US3484697A - Multi-loop antenna and superregenerative detector - Google Patents

Description

Dec. 16, 1969 I. J. ABEND 3,434,697

I MULTI-LOOP ANTENNA AND SUPERREGENERATIVE DETECTOR Filed Aug. 27, 1965 2 Sheets-Sheet 1 JV/4'6 c]. 46600 WWW Dec. 16, 1969 l. J. ABEND 3,434,697

MULTI 'LOOP ANTENNA AND SUPERREGENERATIVE DETECTOR Filed Aug. 27, 1965 2 Sheets-Sheet 2 1N VEN TOR MV/NG (1. 48600 United States Patent 3,484,697 MULTI-LOOP ANTENNA AND SUPER- REGENERATIVE DETECTOR Irving Ll. Abend, Bergenfieltl, N.J., assignor to Lear Siegler, Inc., Santa Monica, Calif., a corporation of Delaware Filed Aug. 27, 1965, Ser. No. 483,186 Int. Cl. H01q 19/00;H04b 1/22 U.S. Cl. 325-373 15 Claims ABSTRACT OF THE DISCLOSURE This invention relates to radio receiving systems and more particularly it concerns a novel antenna and input circuit arrangement for use in connection with receivers of the portable type.

The present invention finds particular utility in connection with electronic paging systems wherein coded signals are sent out from a central station and are monitored by portable receivers carried by various personnel. When a particular receivers code is transmitted only that receiver will respond to indicate that it has been called. The person being called then knows he should report back to the central station.

The individual receivers used in such electronic paging systems must, of course, be very compact. They must possess a high degree of sensitivity and yet they must remain stable under conditions of temperature variation and other ambient changes. Also, since a great number of personnel may be included in a given system, it is important that the construction of these receivers be maintained as simple and as inexpensive as possible.

One particularly critical area in the make up of a receiver of this nature is the antenna. In order to capture incoming signals with a reasonable degree of sensitivity and selectivity, it is important that the antenna have a high area-turns characteristic. The available area however, is limited by the physical confines of the receiver itself. On the other hand, the number of turns in the antenna coil is limited by the fact that a large number of turns reduces the size of the associated capacitor to a point where the distributed capacitance of the antenna coil may have a significant, and to a great extent, uncontrolled elfect. In prior systems which used antenna coils of wire wound about a form, variations in the electrical characteristics of the antenna would occur with changes in temperature as a result of the changes in stress produced on the various turns of the coil due to expansion and contraction. Furthermore, since the wire in the antenna coil was not of uniform cross section and was not wound with absolute uniformity, the changes in antenna characteristic which occurred over a temperature cycle were not predictable and would vary from cycle to cycle.

It is also important that the antenna be made as insensitive as possible to the effects of nearby magnetic materials; and this should be accomplished with as little loss of antenna Q, or sensitivity, as possible. Prior antenna coils were wound about the receiving system with the various metallic components of the system being located 3,484,697 Patented Dec. 16, 1969 directly within the core region of the coils. This of course greatly influenced and destabilized the antenna.

Another critical area in a paging receivers design lies in the circuit arrangement which receives signals from the antenna. This circuit arrangement must be capable of selecting the received signal and of extracting from it the modulation or informational content which was imposed at the transmitter station. Of the various arrangements available in this connection, the superregenerative circuit is most advantageous. This circuit, which sequentially goes into and out of carrier frequency oscillation at an ultra-sonic rate, provides very good signal selectivity and sensitivity with a minimum of components. There are however certain difficulties associated with the use of superregenerative circuits. For example, these circuits in prior arrangements were very sensitive to variations in component characteristics due to temperature effects and aging. They were also quite sensitive to changes in the associated power supply voltage.

The above and other ditficulties are eliminated by the present invention. According to this invention there is provided a radio receiver input arrangement characterized by a high degree of stability and frequency control without any increase in overall size or complexity.

In one aspect the present invention makes use of an antenna configuration comprising several physically displaced but electrically connected loops. As illustratively embodied these loops are formed on a printed circuit board and are displaced near its outer periphery to maintain a large area for efiicient utilization of the incident radio frequency energy. Different portions of each loop are formed on different sides of the printed circuit board and are connected by eyelets or plated conductive connectors. Individually adjustable cores of magnetic material are provided in each loop for flexibility of tuning and maintenance of a high Q factor. There is thus provided a multiple turn antenna coil of large area. The various turns of the coil moreover are individually adjustable for very accurate tuning control. Also, these magnetic core elements serve to confine the magnetic fields of their respective loops, into the region immediately adjacent the loop. This effectively restricts the magnetic fields and keeps them away from the nearby electrical components and other metallic materials so that they Will not affect the antenna characteristics. Because the coil is printed on a circuit board, there is provided an exceptionally high degree of temperature stability. The individual loops are not subject to mechanical stress and the changes which they do experience with temperature variations besides being minimal are also accurately predictable from temperature cycle to temperature cycle and from unit to unit.

In another aspect, the present invention provides a superregenerative circuit configuration using a transistor having an antenna loop tank circuit forming a feedback between its base and collector and a connection through the resistance portion of a base-coupled resistance-capacitance quench circuit to a battery which is also connected through a portion of the antenna coil to the collector element of the transistor. This arrangement renders the circuit less sensitive to variations in transistor characteristics due to temperature changes and aging; and it provides automatic compensation for variations in the voltage source.

There has thus been outlined rather broadly the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. Those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures for carrying out the several purposes of the invention. It is important, therefore, that the claims be regarded as including such equivalent constructions as do not depart from the spirit and scope of the invention.

A specific embodiment of the invention has been chosen for purposes of illustration and description, and is shown in the accompanying drawings, forming a part of the specification, wherein:

FIG. 1 is a perspective view and partial schematic of a receiver input arrangement according to the present invention;

FIG. 2 is an enlarged fragmentary section view taken along lines 2-2 of FIG. 1; and

FIG. 3 is a composite diagram illustrating opposite sides respectively of a printed circuit board incorporating the present invention, said sides being rotated out into a common plane about an imaginary axis X-X.

In the arrangement shown in FIG. 1, there is provided a fiat base board of the type used for printed circuits. Theboard 10 is formed with a plurality ofholes 12 distributed about generally toward its periphery.Tubes 14a of plastic or similar material extend through theholes 12 and protrude out from the top of theboard 10. These tubes are internally threaded, as shown in FIG. 2, to accommodateadjustable cores 16 of solid magnetic material such as powdered iron. Thecores 16 are externally threaded for an adjustable but tight fit in the tubes 14; and they are provided with hexagonal openings 18 in their ends so that they can be turned with an Allen wrench.

As shown in FIG. 3, theboard 10 is plated with conductive metal on both sides thereof to formprinted circuits 20. These circuits which may be formed according to known printed circuit techniques, are specially arranged, as indicated in FIG. 3, to provide proper interconnections and mountings for the various circuit components illustrated schematically in FIG. 1.

The printed circuits also form the basic portion of the novel antenna configuration of the present invention. As shown in FIGS. 1 and 3, the antenna, indicated generally at 21, begins at afirst terminal 22 toward one edge of the board. It proceeds as astrip 24 of plated metal from this first terminal along the top of theboard 10 to partially encircle thefirst tube 14a. Thestrip 24 terminates at a first eyelet 26 which as shown in FIG. 2, extends 4 through theboard 10 to a corresponding point on its opposite side. Asecond strip 28 of plated metal continues to encircle thetube 14a on the bottom of the board to complete a first loop. Thesecond strip 28 then proceeds along the bottom of the board to the second tube 14b, which it also partially encircles. Thesecond strip 28 then terminates at asecond eyelet 30 which extends up to the top of theboard 10. Athird strip 32 proceeds from theeyelet 30 around the tube 14b on the top of the board to complete a second loop and proceeds to the third tube 140. The looping process involving partial encirclement on both sides of theboard 10 is repeated for each of the remainingtubes 14d to 14;. Upon proceeding from the last tube 14 the last conductive strip terminates at asecond terminal 33 where connections are made to the remaining portions of the circuit.

The particular manner in which the remainder of the superregenerative input circuit is attached to the board is not part of the present invention and thus it will be described in conjunction with the schematic diagram of FIG. 1.

As shown in FIG. 1, the six loop coils formed by the above described antenna configuration are connected in parallel with a pair ofcapacitors 34 and 36 to form a resonant tank circuit. Thefirst capacitor 34 is fixed and does not vary with temperature changes. Theother capacitor 36 however is designed to provide a negative temperature characteristic which compensates for the temperature produced variations in the inductance of the antenna coils. This tank circuitis connected via aline 38 to the collector terminal of thetransistor 40. The emitter of thetransistor 40 is'coupled back via a capacitor 42to its collector thus forming a feedback path. This feedback path is connected to ground through acoil 44 which provides a DO path while preventing the short circuiting of the radio frequency signals. Afurther capacitor 46 is connected between thefeedback capacitor 42 and ground to provide an efiective radio frequency voltage divider arrangement in the feedback network so that thetransistor 40 will not be driven too hard by the fed back signals.

Atap 48 is taken beyond one of the antenna loops and is connected via aresistor 50 to the base terminal of thetransistor 40. The base terminal is also coupled to ground through acapacitor 52.

Power is supplied from a battery or other D.C. voltage source (not shown) through a pair of input'terminals 54, connected respectively between ground and to a variable resistor 56. The tapped resistor 56 is connected through afurther resistor 58 to apoint 60 between thetap 48 from the antenna and theresistor 50 leading to the transistor base terminal. Afurther capacitor 62 is connected between thepoint 60 and ground; and demodulated output signals are taken from thepoint 60.

The values of the various resistors, inductors and capacitors in the system are chosen such that during normal operation, the oscillator circuit formed by thetransistor 40, and thefeedback capacitor 42 tends to produce continuous oscillations at the particular radio frequency to which the system is tuned. However, because of the manner in which theresistor 50 andcapacitor 52 are connected between the power supply input terminals 54 and the base of thetransistor 40, there is produced a variation in the base bias of thetransistor 40, causing it to periodically interrupt these oscillations. The rate at which this quenching or interruption of oscillation takes place depends upon the RC time constant of thecapacitor 52 and theresistor 50; and, this is preferably chosen to be within or beyond the audible range, and, of course, beyond the modulation frequency used with the system.

While the circuit alternates between radio frequency oscillation and no oscillation at the quench frequency rate, modulated radio signals from a remote transmitter are received at theantenna 21 and these signals cause the resonant circuit formed by the antenna and thecapacitors 34 and 36 to resonate. The modulation appearing on the incoming signal produces a variation in the average collecfor current of the transistor and this change in average current represents the actual modulation or information carried on the incoming signal.

The collector current also passes through thejunction point 60. The variations in current at this point include the frequency of self oscillation of the transistor arrangement the quench frequency and the modulation frequency. A low pass filter (not shown), such as a pi-type filter, elfectively eliminates all but the modulation frequency which is passed and amplified for use in the receiver system.

Thetransistor 40 serves as a very effective amplifier immediately prior to the onset of oscillation. However, because of circuit instabilities, it is difiicult if not impossible to keep it in this condition. Accordingly, the present system by means of theRC circuit 50, 52, successively biases the transistor above and below the point of self oscillation so that the average overall gain is kept at a high value.

The above described arrangement is particularly suitable for use with miniaturized receiving systems. Theantenna 21 is of multiloop design and encompasses a large area. It thus provides maximum efiiciency in absorbing incident radio frequency energy so that maximum sensitivity is attained. Further, since the core configuration, comprising themagnetic cores 16, is distributed, the sharpness of tuning or Q of the input circuit is maintainedat a high value. Of course, this also results in a minimization of losses.

Another, and very important feature associated with this antenna configuration is that the inductance changes produced by temperature variations are made uniform and predictable, these changes being very small in comparison to inductances wound in the usual manner with ordinary wire. Further, the changes which do take place follow the same pattern from unit'to unit and over each temperature cycle.

By providing the oneloop tap 48 in the antenna, it is possible to eliminate the capacity changes normal to the various components in the tank circuit including the transistor itself. Also, this arrangement reduces all other capacity efiects by the square of the tap ratio.

Theseveral iron cores 16 serve to confine the magnetic fields in the region to the individual loops, thus effectively isolating the antenna from the effects of the other components on the same circuit board. Further, these coils, being individually tuneable to permit variation of the inductance ratio on either side of thetap 48. This provides a convenient way to compensate for component variation and to tune the tank circuit thus allowing optimized performance of the receiver.

It will further be appreciated that the arrangement of the resistor and the first loop to theantenna 21 between the collector and base terminals of thetransistor 40 serves to stabilize the action of the transistor. Further, by using this loop as the power input point, it is possible to stabilize the system from changes in the power supply output.

Having thus described my invention with particular reference to the preferred form thereof, it will be obvious to those skilled in the art to which the invention pertains, after understanding my invention, that various changes and modifications may be made therein without departing from the spirit and scope of my invention, as defined by the claims appended thereto.

What is claimed as new and desired to be secured by Letters Patent is:

1. A multi-loop antenna system comprising a flat, nonconductive base member, a printed circuit arrangement on both sides of said base member, said printed circuit arrangement being configured to form portions of electrically connected but physically displaced and non-overlapping antenna loops on one side of said member and continuations of said loops on the opposite side of said member, said portions being electrically connected to their respective continuations through connector means extending through said base member.

2. An antenna system comprising a generally fiat, nonconductive base member having a plurality of holes formed therethrough, a printed circuit arrangement on both sides of said base member, said printed circuit arrangement being configured to form portions of loops about said holes on one side of said member and continuations of said loops on the opposite side of said base member, said portions being electrically connected to their respective continuations through connector means extending through said base member and individual core elements movable through said holes.

3. A multi-loop antenna system comprising a gener ally fiat, non-conductive base member, a plurality of conductors arranged on opposite sides of said base member, the conductors on one side configured to form portions of electrically connected but physically displaced and nonoverlapping antenna loops and the conductors on the opposite side being configured to form continuations of said loops, said portions being electrically connected to their respective continuations through connector means extending through said base member.

4. An antenna system as in claim 3 wherein said loops are laterally displaced from each other about said base member.

5. In combination with a radio receiving system, an

antenna arrangement comprising a plurality of conductive loops physically displaced from each other and connected in series to form an overall loop and means mounting said conductive loops in displaced array such that said overall loop surrounds the components of said receiving system.

6. A combination as in claim 5 further including individual cores of magnetic material positioned within said conductive loops.

7. A combination as in claim 6 wherein said individual cores are individually adjustable into and out from their respective loops.

8. In combination a generally flat electrically nonconductive base member, said base member being provided with printed wiring on both sides thereof, a radio receiving circuit including electrical components mounted on said base member and connected through said printed wiring, an antenna forming a portion of said radio receiving circuit and mounted on said base member, said antenna comprising a plurality of individual loops distributed about said base member and connected together in series to form a major loop which encloses said electrical components.

9. A combination as in claim 8 wherein said individual loops constitute a portion of said printed wiring on said base member.

10. A combination as in claim 9 wherein portions of said individual loops are formed on one side of said base member and continuations of said individual loops are formed on the opposite side of said base member, each continuation being electrically connected to its corresponding portion through said base member.

11. An antenna system comprising a generally flat electrically non-conductive base member formed with holes therethrough, individual internally threaded tubular elements extending through said holes, a plurality of externally threaded cylindrical core members threadedly engaged in said tubular elements, a plurality of electrically conductive loops extending about said tubular elements and means connecting said loops to each other.

12. An antenna system as in claim 11 wherein said core member are of magnetic material.

13. An antenna system as in claim 11 wherein a portion of each loop is on one side of said base member and the remainder of each loop is on the opposite side of said base member, each portion being connected to its respective remainder through said base member.

14. An antenna system comprising a base member of generally flat non-electrically conductive material, a plurality of individual conductive loops distributed about said base member and connected in series to form an overall loop, a plurality of individually adjustable cores arranged to move into and out of each loop and means for connecting selected groups of loops to a receiving system.

15. An antenna system as in claim 14 wherein said individual loops are provided with individually adjustable cores.

References Cited UNITED STATES PATENTS 2,451,291 10/1948 Koch 325-429 XR 3,005,966 10/1961 StrOm 336-200 XR 3,119,065 1/1964 Blake 325-428 3,151,297 9/1964 Toomin 325-429 3,185,947 5/1965 Freymodsson 326200 3,296,535 l/l967 Murray 325-429 ROBERT L. GRIFFIN, Primary Examiner R. S. BELL, Assistant Examiner US. Cl. X.R.

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