US 3699452 A
For each frequency range, a different signal path is provided between the antenna input and the antenna output. Each path has passive impedance elements which receive the radiant energy and a transistor. Each path may have independent noise matching between the transistor and the passive impedance elements, and/or the operating point of each transistor may be independently adjusted for each path.
Description (OCR text may contain errors)
United States Patent Lindenmeier et al.
154] ACTIVE ANTENNA ARRANGEMENT FOR A PLURALITY OF FREQUENCY RANGES Inventors: Heinz Lindenmeier, Munich; Hans- Heinrich Meinke, Gauting, both of Germany Assignee: Hans Kolbe 8: Co., KG, Bad Salzdetfurth, Germany Filed: Feb. 16, 1970 Appl. No.: 11,569
Foreign Application Priority Data April 18, 1969 Germany ..P 19 19 749.0
US. Cl. ..325/367, 325/373, 325/386, 343/701, 343/752, 343/895 Int. Cl. ..H0lq 1/26, H04b 1/18 Field of Search ..343/701, 860, 895, 752; 325/366, 371, 373,105, 369, 367, 378, 381,
lllllllllllllllllll [451 Oct. 17,1972
References Cit-ed Mayes, Tiny Antennas Push StateofArt Electronics World; March, 1968; pp. 49- 51 Primary Examiner' -Eli Lieberman Attorney-Michael S. Striker  ABSTRACT For each frequency range, a different signal path is provided between the antenna input and the antenna output. Each path has passive impedance elements which receive the radiant energy and a transistor. Each path may have independent noise matching between the transistor and the passive impedance elements, and/or the operating point of each transistor may be independently adjusted for each path.
13 Claims, 2 Drawing Figures PATENTEUMI n ma SHEET 1 or z mum 5 mum I 1 ACTIVE ANTENNA ARRANGEMENT FOR A PLURALITY or FREQUENCY RANGES BACKGROUND OF THE INVENTION the antenna parts receiving the high frequency radiant energy.
In almost every radio network, the necessity exists, to
- receive and/or to transmit in two completely separate frequency ranges. That is, only in very isolated cases, is radio transmission carried on in a limited frequency range which is not readily subdivided. As an example of such radio transmission and reception, and by no means as an exclusive example, may be taken the radio broadcasting and reception in the entertainment field. Here the frequency ranges lie within the longwave, intermediate wave, shortwave and ultra shortwave regions, that is, between frequencies of 0.15 and H MHz a number of frequency ranges, with large gaps therebetween, exist.
Antennas which operate with equal efficiency over the whole frequency region are not economically practical to manufacture. Thus it has been the practice when antennas, herein designated as passive antennas, were used, to interconnect over high frequency combining filters a number of such passive antennas, each of which was particularly effective within a particular range of the overall range. Alternatively, it has been the practice, for example in radial equipment for commercial vehicles, to utilize passive antennas whose tuning and matching to the receiver were only substantially correct in the higher frequency range.
However, such short antennas, tuned for the ultra shortwave region, represent only a small capacitive coupling to the electromagnetic field in the longwave, intermediate wave and shortwave regions. Such antennas are almost exclusively energized by the electrical component of the electromagnetic field.
For such antennas, cables must be used interconnecting the antenna and the receiver, which represent a very small capacitive component, that is, cables, which do not have a well-defined characteristic impedance. This results in the great disadvantage, that in no case, neither in the upper, nor in the lower frequency range, may the antenna output impedance be matched to the characteristic impedance of the cable. Furthermore, rod-like antennas, which are generally employed in a telescopic arrangement in commercial vehicles, are constantly in danger of inadvertent damage.
Similar problems exist in community antennas. The conditions there are somewhat different, in that the overall frequency range is subdivided into a first and second frequency range, so that at least for the ultra high frequency region, a relatively good matching to the connecting cable (lately amost exclusively 60 ohms) may be achieved. However, for the lower frequency region, the same mismatches exist between antenna impedance and cable impedance as is the case in radial equipment for commercial vehicles. In addition, the unavoidable transformation between the relatively high ohmic impedance of the rod-like antennas to the characteristic impedance of the cable (60 ohms) results in undesired resonances, which may in part eliminate the reception in certain frequency ranges.
Also presently known in the art, is a so-called active antenna, as disclosed in Belgian Patent No. 725,370, issued Feb. 14, 1969. It is disclosed in this patent that broadband matching may be achieved between the parts of the antenna receiving the electromagnetic energy and the receiver, or the receiver cable, by use of controllable, three-terminal active elements. These three-terminal, controllable active elements, preferably transistors, are used to make the signal to noise ratio an optimum. This type of matching is hereinafter called noise matching. Since active elements are used in these antenna arrangements with such noise matching, these antenna arrangements will hereinafter be called active antennas. The active antennas described above, as disclosed in the Belgian patent, have a single signal transmission path between the antenna parts receiving the radiant energy and the antenna output, for all frequencies and frequency ranges to be received. Thus, the active antennas disclosed in the Belgian patent still do not constitute an arrangement which eliminates all of the following drawbacks:
1. poor coupling to the electromagnetic field;
2. poor coupling between the antenna and the cable leading to the receiver; and
3. in spite of the relatively poor coupling to the electromagnetic field, relatively large geometric size, and thus a correspondingly large probability of inadvertent destruction.
SUMMARY OF THE INVENTION It is an object of the invention to furnish an antenna arrangement wherein the above-described drawbacks are minimized.
The present invention is an antenna arrangement for receiving radiant energy in a plurality of frequency ranges at an antenna input and furnishing corresponding antenna output signals to an antenna output. It comprises a plurality of passive impedance elements for receiving said radiant energy..lt further comprises active impedance means, and connecting means connecting said passive impedance elements and said active impedance means in such a manner that a signal transmission path having transmission characteristics independent of the transmission characteristics of all other signal transmission paths, is formed between said antenna input and said antenna output for each of said frequency ranges. Thus it is possible that, for each frequency range, the active impedance means may be independently matched to the passive impedance elements. Alternatively, or in addition, the active impedance means may comprise a plurality of active impedance elements, each associated with one transmission path, and the operating point of each active impedance element may be adjusted independently. In this way, an optimum coupling to the electromagnetic field may be combined with an optimum coupling to a cable interconnecting antenna output to the receiver input, and, further, very small antennas may be used, thus decreasing the probability of damage. These advantages are realized within the overall circuit of the active antenna, thus obviating the need for additional outside elements or matching circuits for different frequency ranges. Each signal transmission path with its associated active elements can be matched and adjusted to the corresponding frequency range, so that, in spite of large differences in the frequency ranges, a single antenna may be used for optimum reception in all of these different frequency ranges. These advantages are particularly useful when an active antenna, in accordance with this invention, is used as an antenna in a commercial vehicle. However, such antennas may, of course, be used in any type of antenna arrangement wherein the above-described advantages are useful.
In a particular embodimentof the present invention which is particularly suitable for commercial vehicles, the frequency band to be received is divided into two frequency ranges and two signal transmission paths are provided between the antenna input and the antenna output. Each path may have its appropriate matching and/or amplification. In this way, the two frequency ranges to be received in a commercial vehicle, namely the long, intermediate and shortwave region on the one hand, and the ultra shortwave region on the other hand, may each be received in an optimum manner.
In a modification of the present invention, each of the signal transmission paths may lead to a separate antenna output, thus permitting signals within the two separate frequency ranges to be separately transmitted to, for example, a separate receiver.
In a further embodiment of the present invention, only the active element for the upper, for example the ultra shortwave frequency range, is matched to the passive impedance element on a noise-matching basis. This embodiment is particularly suitable for commercial vehicle antennas functioning in widely-separated frequency regions. Very little equipment is required, and the mismatching in the lower frequency range is acceptable.
In a further embodiment of the present invention, the active element for the upper frequency range is capacitively coupled to the passive impedance elements, which, in this embodiment, are part of both the first and second signal transmission path. The capacitive coupling may be achieved via the shield of a coaxial conductor.
In another embodiment of the present invention, the above-mentioned coaxial conductor is a printed pseudo coaxial cable comprising a first, second and third conducting strip, the first and third conducting strip consisting outer conductors and the shield for the second, or inner conducting strip.
In another embodiment of the present invention, the control electrode of each active element is connected to a choke. The chokes are so designed that all frequencies not within the frequency range of the signal path with which the particular active element is associated, are blocked from said signal path. This type of connection will substantially eliminate coupling between the different signal paths and resulting noise.
In a further embodiment of the present invention, an additional active element is connected in series with the active element associated with the signal transmission .path in the lower frequency range. This reduces the danger of non-linear distortion and results in signal amplification without corresponding noise amplification, thus improving the sensitivity of the antenna.
The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims.
The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic view of the active antenna of this invention; and
FIG. 2 is a schematic circuit diagram showing the active elements of an antenna in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will now be described with reference to the drawing.
The embodiment shown in the drawing is a printed circuit, which is particularly suitable for placement into the mounting of a rear-view mirror in a commercial vehicle. As shown in FIG. 1, conducting strips 1 and 2 are printed as printed circuits on an insulating plate P. These strips serve as inductors. These conducting strips, in conjunction with a top-loading capacity 3, which may be embodied in a rear-view mirror and with the car body or other metallic ground plane, constitute the passive or receiving part of the antenna. The capacity 3 may be varied within predetermined limits, that is as long as the mathematical product of the effective antenna height multiplied by this capacity remains unchanged.
The transformation of the characteristic impedance for optimum noise matching in the lower frequency range, and in particular in the long and intermediate wave region, is difficult for two reasons. First, the characteristic impedance is very low and, secondly, the bandwidth within which this transformation must take place is relatively large. Conducting strips 1 and 2, in particular, constitute the means for transforming the impedance of the parts of the antenna which receive the electromagnetic energy to a value which allows an optimum noise matching to the active impedance elements. These active elements of the active antenna comprise, as will be described in more detail below, the transistors 4 and 5 in the circuit shown in FIG. 2.
The capacity 3 has a definite function both in the upper frequency range, for example the ultra shortwave region, as well as in the lower frequency range, for example the longwave region. In the ultra shortwave region, the capacity 3 together with the conducting strips 1 and 2, constitute the capacity of an oscillator circuit serving as input circuits; in the upper frequency region, that is in the longwave region, the capacity 3 constitutes the main antenna capacity.
The printed conducting strip 1 is continued as the printed inner conductor 7 of a pseudo coaxial cable, which consists of three substantially parallel conducting strips, 2 and 7. The conducting strip 1 and the inner conductor 7 of the pseudo coaxial cable also serves as a connection between the capacity 3 and the active element used in the signal transmission path for the lower frequency range, namely transistor 4. The outer conductor of the pseudo coaxial cable, that is the conducting strip 2, serves as partial inductivity of the input circuit for coupling the active element for the upper frequency region, that is transistor 5, to the receiving,
passive part of the antenna. It further constitutes, together with the input impedance of transistor 4, a part of the transformation circuit for matching the receiving part of the antenna on a noise matching basis to the input impedance of the active impedance element for the upper frequency region, that is transistor 5.
The connection from the conducting strip 2 of the pseudo "coaxial cable to transistor 5, is made via terminal 8 to the printed surface of a coupling capacitor 9 (FIG. 1) and then to terminal 10 (FIG. 1 and FIG. 2) over an additional capacitor 11 to the base of transistor 5. The resistances 12 and 13 shown in FIG. 2 serve to set the operating point of transistor 5.
The connection of transistor 4, the active impedance element for the lower frequency range, with the receiving part of the antenna is made via terminal 14 connected to the inner conductor 7 to the terminal 15 (FIG. 2) and via a choke l6 and a resistance 17 to the base of transistor 4. A diode 18, shown in FIG. 2, protects transistor 4, namely the transistor for the lower frequency range, from static charges.
Reference to the drawing and to the above description thus shows that the overall circuitry comprising the receiving element 1,2 and 3, and the active impedance elements, namely transistors 4 and 5, is divided into two independent signal transmission paths, each for a different frequency range. Both of these signal paths lead to the antenna output 29 which will be described in more detail below. Further, the division into two signal transmission paths is done in such a manner that independent matching conditions between the receiving antenna parts 1,2, and 3 and the active elements, namely transistors 4 and 5, may exist in each frequency region. In addition to which, the operating points of transistors 4 and 5 may also be adjusted independently to result in the optimum signal transmission along each path.
As is further shown in FIG. 2, an additional active element, or amplifier, such as transistor 6, may be connected in series to the active impedance element for the lower frequency range. Two advantages are thus obtained:
l. The danger of non-linear distortion and mixing effects are decreased because of the division of the volt age existing between terminal 15 and ground, 19, between two transistor base circuits.
2. The cascade circuit of transistors 4 and 6 increases the amplification without a corresponding increase in noise, thus effectively improving the sensitivity of the antenna arrangement.
The resistance 30 in the emitter circuit of transistor 6 serves as a feedback resistance and serves to submerge interference resulting from intermodulation into the noise level.
The resistance 17 serves to flatten any possibly existing resonance curves. The choke 16, in conjunction with the resistance 17, serves to decrease interference which may result from electrical equipment associated with the engine of a commercial vehicle, when the active antenna of this invention is used in such a vehicle. Such electrical interference, generated by the abovementioned associated electrical equipment, is radiated into the receiving parts of the antenna and produced by mixing with higher frequencies.
Choke 20 together with capacitor 21 serve as a general filter for the input to transistor 4, while resistance 22 together with capacitor 23 blocks high frequency interference from the input to transistor 4.
This high frequency interference may, for example,-
originate at terminal 24, where the operating voltage for transistor 4 is supplied.
Choke 25 and capacitor 26 serve to de-couple the output voltage of the lower frequency range from the output of transistor 5, which serves to amplify the voltages of the upper frequency range, that is the ultra shortwave region. The output of transistor'6 for the lower frequency range, and the output of transistor 5 for the upper frequency range are both connected to the antenna output. The connection between the antenna output and the receiving means may then be made, for example by a coaxial cable 29.
The other resistors and capacitors shown in FIG. 2 serve, respectively, to supply the correct current to the transistor and to separate points of differing DC. potential. Capacitor 26 serves this function as well as the function mentioned above. Capacitors 27 and 28 serve to supply bias voltages.
Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.
What is claimed as new and desired to be protected by Letters Patent is:
1. An integrated active antenna combination comprising a plurality of interconnected passive impedance elements jointly receiving energy in a first and second frequency band; first noise-matched amplifier means having a control electrode and an output circuit; second noise matched amplifier means having a control electrode and an output circuit; first coupling circuit means capacitively connected to said plurality of interconnected passive impedance elements for passing only frequencies in said first frequency band to said control electrode of said first amplifier means, while rejecting frequencies in said second frequency band; second coupling circuit means inductively connected to said interconnected passive impedance elements for passing only frequencies in said second frequency band to said control electrode of said second amplifier means, while rejecting said frequencies in said first frequency band; antenna output terminal means; and means connecting the output circuit of said first and second amplifier means to said antenna output terminal means, whereby said first coupling circuit means and first amplifier means constitute a first signal transmission path transmitting signals in said first frequency band only, and said second coupling circuit means and second amplifier means constitute a second signal transmission path passing frequencies in said second frequency band only.
2. An integrated active antenna combination as set forth in claim 1, wherein said first and second frequency bands are respectively an upper and a lower frequency band.
3. Active antenna as set forth in claim 1, wherein said upper frequency range is in the ultra shortwave region.
4. Active antenna as set forth in claim 1, wherein said first amplifier means has a first and second output electrode and a control electrode further comprising means determining the operating point of said first amplifier means.
5. Active antenna as set forth in claim 1, wherein said means determining the operating point comprise a voltage source, voltage divider means having a voltage divider tap connected across said voltage source, and means connecting said control electrode to said voltage divider tap; and wherein the voltage at said voltage divider tap is a function of the frequencies in said first frequency band.
6. Active antenna as set forth in claim 1, wherein said antenna output terminal means comprise a first and second terminal respectively furnishing frequencies in said first and second frequency band.
7. Active antenna as set forth in claim 1, wherein said passive impedance elements and said first coupling impedance means comprise printed circuit means.
8. Active antenna as set forth in claim 1, wherein said passive impedance elements comprise printed conducting strips; wherein said passive circuit means further comprise top-loading capacitor means; and wherein said first coupling circuit means comprise printed circuit capacitor means.
9. Active antenna as set forth in claim 1, wherein said passive impedance elements comprise pseudo-coaxial cable means having a first, second and third conducting strip, said first and third conducting strip being situated on either side of said second conducting strip; and wherein a printed circuit capacitor means is connected to said third conducting strip.
10. Active antenna as set forth in claim 9, wherein said second coupling circuit means comprise inductor means; and means connecting said inductor means to said second conducting strip.
11. Active antenna as set forth in claim 10, wherein said second amplifier means comprise emitter follower amplifier means.
12. Active antenna as set forth in claim 11, further comprising third amplifier means cascade-connected to said emitter-follower amplifier means.
13. Active antenna as set forth in claim 12, further comprising decoupling means decoupling the output of said third amplifier means from the output of said first amplifier means.