US3622890A

US3622890A - Folded integrated antenna and amplifier

Info

Publication number: US3622890A
Application number: US793709*A
Authority: US
Inventors: Kyohei Fujimoto; Yoshiyasu Hiroi
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1968-01-31
Filing date: 1969-01-24
Publication date: 1971-11-23
Anticipated expiration: 1988-11-23
Also published as: DE1904138A1; DE1904138B2; FR2001009B1; FR2001009A1; GB1219543A

Abstract

An integrated antenna system comprising a ground plane, at least one vertical element substantially perpendicular to the ground plane, a helically shaped element having horizontal polarization and a solid state circuit located at the junction of the horizontal and vertical elements. The described antenna system facilitates control of the characteristics of the antenna without varying the physical dimensions thereof. Consequently, antenna size may be reduced, related equipment simplified and the overall characteristics of the antenna system improved.

Description

United States Patent Kyohel Fujimoto;

Yoshiyasu 1111-01, both of Yokohama, Japan 793,709

Jan. 24, 1969 Nov. 23, 1971 Matsushlla Electric Industrial Co. Ltd.

[72] lnventors [21 App]. No. [22] Filed [45 Patented [73] Assignee Osaka, Japan [32] Priorities Jan.31,1968

Feb. 15, 1968, Japan, No. 43/1001]; Feb. 15, 1968, Japan, No. 43/110012; Feb. 15, 1968, Japan, No. 43/10013; Nov. 18, 1968, Japan, No. 43/850115; Nov. 18, 1968, Japan, No. 43/ 101235; Nov. 18, 1968, Japan, No. 43/101236 54 FOLDED INTEGRATED ANTENNA AND AMP- LIFIER 11 Claims, 15 Drawing Flgs. [52] U.S. Cl 325/375, 325/383, 325/386, 343/701, 343/702, 343/828, 343/895 [51] Int. Cl 1-101q 1/26 [50] Field of Search 343/701, 895, 908, 702, 828; 325/105, 375, 383, 386

[56] References Cited UNITED STATES PATENTS 3,343,089 9/1967 Murphy et a1. 343/701 3,386,033 5/1968 Copeland et al 343/701 3,496,566 2/1970 Walter et a1. 343/701 3,426,352 2/1969 Fenwick 343/829 3,521,169 7/1970 Turner et al. 343/701 OTHER REFERENCES Mayes; Tiny Antennas Push State-of-art; Electronics World, March 1968, pp. 49- 52 copy 343 701 Primary Examiner-Eli Lieberman AtmrneyStevens, Davis, Miller & Mosher ABSTRACT: An integrated antenna system comprising a ground plane, at least one vertical element substantially perpendicular to the ground plane, a helically shaped element ,having horizontal polarization and a solid state circuit located at the junction of the horizontal and vertical elements. The described antenna system facilitates control of the characteristics of the antenna without varying the physical dimensions thereof. Consequently, antenna size may be reduced, related equipment simplified and the overall characteristics of the antenna system improved.

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ANIE'N/VA OUTPUT NUMBER OF T URN 0F HEL/X INVENTORS Kl/o H51 FuJmw-o DSHIYHJU' H 0R0! ATTORNEY INTEGRATED ANTENNA AND AMPLIFIER This invention relates to an antenna system into which one or more electronic components or circuitry are incorporated in an integral form in order to change the current distribution on the antenna elements, thereby increasing freedom of antenna design, obtaining improved antenna characteristics, facilitating control of antenna characteristics, and making the antenna synthesis feasible.

Recently, antenna engineers have developed a new concept wherein the antenna is loaded with electronic components, thereby making the antenna system quite different from conventional passive antenna systems. The ultimate objective of the antenna engineer is to design an antenna which has such properties as reduced size, high gain, high directivity, low noise and low cost.

Many attempts to reduce the size of an antenna or to obtain high gain, etc. have been made so far; however, there is an unavoidable restriction due to the inherent inflexible property of passive antennas; that is, the antenna characteristics in general are determined uniquely by its dimensions, once they are determined, so that the flexibility of antenna design is limited only to the parameters of its dimensions, and the characteristics cannot be changed unless the dimensions of the antenna are changed.

One solution to this problem is to make use of an electronic components integrated into the antenna structure. By loading electronic components into the antenna structure in integral form, antenna characteristics of course can be changed completely from those of the original antenna structure. This implies that the freedom of design of the antenna is increased due to the-increase of freedom provided by the electronic components. Several types of antenna systems loaded with electronic components such as tunnel diodes and transistors, have been developed previously. Usefulness of such antenna systems is also discussed in the literature. One of these is the work by Prof. H. Meinke of Technische Hochschule, Miinchen, Germany. He reported a miniaturized antenna systems loaded with transistors. I

The earlier work on such integrated antenna systems is mostly concerned with amplifier-antenna system or miniaturization of amplification circuitry. The antennas developed by Prof. Meinke were built in very small structures, but with fairly wide bandwidth, yet having appreciable gain as compared with conventional long stub antennas.

Although these developments are directed towards unification of antenna and electronic components and amplification of signals to compensate for low gain due to small size, they do not offer complete solution to the above problems. For example, small size, may be attained by the use of top loading; however, with such arrangements, there is little flexibility in antenna matching without utilizing transistor circuitry. It is also purported that pattern changes may be obtained by other arrangement, but no special consideration has been given to polarization; the antenna is mainly designed to respond to only one polarization. Furthermore, these developments only were aimed at small sized antenna and/or amplifying antenna systems, and the antenna structure have in general, been simply a unipole or dipole or its modification.

In the present invention, there is employed the concept of an integration of antenna with electronic components whereby the current distribution on the antenna elements is changed, so that a variety of antenna characteristics is realized.

A distinct difference between the antenna used in this invention and the others is that the antenna described in this invention consists of two or more elements which are capable of sensing both vertically and horizontally polarized waves, so that the pattern control and synthesis may be easily accomplished.

In addition to the antenna structure which can respond to two polarization, the present invention employs technique of matching within the antenna circuitry and no extra device for matching is necessary. This makes antenna efficiency very high and compactness of antenna structure can easily be attained. Furthermore, the antenna elements can be arranged in such a way that the frequency characteristics may be made either wider or narrower by taking the parameters of the incorporated circuitry into account.

Accordingly, an object of the present invention is to provide an integrated and unified antenna system with two polarization functions and with properties not obtainable with conventional antenna system.

Another object of the present invention is to provide an antenna system that permits control of the characteristics by varying the parameters of the electronic components incorporated into the antenna.

A further object of the present invention is to provide an antenna system that can be built in very small dimensions with compactness, yet have characteristics comparable with those of conventional antenna systems.

Still another object is to provide an antenna system that permits flexible design with an increased freedom of parameters due to the electronic circuitry incorporated into the antenna structure in addition to the antenna parameters.

Other objects and features of the invention will become apparent from a reading of the following description together with the drawings in which:

FIGS. 1 to 3 are schematic diagrams of a few conventional antenna systems;

FIG. 4 is a block diagram of an antenna system embodying this invention;

FIG. 5 shows the impedance characteristics of the antenna system shown in FIG. 4;

FIG. 6 and 7 are block diagrams of other embodiments of this invention;

FIGS. 8 to 11 are detailed connection diagrams of the antenna system shown in FIG. 6;

FIGS. 12 and 13 show measured characteristics of the antenna output obtained by the antenna system shown in FIG. 6;

FIG. 14 is a block diagram of still another embodiment of this invention; and

FIG. 15 is a connection diagram ofa further embodiment of this invention.

One type of hitherto commonly used antennas is the unipole antenna as shown in FIG. I, which is expressed by a vertical element 3 erected on an infinite ground plane I with infinite conductivity at the driving point 2. The inverted-L antenna is a class of modified linear antenna having a horizontal element attached to the vertical element so as to form an inverted-L with regard to the ground plane. The simplest example of such an inverted-L antenna is shown in FIG. 2, in which the horizontal element is indicated by reference numeral 4. The effective height of the inverted-L antenna may be increased as compared with the unipole antenna which has the same physical height as the vertical element of the inverted-L antenna. The inverted-L-type antenna has so far been widely used in many ways such as radio broadcasting, communication systems, in the LF, HF, and VHF bands. A feature of the inverted-L antenna is the low profile configuration with a total length of approximately a quarter wavelength, measured of both the vertical and horizontal elements. The horizontal element acts as a radiation element as well as a parallel two-wire transmission line, if an image of the element with regard to the ground plane is taken into account. The antenna characteristics such as the driving point impedance, radiation pattern, etc., depend upon both the length of the horizontal element and the vertical element. To utilize the feature effectively, the inverted-L-type antennas are usually used when the height of the antenna is required to be not too high, so that the vertical element is made short.

Though the inverted-L-type antenna is very useful because of its low profile structure with the increased effective height and its adaptability to both vertical and horizontal polarized waves, there are some disadvantages. One of these is that, in the usual antenna, the characteristics are uniquely determined by its physical dimensions, so that any change or control of the characteristics would not be expected, unless its physical dimensions are changed.

Further, reduction of the antenna dimensions will result in a considerable decrease in the gain and bandwidth. This makes use of such an antenna sometimes impractical.

lf desirable, an impedance 5 can be connected to the end of the horizontal element 4 as shown in FIG. 3, in order to make the bandwidth wide. in such an arrangement, however. the current distribution on the antenna elements cannot be freely changed.

The above-described disadvantages of the conventional antennas are eliminated by the present invention.

According to this invention, there is provided an antenna system which has characteristics that differ completely from the conventional passive antennas. By loading electronic components or more specifically, the solid-state circuitry into the antenna structure, the current distribution on said antenna system can be deliberately changed, thereby intentionally making it possible to change the characteristics of the antenna without any change in the physical dimensions.

This change in the current distribution in the antenna brings about change in the characteristics of the antenna such as the driving point impedance, operating bandwidth, gain and radiation pattern. Further, as the current distribution on the antenna can be changed by electronically controlling the active element or circuit, the characteristics are controllable accordingly. Moreover, the antenna containing an active element or circuit may include functions of the active element or circuit itself such as amplification and impedance transformation in addition to the function as an antenna. Therefore, a great deal of reduction of the size, simplification of antenna circuits and cost saving can be expected as a result of the incorporation of electronic components into the antenna. The conventional concept of an antenna is extended to a broader concept by means of loading of electronic components. The active inverted-L antenna has special features in addition to such general features of an active antenna. These are the following:

I. It makes possible changing or controlling the current distribution on the vertical or horizontal elements of the ant'enna separately, so that the radiation pattern may be easily controlled.

2. The horizontal element can be utilized as a matching element as well as a radiation element, so that its impedance can be matched to the impedance of the solid-state circuit.

3. Coupling between the horizontal and vertical elements can be utilized to enhance the change in the current distribution on either of said elements, so that the pattern control may become more accessible.

4. Electronic circuitry is so arranged in conjunction with antenna impedance that the band characteristics may be widened or narrowed.

As described above, according to this invention, an antenna has been endowed with various new functions resulted from the changeability of the current distribution; and an antenna system based on a new concept is realized from the controllability of the antenna characteristics.

Hereunder, this invention will be described in detail in connection with several embodiments thereof.

The present invention is specifically described as to transistor-loaded-inverted-L antennas having the important feature of the integration of antenna and solid-state circuitry having such function as impedance transformation and amplification.

Referring to FIG. 4 which shows an embodiment of this invention applied to an inverted L-type antenna, reference numeral 11 indicates an infinite conductive plane, that is, the ground; 12 a driving point; 13 a vertical element; 14 a horizontal element; and '15 an impedance element connected to an end of the horizontal element 14. Numeral 16 indicates a solid-state circuit including one or more transistors connected at the junction of the vertical element 13 and the horizontal element 14, one terminal of said circuit being connected to the ground 11 through a conductor 17, and numeral 18 indicates a load connected between said driving point 12 and the ground 1 1.

Now, the operation of the above-described antenna system will be explained. Of various operations which this antenna system can perform, amplification of the current of the horizontal element 14 by the transistor circuit 16 in a receiving mode will be described first. It is assumed that the value of the impedance element 15 is infinite; that is, the horizontal element 14 is openterminated.

Electric current of the horizontal element 14 is amplified through the transistor circuit 16 and the amplified current flows through the vertical element 13. Accordingly, both the said amplified current and a current induced in the vertical element 13 are supplied to the load 18.

Thus the antenna system may have higher gain than that without the transistor circuitry. This invention can be applied to small sized antenna. To have an antenna of high efficiency, impedance of the horizontal element should be matched to the input impedance of the transistor circuit. For this purpose the horizontal element can be modified to have an appropriate impedance by using a helical element instead of a rod.

In other application, since the vertical element 13 and the horizontal element 14 respectively receive the vertically and horizontally polarized waves, the variation of the current induced on the horizontal element 14 by means of transistor circuit 16 results in a relative increase of the horizontally polarized wave and thereby varies the receiving directivity of the antenna. If there exists mutual coupling between the vertical and

horizontal elements

13 and 14, a great deal of variation is expected, because the current distributions on both elements may be varied at the same time. Consequently it is made quite feasible to control the receiving pattern of the antenna system by controlling the bias voltage of the transistor circuit 16 and thereby varying the current amplification factor of the circuit.

In a case where the vertical element of the antenna is short as compared with the intended wavelength and the amount of the radiation from the horizontal element is very small, such an antenna usually shows a narrow band characteristics, as the impedance of it is low in the radiation resistance and high in its reactance (capacitive) component, thus presenting a high quality factor Q. However, such an antenna can be modified to have a fairly wide characteristics by incorporating the transistor circuit 16 into the antenna structure. The circuitry may be arranged so that the output impedance of the transistor circuit is little affected by a variation in the input impedance. Further as the current of the horizontal element flows through the vertical element after being amplified by the transistor circuit, it is possible with a small antenna of this type to attain an increase of the power at the load and a good matched condition over a wide frequency band.

FIG. 5 shows a measured impedance curve obtained with an antenna system which consists of a horizontal element of D6 XL-ZOO mm. and a vertical element of D6 XL-lOO and includes a transistor identified as 2SC 568. As shown by the curve A, the driving point admittance assume values near to the center (normalized with l/50 mho) over a broad frequency range, whereas it exhibits a locus far from the center as indicated by curve B if the transistor circuit is not provided. Thus the wide band impedance matching of the antenna to the load can be realized in the antenna incorporated with a transistor.

Though the transistor 16 is shown to be loaded at the junction point of the horizontal element 14 and the vertical element 13 in the above embodiment, it may also be placed in the middle of the horizontal element 14 or the vertical element 13. In such an antenna, though the current distribution becomes discontinuous at the point where the transistor is inserted, the antenna system operates substantially in the same manner as described above and may have particular characteristics according to intended purposes.

Further, the horizontal element 14 or the vertical element 13 is not restricted to be in the shape of a rod. The element may be in the shape of a bar or a coil as indicated by numeral 19 in FIG. 6.

By the use of a helix 19 as shown in FIG. 6 instead of a rodshaped horizontal element 14 as shown in FIG. 4, the effective length of the antenna can be increased without extending the horizontal element. Moreover, nonmetal materials such as a ferrite bar may be inserted in the coil-shaped element 19 as indicated by reference numeral 20 in FIG. 7 to make the impedance adjustable. It is important that antenna elements are provided respectively for the horizontal and vertical polarized waves. Further, it will be understood that the above-described antenna systems can be applied to the transmitters with an appropriate modification in the transistor circuit. It will be needless to say that the active element is not limited to a bipolar transistor, but it may be an MOS or junction type FET, tunnel diode or varactor diode.

In short, the above-described embodiments show antenna systems which comprise a vertical element, a horizontal element and a solid-state circuit, the last circuit being integrally incorporated into the antenna and thereby the current distribution on the system being varied so that the antenna system operates in a manner completely different from the conventional one and is made it possible to have other functions than those of the conventional passive antenna system. Since the current distribution on the antenna system can be varied to a certain extent by the selection of the type of active element, the way in which said element is connected and the position of said element in the antenna system, the freedom of designing the antenna is increased and the characteristics are improved, and functions of the antenna are increased. Moreover, the electronic control of the active element leads to an electronic control of antenna characteristics. The control of antenna characteristics is especially important when the antenna is applied to an antenna array.

If a three-terminal element such as a transistor, or a junction type or MOS type FET is used as the active element, the connection between the active element 16 and the ground 11 is attained either by two conductors l3 and 17 as shown in FIG. 8 or by three

conductors

13, 17 and 22 as shown in FIG. 9, depending on the location of the resistor 21 which serves as the DC load. In FIGS. 8 and 9, reference numeral 23 indicates a power source, 24 an AC load, and 25, 25' indicate bias resistors.

Referring to FIG. 8, the conductors l3 and 17 serve as paths for the DC current and concurrently as a parallel-two-wiretransmission line. They also serve further as radiation elements.

If the distance between the two conductors l3 and I7 is not short, the length of the connection between 16 and 17 becomes appreciable and this portion acts as a horizontal element with a radiation effect, so that the current distribution on 17 and 13 will be changed, thereby changing the antenna characteristics such as radiation pattern, gain, impedance. Such an antenna is difficult to design because it introduces additional complexity to the analysis as the system can no longer be treated as simple transmission line.

On the other hand, if the impedance of the AC load 24 is 50 ohms, as it is in the usual high-frequency circuit, the distance between the two conductors l3 and I7 is required to be very small in order to make the characteristic impedance of the two-wire transmission line 50 ohms. If said distance is not sufficiently small, the characteristic impedance becomes higher than 50 ohms, so that the impedance at the junction point of the transmission line would not easily be matched to the load, thereby bringing about a power loss at thejunction point.

The above-mentioned difficulty is overcome by the arrangement shown in FIG. or in FIG. 11. Namely, the conductors l3 and 17in FIG. 8, or the conductors l3, l7 and 22 in FIG. 9, which constitute the vertical portion of the antenna system between the active element and the ground, are replaced by a coaxial cable 26 in FIG. 10 or 11 respectively.

As the active element 16 is connected to the ground 11 through a single coaxial cable 26 in the above-described arrangement, the undesired horizontal element of the antenna in this portion is eliminated, thus making the design of the antenna easy and the structure simple. Further, the characteristic impedance of 50 ohms is obtained by appropriately selecting the ratio of diameters of the inner and outer conductors of the coaxial cable 26.

Back to FIG. 4, the current distribution on the horizontal portion is affected by the electromagnetic coupling between the current flowing through the vertical element 13 and that through the horizontal element 14. As the current in the vertical element 13 has been amplified through the active element 16, it is usually larger than the current which would flow through the vertical element in which the solid state circuit is not provided. Therefore, its influence on the horizontal element 14 becomes greater accordingly. Also, the amount of electromagnetic coupling depends on the physical dimensions of the horizontal and vertical elements l4, 13 as well as the shape of the horizontal and vertical portions at the junction point.

In order to minimize the influence due to the junction of two elements upon the electromagnetic field, it is desirable to minimize the size of the electronic component and the associated circuits.

This minimization of the size of the circuitry can be attained by the use ofan "integrated circuit."

FIGS. 12 and 13 show examples of the measured results by using such an antenna, FIG. 12 being the output characteristics in relation to number of turns of the helix and FIG. 13 showing the relation between the pitch of the helix and the length of wire that gives maximum output. In FIG. l3, three curves represent three helices which are wound on cores of different materials and different diameters, a being wound on a polypropylene rod of 20 mm. in diameter, b on a foam styrol rod of the same diameter and c on a vinyl chloride pipe of 26 mm. in outer diameter.

Though the output power of the antenna depends on the diameter, length and pitch of the helix, the length of the wire of the helix, etc., the most important factor is the length of the wire. If the length of the wire is selected to be nearly one half of the wavelength, maximum output can be obtained most easily. This fact can conveniently be utilized in the design of an antenna, as the dimension of the helix which gives maximum output can easily be determined from the above relation, with the exception of helices of extremely small pitch.

An example of an actually built small size active inverted-L antenna used in the 40 MHz band is shown in FIG. 15 in which all the components except receiver 11 are the same as those shown in FIG. 11. It consists of a helical element and coaxial line as the horizontal and the vertical part of antenna, respectively, and a transistor circuit as the electronic part. The dimensions of the helical element are 26 mm. in diameter and 250 mm. in length and the number of turns is 45. The vertical element consists of a double coaxial structure with outer diameter of4 mm. and length of 150 mm. A transistor 2SC563 is used for the electronic circuitry. The base terminal of the transistor is connected to the one end of the helical element and the output taken out of the collector terminal of the transistor is led to the load through the vertical element. The load is the receiver. In this antenna system the ground plane is not used but is substituted by the receiver chassis. It does not substantially change the properties of the antenna function. This type of antenna can respond to both the vertically and horizontally polarized waves, although the dimensions of the antenna are very small as compared with the wavelength (4OMHz). The output of this active antenna for the vertical polarization is approximately 10 db. greater than that obtained by the cm. whip antenna which is normally attached to the receiver. Although the bandwidth of the antenna system can be widened by incorporating the transistor circuit, as shown in FIG. 5, it would not be expected to be amply wide.

This type of active antenna can be built within the cabinet of the receiver. As a result, it becomes very handy and safe from physical damage which will be unavoidable if the antenna is built outside the cabinet. The ratio of gain for the vertical polarization to that for thehorizontal polarization can be changed by changing the length of the vertical part of the antenna. This fact can be utilized for the pattern control.

In the above-described embodiments, use of only a single electronic circuit is shown. However, an antenna system utilizing two active circuits can be constituted. An antenna system shown in FIG. 14 comprises, besides the components shown in FIG. 4, a second vertical element 27 and a second active element 28. Electric current induced in the second vertical ele ment 27 is amplified by the second active element 28 and the impedances of both active elements are matched. Thus, the current distribution on the horizontal element 14 may be changed and the input impedance of the active circuit 16 may be varied at the same time.

In principle, the antenna system is built on the ground plane 11; however, it is not always necessary and in some cases the antenna system may be modified to have a structure without a ground plane, as shown in FIG. 15.

Though the present invention has been described heretofore with regard to several embodiments, the gist of the invention will be clear from the following claims.

We claim:

I. An integrated antenna system comprising: a ground plane formed of an electrically conductive plate having infinite conductivity, a vertical element substantially perpendicular to said ground plane and having vertical polarization, a hclically shaped element having horizontal polarization, both said elements forming an inverted L antenna, and a solid state circuit located at the junction of said elements, said circuit including at least one semiconductor element which has at least one function of impedance transformation and amplification, whereby the current distribution on said antenna can be changed by variably changing the circuit constants of the solid state circuit.

2. The antenna system according to claim 1, in which said ground plane is formed of a conductive plate on which the system is carrier.

3. The antenna system according to claim I, in which said ground plane is a metal box on which the system is carried.

4. The antenna system according to claim 3, in which said metal box is the chassis of a radio equipment.

5. The antenna system according to claim 1, in which said vertical element is in the form ofa helix.

6. The antenna system according to claim 1, in which said vertical element is linear.

7. The antenna system according to claim 1, in which at least one of said horizontal and vertical elements includes a plurality of elements.

8. The antenna system according to claim 1, which comprises a second vertical element at the opposite side of said helically shaped polarization element to said junction, and a second solid-state circuit located at the junction of said second vertical element and said horizontal element.

9. The antenna system according to claim 1, in which the length of the wire of the helix is approximately one half of the wavelength of an intended signal.

10. The antenna system according to claim 1, in which said helical element has means including a nonmetal material for varying the impedance of the helix.

11. An inverted-L-type integrated antenna system comprising: a ground plane formed of an electrically conductive plate, a helical element substantially perpendicular to saidground plane and having a vertical polarization, a linearly shaped element having horizontal polarization, both said elements forming an inverted-L antenna structure, and a transistor circuit located at the junction ofsaid elements and having a transistor serving as an active element whereby the current distribution on said antenna can be changed by remotely varying the biasing of the circuit.

* k i i

Claims

1. An inTegrated antenna system comprising: a ground plane formed of an electrically conductive plate having infinite conductivity, a vertical element substantially perpendicular to said ground plane and having vertical polarization, a helically shaped element having horizontal polarization, both said elements forming an inverted L antenna, and a solid state circuit located at the junction of said elements, said circuit including at least one semiconductor element which has at least one function of impedance transformation and amplification, whereby the current distribution on said antenna can be changed by variably changing the circuit constants of the solid state circuit.

2. The antenna system according to claim 1, in which said ground plane is formed of a conductive plate on which the system is carried

3. The antenna system according to claim 1, in which said ground plane is a metal box on which the system is carried.

5. The antenna system according to claim 1, in which said vertical element is in the form of a helix.

11. An inverted-L-type integrated antenna system comprising: a ground plane formed of an electrically conductive plate, a helical element substantially perpendicular to said ground plane and having a vertical polarization, a linearly shaped element having horizontal polarization, both said elements forming an inverted-L antenna structure, and a transistor circuit located at the junction of said elements and having a transistor serving as an active element whereby the current distribution on said antenna can be changed by remotely varying the biasing of the circuit.