GB2131627A - A magnetically tuned resonant circuit - Google Patents

Abstract

A magnetically tuned resonant circuit 209 couples r.f. energy between input and output coupling circuits 210, 120 thereof in a first mode of operation and isolates such energy between such coupling circuits in a second mode. Microstrip transmission lines form the coupling circuits 210, 120, each having a pair of planar spaced strip conductor portions adjacent a resonant body 238 of ferrimagnetic material to provide current paths around the body 238. In the presence of an external static magnetic field HDC, a pulse of current is fed around the current path 214c', 214c'' provided by the input coupling circuit microstrip line and provides a pulse magnetic field HDCp in the region of the resonant body 238 which either aids or opposes the external static magnetic field HDC and in response thereto shifts a resonant frequency omega o of the circuit 209 in accordance with the equation omega o' = gamma (HDC +/- HDCp) where gamma is the gyromagnetic ratio of the body 238. Alternatively, a coil 326 supported on a dielectric substrate 321 provides the current path, the coil 326 being disposed adjacent the resonant body. A pulse of current fed to the coil 326 provides a pulse magnetic field HDCp, and the resonant frequency is shifted in accordance with the equation omega o = gamma (HDC +/- HDCp). <IMAGE>

Description

SPECIFICATION A magnetically tuned resonant circuit This invention relatesgenerallytotunableradio frequency resonant circuits and more particularly to self-protected magneticallytunable radio frequency resonant circuits.

Asis known in the art, tunable radio frequency (r.f.) resonant circuits are often used in r.f. receivers to provide filtering, for example, of received r.f. energy.

A partic-ularclass of tunable r.f. filters are those which can be magnetically tuned of which resonant circuits comprising a body of a ferrimagnetic material disposed between a pair of coupling circuits are the most common.An.externald.c. magnetisfield isapplied to the body oftheferrimagnetic material and energy is fed to an input-oneofsuchcoupling circuits.A portion of such energy 5 then coupled to the resonator body, if such portion of energy has a radian frequency (hereinafter frequency) (o;} which satisfies a resonance condition given as Co = coo, where Cow is a resonant frequency ofthe resonator, given as (oO = yHDc where y is a term referred to as the gyromagnetic ratio, and HDe is the magnitude of the applied D. C.

magnetic field. In many priorart magneticallytunable resonators, the external magnetic field is supplied by a magnetic pole piece and a flux return yoke. The magneticallytuned resonant circuit is generally positioned in a gap between the flux return yoke and the magnetic pole piece.

As is also known in the art, it is often desirable to provide protection to the filterand the receiver, during transmission of energy such as in a radar system. This is particularly important when the receiver and filter are arranged such thattransmitted r.f. energy from a high powertransmitter leaks into a signal path ofthe receiver. Leakage ofthe high level energy into the receiver path either can damage components of the receiver or saturate the resonant body in the r.f. filter such that it is rendered temporarily inoperative.Thus, if during transmission thefilteristuned to the frequency ofsuchtransmitted energy, then the possibility existswhereinthe filterwill become saturated due to the high input power level. the filter is saturated, a relatively long period of time may be requiredforthe saturation effects to dissipate in order to make the filter and hence the receiver operative. During this time, the filter and hence the receiver cannot respond to an echo signal which would normally be received bythe receiverand hense informationcontained in the echo signal will not be processed by the receiver. Several approaches have been used in the prior artto overcome this problem to provide protection to the resonant body in such filters and to the receiver.One approach is to include an r.f.

Iimiterbefore the magnetically tuned resonant circuit to limit the r.f. signal which can passtherethrough.

Asidefrom the cost of adding an additional component, this approach is also undesirable because the limiter has a finite insertion loss which reduces the sensitivity ofthe receiver to the echo signal. A second approach isto provide an electromagnettypically a wire coiled around a portion of the flux return yoke described above. The resonant frequency ofthe magneticallytuned resonator, is shifted by passing a current th rough the electromagnetic coil which creates a field either adding or opposing the d.c.

magnetic field associated with magnetic pole piece, changing the resonant frequency of the filter in accordance with too = V (HDe + HDcP). One problem with the structure is that the electromagnetic coil due to its size, distance from the resonant body, high inductance and tight coupling to the core material has a frequency response unsuitableforrapidlychanging the resonant frequency of a magnetically tuned resonator.

As is also known in the art, the resonance frequency of a YIG sphere is a function of temperature variations for most crystallographic orientations oftheYlG spherewith respect to the external magneticfield HDC.

However, along selective well-known orientations of the crystallographic axis of the sphere relative to the DC magneticfield, it is also well-known that the resonant frequency is substantially invariant with temperature variations. Generally, in the prior art, a partially orientated YIG sphere is disposed between the coupling loops and, in the presence of such loops, an iterative process is used where the resonant frequency ofthe filter is measured with the filter operating over the temperature range, and the sphere's orientation is established when the variation in resonantfrequency is a minimum overthetemperature range. This multi-step process is a time consuming process since two alignment steps are required.It has thus been a goal of VIG filter design to provide a YIG filter coupling structure having easy access to disposed therein a completely orientated YIG sphere having a proper orientation to minimize temperature variations in the resonant frequency ofthe output signal overthe operating range oftemperatures.

In accordance with the present invention, a magneticallytuned resonant circuit includes a pair of planar spaced coupling circuits for selectively coupling r.f.

energy fed to a first one thereof, to a second one thereof, through a resonant body disposed therebe- tween. Each coupling circuit includes a pair of spaced conductors. The spaced conductors are arranged to provide a current path for creating a magnetic field around the resonant body. In a first mode of operation, inthe presenceof a suitable applied magneticfield HDC, r.f. energy having a frequency to; fed to the input coupling circuit is coupled to the output coupling circuit in accordance with the relationship Co = coO where coO = YHDc andy is a term referred to as the "gyromagnetic ratio".In a second mode of operation, a pulse ofcurrent is fed to the current path, including the spaced conductors,to produceacurrentflowand in response thereto a pulsed D.C. magneticfield HDCp around the resonant body. Such field HDCP either aids or opposes the d.c. field HDC, and in response thereto shifts the resonant frequency Co0, of the circuit in accordance with the relation COO = V (HDe + HDcp). The resonant frequency w, is sufficiently changed such that Co j cho0. With such an arrangement, by configuring a coupling circuit to form a pulsed field coil adjacentthe resonant body, a pulsed D.C. magnetic field may be generated proximate the resonant body in response to a current flowtherethrough.Thus, the resonant frequency ofthe circuit may be rapidly shifted, thereby provided protection to the magneticallytuned resonant circuit from high power satura- tion effects without loss of information due to relative slow switching ofthe magnetic field, as in the prior art.

In accordance with an additional aspectofthe present invention, a magnetically tuned resonant circuit includes a separate pulse field coil integrally formed with the magneticallytuned resonant circuit for changing a D.C. magnetic field provided bythe circuit, in accordance with a suitable current pulse fed thereto. With such an arrangement, the integrally formedcoilwhen activated by the suitable current pulse provides self-protection for resonator circuits from a high power pulse. This coil by being integrally formed with the resonant circuit enables fast, efficient switching of the d.c. magnetic field and can be used with various coupling structures.

In accordance with a further aspect of the present invention, a magnetically tuned resonant circuit includes a pair of coupling circuits, formed on a surface of a substrate with portions thereof orthogonally crossing each other and dielectrically spaced from each other at the orthogonal crossing point. A ground plane conductor is formed on an opposite surface of such substrate. Aportion of such ground plane is removed exposing a portion of the underlying substrate and providing a void in the ground plane, such void being aligned with such crossing conductors. A coil supported on adielectric is disposed adjacent such coupling circuit and an aperture is provided through the center of the dielectric which supports the coil.A resonant body is concentrically disposed through the aperture onto the exposed portion of the substrate provided bythevoid intheground plane.

With such an arrangement, a relatively fast, efficiently switched, large pulsed magnetic field is provided.

Further, such a structure also provides easy access to disposed therein an orientated resonant body.

The foregoing features of the invention, as well as the invention itself, may be more fully understood from the following detailed description read together with the accompanying drawings, in which: FIG. 1 isan exploded isometricviewofa magneticallytuned resonant circuit; FIG. 2 is an isometric view of the magnetically tuned resonant circuit shown in FIG. 1; FIG. 3 is a cross-sectional view of FIG. 2taken along lines 3-3; FIG. 4is a diagrammatical view depicting unwanted coupling of magnetic flux lines between input and output transmission lines of the magnetically tuned resonant circuit of FIG. 1; FIGS. 5-7 are isometric views of alternate embodiments ofthe invention with parts common to FIGS. 1-3 shown in phantom; FIG. 8 is an isometric view of the magnetically tuned resonant circuit of FIG. 2 disposed in a housing;; FIG. 9 is an exploded isometrisviewof afour channel dual-stage filter; FIG. 10 is an isometric view of the magnetically tuned resonant circuit shown in FIG. 9; FIG. 11 is an exploded isometric view of a magneti callytuned resonant circuit having coupling circuits for selectively shaping an r.f. magnetic field in the region adjacent a resonant body; FIG. 12 is an isometric view ofthe magnetically tuned resonant circuit shown in FIG. 11; FIG. 13 is a cross-sectional view of FIG. 12 taken along lines 13-13 wherein the circuit is disposed between a magnetic pole piece and flux return yoke;; FIG. l4isadiagrammaticalviewofFlG. 13 graphicallyshowingthe relationship ofthe r.f. magne ticfields and the resonant body; FIG. 15 is a block diag ram of a typical system application for a magnericallytuned resonant body, such as thatshowrrin FIG. FIG.13; FIG. 16 is a diagrammatica Iview of a su rfaceof the magnetically tuned resonant circuit, as shown in FIG.

13, detailing certain geometric relationships which are useful in understanding eertain features of the invention; FIGS.17-17A are a series ofgraphs useful in understanding certain features oilthe invention; FIG. 18 is an exploded isometric view of a dual-stage magneticallytuned resonant circuit having coupling circuits for selectively shaping the r.f. magneticfield in the region adjacent a resonant body; FIG. 19 isan isometricviewofthe dual-stage magnetically tuned resonant circuit shown in FIG. 18; FIG. 20 isa cross-sectional view of FIG. 19 taken along lines 20-20 wherein the circuit is disposed between a magnetic pole piece and a flux return yoke;; FIG. 21 is a plan view ofthe single stage magneticallytuned resonant circuit disposed in a housing; FIG. 22 is an exploded isometric view of a magneti cally tuned resonant circuit having a pulse field coil; FIG. 23 is an isometric view of the magnetically tuned resonant circuit having a pulse field coil shown in FIG. 22; FIG. 23A is a cross-sectional vieEwtaken along line 23A-23A of FIG. 23 of a portion ofthe magnetically tuned resonant circuit; FIG. 24 is a cross-sectional view of FIG. 23 taken along lines 24-24 wherein the circuit is disposed between a magnetic pole piece and a flux return yoke;; FIG. 25 is a diagrammatic view of FIG. 24 graphically showing the relationship ofthe r.f. magnetic field, the D.C. magnetic fields and the resonant body; FIG. 26 is a block diagram of atypical application for a magnetically tuned resonantcireusshaving a pulse field coil, such asthatshown in Fl. 23; FIG. 27 is an exploded isometric-view of a dual-stage magnetically tuned resonant circuit having a pulse field coil in accordance with the invention; FIG. 28 is an isometric view of the dual-stage magnetically tuned resonant circuit as shown in FIG.

27; FIG. 29 is a crnss-sectionalview of FIG. 28taken along lines 29-29 whereinthe circuit is disposed between a magneb;; pole piece and a flux return yoke; FIG. 30 isa planviewofthe magneticallytuned resonant circuit shown in FIG. 23 disposed in a housing; FiGS.3f-33 are a series of plan views of alternate configurations of pulse field current paths provided in accordance with the invention; FIG. 34 is an exploded isometric view of an alternate embodiment of a magnetically tuned resonant ci rcuit having a pulse field coil; FIG. 35 is an isometric view of the embodiment shown in FIG. 34;; FIG. 36 is a cross-sectional view of FIG. 35 taken along lines 36-36 wherein the circuit is disposed between the magnetic pole piece and flux return yoke; FIG. 37 is an exploded plan view of a coil used in the alternate embodiment of the invention shown in FIG.

35; FIG. 38 is a schematic diagram of a drive circuit used to produce a pulse of current to drive the pulse field coil; FIG. 39 is a graphic depicting typical timing relationship used in a typical application ofthe invention such as the system shown in FIG. 26; FIG. 40 is an exploded isometric view of an alternate embodimentofa dual-stage magnetically tuned resonant circuit with a pulsed field coil; FIG.41 is an isometricviewoftheembodiment shown in FIG. 40; FIG. 42 is a cross-sectional view of FIG. 41 taken along lines 42-42; FIG. 43 is an isometric view an apparatus for orientating YIG spheres; FIG. 44 is a plan view of a platform portion of the apparatus shown in FIG. 43;; and FIG. 45 is a cross-sectional viewtaken along lines 45-45 ofthe platform shown in FIG. 44.

Referring nowto FIGS. 1-3, a dual-stage magneticallytuned resonantcircuit9 here a bandpassfilter fabricated in accordance with the teachings of the present invention is shown.

Referring firstto FIG. 1, the magneticallytuned resonant circuit 9 in the presence of a magneticfield HDe generated disposing the circuit between a magnetic pole piece 60a (FIG. 3) and flux return yoke 60b (FIG.

3) is shown to include an input'output coplanar waveguide (CPW) transmission line section 30 having inputCPWtransmission line33a and outputCPW transmission line 30bformed on a common substrate 32, and an interstage CPWtransmission line section 10 having an interstage CPWtransmission line 18 formed on a substrate 12. Input transmission line33a couples resonant energy to outputtransmission line 33b through a pairof spheres 26a, 26b comprised of a ferrimagnetic material and the interstagetransmission line 18, in a mannerto be described. The interstage coplanarwaveguide (CPW) transmission line section 10 includes the dielectric substrate 12 and a ground plane conductor 14formed on one surface thereof.The ground plane conductor 14 is plated out to the periphery of the dielectric 12to provide continuity between the ground plane 14 and a housing 70 such asshown in FIGS. 3 and 8. Selected portions of the ground plane conductor 14 are removed to expose underlying portions ofthe substrate 12 and thus provide a pair of elongated, parallel slots 15, 15' in such ground plane 14 using conventional photolithographic masking and etching techniques. Such slots 15, 15' have a width w, and a length I. The slots 15,15' are separated byan unetched portionoftheground plane conductor 14, here an elongated strip conductor portion 16 having a width w'.The strip conductor portion 16 is here formed integrally with the ground plane conductor 14to provide short circuits at each terminal portion 17,17' oftheelongatedstripconductor region 16.

Terminations ofthe strip conductor portion 16 to the ground plane 14are provided here in order to generate a current maximum so asto maximize the magneticfield component of electromagnetic energy propagating along such CPW transmission line section 10 in a mannerto be described hereinafter. Suffice it to say here, however, that the width w of each slot 15,15' in the ground plane conductor 14, the thickness hand dielectric constant ofthe substrate 12 and the width w' of the strip conductor portion 16 are chosen to providetheCPWtransmission line 10with a predetermined characteristic impedance Zo, as is well-known in the art.

The magneticallytuned resonant circuit 9 is shown to further include a dielectric spacer20, here a dielectric substrate 22, having a thickness substantial ly equal tothethickness ofthe aforementioned substrate 12 and having a pair ofaprtures 24a, 24b provided through a portion ofthe substrate 22. The pair offerrimagnetic spheres 26a, 26b are predisposed in such apertures 24a, 24b. The first ferrimagnetic sphere 26a is chosen to be comprised of a pure single crystal of yttrium iron garnet (YIG), and the second sphere 26b is chosen to be comprised of a doped single crystal of yttrium iron garnet.The second YIG sphere 26b is here suitably doped with a dopant such as gallium, in orderto change the saturation magnetization of such sphere in order to surpress unwanted spurious energy which may be coupled through such magnetically tuned resonant circuit 9, as is known in the art.

The magnetically tuned resonant circuit 9 is shown to also include an input/output (I/O) CPW transmission line section 30. 1/O transmission line section 30 is shown to include a ground plane conductor 34 formed on a first surface of a dielectric substrate 32. Thus, substrates 12,22 and 32 provide a composite dielectric support structure. The ground plane conductor 34 is plated out to the periphery ofthe dielectric substrate 32 to provide continuity between the ground plane 34, the ground plane 14 and the housing 70 (FIGS. 3,8).

Thus, a composite ground plane conductor 52 is provided as shown in FIG. 3. Selective portions ofthe ground planeconductor34are removed to expose underlying portions ofthe substrate 32, providing elongated parallel slots 35a, 35a' and 35b, 35b' in such ground plane conductor 14, each one of such slots 35a, 35a', 35b, 35b' here having a width W. In a similar manner as described above, here pairs of such slots 35a, 35a' and 35b', 35b' provide one of a pair of elongatedstripconductorportions36a, 36bformed from unetched portions of the ground plane conduc tor 34 disposed between slots 35a, 35a', 35b, 35b'.

Each one of such strip conductors has a first end 37a, 37b, here terminated at the edge portion ofthe substrate for external connection, and a second end 37a', 37b' terminated in said ground plane conductor 34. In a similar manner as previously described, the ends 37a', 37b' of each one of such strip conductors 36a, 36b is terminated with the ground plane 34to provide at such ends 37a', 37b' a short circuit in order to maximize currentat such ends 37a', 37b' and hence to maximize at such ends 37a', 37b' the magnetic field component of such electromagnetic energy propagating between such strip conductors 36a, 36b and ground plane conductor34 in order to strongly couple the magnetic field component of such energy in a mannerto be described.As also previously described, the width W of each slot 35a, 35a', 35b, 35b' in the ground plane conductor 34, the thickness and dielec tric constant ofthe substrate 32, and the width w' of each strip conductor portion 36a, 36b are chosen to provide each one ofthe pair of CPW transmission lines 33a, 33b with a predetermined characteristic impedance Zo, as is well-known in the art.

As shown in FIGS. 2,3, the interstage CPW transmission line 10 is joined with the dielectric substrate 22 having the YIG spheres 26a, 26b mounted therein such as with a suitable low loss epoxy, and the input/outputtransmission line section 30. Each of such substrates 12,22 and 32 are arranged such that each YIG sphere 26a, 26b disposed within such corresponding aperture 24a, 24b is coaxially aligned, anddisposedadjacenttheterminations37a',37b' of strip conductor portions 36a, 36b in the ground plane 34 of input transmission line 33a and outputtransmission line 33b, and with the terminations 17, 17' of the strip conductor portions 16 of interstage CPWtrans- mission line section 10. The substrates 12,22 and 32 arefurtherarranged such that strip conductor portion 36a of input transmission line 33a is orthogonally aligned with strip conductor portion 16 of interstage transmission line section 10, and strip conductor portion 36b of outputtransmission line 33b is likewise orthogonally aligned with the strip conductor 16 of interstage transmission line 10. Further, the apertures 24a, 24b provided in interstage substrate 22 are aligned with the region wherein the aforementioned strip conductors orthogonally cross each other.As previously described, YIG spheres 26a, 26b are disposed in the apertures 24a, 24b priorto assembly of the substrates 12,22,32 into the magnetically tuned resonant circuit 9. Preferably, such YIG spheres 26a, 26b are orientated to provide a predetermined relationship between a selected crystallographic direction of such YIG spheres 26a, 26b and the external magneticfield Hoc, in orderto reduce variations in a radian resonantfrequency (cho0) of such spheres 26a, 26b, in the presence of such magnetic field HDo with variations in external temperature. Any method to provide an orientated YIG sphere 26a, 26b may be used.A preferred procedure is described hereinafter in conjunction with FIG. 43 to FIG. 45.

Coupling of a selected portion of a radio frequency signal fed to strip conductor portion 36a of input transmission line 33a to strip conductor portion 36b of output transmission line 33b will now be described. As shown in FIG.3, the external dc magneticfield Hne is generated by disposing the magneticallytuned resonant circuit 9 between a magnetic pole piece 60a, connected to a magnetic flux return yoke 60 (a portion shown) with such field HDe being applied normal to the surface ofthe ground plane conductors 14,34 of the magnetically tuned resonant circuit 9. Radio frequency energy in the presence ofthe dc magnetic field HDC isfed to here input CPW transmission line 33a,via a connector 72a (FIG. 8).As previously described, a short circuit is provided at the opposite end of strip conductor 36a by integrallyforming or terminating such strip conductor 36a with the ground plane conductor 34. A short circuit is provided in such region in order to stronglycouplethe magnetic field component of the radio frequency energyfed to the input transmission line section through the YIG sphere 26a and to the interstagetransmission line section 10. In the absence of a YIG sphere disposed in aperture 24a, 24b, input radio frequency energyfed to strip conductor36a isnotcoupledtotheinterstage transmission line 10 since the input transmission line 36a and the interstage transmission line 16 are orthogonally oriented with respect to each other.With the YIG sphere disposed in aperture 24a, a portion of the energyfed on the strip conductor36a is absorbed bythe YIG sphere 26a. The radian frequency 0 (hereinafterfrequency) ofthis absorbed energy is given as 0 = yoke where yisa quantity referredto as, "the gyromagnetic ratio" and is defined as the ratio of angular momentum and magnetic moment of a spinning electron in a crystal of a ferrimagnetic material in the presence of an applied dc magnetic field, and Hoc is the magnitude ofthe applied dc magnetic field, as previously described.Nonresonant frequency energy which is not absorbed bytheYlG sphere 26a is reflected backwards toward the input source. Energytransfer between the inputtransmission line section 33a and theYIG sphere 26a is thus possible when the frequency oi ofthe input radio frequency signal fed thereto is equal to the natural resonant frequency w, of the YIG sphere as defined by the equation coj = Co0. When this resonant condition is satisfied (co;; = toO), the magnetic field component Hx of inputenergyfedtotheinputtransmission line 33a having afrequency nearthe resonantfrequency (ssO is coupled tothespins ofthe electrons in theYIG sphere 26a by making the electrons precess abouttheirE axis.

Precession ofthe electrons abouttheirE axis produces, in response thereto, a radio frequency magnetic moment about their Y axis, enabling coupling of radio frequency energy to interstagetransmission line section 10 along strip conductor portion 1 6which is disposed alongtheYaxis. Provided atafirstend 17 of strip conductor portion 16 is a second short circuit again used to strongly couple the magnetic field component of the radio frequency energy coupled through the YIG sphere 26a, as previously described.

There is also some transfer of energy having a frequency which deviates from cm0, the resonant frequency. The strength of coupling of such energy and hence the bandwidth ofthe coupling thereof is determined by the proximity of the frequency of such energytothe resonantfrequency. Radio frequency energy coupled to strip conductor 16 of interstage transmission line section 10 propagates between the strip conductor portion 16 and the ground plane 14to the region of strip conductor portion 16 where there is a second short and where the second YIG sphere 26b is disposed in the aperture24b provided in the substrate 22. As previously described, a short circuit is provided at the end 17' of strip conductor 1 6to strongly couple the magnetic field component of the radio frequency energyfedthereto. In a similar manner, as previously described, substantially all the energy fed along strip conductor 16 is transferred to the spins of the electrons in the second YIG sphere 26b and, in a similar manner, as previously described, such energy is then coupled to strip conductor 36b of outputtransmission line section 33b.

As is well-known in the art, the resonantfrequency ofthe YIG sphere in the presence of a dc magnetic field Hoc is a strong function of variations in temperature for most orientations of the YIG sphere crystallographic structure as previously described. However, along selected well-known orientations of the YIG sphere's crystallographic structure with respect to the magneticfield HDC, such resonantfrequency is substantially invariant with temperature variations over a wide operating range oftemperature.Thus,theYIG spheres are here orientated along one of such preferred crystallographic orientations, prior to disposing them in such apertures 24a, 24b. Since the above-described coupling structures are planarstruc- turesfabricated using photolithographictechniques, theYIG sphere may be orientated priorto insertion in the filter. Thus, such YIG spheres may be orientated in relatively large numbers to facilitate YIG filterfabrication unlike priorartstructureswhere, due to the uncertainties ofthe spatial arrangement of the loop type coupling circuit, such pre-orientation of a YIG sphere was generally not possible.

Referring now to FIGS. 5,6 and 7, alternate embodiments ofthe magneticallytuned resonant circuit 9 are shown. As shown in FIG. 5, an alternate embodiment9' includes an input/outputtransmission line section 30' joined with the interstage section 10 (FIG. 1) shown in phantom and dielectric YIG spacer 20 (FIG. 1) shown in phantom. Here input/outputtransmission line section 30' is used to provide reduced direct coupling of r.f. energy fed on input line 33a' to output line 33b'. Such direct coupling may occurfor certain applications of the embodiment shown in FIGS. 1-3.Whetherthiscouplingistolerableis dependent upon the amount of coupling in comparison to the system requirements.The distance between the lines 33a, 33b, the frequency ofthe energy fed thereto and the power level are some factors which will influence direct coupling between lines 33a, 33b. Therefore, the second embodiment 9' is shown which provides reduced direct coupling. This is accomplished by having such lines diverge atterminal portions 39a, 39b thereof, as shown, to thereby increase the distance between such lines and thus reducing coupling of a voltage induced between such lines in accorance with 1/d2 where d is the distance separating such lines. Such direct coupling is further reduced by making innermost slots 41 a', 41 b' narrower in width wa than the widths wb of outer slots 41 a, 41 b.As shown in FlG.4,directcoupling may occur when an input signal, for example, propagates on input line 33a and a voltage is induced in strip conductor 36b of output line 33b, because some ofthe magnetic flux lines (representing the propagation magnetic field component of the input signal) extend outwardly in the vicinity of the output strip conductor 36b. Due to the natu re of CPWtransmission line propagation, a difference in magneticfluxwhich passes through each one of such gaps in the metallization induces a voltage in such output line 33b proportional to such difference.That is, since the flux in each gap will induce a voltage in the strip conductor, with each one of such voltages 180 out of phase with each other, the netcurrentflowing in such strip conductorwill bethedifferencebetweentheindi- vidual components of such current. Thus, if the gaps are equally wide, coupling will occur because the magnetic flux will decrease with increasing distance and the distant or outmost slot will have relatively low amounts offluxtherethrough than the inner slot, and the net currentwill not be zero.The reduced width of inner slots 41 a', 41 b' results in reduced direct coupling if equal currents are induced in each direction, so that the resultant current will be zero and no energy will be coupled intothe output strip conductor36bfrom the input strip conductor 36a. With the magnetically tuned resonant circuit 9' (FIG. 5) the inner slot is made sufficiently narrow (or conversely the outer slot is made sufficiently wide) so as to reduce the amount of magneticfluxtherein to be substantially equal to the magnetic flux in the outer slot, the difference in such flux will be substantially zero and substantial isolation between input and output lines 33a', 33b' will be obtained.

Referring nowto FIG. 6, an alternate embodiment of a magnetically tuned resonant circuit 9" is shown to include a pair of dielectric spacers 20a', 20b' used to hold in placetheYIG spheres26a,26b. Here such spacers 20a', 20b' are joined to interstage section 10 and input/output section 30to provide a slot 41 for slidablydisposing therein a conductor stub 42 for increasing isolation between YIG spheres 24a and 24b. Further, here each dielectric support has formed therein a slot27a, 27bto slidably dispose therein the YIG spheres 26a, 26b which are connected to end portions of dielectric rods 28a, 28b as shown. Final precise adjustments ofthe YIG spheres about the axis maybe madewith this structure.

Referring now to FIG. 7, an alternate embodiment of a magnetically tuned resonant circuit 9"' is shown to include a pair of substrates 31,31' here replacing the input/output substrate 30 of the prior embodiments 9, 9', 9", as shown. Each substrate 31,31 ' has formed thereon a ground plane conductor34a, 34b and has formed therefrom a corresponding one of such input or output CPW transmission lines 33a,33b. Such substrates are joined with pairs of dielectric spacers 20a, 20b as shown.When joined with the dielectric spacers 20a, 20b, a channel 40 is provided therebetween, such channel 40 is here provided to slide therein a conductive slab 42' such that the input line 33a is isolated from the output line 33b and the YIG spheres 24a, 24b are isolated. Edge portions (not shown) of substrate 31,31 ' may be plated and formed integrally with the ground plane conductors 34a, 34b to insure continuity of the slab 42 with the ground planes 34a, 34b.

Referring now to FIG. 8, the magnetically tuned resonant circuit 9 is shown disposed in a housing 70, here of brass. Connected to such housing 70 are a pair of coaxial transmission line connectors72a,72b having center conductors 73a, 73b dielectrically spaced from outer conductors 73a', 73b'. The center conductors are connected to the strip conductor portions 36a, 36b, and the outer conductors 73a', 73b' are connected to the housing 70 to provide input and output connections to the magnetically tuned re sonant circuit 9.

Referring now to FIGS. 9, 10, fabrication of a four channel dual stage filter 80 will be briefly described.

One channel A ofthe four channel dual stage filter 80 is shown to include a firsttriangular shaped CPW transmission line section 82a, a second triangular shaped CPWtransmission line section 82a', spacers 84a, 84a', YIG spheres 85a, 85a' and interstage section 83a disposed in a slot 87a of a housing 81. Such CPW sections are fabricated in a similar manner as described in conjunction with FIGS. 1-3. Coaxial lines 88a, 88a' having center conductors 89a, 89a' are connected to the first and second lines 82a, 82a' as described in conjunction with FIG. 8. In a like manner, each one ofthe remaining slots 89b-89d of housing 81 has disposed therein a similar set of such CPW transmission line sections 82b-82d, 83b, 83b', and spacers 84a, 84a' providing in combination additional channels B-D.With the above structure a relatively compact, multi-channelfilteris provided.

Referring now to FIGS. 11-13, a magnetically tuned resonant circuit 109, here a bandpassfilter, having improved resonant circuit characteristics fabricated in accordance with the teachings ofthe present invention is shown.

Referring first to FIG. 11, the magnetically tuned resonant circuit 109 is shown in the presence of a DC magneticfield intensity HDc, generated by means, not shown. The magnetically tuned resonant circuit 109 includes a first, here input, microstrip transmission line section 110 having a dielectric substrate 112 separating a ground plane conductor 118 and a strip conductor 114. The strip conductor 114 has afirst portion 1 14a of an arbitrary length and a second portion 114b. Strip conductor portions 1 14a and 1 14b are connected together by a pair of outwardly bowed spaced strip conductors 1 14c', 1 14c", here of equal arc lengths, lar as shown. Outward bowed spaced strip conductors 114c',114c" here provide a planar input r.f.

coupling circuit 117 (it is to be noted thatthe strip conductors 114c', 114c"arnspaced a a distance d).

In ordertostronglycouplethemagneticfield component of an r.f. energy signal fed to coupling circuit 117, an effective r.f. short circuit is provided at midpoint 117', 11 7"thereof. To provide such short circuit, the length of strip conductor portion 114bib is chosen to provide, in combination with a portion of the arc length of either one of strip conductors 11 4c', 114c"tothe midpoint 117', 1 17"ofthecoupling circuit 117, a length l=lb+(la/2) substantially equal to one quarter of a wavelength (A/4) where A is the wavelength of the midband frequency component of the resonant circuit.Further, portion 1 14b of strip conductor 114 has a plurality of spaced strip conduc torsegments 1 14b', 1 14b"formed adjacent thereto.

The spaced strip conductor segments 114b', 114b" are used to extend the length of the strip conductor portion 1 l4bforlowerfrequencyapplications by selectively bonding one or more of such segments 114b', 1 14b"together and to the strip conductor portion 1 14b by conductors (not shown) to thereby provide the requisite length l=A'4. Strip conductor portion 11 4b is here terminated in an open circuit at the segment end 11 thereof two provide, at the midpoints 117', 117"respectivelyofthecoupling circuit 117, an effective short ci rcu it to such r.f. energy, as is known in the art, sincethe separation between the open circuit end 115 and the midpoint ofthe coupling circuit is a quarter of a wavelength. A short circuit is thus created at the midpoint 117', 117" of each one of the spaced conductors 1 14a', 1 14a" ofthe coupling circuit 117. The impedance of a stub 119 (such stub being formed from the strip conductor 1 14b,the dielectric 112 and ground plane 118) is selected to provide the resonant circuit 109 with à desired bandwidth.As is known in the art, the impedance Z110 of such a microstrip transmission line section 110 atthe midpoint 117' is related to the characteristic impedance (Ò) of the stub 119, operat- ing wavelength and length la of such a stub 119 byZ110 = -jZ0 cotangent (21Tla/). Thus, the lowerthe characteristic impedance Zo the broader the operating bandwidth sincetherewill beawider range of wavelengths for which E110 Wll be substantially equal to zero (appear as a short circuit) and thus strongly couple the magneticfield component of such signal in a mannerto be described.

Acircularaperture 116 is bored through the substrate 112 and ground plane conductor 118, symmetrically between the spaced strip conductor portions 1 14c', 1 14c". Acircularvoid 118' is formed in the portion ofthe ground plane 118 using conventional masking and etching techniques, exposing an underlying portion of the substrate 112. The void 118' and the aperture 116 are here concentric. Here the void 118' exposes a portion of the substrate 112 extended beyond the periphery of the strip conductors 1 14c', 1 14c"whereas the aperture 116 is here substantially confined to the region between such strip conductors 114c',114ce, as shown more clearly in FIG. 13, and to be described in more detail hereinafter.

The width (w) ofthe strip conductor 1 14a, and the thickness (h) and dielectric constant ofthe substrate 112 are chosen to provide in combination with the ground plane 1 the microstrip transmission line section 110 having a predetermined characteristic impedanceZo, here equal to 50 ohms. The width w' of spaced conductors 1 14c',114c" is chosen to provide such lines with a characteristic impedance Zo, here approximately equal to 100 ohms, with the parallel combination of such pair of lines here providing an impedance of approximately 50 ohms.The character isticimpedanceofsuchtransmission line formed from the strip conductors 114c', 1 14c" is here related to the width of such linesw',thedistanceofsuch linesfrom the ground plane conductor 118 and thethickness and dielectric constant ofthe substrate. Since a void 118' is formed in the ground plane conductor 118, immediately underneath the strip conductors 114c', 1 14c", a transmission line of a predetermined characteristic impedance is provided in part by means of fringe capacitance existing betweentheground plane 118 and strip conductors 11 4c', 1 14c". The size ofthe void 118' in the ground plane 118 is selectedto insure thatthe strip conductor portions 1 14a, 1 14b provide, in combination with such ground plane 118 and dielectric 112, transmission lines having predetermined characteristic impedances as described above, and the size of the void 118' is also selected such that the ground plane 118 does not significantly interfere with coupling of r.f. energy as will be described.

Further, the thickness of all strip conductors are chosen to minimize series resistance and inductance, as would be provided by a thin conductor.

The magneticallytuned resonant circuit 109 also includes a sphere 138 of a ferrimagnetic material, here yttrium iron garnet, and a second, here output, microstriptransmission line section 120 having a strip conductor portion 124 orthogonally spaced from strip conductor portion 114 of the first microstrip transmission line. The second microstrip transmission line also includes a dielectric substrate 122, here separating the second strip conductor 124 and a second ground plane conductor 128, as shown. Strip conductor 124 includes a first portion 1 24a of an arbitrary length and a second portion 124b. Strip conductor portions 1 24a and 1 24b are connected together by a pair of spaced strip conductor portions 124c', 124c", as shown.

Spaced, strip conductors 124c', 124c" here provide a planar output r.f. coupling circuit 127. In a similar manner, as previously described, the length of portion 1 24b is chosen to provide in combination with a portion of strip conductors 1 24c', 1 24c" to midpoints 127', 1 27"thereof a length, I, substantially equal to one-quarter of a wavelength (A/4).Further, end portion 1 24b has strip conductor segments 1 24b', 1 24b" used to extend the length of the strip conductor portion l24bforlowerfrequencyapplications, as described above, and the strip conductor portion 124b is here terminated at the segmentterminusthereofin an open circuitto provide at the midpoints 127', 127" or strip conductors 124c', 124c", a short circuit to resonant frequency r.f. energy. Provided between such split strip conductor portions 124c', 124c" of coupling circuit 127 is an aperture 126 through the dielectric substrate 122.The ground plane conductor 128 is formed on the surface of the dielectric substrate 122 oppositethe strip conductor 124to provide in combination therewith the microstrip transmission line section 120, as shown. Avoid 128' in the ground plane 128 is provided, exposing an underlying portion ofthe substrate 122. In the same manner as described above, the substrate thickness (h), dielectric constant thereof, and the strip conductor 124width (w) are chosen to provide the microstrip transmission line section 120 with a predetermined characteristic impedance, here equal to 50 ohms. In a similar manner, the width of each planar strip conductor 124c', 124c" is chosen to provide each one of such lines with a 100 ohm characteristic impedance, as previously described.In a preferred embodimentofthe invention, microstrip transmission lines 110 and 120 are constructed to be identical in mechanical and electrical characteristics.

As shown more clearly in FIG. 12, the transmission line sections 110 and 120 are joined together to provide a compositetransmission line body 130. The transmission lines 110 and 120 are arranged such that the corresponding apertures 116,126 (FIG. 11) provided in the respective substrates 112, 122 are aligned to provide a common aperture 136 through the joined transmission line sections 110, 120. The transmission line sections 110 and 120 are further arranged such that strip conductor portions 114 and 124thereof are spaced from one another by the separation provided bythesubstrates 112 and 122.

That is, such microstrip transmission line sections 110, 120 are connected together along the surface of each one ofthe respective ground planes 118, 128 to provide a composite ground plane conductor 135, andthe exposed areas 112', 122' of arse aligned to form a void 135' in the composite ground plane conductor 135. The strip conductors 114and 124 of each microstrip transmission line section are here orthogonally disposed with respect to each other, as shown for reasons to be described hereinafter. The sphere 138 of yttrium iron garnet (YlG), is then disposed in the aperture 136, as shown.The aperture 136 provided through the magneticallytu ned re- sonantcircuit 109 hasa diameter equal to the diameteroftheYlG sphere 138 disposed therein. At one end of the aperture 136 in the magneticallytuned resonant circuit 109 is inserted a button-shaped dielectricYIG sphere support 137 (FIG. 13) upon which theYlG sphere 138 may have been previously mounted. The sphere support 137 is disposed in the area between coupling circuit 127 and is used to supportthe YIG sphere 138 in the aperture 136.It is preferable that the YIG sphere 138 be positioned at the center of the magneticallytuned resonant circuit 109 such thatthe plane (not shown) of the ground plane 135 bisects the YIG sphere 138. HeretheYIG sphere 138 has a diameter of 375pom (0.015 inches).

The metallization thicknessforthe ground plane 135 is 511m (0.0002in.) and the thickness ofthe substrate is 375 pom. The diameter of the apertuure 136 is thus 375pom inordertopermitthesphere 138 to be disposed therein. The YIG sphere 138 is preferably orientated priorto insertion within aperture 136 such thatthe external D.C. magneticfield Hoc, provided by disposing the composite body 130 between a magnetic pole piece 140a and a flux return yoke 140 (FIG. 13), is disposed with respect to a predetermined crystallographic direction of the YIG sphere 138, such that coupling of a resonance radianfrequencyenergy(oO (hereinafter resonant frequency) is independent of temperature.A preferred apparatus and method for orientating the YIG sphere 108 is described in conjunction with FIG. 43 to FIG. 45, although other methods for orientating a YIG sphere may be used.

The first ends 1 14a, 124a of strip conductors 114,124 are used to couple the magnetically tuned resonant circuit 1 09to external components such as a system 160, as shown in FIG. 15. Selection of which one of the microstrip transmission lines 110, 120 is used as an input or output line is determined in accordance with its connection to the external components.As previously described, the length of each of such strip conductor portions 1 14b, 1 24b is chosen to have, in combination with a portion ofthe length of the coupling circuits 117, 127, a length I substantially equal to a quarter of a wavelength in orderto provide, in combination with the open circuit termination of such lines, an effective r.f. short circuit at the midpoints 117', 127' of each coupling circuit 117,127, as described above. As is known in the art, a short circuit is provided substantially at the midpoints 117', 127' ofthecoupling circuits 117,127, respectively, in orderto strongly couple the magneticfield compo- nent ofthe electromagnetic energy fed to the input microstrip transmission line section 110 through the YIG sphere 138 and to the output microwave transmission line section 120. A portion of the input energy having a frequency substantially equal tothe re sonantfrequency coO ofthe YIG sphere 138 is coupled from the input microwave transmission line section 110 through the YIG 138 to the outpout microwave transmission line section 120 in a manner to be described.Suffice it here to say that coupling of such microwave frequecy energy having a frequency Co =toO occurs within the region of such spaced strip conductor portions 114c', 114c", 124c', 124c", respectively.

As shown in FIGS. 13,21 a housing 131 here of brass is provided to house the composite transmission line section 130. Such housing includes input and outputcoaxially connectors 131 a-1 31 a' (FIG. 21) and coaxial to microstrip launchers 131 b-131b' to couple transmission lines 110, 120 to external circuit components.

Referring nowto FIG. 15, a typical system 160 which includes the magnetically tuned resonant circuit 109, here a front end filterfor a radio frequency receiver 168 is shown to include a firsttransmission line 164 connected between an antenna 162 and the inputtransmission line 110 ofthe magneticallytuned resonant circuit 109 and second transmission line 166 connected between the output transmission line section 120 ofthe magnetically tuned resonant circuit 109 and the receiver 168. In operation, a radio frequency signal received by the antenna element 162 is fed to the input transmission line 110 ofthe magneticallytuned resonant circuit 109, via transmission line 164.In accordance with the equation noj = #o, a portion of the microwave signal fed to the input transmission line section 110 is coupled to the output transmission line section 120 ofthe magnetically tuned resonant circuit 109 in a mannernowto be described. This coupled signal (not shown) is then fed to the receiver 168.

Referring now to FIG. 13 and FIG. 14, a D.C.

magneticfield Hoc (FIG. 12) is shown with flux lines thereof normal to the plane ofthe ground plane conductor 135 of the magneticallytuned resonant circuitl09.TheDCmagneticfield Hue is here generated by placing the magnetically tuned resonant circuit 109 between the pole piece 140a and flux return yoke 140 (FIG. 13), as shown.In the presence of such a DC magneticfield Hoc applied along a Z axis, for example, an input signal is fed to input transmission line 110 (FIG. 11) and the signal passes th rough the spaced, split or bifurcated strip conductor portions 1 14c', 1 14c" of input coupling circuit 117 disposed along an X axis, for example, producing an r.f. magneticfield H(FlG. 14) in the vicinity of strip conductor 114c',114c", as shown. In the absence of the YIG sphere 138 there is no coupling of the energy fed through the microstrip transmission section 110 to the output microwave transmission line 120 since the input coupling circuit 117 is orthogonally orientated with respect to the output coupling circuit 127.Thus, such energy is reflected backtowardsthe input source, here the antenna 162.

With a YIG sphere disposed in aperture 136, spaced a distanced along a Direction thereof, a portion ofthe energy fed on the input coupling circuit 11 - is transferred to the YIG sphere 138. The YIG sphere is positioned along a direction wherethe X component of r.f. magneticfield Hx has a maximum value.

Further, due to the symmetric structure of the input coupling circuit 117, as shown in FIG. 17, the resultant magnetic field coupling component Hx is relatively uniform through the YIG sphere 138. In the general case, thus, the number of such strip conductors,their shape, and alignment with respect to the YIG sphere 138, are selected to provide through the YIG sphere volume a predetermined magnetic field distribution from a signal fed to such strip conductors. That is, the current fed to such strip conductors is selectively channeled or distributed among the various conductorsto provide a predetermined distribution of the magneticfield generated in response to such current.

Generally, in orderto reduce coupling to higher order resonancemodes,thefield distribution through a spheriod shaped ferrimagnetic body is chosen to be uniform. Otherfield distributions in combination with differently shaped ferrimagnetic bodies can be provided to insure that higher order resonance is suppressed. Suppresson of higher order resonance is further described in conjunction with FIGS. 17, 17A.

The frequency of the energy transferred to the spins of the electrons in theYIG sphere 138 is related to soO = yHDc where y is the quantity referred to as the "gyromagnetic ratio" as previously defined. Nonre sonantfrequency energy not transferred to the YIG sphere 138 is reflected backward toward the input source, here the antenna 162. Energy transfer between the input microwave transmission line section 110 and the YIG sphere 138 thus is possible when the frequency (coy) ofthe r.f. signal fed thereto is equal to the natural precession frequency #o ofthe YIG sphere 138 as defined by the equation toO = y HDc.When this resonant condition is satisfied (j = w,), the magnetic field component Hx ofthe input energyfed to the input coupling circuit 117 having a frequency nearthe resonant frequency (soy) is transferred to the spins of the electrons in theYIG sphere 138 by making the electrons precess abouttheirt axis. Precession of electrons abouttheir zn axis produces in response thereto a magnetic moment aboutthe Y axis, enabling coupling of r.f. energyto outputtransmission line section 120 which is disposed about Y axis by inducing a voltage in output coupling circuit 127 and providing a current flow therein.The frequency of such a coupled signal in the Y axis circuit is loO, as is well-known in the art. Further, there is also transfer of energy having a frequency which deviates from #o, the resonant frequency. The strength of coupling of energy having afrequencywhichdevi- atesfrom w, and hence the bandwidth of the coupling thereof is determined bythe proximity of such frequencyto Coo, the resonantfrequencyand impe dance Z110, Z120 ofthetransmission lines 110, 120 as previously described.

AYIG filter providing a passband offO = 20 at a centerfrequency of fro = 10 MHzwhere f0 = CoJ2Tr, tunable over at least 500 MHz band in the X-band range and having an insertion loss at lessthan 1.3 db, hasthefollowing properties::

svmbol Description Value w I width of strip conductor ll4a, 124c 15 m111 width of strip conductor 114c', 114c'l 3 mini 124c' , 124c' 3 mii w5 | width of stubs 114b, 124b ;30 mil substrate material I alumina substrate thickness ' is miii aperture diameter ; 15 mil k dielectric constant of substrates 112, 122 1 9.3 D diameter of void 1 60 mil d separation of coupling circuit 35 mil conductors 114c', 114c''. 124c'r 124c" } length of coupling eircuit 1 60 nil

Referring now to FIG. 16, the effect of the ground plane conductor 135 of the magneticallytuned resonant circuit 109 on transfer of energy between input and output transmission lines 110, 120 through theYIG sphere 138 will be described.As is known in the art, when a sphere resonator is in close proximity to a conductive wall, such as the coupling loops orthe filter r.f. housing ofthe "wire loop type YIG filter", two principal effects which occur are: a frequency shift in the resosantfrequency (cho0) and a "line broadening" effect. "Line broadening" is a term in the art which refers to an increase in the frequency band which will resonate with the YIG sphere 138, albeit at a reduced efficiency, thereby increasing the resonant frequency insertion loss of the YIG sphere 138.

In most prior art structures (not shown) the YIG sphere 138 is located close to a conductive wall such as the coupling loop orthe filter's r.f. housing. In such cases, a frequency shift results from the proximity of the sphereto the conductive wall becausether.f.

magneticfield (not shown) associated with the precessing magnetization of electrons in the sphere (the vector sum of the precessing magnetization of all the electrons in the sphere) is distorted in the vicinity of the surface ofthe conductive wall due to the conductivity thereof. This distortion of the r.f. magnetic field produces a shift in resonant frequency ofthe resonant circuit. This shift is partially compensated for in the prior art structure by changing the applied D.C. field. However, the frequency shift is also a function of temperature making temperature independant operation more difficultto achieve. With the present invention, as diagrammatically shown in FIG.

16, theYIG sphere 138 is disposed midway through the aperture 136. That is, the YIG sphere 138 is symmetrically disposed through the void 135' in the ground plane conductor 135. Since, under resonant conditions, the precessing magnetization M in the unifrom resonance mode is provided in the Y direction, it is already parallel totheground plane 138 and hence there is no significant distortion of the magnetic field and thus no significant frequency shift caused bythe ground plane conductor 138.

The second effect provided by close proximity of a sphere resonator to a conductive surface is the so-called "line broadening" effectwhich resultsfrom eddy currents flowing in the conductive wall. The eddy currents resultfrom voltages being induced in the conductive wall due to the varying r.f. magnetic field. In the prior artstructures mentioned above, the eddycurrentsand hence the line broadening effect are reduced by positioning the spheres at a greater distance from the conductive wall since the power dissipated due to the "line broadening" effect is proportional to 1/d4where d is the distance between the conductive wall the center ofthe sphere.

However, often this approach reduces the coupling between input and output lines and thereby degrades performance. In the present structure, this problem is substantially eliminated because, as shown in FIG.

16, the ground plane conductor 135 bisects the YIG sphere 138. Since a portion ofthe ground plane conductor 135 can be selectively removed in the area adjacent the YIG sphere 138 providing the void 135', as previously described, eddy current losses can be minimized. That is, since eddy current loss is related to the distanced between the YIG sphere 138 and the conductive surface, here the ground plane conductor 135, the diameter ofthe void 135' through the ground plane conductor 135 can be made sufficietly large without any significant reduction in resonantcou- pling strength, thereby reducing eddy currents in such ground plane and hence reducing the "line broadening effect" and resonant frequency insertion loss.

Referring nowto FIG. 17, an idealized graph of the strength ofthe coupling component Hm,(in free space) ofthe r.f. magnetic field H in the X direction is shown as a function ofthe vertical distance (i.e. along the axis) between the YIG sphere 138 and a pair of conductors which approximate the input coupling circuit 110 for the magnetically tuned resonant circuit 109 (curve 1) in comparison with an idealized graph of the coupling component Hum, as a function of the vertical distance between a single conductor and a YIG sphere, which approximate a single conductor prior art structure (curve 2). The spatial relationship between the conductors 114, 124(FIG. 12) and the YIG sphere 138 and a typical prior art structure are diagrammatically shown in FIG. 17.The magnetic field generated buy a pair of conductors (in free space) in the region where the YIG sphere 138 is disposed (curve 1) is relatively uniform throughoutthe YIG sphere 138 in comparison to the magnetic field generated by a singlewire (curve 2) thattraverses such region. As is known in the art, YIG spheres when used in microwave bandpass filters, for example, due to excitation of nonumiform modes of resonance in the YIG sphere, will transfer spurious energy signals here shown as peaks 1 52a', 1 52b' in FIG. 17A (Case 2) having a frequency outside the passband 152' of the filter, as shown. The transfer ofthis spurious energy is generally undesirable. The spurious energy is transferred by exciting higher order modes offerrimagnetic resonance generally referrred to as "magnetostatic modes of resonance. These modes of resonance occur when the YIG sphere in the presence ofthe D.C. magnetic field HDC is positioned where there is a spatial variation ofthe r.f. magneticfield through the volume of the YIG sphere 138 such as that shown in FIG. 17 for curve 2. It is theorized here that, as a result of this spatial variation of the field across the YIG sphere 138, the electrons in the upper half of the sphere oscillate in phase opposition to the electrons in the lower half of the sphere, thus providing phase and amplitude variations ofthe resonant energy across the YIG sphere.One ofthe advantages of the present invention is the relative uniformityofthe r.f. magneticfieldwhich is provided through the YIG sphere 138, as was described in conjunction with FIG. 17 (curve 1). The present invention provides a reduced excitation of magnetostatic modes of precession and thus reduced spurious energy transfer (peaks 152a, 1 52b), as shown in FIG. 17A, case 1, since the magnetic field through the sphere 138 is in general more uniform.

The orientation ofthe ground plane conductor 135 with respect to the sphere 138 provides an additional advantage over the above-mentioned prior art structures. As previously described, there is no frequency shift since the r.f. magnetic field associated with the uniform mode of precession is a priori provided in a plane parallel to the ground plane 135 without any distortion in the r.f. magneticfield.For most nonumiform modes, however, the r.f. magnetic field associated with the precessing magnetization thereof has components perpendiculartothe ground plane conductorl35.Thus,the resonantfrequencyofsuch modes in the presence of a conductive wall is shifted relative to the resonant frequency of the same mode in the absence of a metalwall. Further, in the ground plane will be induced eddy currents from the magnetostatic resonant energy which will further decrease the stength of spurious energy transmission due to the line broadening effects described earlier. In other words, the coupling circuits 117,127 provide a relatively uniform r.f. excitation of the YIG sphere 138, resulting in reduced magnetostatic resonance and hence lower spurious energy transfer.At the same time, due to the line broadening effect on the magnetostatic resonantfrequency, the coupling circuits 117, 127 provide a significant insertion loss to any nonumiform resonant energy transferred, further reducing spurious responses.

Referring now to FIGS. 18-20, a two stage magneti cally tuned resonant circuit 190 fabricated according to theteachings of the present invention is shown.

Referring firstto FIG. 18, the magneticallytuned resonant circuit 190 is shown to include a first input transmission line section 110, here substantially indentical to the inputtransmission line section 110 described in conjunction with FIG. 11, a first output transmission line section 120 substantially identical to the outputtransmission line section 120 described in conjunction with FIG. 11, an interstage transmission line section 180, and YIG spheres 198a, 198b, as shown. lnterstagetransmission line section 180 here includes a dielectric substrate 182 separating a strip conductor 184 and a ground plane conductor 188, as shown.The strip conductor 184 is provided substan tially across the entire length of the substrate 182 (having a length, II, equal to (2n+1 )A/4wavelengths (where (2n+1) is an odd multiple multiplier, n is an integer) and includes a pair ofquarterwavelength stubs 1 84a, 1 84e, two pairs of spaced or bifurcated strip conductor segments 184b', 184b", and 184d', 184d" providing interstage coupling circuits 185a, 185b and a strip conductor 184ccoupling together such segments 184b', 184b"and 184d', 184d",as shown.Stub portions 1 84a, 1 84e have a length, I, in combination with a portion ofthe coupling circuits 185a, 185bto provide a quarter wavelength stub as previously described in conjunction with FIGS. 11-13.

Provided in the substrate 182 between each pair of such split strip conductors 184b', 184b" and 184d', 184d" is a corresponding aperture 186a, 186b, respec tively,through such substrate 182 and ground plane conductor 188, as shown. A pair ofcircularvoids 188a, 188b are formed in the ground plane conductor 188 in the area adjacent such apertures 186a, 186b exposing portions ofthesubstrate 182 and the apertures 186a, l86btherein, as described in conjunction with FIG. 11. The distance 12 between the centers of such apertures 186a, 186b is an odd multiple (2n+1) of a quarter wavelength A/4where n is an integer.The length, Ii ofthestrip conductor 184 and the distance 12 between the apertures 186a, 186b are chosen to be an odd multiple of a quarterwavelength in orderto presevethe r.f. short circuits atthe center of each aperture 186a, 186b, as previously described, and to maintain a uniform balance of electrical characteristics across such strip conductor 184.

Further,the impedance here approximately 50 is shown to provide desired coupling between the stages.

As shown more clearly in FIGS. 19,20, the input transmission line section 110, the outputtransmission line section 120, and the interstage transmission line section 180 are joined together to provide a composite transmission line body 193. The transmis- sion line sections 110,120 and 180 are joined together providing a composite ground plane 195. A channel 191 is obtained between such microwavetransmission line sections 110, 120 when such section 110,120 arejoined with theinterstagetransmission line section 180. A suitable housing 131' (FIG. 20) similar to the housing 131 shown in FIG. 21 forthe single stage circuit 109) is provided to hold such transmission line sections 110, 120,180 together.A conductive slab 192 is provided in the channel 191 between such transmission line sections 110, 120. Conductive slab 192 here provides a conductive path to the ground plane 195 between inputtransmission line section 110 and outputtransmission line section 120 to preventdirectcoupling ofsignalstherebetween.A pair of apertures 196a, 196b through the dual stage magnetically tuned resonator 190 are provided from apertures 116, 186a and 126, 186b, as previously described in conjunction with FIG. 12,foraperture 136. Each aperture hasassociatedtherewith avoid 195a, 195b in the ground plane 195 as previously described in conjunction with FIG. 12.As shown in FIG. 20, a first stage 190' of the dual stage magneticallytuned resonant circuit 190 is shown to include a YIG sphere 1 98a disposed in aperture 1 96a, and a second stage 190" ofthe resonant circuit 190 is shown to include a YIG sphere 1 98b disposed in aperture 196b.

Coupling of a portion of an r.f. signal fed to the strip conductor 1 l4ofinputtransmission line 1 10 to the strip conductor 124 of outputtransmission line 120 will now be described. As shown, the external D.C.

magnetic field Hoc is here applied normal to the surface of the composite body 193. The DC magnetic field HDe is generated, as previously described, by placing the magnetically tuned resonant circuit between a magnetic pole piece here 140a' and a flux return yoke 140' (FIG. 20). Radio frequency energy in the presence of the DC magnetic field Hoc is fed to strip conductor 114 at portion 1 14a thereof the first stage 190'.In accordance with the equation toO = AHoc,the portion of such input energy having a frequency substantially equal to (1)O is transferred to the spins of the electrons in YIG sphere 1 98a, disposed in aperture 196a, in a similar manner as previously described in conjunction with FIG. 7, by making the electron spins thereof precess aboutthe direction of the external field HDC, here the Z axis.In a like manner, as previously described in conjunction with FIG. 19, the precession of electrons abouttheE axis produces an R.F. magnetic moment in theY direction, enabling coupling of such energytothe first pair ofsplitstrip conductors 184b', 184b"ofthe interstage strip conductor 184.Such coupled energy is then fed along the intermediate strip conductor 184ctothesecond pair of split strip conductors 1 84d', 184d". In a similarmanner,as described above, substantially all ofthe energy fed to split strip conductors 184d', 184d" is transferred to the spins of the electrons in the YIG sphere 198b and, in a similar manner as described above, such energy is then coupled to the strip conductor 124 and fed to the output portion 124a thereof. Suppression of magnetostatic resonance modes, line broadening and frequency shift effects as described in conjunction with FIGS. 16-17, 17A forthe sing le stage magneticallytuned resonant circuit 130 in a like manner applies the dual-stage magneticallytuned resonantcircuit 190.Since in each single stage 190', 190" of the dual-stage magnetically tuned resonant circuit 190 the magnetostatic resonance modes are suppressed, the dual-stage filter may be designed using two pure crystal YIG spheres. Further, the dual resonator 190 will have lower insertion loss and enhanced temperature performance due to reduction or elimination of line broadening and frequency shift effects, as described aboveforthe magnetically tuned resonator 130.

Alternatively, the coupling circuits shown in FIGS.

11-l3and 18-20 may be provided buy a pairof conductive wires coupling such portions ofthe strip conductors together, or by a pair of, straight lengths of conductive wires or strip conductors formed on the substrate or byfourconductors properly disposed for providing a predetermined magnetic field distribution. In addition, such coupling circuits may be directlyterminated to ground through a hole drilled or bored through the substrates and connected with the ground planeto provide electrical contact.

Further, the coupling structure and the mechanical configuration ofthe magnetically tuned resonant circuit disclosed herein may be used with other types of magnetically tuned resonant circuits such as oscillators and the like.

Referring now to FIGS. 22-24, fabrication of a magnetically tuned resonant circuit 209, here a bandpassfilter, having a pulse field coil integrally formed therewith in accordance with the teachings of the present invention will be described. Referring first to FIG. 22, a first, here input, microstrip transmission line section 210 is shown to include a dielectric substrate 212 separating a ground plane conductor 218 and a strip conductor 214. The strip conductor214 has a first portion 214a of an arbitrary length and a second portion 214b. Strip conductor portion 21 4a is split crosswise providing portions 21 4a', 21 4a"there- of with a channel 214a"'therebetween, as shown.

Strip conductor portions 214a' and 214a" are electri cally connected together by a low frequency blocking capacitor 219.

As shown in FIG. 22A, blocking capacitor219 has a first conductive plate 21 9a connected to portion 214a' and a second conductive plate 21 9b connected to portion 21 4a", via a conductive interconnect 21 9c which bridges the channel 214a"'. The plates 219a, 21 9b are spaced apart by a dielectric slab 21 9d. The value of capacitance for capacitor 219 is chosen to provide a very low impedance to radio frequency electromagnetic energy and a relatively high impe dance to lower frequency electromagnetic energy, to isolate such energy from the input portion 214a' of the strip conductor 214. As further shown in FIG. 22, the strip conductor 214 includes a second strip conductor portion 214b.Strip conductor portions 214and 214b are connected together bya pairofspaced strip conductors 214c', 214c", here providing a planar input r.f. coupling circuit 217. The length of strip conductor portion 21 4b is chosen to provide, in combination with a portion of the length of strip conductors 214c, 214c"to mid points 217', 217" of the coupling circuit, a length, I, substantially equal to one quarter of a wavelength (A/4).Further, portion 214b of strip conductor 214 has a plurality of strip conductor segments 214d', 214d" formed adjacent thereto, used to extend the length of the strip conductor portion 214bfor lower frequency applications and hence longer wavelengths by selec tively bonding one or more of such segments to the strip conductor portion 214b. Strip conductor portion 214b is here terminated in an open circuit at the segment end thereof, to provide atthe midpoints 217', 217"ofthe coupling circuit 217, a shortcircuitto such r.f. energy, as previously described in conjunc tion with FIG. 11.Further, the impedance of a stub 219 (such stub 219 being formed from the strip conductor 21 4b, the dielectric 212 and ground plane 218) is selected to provide the resonant circuit with the desired bandwidth, as previously described in con junction with FIG.11 for stub 11 9.

Portion 214b and segments 214d', 214d"thereofare split or etched lengthwise, to provide strip conductor portion 21 4b a first bifurcated portion 214b' and a second bifurcated portion 21 4b" spaced by a channel 21 4b"', as shown. The width of such channel is selected to provide isolation between such conductor portions 214b', 214b"for lowfrequency signals but to provide effectively a single conductor 21 4b due to fringe capacitance between such conductor portions 214b', 214b"for radio frequency signals. The micros trip transmission line section 210 further includes a firstcentertapped half wavelength (A/2) strip conduc tor stub 211' integrally formed at a first end with the bifurcated portion 214b', and terminated in an open circuit at a second end. The center of such stub 211' is connected to an input current feed line 21 5a. A second A/2 centertapped strip conductor stub 211" is shown integrally formed at a first end with the split portion 214b" and terminated ata second end in an open circuit (0). The center ofthe stub 211" provides a second terminal to provide a return flow path for the signal fed to current feed line 21 5a. Strip conductor stubs 211', 21 1"are here provided to block flow of r.f.

energythrough a current pulse source (FIG. 38). Each stub 211', 211", as previously described, is provided with a length equal to A/2. As previously described, an open circuit at a first end of a transmission line will provide at a second end thereof, an effective r.f. short circuit, ifthe distance separating such ends is a quarter of a wavelength, for signals having a quarter wavelength substantially equal to the length of such transmission lines. Similarly, an effective r.f. short circuit at a first end of a transmission line will provide at a second end thereof an effective r.f. open circuit, if the distance separating such ends is a quarter of a wavelength.Here by providing an open circuit at the ends of each stub 211', 211" respectively, an effective r.f. short circuit is provided atthe center taps of each stub, and thus at the ends connected to split conductors 214b', 214b" an effective r.f. open circuit (o) is provided since one quarter of a wavelength therefrom at each centertap there is an effective r.f.

short circuit. Thus, the stubs 211', 211" isolate r.f.

energyfedtostripconductor214b, by providing open circuitstosuch r.f. energywhilefeeding a current pulse to the coupling circuit 217 to produce a magneticfield in response thereto, in a mannerto be described.

Provided through the substrate 212 and ground plane conductor 218 between the planar, spaced strip conductor portions 214c', 214c" is an aperture 216.

The ground plane conductor 218 is formed on the surface of the dielectric substrate 212 opposite the stripconductor214to provide in combination with such strip conductor214and dielectric substrate 212 the microstrip transmission line section 21 0, as shown.Avoid 218' is formed in the ground plane 218 using conventional masking and etching techniques, exposing a portion ofthe underlying substrate 212.

The void 218' in the ground plane 218 is concentrically spaced aboutthe aperture 216 and exposes portions of the substrate 212 extended beyond the periphery of the strip conductors 21 4c', 21 4c". As previously described, the width (w) ofthe strip conductor214, and the thickness (h) and dielectric constant ofthe substrate 212 are chosen to provide in combination with the ground plane 218 the microstrip transmission line section 210 with a predetermined characteristic impedance Zo, here equal to 50 ohms and the width w' of pianar spaced conductors 214c', 214c" is chosen to provide such lines with a characteristic impedance ZOr here approximately equal to 100 ohms, with parallel combination of such lines here providing an impedance of approximately 50 ohms.The thickness of each one of such conductors 214c', 214c" is chosen to minimize series resistance and inductance, as would be provided by a thin conductor.

The magnetically tuned resonant circuit 209 also includes the second, here output, microstrip transmission line section 1 20 as was previously described in conjunction with FIG. 11, and a YIG sphere 238.

As shown more clearly in FIG. 23, the microstrip transmission line section 210 and the microstrip transmission line section 120 are joined togetherto provide a composite transmission line body 230. A single turn pulse field coil 239 for changing the strength ofthe D.C. magneticfield in the area adjacent the YIG sphere 238, is here provided by the A/4 portion 211 a' of stub 211' connected to conductor portion 214b', the planar spaced conductors 214c', 214c", the conductor portion 214b" and the A14 portion 211 a"ofstub 211" connected to conductor portion 214b". The strength ofthefield is changed in a mannerto be described in conjunction with FIGS.

24-25. It is to be noted that the transmission line sections 210 and 120 are arranged in a manner as described in conjunction with FIGS. 24to 25.

Referring nowto FIG. 38,39, a driver circuit 410 (FIG. 38) for providing, in response to a control signal "pulse on" (FIG. 39), a pulse signal to currentfeed line 21 5a will be described. Driver circuit 410 here includes a transmission line 412 connected between a voltage source 416 and a switching element414, here connected to the gate electrode 41 4a of a field effect transistor (FET). (Here a "HEXFET" manufactured by International Rectifier Part Number IRF 221 is used).

Shunt mounted between ground and the gate electrode 41 4a is a termination resistor RT provided to match the impedance ofthetransmission line 412 to that ofthe input impedance ofthe FET 414. The drain electrode 41 4b of FET 414 is connected to a power source +V, filter by capacitors 421 a, 421 b to provide the current pulse, and the source 414c electrode is connected to the current feed line 21 5a, as shown. In response to the "pulse on" signal, a voltage level of here + 10.0 volts is applied to the gate electrode 414 to turn the FET41 4"on" and to permit current to flow from the power supply 418, the currentfeed line 21 5a and through the coil 239 to ground, as shown in FIG.

39. Avoltage level of here zero volts is applied to turn the driver circuit off.

Referring now to FIG. 26, a typical application 260 ofthe magnetically tuned resonant circuit 209, here a front end filterfor a radio frequency receiver 268 is shown to includeafirsttransmission line 264 connected between a duplexer 261 and the input transmission line 210 ofthe magnetically tuned resonant circuit 209 and second transmission line 266 connected between the output transmission line section 220 ofthe magnetically tuned resonant circuit 209 and the receiver 268. The duplexer 261, here an r.f. switch is also connected to a transmitter 263 and an antenna 262. In operation, the transmitter 263 sends out a very high power pulse of microwave energy atthe resonant frequency Co0. The duplexer 261 switches the signal such that most ofthe energy ofthetransmitted signal is fed to the antenna 262.

However, a portion ofthesignal leaks through the duplexertothe received path. In a first mode of the operation,the resonant frequency of such circuit 209 is shifted by changing the magnitude ofthe DC magnetic field Hoc in a mannerto be described and such energy is prevented from coupling through the resonant circuit 209to the receiver 268. After a high powersignal transmission and priorto reception of an echo signal, the transmitter switches the duplexer 261 to connect the antenna 262 to the receiver 268, and the echo signal is fed to the receiver 268 through the magnetically tuned resonant circuit 209 in a mannerto be described.

Referring nowto FIG. 24 and FIG. 25, the magneticallytuned resonant circuit 209 is shown in the presence of the D.C. magnetic field How with flux lines thereof normal to the ground plane 235 of the magnetically tuned resonant circuit 209. The DC magnetic field Hoc is here generated by placing the magnetically tuned resonant circuit 230 between a magnetic pole piece 240a and a flux return yoke 240 (FlG24), as shown.In the presence of such a field Hoc applied along a Taxis, for example, an input signal is fed to inputtransmission line 210 (FIG. 22) andthe signal passes through the split strip conductor portions 214c', 214c" of input coupling circuit 217 disposed along an X axis, for example, producing an r.f. magnetic field H (FIG. 25) in the vicinity of strip conductor 214c', 214c", as shown. Without the YIG sphere 238 disposed in aperture 236, there is no coupling of the energy fed through the microstrip transmission section 210 to the output microwave transmission line 120 as previously described in conjunction with FIGS. 11 to 13.With aYIG sphere disposed in aperture 236, a portion of the energy fed on the input coupling circuit 217 is absorbed by the YIG sphere 238 as previously described in conjunction with FIGS. 11 to 13. In the general case, thus, the number of such strip conductors, their shape, and alignment with respect to the YIG sphere 238, are selected to provide through the YIG sphere volume a predetermined magneticfield distribution from a signal fed to such strip conductors as previously described in conjunction with FIGS. 11 to 13. However, often it is desirable to prevent coupling of r.f.

energy between input section 210 and output section 120 (FIG. 26) through the YIG sphere 238 such as during transmission by a high powertransmitter 263 having a frequency equal to #o, to prevent magnetic saturation of the YIG sphere and potential damageto the receiver 266 during the transmission period from transmitted energy that leaks into the receiver path. In accordancewiththe invention, a pulse signal is fed to currentfed line 215a (FIG. 22) from driver 410 (FIG. 38) providing a current signal flow (Ip) in the strip conductors 214c', 214c" around the aperture 236 as indicated in FIG. 25.The current in such strip conductors 214c', 214c" produces in response thereto a magnetic field HDCP around the resonant body.

Depending upon the direction of current flow, such field either aids or opposes the external D.C. field Hoc.

In any event in response to the combination of the pulsed magneticfield HDCP and the external D.C.

magneticfield Hoc, the shifted resonantfrequency (#os) ofthe magnetically tuned resonant circuit 209 is given as Co05 = V (Hoc + Hocp), or in other words the resonant frequency is changed by an amount equal to + V HOCK. Thus, during transmission of energy having a frequencytoO, in response to a currentflowthrough the coupling circuit 217, the magnetically tuned resonant circuit 209 will iso late such energy from the receiver 268 since the transmitted frequency w, thereofwill not equal co05,theshifted resonant frequency, and thus the resonant condition of absorption of energy will not be satisfied, and such energy will be reflected backwards toward the duplexer 361.

In general, when a plurality of conductors are used to provide a selected r.f. magnetic field distribution, a pulsed currentsignal fed to such conductors will provide in response thereto, a magneticfield prop ortional to the total currentflowtherein. The above structure in addition provides all the improvements in the operating characteristics of the magnetically pulsed tuned resonant circuit 219 such as reduced spurious energy transfer due to reduced activation or coupling to nonuniform resonance modes, reduced eddy current line broadening and substantial elimination of frequency shift, as described in conjunction with FIGS. 16,17, 17A.

AYIG filter providing a passband offO = 20MHz where f0 = #o/2# at a centerfrequencyoffO = 10 GHz, tunable over at least a 500 MHz band in the X-band range having an insertion loss atfO of less than 1 b, and capable of shifting fO by i 25 MHz in less than 100 nanoseconds using driver410 hasthefollowing properties::

Sv=bol Description Value w I width of strip conductor 214a, 224c I 15mil width of strip conductor 214c', 214c' 3 nil 124c', 124c' 3 nil w5 | width of stubs 214b, 124b 30 mil substrate material - alumina wc channel width (214h 2 ) 2 mil h substrate thickness 15 mil substrate diameter 15 mil k I dielectric constant of substrates 212. 122 1 9.3 Dl diameter of void 60 mil d I separation of coupling circuit conductors at midpoint 214c', 214c", 124c', 124c'' 35 mil c length of coupling circuit 60 mil sphere diameter 15 mil Referring now to FIGS. 27-29, the fabrication of a dual stage magnetically tuned resonant circuit 290 each having a single pulse field coil integ rally formed therein according to the teachings of the invention will be described.

Referring first to FIG. 27, the magnetically tuned resonant circuit 290 is shown to include a first input transmission line section 110, here substantially identical to the input transmission line section 110 described in conjunction with FIG. 11, a first output transmission line section 120 substantially identical to the output transmission line section 120 described in conjunction with FIG. 11, an interstage transmission line section 280, and YIG spheres 298a, 298b in the presence of magneticfield Hoc, as shown.

Interstage transmission line section 280 here in cludes a dielectric substrate 282 separating a strip conductor 284 and a ground plane conductor 288, as shown. The strip conductor 284 is provided substantiallyacrosstheentire length ofthesubstrate 282 (having a length, @1, equal to (2n+1 ) A/4wavelengths where (2n+ 1) is an odd multiple multiplier) and includes a pair of quarter wavelength stubs 284a, 284e, two pairs of planar spaced strip conductor segments 284b', 284b", and 284d', 284d" providing interstage coupling circuits 285a, 285b and corresponding strip conductors 284c', 284c" coupling together such segments 284b', 284b" and 284d', 284d", as shown.Stub portions 284a, 284e have length in combination with a portion of a corresponding one of the coupling circuits 285a, 285b to provide a corresponding length, I, as previously described in conjunction with FIG. 11. Provided in the substrate 282 between each pair of such spaced strip conductors 284b', 284b" and 284d', 284d" is a corresponding aperture 286a, 286b, respectively, through such substrate 282 and ground plane conductor 288, as shown. Portions ofthe ground plane conductor 288 in the area adjacent such apertures 286a, 286b are removed, exposing portions 282a, 282b ofthe substrate 282 and the apertures 286a, 286b therein as described in conjunction with FIG. 11.The distance 12 between the centres of such apertures is an odd multiple (2n+1) of a quarter wavelength A/4where n is an integer. Each length, I, ofthe strip conductor 284 and portions ofthe coupling circuits 285a, 285b and the distance 12 between the apertures 286a, 286b are chosen to bean odd multiple of a quarter wavelength in order to preserve the r.f. short circuits at the center of each aperture 286a, 286b, as previously described, and to maintain a uniform balance of electrical characteristics across such strip conductor 284.

The microstriptransmission line 2l0furtherin- cludes a first center tapped half wavelength (A/2) strip conductor stub 281' integrally formed atfirst end with the center of split strip conductor portion 284c' and terminated art a second end in an open circuit (0). The center of such stub 281' is connected to an input current feed line 21 5a. A second A12 center tapped strip conductor stub 281" is shown integrally formed at a first end to the split strip conductor 284c" and terminated ata second end in an open circuit (0). The center of the stub 281 " provides a return path for line 21 5a, as previously described. Strip conductor stubs 281 281" are here provided to block flow of r.f.

energythrough the current bias source, as previously described. Here by providing an open circuit at the ends of each stub 281 281", respectively, a short ci rcuit to r.f. energy is provided at the center taps of each stub, as previously described, and at the ends connected to split conductors 285', 285" an r.f. open circuit (o) to r.f. energy is thus provided since one quarter of a wavelength therefrom at each centertap there is a short circuit. Substantially complete r.f.

isolation from the cu rrent sou rce is thus provided by this configuration since the interstage transmission line section has coupled thereon only resonant frequency energy having a wavelength corresponding to the length of such stubs as described above.

As shown more clearly in FIG. 28, the YIG spheres 298a, 298b, the input transmission line section 110, the output transmission line section 120, and the interstagetransmission line section 280 are joined together to provide a composite transmission line body 293. The transmission line sections 110,120, 180 are joined together providing a single ground plane 295, as shown. A channel 291 is obtained between such microwave transmission line sections 110,120 when such sections 119,120 are disposed on the interstage transmission line section 280. A conductive slab 292 is provided in the channel 291 between such transmission line sections 110,120.

Conductive slab 292 here provides a conductive path to the ground plane 295 between inputtransmission line section 210 and outputtransmission line section 120to prevent direct coupling of signalstherebetween. A pair of apertures 296a, through the dual stage magnetically tuned resonator 290 are provided from apertures 216, 286a and 226, 286b, as previously described in conjunction with FIGS. 11-13, for aperture 136.Each aperture has associated therewith a void 295a, 295b in the ground plane 295, as previously described in conjunction with FIG. 12. A first stage 290' (FIG. 29) ofthe dual stage magnetically tuned resonant circuit 290 is shown to include the YIG sphere 298a disposed in aperture 296a, and a second stage 290" ofthe resonant circuit 290 is shown to include the YIG sphere 298b disposed in aperture 296b.

In a first mode of operation, a portion of an r.f.

signal fed to the strip conductor 114 of input transmission line 110 is coupled to the strip conductor 124 of output trnn,smission line 120 in a mannerto be described. The external D.C. magneticfield Hoc is applied normal to the surface of the resonator 290 with HDCP the pulsed mag netic component zero for the first mode of operation.Input microwave frequency energy is fed to strip conductor 114 at end portion 11 4a to the first stage 290' in the presence ofthe DC magneticfield, HDc. In accordance with the equation J0 = soi, a portion of such input energy having a frequency substantially equal to (oO is transferred to the spins ofthe electrons in YIG sphere 298a, disposed in aperture 296a, as previously described in conjunction with FIGS. 24-25, causing such electron spins to precess in a direction along the Z axis (in a direction parallel to the magnetic field Hoc) ata frequency cho0, as is well-known in the art.In a like manner, as previously described in conjunction with FIGS. 24-25, an r.f. magnetic field is produced about the sphere 298a and a magnetic moment ofthe precession of electrons in the X direction is produced in theYdirection, enabling coupling of such energy to the first interstage coupling circuit 285a. Such coupled energy is then fed along such strip conductor 284c to the second interstage coupling circuit 285b. In a similar manner, as described above, substantially all of the energy fed to coupling circuit 285b is transferred to the spins ofthe electrons in the YIG sphere 298b and in a similar manner as described above such energy is then coupled to the strip conductor224and fed to the output terminus 224a thereof. Suppression of magnetostatic resonance modes, line broadening and frequency shift effects as described in conjunction with FIGS. 16, 17, 17Aforthe single stage resonator 109 in a like manner applies to the magnetically tuned reso nant ci rcu it 290. Since in each single stage 290', 290" of the dual-stage magnetically tuned resonator 290 the magnetostatic resonance modes are surpressed, the dual-stage filter may be designed using two pure crystal YIG spheres. Fu rther, the dual resonator 290 will have lower insertion loss and enhanced temperature performance due to reduction or elimination of line broadening and frequency shift effects, as described above forthe magnetically tuned resonant circuit 209.

In a second mode of operation, r.f. energy is fed to transmission line section 210, but the magnetic fields around the spheres 298a, 298b are modified by pulsed DCmagneticfields Hocptochangethe resonantfrequency of the YIG spheres 298a, 298b and hence prevent coupling of energyto outputtransmission line section 220. In this manner, the magnetically tuned resonant circuit is detuned for r.f. energy of a frequencycoO and thus reflects such energy back towardsthe source and provides protection to the receiver268. Prior to the time of arrival of such r.f.

energy a voltage pulse signal is fed to the driver circuit 410 (FIG. 38) to provide a current pulse on line 215a which is synchronized to the flow of such r.f.

energy, as shown in FIG. 39. A current flow from current line 21 5a in two paths around the YIG spheres 298a, 298b is provided. Afirst path denoted by solid arrows is provided around a single turn coil 297 formed by stub 281', strip conductor portions 284c', 284b', 284b", 284c" and stub 281" providing in response to such currentflowa pulsed d.c. magnetic field Hocp having an orientation normal to the surface of the magneticallytuned resonant circuit 290 and a direction upward,asshown in FIG. 14.A second path is provided around a coil 297' formed by stub 281' strip conductor portion 284c', 284d', 284d" and stub 281" providing in response to such currentflowa pulsed d.c. magnetic HDCpb having an orientation normal to the surface of the magnetically tuned resonant circuit 290 and a direction downward, as shown in FIG. 14. Thus, in the presence of an externally applied d.c. magnetic field How, the pulsed fields Hoca and HDCb either aid or oppose the field HDc, thus shifting the resonance frequency of each resonator accordingly.For resonator A, the shifted resonant frequency Co0A5 is given by(ssOA5 = y(HDe + HDCpa) and for resonator Bthe shifted resonant frequency is given as Clogs = V(Hoc + HDCpb) Referring nowto FIG. 31,32 and 33, alternate configurations for selectively shifting the resonant frequencies ofthe magnetically tuned resonators are shown.An interstagetransmission line 280 shown in FIG. 27 is configured by splitting the strip conductor portion 284a and the strip conductor portion 284cto provide a single current loop here around here around the YIG sphere 298b to frequency shift the resonance frequency of stage 290". No current path is provided around resonator A, since stub 284a was split lengthwise to prevent coupling to a return path.

There is no frequency shift ofthe resonantfrequency of YIG sphere 298a. In FIGS. 32,33 are shown alternate interstagetransmission line sections 280", 280"' provided to shiftylG sphere 298a and YIG sphere 298b in the same direction by providing a current path around each one ofthe resonators and having a current in each path flowing in the same direction around such resonators using a pair of such driver circuits 410 (FIG. 32). In addition as shown in FIG 33, stub portions 281 a, 281 b have A/4 portions which are here connected directly to ground to provide an effective r.f. open circuit at the respective coupling circuits, as is known in the art.

Referring nowto FIGS.34,35,36 and 37 an alternate embodiment of a frequency stepped mag neticallytuned resonant circuit 309 here a bandpass filter will be described.

Referring first to FIG. 34, a coupling circuit section 310 is shown to include a dielectric substrate 311 supporting a first strip conductor 314which is connected to a corresponding quarter wavelength stub314a, via a thinner portion 314' of strip conductor 314 and a second strip conductor 31 6which is connected to a corresponding quarter wavelength stub 31 6a, via a thinner portion 316' of strip conductor 316 and a conductor317 which crosses or bridges over conductor 314' and is dielectrically spaced therefrom. Here a bonding wire is shown as conductor 317, but a plated overlay as known in the art may alternatively be used.On a surface of substrate 311 oppositethe surface supporting the strip conductors 312,314 is provided a ground plane conductor 318. A void 318' is provided in the ground plane conductor 318 exposing an underlying portion ofthe dielectric substrate 311.

The magnetically tuned resonant circuit 309 also includes a YIG sphere 338 and a coil section 320 having a substrate 321 supporting a pair of strip conductors 322,324 and a spiral coil 326. Such a pair of strip conductors 322,324 are provided to make electrical contact to the coil 326, and to provide means to couple thereto a current source such as the circuit 410 described in conjunction with FIG. 38. An aperture 329 is provided in the substrate 321 for disposing therein the YIG sphere 338. The YIG sphere 338 is here held in aperture 329 by a suitable low loss epoxy.

As shown more clearly in FIG. 35, the transmission, line section 310 and coil section 320 are joined together, providing a composite body 330 and such thatthe ground plane conductor318 is intermediate the strip conductors 314,316 and the coil 320. The transmission line section 310 and the coil section 320 are further mounted such thatthe aperture 329 formed in the substrate 321 is concentrically aligned with thevoid 318' in ground plane 318. As shown, the YIG sphere 338 is here exposed in aperture 329. Here in orderto provide maximum pulsed magnetic field intensity, the YIG sphere 338 is disposed in aperture 329 such that the coil 326 is symmetrically disposed aboutthe YIG sphere 338.In a first mode of operation, r.f. energy is coupled between such coupling circuits through the YIG sphere 338, in a manner as previously described. In a second mode of operation, a current pulse signal here fed from driver 310 (FIG. 38) is fed to one of such strip conductor lines such as 322 with line 324 providing a return path. In response to such currentflow around coil 326 a large pulsed D.C.

magneticfield HDCPS provided.Thus,the resonant frequency ofthe YIG sphere 338 is shifted in accordance with the equation coO = V(Hoc + Hock) and substantial isolation of energy having a frequency (oO = yHDc is provided as previously described. The coil 326 (FIG. 22) is here used to rapidly switch the pulsed D.C. magnetic field Hue on and off as desired.As shown in FIG. 25 in operation, when the frequency stepped magnetically tuned resonant circuit 309 is located adjacenttransmitter 263, for example, to prevent a portionofthetransmitted highenergyfrom being coupled through the frequency stepped magneticallytunedfilter, on transmit, a current signal is here fed to such coil 326to rapidlyswitchthed.c.

magnetic field HDCp on and hence to change the resonant frequency in accordance with the equation coO = y(HDc# f HDCp) as previously described. Since a current pulse is being fed through a coil 326 here having a relatively low inductance, and which is proximately and concentrically spaced from the YIG sphere 338, the magnetic field Hocpcan be pulsed on or off rapidly in such region thereby permitting the magnetically tuned resonator to selectively isolate or couple resonantfrequencyto energy fed to the input transmission line 314.Further, by mounting the coil on the surface ofthe substrate 320 (FIG. 21), substrate 312 (FIG. 1), or substrate 382 (FIG. 12), the thermal energy generated by passing a relatively large current signal therethrough is dissipated faster, enabling longer pulsed operation and higher pulse duty cycles, of current to create the pulsed magnetic field HOCK. As previously described in conjunction with FIG. 22, r.f. decoupling A/2 stubs may be used in conjunction with coil 226to prevent coupling of r.f.

energy coupled to such coil 226.

AYIG filter providing a passband off, = 23 MHz whereof, = #o/2#, at a center band frequency offo = 10 GHz, tunable over at least a 500 MHz band in the X-band range, having an insertion loss of lessthan 1 db and capable of shifting f0 by:l:300MHz in CH2 inless than 50 nanoseconds using driver 410, has the following characteristics::

Svmbol Description Value | w width of conductor 314, 316 10 mii width of conductor 314', 316' 2.5 mil w5 width of stub 314a, 316a 30 mil h substrate thickness 10 mil k dielectric constant 9.3 spacer thickness 10 mil n diameter of void 316' 50 50 nil dc - inner diameter of first turn of coil 326 45 mil number of turns 4 mil Referring now to FIGS. 40,41 and 42, an alternate embodiment of a frequency stepped dual-stage magneticallytuned resonant circuit 390 will be described.Referring first to FIG. 40, a dual-stage coupling circuit section 350 is shown to include a dielectric substrate 352 separating a ground plane 354 from strip conductors 356a, 356b, 356c, as shown. Strip conductor350c here includes discrete strip conductors 356c', 356c" and 356c"' connected together by plated overlays (as known in the art) or by here bonding wires 357,357'. In a similar manner as described in conjunction with FIG. 34, such conductors 356a, 356b, 356c here form a pair of coupling circuits 358,358'. Here sections 356a', 356b' of strip conductors 356a, 356b provide A/4 stubs as does sections 356c' and 356c"' as described above.Portions 354', 354" of the ground plane conductors 354 are removed exposing underlying portions ofthe dielectric substrate 352.

The magneticallytuned resonant circuit 320 also includes a pair of coil sections 370a, 370b here substantially identical to the end section 320 pre viously described. Here such coil sections are embed ded in acorresponding pairofapertures382a,382b provided in a housing 380 by a suitable low loss epoxy. In a similar manner, YIG spheres 386a, 386b are likewise epoxied into apertures 384a, 384b provided in coil sections 370a, 370b as previously described. Housing has attached thereto coaxial connectors and launchers 383 and connector384 (to feed current pulses to the coil sections), as shown.

As shown more clearly in FIGS. 41 and 42,the coupling section 350 is disposed in housing 380 as are YIG spheres 384a, 384b and coil sections 370a, 370b to provide the frequency step magnetically tuned dual-stagefilter390. By providing a current to the coil, here lines 392a, 392b which are connected to the coils 370a, 370b, the magnetic fields Hocpa, HDCpb are provided to shift the resonant frequency of each sphere 386a, 386b as previously described in conjunction with FIGS. 34-36.

Alternatively, the coupling section 310 may include a plurality of conductors, forthe coupling sections 314', 316', to distribute energyfed thereto and hence shape the r.f. magneticfield as previously described.

Also, the coil 326 as described above may be incorporated in the embodiments described in conjunction with FIGS. 1-33.

Referring nowto FIG. 43, an apparatus 510 for orientating a ferrimagnetic sphere along a predetermined crystallographic direction includes a first pair of coils 512,512' here including wire conductors 512a, 512a' wound around plastic cores 512b, 512b'.

Coils 512,512' are arranged in a corresponding plastic support 516. Coils 512,512' provide a magnetic field H(1) of here 1000 gauss in a horizontal orY direction, as shown. The apparatus 510 also includes a second pair of coils 522,522' here including wire conductors 522, 522a' wound around plastic cores 522b, 522b'. Coils 522,522' are arranged on the plastic support 516 and are disposed within the region confined by the first pairofcoils 512,512'. The axis of such coils 522,522' are disposed at an angle of here 70.53 with respect to the axis ofthe first pair of coils 512,512' as shown. Coils 522,522' provide a second magnetic H2 Of here 1000 gauss. The apparatus further includes a platform 30 centrallydisposed between such pairs of coils 512,512', 522,522', as shown.Each pair of coils 512,512', 522,522' are arranged in such a way asto provide a magneticfield between each of such pairofcoils having directions which correspond to a so-called "easy axis" ofthe sphere.

Referring now to FIGS. 44 and 45, the platform 530 here of lucite is supported by a support rod 532 here of lucite having afirstsurface 530' here opposite the support rod 32 disposed at a predetermined direction with respect to the horizontal plane ofthe apparatus 510. Here the surface is inclined at an angle d of 5.59 with respect to the horizontal direction. Ath readed aperture 530a is provided the platform 530 and a nylon screw 535 is threaded therein. The nylon screw 535 is inserted normal to the horizontal direction and has an upper portion wherein is embedded a watch jewel 534 here of sapphire.The watch jewel 534 has a recessed portion 534a to supportthe YIG sphere 138 (FIG. 13). The nylon screw 35 is provided to adjust the position of the YIG sphere 138, to accomodatethe apparatus for here a variety of YIG spheres of various diameters. As shown in FIG. 44, the screw 535 and watch jewel 534 have an aperture 539 therein for applying a small negative pressure to hold the YIG sphere in the recess 534a. A cover member 536 having an aperture 536' corresponding in size and shape to the YIG sphere support 37 (FIG. 13) is then fastened with screws 536a and 536b to the platform 530 along the inclined surface portion 530' thereof.

The apparatus 510 is here used to orientate the sphere 138 as follows: a negative pressure is initially applied through aperture 539 to insurethatylG sphere 138 is properly disposed in the recessed portion 534a of watch jewel 534; the negative pressure is then removed; a series of pulses of currentfrom a current means (not shown) are alternatively applied to each coil of such pairs of coils 512,512', 522, 522', in turn, at intervals of here one pulse every 20 seconds, with such pulse having a pulse width of approximately 100 ms;; in response to each pulse ofcurrentto each pair of coils 512,512', 522, 522'a magenticfield H1, H2 is generated in turn, between each pairof coilsandtheYIG sphere 138 rotates in response to each of such fields tending to align itself such that a pair of coplanar body diagonals of the sphere's crystallographic structure are parallel with the directions of the field Hr, H2; afterapprox imately five to six minutes of alternate pulsing of each pairofsuch coils, the YIG sphere 138 is orientated such thatthe magnetic fields H1, H2 are aligned with one ofthe "easy axis" ofthe sphere's structure.

Temperature invariant orientation of the YIG sphere 138 is provided when the sphere support 137 is brought into contactwith the sphere 138 since the sphere support 137 is brought into contact with the sphere 138 normal to the inclined surface 530' and at the bias angle with respecttothe vertical axis ofthe sphere ( is here equal to the incline ofthe platform surface 30').Thus, the YIG sphere 138 is orientated about atemperature invariant axis with respect to the direction of engagement of the YIG sphere support 137 with theYIG sphere 138, since the YIG sphere support 137 engages the YIG sphere at an angle of 5.59 removed from the vertical axis of the sphere 138. Initial alignmentofthe sphere 138 so that the easy axis ofthe sphere's crystallographic structure are aligned with the axes of the coils in combination with a calibrated attachment ofthe sphere support 137 at a predetermined direction with respectto the vertical direction of the initially aligned sphere 138 on the axes of the coils, provides a sphere 138 orientated about a temperature invariant axis. In order to check orientation, several methods may be used including X-ray diffraction analysis as known in the art. or by testing performance of such sphere in one ofthe magnetictuned resonant previously described in conjunction with FIGS. 1-42.

Having described preferred embodiments of the invention, it will now be apparent to one of skill in the art that other embodiments incorporating its concept may be used. It is believed, therefore, that this invention should not be restricted to the disclosed embodiment, but rathershouldbe limited only by the spirit and scope ofthe appended claims.

Claims (18)

1. In combination: a support structure; a pair of coupling circuits disposed on the support structure; a resonant body disposed for coupling energy between such pair of coupling circuits; and means, disposed on the support structure, for pivoting a magneticfield through the resonant body.

2. The combination as recited in claim 1 wherein one of such coupling circuits is integrallyformed with the means for providing the magneticfield through the resonant body.

3. The combination as recited in claim 1 wherein themeansforproviding a magneticfieldincludea coil dielectrically supported adjacent such resonant body.

4. The combination as recited in claim 1 wherein each one of such coupling circuits includes at least one strip conductor.

5. The combination as recited in claim 4wherein the strip conductor a first one of such coupling circuits is disposed in a different plane as the strip conductor of a second one of such coupling circuits.

6. The combination as recited in claim 4wherein the strip conductors of one coupling circuit have portionsthereofdisposed in the same plane as corresponding strip conductors of the second one of the coupling circuits.

7. In combination: a support means; a pair of coupling circuits disposed on the support means, each coupling circuit includes a plurality of spaced conductors; a resonant body disposed for coupling energy between such coupling circuits; means supported by the support means for providing a magnetic field through the resonant body; and wherein the conductors of each of such coupling circuits are arranged to provide a predetermined magnetic field distribution through the support body in response to a signal distributed to such conductors.

8. In combination: a first coupling circuit having a first pair of spaced strip conductors; a second coupling circuit having a second pair of planar spaced strip conductors spaced from the first coupling circuit; and wherein at least one of such pairs of spaced strip conductors is configured to provide a path around such coupling circuitto provide in response to a currentflowtherein a magnetic field.

9. The combination as recited in claim 7 further comprising a substrate which supports and dielectri cally separates such coupling circuits having an aperture therein between such coupling circuits.

10. The combination as recited in claim 8 wherein a resonant body is diposed in said aperture between such spaced coupling circuits and, in the presence of a magneticfield HDC applied thereto in first mode of operation, provides a resonant frequency circuit having a resonantfrequency ZO = V Hoc where y is a quantity known as a gyromagnetic ratio and in a second mode of operation a currentsignal isfed to such configured coupling circuit producing in responsethereto a magnetic field HDCP thus changing the frequency of the resonant circuit in accordance with the equation Co0, = V (HDC+HDCP)-

11.The combination as recited in claim 9 wherein such resonant body is a bodyofferrimagnetic material.

12. The combination circuit as recited in claim 10 wherein such ferrimagnetic material is yitrium iron garnet.

13. Acircuitcomprising: a first pairof planarspaced strip conducters, each conductor being connected together at a first end and unconnected at a second end; a second pair of planar spaced strip conductors spaced from such first pair of planar spaced strip conductors; wherein a resonant body is disposed therebetween for coupling resonantfrequencyenergyfrom an input one of such pair of spaced strip conductors to an output one of such spaced strip conductors; and wherein each unconnected end of such pair of spaced strip conductors is adapted to be connected to a current means for providing a currentflowtherein and in responsetheretoamagneticfield.

14. Acircuitcomprising: a pairofdielectricallyspaced coupling circuits disposed on a substrate; and a coil spaced from such dielectrically spaced coupling circuit disposed on an opposite surface of such substrate.

15. Amicrowavefrequency circuit comprising: a pair of dielectrically spaced coupling circuits supported on a substrate; a magnetic tuning means supported on an opposite side of the substrate for producing in response to a current signal fed thereto, a magneticfield.

16. A microwave frequency circuit comprising: a first conductor having a first bifurcated portion and a second bifurcated portion; a second conductor spaced from said first conductor; and means, including such bifurcated portions of such first conductor for selectively generating a magnetic field in the region of such first bifurcated portions of such conductors.

17. A radio frequency circuit as recited in claim 16 further comprising: means, including a resonant body disposed for coupling energyfedto an input one of such conductors to an output one of such conductors.

18. A radio frequency circuit as recited in claim 17 wherein such magneticfield is generated inthe region ofthe resonant body disposed for coupling energyfed to an input one of such conductors to an output one of such conductors.