Design Methodologies for Optimizing the Electrical and Mechanical Performances of Evanescent Mode Ridge Waveguide Filters

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P. Sotoa, D. de Llanosa, V. E. Boriaa, E. Tarína, S. Cogollosa, M. Taronchera, B. Gimenob a Instituto de Telecomunicaciones y Aplicaciones Multimedia, Universidad Politécnica de Valencia, Figure 1. Symmetric in (a) and asymmetric in (b) evanescent mode ridge waveguide filter topologies under 8G Building - access D - Camino de Vera s/n - 46022 Valencia (Spain) consideration, and significant physical dimensions. b Instituto de Ciencias de los Materiales, Universidad de Valencia, Dr. Moliner, 50 – 46100 Burjasot, Valencia (Spain) Corresponding author: [email protected] have recently been presented to implement inserting shunt capacitive elements through transmission zeros that further improve the skirt the housing. The below cut-off waveguide sec- selectivity [9]. On the other hand, a wide range tions spacing the capacitive elements can be of topological variations have been proposed modeled as impedance inverters with free shunt to improve a particular filter feature, mainly the inductances. The inserted shunt capacitances stopband extent [10]-[12] and/or the filter total combined with the free shunt inductances of the length [13, 14]. But in most cases, the improve- non-propagating housing sections provide the ment in these features is obtained by sacrifying filter resonances, obtaining a bandpass behavior insertion loss and power-handling capabilities, for the whole structure [5]. and usually requires harder and more expen- sive manufacture procedures. In [15] different This paper is focused on conventional rectan- ridge configurations in rectangular and circular gular waveguide evanescent mode filters with Abstract ogy, and appropriately design it to obtain the waveguides are compared with regard to the rectangular cross-section metal inserts as capac- best performance trade-off in order to fulfill the fundamental mode attenuation coefficient and itive elements (see Fig. 1). The centered symmet- In this paper, the trade-offs between out-of- specifications. maximum transversal electric field. Nonethe- ric configuration shown in Fig. 1a, with ridges in band performance, filter length, power-handling less, this study has been carried out considering both the upper and the lower housing walls, as capability and insertion loss of both symmetric Evanescent mode ridge waveguide filters, origi- only the cross-section of the ridge waveguide well as the centered asymmetric configuration, and asymmetric evanescent mode ridge rec- nally proposed in [4, 5] and refined in [6], exhibit and therefore cannot take into account effects with ridges only in the upper wall (see Fig. 1b), tangular waveguide filters are investigated. As a many attractive features. They provide an excel- related to the filtering structure (for instance, will be considered and compared in order to es- result, clear design methodologies for optimiz- lent out-of-band performance with an inherent the ridge lengths, the field distribution along tablish the more appropriate one to refine each ing such performances are proposed. The devel- wide stopband and sharp selectivity. In addition, the resonators or the reactive field in the close filter performance. For the sake of simplicity in oped methodologies are then applied to design they are very compact in comparison with other region to the ridges). the parametric analysis of the structure, all the several evanescent-mode filters, and a complete waveguide filter types. The foremost weakness- metal inserts or ridges are considered to be cen- performance analysis of the symmetric and es come from insertion loss and power consid- In spite of the great practical interest of these tered and to have the same width w and height asymmetric structures is performed. From the erations due to their small size. Although they types of structures, there is a lack of studies on h. In addition, the housing width ah and height performance analysis results, the designer can benefit from the excellent insertion loss and its balance between insertion loss, power-han- bh are kept constant throughout all the structure. choose the more appropriate filter topology and power-handling capability innate to waveguide dling, stopband performance and filter length. design strategy to satisfy the prescribed set of technology, and they have reasonable figures A preliminary study has been recently presented Since the evanescent mode filters under con- specifications. in these parameters in comparison with other in [16], focused on symmetric ridge waveguide sideration can be easily decomposed into uni- waveguide filter types [1], evanescent mode filters. In this paper we perform a more detailed form waveguide sections and planar waveguide Keywords: Waveguide Filters, Design Methodol- ridge filters cannot rival with above-cutoff rec- performance analysis, thus clearer design strate- discontinuities, the accuracy and efficiency of ogy, Computer-Aided Design, Modal Methods, tangular and circular waveguide cavity filters. gies will be proposed. Additionally, the asymmet- modal analysis methods can be exploited [17]. Ridge Waveguide, Bandpass Filters, Losses, Mi- As a result, they are not well-suited to imple- ric configuration is considered and compared To obtain the modal spectrum of the ridge crowave Power Transmission ment narrowband channel filters where a high with the symmetric one. From this paper, the waveguides, an implementation of the BI-RME quality factor Q is required. Nevertheless, eva- designer can identify the more appropriate filter method has been used [18]. The structure de- nescent mode ridge waveguide filters are a suit- topology (symmetric or asymmetric) as well as sign is performed by the systematic decomposi- 1. Introduction able choice for moderate and wideband filters the design strategy to satisfy the prescribed set tion procedure proposed in [19]. To compute the when compact size and excellent out-of-band of electrical and mechanical filter specifications. losses and the electric field of the designed filter, Design requirements for passive waveguide response are involved. For instance, they can be the Ansoft HFSS simulator has been used [20]. filters in modern telecommunication systems used as preselector filters in input and output for both space and terrestrial applications are multiplexers, particularly in satellite applications 2. Structure Description. Analysis becoming more and more restrictive. Low in- where size is a major concern. and Design Techniques 3. Parametric Analysis sertion loss, compact size, high skirt selectivity, wide spurious-free stopband and suitable A high research effort has been devoted during In waveguide technology, an evanescent mode To design an evanescent mode filter, a design power-handling capability are usually required the past in order to improve and take profit of filter is implemented in a hollow below cut-off parameter for each resonator and impedance in- [1]. These increasing demands have stimulated the excellent properties of evanescent mode waveguide commonly referred to as housing, verter is required in order to recover an all-pole the advent and refinement of different types of ridge filters. They have been used to obtain all- which is ended with standard propagating ideal response in the passband. These roles have filters during the last decades [2, 3]. The designer pole bandpass and quasi-lowpass responses of waveguide access ports. The energy transmis- been assigned to the ridge waveguide section must choose a suitable filter class and topol- almost any width [7, 8]. Novel configurations sion between both ports is accomplished by lengths ti and the below-cutoff waveguide sec-

116 ISSN 1889-8297 / Waves · 2010 · year 2 Waves · 2010 · year 2 / ISSN 1889-8297 117 tion lengths li (see Fig. 1), respectively. A modi- collected in Fig. 2 are also very important for the negligible for w < 0.5wopt and a dramatic increase the multipactor effect under the extremely low fication to these parameters does not require filter performances, particularly the out-of-band is observed for w > 0.65w (see Fig. 3a and 3c). pressure conditions in space missions. Hence, to opt The maximum recomputing the waveguide modes, and hence response. The dimensions of the filters designed To reduce the insertion loss it is highly recom- derive the power-handling capability, the maxi- electric field the filter design procedure is sped up. As a re- in section 5 reveal that Fig. 2a is the typical mo- mended to keep w < 0.65w . mum electric field inside the filter has been com- opt depends sult, the housing dimensions ah, bh and the ridge dal chart to be used for the ridges of symmetric puted for a 1W input excitation. From this value, height h and width w are free design parameters evanescent mode filters. On the contrary, Fig. 2b Losses also rise with the ridge depth h, and their the maximum power at the filter input to avoid exponentially that must be previously fixed. They should be shows to be very appropriate for the asymmetric change rate increases with the housing height dielectric breakdown and multipactor can be on the ridge used to obtain the trade-off between insertion filter ridge choice, since the asymmetric ridge (see Fig. 3b and 3d). As a result, the effect of the computed [15, 21]. waveguide loss, power-handling, length and out-of-band modal spectrum can be extracted from the spec- ridge depth h in the insertion loss figure is more gap performance required by the filter design speci- trum of a symmetric double-ridge waveguide important for asymmetric filters. From an inser- The results of the parametric analysis, not shown

fications. with double height and the same w, h and ah. tion loss point of view, particularly for asymmet- for the sake of space, reveal that the maximum ric filters, a small value ofh should be chosen. electric field depends exponentially on the ridge

A parametric analysis has been carried out to The next subsections describe the main conclu- waveguide gap g (g = bh–2h for symmetric filters

find out the effect of such free design param- sions of the parametric analysis carried out for The free design parameter with the greatest in- and g = bh–h for the asymmetric configuration). eters in the filter performances. An ideal 2-pole each particular performance. fluence in the filter insertion loss is the housing Therefore, the filter power-handling capability is

Chebychev bandpass transfer function centered width ah. As expected, a wider housing provides maximized by increasing the housing height bh

at 7 GHz, with 280 MHz bandwidth and 15 dB re- 3.1 Insertion Loss lower losses in both symmetric and asymmetric and by reducing the ridge depth h for a bh set. turn loss has been chosen as reference response. Assuming vacuum for the dielectric material, configurations. To optimize losses it is of para- A wider housing is thus preferred since it allows First, an evanescent mode waveguide filter with the filter losses are only due to conductor ohmic mount importance to take the wider housing to use less deep ridges, and the ridge gap can

WR137 standard waveguide access ports has losses. For waveguide filters with good conduc- that allows to satisfy the remaining filter speci- be increased. Moreover, Emax can be slightly re-

been designed to obtain this response. Then, tors, nonetheless, the losses are very low and fications. The housing height bh, on the other duced by means of a wider ridge. Finally, asym- the structure free design parameters have been their computation is not a simple task. The effect hand, is not relevant provided that the housing metric filters can provide higher ridge gaps and modified over a wide range, taking into account of the return loss ripple in the insertion loss can is high enough (especially in symmetric filters). therefore withstands higher input power levels. manufacture constraints. For each value set, the be significant, and it can hide small variations Anyway, in order to reduce the filter losses a reference response was recovered by using the due to the ohmic losses required to extract the higher housing height normally proves to be 3.3 Filter Length

resonator and housing section lengths li and ti. parametric analysis data. To overcome these more appropriate. The filter length information has been summa- The resulting filter is evaluated in terms of length, difficulties, a metal conductor with moderate rized in Fig. 3 through marks. For usual filter di- spurious-free band, insertion loss and power- conductivity has been considered, and the de- 3.2 Power-Handling Capability mensions, the inverter (i.e. housing section be- handling capability. As a result, several tables viations caused by S11 ≠ 0 are compensated by In payload microwave passive devices, the pow- tween ridges) lengths are the main part of the and graphs relating the free design parameters considering the following modified insertion er handling capability is usually restricted by the filter length. Although a wider housing provides and the filter performances have been obtained. loss figure: dielectric breakdown electric field, as well as by shorter resonators as the ridge cut-off frequency

In addition, the modal spectrum of the ridge 2 2 I ̑.L.(dB) = -10log10(|S11| +|S21| ) waveguides has also been characterized. As shown in Fig. 2, an increase in the ridge depth h [1] reduces the fundamental mode cutoff frequency, whereas the cutoff frequencies of the other which represents the ratio of the total input plotted modes are hardly changed. Therefore, power to the power not dissipated inside the fil- the monomode operating region is increased. ter. Finally, to obtain a more realistic value, this Concerning the ridge width w, a parabolic vari- figure is scaled to copper conductors by correct- ation is observed in the fundamental mode cut- ing the material conductivity factor. off wavelength, with a maximum value at w =

wopt, which is around 0.35ah ~ 0.45ah depending Concerning the ridge width, the parametric

on the housing width to height ratio ah/bh. The analysis for both symmetric and asymmetric cutoff frequencies of the higher-order modes configurations reveals that the losses increase is

Figure 3. Modified insertion loss for copper symmetric evanescent mode filters (in (a),(b)) and for copper asymmetric evanescent mode filters (in (c),(d)) in terms of the structure free design parameters , , and . Marks rep- Figure 2. Normalized cutoff wavenumbers for double-ridge waveguides in terms of w/ah and h/bh. Case w h ah bh resent housing length ( =15 mm, =17.5 mm, =20 mm, +=22.5 mm, +=25 mm, = 27.5 mm,x=30 mm; =32.5 ah=1.4bh in (a) and ah=0.7bh in (b). The first mode of each symmetry class (even(e)/odd(o)) and the second mode of □ ◊ ○ mm). All legend dimensions in mm. the TE10-like symmetry class, TEoe,2, are plotted.

118 ISSN 1889-8297 / Waves · 2010 · year 2 Waves · 2010 · year 2 / ISSN 1889-8297 119 is decreased, the inverter lengths are dramatical- must limit the housing height to avoid TE01 re- ridge width w. However, they have the opposite MHz bandwidth centered at 10 GHz has been ly increased because the evanescent TE mode lated spikes. interest regarding the housing width a and the considered. The filter access ports were standard The two pair 10 h Asymmetric of strategies approaches cut-off and longer housing sections ridge height h. Sometimes a suitable trade-off WR-90 waveguides. filters provide are required to implement the same coupling. between these dimensions must be found to ful- obtained have The global result is a significant filter enlarge- 4. Design Strategies fill the filter specs. The first pair of filters, denoted now onward as better the opposite ment. Hence, a narrower housing must be taken filters A, have been designed to reduce the fil- insertion loss interest to reduce the filter length. From the parametric analysis can be concluded To conclude this section, it is worth to remark ter losses with a rejection greater than 40 dB and much regarding the that the filter performances are improved us- that several techniques have been proposed in in a stopband that ranges from 10.5 GHz to 17 better power- housing width The remaining free design parameters are less ing the highest housing able to satisfy the out- the literature to implement narrower housings, GHz. Filters B have been optimized to improve handling

and the ridge important than the housing width to the total of-band spec. Hence, according to (3), bh will be such as the stepped-wall approach [22] or the the power-handling capability with the same capability for

height filter length. Anyway, a higher housing height always fixed tob h,max. ridge transformer [23]. At expense of insertion stopband specification of filters A. On the other the same set of should be chosen to obtain a shorter structure. loss and power-handling, these techniques can hand, the symmetric and asymmetric filters C specifications Regarding the ridge dimensions, to reduce the To reduce the filter losses and increase its pow- improve the filter spurious-free band and, for have been designed to reduce the structure filter length it is convenient to increase the ridge er-handling capability the widest housing must high order filters, they can also provide shorter length without spurious passbands up to 20

width w (up to wopt since for w > wopt the filter be chosen. The housing width is obtained by structures. Although these topologies are out of GHz. The goal of filters D was to optimize the length reduction is insignificant) and then in- starting from (2) with x = 0.15 and increasing the scope of this paper, most of the procedures stopband extent.

crease their depth h. ah while the length and the out-of-band speci- and conclusions presented herein can be easily fications are fulfilled. In case that the designed extended to these geometries. Following the design strategies described in 3.4 Spurious-free Stopband Response filter does not satisfy these specifications, a nar- this paper, the four pairs of filters have been de- Several factors can produce a first spurious re- rower housing should be taken. To optimize the signed. Five order evanescent mode filters were sponse before the upper frequency of the re- power-handling capability, the maximum ridge 5. Results required to satisfy the selectivity specification. gap must be obtained by choosing the lower Table 1 compares the structure dimensions and quested stopband, fu. The first factor arises from ridge depth . This can be accomplished by set- performances for each designed filter. The man- the propagation and resonance of the TE10 mode h 5.1 Comparative Study of Filter Topol- in the housing rectangular waveguide. The ting w ≈ wopt and then reducing h whereas the ogies and Performances ufacture constraints consisted in a minimum avoidance of this resonance restricts the maxi- filter first inverter can be manufactured, the filter To test the design strategies described in section length for the first inverter of 0.25 mm and ridge total length condition is fulfilled, and the ridge sections longer than 0.9 mm. mum housing width ah to: 4 and evaluate the performance of evanescent section length increase does not introduce the mode ridge waveguide filters, four different filter

TE102 resonance inside the stopband. On the specifications have been considered. A symmet- The insertion loss must be optimized in filters A. other hand, to optimize the filter insertion loss ric and an asymmetric filter have been designed According to section 3.1, the wider housing sat- it is also recommended to take the lower ridge to fulfill each specification, so that both filter isfying the out-of-band requirements must be

[2] depth h but with the width set to w ≈ 0.65wopt as topologies can be compared in terms of inser- sought. On the other hand, for filters B, the ridge

the losses increase severely for w > 0.65wopt. If a tion losses, power-handling, length and stop- gap and therefore the power-handling capabil- where x is a term which takes into account that compromise between insertion loss and power- band. For all the filter specifications, a 0.02 dB ity can be improved on a small scale by choos- the housing sections resonate at the frequency handling must be sought, an intermediate value ripple Chebychev bandpass response with 300 ing a slightly narrower housing. This housing for could be taken. where their lengths become approximately λg/2, w

instead of at the TE10 cutoff frequency. The design procedures to optimize the filter Specs A Specs B Specs C Specs D The second resonance of the ridge sections is length and the out-of-band response are similar. Parameter another effect that can end the filter stopband. In both cases a manufactured filter with the nar- Symm. Asymm. Symm. Asymm. Symm. Asymm. Symm. Asymm. This TE resonance comes from the periodic re- rowest housing must be sought. The following 102 a (mm) 10.550 10.650 10.250 10.400 6.000 6.500 6.790 6.940 sponse of the resonators, and can be controlled algorithm can be used: h

by a suitable choice of the ridge dimensions w bh (mm) 8.815 8.815 8.815 8.815 7.490 7.490 5.275 5.400 and h to keep the ridge length under λ /2 in the 1. For the housing dimensions set, take w ≈ g w (mm) 2.920 2.600 4.620 4.680 2.700 2.440 3.050 2.780 filter stopband. wopt. h (mm) 3.200 4.750 3.020 4.600 3.506 5.650 2.480 4.652 The higher order modes are the last factor that must 2. Increase the ridge depth h up to obtain the be considered to satisfy the stopband specification. smaller ridge length that can be success- gap (mm) 2.415 4.065 2.775 4.215 0.478 1.840 0.315 0.748 These modes can provide an unwanted bridge to fully manufactured. l1=l6 (mm) 3.225 3.145 2.475 2.695 0.250 0.250 0.250 0.250 transfer energy along the structure ridge and hous- t =t (mm) 3.638 2.941 5.460 3.892 0.901 0.900 0.901 0.903 ing sections. Using modal charts similar to Fig. 2, 3. Whereas the first inverter section can be 1 5 manufactured, reduce and goto 1. suitable ridge dimensions w and h can be chosen ah l =l (mm) 12.600 12.235 11.045 11.185 6.610 6.035 7.785 7.685 to avoid the propagation of higher order modes in 2 5

the ridge sections before the stopband end. A very This algorithm provides the shorter filter and t2=t4 (mm) 4.038 3.538 6.258 4.892 1.435 2.965 1.411 1.870 maximizes the stopband. In case of out-of-band important case for evanescent mode waveguide l =l (mm) 14.020 13.690 12.345 12.535 7.065 6.312 8.278 8.138 optimization, as the upper stopband frequency 3 4 filters is the TE01-like mode. The cut-off frequency fu

of this mode in the ridge and inverter sections co- is increased, the housing height must be reduced t3 (mm) 4.030 3.521 6.241 4.860 1.433 2.955 1.411 1.868 incides, causing a low-pass effect that produces together with the housing width to avoid spuri- Length (mm) 79.072 74.619 81.407 75.258 33.953 35.879 38.661 39.560 spikes above their cut-off frequency. Although ous responses from TE01-like modes (see eq. (3)).

from symmetry considerations, the TE01 should not be excited, manufactured structures never hold a Two pair of quite similar strategies have been I ̑.L. (dB) 0.2253 0.2095 0.2552 0.2574 0.4315 0.3781 0.4215 0.3817 perfect symmetry and alignment, and as it will be presented. The first pair optimizes insertion loss shown in section 5, in practice the condition and power-handling capability, whilst the other Emax (V/cm) 423.56 294.39 327.87 206.21 1 899.65 438.23 2 474.26 1 045.86 pair is for filter length and out-of-band response. Stopband Both pair of strategies take the highest housing 10.4-17.0 10.4-17.0 10.4-17.0 10.4-17.0 10.4-20.0 10.4-20.0 10.4-28.4 10.4-27.4 (GHz) height allowed by (3) to satisfy the out-of-band [3] specification, and a very similar value for the Table 1. Symmetric and asymmetric filter dimensions and performances for the four specifications considered.

120 ISSN 1889-8297 / Waves · 2010 · year 2 Waves · 2010 · year 2 / ISSN 1889-8297 121 gives the designer a margin to fulfill the stop- formance. A higher housing was therefore taken. To avoid the band specs since the spurious response goes Nonetheless, spurious appeared in the stopband up in frequency. This margin can be invested in response. The authors have proved that these stopband a ridge section length increase due to a higher spurious come from asymmetries due to manu- spikes that ridge gap choice; resulting in better power-han- facture tolerances and assembly misalignments. come from dling figures (compare filters A-B in Table 1). These impairments excite unexpected modes manufacture (for instance, the TE01 mode) that theoretically

asymmetries, The out-of-band performance and the filter length should not appear in the structure under TE10 the limitation are optimized by using a narrower housing. This incidence. Such modes provide an alternative (3) should be housing can be obtained following the iterative path for the power transmission along the filter, enforced algorithm described in section 4. In filters D, the thus introducing spurious responses in the filter increase in the stopband extent requires a lower stopband. In fact, the first spike in both filters

housing height to keep the TE01 mode below cut- appears exactly at the TE01 cut-off frequency. To off in a wider stopband. This housing increases avoid these spikes, the limitation (3) should be the step in the first structure discontinuity, thus enforced.

reducing the housing section length l1. Hence, when the spurious-free band is optimized, a wider housing is required to be able to implement the 6. Conclusions first filter inverter and a longer filter is obtained. This is the main discrepancy in the design proce- The performance compromises of symmet- dure for filters D and C (see Table 1). ric and asymmetric evanescent mode ridge waveguide filters have been deeply investi- With regard to the comparison between sym- gated. As a result, clear design strategies to metric and asymmetric topologies, the asym- optimize insertion loss, power-handling, out-of- metric filters provide better insertion loss and band response and length have been proposed. much better power-handling capability for the Figure 4. Comparison between simulated and Figure 5. Comparison between simulated and Using these strategies, a complete performance same set of specifications. The only exception to measured response in the passband (a) and the stop- measured response in the passband (a) and the stop- analysis and comparison of both symmetric and this rule comes from the filters designed under band (b) for the manufactured asymmetric filter. band (b) for the manufactured symmetric filter. asymmetric topologies are carried out. From the specs B. In this case the insertion loss is almost methods and results presented in this paper, the equal because the losses increase with the ridge designer can choose the best topology to satisfy width w starts from a lower w in the asymmet- can fulfill the spurious band specifications with where the more sensitive dimension, the ridge a prescribed set of specifications. Furthermore, ric topologies (compare Fig. 3a and 3c). Anyway, lower insertion loss than a symmetric topology. gap, is smaller. Figures 4b and 5b show the fil- he can also select the design strategy to be the results in Table 1 reveal that an asymmetric A 7th order filter was required to satisfy the stop- ter stopband responses. The agreement is very followed in order to achieve the best perform- evanescent mode filter can be easily designed to band requirement at 7.2 GHz. Figure 4 depicts good, but the measured stopband responses are ance trade-off for the evanescent mode ridge provide simultaneously better losses and power- the simulated and measured filter responses. The plagued with very narrow spikes. For these filters waveguide filter structure. handling capability than any symmetric coun- physical dimensions obtained from the structure the housing height constraint was not applied, terpart. Even though slightly shorter filters can dimensional control were employed to perform since from the simulations we wrongly conclude the simulations. The passband measured in- that did not affect to the out-of-band - per be obtained from symmetric configurations op- bh Acknowledgement timized to reduce length, for evanescent mode sertion loss was 0.35 dB, which translates into filters demanding good figures in insertion loss a quality factor of about 3 600. The filter total The authors thank Thales Alenia Space for the and power-handling with moderate stopband length (excluding access ports) was 102.13 mm. manufacturing and measurement of the filter requirements the asymmetric filters are sub- prototypes. stantially shorter. As a result, the use of the sym- For the second filter, the design criterion was to metric topology is only recommended when optimize the filter length with a stopband rang- an extreme optimization of the out-of-band ing between 7.2 and 21 GHz. According to the References performance or the filter length is requested in topology comparative analysis, a symmetric combination with poor requirements in inser- configuration was taken. A filter with 7 resona- [1] J. Uher, J. Bornemann, and U. Rosenberg, tion loss and power-handling capability. tors was required to fulfill the design specifica- Waveguide Components for Antenna Feed tions. Figure 5 compares the simulated (after Systems: Theory and CAD. Artech-House, 5.2 Experimental Results dimensional control) and measured response 1993. of the manufactured filter. In Fig. 6 the pieces Two C-band evanescent mode ridge waveguide [2] G. L. Matthaei, L. Young, and E. M. T. Jones, of the symmetric filter and the final assembled filters have been designed and manufactured to Microwave Filters, Impedance-Matching structure are shown. A very compact C-band validate the design procedures proposed in this Networks, and Coupling Structures. Artech- structure of only 73.62 mm length (excluding paper with real measurements. For both filters, an House, 1980. access ports) was obtained. As it was expected, all-pole 249 MHz bandwidth Chebychev response [3] R. J. Cameron, C. M. Kudsia, and R. R. Man- an increase in the passband insertion loss was centered at 6.966 GHz has been chosen. The pass- sour, Microwave Filters for Communication observed. The measured insertion loss was 0.45 band return loss has been set to 22 dB. Both filters Systems: Fundamentals, Design and Applica- dB, so that the measured quality factor drops to were manufactured from an aluminium block by tions. Wiley-Interscience, 2007. nearly 2 800. using conventional milling techniques, and were [4] G. F. Craven, “Waveguide bandpass filters us- ended with standard WR-137 ports. A silver-plat- ing evanescent modes”, Electron. Lett., vol. 2, As shown in Fig. 4a and 5a, the agreement be- ed coating was applied to the metal conductor no. 7, pp. 251-252, 1966. tween the measured and the simulated band- walls to reduce the ohmic losses. [5] G. F. Craven and C. K. Mok, “The design of eva- pass response is very good, particularly for the nescent mode waveguide bandpass filters for asymmetric filter. The differences can be- at The first filter was designed to optimize insertion a prescribed insertion loss characteristic”, IEEE tributed to manufacture tolerances, whose ef- loss with a rejection greater than 40 dB between Figure 6. Parts of the manufactured symmetric Trans. Microwave Theory Tech., vol. 19, no. 3, fect is more important in the symmetric filter 7.2 and 14 GHz. An asymmetric configuration filter in (a) and assembled structure in (b). pp. 295-308, 1971.

122 ISSN 1889-8297 / Waves · 2010 · year 2 Waves · 2010 · year 2 / ISSN 1889-8297 123 [6] R. V. Snyder, “New application of evanescent down”, The Physical Review, vol. 112, no. 3, Vicente E. Boria Máriam Taroncher mode waveguide to filter design”, IEEE Trans. pp. 681-685, 1958. See page 17 was born in Lliria, Valencia, Microwave Theory Tech., vol. 25, no. 12, pp. [22] R. V. Snyder, “Broadband waveguide filters Spain on October 8, 1979. 1013-1021, 1977. with wide stopbands using a stepped-wall ev- She received the Telecom- [7] A. Kirilenko, L. Rud, V. Tkachenko, and D. Kulik, anescent-mode approach”, in 1983 MTT-S Int. munications Engineering “Design of band-pass lowpass evanescent- Microwave Symp., Boston, pp. 151-153. 1983. degree from the Universi- mode filters on ridged waveguides”, in Proc. [23] J. C. Nanan, J. Tao, H. Buadrand, B. Theron, dad Politécnica de Valen- 29th EuMC, Munich, pp. 239-242, October. 1999. and S. Vigneron, “A two-step synthesis of cia (UPV), Valencia, Spain, [8] Z. M. Liu, J. A. Ruiz-Cruz, W. Chi, and K. A. Zaki, broadband ridged waveguide bandpass in 2003, and is currently “An extremely wideband ridge waveguide fil- filters with improved performances”, IEEE working toward the Ph.D. degree at UPV. From ter”, in 2004 MTT-S Int. Microwave Symp., Fort Trans. Microwave Theory Tech., vol. 39, no. Eva Tarín 2002 to 2004, she was a Fellow Researcher with Worth, pp. 615-618, June. 2004. 12, pp. 2192-2197, 1991. was born in 1983 in the UPV. Since 2004, she has been a Technical [9] J. A. Ruiz-Cruz, M. A. E. Sabbagh, K. A. Zaki, Cheste, Spain. She re- Researcher in charge of the experimental labora- J. M. Rebollar, and Y.Zhang, “Canonical ridge ceived the B.S. degree and tory for high power effects in waveguide devices waveguide filters in LTCC or metallic resona- Biographies M.S. degree in Telecom- at the Research Institute iTEAM, UPV. In 2006 she tors”, IEEE Trans. Microwave Theory Tech., vol. munication Engineering was awarded a Trainee position at the European 53, no. 1, pp. 174-182, 2005. from the Universidad Po- Space Research and Technology Centre, Euro- [10] A. M. K. Saad, J. D. Miller, A. Mitha, and R. Pablo Soto litecnica de Valencia (first- pean Space Agency (ESTEC-ESA), Noordwijk, The Brown, “Analysis of antipodal ridge waveguide was born in 1975 in class honors) in 2005 and Netherlands, where she worked in the Payload structure and application on extremely wide Cartagena, Spain. He re- 2008, respectively. Since 2009 she is a secondary Systems Division Laboratory in the area of Multi- stopband lowpass filter”, in 1986 MTT-S Int. Mi- ceived the M.S. degree in school teacher on mathematics in Valencia. Her pactor, Corona Discharge and Passive Intermod- crowave Symp., Baltimore, pp. 361-363. 1986. Telecommunication En- research interests deals with numerical meth- ulation (PIM) effects. Her current research inter- [11] A. M. K. Saad, J. D. Miller, A. Mitha, and R. gineering from the Uni- ods for the analysis and design of waveguide ests include numerical methods for the analysis Brown, “Evanescent-mode serrated ridge versidad Politécnica de components. Ms. Tarín has been awarded with of waveguide structures and the acceleration of waveguide bandpass harmonic filters”, in Valencia in 1999, where several awards for her outstanding academic the electromagnetic analysis methods. Proc. 17th EuMC, Rome, pp. 287-291. 1986. he is currently working record. She also held a 2005-2006 IEEE MTT pre- [12] A. Kirilenko, L. Rud, V. Tkachenko, and D. toward the Ph.D. degree. In 2000 he joined the graduate scholarship. Kulik, “Evanescent-mode ridged waveguide Departamento de Comunicaciones, Universidad Benito Gimeno bandpass filters with improved perform- Politécnica de Valencia, where he is a Lecturer was born in Valencia, ance”, IEEE Trans. Microwave Theory Tech., since 2002. In 2000 he was a fellow with the Eu- Santiago Cogollos Spain, on January 29, vol. 50, no. 5, pp. 1324-1327, 2002. ropean Space Research and Technology Centre was born in Valencia, 1964. He received the Li- [13] T. Shen and K. A. Zaki, “Length reduction of (ESTEC-ESA), Noordwijk, the Netherlands. His Spain, on January 15, cenciado degree in Phys- evanescent-mode ridge waveguide band- research interests comprise numerical methods 1972. He received the de- ics in 1987 and the PhD pass filters”, in 2001 MTT-S Int. Microwave for the analysis and automated design of passive gree in telecommunica- degree in 1992, both from Symp., Phoenix, pp. 1491-1494. June. 2001. waveguide components. Mr. Soto received the tion engineering and the the Universidad de Valen- [14] M. Capurso, M. Piloni and M. Guglielmi, “Res- 2000 COIT/AEIT national award to the best Mas- Ph. D. degree from the cia, Spain. He was a Fellow onant aperture filters: improved out-of-band ter Thesis in basic information and communica- Polytechnic University of at the Universidad de Va- rejection and size reduction”, in Proc. 31st tion technologies. Valencia, Valencia, Spain, lencia from 1987 to 1990. Since 1990 he served EuMC, London, pp. 331-334. 2001. in 1996 and 2002, respectively. In 2000 he joined as Assistant Professor in the Departamento [15] Y. Rong and K. A. Zaki, “Characteristics of the Communications Department of the Poly- de Física Aplicada y Electromagnetismo at the generalized rectangular and circular ridge Daniel de Llanos technic University of Valencia, where he was an Universidad de Valencia, where he became As- waveguides”, IEEE Trans. Microwave Theory was born in 1979 in Valen- Assistant Lecturer from 2000 to 2001, a Lecturer sociate Professor in 1997. His current research Tech., vol. 48, no. 2, pp. 258-265, 2000. cia, Spain. He received the from 2001 to 2002, and became an Associate interests include the areas of computer-aided [16] P. Soto, D. de Llanos, E. Tarín, V. E. Boria, B. Gi- M.S. degree in Telecom- Professor in 2002. He has collaborated with the techniques for analysis of passive components meno, A. Oñoro, I. Hidalgo, and M. J. Padilla, munication Engineering European Space Research and Technology Cen- for space applications, waveguides and cavities “Efficient analysis and design strategies for from the Universidad tre of the European Space Agency in the devel- including dielectric objects, electromagnetic evanescent mode ridge waveguide filters”, in Politécnica de Valencia in opment of modal analysis tools for payload sys- band-gap structures, frequency selective sur- Proc. 36th EuMC, Manchester, pp. 1095-1098, 2003. In 2003 he joined tems in satellites. In 2005 he held a post doctoral faces, and non-linear phenomena appearing in September. 2006. the research group BET research position working in the area of new syn- power microwave subsystems (multipactor and [17] G. Conciauro, M. Guglielmi, and R. Sorren- (Bioengineering, Electronics and Telemedicine), thesis techniques in filter design at University of corona effects). tino, Advanced Modal Analysis, John Wiley & from the Universidad Politécnica de Valencia, Waterloo, Waterloo, Ont., Canada. His current re- Sons, 2000. working in a project sponsored by Telefónica search interests include applied electromagnet- [18] S. Cogollos, S. Marini, V. E. Boria, P. Soto, A. Móviles. In 2004 he joined the company Motoro- ics, mathematical methods for electromagnetic Vidal, H. Esteban, J. V. Morro, and B. Gimeno, la S.A, Madrid, inside the group GSM Networks, theory, analytical and numerical methods for the “Efficient modal analysis of arbitrarily shaped where he is currently working as UMTS UTRAN analysis of waveguide structures, and design of waveguides composed of linear, circular, and Optimization Engineer. waveguide components for space applications. elliptical arcs using the BI-RME method”, IEEE Trans. Microwave Theory Tech., vol. 51, no. 12, pp. 2378-2390, 2003. [19] M. Guglielmi, “Simple CAD procedure for microwave filters and multiplexers”, IEEE Trans. Microwave Theory Tech., vol. 42, no. 7, pp. 1347-1352, 1994. [20] HFSS, Ansoft Corporation, Pittsburgh. [21] A. J. Hatch and H. B. Williams, “Multipacting modes of high-frequency gaseous break-

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