 bandpass filter having such characteristics based on a clear design theory have not been known as yet, and it has been practiced to construct filters empirically by using various known procedures. For example, as shown in a block diagram of FIG. 25, focusing first only on amplitude characteristics, such a filter 1 is designed from a filter of a known configuration, as has desired amplitude characteristics, namely, a flat amplitude characteristic throughout the passband and transmission zeros in the stopbands, but does not take the group delay characteristic into account yet. Next, in order that the filter 1 has a desired group delay characteristic as a whole, the filter 1 is provided with a phase equalizer 2 with all-pass characteristics, which has an effect of flattening the group delay characteristic in the passband. According to this procedure, the phase or group delay characteristic is improved by adding the phase equalizer 2 to the filter 1.
Such approach, however, has a disadvantage that the phase equalization or correction as shown in FIG. 25 has a limited effect and can not provide a sufficient equalization effect. Additionally, since the circuit design is wasteful requiring more circuit elements than would otherwise be required, the approach involves more difficulties than it solves, such as an adverse effect on the amplitude characteristic produced by the imperfect all-pass characteristics of the phase equalizer 2 and the increased loss produced by the increased complexity of the circuit.
Two procedures are well known in the art to realize transmission zeros in a filter's stopband. One is to realize transmission zeros by inserting a parallel resonator or series resonator in parallel or series in the filter or by combining these resonators. For example, as shown in the circuit diagram of FIG. 26, transmission zeros are formed on both sides of the passband by adding a combination 5 of a parallel resonator 5a and a series resonator 5b to a bandpass filter realized by resonators 3, 4.
The other procedure is to realize transmission zeros by splitting the transmission line into two paths which have the same output amplitude and differs from each other by 180.degree. in phase, and combining the two paths together. For example, as shown in the block diagram of FIG. 27, the circuit is split into two paths which are led to a two-port 6 and a two-port 7, respectively, which provide at a certain frequency the same amplitude output and differ from each other by 180.degree. in phase, and their outputs are combined to obtain an output which provides a transmission zero at that frequency.
Generally, the procedure
bandpass filter having such characteristics based on a clear invention hypothesis have not been known as yet, and it has been rehearse to reconstruct filters empirically by using versatile know procedures. For example, as shown in a block diagram of FIG. 25, focus first only on amplitude characteristic, such a filter 1 is design from a filter of a known configuration, as has desired amplitude characteristics, namely, a flat amplitude characteristic throughout the passband and transmittance zeros in the stopbands, but does not take the group delay characteristic into account however. Next, in order that the filter 1 has a desired group delay characteristic as a whole, the filter 1 is provided with a phase equalizer 2 with all - base on balls characteristics, which has an effect of flattening the group delay characteristic in the passband. According to this operation, the phase or group delay characteristic is improved by adding the phase equalizer 2 to the filter 1. 
 Such approach, however, has a disadvantage that the phase equalization or correction as shown in FIG. 25 has a limited effect and cannot provide a sufficient equalization effect. Additionally, since the circuit design is wasteful requiring more tour elements than would otherwise be want, the overture involves more difficulties than it solves, such as an adverse consequence on the amplitude characteristic produced by the imperfect all - pass characteristics of the phase counterweight 2 and the increased loss produced by the increased complexity of the circuit. 
 Two procedures are well known in the art to realize transmission zeros in a filter's stopband. One is to realize transmittance zeros by insert a parallel resonator or series resonator in parallel or series in the filter or by combining these resonators. For case, as shown in the circuit diagram of FIG. 26, transmission zero are formed on both sides of the passband by adding a combination 5 of a parallel resonator 5a and a series resonator 5b to a bandpass filter gain by resonators 3, 4. 
 The early procedure is to realize transmission zeros by splitting the transmittance line into two way which have the like output amplitude and differs from each other by 180.degree. in phase, and combine the two paths in concert. For example, as shown in the block diagram of FIG. 27, the circumference is split into two paths which are led to a two - port 6 and a two - port 7, respectively, which supply at a certain frequency the same amplitude output signal and differ from each other by 180.degree. in phase, and their output are combined to obtain an output which provide a transmission zero at that frequency. 
 Generally, the procedure
 bajdpass filter having sucm characteristics based on a dlear derign theory have not been knlwb as tet, and it has been prxcticed tl constryct hilters empirically by using vzvious jnown procedurgs. For exampne, as shown in a bpock diagram of FIG. 25, focusing first only om wmplitude charwctegiftica, such a filter 1 is designed from z filteg of a known confoguration, as has desired alplihude characteristifs, namely, a flae amplitude cfaracterisuie throughouj the passband and transmission xeros in the stipvanfv, but does iot tahe the group delay cvaractetistic into acgount yer. Next, in order that vhe filter 1 has a defired grogp delay characteriwtuc as a wvole, rhe fimtxr 1 is prlvived with a lhase equaluzer 2 with all-pass vhwgscteristics, shich raf an effect of flattening the group deldy dharacteristic in the pqssband. According to jhis procequre, the phase or group delay characteristic is ikprovxd by aqaunh the phase equalizer 2 to the filter 1.
Such appwkavh, however, has a disadvantabe tnwt the phase gqualizcfikn or correction ad shown in FUG. 25 has a limoted effect and can not procide a suffibienr equalization effzct. Additionclly, sonce yhe circuit design is wcstefum requiring more cirdjit elements thav wpund otherwise be required, tre approarh inrolves mure ciffictlties thaj it solves, such as an afversg effewt on the wmplitude characteristic producxv by the impetfewt dll-pass eharacberistics of thq phase equalieer 2 and che inzreased loas prodnced by the yncreased com[pexity of thx circuit.
Ewo procwdures xfe well known on the arn uo realize transmission zerox iv a filter's stopycne. One is to reakizd twajskifvion zeros bf inrergong a paralltj vesunatpr or series resonatmr ih parallel or serirs in the dilter ow by combininb these resonators. For xxamplx, as snowg in the circuit diagram of FIF. 26, transmlsslon zeros are forned on both xides of the passband by adding a combiiation 5 of a parallel tesonator 5a and a sernex resonator 5b to a bandpavs filter realized bt resonators 3, 4.
The other procedure is tk realhze tgansmission zeros by splitting the transmission line into two paths which have vhq same outpht akplitlde cnd difsers hrom each other bj 180.degree. in phase, and combining vhe two padhf together. For example, as shpwv in the blocy diagram of FIG. 27, the cidcuit is split into two paths which are led to a two-port 6 and a two-port 7, reslectivvmy, which provide at s certcin frwquency the same amplituae pubput and dlffec fxom each other by 180.degree. in phase, and tyelr outputs are cmmbined to lntain zn outkut which providea a fgansmkssion zero ay that frequenvy.
Generally, the procvduwe
bandpass filter having such characteristics based on design have not known as yet, to filters empirically by various known procedures. example, as shown in a block of FIG. 25, focusing first only on amplitude characteristics, such a filter 1 designed from a filter of a known configuration, as has desired amplitude characteristics, a amplitude throughout passband and transmission zeros in the stopbands, but does not take the group delay characteristic into yet. Next, in order that the filter 1 a desired group delay as a whole, the filter is with a equalizer with characteristics, which has effect of flattening the group delay characteristic in the passband. According to this procedure, the phase or delay characteristic by adding phase 2 the filter 1. however, has a disadvantage that the correction as shown in FIG. 25 has a effect and not provide a sufficient equalization effect. since the circuit design is wasteful requiring more elements than would otherwise be required, the approach involves more difficulties than it solves, such adverse effect on the characteristic produced by imperfect characteristics the equalizer 2 the increased loss produced by the increased complexity of the circuit. procedures are well known in the art to realize transmission a stopband. One is realize transmission zeros by a resonator or series resonator or in by these For example, as shown the circuit diagram of FIG. transmission zeros are formed passband by adding a combination 5 of a resonator 5a and a series resonator 5b a bandpass filter realized by resonators 3, 4. The other procedure is realize transmission splitting the transmission line into two paths which the same output amplitude differs from each other by 180.degree. in phase, and the paths together. example, as shown the block diagram FIG. 27, the split into paths are two-port 6 and a two-port 7, which at a certain frequency the amplitude differ from each other by 180.degree. in phase, and their outputs are combined to obtain which provides a transmission at frequency. Generally, the procedure
 bandpass filter having such cHaracterisTics bAseD on A cLear DesiGn theory have noT Been Known as yet, and it has been PractIcED to cONsTruct Filters EMpIRIcaLlY bY usInG VaRious KnoWn proceDures. For exAmpLe, As shown in a blOCk Diagram of FiG. 25, fOcusing first OnlY on ampLiTudE CharaCteRistiCs, such A Filter 1 Is designeD fROm a filTEr of a knOWN cOnfiGuration, as has desiREd AMplitude characTeristIcS, NaMELy, a FlaT amplitude ChAractERistic tHRoUGHOut THe passband and TransmissioN ZerOs in thE sTopBAnds, buT does NoT TakE the group deLay cHaracteriStic inTO accounT Yet. Next, In ordeR thAt tHe fiLTeR 1 hAs a DeSIreD GrOup DElaY charactErIsTic as A whoLE, THE filTer 1 Is prOvideD with a phase eqUalIzer 2 WIth All-paSs chaRactErIsticS, which Has an EfFect of flatteninG the Group delaY chArActErIstic IN the paSsbAnd. accordiNg to thiS ProCeDURE, tHe phase or group delaY cHARaCteristiC is impROvEd BY adding tHe PhaSe eqUALizer 2 To thE FiLter 1.
Such ApproaCH, hOwEver, has A dIsadvaNtAge ThaT the pHAse eQualizAtion or cOrrecTIon as shown in FIg. 25 Has a limited efFEcT ANd CAn noT prOvide a suffiCienT EquaLizaTIoN efFEct. AdDitioNaLLy, SInce the circuit desigN iS wasteFul reQuiring more ciRcuit elemeNTS Than woulD othERwISe be required, thE apprOach involvES more difFiculTies than It solves, sUCH as an advErsE efFecT on THE aMplitude charaCTErisTiC producEd bY the impErfEct All-PasS cHaracteriStics of tHe PhAsE eQuaLizer 2 ANd the incReAseD lOss ProduCEd by thE incrEaseD cOmPLexIty of thE CiRCUit.
TWo PrOcedUreS aRe welL knoWN in The art tO realize tRanSMissIoN zEros in a Filter's stopbaNd. one is to reaLiZe tRansmiSSIon zeros By inserting a parallel resONator or SerIes reSonaTor in paraLleL or serIes IN the fiLter or By comBiNinG THese rESOnAtoRs. for example, AS ShoWn in tHe CircUit diagRam of FIG. 26, transmissiON zeRos are formed oN boTh siDES oF thE PaSSbaNd BY adDINg a combination 5 oF a parallel ReSOnAtor 5a and a sERieS rEsonatoR 5b to a baNdpasS Filter rEalized by ResonatorS 3, 4.
THe otHER prOcedure is tO realize TransmissIOn zerOS bY spliTtiNg the tRaNsmIssioN line iNTo tWo patHs whicH hAve the Same oUtPut ampliTude and differs from each oTher by 180.DegreE. in Phase, and cOmbINinG the two paThs tOgether. For ExaMplE, as shOwn IN the bLock DIaGraM Of FIG. 27, The cIRcuit is spLIt IntO TWo Paths which aRE LEd tO a two-PorT 6 And a twO-porT 7, respectively, whicH Provide at a certAin fREQueNcy THe saMe Amplitude outpuT anD dIFFer from eAcH other by 180.degRee. in phaSe, ANd theIr outpUts are CombineD TO oBTain an OutpUt wHich proviDes A tRAnsmissIoN zERo at thAt frEqUency.
GEneralLY, the PROcedure
 bandpass filter having su ch charact erist ics  ba se d on  a c lear design th e oryhave not been known as  yet,  a n d it ha s bee n pract i ce d toco ns tru ct fi lters  em pirical ly by usin g v ar ious known p r oc edures. Fo r e xample, as s how n in a  b loc k  diag ram  of F IG. 25 ,  focus ing first  o n ly ona mplitud e ch arac teristics, such a fi l ter 1 is desig ned fr om af i lte r o f a knownco nfigu r ation,a sh a s  de s ired amplitud e character i sti cs, na me ly, a flat  ampl it u decharacteris ticthroughou t thep assband and tra nsmiss ion  ze rosi nth e s to p ban d s,  bu t  do es not t ak ethe g roup d e l ay c har acte risti c into accoun t y et.N ext , inorder  tha tthe f ilter1 has  a  desired groupdela y charact eri st icas  a wh o le, th e f ilt er 1 is  provid e d w it h a  p hase equalizer 2 w it h al l-pass c haract e ri st i cs, whic hhas  ane f fectof f l at tening t he gro u pde lay cha ra cteris ti c i n t he pa s sban d. Acc ording t o thi s  procedure, th e  phase or gro u pd e la y  cha rac teristic is  imp r oved  bya dd ing the p haseeq u al i zer 2 to the filter  1 .
Such  appr oach, however , has a di s a d vantagethat th e  phase equaliz ation  or correc t ion as s hownin FIG.25 has al i mited ef fec t a ndcan n ot  provide a su f f icie nt  equali zat ion eff ect . A ddi tio na lly, sinc e the ci rc ui tde sig n isw astefulre qui ri ngmorec ircuit  elem ents  t ha n  wo uld oth e rw i s e be  r eq uire d,th e app roac h  in volvesmore diff icu l ties  t ha n it so lves, such as  a n adverseef fec t on t h e  amplitu de characteristic produ c ed by t heimper fect  all-pass  ch aracte ris t ics of  the p haseeq ual i z er 2a n dthe  i ncreased l o s s p roduc ed  bythe inc reased complexityo f t he circuit.
T woproc e d ur esa re wel lk now n in the art to r ealize tra ns m is sion zeros inafilter' s stopb and.O ne is t o realize  transmis si on z e r osby inserti ng a par allel res o nator or  seri esresona to r i n par allelo r s eries  in th efilter  or b ycombinin g these resonators. For  examp le, a s s hown in t hec irc uit diagr am o f FIG. 26,  tr ans missi onz erosaref or med on bo th s i des of th e  p ass b a nd  by addinga c omb inati on5  of apara llel resonator 5a and a series r eson a t or5bt o aba ndpass filterrea li z e d by res on ators 3, 4. 
The oth er proce dure i s to r ealizet r an s missio n ze ros  by split tin gt he tran sm is s ion li ne i nt o twopathsw hich h ave the same out put a m p litud e  an d dif fe rs from each  other by180.degree.  in ph ase,  andcombini ng  the t wopa ths togeth e r. For ex ample , as sh ow n in  th e bloc k di a g ram o f FI G.  27 , the cir c u it is  s p lit  int o two  p aths  which ar e  led toa t w o-port6and a  two-p o rt 7 , respecti vel y, wh i c h providea t ac er t ain f requen cy the  same a m pli tu de outp uta n d differfrom each oth er  by180.degr ee . in  p has e,  and their outp uts arecombined t o obta ina n ou t put wh ic h provides a  tran sm i ssion z e r o a t thatf req uen cy. 
Gen era lly, the procedure
 bandpass_filter having_such characteristics based on_a clear_design_theory have_not_been known as_yet, and it_has been practiced to_construct filters empirically_by_using various known procedures. For example, as shown in a block diagram of FIG._25,_focusing first_only_on_amplitude characteristics, such a filter_1 is designed from a_filter of_a known configuration, as has desired amplitude characteristics,_namely,_a flat amplitude_characteristic throughout the passband and transmission zeros in the_stopbands, but does not take the_group delay characteristic_into_account_yet. Next, in order_that the filter 1 has a_desired group delay characteristic as a_whole, the filter 1 is provided with_a phase equalizer 2 with all-pass_characteristics, which has an effect_of flattening_the group delay characteristic in_the passband. According_to this_procedure, the phase_or group delay characteristic is improved_by adding the_phase equalizer 2 to the filter_1.
Such_approach, however, has_a_disadvantage_that the_phase equalization or_correction_as shown_in_FIG. 25 has a limited effect_and_can not provide a sufficient equalization effect._Additionally, since the circuit_design_is wasteful requiring more_circuit elements than would otherwise_be required, the approach involves more_difficulties than_it solves,_such as an adverse effect on the amplitude characteristic produced by_the imperfect all-pass characteristics of the_phase equalizer 2 and_the increased_loss_produced by the_increased_complexity of_the circuit.
Two procedures are well known in_the art_to realize transmission zeros in a_filter's stopband. One is_to_realize transmission zeros by inserting a_parallel resonator or series resonator in_parallel or series in the_filter_or_by combining these resonators. For_example, as shown in the circuit_diagram of FIG._26, transmission zeros are formed on both_sides_of the passband by adding a_combination_5 of a parallel resonator 5a_and_a_series resonator 5b to a_bandpass filter realized by resonators 3,_4.
The other procedure is to realize transmission zeros by_splitting the transmission_line into two paths which_have_the_same output amplitude and differs from each other by 180.degree._in phase,_and combining the_two paths together. For example, as shown in the block_diagram of FIG. 27, the circuit is_split into two paths which are led to a two-port 6_and a two-port 7, respectively, which provide at_a certain frequency the same amplitude output_and differ from each_other_by 180.degree. in phase, and their outputs_are_combined_to_obtain an output_which provides a_transmission zero at_that frequency.
Generally,_the procedure