диафрагмированные волноводные фильтры / d0182895-8230-4978-9c13-dfa6aa780d86

Abstract—A novel integratable planar T-junction waveguide power divider, a so-called TEH(E-plane input and H-plane output) junction waveguide power divider, with anti-phase outputs and full bandwidth is proposed in this letter. It is basically a E-plane waveguide T-junction with its input port rotated around the axis of the two output ports by 90 degrees to form a planar structure. In order to expand its operation bandwidth, several stages of matching sections are added between the coupling cavity and each port. In order to verify the concept, a standard waveguide port TEH junction divider is designed and tested as an example. From the tested results, the reflection coefficient is lower than −20 dB and phase difference between the two output ports is within 177 +/−3 degrees in the full bandwidth from 26.3 to 40 GHz.

Index Terms—Anti-phase, full bandwidth, planar, power divider, waveguide.

I. INTRODUCTION

DUE to low insertion loss, waveguide power dividers are often used in microwave systems to split or to combine signals. Among various waveguide power dividers, E-plane [1], [2] and H-plane [3], [4] waveguide T-junctions are most popular due to its simple, symmetric and compact structures. Both kinds of waveguide T’s are planar in the sense that all axes of the three ports are in the same plane and however, their phase difference between the two output ports are always zero. This feature might be very attractive in many applications such as in power combiners and phased arrays. However, in some other applications [5]–[10], especially in planar integration, wideband anti-phase outputs may be necessary, conventional T-junction

waveguide power divider may be not practical.

In this letter, a novel planar waveguide T-junction power divider with anti-phase and full bandwidth outputs will be proposed. It can realize planar anti-phase output in the true sense. In order to verify the concept, a sample power divider with standard WR28 waveguide (a = 7.112 mm, b = 3.556 mm) port will be designed and tested. The design consideration, configuration, and the optimized results will also be presented together with the tested results.

II. DESIGN CONSIDERATION AND POWER

DIVIDER CONFIGURATIONS

In an conventional H-plane or E-plane T-junction waveguide power divider, the axis of the input port is in the H-plane or

Manuscript received March 4, 2016; revised April 21, 2016; accepted May 10, 2016. Date of publication July 22, 2016; date of current version August 5, 2016.

The authors are with the School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China (e-mail: zhaopeng122@126.com; qywang2002@126.com).

Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/LMWC.2016.2587835

Fig. 1. Bent T-junctions power dividers. (a) An H-plane junction. (b) An E-plane junction. (c) A TEH junction.

Fig. 2. (a) Basic elements of a planar TEH junction. (b) 3-dimensional view with several matching sections added to each port.

E-plane of the two output ports, respectively, and the two output ports are symmetrically arranged at the both side of the input port. When the two output ports are bent in their H-plane or E-plane symmetrically towards the same direction of the input port, as shown in Fig. 1(a) and (b), the phase difference between the two output ports in each case is zero. For the E-plane junction, anti-phase output can be realized if we bend the two output ports towards the vertical direction of the input port but the power divider will become a 3-dimensional device because the axis of the input port will be perpendicular to that of the two output ports, this will make the power dividers difficult to fabricate and assemble. Bearing this in mind, if we further arrange the input port in the H-plane of the two output ports, as shown in Fig. 1(c), because the operation mode (TE10 mode) of transmission does not change, its field will rotate in the coupled cavity and a planar T-junction waveguide power divider with anti-phase and equal amplitudes is realized. we can call it TEH (E-plane input and H-plane output) junction for short.

As shown in Fig. 2, the configuration of the proposed TEH junction includes basically a coupling cavity, a vertically positioned input port and two horizontally positioned output ports. For equal amplitude dividing, the whole structure is assumed symmetrical with respect to the H-plane of the input port. The full height input port and output ports are broadband matched to coupling cavity via using three stepped impedance transformers respectively. The dimensions of the each stepped impedance transformer width, height and length are aij , hij , dij , respectively, with i = 1, 2, j = 1, 2, 3, and 4. Because the operating bandwidth of ridge waveguide is wider than empty

Fig. 3. (a) Top view with configuration parameter definitions. (b) Front view watched along input port with configuration parameter definitions.

waveguide in the same size, we arranged a ridge at bottom of each waveguide section in the output ports for the purpose of expanding the operation bandwidth. The width and height of the ridge in each matching section in the output port is w2i, g2i, respectively, with i = 1, 2, 3, and 4. All the center lines of the waveguide sections and the ridges in each output port are aligned with the axis of the same output port. To further expand the operation bandwidth and reduce the reflection to a certain extent, a rectangular slot with width w, height g and length d is added on the bottom of the coupling cavity to add new discontinuity to offset the original discontinuity. Fig. 3(a) and (b) are its top view and front view with most of the configuration parameter definitions, in which we can see that, the coupling cavity width is b, length is a, the first section in the output port is offset from the rear wall of the cavity by off. The top surfaces of all the structures are aligned in a common horizontal plane in order to facilitate the fabrication of a power divider and especially a power divider network integrated from such power dividers.

III. OPTIMIZATION RESULTS

The design concept described in Section II is verified by a sample power divider built and optimized by a commercial simulation software “CST microwave studio.”

The center frequency is set at 33.2 GHz. The dimensions of the input and output port are all assumed the same as a standard WR28 waveguide. As shown in Fig. 2(b), the initial length of each stepped impedance transformer is assumed λ/4 (λ is the wavelength corresponding to the center frequency), and the initial dimensions of the waveguide width and height are assumed the same as that of the input port. Considering the requirements of single mode transmission and characteristic impedance, we set the initial proportion w2i/a2i, g2i/b2i at 0.2, with i = 1, 2, 3, and 4. In order to facilitate the fabrication

Fig. 4. (a) Transmission coefficient. (b) Reflection coefficient. (c) Phase difference. (d) Isolation coefficient of the sample power divider after optimization.

through a conventional computer numerical controlled milling machine, in the last model, all the inner corners are blended by a radius of 0.75 mm. Because T-junction power divider is a simple lossless and reciprocal three-port network and the structure is symmetric with the H-plane of the input port, there will be no isolation between the two output ports and there will be a mismatch looking into the output ports [12]. So only S11 parameters need to be optimized. The configuration parameters of the optimized sample power divider is given in Table I. The S11, S21, and S31 parameters at the three ports are shown in Fig. 4, from which we can see that transmission coefficient is about −3.025 ± 0.02 dB, the phase difference of the out puts is 180 degree and the reflection coefficient S11 is lower than −23.5 dB in the full bandwidth from 26.3 to 40 GHz. It also shows the isolation parameter S23 which is lower than −6 dB.

IV. TESTED RESULTS AND COMPARISON

A sample TEH junction power divider was fabricated according to the configuration parameters given in Section II and disassembled photos are shown in Fig. 5. We can see that the power divider is indeed very compact and its dimensions are 25 mm 24 mm 21 mm. The tested results are shown in Fig. 6, from which we can see the reflection coefficient is lower than −20 dB, insertion loss in the two output ports within −3.02 ± 0.03 dB. The phase difference between the two output ports is 177 ± 3.3 degrees.

Fig. 5. Photo of the sample power divider with its cover removed.

T-junction waveguide power divider with its input port rotated around the axis of the two output port from their E-plane to its H-plane. Three-stepped-impedance transformers and some ridges were added between the center coupling cavity and each of the three ports. The structure or a network integrated from it can have a common top plane so that the whole structure can be easily fabricated with conventional computer-numerical- controlled milling machine. The model of a sample power divider was built and then optimized for matched input. In the last round of optimization, all the inner corners have been blended to facilitate its fabrication. The sample power divider was then fabricated and tested. Tested results show that the sample power divider works well in the full operation bandwidth of a standard WR28 waveguide, with reflection coefficient lower than −20 dB, insertion loss lower than 0.1 dB, amplitude error within 0.1 dB and the two output port is in anti-phase within an error of −3 +/−3 degrees.

We found that the two output ports appears a little unbalanced in amplitude and its phase difference a little away from 180 degrees. We believe these two errors mainly come from the fabrication error and assembling error. Connection tightness between the flanges of the coaxial-waveguide adapters and each of the two output ports might be different and the flanges might not be perfectly flat, which are the two more factors leading to the testing errors. We believe that with better fabrication accuracy and assembling accuracy, and better contacting conditions between the flanges, lower insertion loss, better amplitude balance and better anti-phase between the two output ports can be achieved.

Fig. 6. Tested results from the sample power divider. (a) Reflection coefficient.

(b) Transmission coefficient. (c) Phase difference of the output ports.

TABLE II

STATE-OF-ART OF WAVEGUIDE POWER DIVIDERS

Table II lists the performance parameters of this work and some recently reported waveguide power dividers. From the table we can see that the TEH junction power divider reported in this letter is superior in these aspects. First, the phase difference of the bent power divider in this work is approximate 180 degrees while others is 0 degree. Second, its fractional bandwidth and input port return loss are much better. And Third, it is easier to be fabricated and assembled.

V. CONCLUSIONS AND DISCUSSIONS

In this letter, we proposed a novel planar T-junction waveguide power divider with equal-amplitude, anti-phases and full bandwidth. The power divider is similar to a conventional E-plane

REFERENCES

[1]Y.-S. Liu, D.-C. Niu, and E. S. Li, “Three-port E-plane bifurcated waveguide power divider at millimeter-wave frequencies,” in Proc. APMC, 2012, pp. 998–1000.

[2]M. Zou, Z. H. Shao, J. Cai, and L. Liu, “Ka-band rectangular waveguide power dividers,” in Proc. Int. Conf. ICCP, 2011, pp. 375–377.

[3]S. Yang and A. E. Fathy, “Synthesis of a compound T-junction for a twoway splitter with arbitrary power ratio,” in Proc. IEEE MTT-S Int. Dig., 2005, pp. 985–988.

[4]J. Ding, Q. Wang, Y. Zhang, and C. Wang, “A novel five-port waveguide power divider,” IEEE Microw. Wireless Compon. Lett., vol. 24, no. 4,

pp.224–226, Apr. 2014.

[5]A. Navarrini, T. Pisanu, and R. Nesti, “A waveguide cavity 180◦ hybrid coupler with coaxial ports,” Microw. Optical Technol. Lett., vol. 51, no. 7,

pp.1646–1649, Jul. 2009.

[6]J. Hirokawa, K. Morimoto*, and M. Ando, “Beam-switching single-layer

post-wall waveguide slot array controlling crossover & sidelobes?” in Proc. 2nd Eur. Conf. Antennas Propag. (EuCAP), Nov. 11–16, 2007,

pp.1–5.

[7]C.-F. Yu and T.-H. Chang, “High-performance circular TE01-mode converter,” IEEE Trans. Microw. Theory Techn., vol. 53, no. 12,

pp.3794–3798, Dec. 2005.

[8]H. Guan-Long, Z. Shi-Gang, C. Tan-Huat, and Y. Tat-Soon, “A Ku-band 8 × 8 dual-polarized high-gain array with mirror-symmetric hybrid feeding network,” in Proc. 8th Eur. Conf. Antennas Propag. (EuCAP), Apr. 2014, pp. 635–656.

[9]G. Engargiolaa and R. L. Plambeck, “Tests of a planar L-band orthomode transducer in circular waveguide,” Rev. Scientific Instrum., vol. 74, no. 3,

pp.1–10, Mar. 2003.

[10]G. Valente, G. Montisci, T. Pisanu, A. Navarrini, P. Marongiu, and G. A. Casula, “A compact L-band orthomode transducer for radio astronomical receivers at cryogenic temperature,” IEEE Trans. Microw. Theory Tech., vol. 63, no. 10, pp. 3218–3227, Oct. 2015.

[11]G. Valente, A. Navarrini, and T. Pisanu, “Double ridged 180 hybrid power divider with integrated band pass filter,” IEEE Microw. Wireless Compon. Lett., vol. 21, no. 1, pp. 13–15, Jan. 2011.

[12]D. M. Pozar, Microwave Engineering [M], 3rd ed. Beijing, China: Publish House of Electronics Industry, pp. 315–316.