陕西理工学院毕业设计
致谢
首先，我要感谢我的指导老师贾建科老师。在本次毕业设计中，贾老师给了我很大的帮助，本篇论文是在贾老师的悉心指导下完成的。遇上的各种问题都回去找他寻找帮助，在他的指导下都很好的解决了遇到的问题。他以其严谨的学术态度、和善的待人态度、独到的专业见解给予我精心的指导和帮助，所以我要衷心感谢我的指导老师贾建科老师，在此向老师表示深深的谢意!
我还要感谢我的同学在四年的大学学习期间，我们共同度过了美好又充满欢笑的大学生活。你们不仅在学习上给予了我无私的帮助，在生活上也给我留下了美好的回忆。在这次毕业设计中也有好多同学给我很大的帮助。我要特别感谢，晁震、刘帅、石晟和邹宇航同学，在本次设计中这几位同学和我一起查找资料，一起进行理论验证，为我毕业论文的顺利完成给与了非常大的帮助，谢谢他们。
这是我的大学最后的一个学期，随着毕业设计工作的完成，我的大学生涯也马上将要结束。回首四年的学习成长经历，充满了老师和朋友同学的关心与爱护，在这个终于顺利撰写完成我的毕业论文的时候，对曾经给予我帮助和鼓励的父母、师长、同学、朋友致以衷心的感谢。
第 36 页 共 48 页
陕西理工学院毕业设计
附录A 外文文献
COUPLED LINE FILTERS
The parallel coupled transmission lines discussed in Section 7.6 (for directional couplers) can be used to construct many types of filters. Fabrication of multisection bandpass or bandstop coupled line filters is particularly easy in microstrip or stripline form for band- widths less than about 20%. Wider bandwidth filters generally require very tightly coupled lines, which are difficult to fabricate. We will first study the filter characteristics of a single quarter-wave coupled line section, and then show how these sections can be used to design a bandpass filter [7]. Other filter designs using coupled lines can be found in reference [1].
Filter Properties of a Coupled Line Section
A parallel coupled line section is shown in Figure 8.42a, with port voltage and current definitions. We will derive the open-circuit impedance matrix for this four-port network by considering the superposition of even- and odd-mode excitations [8], which are shown in Figure 8.42b. Thus, the current sources i1 and i3 drive the line in the even mode, whilei2 and i4 drive the line in the odd mode. By superposition, we see that the total port currents, Ii , can be expressed in terms of the even- and odd-mode currents as
I1 = i1 + i2, (8.87a)
I2 = i1 - i2, (8.87b)
I3 = i3 - i4, (8.87c)
I4 = i3 + i4. (8.87d)
First consider the line as being driven in the even mode by the i1 current sources. If the other ports are open-circuited, the impedance seen at port 1 or 2 is
eZin=-jZ0ecotβl (8.88)
The voltage on either conductor can be expressed as
v(z)=v(z)=V[e+e1a1b+e_jβ(z_l)+e_jβ(z_l)=2Vcosβ(lz)1+ev1a(0)=vb(0)=2Vecosβl=i1Zin
(8.89)
so the voltage at port 1 or 2 is
This result and (8.88) can be used to rewrite (8.89) in terms of i1 as
v(z)=v(z)=jZ0e1a1b_cosβ(l_z)i (8.90)
sinβl1 第 37 页 共 48 页
陕西理工学院毕业设计
（a） (b)
(c)
FIGURE Definitions pertaining to a coupled line filter section. (a) A parallel coupled line section with port voltage and current definitions. (b) A parallel coupled line section with even- and odd-mode current sources. (c) A two-port coupled line section having a bandpass response.
Similarly, the voltages due to current sources i3 driving the line in the even mode are
33va(z)=vb(z)=_jZ0ecosβzi (8.91) sinβl3Now consider the line as being driven in the odd mode by current i2. If the other ports are open-circuited, the impedance seen at port 1 or 2 is
0_Zin=jZ0ocotβl (8.92)
The voltage on either conductor can be expressed as
22va(z)=_vb(z)=V0+[e_jβ(z_l)+ejβ(zl)=2V0+cosβ(l_z) (8.93)
_Then the voltage at port 1 or port 2 is
220 va(0)=_vb(0)=2V0+cosβl=i2ZinThis result and (8.92) can be used to rewrite (8.93) in terms ofi2as
22va(z)=_vb(z)=_jZ0ocosβ(l_z)i (8.94)
sinβl2Similarly, the voltages due to currenti4 driving the line in the odd mode are
第 38 页 共 48 页
陕西理工学院毕业设计
44va(z)=_vb(z)=_jZ0ocosβzi (8.95) sinβl4The total voltage at port 1 is
234V1=v1a(0)+va(0)+va(0)+va(0)=_j(Z0ei1+Z0ei2)cotθ_j(Z0ei3+Z0ei4)cscθ (8.96)
where the results of (8.90), (8.91), (8.94), and (8.95) were used, and θ = β .Next, we solve (8.87) for the i j
in terms of the I s:
1i1 =(I1＋I2), (8.97a)
21i2 =(I1－I2), (8.97b)
21i3 =(I3＋I4), (8.97c)
21i4 =(I4－I3), (8.97d)
2and use these results in (8.96):
jV1=(Z0eI1+Z0eI2+Z0oI1_Z0oI2)cotθ2 (8.98) _j=(Z0eI3+Z0eI4+Z0oI4_Z0oI3)cscθ2This result yields the top row of the open-circuit impedance matrix [Z ] that describes the coupled line section. From symmetry, all other matrix elements can be found once the rst row is known. The matrix elements are then
__Z11=Z22=Z33=Z44=j(Z+Z0o)cotθ (8.99a) 20e_Z12=Z21=Z34=Z43=j(Z0e__Z0o)cotθ (8.99b) 2j(Z0e__Z0o)cscθ (8.99c) 2_Z13=Z31=Z24=Z42=jZ14=Z41=Z23=Z32=(Z+Z0o)cscθ (8.99d)
20e A two-port network can be formed from a coupled line section by terminating two of the four ports with either open or short circuits, or by connecting two ends; there are 10 possible combinations, as illustrated in Table 8.8. As indicated in the table, the various circuits have different frequency responses, including low-pass, bandpass, all pass, and all stop. For bandpass filters, we are most interested in the case shown in Figure 8.42c, as open circuits are easier to fabricate in microstrip than are short circuits. In this case,
_I2=I4=0.
第 39 页 共 48 页
陕西理工学院毕业设计
The real part of the image impedance of the bandpass network of Figure 8.42c. so the four-port impedance matrix equations reduce to
V1?Z11I1?Z13I3 (8.100a)
V3?Z31I1?Z33I3 (8.100b)
第 40 页 共 48 页