EP0577227A1 - Absorbierendes Mikrowellen-Dämpfungsglied zur Leistungsregelung eines linearen Festkörperleistungsverstärkers - Google Patents

Absorbierendes Mikrowellen-Dämpfungsglied zur Leistungsregelung eines linearen Festkörperleistungsverstärkers Download PDF

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Publication number
EP0577227A1
EP0577227A1 EP93202600A EP93202600A EP0577227A1 EP 0577227 A1 EP0577227 A1 EP 0577227A1 EP 93202600 A EP93202600 A EP 93202600A EP 93202600 A EP93202600 A EP 93202600A EP 0577227 A1 EP0577227 A1 EP 0577227A1
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EP
European Patent Office
Prior art keywords
waveguide
sspa
attenuator
output
absorber
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP93202600A
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English (en)
French (fr)
Inventor
William E. Mcgann
John R. Todd
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
AT&T Corp
Original Assignee
American Telephone and Telegraph Co Inc
AT&T Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by American Telephone and Telegraph Co Inc, AT&T Corp filed Critical American Telephone and Telegraph Co Inc
Priority to EP93202600A priority Critical patent/EP0577227A1/de
Publication of EP0577227A1 publication Critical patent/EP0577227A1/de
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/22—Attenuating devices
    • H01P1/222—Waveguide attenuators

Definitions

  • the present invention relates in general to satellite communication systems, and is particularly directed to a scheme for controlling the output power of a microwave solid state power amplifier through the use of ferrite absorber element, the insertion of which into a section of output waveguide is adjustable.
  • the solid state (GaAs) power amplifier (SSPA) is a commonly employed component of the uplink transmitter of a VSAT (very small aperture terminal) Ku band earth station.
  • the (gain) transfer (power output vs. power input) characteristic of a typical SSPA has a positive sloped linear region which gradually decreases over a knee portion to a slightly negative-sloped Saturation region.
  • the frequency response of the SSPA has a substantially smooth profile over its intended operational range.
  • the output power at the 1dB gain compression point is on the order of two watts, which may be considerably greater than the power required by the link (e.g. one watt). Consequently, it is necessary to reduce the output power transmitted by the uplink terminal. Ideally, this power reduction would be accomplished by simply reducing the input power to the SSPA, as its output linearly tracks its input over the linear portion of its transfer characteristic below the 1dB compression point. Unfortunately, the frequency response of the SSPA does not follow suit. Instead, the frequency response drastically departs from the smooth flat profile at 1dB compression and ripples significantly across the transmit passband.
  • the objective discussed above is achieved by effectively operating the SSPA at the 1dB compression point, where the passband ripple does not exist, and controllably reducing, downstream of the SSPA, the power output produced by the SSPA to the level required by the link.
  • the present invention is directed to a mechanism for controllably inserting a relatively thin tapered blade of ferrite material into a waveguide coupling section downstream of the SSPA.
  • the ferrite material is comprised of epoxy-bonded carbonyl steel particles of sufficient thickness to withstand the heat induced in the course of its absorbing microwave energy at the SSPA output, while being of a narrow or thin configuration and oriented for insertion into the absorbing section of waveguide so as to not effectively alter the characteristics of the signal profile of the electromagnetic wave.
  • FIG. 1 there is illustrated a schematic block diagram of a power control section containing a solid-state power amplifier and attenuator waveguide section incorporated in the up-converter circuitry between the IF input and RF output of a VSAT earth station.
  • an input signal (e.g. an intermediate frequency signal having a frequency of 140MHz) is coupled to an up-converter 12 of the earth station transmitter.
  • the output of up-converter 12 has a frequency corresponding to the transmission frequency of the earth terminal, as beamed from the earth terminal antenna to the satellite. For purposes of the present description, it will be assumed that this output frequency lies in a Ku band range of 14.0-14.5GHz.
  • the up-converter 12 is coupled to a solid state power amplifier (SSPA) 13, the output of which is coupled to an attenuator waveguide section 14, the details of which will be described below in conjunction with the description of Figures 2 and 3.
  • SSPA solid state power amplifier
  • Attenuator waveguide section 14 serves to controllably attenuate the output of SSPA 13 to the level required by the satellite link.
  • SSPA 13 is operated at its 1dB gain compression point so that its frequency response is substantially flat over the range of frequencies of interest (e.g. 14.0-14.5GHz).
  • waveguide section 14 is coupled through a waveguide filter stage 16 to an orthomode transducer 18.
  • Waveguide filter stage 16 is comprised of a pair of cascaded filters, specifically a harmonic output rejection filter for SSPA 13 and a receive band noise power rejection filter.
  • the output of orthomode transducer 18 is coupled over link 19 to an antenna feedhorn (not shown).
  • the behavioral characteristics of a typical SSPA 13 are such that its gain varies considerably with a change in frequency when operated below its 1dB gain compression point.
  • SSPA 13 is operated at its 1dB gain compression point so that its output characteristic is substantially flat over the frequency range of interest.
  • the output power of the terminal may be on the order of several watts or less.
  • the 1dB gain compression point produces an output on the order of two watts.
  • the power required by the satellite link can be expected to be between one and two watts, so that the output of the SSPA must be reduced.
  • the present invention operates the SSPA at a gain where its frequency response is substantially flat (for example at its 1dB gain compression point) and attenuates the substantially full power output level of the SSPA.
  • the output of attenuator waveguide section 14 is coupled over link 21 to a comparator 22.
  • a second input of comparator 22 is coupled over link 23 to an attenuation reference voltage, corresponding to the desired power level on the satellite output link.
  • Such an attenuation reference voltage may be derived directly from a manually set voltage source or from a voltage combining circuit (e.g. summing circuit), shown in broken lines at 26 in Figure 1, the output of which represents the sum or (or difference between) the manually set voltage and one or more monitored system parameters, such as a signal representative of E b /N o used for uplink power control for compensating for a reduction in signal level (e.g. rain fade at the local site).
  • the difference between the actual output produced by attenuator section 14 and the desired level produces a signal at the output of comparator 22 which is supplied to an attenuator insertion controller 24.
  • Attenuator insertion controller 24 is essentially comprised of a linear DC actuator which controls the insertion of a ferrite attenuator element to be described below into waveguide section 14.
  • Attenuator waveguide section 14 is shown as comprising a rectangular waveguide 34 having a slot 35 at the top thereof which is sized to accommodate a tapered ferrite attenuator element 33.
  • Element 33 is coupled to one end of the output displacement arm of linear DC actuator 24, shown diagrammatically at 32 in Figures 2 and 3.
  • linear actuator 24 displaces its output arm 32 in accordance with the differential signal supplied at the output of comparator 22.
  • the displacement of output arm 32 and, consequently, the degree of insertion of attenuator element 33 through slot 35 in waveguide 34 controls the degree of absorption of the 14.5-15.0GHz electromagnetic wave travelling through the waveguide.
  • slot 35 is preferably situated in a direction parallel with the longitudinal axis (the z axis) of the waveguide and symmetrical about a center line 40 of the waveguide.
  • the attenuator element itself is preferably comprised of a microwave absorber material that offers both strength and heat dissipation robustness with respect to the electromagnetic energy which is coupled through the waveguide section 34.
  • element 33 may comprise a tapered blade of magnetically loaded epoxide, such as ECCOSORB MF materials manufactured by Emerson and Cuming.
  • ECCOSORB MF 117 type material may be employed as absorber element 33.
  • the physical configuration of the absorber element is such that it is symmetrically tapered at regions 41 and 43 about a vertical plane line 50 which is intended to be coincident with the center line 40 of waveguide section 14 when the absorber is inserted into slot 35 at the top of the waveguide shown in Figures 2 and 3.
  • Region 41 has a pair of tapered faces 51 and 52 which extend from a pair of parallel sidewalls 46 and 47 and taper to a point 55 at one end of the absorber.
  • region 43 which is contiguous with a central region 42 of the absorber, has a pair of tapering side faces 53 and 54 which extend to an edge 57.
  • the tapering of faces 51-54 follows a Tschebyscheff binomial taper.
  • the length L T of regions 41 and 43 and the length of L C of central region 42 between tapered regions 41 and 43, as well as the width or thickness W C of central region 42 of absorber blade 33, depends upon the size of the waveguide, the frequency of the energy being absorbed, the degree of absorption to be obtained, any external cooling that may be supplied, etc.
  • the dimensions may lie in the following ranges: 0 ⁇ L T ⁇ 0.750; 0 ⁇ L C ⁇ 0.500; 0 ⁇ W C ⁇ 0.050, where the material is ECCOSORB MF 117.
  • the electromagnetic wave travelling through the waveguide does not abruptly encounter the absorber material, thereby minimizing its effect on the voltage standing wave ratio.
  • the top and bottom surfaces 36 and 37 of absorber 33 are substantially parallel to the top and bottom surfaces of the waveguide 34, the separation between which corresponds to the interior height or b dimension of the waveguide 34.
  • maximum absorption is provided when the absorber 33 is inserted fully into the waveguide and extends from the top interior surface of the waveguide to the bottom interior surface thereof as delineated by broken lines 38 in Figures 2 and 3.
  • the absorber can provide approximately 100dB of absorption capability when fully inserted into the waveguide.
  • the range of absorption is on the order of 0-15dB, to provide the transmitter output power levels mentioned previously.
  • a sheet or bar of the absorber material such as the ECCOSORB MF series of material, manufactured by Emerson & Cuming, may be individually cut and machined to provide the requisite cross-section.
  • the absorber material which basically comprises a steel carbonyl microsphere paste, is formed into the prescribed state of molding. This permits the absorber blade element to be inexpensively mass-produced.
  • the absorber configuration of the present invention is a cost effective alternative to the look-up table frequency response correction scheme for correcting for the nonlinearity of the operation of the SSPA as described in the above-referenced copending application.
  • the present invention may be incorporated into the system described in that application and, in so doing, the monitor and control processor and associated memory through which the frequency response correction is carried out can be eliminated.
  • the present invention is inserted at the downstream end of the SSPA, as shown in Figure 1, while the temperature correction and down link AGC correction networks are retained at the upstream end of the link.
  • the SSPA is operated at its 1dB compression point to obtain the essentially flat frequency response characteristic.
  • Controlled insertion of the absorber element into a section of slotted waveguide thereby offers a simple and relatively inexpensive mechanical expedient to the electronically implemented look-up table tracking procedure of the system described in the foregoing application.
  • the present invention equips the VSAT with a cost effective power control mechanism for simplifying adjustment of SSPA output power.
  • the temperature control and AGC downlink control portions of the system described in the copending application which form an upstream input controller to the SSPA, be combined with the downstream attenuator absorber mechanism of the present invention.

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EP93202600A 1987-05-04 1988-04-19 Absorbierendes Mikrowellen-Dämpfungsglied zur Leistungsregelung eines linearen Festkörperleistungsverstärkers Withdrawn EP0577227A1 (de)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP93202600A EP0577227A1 (de) 1987-05-04 1988-04-19 Absorbierendes Mikrowellen-Dämpfungsglied zur Leistungsregelung eines linearen Festkörperleistungsverstärkers

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
US4541487A 1987-05-04 1987-05-04
US45414 1987-05-04
EP93202600A EP0577227A1 (de) 1987-05-04 1988-04-19 Absorbierendes Mikrowellen-Dämpfungsglied zur Leistungsregelung eines linearen Festkörperleistungsverstärkers

Related Parent Applications (1)

Application Number Title Priority Date Filing Date
EP88905262.7 Division 1988-04-19

Publications (1)

Publication Number Publication Date
EP0577227A1 true EP0577227A1 (de) 1994-01-05

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EP93202600A Withdrawn EP0577227A1 (de) 1987-05-04 1988-04-19 Absorbierendes Mikrowellen-Dämpfungsglied zur Leistungsregelung eines linearen Festkörperleistungsverstärkers

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS57194604A (en) * 1981-05-27 1982-11-30 Nec Corp Waveguide variable attenuator
JPS5810937A (ja) * 1981-07-14 1983-01-21 Nec Corp 衛星通信地球局送信電力制御方式
US4485349A (en) * 1983-04-08 1984-11-27 Varian Associates, Inc. Stabilized microwave power amplifier system
JPS6032421A (ja) * 1983-08-02 1985-02-19 Fujitsu Ltd Ａｇｃ増幅装置

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS57194604A (en) * 1981-05-27 1982-11-30 Nec Corp Waveguide variable attenuator
JPS5810937A (ja) * 1981-07-14 1983-01-21 Nec Corp 衛星通信地球局送信電力制御方式
US4485349A (en) * 1983-04-08 1984-11-27 Varian Associates, Inc. Stabilized microwave power amplifier system
JPS6032421A (ja) * 1983-08-02 1985-02-19 Fujitsu Ltd Ａｇｃ増幅装置

Non-Patent Citations (4)

* Cited by examiner, † Cited by third party
Title
-: "Waveguide Hardware", EDN ELECTRICAL DESIGN NEWS, vol. RT-119, no. 9, September 1964 (1964-09-01), NEWTON, MASSACHUSETTS US, pages 6 - 7 *
PATENT ABSTRACTS OF JAPAN vol. 007, no. 045 (E - 160) 23 February 1983 (1983-02-23) *
PATENT ABSTRACTS OF JAPAN vol. 007, no. 084 (E - 169) 7 April 1983 (1983-04-07) *
PATENT ABSTRACTS OF JAPAN vol. 009, no. 154 (E - 325) 28 June 1985 (1985-06-28) *

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