US3720878A

US3720878A - Transmission line impedance matching circuit

Info

Publication number: US3720878A
Application number: US00145926A
Authority: US
Inventors: R Rosenberry
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-05-21
Filing date: 1971-05-21
Publication date: 1973-03-13
Anticipated expiration: 1990-03-13

Abstract

An impedance-matching solid state amplifier circuit for an antenna circuit in which the impedance matching circuit can be connected at either terminus of the transmission circuit or at any point therebetween and in which the amplifier circuit need not be relied upon for any tuning effect as it relies upon the reflected impedance of the load in the matched impedance transmission circuit.

Description

United States Patent Rosenberry 1Malch 13, 1973 TRANSMISSION LINE IMPEDANCE [56] References Cited MATCHING CIRCUIT UNITED STATES PATENTS [76] lnventor: Raymond A. Rosenberry, 6645 2 663 767 12/1953 Reeves et al 330/40 Rmheue Boulevard Parma Heights 3 027 524 3/1962 May Jr "1.21:: llllllllllllll p 3,336,540 8/1967 Kwartnoffetal ..333 & x [22] Filed: May 21,1971

Primary Examiner-Nathan Kaufman [21] Appl. No.1 145,9 6 Att0rney-lsler & Ornstein Related U.S. Application Data [57] ABSTRACT [63] continuafion'inpan of 738969 June An impedance-matching solid state amplifier circuit 1968' abandoned" for an antenna circuit in which the impedance matching circuit can be connected at either terminus [52] U.S. CI. ..330/12, 330/40, 333/32 f th transmission circuit or at any point [51] Int. Cl. .I-I03f 3/04 therebetween and in which the amplifier circuit need [58] not be relied upon for any tuning effect as it relies Field of Search ..333/32, 8;330/40, 12

upon the reflected impedance of the load in the matched impedance transmission circuit.

7 Claims, 3 Drawing Figures PATENTED MAR 1 3 I975 3. 7210 .878

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\3 Rmnono kkoseusemur wxm INVENTOR.

TRANSMISSION LINE IMPEDANCE MATCHING CIRCUIT CROSS-REFERENCES TO RELATED APPLICATIONS LINE IMPEDANCE MATCHING AMPLIFIER FOR REFLECTED TUNING.

BACKGROUND OF THE INVENTION This invention relates broadly to receiving antennas for TV, UHF and FM broadcast frequencies in which a receiver or receiving set is connected to an appropriate antenna by means of which the signals received by the antenna at the selected frequencies are transmitted to the receiver. Considerable progress has been made in reducing the physical size of receiving antennas and in the design of broad-band antenna systems for the multiplicity of receiving bands for which receivers are now adapted. In effecting such reduction of physical size and broad-banding characteristics, it has been observed that some of the gain characteristics of these reduced size antennas, although sufficiently adequate in strong signal areas, are border line or inadequate in weak signal areas or in poor environmental conditions.

, In order to increase the gain characteristics of such reduced size antennasystems, or even of the conven' tional full size antenna systems, it has been suggested or proposed that electronic amplification means be applied to the input signal to the antenna, these amplification means being tuned to the desired receiving frequency, and thus increasing the signal strength to the antenna which, in turn, is transmitted to the receiver through the transmission line circuit. This proposed system of amplification appears to provide a solution for the problem it is intended to solve, but is restrictive in its application in that it requires amplifying multi-tuned circuitry broad-tuned to cover a band of receiving frequencies and will not adequately serve any other frequencies than those for which its tuning circuit is designed.

In such prior art devices which are connected between the antenna and the receiver, the amplifier circuitry includes blocking components, e.g., vacuum tubes or blocking capacitors or other devices, which serve to decouple or isolate the input matching trans former circuit from the output matching transformer circuit; and the amplifying device itself, which is connected between this input and output circuitry, functions only for power-energized signal amplification. Therefore, the load impedance established in the tuning of the receiver cannot be reflected directly to the antenna, as would be the case ifthe amplifying circuitry were not there. The tuning of the receiver is reflected only to the output of the amplifier circuitry, not to the antenna.

SUMMARY OF THE INVENTION In the present invention, signal amplification is obtained by an amplifier circuit which need not be designed or built'to any particular tuned frequency, but only need be impedance matched in the transmission line circuit of the antenna system and can be installed at any point in that transmission line circuit.

The invention depends for its functioning upon the fact that in any matched impedance transmission circuit wherein the load impedance is matched to the transmission line and input circuit impedance, the terminating impedance of the load is reflected to the generator at every and any point along the transmission circuit. The invention provides an amplifier circuit which does not isolate the input circuitry from the output circuitry, but in which the amplifying device is a directly coupled component of the input and output circuitry, so that the receiver load impedance will be reflected directly to the antenna just as if the amplifying circuit were not there.

By providing an amplifier circuit which matches the load and generator circuit impedances of the transmission lines and thereby satisfies this matched impedance condition, the amplifying means can be connected in the transmission circuit at either terminus thereof or at any point inbetween and, as the circuit is already tuned and the impedance reflected at the point of connection of the amplifier means, there is no need to separately tune the amplifier means as it will serve to amplify the signal on the overall antennareceiver system.

BRIEF DESCRIPTION OF THE DRAWING FIG. I of the drawing is a diagrammatic representation of an antenna system embodying the impedance matching circuitry and amplifying means of my invention.

FIG. 2 is a circuit diagram of the impedancematching circuit and amplifier means.

FIG. 3 is the circuit diagram of FIG. 2 modified to accommodate a condition of unbalanced input and output such as would occur in the impedance matching of a coaxial transmission line.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more particularly to FIGS. 1 and 2 of the drawing, I have shown a receiving antenna 10, here represented as a conventional dipole element, which if desired, can be equipped with any suitable artificial reactance modifiers, such as the loading coil 11.

The antenna, which can be considered as the signal generator, terminates in the feed points 12 and presents a definite and characteristic value of impedances to the transmission line 13 in the resonant frequency range for which it is designed. The transmission line 13 serves to connect the receiver 14 to the feed points I2 of the antenna and transmits the signal or energy wave from the antenna to the receiver, which; can be considered as the load. When the impedance of the load is matched by the transmission line and antenna circuit impedances, as they should be, the resulting overall matched circuit is effectively a tuned circuit in which the tuning causes the impedances to be reflected at each and every point along the transmission line. This characteristic of a matched impedance transmission circuit can be utilized to obtain signal strength amplification of the antenna system and achieve inherent tuning of the amplifier means, if a directly coupled solid state impedance-matching amplifier is introduced into the transmission line at any point. Such an impedancematching amplifier, indicated by the reference numeral 15, is shown in FIG. 1 as being connected in the transmission line 13 at a point which can be considered as midway or intermediate the receiver 14 and the receiving antenna 10. However, as previously noted, this point of connection of the amplifier 15 is merely illustrative and the amplifier could with equal effect be connected at any other point on the transmission line or at the terminals of the connection of the transmission line to the receiver 14 or to the antenna 10.

One form of impedance-matching circuitry for the amplifier 15 is illustrated in FIG. 2 of the drawings and a slightly modified form of this circuitry for an unbalanced input and output is shown in FIG. 3 of the drawings. Referring now to FIG. 2 of the drawings, l have shown an electrically powered, solid state impedance-matching amplification circuit for the incoming signal or energy wave which, at its input and output terminals, is preferably provided with non-oscillatory coupling coils for direct coupling of the unbalanced solid state device to the balanced transmission line 13. These coils serve to provide a low resistance DC path anda high impedance for AC so that a radio frequency (RF) voltage can be developed across the coils. Any other suitable direct coupling connection means could be used which would maintain the matched impedance characteristic of the tuned circuits reflected by the antenna and the receiver.

The energy input of the signal generator or antenna is fed to one winding 17 of a double-wound coupling coil 16 whose other winding 18 is connected into the amplification circuit. The windings l7 and 18 are in ductively coupled to each other and are preferably wound adjacent to each other in the same direction so as to prevent or minimize undesirable oscillation characteristics. The primary amplification component of the amplifying circuit is a gated RF transistor 19 whose base. 19a is connected to one end of the winding 18. The collector 19b of the transistor 19 is connected to one terminus of the winding 21 of the double-wound coupling coil 20, whose inductively coupled other winding 22 is connected to the receiver or load 14. This arrangement connects the semi-conductor 19 in nonblocking or non-isolating RF relationship to the input and output impedances to which it is terminated.

The other terminus of the winding 21 is connected to a suitable DC power supply 23, here indicated as a power cell, and bypassed to ground through capacitor 24 which also bypasses the power cell. The opposite terminus of the winding 18 is connected to the other pole of the DC power supply 23 through a base resistor 29 which is bypassed to ground and is also connected to the winding 21 through a biasing resistor 25. The emitter 190 on the transistor 19 is connected through emitter resistor 26 to ground and the emitter is also bypassed to ground. The amplifier circuit is connected, as at 27, to a common point or reference ground.

The emitter resistor 26 controls the current flow in the emitter-collector circuit of the semi-conductor 19. The base resistor 29 controls the current flow in the base-emitter circuit. The base biasing resistor 25 controls the current flow and sets the class of operation which, in conjunction with the

current control elements

26 and 29 establishes the input and output impedances presented by the DC powered circuit to the RF signal, and also establishes the amplification factor.

The transistor 19 should be appropriate to provide the desired amplification characteristics and, in its selection, it is also necessary to keep in mind the necessity of obtaining impedance-matching characteristics through voltage-current operating values, as determined by the manufacturers characteristic curves. The other components of the amplifying circuit must be of suitable values to accomplish their required or desired function. The

coupling coils

16 and 20 have no impedance-matching function in relation to the amplifier circuit. However, they must each be designed to match the generator circuit impedance and load circuit impedance, respectively, and therefore must be made of wire sizes in an appropriate number of turns properly spaced to achieve this objective. Thus, if the transmission line circuit is a matched impedance 300 ohm tuned circuit, the double wound coupling coils l6 and 20 will be designed to present 300 ohms of impedance to the transmission line at its point of input and output connection therewith.

By way of example, the components of the abovedescribed circuit of FIG. 2 could have the following values and characteristics for matched impedance of a 300 ohm input and output line between an antenna and receiver for the FM frequency range of 88-108 MHz, using a Motorola HEP 2 germanium PNP small-signal transistor having a cut-off frequency of 750 MHz:

The

coupling coils

17 and 18 would each be four turns, 5/16 inch diameter, of No. 24 enameled wire, spaced one-half inch from end to end. The

output coupling coils

21 and 22 would each be six turns, instead of four, but are otherwise the same as the

input coupling coils

17 and 18. The combined resonance point of the couplings in conjunction with the capacitance presented by the transistor should be well above the FM operating frequency, for reasons well known to the art.

The base resistor 29 would be a 4.7K /4-watt carbon resistor; the biasing resistor 25 would be a 5.6K /4- watt carbon resistor; the emitter resistor 26 can have a very low value of 10 ohms or less; the condensers across

resistor

26 and 29, as well as the condenser 24, can each have a value of 0.001 mfd.; and a 1.5V dry cell provides the DC power source 23.

All values are initially determined by empirical testing for optimum gain, using RC substitution boxes or pots or other variable voltage devices to regulate current flow through the selected transistor or other gated solid state device to establish the desired matching input and output impedances of the circuit.

The described circuitry has two significant functions which are here described as inter-related, but one of which could be utilized independently of the other. One of these functions is the impedance-matching function which is accomplished empirically, as described, by initially varying the input and output characteristics of the semi-conductor 19 by current and voltage control circuit elements to determine and establish an impedance match to both the input and output impedances to which it is terminated. The circuit thereby provides an impedance-matching means which has utility for that purpose independently of any gain or amplification function, which may not necessarily be required or desired. If impedance-matching is the only desired function of the'circuit, the semi-com ductor need not be selected for any particular gain or amplification characteristic. However, if a gated semiconductor is selected having a distributed form characteristic, the transistor 19 will present or provide a transmission line effect which couples its RF input to its RF output to achieve RF signal pass through even when there is no DC energization ofthe circuit.

When the transistor 19 is also selected for a gain characteristic which will cover the frequency range at which it is to be used, the impedance-matching circuit also becomes an amplifier circuit.

Inasmuch as the amplifier is connected into the transmission line and is a directly coupled component thereof whose input and output circuits are not isolated with respect to the signal, the amplifier itself need not be tuned as it reflects the impedances resulting from the tuning of the antenna and receiver circuits and will serve to amplify or increase the gain under those circumstances where the non-amplified signal is too weak to be effectively received by the receiver 14. This characteristic of the amplifier depends upon the impedance-matching function of the circuitry, but the impedance-matching function can exist and be useful independently of the amplification feature.

A cut-out switch 28 may be provided in the amplifier circuit so as to eliminate the amplifier function from the transmission line circuit in circumstances where high-gain signals are obtainable without amplification in strong signal areas. The previously described distributed form or transmission line effect of a properly selected transistor 19 will permit the signal to pass through when the switch 28 de-energizes the DC circuit, as there is no RF isolation or blocking of the amplifier circuit. However, when the switch cuts out the DC power supply, the previously described impedancematching function of the DC powered circuit is no longer effected and a condition of some degree of impedance mismatch will exist. But this degree of mismatch will still not prevent high-gain signal pass through.

It will be understood that suitable traps can be utilized in connection with the circuitry to eliminate interferences at selected frequencies.

In FIG. 3 of the drawings, I have shown the amplifier circuit of FIG. 2 as it is modified for a condition of unbalanced input arid output, such as would occur when using a coaxial transmission line. Under such circumstances, an unbalanced arrangement of the

coils

16 and 20 would be utilized, in which, for example, the number of turns in the coupling coil 16 would be more or less than the number of turns in the output coupling coil 20 and, additionally, the windings l7 and 22 of the respective coupling coils 116 and 20 would be connected to the common point 27, as indicated.

The described form of amplifier means lends itself readily to compact printed circuitry and, as it need not be disposed in any particular relationship to the antenna on the transmission line, it can conveniently be disposed closely adjacent to the receiver, even at the input terminals on the receiver so that the power cell can be replaced or other necessary maintenance services can be provided conveniently. Although the described amplifying circuit has been illustrated with one transistor component, the circuit could include additional transistors or other components, asis known to those skilled in the art, to attain he desired impedancematching and amplification.

It is to be understood that the forms of my invention, herewith shown and described, are to be taken as preferred examples of the same, and that various changes in the shape, size and arrangement of parts may be resorted to, without departing from the spirit of my invention, or the scope of the subjoined claims.

Having thus described my invention, I claim:

1. A DC powered circuit for matching the load circuit impedance and generator circuit impedance on the transmission line of a radio frequency circuit, consisting of a solid state RF semi-conductor device, first means for establishing current and voltage parameters for said device in said DC powered circuit to provide an input impedance for said DC powered circuit matching said generator circuit output impedance and an output impedance for said DC powered circuit matching said load circuit impedance, said first means being directly connected to the elements of said semi-conductor in said DC circuit, and second means connecting the elements of said semi-conductor device to the transmission line in non-isolating RF relationship to the input and output impedances to which the device is terminated.

2. A DC powered impedance-matching circuit as defined in claim 1, wherein said semi-conductor device has a signal gain characteristic to provide signal amplification between said generator and said load.

3. A DC powered impedance-matching circuit as defined in claim 1, wherein said semi-conductor device is gated.

4. A DC powered impedance-matching circuitas defined in claim 1, wherein said first means comprises current-control circuit elements of empirically determined values connected to said semi-conductor device to establish the input and output impedances of the DC powered circuit.

5. A DC powered impedance-matching circuit as defined in claim I, wherein said second means comprises coupling coils.

6. A DC powered impedance-matching circuit as defined in claim 1, including switch means for selectively de-energizing the DC power.

7. A DC powered impedance-matching circuit as defined in claim 6, wherein said solid state RF semiconductor device is gated to provide a transmission line effect to couple its RF input to its RF output when said circuit is de-energized by said switch means.

Claims

1. A DC powered circuit for matching the load circuit impedance and generator circuit impedance on the transmission line of a radio frequency circuit, consisting of a solid state RF semiconductor device, first means for establishing current and voltage parameters for said device in said DC powered circuit to provide an input impedance for said DC powered circuit matching said generator circuit output impedance and an output impedance for said DC powered circuit matching said load circuit impedance, said first means being directly connected to the elements of said semi-conductor in said DC circuit, and second means connecting the elements of said semi-conductor device to the transmission line in non-isolating RF relationship to the input and output impedances to which the device is terminated.

4. A DC powered impedance-matching circuit as defined in claim 1, wherein said first means comprises current-control circuit elements of empirically determined values connected to said semi-conductor device to establish the input and output impedances of the DC powered circuit.

5. A DC powered impedance-matching circuit as defined in claim 1, wherein said second means comprises coupling coils.