US2773244A - Band pass filter - Google Patents

Band pass filter Download PDF

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Publication number
US2773244A
US2773244A US302292A US30229252A US2773244A US 2773244 A US2773244 A US 2773244A US 302292 A US302292 A US 302292A US 30229252 A US30229252 A US 30229252A US 2773244 A US2773244 A US 2773244A
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United States
Prior art keywords
filter
bypass
signal
tuning
probes
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Expired - Lifetime
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US302292A
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English (en)
Inventor
Donald D Grieg
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TDK Micronas GmbH
International Telephone and Telegraph Corp
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Deutsche ITT Industries GmbH
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Priority to NLAANVRAGE8006808,A priority Critical patent/NL180280B/xx
Priority to BE521895D priority patent/BE521895A/xx
Application filed by Deutsche ITT Industries GmbH filed Critical Deutsche ITT Industries GmbH
Priority to US302292A priority patent/US2773244A/en
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Publication of US2773244A publication Critical patent/US2773244A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/20—Frequency-selective devices, e.g. filters
    • H01P1/207—Hollow waveguide filters

Definitions

  • This invention relates -to bandpass filters and more particularly to tunable microwave bandpass filter systems for utilization in heterodyne receivers or similar equipment to provide ease of tuning the filter and associated equipment over a wideband of microwave frequencies.
  • microwave receivers In microwave receivers the need for an etiicient and practical microwave filter has always been considered of paramount importance.
  • the principal purpose of such a filter is to eliminate the possibility of receiver responses to an image signal which could either interfere with the desired signal or completely capture a ⁇ receiver utilizing limiter stages as are commonly found in communication receivers.
  • the problem resolves itself into the construction of a microwave circuit which provides the required attenuation at the image frequencies, while yet passing the desired signal spectrum free from attenuation and distortion.
  • the microwave receivers presently being employed are required in many applications to be operable over a large frequency range it is imperative that the filters employed in conjunction therewith be tunable over the desired frequency band and have characteristics which are uniform over this band. These characteristics include the width of passband, image attenuation, insertion loss, and accuracy of tuning.
  • a typical filter design is an alignment of tunable cavities in a straight section of waveguide, with a separation of a quarter wavelength between adjacent cavities.
  • many mutually coupled parameters must be adjusted.
  • the passband shape adjustments, and often adjustments between adjacent cavities must be provided for.
  • the passband shape adjustments, and often adjustments between adjacent cavities must be provided for.
  • many as nine mutually dependent adjustments may be required in order to tune to an adjacent frequency.
  • a modern microwave receiver consisting of a preselector filter unit for providing the required image rejection and selectivity plus a mixer or converter, a local oscillator, and I. F. amplifier, and the remaining units making up the conventional heterodyne receiver must each be tuned separately to tune in the desired signals since Vit is not practical to gang all these tuning elements with sufficient accuracy. Therefore, it is extremely difiicult when hunting for a signal to insure that all the receiver components or units are appropriately aligned and to maintain the alignment with the result that the tuning and alignment procedure required by such a receiver is reduced to a trial and error method. This often results in an inability to locate a given signal or the expenditure of considerable time and effort to do so. If the filter is reasonably selective as is required for good image rejection, the tuning problem becomes particularly onerous.
  • Another object of this invention is a retractable probed shunt which when inserted into the signal energy path does not disturb appreciably the signal propagation mode of the filter and permits the signal energy to be partially bypassed around the filter unit to reduce the filter selectivity and thereby provide an opportunity to broadly align and tune the filter unit as well as the remaining units of a conventional microwave receiver of the heterodyne type, and when retracted from the signal energy path the receiver is substantially selectively aligned with little further tuning adjustments necessary.
  • a feature of this invention is the insertion of a retractable probed coaxial shunt into resonant waveguide filter sections as an integral portion of a tunable waveguide filter for shunting a portion of the signal energy from said tunable filter section.
  • Another feature of this invention is the insertion of a retractable probe coaxial shunt into waveguide sections adapted to be connected prior to and following the main tunable waveguide filter sections.
  • Still another feature of this invention is the employment of a coaxiai section prior to and following a coaxial type microwave filter wherein the signal energy is coupled capacitively to and from a transmission line.
  • a further feature of this invention is the employment of means for controlling remotely the operation of the bypass communication.
  • Still a further feature of this invention is the employment of a probed transmission line wherein the energy flow through said transmission line is adjusted to control the operation of the bypass communication.
  • Fig. l is a block diagram of a heterodyne receiver employing an embodiment of the bandpass filter following the principles of this invention
  • Fig. 2 is a plan view, partially in section, of the preselector filter of Fig. l incorporating an embodiment of the bypass means of this invention
  • Fig. 2a is a graphical representation of the method for tuning a microwave receiver when employing an embodiment of this invention
  • Fig. 3 is a sectional view of another embodiment of the bypass means arranged for coupling with a given preselector filter
  • Fig. 4 is a sectional view of still another embodiment of the bypass means in accordance with the principles of this invention.
  • Fig. 5 is a cross-sectional view of an embodiment for achieving the bypass coupling alternate to that shown in Fig. 4;
  • Fig. 6 is a plan view of another embodiment of the bypass means arranged for coupling with a given preselector filter
  • Fig. 7 is a fragmentary sectional view taken along line 7-7 of Fig. 6;
  • Fig. 8 is a plan view of an embodiment of the means controlling the bypass communication which may be incorporated with the transmission line of Fig. 6.
  • a simple block diagram of a microwave heterodyne receiver comprising a preselector filter 1, a mixer 2, and local oscillator 3, an I. F. amplifier section 4, a detector 5, and an intelligence utilizing circuit 6.
  • the units illustrated therein employ "conventional microwave circuits arranged in a manner n such a system, for instance the range of 4400 to 5000 mc., which is employed herein for descriptive purposes.
  • a signal in thisV range received by 'the antenna 7 is coupled "t'o the preselector filter 1, beat with the local oscillator 3, such as a klystron oscillator in the mixer 2.
  • the local oscillator may also operate in the abovementioned frequency range to provide a predetermined intermediate frequency, for instance, in the'range of 30 mc. to 100 mc.
  • the remaining circuits 5 and 6 may be arranged in a predetermined manner to recover and utilize the intelligence signals of the audio type, ⁇ or as more often employed,'may be employed in any of the many types of pulse communication links.
  • Preselector filter 1 of Fig. 2 comprises a Wideband tunable microwave filter 8 and a shunting line 7.
  • Filter 8 may comprise any conventional waveguide filter Wherein there is preferably an alignment of tunable cavities in a straight section of waveguide, with a separation of a quarter wavelength between adjacent cavities.
  • the tunable cavities are bounded by fixed susceptance irises, the only tuning necessary therein being that of the resonant cavities by means of micrometer tuning heads controlling tuning probes inserted in the resonant cavities.
  • Shunting line 7 may be coaxial line as shown, or any other suitable transmission line, coupled to the first tunable filter section 9, tunable by means of tuning probe 10, such that a retractable probe 11 may be inserted into section 9 to remove therefrom a portion of the received signal energy without disturbing materially the mode of propagation in the filter, or disturbing the resonance of the cavity into which probe 11 is inserted.
  • This extracted energy is fed through line 7 to the last filter section 12, tunable by probe 13, the bypass signal energy being injected therein by shunt probe 14.
  • This relatively wideband shunted signal is then coupled to the remaining receiver circuits enabling an alignment and tuning of these circuits to a desired signal quickly and easily, since the filter has been shunted and as a result provides a less selective band of signals through which the desired signal may be hunted for, and at the same time filter 1 is tuned to a desired selective band, if it is not already tuned for the selective band.
  • shunt probes 11 and 14 are preferably retracted from cavities 9 and 12, respectively, such that the bypass communication is discontinued. This may be accomplished by withdrawing probe 11 by means of knob 15 and probe 14 by means of knob 16.
  • the means for accomplishing the retraction of the probes may be manual if the filter unit is accessible, or if not accessible a motor driven cam arrangement or other known mechanical linkages, activated from a front panel, may be incorporated to withdraw the probes sufliciently to discontinue the bypass communication.
  • a preferred means of discontinuing the bypass communication is illustrated in connection with Fig. 3 and will be disclosed hereinbelow. Electrical continuity is provided between probes 11 and 14 and the center conductor 17 of line 7 by properly constructed sliding contacts at points 18 and 19, the details of which will be obvious to those skilled in the art.
  • probes 11 and 14 allows the selective 4 characteristic of filter 8 to dominate and thus provides an overall selective microwave receiver.
  • the removal of probes 11 and 14 from cavities 9 and 12 does not alter substantially the alignment of the receiver components as established during the bypass communication, due to the fact that the insertion of probes 11 and 14 is limited to an amount just suiiicient to bypass a portion of the received signal energy and not to materially disturb the propagation mode and resonance of the filter section.
  • Fig. 2a illustrates the tuning of a receiver having a preselector filter 1 employing the bypass means disclosed herein.
  • curve 20 illustrates the relative bandwidth of signal energy present for application to the othenreceiver units. This bandwidth allows easier trackingy or hunting of a desired signal and final tuning to this signal. The wide bandwidth accompanied by a reduced amplitude does not materially hinder the alignment procedure. Having the filter sections tuned to a desired selective frequency band prior to the time of discontinuing bypass communication, the discontinuing ofthis communication results in the curve 21 which illustrates the desired selectivity desired for the overall receiver.
  • FIG. 3 another embodiment is shown whereby a portion of the received signal energy is removed preceding th ⁇ e signal input means to a waveguide filter 22, of any desired conventional form, by means of a probe shunt line 23 similar to that shown in Fig. 2, with thel exception that the Vextracting probe 2 4 ispinserted into a waveguide section 25 to a depth which is just suiicient to remove a desired amount of signalrenergy without disturbingrth-e propagation modeof the filter.
  • This energy is transferred through line 23 and injected by probe 26 into a waveguide section 27 succeeding the signal output means of the waveguide filter 22.
  • the energy is coupled therefrorn'to the remaining circuits of the receiver to achieve the desired alignment in a manner as described in connection with the embodiment of Fig. 2.
  • Means to control remotely the operation of the bypass communication, whereby after tuning the communications may be limited to the characteristics of filter 22, is accomplished by means of solenoid coils 28 and 29 located in association with the respective shunting probes 24 andj26.
  • the opening of switch 30 discontinues the liow of current through coils 28v andv 29, deenergizing these coils and as a result probes 24 and 26 are retracted from their re.
  • spective lter or waveguide coupling sections as the case may be, by the action of compressed springs 32'and 33. Insertion of the probes into the respective cavities is vaccomplished by closing switch 30 allowing the current from the D. C.
  • Switch 30 is preferably located on a front panel of the equipment incorporating an inaccessible lterunit including the shunting line to provide a convenientmeans to insert and remove the probes from their corresponding waveguide sections.
  • Fig. 4 illustrates an embodiment of my invention erriployed in conjunction with a tunable coaxialtype microwave filter 34.
  • Coaxial sections35 and v36 are added to a conventional coaxial filter for ⁇ the purpose of having coupled thereto the shunt line 37 similar to line 7V shown in Fig. 2.
  • Bypass of the signal'energy herein is yaccomplished by the capacitive coupling between probe 38 and the center conductor 39 of section 35 preceding the signal input means'to filter 34.
  • the bypass signal is returned to the system by capacitive coupling between probe40 and center conductor 41 of section 36 which succeeds the signal output meansl of filter 34.
  • Means for controlling the bypass communication is provided by plunger 42 which is located a half wavelength, or a multiple thereof, from probes 38 and 40.
  • plunger@ is located a half of wavelength from probe 38 and a full Wavelength from probe 40 and when moved invvardl it provides a short between the inner and outer conductors of line 37.
  • the bypass communication plunger 42 may be operated by the solenoid controlling means illustrated in Fig. 3, or the alternate methods suggested in connection with Fig. 2.
  • To discontinue or disrupt bypass communication plunger 42 is inserted into line 37 to short center conductor 42a whereby due to the half wavelength relationship probes 38 and 40 are effectively shorted. This means of discontinuing the bypass communication allows the probes 38 and 40 to remain inserted in the path of the signal energy and thereby does not upset, even a slight amount, the overall tuning and alignment achieved during the bypass communication.
  • Fig. 5 illustrates another embodiment for obtaining coupling between probe 38 and center conductor 39 of Fig. 4.
  • a spring metal loop 43 is secured to probe 38 and a lever 44 may also be secured thereto, extending through a slot 45 of line 37.
  • Coupling between probe 38 and center conductor 39 is achieved by moving lever 44, composed of insulated material, downward to position loop 43 as shown by the dotted line, thus achieving the desired bypass of signal energy from the input to the filter.
  • lever 44 is moved inwardly such that spring loop 43 conforms substantially to the shape of the outer conductor of section 3S, but separated therefrom by dielectric material 46. This removes the loop 43 from the field of the signal energy and discontinues the bypass communication.
  • the lever 44 may be provided with solenoid means 28a and spring 32a similarly as shown in Fig. 3.
  • FIGs. 6 and 7 another embodiment of the bypass means is illustrated wherein the probes 47 and 48 are inserted permanently into the first and last filter sections of a waveguide filter 49 through openings 50 and 51, respectively.
  • the transmission line 52 interconnecting probes 47 and 48 is of the line-above-ground type.
  • the details of this type of transmission line incorporating controlling means, substantially as herein illustrated and ncluding other embodiments applicable to the present invention, are disclosed in copending applications, Serial Nos. 227,896, filed May 23, 1951, now abandoned; 234,503, filed June 30, 1951, now Patent No. 2,721,312, issued October 18, 1955; and 286,764, filed May 8, 1952.
  • Transmission line 52 is of the printed circuit type comprising a first or line conductor 53 and a second or ground conductor 54, herein the wall of the microwave filter 49, with a layer 55 of insulating material therebetween.
  • the method of applying the conductive material to the layer of insulation, the width relation between ground conductor and line conductor and the required characteristic of field concentration are disclosed in the aforementioned copending applications.
  • the tapered sections S6 and 57 of line conductor 53 provide means to match the transmission line characteristic impedance of the system including probes 47 and 48 thus affording properly determined means to couple signal energy from filter 49, as illustrated, and establish the desired bypass communication.
  • This small variation in the width of the line conductor may produce variations in the characteristic impedance of transmission line 52 as desired for impedance matching, but the field distribution with respect to the ground conductor is not materially disturbed, or if disturbed it quickly stabilizes itself to provide the desired bypass communication Without undue signal reflection.
  • the means to control the bypass communication shown in Figs. 6 and 7 comprises a pivot segment 58 substantially identical to the line conductor 53, the segment being pivoted as indicated by pin 59 which may comprise conductive metal or dielectric material. In either case, when the switch portion 58 is in the closed position, indicated by the dotted lines, the pin has substantially no effect on the flow of current along the line.
  • switch 58 is located a distance from each of the probes 47 and 48, where N is equal to an odd integral.
  • the switch 58 occurs a quarter wave length from one of the probes while the distance to the other probe is any odd number of quarter lengths.
  • the probes 47 and 48 remain in the path of signal propagation at all times with bypass communication being controlled by discontinuing said communication through the interruption of the continuity of the transmission line and thereby reflecting substantially an effective short to the point where signal coupling is accomplished. By leaving the coupling probes in the path of signal energy any alignment and tuning accomplished during bypass communication will not be disturbed.
  • Fig. 8 illustrates an attenuator which may replace the switch 58 of Figs. 6 and 7 to provide a means to control the bypass communication.
  • Line conductor 53a is continuous from one coupling proble to the other in this embodiment.
  • Pivoted segment 60 comprises a lossy conductor material capable of absorbing microwave signal energy, the segment being pivoted by means of pin 61.
  • To disrupt the bypass communication attenuator portion 60 is pivoted to the position shown by the dotted lines whereby the bypass energy is absorbed by said attenuator. This, as in the other embodiments introduces the selectivity characteristic of the microwave filter to the system.
  • a shorting screw may be provided in the line 7 located a half wavelength or multiple thereof from the coupling probes 47 and 48.
  • FIGs. 6, 7, and 8 comprise the subject matter of my copending application Serial No. 302,293, filed August 2, 1952, now Patent No. 2,735,073, issued February 14, 1956.
  • a microwave bandpass filter comprising a hollow waveguide filter of the distributed parameter 'type having signal input and output sections, each of said sections having an opening therein, a coaxial transmission line coupled between said sections with the inner conductor thereof extending through the openings into said sections to provide a bypass communication about said waveguide filter to bypass aporti'onof the signal yenergy from said.
  • said bypass coaxial transmission line including a coupling section coupled to each of said input and output sections and a central section coupled between said coupling sections, the center conductor of said coupling sections being disposed in sliding contact relation with the ends of the center conductor of said centralY section, the ends of the center conductor of said coupling sections extending through the opening in said input and output sections to provide a probe type coupling in said input and output sections, said coupling sections being extended beyond the point of sliding contact with the center conductor of said central section, and meansA included in this extended portion to short the inner and outer conductors of said coupling sections to provide a quarter wave choke section therein at the operating frequency ofsaid lter to cooperate in impedance matching,4 and said means to interrupt bypass communication includes means coupled to the center conductors of said'coupling sections to control the probe ⁇ lengths thereof extending into said input and

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NLAANVRAGE8006808,A NL180280B (nl) 1952-08-02 Werkwijze voor het bereiden van een katalysator op basis van molybdeen- en ijzeroxyde voor de oxydatie van methanol tot formaldehyde.
BE521895D BE521895A (en(2012)) 1952-08-02
US302292A US2773244A (en) 1952-08-02 1952-08-02 Band pass filter

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3013212A (en) * 1953-08-28 1961-12-12 Itt Aural detection apparatus comprising an acoustical delay line having external feedback circuit
US3132312A (en) * 1960-10-03 1964-05-05 North American Aviation Inc Microwave phase shifter adjusted by simultaneously altering two dimensions so as to keep frequency dependent phase dispersion constant
DE1218084B (de) * 1959-10-09 1966-06-02 Telefunken Patent Siebanordnung fuer Mikrowellen mit kontinuierlich veraenderbarer UEbertragungs-charakteristik
FR2512593A1 (fr) * 1981-09-04 1983-03-11 Thomson Csf Filtre en guide d'onde
US5106826A (en) * 1989-07-24 1992-04-21 At&T Bell Laboratories System for transmitting and/or receiving electromagnetic radiation employing resonant cavity including high Tc superconducting material
US20040000973A1 (en) * 2002-06-28 2004-01-01 Mccandless Jay Compact waveguide filter and method

Citations (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2161593A (en) * 1935-03-29 1939-06-06 Rca Corp Band-pass filter
US2218980A (en) * 1938-11-23 1940-10-22 Hazeltine Corp Tunable band-pass selector
US2226686A (en) * 1937-11-16 1940-12-31 Mackay Radio & Telegraph Co High frequency transmission network
US2390768A (en) * 1944-10-07 1945-12-11 Gen Electric Variable selectivity amplifier
US2498073A (en) * 1946-05-11 1950-02-21 Bell Telephone Labor Inc Microwave electrical testing system
US2509062A (en) * 1945-09-07 1950-05-23 Emi Ltd Selectable band width coupling network
US2530979A (en) * 1945-09-27 1950-11-21 Westinghouse Electric Corp Radio frequency control system
US2566020A (en) * 1945-01-04 1951-08-28 Willard H Fenn High-frequency detecting device
US2667597A (en) * 1948-06-14 1954-01-26 Int Standard Electric Corp Velocity modulated electron discharge device
US2735073A (en) * 1952-08-02 1956-02-14 Bandpass
US2749523A (en) * 1951-12-01 1956-06-05 Itt Band pass filters

Patent Citations (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2161593A (en) * 1935-03-29 1939-06-06 Rca Corp Band-pass filter
US2226686A (en) * 1937-11-16 1940-12-31 Mackay Radio & Telegraph Co High frequency transmission network
US2218980A (en) * 1938-11-23 1940-10-22 Hazeltine Corp Tunable band-pass selector
US2390768A (en) * 1944-10-07 1945-12-11 Gen Electric Variable selectivity amplifier
US2566020A (en) * 1945-01-04 1951-08-28 Willard H Fenn High-frequency detecting device
US2509062A (en) * 1945-09-07 1950-05-23 Emi Ltd Selectable band width coupling network
US2530979A (en) * 1945-09-27 1950-11-21 Westinghouse Electric Corp Radio frequency control system
US2498073A (en) * 1946-05-11 1950-02-21 Bell Telephone Labor Inc Microwave electrical testing system
US2667597A (en) * 1948-06-14 1954-01-26 Int Standard Electric Corp Velocity modulated electron discharge device
US2749523A (en) * 1951-12-01 1956-06-05 Itt Band pass filters
US2735073A (en) * 1952-08-02 1956-02-14 Bandpass

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3013212A (en) * 1953-08-28 1961-12-12 Itt Aural detection apparatus comprising an acoustical delay line having external feedback circuit
DE1218084B (de) * 1959-10-09 1966-06-02 Telefunken Patent Siebanordnung fuer Mikrowellen mit kontinuierlich veraenderbarer UEbertragungs-charakteristik
US3132312A (en) * 1960-10-03 1964-05-05 North American Aviation Inc Microwave phase shifter adjusted by simultaneously altering two dimensions so as to keep frequency dependent phase dispersion constant
FR2512593A1 (fr) * 1981-09-04 1983-03-11 Thomson Csf Filtre en guide d'onde
EP0075498A1 (fr) * 1981-09-04 1983-03-30 Thomson-Csf Filtre à cavités, présentant un couplage entre cavités non adjacentes
US5106826A (en) * 1989-07-24 1992-04-21 At&T Bell Laboratories System for transmitting and/or receiving electromagnetic radiation employing resonant cavity including high Tc superconducting material
US20040000973A1 (en) * 2002-06-28 2004-01-01 Mccandless Jay Compact waveguide filter and method
US7009469B2 (en) * 2002-06-28 2006-03-07 Harris Corporation Compact waveguide filter and method

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NL180280B (nl)

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