A Compact Wide Bandpass Filter based on Substrate Integrated Waveguide (SIW) Structure

Transcription

1 Journa of Communication Engineering, Vo. 4, No., Juy-December 5 3 A Compact Wide Bandpass Fiter based on Substrate Integrated Waveguide (SIW) Structure Mostafa Danaeian, Ai Ganji ashkezari, Kambiz Afrooz and Ahmad Hakimi Department of Eectrica Engineering, Shahid Bahonar University of Kerman, Kerman, Iran. Department of Eectrica Engineering, Shahid Beheshti University of Tehran, Tehran, Iran. m.danaeian@gmai.com, ai_ganji_yazd@yahoo.com, afrooz@uk.ac.ir, hakimi@uk.ac.ir Corresponding author: m.danaeian@gmai.com Abstract: In this pare, a wideband three-order bandpass fiter (BPF) is proposed. The proposed wideband fiter is designed using the substrate integrated waveguide (SIW) structure by oading T-shape sots. A BPF with two resonators is formed by etching T-shape sots with different size on the top meta pane of the SIW structure. The proposed fiter is investigated with the theory of couped resonator circuits. The T-shape sots which etched on the SIW structure are used to form up a new mutipe-mode resonator (MMR) in order to achieve a wide passband of operation whie keeping the overa size of the proposed fiter to be much compact. The design procedure as we as design curves of the fiter are given and discussed here. Compared with some other reported BPFs with SIW technique, the presented BPF using the SIW structure oaded by T- shape sot has great improvements on size reduction and seectivity. In order to prove the vaidity, the proposed wideband SIW BPF on a singe ayer printed circuit board (PCB) is designed and experimentay examined. The measured resuts show that the fiter achieves an insertion oss of. db at 6.4 GHz and a return oss of higher than db. The proposed fiter has a pass-band covers 5. to 7.99 GHz and its simuated and measured 3 db fractiona bandwidth is about 44.3%. The measured resuts are in a good agreement with the simuated resuts. Index Terms- microwave fiter, substrate integrated waveguide (SIW), wide bandpass. I. INTRODUCTION Recenty, the substrate integrated waveguide has provided a very attractive patform to design of various fiters with ow-cost, high quaity factor, and easy integration with panar circuits [-]. The SIW structure is synthesized on a panar substrate with inear periodic arrays of metaic vias or metaic sots by standard printed circuit board (PCB) or other panar circuit processes. In the other words, the SIW structure is a type of rectanguar waveguide synthesized in a substrate, which is composed of two rows of metaized via-hoes or channes connected with two meta pates on the top and bottom sides [3]. The Manuscript received 6-August-5 and revised 9-Oct.-5, P- ISSN: Accepted on 6-Dec.-5 E- ISSN:

2 33 A Compact Wide Bandpass Fiter... working mechanism of SIW is quite simiar to a traditiona rectanguar waveguide however, the Q-factor of an SIW is smaer than a cassic air-fied meta rectanguar waveguide because of the dieectric fiing and voume reduction [4]. One key advantage of the SIW structure is the easy connection between SIWs and other types of transmission ines or circuits which are embedded in or surface mounted on the mutiayer substrate. Therefore, this structure is widey used in the reaization and impementation of microwave devices such as fiters, power dividers, dipexers and etc. On the other hands, wideband radio system design techniques have been attractive in academia and industry and they are very suitabe for its high data rate and supporting mutipe adjacent narrow bands transmission. Fiters with a wide passband, sharp frequency cutoff edges, and fat group deay are essentia for broadband communication systems. For these reasons, various researchers works on the design of wideband BPFs to meet some advantages such as compact size, broad-bandwidth, ow insertion oss and high return oss with sharp rejection. For exampe, in [5], a SIW fiter using eectric couping formed by sots is introduced. In [6], a super-wide SIW bandpass fiter (BPF) is designed by using the periodic structure. In [7], a wideband FSIW fiter combined with stripine resonant ces is proposed. But, the above mentioned wideband fiters have drawbacks such as narrow fractiona bandwidth, arge size and design compexity. To overcome such disadvantages and miniaturize the overa size, an effective procedure based on the mutipe-mode resonator (MMR) has been proposed in []. This method has been broady used to design of numerous wideband BPFs [8-5]. In this paper, a nove wideband SIW fiter by oading two T-shape sot with different sizes on the metaic pate of a SIW structure are introduced which is provided a few resonant modes. The T-shape sots on the metaic pate of the SIW structure coud produce three transmission poes which make the wide passband and one transmission zero, aiming to sharpen the seectivity and extend the upper stopband. After geometric optimization, a three order wideband BPF is designed in a singe ayer panar circuit board (PCB). With this proposed structure, the ow insertion oss performance in the passband, high Q factor and compact size coud be obtained. In comparison with the previous works, due to the sma eectrica size of the T-shape sots, the proposed SIW fiter is very compact. II. ANALYSIS OF PROPOSED MULTI-MODE SIW LOADED BY T-SHAPE SLOTS The design procedure is based on the theory of the couped resonator circuits. The magnetic and eectric coupings are used in this structure in order to designing the BPF operating at 6.5 GHz. The magnetic couping create by the via-hoes whie the eectric couping is simpy controed by adjusting the physica dimension of the T-shaped sots etched on the surface of SIW structure. The configuration of the proposed SIW fiter is depicted in Fig.. As shown in Fig., the proposed fiter consists of two microstrip feed ines which the 5 Ω microstrip feed ine used here for the purpose of measurement. The

3 Journa of Communication Engineering, Vo. 4, No., Juy-December 5 34 parameter s is used to contro and adjust the couping between the SIW structure, input and output ports. On the other hand, there are two etching T-shape sots on the top meta ayer of the SIW structure in order to divide the SIW structure into two resonators with different sizes. The designed T-shape resonators are excited by the eectric couping. The couping topoogy between the T-shaped resonators is given in Fig.. S and L stand for the source and oad excitation. According to the couping topoogy shown in Fig., the adjacent couping between two resonators with different sizes are strong couping which is produced two poes and the passband. The proposed SIW structure is designed to have a cutoff frequency of 5. GHz and the T-shaped are designed to have a stopband at 8 GHz initiay. By adjusting the parameters of T-shaped unit ces, the proposed SIW fiter with wide passband coud be constructed. Fig.3 iustrate transmission poes and zero produced by the proposed fiter under weak couping. The components of the designed T-shape sots are mainy targeted to produce a few resonant modes in the SIW structure. By using two different sizes of T- shape sot two transmission poes are produced. The resonant modes between the T-shape sot are used to create the wide passband and the eectric couping between the T-shaped resonators can aso generate a transmission zero in the upper-stopband to improve the upper-stopband performance. Due to the presence of the magnetic couping, the first transmission poe namey f which is reated to the initia highpass band of the SIW structure is obtained. Because of the presence of the eectric couping, the other transmission poes f, f 3 and aso transmission zero f z are achieved. It shoud be noted that, the increasing height of the sots in T-shaped unit ces ead to that f 3 and the transmission zero f z, to shift to the ower frequencies and thus causing a narrow passband. Therefore, the proposed T-shaped resonators gives a zero-transmission frequency at f z c = w εµ eff r r Tabe I exhibits the dimensions of the proposed SIW fiter shown in Fig., where a of them are in miimeters. () Tabe I Dimensions of the proposed SIW fiter (units: mm) SIW = = 3.9 w eff = =.4 s =.8 4 = d =.5 w = 4.3 = 4.8 w = 4

4 35 A Compact Wide Bandpass Fiter... Fig.. Configurations of the proposed SIW T-shape sot fiter. Fig.. Couping topoogy of a proposed SIW fiter with two poes. Accordingy, the tota size of the fiter is ess than 3.8mm mm. The substrate is chosen to be Rogers RO43 with the reative permittivity 3.55 and the thickness of.58 mm. In the simuations, the metaic and dieectric osses have been taken into account by using the conductivity of copper σ =5.8 7 S/m and the oss tangent tan δ=.7 of the substrate. As anayzed above, the SIW structure with T-shape sots coud be used to design a compact wideband SIW fiter. As iustrated in Fig. 4, by changing the size of the T-shaped resonators, the resonant frequency of the T-shaped resonators coud be easiy moved and varied passband characteristics are observed. Note that, as shown in Fig. 4, compared with T-shaped resonators of Fig., T-shaped unit ce is scaed by a factor of.8 and.. As we as, the bandwidth of this fiter coud be easiy tuned by the couping between two T-shaped resonators.

5 Journa of Communication Engineering, Vo. 4, No., Juy-December 5 36 f - f f 3 - S (db) f z Freq(GHz) Fig.3. Simuated frequency responses of the proposed fiter with weak couping. - - S (db) - -3 Scaed Factor=.8 Scaed Factor= Scaed Factor= Freq (GHz) -3 Scaed Factor=.8-4 Scaed Factor= Scaed Factor= Freq (GHz) (a) (b) Fig.4. Frequency responses (a) S and (b) S of the proposed SIW fiter when the whoe dimensions, mutipe in variation factor. S (db) - Since the fiters are based on the construction of periodic structures, so by inserting more ces better performance with a higher seectivity can be achieved. Consequenty, T-shaped SIW fiter with seriescascaded two ces is aso designed. Fig. 5 shows the configuration of the designed two-stage SIW fiter using the unit ce shown in Fig. which is achieved after some simpe tuning. The simuated response of the proposed two-stage SIW fiter is aso potted in Fig. 6 and their geometric parameters are provided in Tabe II. The designed two-stage SIW fiter has a simuated center frequency of 6.5 GHz and a 3-dB bandwidth of 3 GHz. Its minimum passband insertion oss is approximatey db, which incudes the extra oss caused by increasing the tota size of the fiter. Its in-band return oss for designed two-stage SIW fiter is better than db. Due to the existence of the transmission zeros, this fiter exhibits a stopband rejection better than 4 db up to 6 GHz, as observed in Fig. 6. Aso, by cascading two T-

6 37 A Compact Wide Bandpass Fiter... s w 4 3 w w 4 3 w w eff c s d Fig.5. Configuration of the proposed two-stage SIW fiter with its geometric parameters isted in Tabe II. Tabe II Geometric parameters of the proposed SIW fiter (units: mm) = = 3.9 SIW w = =.4 eff s =.8 4 = d =.5 w = 4.3 = 4.8 w = 4 = = 3 s c S & S (db) S S Freq (GHz) Fig.6. Simuated resuts for the SIW fiter oaded by two-ces of the T-shaped resonators. shaped resonators, the proposed SIW fiter exhibits an abrupt transition band at the ower or upper edges of the fiter.

7 Journa of Communication Engineering, Vo. 4, No., Juy-December 5 38 S & S (db) S (Sim.) -4 S (Sim.) -5 S (Meas.) S (Meas.) Freq (GHz) Fig. 7. Simuated and measured frequency responses of the proposed wideband fiter. III. EXPERIMENTAL RESULTS AND DISCUSSION A wideband bandpass SIW fiter operating at the frequency range of GHz is designed, fabricated and tested. The simuated frequency responses of the peropsed fiter is achieved using a 3-D eectromagnetic simuator (Advanced Design System (ADS)). Fig. 8 shows the simuated (dashed ine) and measured (soid ine) transmission responses of the proposed SIW fiter which has been measured by the empoyment of a network anayzer Rohde & Schwarz, zkv. The proposed bandpass SIW fiter exhibits an insertion oss smaer than. db, and a return oss more than db in both simuated and measured resuts. The proposed BPF fiter has a 3 db fractiona bandwidth of 44.3%. Meanwhie, a wide upperstopband with the insertion oss higher than 4 db in the range of 8 to 6 GHz is achieved. Three transmission poes and one transmission zero are observed within the pass-band. The transmission zero is created to improve the upper-stopband performance. Furthermore, due to the use of T-sots in the proposed SIW structure, these sots may produce radiation in the upper haf space. The simuated radiation oss is iustrated in Fig.8 (a) which extracted by using the beow equation: r = () R S S The radiation oss is ess than.6% within the desired frequency band with oss free dieectric and meta. This impies that the sots have a itte effect on the radiation oss. Aso, in Fig. 8(b), a comparison by incuding a the osses (which contain radiation oss + dieectric oss + conductor oss) for these resonators is presented which finay eads to a. db insertion oss for the proposed structure. Finay, Tabe III summarizes the comparison of the proposed fiter with other reported fiters. As iustrated in Fig. 9, the group deay is ess than.36 ns in the passband of the designed SIW fiter.

8 39 A Compact Wide Bandpass Fiter Radiation Loss(%) Tota Loss(%) Freq(GHz) Freq(GHz) (a) (b) Fig.8. (a) The simuated radiation oss and (b) The simuated tota osses of the proposed fiter. x Group Deay(sec) Freq(GHz) Fig.9. Simuated group deay of the proposed fiter. A photograph of the fabricated fiter is shown in Fig., which demonstrates the quite sma size of the fiter. The measured resuts has a good agreement with the simuation one. Some minor discrepancies between measured and simuated resut may be caused by the imited precision of fabrication and measurement.

9 Journa of Communication Engineering, Vo. 4, No., Juy-December 5 4 Fig.. Photograph of the fabricated fiter. Reference number Tabe III: Performance comparisons of the recent fiter with the other. FBW (%) IL (db) RL (db) g Size λ λ g [7] [8] [9] [] This Work (3.8 mm ) IV. CONCLUSION A compact wideband BPF SIW fiter by oading the T-shape sots has been presented in this paper. The characteristic of the proposed resonators has been simuated to anayze and verify in detais. The proposed wideband fiter has three transmission poes and one transmission zero. The transmission zero is created to improve upper-stopband performance. The proposed SIW fiter exhibits the passband of GHz. The insertion oss is smaer than. db and the return oss is more than 3.6 db in simuated resuts. In addition, a wide upper-stopband with the insertion oss higher than 4 db in the range of 8 to 6 GHz is achieved. It is shown that this fiter is very compact and easy integrated with the other panar circuits. Finay, the proposed SIW fiter has been fabricated and measured. The measured insertion oss is better than. db with the return oss better than db. As we as the FBW is 44.3% and confirmed in experiment.

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