CA2213848A1 - Dual frequency antenna with integral diplexer - Google Patents
Dual frequency antenna with integral diplexerInfo
- Publication number
- CA2213848A1 CA2213848A1 CA002213848A CA2213848A CA2213848A1 CA 2213848 A1 CA2213848 A1 CA 2213848A1 CA 002213848 A CA002213848 A CA 002213848A CA 2213848 A CA2213848 A CA 2213848A CA 2213848 A1 CA2213848 A1 CA 2213848A1
- Authority
- CA
- Canada
- Prior art keywords
- frequency
- antenna
- diplexer
- dual frequency
- communication system
- 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.)
- Abandoned
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q5/00—Arrangements for simultaneous operation of antennas on two or more different wavebands, e.g. dual-band or multi-band arrangements
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
- H03H7/38—Impedance-matching networks
- H03H7/383—Impedance-matching networks comprising distributed impedance elements together with lumped impedance elements
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q5/00—Arrangements for simultaneous operation of antennas on two or more different wavebands, e.g. dual-band or multi-band arrangements
- H01Q5/30—Arrangements for providing operation on different wavebands
- H01Q5/307—Individual or coupled radiating elements, each element being fed in an unspecified way
- H01Q5/314—Individual or coupled radiating elements, each element being fed in an unspecified way using frequency dependent circuits or components, e.g. trap circuits or capacitors
- H01Q5/335—Individual or coupled radiating elements, each element being fed in an unspecified way using frequency dependent circuits or components, e.g. trap circuits or capacitors at the feed, e.g. for impedance matching
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q7/00—Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
- H03H7/38—Impedance-matching networks
Landscapes
- Details Of Aerials (AREA)
- Variable-Direction Aerials And Aerial Arrays (AREA)
Abstract
A dual frequency communication system utilizes an antenna (100) and a diplexer (102) for operating at a first frequency and a second, preferably widely separated, lower frequency. The antenna is preferably a loop antenna (100) and the diplexer (102) including both capacitative (104, 106, 108) and inductive (110, 112) elements provides an impedance match at both the first and second operating frequencies as well as combines both signals such that a single coaxial cable may be used with the antenna. In a preferred embodiment, the antenna is fabricated on a standard printed circuit board using a standard printed circuit board fabrication process. The passive electrical elements of the diplexer are also fabricated on the same board, thereby resulting in an integrated planar dual frequency antenna system.
Description
W 096t29756 PCTnUS96102637 DUAL FREQUENCY ANTENNA WITU lNTEGRAL DIPLEXER
Field of the Invention The present invention relates generally to the field of Ante.nnAc used for s communications. More particularly, it relates to a dual frequency AntçnnA which can Llanslllil and receive on two di~el~nL frequencies.
Background of the Invention Many communication systems operate at two frequencies, one for 0 trancmittin~ hlrollllaLion and one for receiving information. ~nt~nnAc with relatively wide bandwidth are preferable in such systems to allow both functions within the single frequency band. When size, space and weight limitations are a consideration, however, planar Ant~nnAc are desirable, such as microstrip Ant~nnAc Because microstrip -AntçnnAc have a high Q and have a relatively narrow bandwidth, m~t~hing networks have been developed to provide matched impedances over a wider range of frequçn~.içc thereby widening the bandwidth of a microstrip Ant~nnA to allow both trAncmiccion and receiving of information within a single passband. Therefore, microstrip ~nt~nnAc with Ill-Atçhil)g networks, such as the m-Atçhing device described in U.S. Patent No. 5,233,360 toKuroda et al., provide a small in size and simple in construction ~ntennA that had a wide bandwidth allowing for radio communication operating at two di~l~llL frequencies.
In other communication systems, however, it is highly desirable to operate in two widely separated frequency bands instead of a single frequency band. The cost of imple.rn~ntAtion of communication systems, system requirements, such as power and bandwidth, and federal regulatory limitations all can make it desirable to operate at two widely separated frequency bands. To operate a L1A~ r and receiver in combination can easily be implemented with two separate ~nt~.nnAc, as shown in Figure 1 a. A first ll AnCI 1 l; ~ I; I ISJ antenna 2 and a second receiving antenna 4 each have a separate coaxial cable feed, cables 6 and 8, respectively. Transmitter 10 transmits at a first frequency using lIAI1~III;~I;IIg antenna 2 while receiver 12 receives information at a second frequency using receiving antenna 4. While the system of Figure 1 a operates at two discrete frequency bands, it is desirable, particularly where saving space, weight, material or cost is a consideration, to integrate one or more of the functions of the systern shown in Figure 1 a.
W 096/297~6 PCTrUS96/02637 Figure Ib shows another system that operates at two discrete frequency bands. Similar to the system of Figure 1 a, the system of Figure lb has a first Lld~cl.l;ll;l~sg antenna 22 tr~ncmitfing at a first frequency and a second ~ ",;ll;"g ~ntenn~ 24 Ll;~--''-ll;ll;l-~ at a second frequency. The signals fromthetwo antenn~c are combined at duplexer 34, or isolator, thereby allowing both signals to be fed down a single coaxial cable 26. At the tl~ns",iLLer 30 and receiver 32, the signals are sepal~ed at block 28 using either a duplexer or isolator. While the system of Figure lb allows the combination of the two coaxial cables used in the system of Figure 1 a, it requires additional hal.lwa,e, namely the duplexers.
0 Other systems have used two or more parasitic microstrip patch ~nt~nn~s stacked on top of each other or placed side by side to reduce size or weight. Also, single element microstrip patch ~nt.onn~c have been developed for dual frequencyoperation. For example, U.S. Patent No. 4,771,291 to Lo et al. describes a microstrip antenna that inrllldec shorting pins at particular locations in the patch to vary the ratio of two band frequencies, thereby allowing a single element microstrip ~ntenn~ the capability of two or more bands of operation.
Another way of allowing a single antenna to cimlllt~n~ously feed a receiver and be fed from a tr~ncmirter is to utilize a diplexer. One co.",l,on diplexer is realized using a circulator. A circulator is a three-port RF component that passes RF
energy from port to port in one direction. A L".n~",;l~er, a receiver and an antenna are conn~c~ed to each of the three ports of the circulator. The power input from theLl;~ el in a first port exits the second port to the antenn~ The power received from the antenna enters the second port and exits the third port to the receiver. Because any micm~t~h from the ~ntenn~ in the t,an~""iL mode is reflected into the receiver port, for example, proper operation of the circulator is highly dependent upon the presence of a matched load at each of the three ports to maximize isolation.
Summarv of the Invention To overcome the limitations in the prior art described above, and to overcome other limitations that will become appa,~"~ upon reading and underst~n~ling the present specification, the present invention provides a dual frequency antenna capable of operating at two widely separated frequencies. The communication system is pl~re,~,bly implemented on a planar substrate with a loop antenna and a diplexer. The W 096/29756 PCTrUS96/02637 diplexer comprises a passive electrical elements for l,laLch.llg imped~es ofthe loop antenna at two operating frequency bands. The diplexer further combines the signals of the two frequency bands such that a single coaxial cable can carry the signals from the two freq~l~nries BriefDescription of the Drawin s The present invention will be more fully described with reference to the accompanying drawings wherein like reference numerals identify corresponding components, and:
o Figures la and lb show prior art communication systems for operating at two widely separated frequency bands;
Figure 2 shows an m~tr.hing network for m~trhing the antenna impedance with the impedance of a coaxial cable;
Figure 3 shows a specific m~tching network topology for an electrically large loop antenna;
Figure 4 shows a specific m~trhing network topology for an electrically small loop ~ntf~nn~
Figure 5 shows a m~tçhing network topology incorporating the m~trhing functions of the m~trhing networks of Figures 3 and 4;
Figures 6 and 6a are SWR plots for an ~nte.nn~ system of the present invention;
Figure 7 shows a first embodiment of an antenna and diplexer of the present invention implrmçnted on a planar substrate, not shown, with the two met~lli7~tion layers; and Figures 8a and 8b show a front and back view of a dielectric substrate of a second embodiment of an antenna and diplexer of the present invention.
Detailed Description of a Preferred Embodiment In the following detailed description of the preferred embodiment, reference is made to the accompanying dldwillgs which forrn a part hereof, and in which is shown by way of illustration a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural rh~nge5 may be made without departing from the scope of the present invention.
W 096/29756 PCTrUS96/02637 The present invention will be described with respect to a loop slnt~nn~
although those skilled in the art will readily recognize that many di~e~ types of ~ntPnn~c may be used. For example, a microstrip dipole or a monopole ~ntenn~ could also be used as the ~nt~nn~ portion of the present invention. A single-turn loop antenna is a metallic conductor formed into the shape of a closed curve, such as a circular wire, with a gap in the conductor to form the terminals. The loop ant~nn~ may impl~mented in a shapes other than circular, such as square, rect~n~ r, ellipsoid or rhombic. Loop ~nt~nn~e are ~l~rel~ble in many applications, such a vehicle to roadside communications, because they are conrollllable7 can withct~nt1 temperature variations and are relatively o forgiving in m~mlf~c.tllring.
The loop antenna of the present invention is preferably deci~n~tl or optimized at the higher of the operational frequency bands. The length of the loop is desi n~d to be an electrically large loop, preferably near resonant size at the higher operational frequency such that the circull~lel,ce of the loop is appl~,~illla~ely equal to one wavelength. Because the length of the loop is dependent on the frequency chosen, by d~cigning at the higher frequency, and therefore shorter wavelength, the size of the loop is .~ By ".;..;...;,;.-g the size ofthe loop, it allows flexibility in applications because the size, cost and weight ofthe antenna is "~ ;",;,~l While decigning the electrically large loop to be near resonant size is preferable, it a design choice and not necpsc~ry Decigning near resonance assists in impedance m~tching as the impedance stays relatively collsLan~ over a relatively wide bandwidth when the loop is near resonant size. Referring to Figure 2, the theoretical input impedance 40 looking into antenna 42 is apl)rox~lllately 100 + j 100 ohms when the circumference of loop antenna 42 is near resonant size. Antenna 42 sends received signals to or receives signals to be tr~ncmitte(l from coaxial cable 44, which typically has a impedance of S0 ohms. The difference in impedance between antenna 42 and coaxial cable 44 requires m~tchin~ network 46 to match the impedances to opLi~ e the amount of power reaching the ~nt~nn~ Figure 3 shows a possible m~tching network topology utili7in~ a shunt capacitor 50 and a series inductor 52 to match ~ntt?nn~ impedance 40 with the impedance of coaxial cable 44. ~tchinSg network 46 may be utilized using discrete passive circuit element components.
While the antenna of the present invention is preferably clesi~;nec~ to operate at a first higher frequency, it also is tuned to operate at a lower frequency. The -W 096/29756 PCT~US96/02637 ~ntenn~ can be tuned to operate at a frequency band right outside the-p~csb~nrl ofthe higher frequency. In many applications, however, it is preferable to operate at frequency bands that are widely separated. The present invention allows the ~nter~n~ to operate at frequencies such that the loop ~nt~nn~ applox~lllales an electrically small loop ~ntçnn~ at the lower operating frequency. The total con~llctor length of electrically small loop ~ntenn~c is small conlpalt;d with the wavelength in free space, typically less than applox.lllalely one tenth ofthe operating wavelength. Electrically small loop ~nt~nnzlc have ullirollll axial current distribution and have a consL~llL field ra~ ting from the ~ntenn~
lo Referring back to Figure 2, when antenna 42 is operating at a lower frequency such that it approximates an electrically small loop ~ntenn~ its theoretical input impedance 40 is appro~,..ately 2 + j lOO ohms, which requires a dirre. e..L m~tc.hing te~hnique. than used for the electrically large loop ~ntçnn~ and shown in Figure 3.
Figure 4 shows a possible m~tchinp network topology when antenna is utilized as an electrically small loop ~nt~nn~ and utilizes a shunt c~ra~itor 54 and a series capacitor 56 to match antenna impedance 40 with the impedance of coaxial cable 44. Similar towhen ~nt~nn~ 42 is op~-~Ling at a higher frequency",.~l~,hi.lD network 46 may beutilized using discrete passive circuit element components when operating at a lower frequency.
To allow antenna 42 to operate both at a first higher frequency and a second lower frequency, the present invention incol~ol,l~es the network ",i1lf.1,;,.g functions for both frequencies in a single diplexer topology. A diplexer allows a single antenna to ~iml]lt~nçously feed a receiver and be fed from a Ll~ ÇI . The diplexer of the present invention allows the ~nt~nn~ to Ll ~IlSllliL at a first frequency by providing a m~t~hin~ topology that both allows the antçnn~ to transmit at the first frequency and also allows the antenna to receive at a second frequency.
Figure 5 shows a diplexer topology that incorporates the network m~t~hing functions for the two frequencies shown in Figures 3 and 4 in a single diplexer topology. Diplexer 60 performs two functions. It first provides an impedance match from the antenna to the Ll~.sn,iLLel and receiver at both high and low frequencies. It also combines the signals for the L-i-ll'~l l;l 1~ and receiver onto a single coaxial cable 44.
At the high frequency operation, inductor 62, Lblock~ has a very high impedance and removes c~rasitor 64, C,Ow~, from the circuit. At the high frequency, c~pa~itor 70, Clo~2 W 096/29756 PCTrUS96/02637 has a very low impedance and is effectively a short, and only c~r~itor 66, C~g " and inductor 68, Lhi~h, are electrically in the circuit. Thus, at the high frequency, diplexer 60 f~m~ tçc the m~tchin~ network shown in Figure 3. At the low frequency operation,however, inductor 62, Lblock~ has a very low impedance and s~p~citor 64, C~0wl, is electrically in the circuit in parallel with capacitor 66, Chj~,. Inductor 68, Lhj~h, has a very low impedance and is effectively a short, and only c~pacitQr 70, ClOw2, and ç~p~citor 64 in parallel with capacitor 66 are electrically in the circuit. Thus, at the low frequency, diplexer 60 çmlll~tçs the m~t~hing network shown in Figure 4.
As described above, the diplexer of the present invention allows the o ~nt~nn~ to operate at a first higher frequency and a second lower frequency. Figure 6 shows a SWR plot of an antenna between the frequencies of 45 MHz and 1 GHz, the antPnn~ being operational at two widely separated frequencies, a first higher frequency, fi, and a second lower frequency, f2. Specifically, in the plot of Figure 6, the first higher frequency is 904.~ ~Iz and the second lower frequency is 49.7 ~Iz. The ~ntçnn~ is ~l~ci~ned at the first frequency, preferably as a resonant wavelength ~nt~onn~ which results in a relatively wider bandwidth 80, where the SWR is two. Specifically, the bandwidth at the higher frequency is 296.6 MHz. The frequency of second lower frequency f2 is a design choice ofthe system, although at a minimllm it is neces~ly to design the antenna to operate outside the p~cs~n~1 of the first frequency when operating at the lower frequency. For example, it would be possible to tune the antenna to operate at app~ ately 658 MHz, the lower end of bandwidth 80. While it is possible for the upper frequency limit of the bandwidth of second lower frequency to f2 to be ~ cent the lower frequency limit of the bandwidth of first higher frequency fi, it is more preferable for the lower frequency to operate at a relatively widely separated frequency.
Figure 6a shows a detailed version of the SWR plot between the frequencies of 40 MHz and 60 MHz of the ~ntenn~ operating at the widely separated lower frequency of 49.7 MHz. The lower bandwidth 82 ofthe lower operating frequency is approximately 930KHz. Thus, the present invention allows an ~ntenn~ to operate at two relatively widely separated frequencies.
While the present invention can be impl~m~nted using a standard wire loop antenna and discrete components, Figure 7 shows a plerel,ed impl~.m.-nt~tion of the present invention in a planar structure. Loop ~ntçnn~ 100 can be constructed on a first side of any a~plc,p~ e planar substrate, not shown. such as FR4, mylar, polyester, W O 96129756 PCTrUS96/02637 polypropylene, Duroid, or dielectric foams. Diplexer 102 is preferably integrated on the same substrate as antenna 100 and can be constructed on the first side, the second side or both sides of ~he substrate, depending on the complexity of the diplexer. Diplexer 102 and antenna 100 may be fabricated in any of many standard printed circuit board mz n11fzlçtllring techniques, such as mzlckin~ and etçhing pattern, print and release, hot stamp, laser ablation and conductive print. The m~tzllli7zltion layers are preferably copper, although any conductive material may be used, such as ~llmim-m gold, tin, nickel, or silver.
Diplexer 102 can be realized using standard inductors and capacitors lo connected to the substrate. By ~ltili7in~ the structure that antenna 100 is constrilcted on allows an integrated unit inel~ in~ both antennzi 100 and diplexer 102. Inductors and cz pa~itQrS needed for the diplexer can be created from the metzllli7zltion layers on the substrate. Area cz~pzicitors can be realized with aligned m~tzllli7zition areas on both sides of the dielectric substrate. Inductors can be realized by thin metzilli7.ed strips of applopliate length.
Figure 7 shows the diplexer 60 of Figure 5 impl~m~nted as diplexer 102 on a planar substrate, not shown for clarity of the two metzllli7~tion layers. Capzi~itQrs C~OWl 64, Ci~jgh 66 and Clow2 70 in Figure 5 are realized in Figure 7 as capacitors ClOWl 104, Ciligh 106 and C~OW2 108, respectively. Blocking inductor Lblock 62 in Figure 5 is realized by inductor Lbloci~ 110 in Figure 7 and inductor Lhigh 68 is realized by inductor Li~jgh 112.
Input 114 is adapted for a single coaxial cable input. In one embodiment, the substrate is FR4, a fiberglass epoxy board, mzlnllfzlstllred by AlliedSignal J.ziminzlte Systems Inc.
of LaCrosse WI and has a thickness of 31 mils (.0787 cm). A standard 1 oz. copper metzllli7zition layer (34 ~m thick) is applied to both sides of the substrate and removed to produce the antenna and diplexer components. Loop antenna 100 is implçmented as a rectz n~-lz r loop, with a length L of 3800 mils (9.652 cm) and a width W of 2780 mils (7.0612 cm). Capacitors C~OWl 104, Chigh 106 and ClO~2 108, have values of 23.5 pF, 5.5 pF, and 4.6 pF, respectively. Inductor Lbioci; 110 and inductor Lhigh 68 have values of 25 nH and 10 nH, respectively. This implementation of the antenna allows the antenna to operate at a first higher frequency of 904.5 MHz and a second lower frequency of 49.86 MHz. The length ofthe rectzln~llzlr loop is designed to be the resonant length at 904.5 MHz and the impedance looking into the loop at that frequency is 15j33.3 ohms. At W 096/29756 PCTrUS96J02637 49.86 MHz, the ~nt~nn~ is an electrically short loop ~nt~nn~ and the input impedance was measured as .95+j95.8 ohms.
By impl.om~ntinp the diplexer components on the same substrate as ~nt~nn~ 100, the cost ofthe ~nt~nn~ is lower and the complete system can be fabricated using a low cost substrate and a standard printed circuit board process. Moreover, there are no discrete components and therefore no assembly issues and associated costs as well as improved reliability. Finally, the integration of the antenna and diplexer on a single board keeps the size of the system relatively small in size.
Figures 8a and 8b show a first side and a second side of substrate 120, respectively, for a second embodiment of the present invention. Loop ~nt~nn~ 122 is forrned on a first met~lli7~tion layer on the first side of substrate 120 and is ,holl,l oidal in shape and had a characteristic illlpedances of 48.6 - j 11.8 ohms at 905 MHz. Loop ~nt~nn~ 122 further has multiple loops, specifically loop portion 124 that gives loop ~nt~nn~ 122 a~plo.~illlaLely 1 1/3 loops. Multiple loops can f~ it~te impedance m~t~.hinsg when attempting to Illill;,-,;,e the r~act~nce component ofthe input impedance of the ~nt~nn~ On the first side of substrate 120, thin met~li7ed strips 129 and first m~-t~1i7ed plates 126 and 128 are formed that are rtec~c:i~.y for passive electrical m~ntc such as inductors and c~ra~itors~ for the diplexer. In Figure 8b, a second side of substrate 120 is shown with additional structure necessary for the passive electrical elements formed on a second met~lli7~tion layer. Thin m.ot~li7ed strip 134 acts as an inductor while second m.ot~li7Pd plates 130 and 132 are aligned with first met~li7ed plates 126 and 128, respectively, to form capacitors.
Although a ~I~;r~lled embodiment has been illustrated and described for the present invention, it will be appreciated by those of ordinary skill in the art that any method or apparatus which is ç~lr.~ tecl to achieve this same purpose may be substituted for the specific configurations and steps shown. This application is intentled to cover any adaptations or variations of the present invention. Therefore, it is manifestiy intentled that this invention be limited only by the appended claims and the equivalents thereof.
Field of the Invention The present invention relates generally to the field of Ante.nnAc used for s communications. More particularly, it relates to a dual frequency AntçnnA which can Llanslllil and receive on two di~el~nL frequencies.
Background of the Invention Many communication systems operate at two frequencies, one for 0 trancmittin~ hlrollllaLion and one for receiving information. ~nt~nnAc with relatively wide bandwidth are preferable in such systems to allow both functions within the single frequency band. When size, space and weight limitations are a consideration, however, planar Ant~nnAc are desirable, such as microstrip Ant~nnAc Because microstrip -AntçnnAc have a high Q and have a relatively narrow bandwidth, m~t~hing networks have been developed to provide matched impedances over a wider range of frequçn~.içc thereby widening the bandwidth of a microstrip Ant~nnA to allow both trAncmiccion and receiving of information within a single passband. Therefore, microstrip ~nt~nnAc with Ill-Atçhil)g networks, such as the m-Atçhing device described in U.S. Patent No. 5,233,360 toKuroda et al., provide a small in size and simple in construction ~ntennA that had a wide bandwidth allowing for radio communication operating at two di~l~llL frequencies.
In other communication systems, however, it is highly desirable to operate in two widely separated frequency bands instead of a single frequency band. The cost of imple.rn~ntAtion of communication systems, system requirements, such as power and bandwidth, and federal regulatory limitations all can make it desirable to operate at two widely separated frequency bands. To operate a L1A~ r and receiver in combination can easily be implemented with two separate ~nt~.nnAc, as shown in Figure 1 a. A first ll AnCI 1 l; ~ I; I ISJ antenna 2 and a second receiving antenna 4 each have a separate coaxial cable feed, cables 6 and 8, respectively. Transmitter 10 transmits at a first frequency using lIAI1~III;~I;IIg antenna 2 while receiver 12 receives information at a second frequency using receiving antenna 4. While the system of Figure 1 a operates at two discrete frequency bands, it is desirable, particularly where saving space, weight, material or cost is a consideration, to integrate one or more of the functions of the systern shown in Figure 1 a.
W 096/297~6 PCTrUS96/02637 Figure Ib shows another system that operates at two discrete frequency bands. Similar to the system of Figure 1 a, the system of Figure lb has a first Lld~cl.l;ll;l~sg antenna 22 tr~ncmitfing at a first frequency and a second ~ ",;ll;"g ~ntenn~ 24 Ll;~--''-ll;ll;l-~ at a second frequency. The signals fromthetwo antenn~c are combined at duplexer 34, or isolator, thereby allowing both signals to be fed down a single coaxial cable 26. At the tl~ns",iLLer 30 and receiver 32, the signals are sepal~ed at block 28 using either a duplexer or isolator. While the system of Figure lb allows the combination of the two coaxial cables used in the system of Figure 1 a, it requires additional hal.lwa,e, namely the duplexers.
0 Other systems have used two or more parasitic microstrip patch ~nt~nn~s stacked on top of each other or placed side by side to reduce size or weight. Also, single element microstrip patch ~nt.onn~c have been developed for dual frequencyoperation. For example, U.S. Patent No. 4,771,291 to Lo et al. describes a microstrip antenna that inrllldec shorting pins at particular locations in the patch to vary the ratio of two band frequencies, thereby allowing a single element microstrip ~ntenn~ the capability of two or more bands of operation.
Another way of allowing a single antenna to cimlllt~n~ously feed a receiver and be fed from a tr~ncmirter is to utilize a diplexer. One co.",l,on diplexer is realized using a circulator. A circulator is a three-port RF component that passes RF
energy from port to port in one direction. A L".n~",;l~er, a receiver and an antenna are conn~c~ed to each of the three ports of the circulator. The power input from theLl;~ el in a first port exits the second port to the antenn~ The power received from the antenna enters the second port and exits the third port to the receiver. Because any micm~t~h from the ~ntenn~ in the t,an~""iL mode is reflected into the receiver port, for example, proper operation of the circulator is highly dependent upon the presence of a matched load at each of the three ports to maximize isolation.
Summarv of the Invention To overcome the limitations in the prior art described above, and to overcome other limitations that will become appa,~"~ upon reading and underst~n~ling the present specification, the present invention provides a dual frequency antenna capable of operating at two widely separated frequencies. The communication system is pl~re,~,bly implemented on a planar substrate with a loop antenna and a diplexer. The W 096/29756 PCTrUS96/02637 diplexer comprises a passive electrical elements for l,laLch.llg imped~es ofthe loop antenna at two operating frequency bands. The diplexer further combines the signals of the two frequency bands such that a single coaxial cable can carry the signals from the two freq~l~nries BriefDescription of the Drawin s The present invention will be more fully described with reference to the accompanying drawings wherein like reference numerals identify corresponding components, and:
o Figures la and lb show prior art communication systems for operating at two widely separated frequency bands;
Figure 2 shows an m~tr.hing network for m~trhing the antenna impedance with the impedance of a coaxial cable;
Figure 3 shows a specific m~tching network topology for an electrically large loop antenna;
Figure 4 shows a specific m~trhing network topology for an electrically small loop ~ntf~nn~
Figure 5 shows a m~tçhing network topology incorporating the m~trhing functions of the m~trhing networks of Figures 3 and 4;
Figures 6 and 6a are SWR plots for an ~nte.nn~ system of the present invention;
Figure 7 shows a first embodiment of an antenna and diplexer of the present invention implrmçnted on a planar substrate, not shown, with the two met~lli7~tion layers; and Figures 8a and 8b show a front and back view of a dielectric substrate of a second embodiment of an antenna and diplexer of the present invention.
Detailed Description of a Preferred Embodiment In the following detailed description of the preferred embodiment, reference is made to the accompanying dldwillgs which forrn a part hereof, and in which is shown by way of illustration a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural rh~nge5 may be made without departing from the scope of the present invention.
W 096/29756 PCTrUS96/02637 The present invention will be described with respect to a loop slnt~nn~
although those skilled in the art will readily recognize that many di~e~ types of ~ntPnn~c may be used. For example, a microstrip dipole or a monopole ~ntenn~ could also be used as the ~nt~nn~ portion of the present invention. A single-turn loop antenna is a metallic conductor formed into the shape of a closed curve, such as a circular wire, with a gap in the conductor to form the terminals. The loop ant~nn~ may impl~mented in a shapes other than circular, such as square, rect~n~ r, ellipsoid or rhombic. Loop ~nt~nn~e are ~l~rel~ble in many applications, such a vehicle to roadside communications, because they are conrollllable7 can withct~nt1 temperature variations and are relatively o forgiving in m~mlf~c.tllring.
The loop antenna of the present invention is preferably deci~n~tl or optimized at the higher of the operational frequency bands. The length of the loop is desi n~d to be an electrically large loop, preferably near resonant size at the higher operational frequency such that the circull~lel,ce of the loop is appl~,~illla~ely equal to one wavelength. Because the length of the loop is dependent on the frequency chosen, by d~cigning at the higher frequency, and therefore shorter wavelength, the size of the loop is .~ By ".;..;...;,;.-g the size ofthe loop, it allows flexibility in applications because the size, cost and weight ofthe antenna is "~ ;",;,~l While decigning the electrically large loop to be near resonant size is preferable, it a design choice and not necpsc~ry Decigning near resonance assists in impedance m~tching as the impedance stays relatively collsLan~ over a relatively wide bandwidth when the loop is near resonant size. Referring to Figure 2, the theoretical input impedance 40 looking into antenna 42 is apl)rox~lllately 100 + j 100 ohms when the circumference of loop antenna 42 is near resonant size. Antenna 42 sends received signals to or receives signals to be tr~ncmitte(l from coaxial cable 44, which typically has a impedance of S0 ohms. The difference in impedance between antenna 42 and coaxial cable 44 requires m~tchin~ network 46 to match the impedances to opLi~ e the amount of power reaching the ~nt~nn~ Figure 3 shows a possible m~tching network topology utili7in~ a shunt capacitor 50 and a series inductor 52 to match ~ntt?nn~ impedance 40 with the impedance of coaxial cable 44. ~tchinSg network 46 may be utilized using discrete passive circuit element components.
While the antenna of the present invention is preferably clesi~;nec~ to operate at a first higher frequency, it also is tuned to operate at a lower frequency. The -W 096/29756 PCT~US96/02637 ~ntenn~ can be tuned to operate at a frequency band right outside the-p~csb~nrl ofthe higher frequency. In many applications, however, it is preferable to operate at frequency bands that are widely separated. The present invention allows the ~nter~n~ to operate at frequencies such that the loop ~nt~nn~ applox~lllales an electrically small loop ~ntçnn~ at the lower operating frequency. The total con~llctor length of electrically small loop ~ntenn~c is small conlpalt;d with the wavelength in free space, typically less than applox.lllalely one tenth ofthe operating wavelength. Electrically small loop ~nt~nnzlc have ullirollll axial current distribution and have a consL~llL field ra~ ting from the ~ntenn~
lo Referring back to Figure 2, when antenna 42 is operating at a lower frequency such that it approximates an electrically small loop ~ntenn~ its theoretical input impedance 40 is appro~,..ately 2 + j lOO ohms, which requires a dirre. e..L m~tc.hing te~hnique. than used for the electrically large loop ~ntçnn~ and shown in Figure 3.
Figure 4 shows a possible m~tchinp network topology when antenna is utilized as an electrically small loop ~nt~nn~ and utilizes a shunt c~ra~itor 54 and a series capacitor 56 to match antenna impedance 40 with the impedance of coaxial cable 44. Similar towhen ~nt~nn~ 42 is op~-~Ling at a higher frequency",.~l~,hi.lD network 46 may beutilized using discrete passive circuit element components when operating at a lower frequency.
To allow antenna 42 to operate both at a first higher frequency and a second lower frequency, the present invention incol~ol,l~es the network ",i1lf.1,;,.g functions for both frequencies in a single diplexer topology. A diplexer allows a single antenna to ~iml]lt~nçously feed a receiver and be fed from a Ll~ ÇI . The diplexer of the present invention allows the ~nt~nn~ to Ll ~IlSllliL at a first frequency by providing a m~t~hin~ topology that both allows the antçnn~ to transmit at the first frequency and also allows the antenna to receive at a second frequency.
Figure 5 shows a diplexer topology that incorporates the network m~t~hing functions for the two frequencies shown in Figures 3 and 4 in a single diplexer topology. Diplexer 60 performs two functions. It first provides an impedance match from the antenna to the Ll~.sn,iLLel and receiver at both high and low frequencies. It also combines the signals for the L-i-ll'~l l;l 1~ and receiver onto a single coaxial cable 44.
At the high frequency operation, inductor 62, Lblock~ has a very high impedance and removes c~rasitor 64, C,Ow~, from the circuit. At the high frequency, c~pa~itor 70, Clo~2 W 096/29756 PCTrUS96/02637 has a very low impedance and is effectively a short, and only c~r~itor 66, C~g " and inductor 68, Lhi~h, are electrically in the circuit. Thus, at the high frequency, diplexer 60 f~m~ tçc the m~tchin~ network shown in Figure 3. At the low frequency operation,however, inductor 62, Lblock~ has a very low impedance and s~p~citor 64, C~0wl, is electrically in the circuit in parallel with capacitor 66, Chj~,. Inductor 68, Lhj~h, has a very low impedance and is effectively a short, and only c~pacitQr 70, ClOw2, and ç~p~citor 64 in parallel with capacitor 66 are electrically in the circuit. Thus, at the low frequency, diplexer 60 çmlll~tçs the m~t~hing network shown in Figure 4.
As described above, the diplexer of the present invention allows the o ~nt~nn~ to operate at a first higher frequency and a second lower frequency. Figure 6 shows a SWR plot of an antenna between the frequencies of 45 MHz and 1 GHz, the antPnn~ being operational at two widely separated frequencies, a first higher frequency, fi, and a second lower frequency, f2. Specifically, in the plot of Figure 6, the first higher frequency is 904.~ ~Iz and the second lower frequency is 49.7 ~Iz. The ~ntçnn~ is ~l~ci~ned at the first frequency, preferably as a resonant wavelength ~nt~onn~ which results in a relatively wider bandwidth 80, where the SWR is two. Specifically, the bandwidth at the higher frequency is 296.6 MHz. The frequency of second lower frequency f2 is a design choice ofthe system, although at a minimllm it is neces~ly to design the antenna to operate outside the p~cs~n~1 of the first frequency when operating at the lower frequency. For example, it would be possible to tune the antenna to operate at app~ ately 658 MHz, the lower end of bandwidth 80. While it is possible for the upper frequency limit of the bandwidth of second lower frequency to f2 to be ~ cent the lower frequency limit of the bandwidth of first higher frequency fi, it is more preferable for the lower frequency to operate at a relatively widely separated frequency.
Figure 6a shows a detailed version of the SWR plot between the frequencies of 40 MHz and 60 MHz of the ~ntenn~ operating at the widely separated lower frequency of 49.7 MHz. The lower bandwidth 82 ofthe lower operating frequency is approximately 930KHz. Thus, the present invention allows an ~ntenn~ to operate at two relatively widely separated frequencies.
While the present invention can be impl~m~nted using a standard wire loop antenna and discrete components, Figure 7 shows a plerel,ed impl~.m.-nt~tion of the present invention in a planar structure. Loop ~ntçnn~ 100 can be constructed on a first side of any a~plc,p~ e planar substrate, not shown. such as FR4, mylar, polyester, W O 96129756 PCTrUS96/02637 polypropylene, Duroid, or dielectric foams. Diplexer 102 is preferably integrated on the same substrate as antenna 100 and can be constructed on the first side, the second side or both sides of ~he substrate, depending on the complexity of the diplexer. Diplexer 102 and antenna 100 may be fabricated in any of many standard printed circuit board mz n11fzlçtllring techniques, such as mzlckin~ and etçhing pattern, print and release, hot stamp, laser ablation and conductive print. The m~tzllli7zltion layers are preferably copper, although any conductive material may be used, such as ~llmim-m gold, tin, nickel, or silver.
Diplexer 102 can be realized using standard inductors and capacitors lo connected to the substrate. By ~ltili7in~ the structure that antenna 100 is constrilcted on allows an integrated unit inel~ in~ both antennzi 100 and diplexer 102. Inductors and cz pa~itQrS needed for the diplexer can be created from the metzllli7zltion layers on the substrate. Area cz~pzicitors can be realized with aligned m~tzllli7zition areas on both sides of the dielectric substrate. Inductors can be realized by thin metzilli7.ed strips of applopliate length.
Figure 7 shows the diplexer 60 of Figure 5 impl~m~nted as diplexer 102 on a planar substrate, not shown for clarity of the two metzllli7~tion layers. Capzi~itQrs C~OWl 64, Ci~jgh 66 and Clow2 70 in Figure 5 are realized in Figure 7 as capacitors ClOWl 104, Ciligh 106 and C~OW2 108, respectively. Blocking inductor Lblock 62 in Figure 5 is realized by inductor Lbloci~ 110 in Figure 7 and inductor Lhigh 68 is realized by inductor Li~jgh 112.
Input 114 is adapted for a single coaxial cable input. In one embodiment, the substrate is FR4, a fiberglass epoxy board, mzlnllfzlstllred by AlliedSignal J.ziminzlte Systems Inc.
of LaCrosse WI and has a thickness of 31 mils (.0787 cm). A standard 1 oz. copper metzllli7zition layer (34 ~m thick) is applied to both sides of the substrate and removed to produce the antenna and diplexer components. Loop antenna 100 is implçmented as a rectz n~-lz r loop, with a length L of 3800 mils (9.652 cm) and a width W of 2780 mils (7.0612 cm). Capacitors C~OWl 104, Chigh 106 and ClO~2 108, have values of 23.5 pF, 5.5 pF, and 4.6 pF, respectively. Inductor Lbioci; 110 and inductor Lhigh 68 have values of 25 nH and 10 nH, respectively. This implementation of the antenna allows the antenna to operate at a first higher frequency of 904.5 MHz and a second lower frequency of 49.86 MHz. The length ofthe rectzln~llzlr loop is designed to be the resonant length at 904.5 MHz and the impedance looking into the loop at that frequency is 15j33.3 ohms. At W 096/29756 PCTrUS96J02637 49.86 MHz, the ~nt~nn~ is an electrically short loop ~nt~nn~ and the input impedance was measured as .95+j95.8 ohms.
By impl.om~ntinp the diplexer components on the same substrate as ~nt~nn~ 100, the cost ofthe ~nt~nn~ is lower and the complete system can be fabricated using a low cost substrate and a standard printed circuit board process. Moreover, there are no discrete components and therefore no assembly issues and associated costs as well as improved reliability. Finally, the integration of the antenna and diplexer on a single board keeps the size of the system relatively small in size.
Figures 8a and 8b show a first side and a second side of substrate 120, respectively, for a second embodiment of the present invention. Loop ~nt~nn~ 122 is forrned on a first met~lli7~tion layer on the first side of substrate 120 and is ,holl,l oidal in shape and had a characteristic illlpedances of 48.6 - j 11.8 ohms at 905 MHz. Loop ~nt~nn~ 122 further has multiple loops, specifically loop portion 124 that gives loop ~nt~nn~ 122 a~plo.~illlaLely 1 1/3 loops. Multiple loops can f~ it~te impedance m~t~.hinsg when attempting to Illill;,-,;,e the r~act~nce component ofthe input impedance of the ~nt~nn~ On the first side of substrate 120, thin met~li7ed strips 129 and first m~-t~1i7ed plates 126 and 128 are formed that are rtec~c:i~.y for passive electrical m~ntc such as inductors and c~ra~itors~ for the diplexer. In Figure 8b, a second side of substrate 120 is shown with additional structure necessary for the passive electrical elements formed on a second met~lli7~tion layer. Thin m.ot~li7ed strip 134 acts as an inductor while second m.ot~li7Pd plates 130 and 132 are aligned with first met~li7ed plates 126 and 128, respectively, to form capacitors.
Although a ~I~;r~lled embodiment has been illustrated and described for the present invention, it will be appreciated by those of ordinary skill in the art that any method or apparatus which is ç~lr.~ tecl to achieve this same purpose may be substituted for the specific configurations and steps shown. This application is intentled to cover any adaptations or variations of the present invention. Therefore, it is manifestiy intentled that this invention be limited only by the appended claims and the equivalents thereof.
Claims (12)
1. A dual frequency communication system comprising:
an antenna; and a diplexer, said diplexer comprising:
means for receiving input signals for transmission by said antenna and for sending output signals received by said antenna;
passive electrical elements for matching impedances at a first frequency and a second frequency and for combining said input signals and said output signals into a single signal.
an antenna; and a diplexer, said diplexer comprising:
means for receiving input signals for transmission by said antenna and for sending output signals received by said antenna;
passive electrical elements for matching impedances at a first frequency and a second frequency and for combining said input signals and said output signals into a single signal.
2. The dual frequency communication system according to claim 1, further comprising:
a transmitter for transmitting said input signals; and a receiver for receiving said output signals received by said antenna.
a transmitter for transmitting said input signals; and a receiver for receiving said output signals received by said antenna.
3. The dual frequency communication system according to claim 1, wherein said antenna is a loop antenna.
4. The dual frequency communication system according to claim 1, wherein said passive electrical elements of said diplexer comprise:
means for providing inductance; and means for providing capacitance.
means for providing inductance; and means for providing capacitance.
5. The dual frequency communication system according to claim 1, wherein said means for receiving input signals for transmission by said antenna and for sending output signals received by said antenna comprises a coaxial cable.
6. The dual frequency communication system according to claim 1, wherein said first frequency is widely separated from said second frequency.
7. The dual frequency communication system according to claim 3, wherein said loop antenna is approximately resonant in size for said first frequency.
8. A planar dual frequency antenna system comprising:
a dielectric substrate having a first side and a second side;
a first metallization layer on said first side of said dielectric substrate, said first metallization layer forming:
a conductive loop having a first end and a second end;
first metalized plates for capacitors; and first metalized line means for receiving input signals at a first frequency and for sending output signals at a second frequency;
a second metallization layer on said second side of said dielectric substrate, said second metallization layer forming:
second metalized plates aligned with said first plates for said capacitors;
thin metalized strips for inductors; and second metalized line means for receiving input signals at a first frequency and for sending output signals at a second frequency.
a dielectric substrate having a first side and a second side;
a first metallization layer on said first side of said dielectric substrate, said first metallization layer forming:
a conductive loop having a first end and a second end;
first metalized plates for capacitors; and first metalized line means for receiving input signals at a first frequency and for sending output signals at a second frequency;
a second metallization layer on said second side of said dielectric substrate, said second metallization layer forming:
second metalized plates aligned with said first plates for said capacitors;
thin metalized strips for inductors; and second metalized line means for receiving input signals at a first frequency and for sending output signals at a second frequency.
9. The planar dual frequency antenna system according to claim 8, further comprising:
a coaxial cable connected to said first and second metalized line means;
a transmitter for transmitting said input signals; and a receiver for receiving said output signals received by said antenna.
a coaxial cable connected to said first and second metalized line means;
a transmitter for transmitting said input signals; and a receiver for receiving said output signals received by said antenna.
10. The planar dual frequency antenna system according to claim 8, wherein said first frequency is widely separated from said second frequency.
11. The planar dual frequency antenna system according to claim 8, wherein said conductive loop is approximately resonant in size for said first frequency.
12. A method of making a dual frequency antenna and diplexer, said method comprising the steps of:
forming a conductive loop of resonant size for a first frequency;
measuring input impedance of said conductive loop operating at said first frequency;
constructing a first matching network to match said measured input impedance with a coaxial cable impedance;
selecting a second lower frequency;
measuring input impedance of said conductive loop operating at said second frequency;
constructing a second matching network to match said measured input impedance with said coaxial cable impedance; and constructing a diplexer incorporating functions of said first matching network and said second matching network.
forming a conductive loop of resonant size for a first frequency;
measuring input impedance of said conductive loop operating at said first frequency;
constructing a first matching network to match said measured input impedance with a coaxial cable impedance;
selecting a second lower frequency;
measuring input impedance of said conductive loop operating at said second frequency;
constructing a second matching network to match said measured input impedance with said coaxial cable impedance; and constructing a diplexer incorporating functions of said first matching network and said second matching network.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US40656595A | 1995-03-20 | 1995-03-20 | |
| US08/406565 | 1995-03-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2213848A1 true CA2213848A1 (en) | 1996-09-26 |
Family
ID=23608539
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002213848A Abandoned CA2213848A1 (en) | 1995-03-20 | 1996-03-11 | Dual frequency antenna with integral diplexer |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP0815613A1 (en) |
| JP (1) | JPH11502386A (en) |
| KR (1) | KR19980702904A (en) |
| AU (1) | AU696840B2 (en) |
| BR (1) | BR9607695A (en) |
| CA (1) | CA2213848A1 (en) |
| WO (1) | WO1996029756A1 (en) |
Families Citing this family (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6396458B1 (en) * | 1996-08-09 | 2002-05-28 | Centurion Wireless Technologies, Inc. | Integrated matched antenna structures using printed circuit techniques |
| KR19990015772A (en) * | 1997-08-09 | 1999-03-05 | 윤종용 | Antenna circuit with built-in matching circuit and its implementation method |
| US6329886B1 (en) | 1998-05-12 | 2001-12-11 | Nec Corporation | Impedance-matching method and circuit at different frequences |
| JP3883707B2 (en) * | 1998-08-28 | 2007-02-21 | 三菱電機株式会社 | Dual frequency matching circuit |
| SE514515C2 (en) * | 1999-08-11 | 2001-03-05 | Allgon Ab | Compact multi-band antenna |
| US6400336B1 (en) * | 2001-05-23 | 2002-06-04 | Sierra Wireless, Inc. | Tunable dual band antenna system |
| US7103382B2 (en) | 2001-07-10 | 2006-09-05 | Kyocera Wireless Corp. | System and method for receiving and transmitting information in a multipath environment |
| KR100913660B1 (en) * | 2002-02-21 | 2009-08-24 | 키오세라 와이어리스 코포레이션 | System and method for providing gps-enabled wireless communications |
| DE10318815A1 (en) * | 2003-04-17 | 2004-11-04 | Valeo Schalter Und Sensoren Gmbh | Slot-coupled radar antenna with radiation areas |
| US7469131B2 (en) | 2004-09-14 | 2008-12-23 | Nokia Corporation | Terminal and associated transducer assembly and method for selectively transducing in at least two frequency bands |
| KR100735356B1 (en) * | 2005-12-12 | 2007-07-04 | 삼성전기주식회사 | Broadband antenna comprising coupling pattern |
| WO2009088231A2 (en) * | 2008-01-08 | 2009-07-16 | Ace Antenna Corp. | Multi-band internal antenna |
| DE102008050743B4 (en) * | 2008-10-08 | 2016-11-17 | Qualcomm Technologies, Inc. (N.D.Ges.D. Staates Delaware) | Impedance matching circuit for adapting planar antennas |
| DE102018126361A1 (en) | 2018-10-23 | 2020-04-23 | Fuba Automotive Electronics Gmbh | Foil antenna |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB9007979D0 (en) * | 1990-04-09 | 1990-06-06 | Panorama Antennas Ltd | Matching element for mobile antenna |
| DE69131660T2 (en) * | 1990-07-30 | 2000-04-06 | Sony Corp | Adaptation device for a microstrip antenna |
| JP2826433B2 (en) * | 1993-02-26 | 1998-11-18 | 日本電気株式会社 | Dual frequency matching circuit for antenna |
-
1996
- 1996-03-11 KR KR1019970706312A patent/KR19980702904A/en not_active Application Discontinuation
- 1996-03-11 WO PCT/US1996/002637 patent/WO1996029756A1/en not_active Application Discontinuation
- 1996-03-11 CA CA002213848A patent/CA2213848A1/en not_active Abandoned
- 1996-03-11 EP EP96908536A patent/EP0815613A1/en not_active Withdrawn
- 1996-03-11 BR BR9607695A patent/BR9607695A/en not_active Application Discontinuation
- 1996-03-11 JP JP8528427A patent/JPH11502386A/en active Pending
- 1996-03-11 AU AU51748/96A patent/AU696840B2/en not_active Ceased
Also Published As
| Publication number | Publication date |
|---|---|
| AU5174896A (en) | 1996-10-08 |
| EP0815613A1 (en) | 1998-01-07 |
| AU696840B2 (en) | 1998-09-17 |
| BR9607695A (en) | 1998-07-07 |
| WO1996029756A1 (en) | 1996-09-26 |
| KR19980702904A (en) | 1998-09-05 |
| JPH11502386A (en) | 1999-02-23 |
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