A Wideband Compact Broadside Coupler-based Impedance Transformer

A Wideband Compact Broadside Coupler-based Impedance Transformer with 6:1 Bandwidth

Wei Jia Lu

Temasek Laboratories

National University of Singapore

Singapore tsllwj@https://www.sodocs.net/doc/bb17314911.html,.sg

Kian Sen Ang

School of EEE

Nanyang Technological University

Singapore

akiansen@https://www.sodocs.net/doc/bb17314911.html,.sg

Koen Mouthaan

Department of ECE

National University of Singapore

Singapore

k.mouthaan@https://www.sodocs.net/doc/bb17314911.html,.sg

Abstract —A compact broadband impedance transformer using a broadside coupler is presented. The tradeoff between good return loss and design parameters that can be realistically implemented is considered during the design. To implement the coupler and the required high impedance transmission line, a combination of stripline and microstrip is used. The circuit transforms 50 Ω to 100 Ω from 1 GHz to 6 GHz. The measured return loss is larger than 15 dB from 1.1 GHz to 6.4 GHz. In general, the measured results agree well with the simulated results.

Keywords-Impedance transformer; broadside coupling; passive circuit

I. I NTRODUCTION

Impedance transformers are used in impedance matching, power splitting and power combining circuits. Commonly used impedance transformer include conventional quarter-wavelength impedance transformer, coupled line impedance transformer, tapered impedance transformer, balun impedance transformers and coaxial line impedance transformer [1]-[4]. The conventional quarter-wavelength impedance transformer is easy to implement but is typically narrowband. The bandwidth can be increased by using multiple sections of quarter wavelength line or long tapered transmission line at the expense of a larger physical footprint. Coaxial line impedance transformers such as Guanella [5] and Ruthroff [6] are able to provide a large bandwidth. These transformers typically operate in radio frequencies and the use of coils and ferrite cores limits the smallest physical size achievable. As such, compact impedance transformers are useful in practical applications with space constraint.

A compact broadband impedance transformer with three reflection zeros was proposed in [7]. The transformer employs a coupler with a high coupling coefficient and a high impedance transmission line loop as shown in Fig. 1(a). A 50 to 110 Ω stripline impedance transformer was demonstrated using edge-coupled transmission lines. It achieved better than 25 d

B return loss from 0.6 GHz to 1.6 GHz. As the realizable bandwidth is dependent on the maximum realizable coupling, the achieved bandwidth or impedance transformation ratio is

limited by the realizable gap between the coupled lines.

Fig. 1 (a) Schematic diagram of the proposed quarter-wavelength impedance transformer [7] (b) Quarter-wavelength impedance transformer using broadside coupler (c) Cross-sectional view of the impedance transformer.

Proceedings of the 42nd European Microwave Conference

An alternative method to implement the circuit using the

Vertically Installed Planar (VIP) coupler is presented in [8]. The method is able to achieve strong coupling without being restricted by the minimum gap size between two transmission lines. However, the drawback of this topology is the difficulty in determining the electrical length of the loopback transmission line. In addition, the vertical component of the

structure is more difficult to fabricate and deploy when

compared to the solution presented in [7].

In this paper, the impedance transformer is implemented

using a stripline broadside coupler and a microstrip transmission line. For the same line width, a microstrip can provide higher characteristic impedance compared to stripline. Furthermore, for a given physical length, microstrip has a longer electrical length since its effective permittivity is smaller. As such, the physical length of the loopback transmission line is longer than the coupled-line section, which allows easy practical implementation of the loopback transmission line. II. S TRUCTURE O F T HE I MPEDANCE T RANSFORMER Fig. 1(a) shows the schematic diagram of the impedance transformer. It transforms the impedance from Z 1 to Z 2. Fig. 1(b) shows our proposed implementation of the circuit and Fig. 1(c) is the cross sectional view of the impedance transformer. The stack up has four metal layers and three substrate layers. The top and bottom metal layers are the ground. The input and output transmission lines and part of the coupled line section are implemented on the second metal layer. The loopback transmission line and the other components of the coupled line section are implemented on the third metal layer. As the coupled line and loopback transmission line are both quarterwave in length, for the convenience of implementation, the loopback transmission line is realized partially in microstrip. It was done by removing a rectangular window of the top metal layer and the top and middle substrate, as shown in Fig. 1 (b). A vertical interconnect joins the loopback transmission line on the third metal layer to the second metal layer. The quarter

wavelength is determined at the center operating frequency.

III. C HARACTERISTICS O F T HE I MPEDANCE T RANSFORMER The impedance transformation ratio and the bandwidth are controlled by the characteristic impedance, Z 0, of the loopback transmission line and the even mode impedance, Z 0e , and odd mode impedance, Z 0o , of the coupled lines. Given the desired impedance transformation ratio and the bandwidth, the design curves in [4] can be used to determine the required Z 0o , Z 0e and Z 0. However, when the bandwidth and the impedance transformation ratios are large, it may be difficult to

implement it if one refers to the design curves. Simulation

using Agilent’s Advanced Design System (ADS) shows that Z 0 and Z 0o have greater impact on the bandwidth and the return loss of the circuit while Z 0e mainly affects the return loss. A very large return loss at some frequencies will result in extreme dimensions which cannot be realistically achieved. Therefore, a compromise between return loss and practically

achievable printed circuit dimensions is necessary.

Fig. 2 and Fig. 3 show the simulated S-parameters of the same impedance transformer but with different sets of design parameters. Fig. 2 has a better return loss but requires an impedance of 250 Ω, which is difficult to realize. Fig. 3 has a

moderate return loss performance but with a more realistic

Fig. 2 ADS simulation of a 50 Ω to 100 Ω impedance transformer with parameters: Z 0 = 250 Ω, Z 0e = 155 Ω and Z 0o = 27.5 Ω

.

Fig.

3 ADS simulation of 50 Ω to 100 Ω impedance transformer with different parameters: Z 0 = 155 Ω, Z 0e = 17

4 Ω and Z 0o = 21 Ω.

impedance requirement of 155 Ω. As such, the following section will focus on this design. IV. F ULL W AVE S IMULATION A 50 Ω to 100 Ω impedance transformer with a centre frequency of 3.5 GHz is designed and simulated. The bandwidth of the impedance transformer is 142.9%. It covers 1 GHz to 6 GHz. The required Z 0, Z 0e and Z 0o are 155 ?, 174 ? and 21 ? respectively.

The physical structure of the impedance transformer is

simulated in Ansys HFSS. Further optimization has been done to take into consideration the effect of the vertical

interconnect. The circuit is implemented using Rogers 5880.

The top and bottom substrate are 62 mils while the middle

substrate is 5 mils. The slot on the top substrate is 17.1 mm by 4 mm. The section of circuit used for impedance

transformation is 13.7 mm in length. Using [9], the width of

Fig. 4 HFSS simulation result for |S 11| and |S 21|.

Fig. 5 Different layers of the fabricated quarter-wavelength impedance transformer.

Fig. 6 Photo of the fabricated quarter-wavelength impedance

transformer.

Fig. 7 Measured |S 11| and |S 21| (solid line) and simulated |S 11| and |S 21| (dot dash line) with Z 1 = 50 Ω and Z 2 = 100 Ω.

Fig. 8 Measured |S 12| and |S 22| (solid line) and simulated |S 12| and |S 22| (dot dash line) with Z 1 = 50 Ω and Z 2 = 100 Ω.

the required coupled line is about 0.8 mm. The width of the loopback transmission line is 0.3 mm. The distance between the coupled line and the transmission line is 1.7 mm. The screws that hold the PCBs together are modeled as cylindrical perfect electric conductors.

Fig. 4 shows the HFSS simulation results for |S11| and |S21|. Three dips are observed in the |S11| response. The return loss is better than 15 dB from about 0.9 GHz to 5 GHz and better than 10 dB from 5 GHz to 5.8 GHz. The bandwidth of the impedance transformer is narrower than the designed bandwidth. The dip observed at 5.8 GHz is probably caused by a cavity resonance. Additionally, the vertical interconnection used to join the loop back transmission line and the top layer of the coupled line, is also a source of error.

V.M EASUREMENT A ND D ISCUSSION

Fig. 5 and Fig. 6show the fabricated circuit. The overall dimension of the circuit is 45 mm by 29.5 mm. A length of 50 Ω transmission line is added to the input and output ports respectively for calibration purposes. M2 screws are used to hold the three substrates together. The top and bottom grounds are soldered to the ground of the SMA connectors. The loopback transmission line is connected to the top layer of the coupled line by soldering.

The circuit is then measured using a HP8510C Vector Network Analyzer (VNA). A TRL calibration set for the coaxial to stripline transition was designed and used to calibrate out the effect of the 50 Ω connectors and the coaxial to stripline transitions. As the test ports of the VNA are 50 Ω, the data collected was inserted into ADS where 100 Ω load terminations can be readily used.

Fig. 7 and Fig. 8 show the simulated and measured performance of the impedance transformer. When terminated with 100 Ω at port 2, the fabricated impedance transformer achieves a return loss larger than 15 dB from 1.1 GHz to 4.6 GHz and from 4.8 GHz to 6.4 GHz. The circuit still has a return loss better than 10 dB between 4.4 GHz and 4.8 GHz despite an observed resonance.

A shift in resonance frequency is observed in the operation band of the fabricated impedance transformer towards lower frequencies as compared to the simulation results. The explanation is the presences of stray capacitance introduced by the vertical interconnect. Further studies using optimization on these parts are necessary for improvement of the performance.

VI.C ONCLUSION

A compact broadband impedance transformer using a broadside coupler and loopback transmission line is presented. The method overcomes the minimum gap limitation encountered in couplers using edge coupling. The device is able to achieve a 6:1 bandwidth with a length of a quarter wavelength, which is significantly smaller than the traditional multi-section counterpart. The device will be useful in broadband power dividers and broadband matching for antennas. The drawback of the circuit is the difficulty in making the vertical interconnect between the top and bottom layer PCBs in a laboratory. PCBs made in an industrial process, which incorporates plated through vias and blind vias, will solve this problem.

A CKNOWLEDGMENT

The authors would like to thank Mr Ray Fang and Madam Lee Siew Choo from the National University of Singapore for their technical support in the TRL calibration set design and the circuit fabrication.

R EFERENCES

[1] E.G. Cristal, “Meander-line and hybrid meander-line transformer,”

IEEE Trans. Microw. Theory Tech., vol. MTT-21, pp. 69-75, Feb 1973. [2]G. L. Matthaei, L. Young, and E. M. T. Jones, “Short-step Chebyshev

impedance transformers,” IEEE Trans. Microwave Theory Tech., vol.

MTT-14, pp. 372-383, Aug. 1966.

[3] A. Podcameni, “Symmetrical and asymmetrical edge-coupled-line

impedance transformers with a prescribed insertion loss design,” IEEE Trans. Microwave Theory Tech., vol. MTT-34, pp. 1-7, Jan 1986.

[4] A. Grebennikov, RF and Micrwave Transmitter Design, 1st ed.

Hoboken, NJ: Wiley, 2011, ch. 4.

[5] C. L. Ruthroff, “Some Broadband Transformers,” Proc IRE, Vol 47,

August 1959, pp 1337-1342.

[6]G. Guanella, “New Method of Impedance Matching in Radio-

Frequency Circuits”, Brown Boveri Review, September 1944, pp. 327-

329.

[7]K. S. Ang, C. H. Lee, and Y. C. Leong, “A broadband quarter-

wavelength impedance transformer with three reflection zeros within passband,” IEEE Trans. Microwave Theory Tech, vol. 52, no. 12, pp.

2640-2644, Dec. 2004.

[8]W. Lu, K. S. Ang, and K. Mouthaan, “A Broadband Quarter-

wavelength Impedance Transformer Using Vertically Installed Planar Coupler,” Microwave Symposium Digest (MTT), 2011 IEEE MTT-S International, vol., no., pp.1, 5-10 June 2011

[9]Cohn, S.B., "Characteristic Impedances of Broadside-Coupled Strip

Transmission Lines," Microwave Theory and Techniques, IRE Transactions on , vol.8, no.6, pp.633-637, November 1960.

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谓语动词单复数用法: 主谓一致是指： 1）语法形式上要一致，即单复数形式与谓语要一致。 2）意义上要一致，即主语意义上的单复数要与谓语的单复数形式一致。 3）就近原则，即谓语动词的单复形式取决于最靠近它的词语， 一般来说，不可数名词用动词单数，可数名词复数用动词复数。 There is much water in the thermos. 但当不可数名词前有表示数量的复数名词时，谓语动词用复数形式。 Ten thousand tons of coal were produced last year. 1 并列结构作主语时谓语用复数 Reading and writing are very important. 注意：当主语由and连结时，如果它表示一个单一的概念，即指同一人或同一物时，谓语动词用单数，and 此时连接的两个词前只有一个冠词。 The iron and steel industry is very important to our life. 2 主谓一致中的靠近原则 1）当there be 句型的主语是一系列事物时，谓语应与最邻近的主语保持一致。 There is a pen, a knife and several books on the desk.. There are twenty boy-students and twenty-three girl-students in the class. 2）当either… or… 与neither… nor，连接两个主语时，谓语动词与最邻近的主语保持一致。如果句子是由here, there引导，而主语又不止一个时，谓语通常也和最邻近的主语一致。 Either you or she is to go. Here is a pen, a few envelops and some paper for you. 3 谓语动词与前面的主语一致 当主语后面跟有with, together with, like, except, but, no less than, as well as 等词引起的短语时，谓语动词与前面的主语一致。The teacher together with some students is visiting the factory. He as well as I wants to go boating. 4 谓语需用单数 1）代词each和由every, some, no, any等构成的复合代词作主语，或主语中含有each, every, 谓语需用单数。 Each of us has a tape-recorder. There is something wrong with my watch. 2）当主语是一本书或一条格言时，谓语动词常用单数。 The Arabian Night is a book known to lovers of English. <<天方夜谭>>是英语爱好者熟悉的一本好书。 3）表示金钱，时间，价格或度量衡的复合名词作主语时，通常把这些名词看作一个整体，谓语一般用单数。(用复数也可，意思不变。) Three weeks was allowed for making the necessary preparations. Ten yuan is enough. 5 指代意义决定谓语的单复数

中国姓氏英语翻译大全

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常--Chiong 车--Che 陈--Chen/Chan/Tan 成/程--Cheng 池--Chi 褚/楚--Chu 淳于--Chwen-yu D: 戴/代--Day/Tai 邓--Teng/Tang/Tung 狄--Ti 刁--Tiao 丁--Ting/T 董/东--Tung/Tong 窦--Tou 杜--To/Du/Too 段--Tuan 端木--Duan-mu 东郭--Tung-kuo 东方--Tung-fang E: F:

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双语：中国姓氏英文翻译对照大合集

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D: 戴/代Day/Tai 邓Teng/Tang/Tung 狄Ti 刁Tiao 丁Ting/T 董/东Tung/Tong 窦Tou 杜To/Du/Too 段Tuan 端木Duan-mu 东郭Tung-kuo 东方Tung-fang F: 范/樊Fan/Van

房/方Fang 费Fei 冯/凤/封Fung/Fong 符/傅Fu/Foo G: 盖Kai 甘Kan 高/郜Gao/Kao 葛Keh 耿Keng 弓/宫/龚/恭Kung 勾Kou 古/谷/顾Ku/Koo 桂Kwei 管/关Kuan/Kwan

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花/华Hua 宦Huan 黄Wong/Hwang 霍Huo 皇甫Hwang-fu 呼延Hu-yen J: 纪/翼/季/吉/嵇/汲/籍/姬Chi 居Chu 贾Chia 翦/简Jen/Jane/Chieh 蒋/姜/江/ Chiang/Kwong 焦Chiao 金/靳Jin/King 景/荆King/Ching

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图像处理中常用英文词解释

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All the employees except the youngest one (work) very hard II .主语的“数”决定谓语动词的形式。 1.“不可数名词、可数名词单数、单数代词、不定式（短语）、动名词（短语）”或“从句”等作主语，用单数谓语形式。e.g. ①The work is important . 这项工作重要。 ②To serve the country is our duty . 为祖国服务是我们的义务。 ③How and why he left was a sad story . 他离开的经过和原因是一段伤心的经历。 2. 复数的名词、代词一般接复数谓语形式。e.g. ①The children are taken good care of . 孩子们得到很好的照料。 ②They have gone to Chengdu . 他们去成都了。 II. 以“and ”或“both… and”连接的并列主语： 1.通常作复数用。e.g. ①Plastics and rubber never rot . 塑料和橡胶从不腐烂。 ②What he says and what he does do not agree. 他言行不一致。 ③Both Tom and I are fond of medicine . 我和汤姆都喜欢医学。 2. 如果并列主语指的是“同一个”人（事、物、抽象概念），作单数用。 e.g. ①The worker and writer has come . 这位工人作家来了。 ②A cart and horse was seen in the distance . 远处能看见有一套马车。 ③Truth and honesty is the best policy . 真诚是最好的策略。

塑壳断路器附件功能与选用

塑壳断路器附件功能与选用 塑壳断路器(以下简称断路器)的附件作为断路器功能的派生和补充，为断路器增加了更多的控制手段，同时也扩大了保护功能。因此，目前已经成为断路器不可分割的一个重要部分。 1 断路器附件的种类 分为机内附件和机外附件两类。 机内附件是安装在断路器内部的附属装置，包括分励脱扣器、欠电压脱扣器、辅助开关和报警开关等四种。机外附件则是安装在断路器外部的附属装置，包括辅助手柄、外部操作手柄、电操机构、手柄闭锁装置、机械联锁装置、电气联锁装置、板后接线装置、插入式安装台和辅助接点装置等。 2 表示断路器状态的附件 辅助开关和报警开关的区别在于： 辅助开关主要用于断路器的分合状态的显示，通过断路器的分合对其他相关电器实施控制或联锁，报警开关主要用于断路器因故障而断开时的状态显示，在断路器负载发生故障时及时向其他相关电器实施控制或联锁。 3 实现断路器欠电压保护功能的附件 欠电压脱扣器是一种保护性附件，当电源电压下降到欠电压脱扣器额定电压的35%～70%时，欠电压脱扣器能使断路器脱扣；当电源电压低于欠电压脱扣器额定电压的35%时，欠电压脱扣器能保证断路器不合闸；当电源电压高于欠电压脱扣器额定电压的85%时，欠电压脱扣器能保证断路器正常工作。 4 实现断路器操作功能的附件 (1)分励脱扣器是一种实现断路器的远距离分闸的附件，通常用于应急状态下对断路器进行远距离分闸操作和作为漏电继电器等保护电器的执行元件。 (2)电操机构也是一种远距离操作断路器的机外附件，既可用来实现断路器的远距离分闸操作，也能实现断路器的合闸操作。 (3)辅助手柄一般用于600A及以上的大容量断路器上，进行手动分合闸操作。 (4)外部操作手柄是一种具有将断路器的上下扳动操作转换成旋转操作功能的机外附件。 5 实现断路器锁定功能和联锁功能的附件 (1)手柄闭锁装置是一种能使断路器操作手柄可靠地处于打开或闭合位置(即分闸或合闸锁定)，而在机械上并不影响断路器自由脱扣的保护装置。 (2)机械联锁装置也是一种保护装置，主要用于双电源供电电路中两台断路器不可同时通电的场合。 (3)电气联锁装置(也称自动电源切换装置)为自动实现切换的双电源保护装置。 6 实现断路器多种安装接线方式的附件