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Terminated microstrip antenna

Info

Publication number
CA1097428A
CA1097428A CA 318571 CA318571A CA1097428A CA 1097428 A CA1097428 A CA 1097428A CA 318571 CA318571 CA 318571 CA 318571 A CA318571 A CA 318571A CA 1097428 A CA1097428 A CA 1097428A
Authority
CA
Grant status
Grant
Patent type
Prior art keywords
circuit
line
short
resonant
antenna
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.)
Expired
Application number
CA 318571
Other languages
French (fr)
Inventor
John L. Kerr
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.)
US Secretary of Army
Original Assignee
US Secretary of Army
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
Grant date

Links

Classifications

    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01QAERIALS
    • H01Q9/00Electrically-short aerials having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
    • H01Q9/04Resonant aerials
    • H01Q9/0407Substantially flat resonant element parallel to ground plane, e.g. patch antenna
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01QAERIALS
    • H01Q5/00Arrangements for simultaneous operation of aerials on two or more different wavebands, e.g. dual-band or multi-band arrangements
    • H01Q5/30Arrangements for providing operation on different wavebands
    • H01Q5/307Individual or coupled radiating elements, each element being fed in an unspecified way
    • H01Q5/314Individual or coupled radiating elements, each element being fed in an unspecified way using frequency dependent circuits or components, e.g. trap circuits or capacitors
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01QAERIALS
    • H01Q5/00Arrangements for simultaneous operation of aerials on two or more different wavebands, e.g. dual-band or multi-band arrangements
    • H01Q5/30Arrangements for providing operation on different wavebands
    • H01Q5/307Individual or coupled radiating elements, each element being fed in an unspecified way
    • H01Q5/342Individual or coupled radiating elements, each element being fed in an unspecified way for different propagation modes
    • H01Q5/357Individual or coupled radiating elements, each element being fed in an unspecified way for different propagation modes using a single feed point
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01QAERIALS
    • H01Q9/00Electrically-short aerials having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
    • H01Q9/04Resonant aerials
    • H01Q9/0407Substantially flat resonant element parallel to ground plane, e.g. patch antenna
    • H01Q9/0442Substantially flat resonant element parallel to ground plane, e.g. patch antenna with particular tuning means

Abstract

Abstract of the Disclosure A microstrip antenna design according to which a plurality of resonant frequencies can be obtained for a given size radiator, to increase the usefulness of the antenna by providing for frequency diversity operation and by making the microstrip antenna tunable over a range of frequencies.
As will be seen, the microstrip antenna is provided with an output termin-ation which can be open-circuited or short-circuited, and at varying lengths, to change the frequency at which the microstrip antenna can be made resonant.

Description

~7~2~
This inventioll relates to microstrip antennas and, more particular-ly, to an antenna design whicll permits a single antenna construction to operate over a range of frequencies with acceptable voltage-standing-wave-ratios (VSWR).
As is well known and understood, a microstrip antenna is a printed circuit device in whicll tlle radiating e]ement is typically a rectangular patch of metal etched on one side oE a dual-clad circuit board. As is also well known and understood, the microstrip antenna is a narrow band device which operates at a single resonant frequency. If diEferent resonant frequen-cies are desired, then different circuit board constructions are needed,either changing the dielectric c~nstant of the circuit board material for a given element size, or changing the size of the radiating element for the same dielectric constant. If it werc desired to usc s~lch microstrip antennas in secured communications systems, Identification Fricnd or Foe systems or similar systems req~l;ring operation in two or more discrete bands, it will be readily apparcnt that sucll arrangement would be fairly cumbcrsome and of increased manu~acturing cost.
~ s will become clear hereinafter, the microstril~ antenna design of the invention follows from a finding that the resonant frequency of a given size radiator can be changed by providing it with an output termination, and by open-circuiting or short-circuiting that termination. With the additional finding that the location of the open-circuit or short-circuit meas~1red with respect to the output termination will determine the frequency at which t~e antenna resonates, it becomes possible to operate the antenna at different frequencies simply by positioning the open-circuit and shor-t-circuit positions.
When added to the further finding that the resonant frequency will change from an open-circuit termination to a short-circuit termination, it will thus be apparent that a tunable microstrip antenna can be easily fabricated, simply by varying the termination length and/or the output condition, either open-circuit or short-circuit. As will also be readily apparent to those skilled in the art, the open-circuit and short-circuit conditions and locations can be changed either locally or remotely, as by electronically contro]ling the - 1 - ~

.: :

7~

effective length or a strip l;ne set ul, to permit diverse frequency opera-tions.
These and other features of the present invention ~ill be more clearly ~mderstood from a consideration of the following clescription, taken in connection with the accompanying drawing in which:
Figure 1 shows a microstrip antenna constructed in accordance with the prior art;
Figure 2 shows a terminated microstrip antenna constructed in accordance with the invention;
Figures 3 and 4 are a series of curves showi~g resonant frequency characteristics as exemplified by microstrip antennas constructed in accor-dance with the present invention; and Figures 5-lO show typical radiation patterns obtained using the terminated microstrip antenna technique oE the invention.
In Figure 1, ~he microstrip antenna 10 is shown as comprising a circuit board 12, the back side of whicll (not shown) is clad entirely of a metal material, typically copper. In conventional con,tructions, the Eront side of the circuit board is clad oE like material, except in the areas 14 and 16, where the metal is etched away to reveal the dielectric material 17 underneath. tIn the preferred embodiments of the invention described, dielectric materials available under the tradenames Polyguide and Duroid were employed.) A section of met:l extends from the rectangular metal plate 20 so formed, to operate as a microstrip transformer in matching the impedance at the input to the patch 22 to the impedance at -the signal imput jack 24, usually the output from a coaxial cable coupled through the back side of the - circuit board 12. In one embodiment of the construction, a circuit board clad with copper 1-l/2 mils thick overlying a 1/8 inch thick Duroid dielec-tric was employed for radiating in the L-band of frequencies. When con-structed 4~655 inches on a side, and with the etched areas 14, 16 extending approximately 0.988 inches each, the microstrip antenna of Figure 1 exhibits a resonant frequency of some 1370 ~l~lz, and exhibits a resonant frequency : ~)97~Z~3 . .

characteristic as shown by the curve A in Figure 3. The dimensions of the microstrip transformer 18, illustrated by reference numerals 25~30 were as ollows:

Length 25 ........... 0.772 inches Length 26 ~ O~ 0.872 inches Arc 27 ~OO~O~ 0.600 inch radius Arc 28 ~O~ 0.400 inch radius Width 29 ............ 0.200 inches Distance 30 ......... 0.500 inches, measured with respect to the vertical center line of the circuit board 120 In accordance with the present invention, however, I have fo~md that the resonant frequency of this described radiator can be changed by providing it with an output termination, and by open-circuiting or short-circuiting that termination. For example, and referring to the microstrip antenna of Figure 2 (wherein like re:Eerence numerals are employed to identify parts corresponding to those in Figure 1), I have found that if an output termination corresponding in dimension to the impedance matching input trans-former were provided at the opposite side of the rectangular metal plate 20, and then short-circuited, that the resultant resonant frequency would be reduced to approximately 1360 MHz, with the resonant frequency characteristic then being shown by the curve B in Figure 3. I have further found that if this output termination were open-circuited instead, the resonant frequency of the radiator would be increased to approximately 1410 MHz, with the micro-strip antenna then having a resonant frequency characteristic as depicted by tle curve C in Figure 3. In other words, with the dimensions of this output termination 32 being as follows:
Length 33 ~OOO~ 0.772 inches Length 34 ........... 0.872 inches Arc 35 ~OO~O~ OOO 0.600 inch radius Arc 36 ~ O~O~ 0.400 inch radius Width 37 ~O~OOO~ 0.200 inches `

1~397428 Distance 38 ~ O 0.500 inches, measured with respect to the vertical center line of the circuit board l2~ the resonant frequency of the microstrip antenna can be lowered by some 10 ~IIIz or raised some ~lllz simply by short-circuiting or open-circuiting, respectively, the output terminal 40 of the termination 32.
In the foregoing description, it will be understood that a coaxial connector was employed at the output terminal 40 to perform the short-circuit-ing and open-circuiting conditions.
I have further found that different changes iTI the resonant fre-quency could be effected by adding different lengths of coaxial line onto the connector, and then short-circuiting or open-circuiting their ends. For example, I have found thnt the microstrip racliator will resonate at 1310 MHz if a 2.55 cm coaxial line were added to the output connector and its remote end short-circuited, whereas a resonant frequency of approximately 1385 Mllz would be exhibited if the remote en(l of that 2.55 cm line were open-circuited lnstead. Curves D and E in FLgure 3 illustrate the resonant Erequency charac-terlstics, respectively, Cor these conditions. Other resonallt frelluencies have been implemented by the addition of diff~erent lengths o coaxial line to the output connector at terminal 40, and altering the termination condition from short-circuit to open-circuit at the end of the added line.
I have additionally found that it is possible to obtain double-resonance conditions from a microstrip radiator having a single length of short-circuited line added to the output connector. In particular, with a short-circuit condition providing a resonant frequency of 1312 Mllz measured for a 2.55 cm line, the addition of an added length equal to ~/2 at this frequency, produces the original resonance at 1312 MHz, but a second resonance simultaneously at 1457 M~lz, the overall length being then 13.8 cm from the output terminal 40. Such characteristics are illustrated by the curve A and B of Figure 4. Experimentation has shown that it is possible to shaft these two resonant frequencies by varying the length of tlle terminating line. Thus, in one experiment, one length of short-circuited line resulted in a resonant frequency of 1260 M~lz an(l a VSWR oE 1.58:1 at its low end, and a second, ~L~)9~21!3 higher resonant frcquency of 1400 ~IHæ with a VSWR of l.01 1. A second length oL short-circuitcd line yielded a i-esonant frequency oE 1330 Mllz at a VSWR of 1.35:1, and a second resonance of 1450 Mllz at a VSWR o~` 1.22:1. A
further length experimented with, when sllort-circuited, yielded a resonant frequency of 1352 ~II-Iz at a VSWR of 1.14:1; and a highcr rcsonance of 1500 ~]llz at a 1.48:1 VSWR. Analysis has shown that multiple resonances are also possi-ble by further increases in the terminating line length as the impedance of the line repeats itself every one-half wavelength. Analysis has also indica-ted that similar double, triple, etc. resonances can be obtained by adding such lengths of line to the output terminal 40, and then open-circuiting their remote ends.
I have also found that the microstrip antenna configurat;on oE
Figure 2 can be made t~mable by terminating the o~ltptlt port 40 Witll a variable short-circuit length. Results using such technique are ~abulate(l below for tuning to a minimum VSWR at the indicated frequencies by varying the length of the short-circuited iinc.
f ~IIIZ VSW~
1200 1.80:1 1250 1.70:1 1300 1.35:1 1350 1.14:1 1400 1.01:1 1450 1.22:1 1500 1.48:1 1550 2.20:1 As will be readily apparent to those skilled in the art, these results indi-cate that a microstrip antenna terminated in accordance with the present invention can operate over a range of frequencies more than 200 ~z, and with a VSWR of less than 1.50:1, simply by having a calibrated length of line which can be short-circuited at select locations. The experimental results also indicated that the instantaneous bandwiclth obtained is comparable to those of the curves oE Figures 3 and 4, and the single m;crostrip antenna 742~3 still operate narrow band. As will be understood, prior art teachings of microstrip antennas indicated the need for a diffcrent antenna coniiguration for each frequency of operation desired. Analysis has shown thaL not only will the variable short-circuit mode of working with a terminated line provide this tunable embodiment, but that similar tuning could be obtained with appropriate design of a variable open-circuited line.
The radiation patterns of Figures 5-10 show typical E- and }1- plane patterns for the terminated microstrip antenna of the invention, the "dashed"
pattern being that for the E- plane and the "solid" pattern being that for the H- plane. In particular, Figure 5 shows the pattern for tlle 1360 MHz operation with the outp~lt terminal 40 short-circuited, whereas Figure 6 shows the pattern for the 1410 Mllz operation with the output terminal 40 open-cir-cuited; Figure 7 similarly shows the radiatic)n pnttcrn for 13]2 ~IIIz witll a short-circuit 2.55 cm from terminal 40, wllereas the patterns oE Figllre 8 show the operation at 1385 ~IIIz for an open-circuit 2.55 cm Erom terminal 40; and the patterns of Figures 9 and 10 represent those obtained with a short-circuit condition 13.8 cm rrom thc output terminnl 40, thc doul)ly rcsonanL condLLion, in which Figure 9 indicates the pattern at the lower resonance of 1312 MHz while Figure 10 represents the pattern at the higher resonant frequency, 1457 ~l~lz. As will be appreciated, àny differences illustrated by these patterns obtained sre very slight and insignificant.
In the simplest form of the invention, therefore, it will be seen that the microstrip antenna of the present invention provides an increase in usefulness of permitting a frequency diversity operation at two different frequencies, merely by changing the output termination from a short-circuit to an open-circuit condition. In transponder operation, for example, where trans missions are at one frequency and receptions are at another frequency, the usefulness of the terminated microstrip antenna will be evident, with the changes in termination being done manually, or made remotely through electro-mechanical or electronic means. For secured communications systcms, or otherarrangements requiring operation over two or more discretc bands, the tunahle version of the invention will be seen to be the more attractive one, where ~1~97~28 different frequenc;es of operati.on can be had by terminati.ng the ].i.ne lengths at calibrated locations. Where the termination is to be by short-ci.rcuit, furthermore, it becomes a relatively easy matter to print a 3.engtll of micro-strip line on the microstrip circuit board itself, with apertures along the length thereof, for example, into which short-circuiting metallic p:ins could be insertecl ~o provi~e the short-circuit termination at Lhc clesired location.
With such a version, the simplicity of the approach oi~. the i.nventi.cn, its associated Icw cost, and concomitant light weight wi.ll be apparent.
While there have been described what are considered to be preferred embodiments oE the present invention it will be appreciated that changes may be made by those skilled in the art without departing from the scope of the teachings herein of ehanging the resonant frequency of a microstri.p antenna by terminati.ng the antenna with short-circuit or open-ci.reui.t condi.tions. For at least such reason, resort should be had to the claims appencled llereto for a correct understanding of the scope of the invention.

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Microstrip antenna apparatus comprising:
a circuit board of dielectric material having front and back sides with a metallic ground plane on the back side thereof;
a radiating element in the form of a patch of metal etched on the front side of said board;
first transmission line means connected along a center line of said radiating element to a first point at one side of the center thereof for coupling to radio equipment;
second transmission line means connected along said center line of the radiating element to a second point at the opposide side of the center, terminated in an impedance very substantially different from the characteristic impedance so that the radiating element is tunable to resonant frequencies depending on the length of the second transmission line means and the value of said impedance, whereby the radiating element may be caused to resonate for a plurality of separate frequencies with the first transmission line means having a low standing wave ratio.
2. The apparatus of claim 1, wherein said radiating element is in the form of a rectangular patch of metal, and wherein said second transmission line means includes a microstrip line etched on the front side of said board from said second point to a third point to form a terminating impedance trans-former.
3. The apparatus of claim 2, further including a coaxial jack mounted on said back side of the board with a center conductor connected through the circuit board to said third point and an outer conductor connected to said ground plane, wherein said impedance terminating the second transmission line means is selectively either an open circuit at said jack or a short circuit formed by placing a shorted coaxial plug on the jack, so that either of two different resonant frequencies may be selected.
4. The apparatus of claim 2, wherein said second transmission line means further includes a coaxial line having a center conductor connected through the circuit board to said third point and an outer conductor connected to said ground plane, so that the resonant frequency of said radiating element may be selected in accordance with the length of the coaxial line and whether the coaxial line is open or short circuited.
5. The apparatus of claim 2, wherein said first point is at the edge of said radiating element opposite the second point, wherein said first trans-mission line means includes a microstrip line etched on the front side of said board from the first point to a fourth point to form an input impedance trans-former having substantially the same dimensions as said terminating impedance transformer, the first transmission line means further including a coaxial line having an inner conductor connected through the circuit board to the first point and an outer conductor connected to said ground plane.
6. The apparatus of claim 5, further including a coaxial jack mounted on said back side of the board with a center conductor connected through the circuit board to said third point and an outer conductor connected to said ground plane, wherein said impedance terminating the second transmission line may selectively be an open circuit at said jack or a short circuit formed by placing a shorted coaxial plug on the jack, so that either of two different resonant frequencies may be selected.
7. The apparatus of claim 6, further including at least one length of coaxial line having a plug on one end for connection to said jack and selectively either a short or open connection at the other end to provide for the selection of additional resonant frequencies.
8. The apparatus of claim 7, wherein for each resonant frequency when selected, said standing wave ratio is less than 1.5, with a relatively narrow bandwidth compared to the variation between the minimum and maximum resonant frequencies which may be selected.
CA 318571 1978-03-13 1978-12-22 Terminated microstrip antenna Expired CA1097428A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US05885727 US4167010A (en) 1978-03-13 1978-03-13 Terminated microstrip antenna
US885,727 1978-03-13

Publications (1)

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CA1097428A true CA1097428A (en) 1981-03-10

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5400041A (en) * 1991-07-26 1995-03-21 Strickland; Peter C. Radiating element incorporating impedance transformation capabilities

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US4320401A (en) * 1978-05-16 1982-03-16 Ball Corporation Broadband microstrip antenna with automatically progressively shortened resonant dimensions with respect to increasing frequency of operation
US4445122A (en) * 1981-03-30 1984-04-24 Leuven Research & Development V.Z.W. Broad-band microstrip antenna
US4475108A (en) * 1982-08-04 1984-10-02 Allied Corporation Electronically tunable microstrip antenna
US4709239A (en) * 1985-09-09 1987-11-24 Sanders Associates, Inc. Dipatch antenna
US5231407A (en) * 1989-04-18 1993-07-27 Novatel Communications, Ltd. Duplexing antenna for portable radio transceiver
US5497165A (en) * 1990-12-14 1996-03-05 Aisin Seiki Kabushiki Kaisha Microstrip antenna
EP0697139B1 (en) * 1994-03-08 2002-12-18 Telit Mobile Terminals S.p.A. Hand-held transmitting and/or receiving apparatus
US6314275B1 (en) 1997-08-19 2001-11-06 Telit Mobile Terminals, S.P.A. Hand-held transmitting and/or receiving apparatus
US6466131B1 (en) * 1996-07-30 2002-10-15 Micron Technology, Inc. Radio frequency data communications device with adjustable receiver sensitivity and method
GB0002406D0 (en) 2000-02-02 2000-03-22 Nokia Mobile Phones Ltd An antenna for a handset
US6806812B1 (en) * 2000-04-26 2004-10-19 Micron Technology, Inc. Automated antenna trim for transmitting and receiving semiconductor devices
JP4121087B2 (en) * 2003-11-27 2008-07-16 アルプス電気株式会社 The antenna device
US7333068B2 (en) 2005-11-15 2008-02-19 Clearone Communications, Inc. Planar anti-reflective interference antennas with extra-planar element extensions
US7480502B2 (en) * 2005-11-15 2009-01-20 Clearone Communications, Inc. Wireless communications device with reflective interference immunity
US7446714B2 (en) * 2005-11-15 2008-11-04 Clearone Communications, Inc. Anti-reflective interference antennas with radially-oriented elements
US7495623B2 (en) * 2007-03-15 2009-02-24 Gary Brist Modular waveguide inteconnect

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US4079268A (en) * 1976-10-06 1978-03-14 Nasa Thin conformal antenna array for microwave power conversion
US4053895A (en) * 1976-11-24 1977-10-11 The United States Of America As Represented By The Secretary Of The Air Force Electronically scanned microstrip antenna array

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5400041A (en) * 1991-07-26 1995-03-21 Strickland; Peter C. Radiating element incorporating impedance transformation capabilities

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Publication number Publication date Type
US4167010A (en) 1979-09-04 grant
CA1097428A1 (en) grant

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