The present invention relates to an improvement in microwave miltigate junctions or circulators especially for radar applications.
More specifically, the present invention has as its object to provide multigate junctions in which the adaptation between the TEM (Transverse Electro Magnetic Wave) modes of propagation along the transmission lines and the peripheral modes are accomplished by means of magnetic tapering.
As is well known in the prior practice in the field of application of microwave devices, and even more especially in that of the radar applications, there have been proposed multigate junction systems in which the width of the useful band, however, was not sufficient, in many cases to allow satisfactory service. In order to eliminate or substantially to reduce that drawback, there have been suggested and there have been described in the literature, as for example U.S. Pat. No. 3,555,459, systems in which the widening of the useful band is obtained through the elimination of the undesired modes by dissipation of the energy. Such a solution, however, means an appreciable loss of useful signal. Another solution of the problem of attempting to improve the efficiency of the system, is based on the use of very gradual "taperings" in the adaption geometry between the transmission lines and the peripheral mode structure. In this case, also, the solution is not free from drawbacks, because it deprives the component of those miniaturization characteristics which, on the contrary, it must have.
The principal object of the present invention is that of providing a multigate junction, which possesses a satisfactory width of useful band.
Another object of the present invention is that of providing a component in which the losses of energy are appreciably reduced.
Still another object of the present invention is that of providing a component the dimensions of which are appreciably reduced.
The described embodiment of the present invention makes possible the simultaneous achieving of the stated objects, eliminating, in the meanwhile, the disadvantages of the prior art techniques, which have been mentioned. Recently, the use of peripheral waves, or peripheral modes, in the field of ferrite devices operating at microwave frequency, has excited much interest. These are discussed for example in: Hines M.E., "A New microstrip Isolater and Its Application to Distribution Diode Amplification," IEEE G-NIT 1970. International Microwave Symposium, Newport Beach (Cal.), Digest of papers, pp. 304-307; Hines M.E., "Ferrite Phase Shifters and Multiport Circulators in Microstrip and Strip Line," IEEE G-MTT 1971, International Microwave Symposium, Washington D.C., Digest of papers, pp. 108-109; De Santis P., Pucci F., "Novel Type of M.I.C. Symmetrical 3-Port Circulator" Electronics Letters Vol. 8, No. 1, pp. 12-13, January, 1972; De Santis P., Pucci F., "Experiments on the Optimization of a Novel M.I.C. Symmetrical Three Port Circulator," IEEE G-MTT 1972, International Microwave Symposium, Chicago, Illinois, Digest of papers, pp. 238-240.
In order to better illustrate the significance of the present invention, there will briefly be summarized the characteristics of the functioning of the peripheral wave devices. A peripheral wave is a wave which propagates itself along the edge of the radio-frequency conductor in a microstrip on a ferrite member magnetized perpendicularly to the plane of the mass. This is a unidirectional wave in that for a given orientation of the magnetic field of polarization, it has a given manner or direction of propagation. By reversing the orientation of the magnetic field of polarization, there is also reversed the line or direction of propagation. This property of being unidirectional may be taken advantage of to build non-reciprocal multigate junctions or circulators. In a typical structure, the electromagnetic energy is introduced into one gate and withdrawn from the successive gates through lines of transmission (for example isotropic lines in microstrip, in line with strip or in coaxial conductor the characteristic impedance of which must be suited to the impedance of the peripheral wave circuit. This adaptation of impedance generally is obtained by means of tapered sections in the microstrip. In other words it can be said that the TEM waves or modes which propagate themselves along the transmission lines are converted into peripheral waves or modes through the use of tapered arms in the microstrip.
It is the specific object of the present invention to provide a peripheral wave or mode excited multigate junction having a tapered arm conductive structure on a magnetized ferrite, magnetized perpendicularly to the plane of its mass, characterized by the fact that it presents, through the adaptation between the TEM wave or mode and said peripheral wave or mode, a distribution of the effective permeability of the ferrite, spatially non-uniform in correspondence with the tapering zones or arms which are adapted for connection with the transmission lines. Henceforth, such spatial non-uniform distribution of the magnetic permeability will be indicated by the expression "magnetic tapering." Said magnetic tapering is obtained, according to the present invention, through the use of magnetic fields, of spatially non-uniform polarization. Said magnetic fields of polarization in their turn are obtained by the use of permanent magnets and possibly with the addition of a ferro-magnetic element inserted into the magnetic circuit.