DIELECTRIC RESONATOR
FIELD OF THE INVENTION
This invention relates, in general, to improved dielectnc resonators wherein the spunous frequency modes are highly subsided
BACKGROUND OF THE INVENTION
Microwave filters and dielectnc resonator oscillators are widely used in the field of communication electronics especially in microwave telecom systems for Satellite telecom as well as Terrestrial links and Cellular/mobile handsets Dielectnc Resonators are key microwave passive components finding wide applications in miniature microwave filters and oscillators for generating resonating frequencies for communication The resonance mode spectrum of a DR is so dense that the spunous (undesirable, HE11, HE12 or TM018,) modes may interfere with the dominant (desirable, usually TE01δ) mode Thus it is necessary to subside the spunous modes for efficient transmission of the dominant (desirable) mode
There have been several studies to improve the spunous free response of a DR configuration, though providing limited or no results on influence of Q-factor for the respective DR configuration
The mode separation (in frequency) of the dominant (fo, desirable) and the nearest higher (the undesirable) mode has been found to be 0 58f0 for a case of Ring DR shielded in a circular metal cavity The comparative separation however tends to reduce for the DR in MIC configuration to (0 35 to 0 38)fo
US patent No 4,706,052 descnbes a design of dielectnc resonator with TE sub 01 delta mode being the pnmary mode used The design is provided with a dielectnc resonator having a plurality of dielectnc resonator units which are combined into one umt by a connecting means, with a boundary being formed between adjacent dielectnc resonator units The dielectnc resonator units are
accommodated in a metallic conductive case with input and output members for electrical connection of said dielectnc resonator with an external circuit The design shifts a resonant frequency of spunous mode into a frequency zone higher than a resonant point by causing said spunous mode to pass through boundary surfaces or layers
US patent No 5,059,929 provides a design of dielectric resonator which is constructed by piling a plurality of plate-shaped dielectncs one on the other under pressure or adhenng respective dielectncs with an adhesive to each other so that faces thereof to which pressure is applied or faces thereof adhered to each other are parallel with an electnc field in the dominant resonance mode of the dielectric resonator The dielectnc constant in the spaces to which pressure is applied or in the spaces in which the adhesive exists is low making it difficult for an electnc field in a resonance mode other than a dominant resonance mode to pass through the spaces between the faces of the dielectncs to which pressure is applied or the faces thereof adhered to each The spunous response is thus suppressed
The disadvantages of the resonators of the said patents is that the mode separation changes with the change in the substrate thickness which does not provide versatility for choosing the substrate Further, the mode separation degrades while tuning the device
Thus there is still no dielectnc resonator available in the art which efficiently generates the dominant desirable mode by subsiding the spunous modes To fulfill this need, the present invention provides an improved dielectnc resonator which overcomes all the above limitations
OBJECTS OF THE INVENTION
The main object of the present invention is to provide a design for a dielectnc resonator for an improved mode separation in MIC (microwave integrated circuit) environment
SUMMARY OF THE INVENTION
The present invention provides an improved design for a dielectric resonator as called here "Novel Dielectric Resonator" configuration for an improved mode separation in MIC environment The obtained mode separation in present invention is the best ever reported for shielded Ring DR placed on a substrate The dominant (interested) mode in the present invention is TE01δ and the nearest spurious mode is the TM01δ or the hybnd modes To get a better mode separation we need to influence the resonance frequencies of TM01δ and hybnd modes by influencing their resonance fields respectively Accordingly, when some matenal from the nng DR is removed as proposed here (in Fig 1(c)), the hybnd fields can be influenced more and better spunous free response could be obtained The DR of the present invention shows no deterioration Q-factor of fundamental mode as companng to Ring DR in MIC environment The design gives mode separation that is higher over the nng DR even after changing the substrate thickness and the ratio of Q-factor of fundamental to nearest mode is also better over nng DR The design also exhibits much lower degradation of mode separation than the conventional nng resonator while tuning and offers versatility in choosing the substrate thickness which is limited in a nng resonator
In one embodiment the present invention provides a dielectnc resonator comprising
a conductive case having a plurality of walls which together define an inner
space,
a substrate placed at the bottom of said conductive space, and
a cyhndncal dielectnc resonator unit, mounted centrally on the substrate
having a central longitudinal axis, said unit compnsmg a dumbbell shaped
hole located centrally in the said resonator unit extending from a top to a
bottom of the resonator umt
said dumbbell shaped hole including a top 1st layer, a bottom 3rd layer and a
2nd layer sandwiched between the 1st and 3rd layers
said substrate and resonator unit enclosed inside the conductive case
In another embodiment of the present invention the 1st layer and 3rd layer have same depth
In yet another embodiment of the present invention the conductive case is cylmdncal in nature
In another embodiment of the present invention the substrate is cylmdncal in nature
In still another embodiment of the present invention the 1st layer, 2nd layer and 3rd layer are cylmdncal in nature
In yet another embodiment of the present invention the 1st layer and the 3rd layer have the same radius
In still another embodiment of the present invention the 2nd layer has a radius smaller than 1st and 3rd layers
In another embodiment of the present invention the 1st and 3rd layers are cone shaped
In still another embodiment of the present invention the 1st and 3rd layers are arc shaped
BRIEF DESCRIPTION OF THE DRAWINGS
FIG 1(a) is a cross sectional diagram of a prior art Circular rod dielectnc resonator
FIG 1(b) is a cross sectional diagram of a pnor art Ring dielectnc resonator
FIG 1(c) is a cross sectional diagram of the modified Ring resonator according to one embodiment of the present invention
FIG 2 is top view of a modified ring dielectric resonator
FIG 3 shows the mode separation (in %) of TE015 with nearest mode of modified ring resonator with the vanation of d shown in fig 1 (c) for three particular ring radius c/a=0 3, c/a=0 4, c/a=0 5
FIG 4 gives a companson of mode separation of TE018 mode with the nearest mode for the three configurations shown in Fig 1 with the vanous substrate thickness (t) (For nng c/a=0 4, for modified nng c/a=0 4, c/d=0 6)
FIG 5 shows the separation of Q-factor of TE01δ mode with the nearest mode with the vanation of substrate thickness (t) This plot has been denved from the data given in Fig 5
FIG 6 (a) Metal tuning screw with the diameter Ds for a ring DR (c/a=0 3 or 0 4)
FIG 6 (b) Metal tuning screw with the diameter Ds for a modified ring DR
FIG 7(a) The mode separations with vanous positions of tuning screw for the configurations in Fig 7 for diameter a
FIG 7(b) The mode separations with vanous positions of tuning screw for the configurations in Fig 7 for diameter 2a
FIG 8 Alternative designs of the dielectnc resonator
DESCRIPTION OF INVENTION
To fulfill the objects, the present invention provided an improved design of a dielectric resonator wherein the spurious free response of the proposed dielectric resonator is about 6% better as compared to the conventional devices
To get a better mode separation we need to influence the resonance frequencies of TM015 and hybrid modes by influencing their resonance fields respectively The electric field of TE01δ (fundamental mode) is basically confined near to circumference of dielectric resonator but rest three modes (undesirable, HEn, HE12 or TM01δ,) are basically confined at the central region of the DR By removing the plug from the central region in axial direction, we disturb the electric fields of only undesirable modes (HEn, HE12 or TM015,) and influence the resonant frequencies The resonant frequency of TE015 does not change because at the central region of DR there in no electric field due to TE01δ mode
FIG 1 shows the pnor art circular rod resonator (FIG 1(a)), a nng resonator (FIG 1(b)) and the proposed novel structure (modified nng resonator) Fig 1(c) The nng resonator as is known is a modification of circular rod resonator where the dielectnc plug is removed from the central region in axial direction, to provide an improved mode separation between the dominant TE01δ and the nearest higher mode In the modified nng resonator of the present invention, some dielectric is removed from the central region of top and some from the bottom of the ring resonator in axial direction as shown in Fig 1(c) Thus by influencing the resonance fields of this central region of top layer, the hybnd mode fields can be influenced more with lesser influence on the TE01δ mode Accordingly, when some material from the ring DR is removed as proposed here (in Fig 1(c)), the hybnd fields can be influenced more
For the given configurations in Fig 1 the dominant (interested) mode is TE015 and the nearest spunous mode is the TM01δ or the hybnd modes
Thus the structure of Fig 1 comprises three layers 1, 2 and 3 as shown in Fig 1(c) having a hole in axial direction but only the radius of top and bottom holes are same (d) and the sandwiched layer having a different hole radius (c) The depth p of top and bottom layer is the same as shown in Fig 1(c) The resonator is on substrate having ground plane, which encloses the DR The substrate could be any material with permittivity in the range of 2 2 to 9 3 with the preferred permittivity being 2 2 The material used in the present invention is RT Dunde
Fig 2 is the top view of modified ring DR
A comparative study was done on the dominant and nearest resonance modes as well as their Q-factors for the ring resonator and modified ring resonator The DR characteristic and other structural parameters for the configurations are provided in Fig 1 The substrate ground plane and the metal enclosure could me of any metal having high conductivity but are preferably gold plated (σ=4 lx 107 mhos/cm) to avoid corrosion The unloaded Q-factor of all three resonator configurations takes into consideration the loss of the ground plane, the substrate, the dielectric resonator, the side of metal enclosure and the top and bottom cover plate The mode separation between the dominant (TEois) mode and the nearest adjacent (hybnd or TM type) is defined by the following
(Equation Removed)
The resonant frequencies and Q-factors obtained in the simulations have been used for the analysis of the ring and modified ring structure The Fig 3 shows the separation of TE01δ with the nearest mode of the modified ring resonator for the vanous values of the c/d ratio for the c/a range between 0 3 to 0 5 The chosen c/a range is according to the past studies of the ring resonator where the best mode separations have been observed at c/a = 0 25 to 0 5 It is seen from Fig 3 that for vanous c/a ratios the maximum separation occurs at different c/d values At c/d=l the
modified ring resonator becomes the nng resonator Hence in the plot in Fig 4 the maximum separation of the modified nng is being compared with nng resonator (c/d=l) The modified nng resonator always shows a better mode separation over the conventional nng resonator with best improvement of 6%
In the MIC environment the thickness of the substrate is an important design issue Hence, the analysis has been earned out for vanous thickness of the substrate The influence of substrate thickness (expressed here by t/1) on mode separation for the three configurations is shown in Fig 4 It is evident that (l) the mode separations monotomcally increase with the thickness of the substrate for all the three configurations, (n) the modified nng DR always gives the best mode separation compared to nng DR and circular rod for vanous t/1 ratios A simultaneous evaluation of a Q-factor for these configurations at the chosen parameters (as m Fig 4), reveals that the Q-factor for TE018 mode do not degrade for any of the configurations However a more remarkable observation is about the Q-factors of the nearest higher (and potentially interfenng mode with the dominant) modes Clearest for modified nng DR do not vary with substrate thickness, but for the nng it undergoes a peak at t/l=0 4 while for a rod DR it monotomcally increases This behavior for vanous substrate thickness implies that the energy filling factor for the interfenng modes (I) increases undesirably for a rod resonator, (n) needs to be optimized for a nng resonator, (m) do not influence the modified nng resonator This result renders versatility to the modified ring DR configuration, in respect to choice of substrate thickness and may be interest in optimized filter designs
The proposed modified nng resonator provides an improved mode separation, to an extent of 6% over a corresponding nng DR configuration in a MIC environment A further advantage of the proposed modified nng DR is its versatility in respect to substrate thickness, for an optimized mode separation design, which for a circular rod or nng DR is not available
A tuning element is an essential structure in a DR configuration, to compensate the shift in resonance frequencies, which appear due to the allowed fabrication tolerances, operating temperature variations and also to accommodate for the inevitable errors due to the theoretical predictions The tunability performance for the proposed configurations has been examined not alone for the range of resonant frequencies the tuning can provide, but also for its influence on the mode separations This is considered important, since, a tuning metal screw tends to degrade the spurious free response The tuning structure for nng DR and modified nng DR are presented in Fig 6 The diameter of tuning screw is kept at Ds=a or Ds=2a Evaluations for the resonant frequencies and Q-factors for the TE01δ mode with the gap dimension g were done The tunability is determined from where the frequency without tuner corresponds to maximum g value

(Equation Removed)
The tuning range with the larger diameter screw, Ds=2a, is higher for all the configurations Significantly, for the case of modified nng DR configuration, where a maximum mode separation improvement had been observed the tuning range (6 079%) is maintained close to comparative nng DR tuning range (6 335%) This observation ensures that mode separation improvement obtained in the proposed modified nng DR, is not at the cost of tunability On considenng results of the studies done with respect to tuning effects, it was observed that while tuning ranges are generally higher for larger diameter screw, the degradation in Q-factors is also higher However, the Q-factors in general remain higher for the modified nng case over the comparative nng DR configuration, and more so when Ds=a
A more important object of this tunability study is regarding the behaviour of mode separation with tuning The plots (Fig 7) show that in general the mode separations reduce with tuning for all the configurations, though to a lesser extent for the smaller

diameter screw Ds=a (Fig 7(a)) Further in Fig 7(a), it may be seen that degradation in mode separation with reducing g (or increasing tuning) is far lesser for the modified nng DR than a comparative nng DR The extent of degradation in mode separation, for the available tuning range has been determined from these plots (Fig 7(a) & (b)) using a following definition
(Equation Removed)
Sgmax is maximum mode separation (at max value of g (without tuning screw)) and Sgmin is minimum mode separation (at mm value of available g)]
Obviously, a smaller SD signifies a lower degradation and hence a better spunous free response over the tunabihty range as may be provided in a given configuration The modified nng DR, provides a lesser degradation in mode separation than a comparative nng DR The degradation is found to be least (0 285) for the modified nng DR configuration for Ds=a, where tunabihty is 1 622% In a comparative nng DR, the degradation SD increases twofold (0 56) with only a slightly higher tuning range (2 27%) It may also be noted that a higher tunabihty range can be obtained though at the cost of higher degradation of mode separation for the case when screw Ds=2a
The pnnciple used in the present invention could also be applied for designing alternative designs of the dielectnc resonator to provide better spurious free response Fig 8a shows an arc shaped modified nng resonator and Fig 8b shows a cone shaped modified nng resonator The following table-1 shows the mode separations of TE015 mode with the nearest modes for the nng DR and modified nng DR of arc and cone shapes For c/a = 0 40 and k = 0 75 and k = 0 075 It can be easily seen that the modified nng resonator of the arc and cone types provide better mode separation
(Table Removed)
The mode separation obtained in present invention is the best ever reported for shielded Ring DR placed on a substrate
ADVANTAGES OF THE PRESENT INVENTION
1 The present invention provides a design for a dielectric resonator which provides
6% in absolute terms and 12-15% in comparative values improved mode
separation as compared with the conventional devices
2 The novel design shows no deterioration Q-factor of fundamental mode as
comparing to Ring DR in MIC environment
3 The present invention provides a modified design of the dielectric resonator,
wherein the mode separation is still higher over the ring DR even after changing
the substrate thickness and the ratio of Q-factor of fundamental to nearest mode is
also better over ring DR
4 The filling factor of the interfering modes does not influence the modified nng
resonator for various thickness of the substrate
5 The modified design exhibits much lower degradation of mode separation than
the conventional ring resonator while tuning
6 Another advantage of the present is that the modified dielectric resonator offers
versatility in choosing the substrate thickness.

We Claims :-
1 A dielectnc resonator compnsmg
a conductive case having a plurality of walls which together define an inner
space,
a substrate placed at the bottom of said conductive space, and
a cyhndncal dielectnc resonator unit, mounted centrally on the substrate
having a central longitudinal axis, said unit compnsmg a dumbbell shaped
hole located centrally in the said resonator unit extending from a top to a
bottom of the resonator unit
said dumbbell shaped hole including a top 1st layer, a bottom 3rd layer and a
2nd layer sandwiched between the 1st and 3rd layers
said substrate and resonator unit enclosed inside the conductive case
2 The dielectnc resonator as claimed in claim 1, wherein the Vx layer and 3rd layer have same depth
3 The dielectnc resonator as claimed in claim 1 and 2, wherein the conductive case is cyhndncal in nature
4 The dielectnc resonator as claimed in claim 1 to 3, wherein the substrate is cyhndncal in nature
5 The dielectnc resonator as claimed in claims 1 to 4, wherein the 1st layer, 2nd layer and 3rd layer are cyhndncal in nature
6 The dielectnc resonator as claimed in claims 1 to 5, wherein the 1st layer and the 3rd layer have the same radius
7 The dielectnc resonator as claimed in claims 1 to 6, wherein the 2nd layer has a radius smaller than 1st and 3rd layers
8 The dielectnc resonator as claimed in claim 1, wherein the 1st and 3rd layers are cone shaped
9 The dielectnc resonator as claimed in claim 1, wherein the 1st and 3rd layers are arc shaped

10 The dielectric resonator as claimed in claim 1, wherein the conductive casing is made of a metal
11 The dielectnc resonator as claimed in claim 10, wherein the conductive casing is gold plated
12 A dielectnc resonator substantially as herein descnbed with reference to the accompanying drawings.