IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, VOL. 28, NO. 1, JANUARY 2018
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A Low-Loss Self-Packaged Magic-T With Compact Size Using SISL Technology Yongqiang Wang, Kaixue Ma , Senior Member, IEEE, and Shouxian Mou Abstract— This letter proposes a low-loss self-packaged magic-T with compact size using substrate integrated suspended line (SISL) technology. The microstrip-slot transition is embedded inside the SISL multilayer structure and thus the radiation loss caused by the slot can be reduced to minimum. The measured results, which agree well with the simulation ones, show that from 5 to 9 GHz, i.e., 57% fractional bandwidth, the measured return loss of each port is better than about 10 dB, the measured isolation between difference port and sum port is better than 35 dB, and the measured amplitude imbalance and phase imbalance are ±0.8° and ±0.14 dB, respectively. The implemented magic-T has a compact size of 0.18λ g × 0.43λ g , which is much smaller than previous designs.
Fig. 1.
3-D view of the proposed low-loss self-packaged SISL magic-T.
Index Terms— Compact size, low-loss, magic-T, microwave hybrid, self-packaging, slotline, substrate integrated suspended line (SISL).
I. I NTRODUCTION
A
S A fundamental component in microwave and millimeter-wave circuit and systems, magic-T can be applied in balanced mixers, and antenna feeding networks. In wideband magic-T design, the transitions between slotline [1] and other transmission lines can be used for out-of-phase dividing structure, such as microstrip-coupled slotline or slotline-coupled microstrip transitions [2], coplanar waveguide-slotline transition [3], microstrip-slot transitions [4]–[7], and double-sided parallel-strip line-slotline transition [8], and good performances have been achieved. In previous magic-T designs [2]–[8], the radiation loss of the slotline is considerable, causing an additional loss, e.g., as large as 2 dB in [7]. In [6], a broadband magic-T with excellent performance is presented, and the radiation loss is reduced by designing small microstrip-slotline tee junction with minimum size slotline terminations. Generally, designers prefer to use high permittivity substrate [2]–[6], which makes that the slot-mode wavelength becomes small compared to free-space wavelength and the fields will be confined to the slot [1], which helps to reduce the radiation loss. However, high permittivity substrates are not always available in
Manuscript received August 31, 2017; accepted October 19, 2017. Date of publication November 8, 2017; date of current version January 8, 2018. This work was supported in part by the National Natural Science Foundation of China under Grant 61471092, in part by National Science Fund for Distinguished Young Scholars under Grant 61625105, and in part by the Fundamental Research Funds for the Central Universities under Grant ZYGX2016Z002. (Corresponding author: Kaixue Ma.) The authors are with the School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China (e-mail:
[email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LMWC.2017.2766566
Fig. 2. (a) Cross section view of the proposed self-packaged SISL magic-T. (b) EM simulation model in HFSS.
practical engineering applications. The radiation of the slotline still exists even for high permittivity substrates. Moreover, the circuit size of the magic-T in [2]–[8] is large due to the use of impedance matching sections or quarter-wavelength lines. In this letter, a low-loss self-packaged magic-T with compact size is proposed. Substrate integrated suspended line (SISL) technology [9]–[12] is utilized. By embedding the used slotline transition inside the SISL multilayer structure as shown in Figs. 1 and 2, rather than exposing it to the air outside, the radiation loss of the slotline can be reduced to minimum. Very low insertion loss of the proposed magic-T is achieved, when compared with previous magic-T designs [2]–[8]. Besides, as a self-packaged whole, the implemented magic-T has a compact circuit size of 0.18λg ×0.43λg , which is much smaller than that of previous magic-T designs [2]–[8]. Moreover, the proposed SISL magic-T does not require any mechanical housing to shielding for practical applications as compared to that of the traditional slotline circuit. The proposed circuit can be used to connect to the SMA connectors or used in surface mount integration. II. C ONSIDERATION AND M AGIC -T D ESIGN To solve the radiation problem of the slotline, a novel selfpackaged magic-T as the 3-D view in Fig. 1 is presented. It is composed of ten metal layers named G1 to G10, and five layers of substrates, named substrate1 to substrate5. The second and fourth layers are hollowed, and two air
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IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, VOL. 28, NO. 1, JANUARY 2018
Fig. 4. Electric field and current distribution of the proposed SISL magic-T. (a) Out-of-phase case. (b) In-phase case.
Fig. 3. (a) Planar view of the proposed SISL magic-T which features self-packaging and compact size. (b) Equivalent circuit.
cavities will be formed when all the five layers of substrates are stacked up in order, as shown in Fig. 2. As shown in Fig. 3(a), microstrip-slot transition is utilized and the slot is etched on G6 layer. Many via holes are designed around the air cavities. This via fence together with the metal layers of G1, G2, G9, and G10, will constitute an approximately ideal electromagnetic (EM) shielding environment. Therefore, the EM field will be confined inside the air-cavity-embedded SISL structure, and the radiation loss of the slotline will be reduced to minimum. Fig. 3(b) gives the simplified equivalent circuit. Fig. 4 plots the electric field distribution of the slotline on G6 layer, and the current distribution of the microstrip on G5 layer. For the out-of-phase case as shown in Fig. 4(a), if a signal inputs from port1, the plane AA’ can be treated as a virtual microstrip short plane. From port1, the signal flows along the microstrip on G5 layer, and then couples to the slotline (width of w S and length l S ) on G6 layer. Due to the inherent property of the slotline [1], the slot-mode E-field extends across the slot. When the signal from the slotline couples to the microstrip in series, two arms of the microstrip will have opposite E-fields, i.e., port2 and port3 will receive signals with out-of-phase difference. For the in-phase case as shown in Fig. 4(b), if a signal inputs from port4, the plane AA’ can be treated as a microstrip virtual open plane. From port4, the signal flows along the microstrip on G5 layer, and the two arms of the microstrip will have the same E-fields. E-fields in the slotline at the B–B’ will be canceled, and port1 has no signal. To guarantee the microstrip-slot transition operation, the end of slotline require inductive elements for compensation, while the end of microstrip is loaded with capacitive elements, which
are both implemented with rectangle shape for easy modeling. Since the trace of microstrip is very close to the rectangle slot, as shown in Fig. 3(a), the ground of the microstrip is not complete. Besides, due to the existence of metal layers of G2 and G9 as shown in Figs. 1 and2, the metal layer of G6 is not the only ground layer, and instead, all the ground layers of G2, G6, and G9 should be considered during design. Furthermore, in order to miniaturize the circuit size, the space between the magic-T circuit and those via holes arranged around the air cavity is designed to be very small, as shown in Fig. 3(a). Since this via fence is close to the main circuit of the magic-T, it might have a slight effect on the performance of the magic-T. For instance, the impedance of the microstrip trace might become a little smaller if they are getting closer to the via fence together with the electric boundary around. This slight effect should be considered and can be solved with the help of EM simulation software. The parameters in Fig. 3(b) are Z 1 = 40 , θ1 = 63°, Z S1 = 95 , θS1 = 36°, Z 2 = 42 , θ2 = 23°, Z 3 = 56 , θ3 = 116°, and n = 0.73. The initial dimensions of the microstrip-slot transition can be chosen according to [13]. Transitions are designed to connect the SISL magic-T and SMA connectors outside for measurement. III. R ESULTS AND D ISCUSSION Rogers 5880 with 2.2 dielectric constant and 0.254-mm thickness is chosen for substrate3 for performance consideration. To reduce fabrication cost, Fr4 with dielectric constant of 4.4 are chosen, 2-mm thickness for substrate2 and substrate4, and 0.6-mm thickness for substrate1 and substrate5. Based on EM simulation and optimization, the dimensions shown in Fig. 3(a) are as follows: w01 = 0.58 mm, w02 = 0.78 mm, w03 = 5.8 mm, w04 = 3 mm, w05 = 0.6 mm, w06 = 0.78 mm, l01 = 1.5 mm, l02 = 4.5 mm, l03 = 1.8 mm, l04 = 1 mm, w1 = 1.03 mm, w2 = 0.69 mm, w3 = 1.09 mm, r1 = 2.67 mm, r2 = 3.43 mm, l1 = 8.01 mm, l2 = 3.99 mm, l S = 3.67 mm, and w S = 0.16 mm.
WANG et al.: LOW-LOSS SELF-PACKAGED MAGIC-T WITH COMPACT SIZE USING SISL TECHNOLOGY
Fig. 5. Simulated and measured insertion loss of the proposed self-packaged SISL magic-T with compact size for in-phase and out-of-phase, respectively.
Fig. 6. Simulated and measured return loss of each port of the proposed self-packaged SISL magic-T.
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and amplitude imbalance are within ±0.8° and ±0.14 dB. The measured minimum insertion loss is about 3.1 dB, which is close to ideal 3-dB splitting. It should be emphasized that the losses introduced by the transitions and SMA connectors have been de-embedded from the final measurement results. The circuit size of the proposed magic-T is 0.18λg × 0.43λg , which is much smaller compared with previous magic-T designs [2]–[8]. Besides, the implemented SISL magic-T is self-packaged with EM shielding properties. Compared with previous designs [2]–[8], where a bolster is strongly required in practical situations to make the circuit board suspended for the slot operation, the proposed magic-T in this letter has avoided that problem and is very easy to integrate with other circuits or components based SISL platform. Table I summarizes the performance comparison, which shows the SISL magic-T has advantages of low loss, compact size, and self-packaging. Fig. 8(b) gives the fabrication photograph. IV. C ONCLUSION
Fig. 7.
Simulated and measured isolation of the proposed SISL magic-T.
In this letter, a novel magic-T based-SISL technology is presented and good performance is obtained. Due to the benefits of SISL platform, the implemented SISL magic-T is self-packaged and the radiation loss of the conventional slotline can be reduced to minimum, and thus low insertion loss is achieved. The implemented SISL magic-T also has a compact size compared with previous designs. Since the slot is embedded within the SISL structure, more circuits based on slotline with low loss can be implemented in the future. R EFERENCES
Fig. 8. (a) Simulated and measured phase imbalance of the proposed magic-T. (b) Photograph of the fabricated self-packaged SISL magic-T. TABLE I P ERFORMANCE C OMPARISON OF THE M AGIC -T
As shown in Figs. 5–8, from 5 to 9 GHz, i.e., 57% fractional bandwidth, the measured return loss of each port is better than about 10 dB, the measured isolation between port1 and port4 is better than 35 dB and the measured phase imbalance
[1] S. B. Cohn, “Slot line on a dielectric substrate,” IEEE Trans. Microw. Theory Techn., vol. 17, no. 10, pp. 768–778, Oct. 1969. [2] M. Aikawa and H. Ogawa, “A new MIC magic-T using coupled slot lines,” IEEE Trans. Microw. Theory Techn., vol. 28, no. 6, pp. 523–528, Jun. 1980. [3] C.-H. Ho, L. Fan, and K. Chang, “New uniplanar coplanar waveguide hybrid-ring couplers and magic-T’s,” IEEE Trans. Microw. Theory Techn., vol. 42, no. 12, pp. 2440–2448, Dec. 1994. [4] J. P. Kim and W. S. Park, “Novel configurations of planar multilayer magic-T using microstrip-slotline transitions,” IEEE Trans. Microw. Theory Techn., vol. 50, no. 7, pp. 1683–1688, Jul. 2002. [5] B. Henin and A. Abbosh, “Wideband hybrid using three-line coupled structure and microstrip-slot transitions,” IEEE Microw. Wireless Compon. Lett., vol. 23, no. 7, pp. 335–337, Jul. 2013. [6] K. U-Yen, E. J. Wollack, J. Papapolymerou, and J. Laskar, “A broadband planar magic-T using microstrip–slotline transitions,” IEEE Trans. Microw. Theory Techn., vol. 56, no. 1, pp. 172–177, Jan. 2008. [7] M. E. Bialkowski and Y. Wang, “Wideband microstrip 180° hybrid utilizing ground slots,” IEEE Microw. Wireless Compon. Lett., vol. 20, no. 9, pp. 495–497, Sep. 2010. [8] W. Feng, Q. Xue, and W. Che, “Compact planar magic-T based on the double-sided parallel-strip line and the slotline coupling,” IEEE Trans. Microw. Theory Techn., vol. 58, no. 11, pp. 2915–2923, Nov. 2010. [9] K. Ma and K. T. Chan, “Quasi-planar circuits with air cavities,” WO Patent 149 046, Dec. 27, 2007. [10] Y. Wang, K. Ma, and S. Mou, “A high performance tandem coupler using substrate integrated suspended line technology,” IEEE Microw. Wireless Compon. Lett., vol. 26, no. 5, pp. 328–330, May 2016. [11] Y. Wang, K. Ma, and S. Mou, “A compact branch-line coupler using substrate integrated suspended line technology,” IEEE Microw. Wireless Compon. Lett., vol. 26, no. 2, pp. 95–97, Feb. 2016. [12] Y. Wang, K. Ma, N. Yan, and L. Li, “A slow-wave rat-race coupler using substrate integrated suspended line technology,” IEEE Trans. Compon., Packag., Manuf. Technol., vol. 7, no. 4, pp. 630–636, Apr. 2017. [13] B. Shuppert, “Microstrip/slotline transitions: Modeling and experimental investigation,” IEEE Trans. Microw. Theory Techn., vol. 36, no. 8, pp. 1272–1282, Aug. 1988.
