An Improved Wideband 180-Degree Hybrid Applied to Balanced Mixer

Transcription

1 Progre In Electromagnetic Reearch Letter, Vol. 51, , 215 An Improved Wideband 18-Degree Hybrid Applied to Balanced Mixer Wei Zhao, Yong Zhang *,ShuangLiu,LiLi,andRuiminXu Abtract In thi paper, an improved wideband millimeter-wave 18 hybrid i propoed to apply to balanced mixer and multiplier. The propoed hybrid conit of a tranition of tandard waveguide to upended coplanar waveguide (SCPW) and a tranition of SCPW to upended tripline. According to the inherent electromagnetic field characteritic of the two tranition, the propoed hybrid ha merit of broadband power ditribution and high iolation, which doe not rely on reonant circuit. The meaured inertion loe and iolation of two tranition at Ka-band are typically 1.4 db and 25 db, repectively. To verify the application of the propoed hybrid, A W-band ingle balanced mixer baed on the hybrid ha been deigned and fabricated. The meaured ingle-ideband (SSB) converion loe of the fabricated mixer are le than 9.5 db for the radio frequency (RF) range from 8 to 18 GHz. The preented hybrid ha been proven to be efficient for the deign of millimeter-wave balanced mixer and could be well applied in multiplier and other integrated circuit. 1. INTRODUCTION Rapidly expanding activitie in millimeter-wave ytem development have created an urgent need for broadband mixer and multiplier ued in electronic warfare, meteorology, radio meter and communication ytem. The cro-bar balanced mixer and multiplier are preferred in millimeterwave band for merit of low lo, high iolation and broad band, owing to the inherent mode iolation between the radio frequency (RF) and local ocillator (LO) ignal or between the input and output ignal [1 8]. In cro-bar mixer, the cro-bar balanced architecture with a pair of balanced diode phyically locate inide either the LO waveguide [1] or the RF waveguide [2 4]. In cro-bar multiplier, the cro-bar balanced architecture with a pair of balanced diode phyically locate inide either the input waveguide [5 7] or the output waveguide [8]. However, the deign of the cro-bar hybrid relie on the cro-bar tructure with a pair of balanced diode, which cannot be pre-deigned a a implex hybrid like the rat-race hybrid or the other [9, 1]. In thi paper, an improved wideband millimeter-wave 18 hybrid baed on the cro-bar tructure i propoed. The propoed hybrid conit of a tranition of tandard waveguide to upended coplanar waveguide (SCPW) and a tranition of SCPW to upended tripline. The phae, power ditribution and iolation characteritic of the 18 hybrid are inherently achieved by field tranformation of the two tranition. The tapered tructure i employed for reducing the inertion lo and impedance matching. And the improved hybrid could be pre-deigned a a implex circuit. The propoed hybrid ha merit of low lo, high iolation, and broad band and could be well applied in mixer, multiplier and other integrated circuit. A W-band ingle balanced mixer baed on the propoed hybrid ha been deigned and fabricated to demontrate the function of the hybrid. Received 17 December 214, Accepted 1 February 215, Scheduled 14 February 215 * Correponding author: Yong Zhang (yongzhang@uetc.edu.cn). The author are with the Fundamental Science on EHF Laboratory, Univerity of Electronic Science and Technology of China, Chengdu , China.

2 11 Zhao et al. 2. HYBRID DESIGN The configuration of the improved hybrid i hown in Fig. 1(a). It conit of a tranition of tandard waveguide to SCPW and a tranition of SCPW to upended tripline. The SCPW tructure can upport both the odd mode and even mode of propagation [11]. However, only one mode could be excited in the SCPW tructure when ignal are fed into the hybrid from the Port 1 and Port 2, repectively. Only odd mode i excited in the SCPW when ignal i incident at Port 1 through the tranition of tandard waveguide to SCPW and the even mode of the SCPW i prevented from propagating into the waveguide. Only even mode i excited in the SCPW when the ignal i incident at Port 2 through the tranition of upended tripline to SCPW and the odd mode of the SCPW i prevented from propagating into the upended tripline tructure. Conequently, the phae and iolation have wideband performance, which are inherently achieved by field tranformation through phyical tranition and do not rely on reonant circuit. Compared with the traditional cro-bar tructure a hown in Fig. 1(b), the conductor width (w) and the lit width () can be eaily adjuted to meet the ize of the diode placed on the ubtrate, when the width of the waveguide metal cavity i fixed. Thi eliminate the need for the pecial beam lead connecting the diode with the metal cavity in the cro-bar tructure, which will lead to dicontinuitie of the electric field. Meanwhile, a tronger electric field at diode i obtained becaue the ignal are contrained in the interior of the SCPW tructure. The inertion lo i reduced becaue of the introduced taper. And the improved hybrid can be predeigned a a implex circuit. Port1 Waveguide A A' A Waveguide to SCPW tranition Supended tripline to SCPW tranition B C D E Port2 w Supended tripline D' E' C' B' Metallization on the ubtrate (a) B Subtrate C Port1 Waveguide A' w B' Metallization on the ubtrate (b) Subtrate C' Port2 Supended tripline Figure 1. (a) Configuration of the improved hybrid. (b) Configuration of the traditional hybrid. In order to verify the inertion lo and iolation performance of the hybrid, three kind of tet tructure at Ka-band have been deigned and fabricated, including a back-to-back tructure of tandard waveguide to SCPW for teting inertion lo from Port 1 to Port 1, a tranition tructure of tandard waveguide to SCPW to upended tripline to tandard waveguide for teting iolation from Port 1 to Port 2 and a back-to-back tructure of tandard waveguide to upended tripline to SCPW for teting inertion lo from Port 2 to Port 2, a hown in Fig. 2. The Port 1 and Port 2 hown in Fig. 2 correpond to the port hown in Fig. 1. The tet tructure are meaured by Agilent E8363B vector network analyzer (VNA) from 26.5 GHz to 4 GHz. A hown in Fig. 3, the meaured inertion loe of the two tranition and the iolation are typically 1.4 db and 25 db, repectively. The reult how that the propoed hybrid ha merit of low lo, high iolation, and broad band. Two Schottky diode could be placed in the D-D -E-E zone along the B-B plane which referred to the line in Fig. 1(a) with two topology type a hown in Fig. 4(a) and Fig. 4(b). When diode are

3 Progre In Electromagnetic Reearch Letter, Vol. 51, Magnitude of S 11' and S 22' (db) S 11' S S 22' Magnitude of S 21 (db) Figure 2. Tet tructure of the hybrid. Figure 3. Meaured reult of the tet tructure. D E D E Port1 Port2 Port1 Port2 D' (a) E' D' (b) E' Figure 4. Circuit Topology: (a) type I and (b) type II. placed in erie a hown in Fig. 4(a), the ignal voltage fed from Port 1 are applied to the diode with the ame phae, and the ignal voltage fed from Port 2 are applied to the diode with the oppoite phae. When the diode are placed in anti-erie a hown in Fig. 4(b), the ignal voltage fed from Port 1 are applied to the diode with the oppoite phae, and the ignal voltage fed from Port 2 are applied to the diode with the ame phae. Becaue the tructure i ymmetric relative to the median of the upper and lower of the view a hown in Fig. 1(a), the tranition of waveguide to SCPW and the tranition of upended tripline to SCPW act a 3-dB power divider, which divide equal power to two diode. Therefore, both type of hybrid are 18 hybrid which contitute the baic tructure of ingle balanced mixer and multiplier. The new hybrid could be well applied in mixer, multiplier and other integrated circuit. 3. DESIGN OF THE BALANCED MIXER For the millimeter-wave mixer and multiplier, the general deign method i extracting the paraitic parameter of diode to obtain the equivalent circuit model, imulating the different part of the circuit eparately by uing three-dimenional field imulation oftware, uch a High Frequency Structure Simulator (HFSS), and then exporting the imulated reult a S-parameter Touchtone file into Advanced Deign Sytem (ADS) to further obtain and optimize the converion lo and other characteritic. However, becaue the characteritic of the orthogonal field tructure with two propagating mode at one port cannot be repreented in ADS uing one port, the cro-bar balanced mixer, which ue RF and LO orthogonal field to form a broadband 18 hybrid, cannot be well deigned by the above method. Currently, the 3D electromagnetic model of the Schottky diode i built to eliminate the limitation of the deign. The 3D electromagnetic model of the Schottky diode ha been built for accurately extracting paraitic parameter of the diode and the deign of ubharmonic mixer, tarting

4 112 Zhao et al. with the work of Heler [12]. A hown in Fig. 5, the epitaxial GaA tructure upon the emi-inulating (S.I.) GaA ubtrate conit of a thick, heavily doped (n++ GaA) layer and a thin, lightly doped (n GaA) layer. The anode and pad are formed on n GaA layer, and n GaAlayeriformedonn++GaAlayer. The n GaA layer with finger and n++ GaA layer with cathode pad are leading to Schottky contact and ohmic contact, repectively. By etting the port in the 3D electromagnetic model of the diode, the tranmiion line port with two propagating mode i replaced by the diode port with one mode. So the S-parameter Touchtone file of the HFSS imulated reult could be exported into ADS to further obtain and optimize the converion lo and other characteritic. However, the tructure and dimenion of the diode 3D electromagnetic model are et according to the Schottky diode baic phyical tructure. The tructural dimenion need to know in advance, which i difficult to obtain from manufacturer when commercial diode ued. In thi paper, the 3D electromagnetic model of the Schottky diode i built by calculation of diode electrical parameter. Revere breakdown voltage i mainly determined by epitaxial layer doping level N d [13], V br = N.77 d (1) So we can approximate calculate the N d through V br. The non-linear junction capacitance, C j (V j ) i mainly determined by anode area A a [14]. The A a can be inferred through q Nd ε C j = A a (2) 2 V bi In order to decreae the erie reitance, the epitaxial layer thickne wa required to be a mall a poible but larger than the maximum width of the depletion layer in order to avoid punch-through, o the epitaxial layer thickne t epi i much larger than w(v br ) [14]. [ 2ε (V bi V br ) w(v br )= qn d For the commercial diode M/A-COM MA4E238 ued in thi paper, the main electrical parameter and calculated tructural dimenion are hown in Table 1. Baed on the propoed hybrid and the 3D electromagnetic model of the Schottky diode, a W-band ingle balanced mixer ha been deigned. The configuration of the W-band balanced mixer i hown in Fig. 6. The polaritie of the LO and RF voltage at the diode are elected a hown in Fig. 4(a). RF input from Port 1 and LO input from Port 2. The architecture of the balanced mixer implie that the pair of Schottky diode i een in erie by the RF ignal and in anti-parallel configuration by the LO and intermediate frequency (IF) ignal. The RF voltage applied to the diode ha the ame ] 1 2 (3) Diode IF Port Waveguide to upended tripline tranition LPF RF Port 18 o Hybrid BPF LO Port Figure 5. 3D electromagnetic model of the Schottky diode. Figure 6. Configuration of the balanced mixer.

5 Progre In Electromagnetic Reearch Letter, Vol. 51, Table 1. Main electrical parameter and tructural dimenion of MA4E238. C j R A a N d T epi 7V 15 ff µm 2 3.7e17/cm 3.2 µm phae, and the LO voltage pump the diode out of phae. The RF ignal i coupled into the diode through a tranition of WR-1 tandard waveguide to SCPW. And the LO ignal i coupled into the diode through the tranition of WR-1 tandard waveguide to upended tripline, upended tripline bandpa filter and the tranition of upended tripline to SCPW. The tranition of waveguide to upended tripline i eay to be fabricated and ha the advantage of wide bandwidth. The bandpa filter i required to pa the LO ignal and reject the IF ignal. Here, the reonator are coupled on both ide of the upended tripline. Thi kind of filter ha maller volume and wider pa-band, compared with the traditional upended tripline filter with terminal coupling. The IF output i taken by a microtrip five-tage low-pa Chebyhev filter and a SMA connector. The balanced mixer ha been deigned on the RT/Duriod588 ubtrate with dielectric contant of 2.2, thickne of.127 mm. Since the 3D electromagnetic model of Schottky diode i ued, the S- parameter Touchtone file obtained by uing HFSS could be exported into ADS to further obtain and optimize the converion lo. By proper deign and optimization, the imulated converion loe of the mixer are hown in Fig. 7. The imulated ingle-ideband (SSB) converion loe of the fabricated mixer are le than 9 db for the RF range from 8 to 18 GHz with LO frequency fixed at 94 GHz. 35 Converion Lo (db) Figure 7. mixer. Simulated Converion Lo Simulated converion loe of the Figure 8. Photograph of the fabricated mixer. 4. PERFORMANCE OF THE BALANCED MIXER We fabricated and evaluated the balanced mixer which wa deigned uing the propoed hybrid. The photograph of the fabricated mixer i hown in Fig. 8. For the mixer meaurement, the LO ignal wa obtained in the way that the initial ignal wa generated by a PSG analog ignal generator Agilent E8257D and then it wa multiplied and amplified by microwave amplifier HP 8549B with an mm-wave ource module Agilent 83558A and a home-made W-band amplifier. The RF ignal wa obtained by a wept ignal generator Agilent 83623B with an mm-wave ource module Agilent 83558A. The LO power ued in the meaurement wa 13 dbm with frequency fixed at 94 GHz, and the RF power wa dbm. A pectrum analyzer HP 8563E wa ued to meaure the output power of the IF ignal. The meaured and imulated converion loe of the fabricated W-band balanced mixer veru RF frequency are hown in Fig. 9. The meaured SSB converion lo i le than 9.5 db for the frequency range from 8 to 18 GHz. And the bet SSB converion lo of 5.8 db i achieved with RF of 14 GHz. The meaured reult agree well with the imulated reult.

6 114 Zhao et al LO-RF Iolation RF-LO Iolation Converion Lo (db) Meaured Converion Lo Simulated Converion Lo Iolation (db) Figure 9. Meaured and imulated converion loe of the mixer. Figure 1. Meaured LO-RF and RF-LO iolation of the mixer. The important port-to-port iolation in mixer i the iolation of LO-RF, RF-LO and LO-IF. The LO-RF iolation i meaured under large-ignal condition. The LO port i terminated by the LO power chain, the RF port i terminated by the pectrum analyzer with GHz extended mixer and the IF port i terminated by a 5 Ω load. The RF-LO iolation i meaured under mall-ignal condition. The RF and LO port are terminated by the Rohde & Schwarz ZVA67 VNA with ZVA-Z GHz frequency extender and the IF port i terminated by the 5 Ω load. The frequency i meaured from 8 GHz to 1 GHz for the limitation of the operating frequency of the LO chain. The meaured LO-RF and RF-LO iolation of the mixer are hown in Fig. 1. Both LO-RF and RF-LO iolation have good performance motly more than 3 db iolation. The LO-IF iolation i conidered good for the ue of IF low-pa filter and the SMA connector. The SMA connector i recommended to work below 18 GHz which cannot work at W-band. The meaured reult how that the propoed hybrid can be ufficiently ued for the deign of millimeter-wave balanced mixer. 5. CONCLUSION An improved wideband millimeter-wave 18 hybrid i propoed and a 3D electromagnetic model of the commercial diode i preented in thi paper. Baed on the propoed hybrid and the 3D electromagnetic model of the Schottky diode, a W-band ingle balanced mixer ha been deigned, fabricated and meaured. The reult demontrate that the propoed hybrid ha merit of low lo, high iolation, and broad band, which could be well applied in mixer, multiplier and other integrated circuit. ACKNOWLEDGMENT Thi work wa upported by the National High-tech R&D Program of China (863 Program) under Grant 211AA123. REFERENCES 1. Schlecht, E. T., J. J. Gill, R. H. Lin, R. J. Dengler, and I. Mehdi, A GHz crobar balanced fundamental Schottky mixer, IEEE Microw. Wirele Compon. Lett., Vol. 2, No. 7, , Well, J. A., N. J. Cronin, and P. H. Reece, Rugged 94 GHz crobar balanced mixer, IEE Proc. H Microwave, Antenna Propag. Vol. 137, No. 4, , Erickon, N. R. and T. M. Goyette, Terahertz Schottky-diode balanced mixer, 21t International Sympoium on Space Terahertz Technology, , Oxford, March 21.

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