MICROSTRIP ANTENNA WITH CONTROL OF THE DIRECTION OF THE AXIS OF MAXIMUM RADIATION

Abstract: The microstrip antenna consists of a radiating metallic portion, laid on a first dielectric substratum (S1), under which a metallic mass plane (GP) is present, in which two non resonant coupling slots (SA and SB) are constructed, in correspondence with MP. Below the metallic plane (MP) there is a second dielectric substratum (S2) under which two metallic feeder lines (LA and LB) are constructed, in correspondence with the relevant slots. The control of the direction of the axis of maximum radiation is obtained either by feeding the two metallic lines with voltages of different phases or in a variant feeding only one line and closing in short circuit the other line in variable position along it.

Description: " MICROSTRIP ANTENNA WITH CONTROL OF THE DIRECTION OF THE AXIS OF MAXIMUM RADIATION " Field of the Invention The present invention relates to the field of microstrip antennas, and more precisely to a microstrip antenna with control of the direction of the axis of maximum radiation. The control of the direction of the axis of maximum radiation in microstrip aerials is becoming an increasingly important characteristic in point-multipoint radio transmission systems and in particular in mobile systems. The construction in microstrip makes all the transmission-receiving systems very attractive in terms of efficiency, costs reduction, bulk reduction. Background Art Microstrip aerials like those described in the article: "Analysis of an infinite phased-array of aperture-coupled microstrip patches", by D.M. Pozar, IEEE Transactions on Antennas, Vol. 37, No. 4, April 1989, are already known in technology. These known antennas are essentially composed of a radiating circuit constructed by means of an elementary metallic portion, with different types of geometrical shapes (e.g. rectangular, square, round, elliptic etc.), laid on a dielectric support under which metallic plane of mass solidly connected to this dielectric support is situated. This elementary metallic portion is coupled to a feed line in various ways, for example: - direct connection of the feeder line to the elementary metallic portion; coupling to a microstrip line situated below this dielectric support, through an aperture made in this mass plane in correspondence with this radiating metallic portion. These elementary radiating circuits may be multiplied on a support of larger dimensions to obtain a socalled "phased-array" structure in order to control the direction of maximum radiation thus obtained, through a suitable feed in amplitude and phase of the single elements. Object of the Invention The primary objective of this invention is to produce a new improved layout of this microstrip antenna which has the characteristic of varying and finely controlling the direction of maximum radiation also in the configuration of microstrip antenna with single elementary radiating circuit, unlike the known structure where the direction of maximum radiation is fixed and normal at the plane of the antenna. Summary of the Invention To achieve these objects, this invention is addressed to a microstrip antenna with control of the direction of the axis of maximum radiation, which in all its variants provides two coupling slots in the metallic plane, substantially as illustrated in claims 1 to 5. The microstrip antenna object of the invention, in all its variants, has the principle advantage of permitting an easy control of the direction of maximum radiation, obtainable either during construction or installation through an easy calibration operation or during use in dynamic mode. A further advantage consists in the simple inexpensive construction. Another advantage consists in the possibility of constructing antennas in thin film, or integrated in active microwave circuits, on different substrata (e.g. GaAs, silicium, insulating material of printed circuits etc.). The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. Brief description of the drawings The invention, together with further objects and advantages thereof, may be understood with reference to the following description, taken in conjuction with the accompanying drawings, and in which: in figure 1 a constructive layout of the antenna object of the invention is indicated in plan (Fig. 1a. viewed from the feeder lines side) and in section (figlb.); - in figures 2a. and 2b. the arrangements of the electric field vectors (E1 and E2 respectively) in the equivalent radiating apertures (AR1 and AR2 respectively) of the antenna are indicated; in figure 3 a constructive particular of the second variant is indicated. Detailed description of preferred embodiments In fig. 1 , MP indicates an elementary radiating metallic portion of the microstrip antenna, laid on a first dielectric substratum S1 , below which a metallic mass plane GP of larger dimensions than the metallic portion is present. On the basis of a fundamental characteristic of this invention, two substantially parallel non resonant coupling slots SA, SB are constructed in correspondence with MP. Below the metallic plane GP there is a second dielectric substratum S2 under which two metallic feeder lines LA, LB are constructed, in correspondence with the relevant slots, respectively SA, SB, and substantially perpendicular to them. As already known in itself, the metallic portion MP of the microstrip antenna radiates through the two equivalent apertures (between MP and GP) indicated in fig. 1 with AR1 and AR2, independently from the method of coupling to the feeder line or lines. In the case of this invention, some supply voltages forming the antenna signal are carried to the feeder lines LA, LB which produce some electric fields in the respective equivalent apertures AR1 , AR2. Through the voltage application to the line LA, an electric field E1a is induced in the equivalent aperture AR1, and also an electric field E2a in the equivalent aperture AR2. The two electric fields are linked to a proportionality constant α12, indicated as coupling coefficient between the equivalent apertures AR1 and AR2. Similarly, applying a voltage to the line LB, an electric field E2b is induced in the equivalent aperture AR2, and also an electric field E1 b in the equivalent aperture AR1. Also in this case the two fields are linked to a proportionality constant α21. Due to the reciprocity effects α21 = α12 = α, definable as coupling coefficient between the two radiating apertures. For the principle of superposition of the effects we have: E1 = E1a = α12 E2b = E1a + α E2b E2 = α21 E1a + E2b = α E1a + E2b, where E1 and E2 are the total electric fields respectively in the two radiating apertures AR1. AR2. With reference to fig. 2, if φ is the phase difference between the two supply voltages, the phase difference between the two electric fields E1 and E2 is: γ = γ2 - γ1 , where γ1 is the phase angle between E1 and E1a and γ2 is the phase angle between E2 and E1a. It may be geometrically demonstrated that: tgγl = α sin φ / (1 + α cos φ) tgγ2 = sin φ / (α + cos φ) With reference to the known theory of the array antennas, the direction of maximum radiation θ of the total structure of fig. 1 is given by: θ = arccos (γ / βd) where β is the phase constant in the vacuum; d is the distance between the two radiating apertures AR1, AR2, coinciding with the non radiating side of MOP. Notoriously d s λ 2. Putting φ = 90°, it was experimentally obtained that θ = 77°, and therefore α s 0.605, with a distance h/λ between the coupling slots Sa, SB of approximately 0.25, where λ is the wave length of the antenna signal. Therefore, varying the phase displacement between the two supply voltages to the lines LA and LB, it is possible to deviate the direction of maximum radiation θ of the totai structure, and therefore the direction of the main lobe of the radiation diagram of the antenna. Therefore, while a particular embodiment of the present invention has been shown and described, it should be understood that the present invention is not limited thereto since other embodiments may be made by those skilled in the art without departing from the scope thereof. In a different embodiment, with reference to figures 1 and 4, the structure is fed through only one of the feeder lines, for example LA, while the other, for example LB, is not fed, and is composed of a line section of suitable length, terminated in short circuit at one of its ends through electrical connection with the mass plane GP, constructed in manner technologically known in itself. Moreover, in suitable intermediate positions along LB, other connections with the mass plane GP are made, always in technologically known manner, through controlled electronic circuit breakers, like PIN or Varicap diodes, which behave like terminations of controlled short circuit. The latter make it possible, through their differentiated activation, to connect this line LB with mass at various distances from the slot SB, thus realizing, as known in itself from the theory of the transmission lines, different reactive closures of the electric field existing in the slot, with consequent variation of its phase and therefore of the direction θ of maximum radiation of the total structure which therefore depends on the distance of the reactive closure. In this way, when there is a variation of the termination of the line LB, there may be a variation of the direction of maximum radiation θ of the total structure, and therefore the direction of the main lobe of the radiation diagram of the antenna, since the phase displacement of the wave reflected by the line LB may vary. In fact, if the line LA is fed with a voltage, an electric field E1a is consequently excited in the equivalent aperture AR1 and an electric field E2a in the equivalent SUBSTΓTUTE SHEET (RULE 26) aperture AR2, as in the previous case. To the coupling slot SB is however connected a transmission line formed by the line LB and the presence of the electric field E2a therefore excites a wave of voltage in the same line. The wave, spreading, meets the open end of the line; a reflected wave of voltage is thus created which, returning towards the coupling slot, excites another electric field component in the equivalent radiating aperture, delayed by a certain angle proportional to the path of the feeder line. A further field component is also generated with a phase displacement due to the termination in short circuit. These two components of reflected electric field, spreading, reach the equivalent radiating aperture AR1. Therefore, similarly to the previous case, it is obtained that: tgγl = α 2 (sin φ1 + sin φ2) / [1 + 2 (cos φ1 + cos φ2)] tgγ2 = (sin φ1 + sin φ2) / (1 + cos φ1 + cos φ2) Therefore the electric field in the slot SB has a different phase from that of the electric field in the slot SA. Consequently, the electric field in the equivalent aperture AR" has a phase γ2 different from γ1 of the field in the aperture AR1, and a phase displacement γ = γ2 - γ1 is therefore generated, which, as in the previous case, generates a deviation of the main lobe, for which also in this case the relation θ = arccos (γ / βd) is valid. The antenna obtained in each of the variants described above may form the basic element of a phased-array structure, i.e. a structure multiplexed on a support of larger dimensions, to obtain even complex radiation diagrams in which the deviations of the single lobes may be separately controlled, through a suitable feed in amplitude and phase of the single elements. For example, a structure of two elements, like those of fig. 1 , flanked, forming an wide lobe, may be obtained from the combination of the single lobes deviated in opposite directions. Therefore, while some embodiments of the present invention have been shown and described, it should be understood that the present invention is not limited thereto since other embodiments may be made by those skilled in the art. It is thus contemplated that the present invention encompasses any and all such embodiments covered by the following claims. SUBSTΓΓUTE SHEET (RULE 26)

Claims: CLAIMS 1. Microstrip antenna with control of the direction of the axis of maximum radiation, characterized by the fact that it includes the following layers in succession: an elementary radiating metallic portion (MP); - a first dielectric substratum (S1); a metallic ground plane (GP), placed in correspondence with said metallic portion (MP), and in which are constructed a first (SA) and a second (SB) non resonant coupling slot; a second dielectric substratum (S2); - a first (LA) and a second (LB) metallic line in correspondence respectively with said first (SA) and second (SB) slot, in substantially perpendicular position with respect to the respective slots, to feed the antenna and perform said control of the direction of the axis of maximum radiation. 2. Microstrip antenna according to claim 1 , characterized in that said first (LA) and second (LB) metallic lines are feeder lines, to which respective supply voltages forming the antenna signal are carried, and in that varying the phase displacement of said supply voltages a variation of the direction of the axis of maximum radiation is obtained. 3. Microstrip antenna according to claim 1 , characterized by the fact that one (LA or LB) of said first and second metallic lines is a feeder line to which a supply voltage forming the antenna signal is carried and that the other (LB or LA) of said first and second metallic lines forms a line section of predeterminate length, terminated in short circuit by means of electrical connection with said mass plane (GP), in variable position along it, in such a way that, when there is a variation of the position of short circuit, there is a variation of the electrical length of the line and a corresponding variation of the direction of the axis of maximum radiation of the antenna is obtained. 4. Microstrip antenna according to claim 3, characterized by the fact that said short circuit in variable position along said line section of predeterminate length is obtained through termination in short circuit at one of its ends by means of electrical connection with said mass plane (GP) and also, in suitable intermediate positions of its length, through other connections with said mass plane (GP) through controlled electronic circuit breakers, such as PIN or Varicap diodes, which behave like terminations of controlled short circuit. 5. Microstrip antenna array with control of the direction of the axis of maximum radiation, characterized by the fact that on a support of larger dimensions are multiplexed basic elements formed by microstrip antennas according to any of the previous claims, in which the variations of the direction of the axis of maximum radiation of each of the basic elements may be separately controlled, through a suitable feed in amplitude and phase, to obtain radiation diagrams of the array variables.

Inventors: SAINI ALDA, STEFANI MAURO, SAINI, ALDA, STEFANI, MAURO
Applicants: ITALTEL SPA, SAINI ALDA, STEFANI MAURO, ITALTEL S.P.A., SAINI, ALDA, STEFANI, MAURO
Application year: 1997
Main classification: H01Q3
IPC codes: H01Q3, H01Q9, H01Q21, H01Q23