated at the same time as the fundamental frequency f
o
. This is an undesired phenomenon, because it does not give the test engineer (or the design engineer, as they can be the same person) the possibility to optimize the impedances at the harmonic frequencies independently of the fundamental frequency.
In order to obviate this problem, a number of sophisticated techniques have been developed to permit separation of the fundamental frequency from the harmonic frequencies. Among others, the use of frequency discriminators (diplexers, triplexers or multiplexers in combination with adjacent wideband tuners) and “active” load pull solutions have been proposed, which use amplifiers to overcome multiplexer losses. The most used and best known of the above techniques are: active harmonic load pull; active harmonic load pull-split method; and passive harmonic load pull method using a triplexer.
An active harmonic load pull system consists of a test fixture connected to an active load (AL) or a test fixture and a feedback loop (split method). In both cases, the signal returned to the output port of the DUT is generated by an amplifier and is of the same frequency and varying amplitude and phase as the signal injected into the DUT.
FIG. 4
shows an active harmonic load pull system using active loads at the harmonic frequencies f
o
, 2f
o
and 3f
o
.
The DUT generates an output signal that contains the fundamental frequency f
o
and the harmonic frequencies 2f
o
and 3f
o
. These three frequency components are extracted using a wideband coupler and amplified in three different filtered (F), phase controlled (&PHgr;) and amplified (A) loops These signals are then re-injected into the output port of the DUT, generating a virtual load at all three harmonic frequencies. The disadvantage of this technique lies in the power limitation of the output amplifiers, the risk of parasitic oscillations during the test, and the impossibility to precalibrate the system. This last aspect implies “on-line” operation with a very expensive vector network analyser, and additional couplers and calibration standards must be added; consequently, the setup becomes very complex. Even though this technique is attractive from a theoretical point of view, it never became popular due to the practical disadvantages.
By contrast, in the split method illustrated in
FIG. 5
, the signal is split directly behind the source and before entering the DUT. Each frequency branch (f
o
, 2f
o
and 3f
o
) is amplified separately and the combined signal is injected into the output of the DUT. The amplitude and phase of each signal is controlled separately thus creating independently tunable impedances at the harmonic frequencies. The disadvantage of this method is that it loses its calibration when the input power is increased because each branch amplifier saturates differently than the DUT, so that the gain of the loop changes during a power sweep. Furthermore, this method requires a multitude of components and becomes awkward and uneconomical to build.
Finally, the passive harmonic load pull method using a triplexer is shown in FIG.
6
. it consists of a test fixture and a triplexer at the output with three wideband tuners connected thereto. The disadvantage of this method lies in the losses of the triplexer and its limited frequency bandwidth. Parasitic reflections outside the operation frequency range may also cause parasitic oscillations in the DUT, making a test almost impossible.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a harmonic rejection load pull tuner where at least one of the harmonic frequencies can be efficiently reflected. In accordance with the invention, this object is achieved with a harmonic load pull tuner comprising:
a large-bond tuner having an input and an output; and means for rejecting at least one harmonic frequency of a base frequency, said means having an input and an output, said input being connected to an output of a device under test (DUT) and said output being connected to the input of said large-band tuner.
In a preferred embodiment of the invention, the means for rejecting at least one harmonic frequency include a transmission line having a longitudinal axis and at least one stub in parallel with the transmission line, the stub having a length adapted to reflect out an nth order harmonic of a base frequency, where n is an integer greater than 1.
In another aspect of the invention, the means for rejecting at least one harmonic frequency of a base frequency are placed at the input of the DUT.
The invention also concerns a method for performing input characterization of a DUT, and a method for performing output characterization of a DUT.
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patent: 3613035 (1971-10-01), Askew
patent: 3697902 (1972-10-01), Louvel
patent: 4262266 (1981-04-01), Chern
patent: 4535307 (1985-08-01), Tsukii
patent: 4697159 (1987-09-01), Sechi et al.
patent: 5017865 (1991-05-01), Oldfield
patent: 5115217 (1992-05-01), McGrath et al.
patent: 5276411 (1994-01-01), Woodin, Jr. et al.
patent: 0381398 (1990-08-01), None
patent: 2100526 (1982-12-01), None
“A load Pull System for Digital Mobile Radio Power Amplifiers”, ATN Microwave Inc. Product Feature, Published in Microwave Journal, pp. 116-118, Mar. 1995.*
New Programmable Harmonic Tuners, Wireless Product Digest, Feb. 1999, p. 70-71, Focus Microwaves.
An Improved Coaxial Coupler for Measurement of the Microwave Hall Effect, 8127 Review of Scientific Instruments 62 (1991) Dec., No. 12, New York, US, p. 3089-3091, A. Y. Al Zoubi, T. E. Cross, and D. A. Mohamed Isa.
A Load Pull System with Harmonic Tuning, Microwave Journal, Mar. 1996, p. 128, 130 & 132, ATN Microwave Inc.
A Load Pull System for Digital Mobile Radio Power Amplifiers, Microwave Journal, Mar. 1995, p. 116 & 118, ATN Microwave Inc.
An Affordable Harmonic Load Pull Setup, Microwave Journal, Oct. 1998, p. 180-182, Focus Microwaves Inc.
Deb Anjan K
Focus Microwaves Inc.
Kramer Levin Naftalis & Frankel LLP.
Metjahic Safet
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