диафрагмированные волноводные фильтры / b14f7119-56a1-485f-9911-a62e0976aa2e

I. INTRODUCTION

With fast development of electronic technology, millimeter-wave has been widely applied in radar, wireless communication, and electronic antagonism technologies. At the same time, these systems require excellent performances and high level of integration for transmitter, receiver, and transceiver modules [1–4]. Switch filter module is a crucial part for some transceivers, especially in electronic antagonism systems. Moreover, band-pass filters are the most significant components in these modules. Based on different requirements, numerous publications have dealt with the development of diversified filters, such as planar microstrip filters [5–7], metal cavity filters [8], substrate integrated waveguide filters [9, 10],

Correspondence to: Z. Wang; e-mail: zhigangwang@uestc.edu.cn DOI: 10.1002/mmce.20863

Published online 00 Month 2014 in Wiley Online Library (wileyonlinelibrary.com).

three-dimensional (3-D) low temperature cofired ceramic (LTCC) filters [11] and dual-mode filters [12].

The microstrip parallel coupled-line filter has been one of the most commonly used filters for several decades [13, 14]. But, there are some drawbacks for this kind of filters, the most important one of which is the small line spacing of the first and last coupling stage for wideband band-pass filters. For overcoming the drawbacks of the filters, the three-line filter is proposed [15–17]. The proposed three-line filter has the following two important features for design of wideband filters: the tight line spacing of end stages can be relaxed; and the stop-band rejections are also improved. However, the filter has discontinuities between adjacent sections, and also has many parameters of design. In this article, a novel threeline microstrip structure filter is proposed. Compared with the traditional three-line filter, the proposed filter has three important improvements as follows: avoiding the discontinuities between adjacent sections, decreasing

2 Wang et al.

Figure 1 The block diagram of the Ka-band two-way switch filter module.

parameters of design, and enhancing pass-band matching performance by joining matching networks of diamond structure at input/output ports. The proposed filter also retains virtues of the filter in [16]. But, the proposed filter structure also has two limitations: first, the spurious passband could be closer to the working pass-band than the traditional one for adopting the uniform line width adjacent sections; second, since the number of design parameters is decreased, this could add the mutual influence among the structure parameters, which leads to the greater difficulty of the optimization process. Additional, E-plane metal insert technology is a conventional cost-effective implementation of direct-coupled cavity filters, and their ease of manufacturing and availability of accurate design software have made E-plane metal insert filter widely used in microwave and millimeter-wave applications for over 20 years [8, 18]. This article proposes an E-plane iris filter, which is a transfiguration of E-plane metal insert filter. For using printing technology, this filter improves precision of process, is suitable for vast production.

In this article, a Ka-band ultrawideband two-way switch filter module is proposed. The module covers whole Ka-band (26–40 GHz), and consists of two millimeter-wave wideband band-pass filters and two monolithic microwave integrated circuit (MMIC) SP2T switches. Using the novel three-line structure filter and the E-plane iris filter proposed above, and two MMIC SP2T switches, the switch filter module is fabricated, and excellent performances are obtained.

II. DESIGN OF COMPONENTS

The block diagram of the millimeter-wave ultrawideband two-way switch filter module developed in this article is shown in Figure 1. It can be seen from Figure 1 that the switch filter module is composed of two MMIC SP2T switches and two millimeter-wave wideband band-pass filters. The two MMIC SP2T switches adopt MA4AGSW2 of MA/COM. One filter is realized using novel 11-pole three-line microstrip structure band-pass filter, which include the pass-band 26–34 GHz. Another is realized using proposed E-plane iris waveguide band-pass filter, which include the pass-band 34–40 GHz. The selection of pass-bands is based on the scheme of whole transceiver system.

A. Three-Line Microstrip Structure Band-Pass Filter

The basic configuration of the three-line microstrip structure filter is shown in Figure 2. Figure 2a is the traditional three-line filter, and Figure 2b is the proposed novel threeline filter. Obviously, the proposed three-line filter has more simple circuit configuration than the traditional three-line filter. It can be easily seen from Figure 2b for the proposed three-line filter, the middle lines of all sections have the same width inducing its design parameters decreased, effectively; conjoint sections have the same line-width avoiding the discontinuities between adjacent sections; and diamond structures are intervened into input/ output ports as matching circuits. For the presented threeline filter, inductance inconsistence exists among the neighboring resonators, which yields to capacitance seen from the Input/Output ports. So, the compensating of capacitance is added at the I/O ports. At the same time, to broaden the bandwidth of the filter, a compensating of shadowing capacitance is designed, that is, diamond structure matching line. The length of matching line is approximately kg/4, and has lower impedance compared with main transmission line. The design method of the proposed three-line filter is uniform with that of the traditional three-line filter [16]. The major idea of the design method is transforming six-port network of three-line structure into two-port network, and using the design method of traditional parallel coupled-line filter. The idea of equivalent transforming is shown in Figure 3. Figure 3a is three-line

structure as a six-port network, Figure 3b is equivalent admittance inverter, and Figure 3b is further equivalent admittance inverter.

The initial dimensions of filter can be obtained by the design method in [16]. Through simulation and optimization using commercial full-wave 3-D FEM simulator (Ansoft HFSS), the final line width and line spacing of coupled-line can be obtained, including the dimensions of diamond structure. For avoiding cavity effect in millimeter-wave, the size of filter should be enough small. So Al2O3 is selected as the substrate, which has relative dielectric of 9.9, thickness of 0.254 mm, and loss tangent of 0.001 (1 MHz). According to the requirements of the switch filter module, a 11-pole three-line microstrip structure band-pass filter including pass-band 26–34 GHz and 0.5 dB pass-band ripple is designed, the length of each coupled line section is approximately kg/4 (kg is the guided wavelength at the center frequency). The layout of the filter is shown in Figure 4. The initial values of the

Ansoft HFSS, the geometric dimensions are determined as

follows: W0 50.23 mm, W1 50.21 mm, W2 50.23 mm,

designed filter is 16 3 3 3 0.254 mm3. The simulated results of the filter are shown in Figure 5. It can be seen from Figure 5 that the results meet the pass-band requirement of the switch filter module.

B. E-Plane Iris Waveguide Band-Pass Filter

The structure of the E-plane iris waveguide filter is shown in Figure 6. In the filter, a substrate printed ladder-type pattern is located in a rectangular waveguide. The filter is a transfiguration of E-plane metal insert filter. The electrical performance of E-plane filters is mainly determined by the ladder-type pattern on substrate.

The E-plane filter is direct-coupled resonator filter, and consists of seven half-wavelength resonators, as shown in Figure 6. The evanescent waveguide can be represented with an impedance inverter (K-inverter) circuit, as shown in Figure 7. The reactance values of Xs and Xp are functions of sizes (Wj) for an evanescent waveguide. Normalized inverter value and negative electrical length u are given by [19]

Figure 5 Simulated results of the fabricated 11-pole three-line band-pass filter.

where Zg is wave impedance of rectangular waveguide. At the same time, the normalized inverter values for an equal-ripple band pass filter are [20]

where gi’s are the element values of Chebyshev lowpass prototype filter, FBW is the fractional bandwidth, and n is the order of the filter. The values of the K-inverters are controlled by changing sizes (Wj). By method of parameter-extraction, relationship between values of the K-inverters and Wj can be established. Based on this way, a 0.1-dB ripple seven-order Chebyshev band-pass filter including pass-band 34–40 GHz is designed. The initial

Figure 7 impedance inverter (K-inverter) circuit for evanescent waveguide.

values of the E-plane filter are approximate: a 56.5 mm, b 53.2 mm, W1 50.13 mm, W2 50.9 mm, W3 51.4 mm, W4 51.6 mm, and L 52.8 mm. A commercial full-wave 3-D FEM simulator (Ansoft HFSS) is used to analyze and optimize the filter after the initial

W3 51.3 mm, W4 51.42 mm, and L 53.02 mm. Obviously, the waveguide is not standard waveguide. Finally, microstrip-probe transitions are added at the input/output ports of the designed filter for integration with other circuits, the simulated results are shown in Figure 8. It can be easily seen from Figure 8 that the results meet the pass-band requirement of the switch filter module.

III. KA-BAND SWITCH FILTER MODULE AND EXPERIMENTAL RESULTS

Using the 11-pole three-line microstrip structure bandpass filter and the seven-order E-plane iris filter, designed in Section II, and two MMIC SP2T switches (MA4AGSW2), the millimeter-wave ultrawideband twoway switch filter module is fabricated. The size of entire module fabricated is 51 3 26 3 9.8 mm3. Photograph of the fabricated switch filter module is shown in Figure 9 (including a pair of test fixture).

The measurements are taken using Agilent E8363B vector network analyzer. For measuring expediently, a pair of test fixture is connected at the input/output ports of the switch filter module by bond wires as shown in Figure 9. The measured results of the module are shown in Figure 10. The module exhibits excellent performances.

Figure 9 Photograph of the fabricated Ka-band two-way switch filter module.

As can be seen: for the first state, the switch filter module exhibits insertion loss and return loss of better than 6 dB and 10 dB in pass-band of 26–34 GHz, respectively, and rejection of better than 48 dB in 38–40 GHz; for the second state, it exhibits insertion loss and return loss of better than 7 and 10 dB in pass-band of 34–40 GHz, respectively, and rejection of better than 45 dB in 26–30 GHz;

Figure 10 Measured results of the fabricated Ka-band two-way switch filter module (a) state one (26–34 GHz) and (b) state two (34–40 GHz).

The measured insertion loss includes the loss of the designed test fixture. A simple calculation is that through testing, the insertion loss of the test fixture is about 2 dB, and approximately 1 dB for a switch, and about 0.5 dB for mismatching and additional line loss, so the insertion loss for the filter could be 1.5–2.5 dB. In addition, switch time measured is smaller than 10 ns, which is controlled by switch driver and switch self.

IV. CONCLUSION

In this article, a millimeter-wave ultrawideband two-way switch filter module has been fabricated and measured. The switch filter module covers whole Ka-band (26– 40 GHz). Based on requirements of the module, an 11pole three-line microstrip structure band-pass filter and a seven-order E-plane iris filter have been designed. The proposed three-line structure filter simplifies the traditional three-line filter, and still retains its virtues and high performance. The fabricated switch filter module exhibits excellent performances.

ACKNOWLEDGMENTS

This work was partially supported by Fundamental Research Funds for the Central Universities (ZYGX2012J022), China Scholarship Fund, and Over Academic Training Founds, University of Electronic Science and Technology of China.

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Zhigang Wang was born in Henan Province, China, in 1978. He received the B.S., M.S., and Ph.D. degrees in Electromagnetic and Microwave Technology from University of Electronic Science and Technology of China (UESTC), Chengdu, in 2003, 2006, and 2010, respectively. He is currently an associate professor with UESTC. His research interests include

RF, microwave and mm-wave circuit, and modules based on hybrid or MMIC technology.

Ruimin Xu was born in Sichuan Province, China, in 1958. He received the B.S., M.S., and Ph.D. degrees in Electromagnetic and Microwave Technology from University of Electronic Science and Technology of China (UESTC), Chengdu, in 1982, 1987, and 2008, respectively. He is currently a professor with UESTC. He was an Engineer at Agilis Communication

Ltd. Company, Singapore, from 1993 to 1996. He was serves as the Director of the Microwave Engineering Department of UESTC from 2004 to 2008. He has authored or coauthored over 100 papers in technical journals and conferences. His research interests include electromagnetic guide waves, microwave and mm-wave circuit and system, as well as nonlinear microwave solid circuit.

Bo Yan was born in Sichuan Province, China. He received the B.S., M.S., and Ph.D. degrees in Electromagnetic and Microwave Technology from University of Electronic Science and Technology of China (UESTC), Chengdu, in 1990, 1994, and 1998, respectively. He is currently a professor with UESTC. His research interests include microwave theory, micro-

wave and mm-wave circuit and system based on hybrid or LTCC technology.