диафрагмированные волноводные фильтры / 2a1f6d27-bb3a-4244-9c79-446ee6a138a3
.pdfBalun bandpass filter based on multilayer substrate integrated waveguide power divider
J.N. Hui, W.J. Feng and W.Q. Che
A compact multilayer substrate integrated waveguide (SIW) balun bandpass filter is proposed. A 1808 reverse phase characteristic between the input/output ports can be easily achieved by the middle metal-ground of the SIW power divider. Four inductive posts are added to the multilayer SIW power divider to realise a passband. Good in-band balance performance (amplitude and phase imbalance are less than 0.35 dB and 28) over the passband are achieved for the balun bandpass filter.
Introduction: As one of most important RF front-end functional passive devices, the balun bandpass filter integrating balun and bandpass filter is a necessary component for converting a balanced signal into an unbalanced one for a specified bandpass characteristic in RF/microwave communication systems. In the past few years, several techniques have been proposed to design narrow/dual-band, and wideband balun bandpass filters [1–4]. The characteristics of balun and bandpass filtering can be easily realised in these filter structures. However, the application of these filters is limited because the optimisation of the in-band balun performances is not convenient to realise.
In the authors’ previous works [5, 6], two planar substrate integrated waveguide (SIW) magic-T structures with wide band and simple design based on E-plane power dividers were proposed. Compared with the T/Y-junction planar SIW power divider structures [7], the size reduction of the circuits is almost 50 and 75%, respectively. In this Letter, a compact balun bandpass filter with four inductive posts based on the multilayer SIW power divider [5] is designed. A high-order passband (centre frequency 12.5 GHz, bandwidth 4.8%) with high selectivity and extended stopband for the balun filter can be achieved.
|
|
port 2 |
|
|
|
|
|
|
|
|
|
upper |
|
|
|
|
|
|
|
|
|
|
|
layer |
|
|
|
|
|
|
|
|
|
|
|
port 1 |
|
|
|
|
|
|
|
|
port 2 |
|
|
via |
|
|
middle |
|
|
|
|
|
|
||
|
|
|
|
|
d |
w |
|
|
|
||
|
|
layer |
|
|
|
|
|
|
|||
holes |
|
|
|
tw1 |
|
w51 |
|||||
|
|
port 3 |
|
|
tw |
2 |
|||||
|
|
|
port 1 w50 |
tl |
|
a |
|
|
|
|
|
|
|
|
|
1 |
|
|
|
|
|||
|
|
|
|
|
|
tl2 |
|
|
|
||
bottom |
|
|
|
|
|
|
|
l3 |
w |
51 |
|
|
|
|
|
|
|
l1 |
|
|
|
||
layer |
|
a |
|
|
|
|
l2 |
|
port 3 |
|
|
|
|
|
|
|
|
A |
|
|
|
||
|
|
|
|
|
|
b |
|
|
|
||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
upper |
|
|
|
|
|
|
|
|
|
|
(+) |
layer |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
er |
|
|
h |
|
|
|
|
|
|
|
|
|
|
|
(0) |
|
|
|
|
|
|
|
|
|
|
(–) |
|
|
|
|
|
|
|
|
|
|
middle |
|
bottom |
|
|
|
|
|
|
|
|
|
layer |
|
|
|
|
|
|
|
|
|
|
|
c |
layer |
|
|
|
|
d |
|
|
|
|
|
|
|
|
|
|
|
|
|
|||
|
|
|
|
|
|
|
|
|
|
magnitude, dB
0
–5
–10
–15
–20
–25
–30
–35
–40
|S11| |S21| |S31|
8 9 10 11 12 13 14 15 16 17 18
frequency, GHz
phase, deg
250 |
|
|
|
|
|
|
|
|
|
|
200 |
|
|
|
|
|
|
|
|
180 |
deg |
150 |
|
|
|
|
|
|
|
|
176 |
|
0 |
|
|
|
|
|
|
|
|
difference, |
|
100 |
|
|
|
|
|
|
|
|
178 |
|
50 |
|
|
|
|
|
|
|
|
|
phase- |
–100 |
|
|
|
|
|
|
|
|
|
|
–50 |
|
|
|
|
|
|
|
|
174 |
|
|
|
|
|
|
|
|
|
|
|
|
–150 |
|
|
|
|
|
|
|
|
172 |
-of |
–200 |
phase of |S21| |
|
|
|
|
|
out |
|||
|
out-of-phase difference |
|||||||||
|
|
|||||||||
|
phase of |S31| |
|
|
|||||||
–250 |
|
|
|
|
|
|
|
|||
|
|
|
|
|
|
|
|
|
|
|
8 |
9 |
10 |
11 |
12 |
13 |
14 |
15 |
16 |
17 |
|
|
|
|
frequency, GHz |
|
|
|
|
e |
f |
Fig. 1 3D view, and top view of the E-plane SIW power divider; electric field distribution at A-A′ plane; dominant mode coupling of multilayer SIW power divider; simulated magnitudes, phases of E-plane SIW power divider
a 3D view of E-plane SIW power divider b Top view of E-plane SIW power divider c Electric field distribution at A-A′ plane
d Dominant mode coupling of multilayer SIW power divider e Simulated magnitudes of E-plane SIW power divider
f Simulated phases of E-plane SIW power divider
70 mm× 20 mm, 7.2lg × 1.2lg W50 ¼ 2.8 mm, W51 ¼ 1.4 mm, L1 ¼ 11.0 mm, L2 ¼ 37.0 mm, L3 ¼ 6.0 mm, a ¼ 12.0 mm, d ¼ 0.6 mm, w ¼ 1.0 mm, tl1 ¼
5.0 mm, tw1 ¼ 5.12 mm, tl2 ¼ 5.0 mm, tw2 ¼ 5.11 mm, s ¼ 2.54 mm, 1r ¼ 2.65, h ¼ 1.0 mm, tan d ¼ 0.002
Filter design: Figs. 1a and b illustrate the 3D view and the top view of the E-plane SIW power divider, consisting of two substrate layers with a metal ground located in the middle of the structure with two ports (port
2, 3) on top and bottom planes. The electric field at the A-A′ plane and the dominant mode coupling of the SIW power divider are described in Figs. 1c and d. We may note that the E-field orientations of the two ports (port 2, 3) are different from each other, indicating a 1808 phase difference. At the same time, the power from port 1 can be divided equally at ports 2 and 3. Figs. 1e and f show the simulated results of the SIW power divider, the return loss S11 is greater than 15 dB (9.2–17.5 GHz), while the phase difference between S21 and S31 is approximately 1808 within 8–17.5 GHz.
|
|
|
A |
|
|
|
port 2 |
|
|
|
|
|
|
|
|
d |
w |
|
|
|
w51 |
|
|
|
|
|
tw1 |
|
|
|
tw |
|
|
|
|
|
||
|
|
|
|
2 |
|
|
a |
jXa |
jXa |
|||
port 1 w50 |
|
|
a d1 |
d2 |
|
|
|
|
|
|||
tl |
1 |
|
|
|
|
|
|
|||||
|
|
|
|
|
|
|
|
|
|
|
||
|
|
|
l3 l4 |
l5 |
l4 |
l6 tl2 |
l7 |
w51 |
h |
|
jXb |
|
|
|
|
|
|
|
|
|
|
|
|||
|
|
|
l1 |
l2 |
|
|
|
port 3 |
|
|
Z0 |
Z0 |
|
|
|
A |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
a |
|
|
|
|
|
|
b |
|
Fig. 2 Top view of proposed SIW balun bandpass filter; inductive post in SIW and equivalent circuit
a Top view of proposed SIW balun bandpass filter b Inductive post in SIW and equivalent circuit
W50 ¼ 2.8 mm, W51 ¼ 1.4 mm, L1 ¼ 11.0 mm, L2 ¼ 37.0 mm, L3 ¼ 5.2 mm, L4 ¼ 8.9 mm, L5 ¼ 10.0 mm, L6 ¼ 4.0 mm, L7 ¼ 6.0 mm, a ¼ 12.0 mm, d ¼ 0.6mm, d1 ¼ 0.86 mm, d2 ¼ 2.2 mm, w ¼ 1.0 mm, tl1 ¼ 5.0 mm, tw1 ¼ 5.12 mm, tl2 ¼ 5.0 mm, tw2 ¼ 5.11 mm, s ¼ 2.54 mm
Fig. 2a shows the top view of the proposed balun bandpass filter. Four inductive posts are added to realise a Chebyshev filter for the balun bandpass filter structure [8, 9]. The equivalent circuit of the inductive post is shown in Fig. 2b, and the equivalent circuit parameters jXa and jXb can be calculated from the S-parameters of the equivalent circuit as follows (Z0 ¼ 50 V):
jXa/Z0 = (1 + S11 − S21)/(1 − S11 + S21) |
(1) |
jXb/Z0 = 2S21/[(1 − S11)2 − S212 ] |
(2) |
The distance between each inductive post (Ln) can be given by [9]:
Ln = lg0un/2p |
(3) |
un = p + 0.5 × (fn + fn+1) |
(4) |
f = − arctan(Xa/Z0 + 2Xb/Z0) − arctan(Xa/Z0) |
(5) |
lg0 is the guided wavelength of the centre frequency of the passband. The simulated results of the SIW balun filter are shown in Figs. 3a and b. The simulated 3 dB fractional bandwidth is 4.37% (12.3– 12.85 GHz), the minimum insertion loss is 3.4 dB for each path, a three-order passband with return loss greater than 13.5 dB and over 35 dB upper stopband (13.7–16 GHz) is thus realised. In addition, the amplitude and phase imbalances of the balun bandpass filter are less than 0.15 dB and 1.88, respectively.
magnitude, dB
0
|
–2 |
|
|
|
|
|
|
|
|
–10 –3 |
|
|
|
|
|
|S11| |
|
||
|
–4 |
|
|
|
|
|
|
||
|
|
|
|
|
|
|
|
|
|
–20 –5 |
|
|
|
|
|
|
|
|
|
–30 |
–6 |
12.5 |
|
13.0 |
|
|
|
|
|
12.0 |
|
|
|
|
|
||||
–40 |
|
|
|
|
|
|
|
|
|
–50 |
|
|
|
|
|S21| and |S31| |
|
|
|
|
–60 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
simulated results |
|
|
||
–70 |
|
|
|
|
measured results |
|
|
||
–80 |
9 |
10 |
11 |
12 |
13 |
14 |
15 |
16 |
|
|
frequency, GHz
a
upper layer
middle layer 2
|
2 |
|
|
|
|
|
200 |
|
imbalance,amplitudedB |
1 |
|
|
|
|
|
195 |
imbalance,phasedeg |
|
|
|
|
|
|
|||
0 |
|
|
|
|
|
|
||
|
–1 |
|
|
|
|
|
190 |
|
|
|
|
simulated results |
|
|
|
||
|
–2 |
|
measured results |
|
185 |
|
||
|
–3 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
–4 |
|
|
|
|
|
180 |
|
|
|
|
|
|
|
|
|
|
|
–5 |
|
|
|
|
|
175 |
|
|
120 |
122 |
124 |
126 |
128 |
130 |
|
frequency, GHz
b
middle layer 1
bottom layer
c
Fig. 3 Measured and simulated magnitudes, amplitude and phase imbalances of SIW balun bandpass filter; photograph of proposed SIW balun bandpass filter
a Measured and simulated magnitudes of SIW balun bandpass filter b Measured and simulated amplitude and phase imbalances
c Photograph of proposed SIW balun bandpass filter
ELECTRONICS LETTERS 10th May 2012 Vol. 48 No. 10
Experimental results: Fig. 3c shows the photograph of the proposed SIW balun bandpass filter, the measured results of the proposed balun bandpass filter are also shown in Figs. 3a and b. The measured 3 dB fractional bandwidth is 4.8% (12.2–12.8 GHz); the maximum insertion loss is 4.0 dB in each path, the return loss is greater than 13 dB in the passband, and over 35 dB upper stopband is obtained from 13.5 to 16 GHz. In addition, the amplitude and phase imbalances in the passband of the balun bandpass filter are less than 0.35 dB and 28. The slight frequency discrepancy for the measured results may be caused by the limited fabrication accuracy and measurement errors.
Conclusions: A compact balun bandpass filter with high selectivity using four inductive posts based on a multilayer substrate integrated waveguide power divider is proposed. Equal out-of-phase power division can be easily achieved between the input/output ports. The proposed wideband balun bandpass filter shows advantages of controllable fractional bandwidth, high selectivity, good in-band balance performance and extended upper stopband, indicating a good candidate for wideband wireless communication applications.
Acknowledgments: This work was supported by the National Natural Science Foundation of China (60971013) and the 2010 Innovative Projects for Graduates of Jiangsu Province.
# The Institution of Engineering and Technology 2012
23 February 2012
doi: 10.1049/el.2012.0479
One or more of the Figures in this Letter are available in colour online.
J.N. Hui, W.J. Feng and W.Q. Che (School of Electronic and Optical Engineering, Nanjing University of Science & Technology, Nanjing 210094, People’s Republic of China)
E-mail: yeeren_che@yahoo.com.cn
References
1 Jung, E.Y., and Hwang, H.Y.: ‘A balun-BPF using a dual mode ring resonator’, IEEE Microw. Wirel. Compon. Lett., 2007, 17, (9), pp. 652–654
2 Yeung, L.K., and Wu, K.-L.: ‘A dual-band coupled-line balun filter’,
IEEE Trans. Microw. Theory Tech., 2007, 55, (11), pp. 2406–2411
3Zhang, Z.Y., and Wu, K.: ‘A broadband substrate integrated waveguide planar balun’, IEEE Microw. Wirel. Compon. Lett., 2007, 17, (12), pp. 843–845
4Eom, D., Byun, J., and Lee, H.Y.: ‘Multi-layer substrate integrated waveguide four-way out-of-phase power divider’, IEEE Trans. Microw. Theory Tech., 2009, 57, (12), pp. 3469–3476
5 Feng, W.J., Che, W.Q., and Deng, K.: ‘Compact planar Magic-T using E-plane substrate integrated waveguide (SIW) power divider’, IEEE Microw. Wirel. Compon. Lett., 2010, 20, (6), pp. 331–333
6Feng, W.J., Che, W.Q., and Eibert, T.F.: ‘Compact planar Magic-T using half mode substrate integrated waveguide and slotline coupling’, IEEE
MTT-S Int. Microw. Symp. Dig., June 2011, pp. 1–4
7Germain, S., Deslandes, D., and Wu, K.: ‘Development of substrate integrated waveguide power dividers’, IEEE Electr. Comput. Eng., 2003, 3, pp. 1921–1924
8Marcuvitz, N.: ‘Waveguide handbook’ (MIT Radiation Laboratory Series, McGraw-Hill, 1951, Vol. 10)
9Deslandes, D., and Wu, K.: ‘Millimeter-wave substrate integrated waveguide filters’. Proc. IEEE Canadian Conf. Electrical Computer
Engineering, (CCECE’03), Montreal, Canada, 2003, Vol. 3, pp. 1917–1920
ELECTRONICS LETTERS 10th May 2012 Vol. 48 No. 10