4.4 Coplanar Filter Miniaturization Using Advanced Technologies
4.4.2 A Modified Miniaturized LTCC Hairpin-combline Resonator
4.4.2.4 Two Proposed Designs Using LTCC
1. A coplanar bandpass filter is designed to meet the specifications:
Center frequency 2.5 GHz Passband return loss <-15 dB 2. Substrate specifications:
Permittivity (εr): 5.9 Thickness (h): 45 mils
3. The overall length of the thin line resonator is around λe at center frequency (i.e. 2.5 GHz) as shown in Fig. 68. The characteristic impedance of the
resonator is optimized using the above derived equation for matching purpose (normally >100 ).
4. To achieve a pact design in both the horizontal and vertical directions, we extend the meander line outwards to form a square loop as shown in Fig. 71.
5. In order to move the outer pole to 2.5 GHz, the proposed filter needs to be loaded with a capacitor. In order to merge the two split resonant peaks together, we introduce additional triangular protrusions between the meander lines as illustrated in Fig. 73.
he physical dimensions of the bandpass filter given in Fig. 73 are the same as those provided in Fig. 71, but with the additio l triangular protrusions. The simulated
results is
ompact in size, and has a good stop-band performance and low insertion loss of approximately 2 dB. The effective circuit area for this design is
and the guided wavelength for this case is approximately Ω
more com
6. Fine tune the structure to improve the matching.
T
na
of the filter are depicted in Fig. 74. This proposed single-layered structure c
6.54 mm 8.564 mm× , 68 mm
λe = .
2.78 mm
Fig. 73 Proposed coplanar bandpass filter
Fig. 74 Simulated (IE3D) results for the structure in Fig. 73
To further reduce the filter size and to fully utilize the LTCC multilayered capability, a two-layered structure with a single via-hole is introduced in Fig. 75. As mentioned
above, additional capacitance is needed in order to merge the two resonant peaks.
a tria
yer and 2nd layer in the second proposed design. The overall
nd
st nd
Instead of using ngular protrusion, the additional capacitance is realized through the coupling between 1st la
circuit area is reduced due to open meandered stubs in the 2 layer, as shown in Fig.
75. The connection of the 1 layer and the 2 layer is realized using a via hole. Quasi- elliptic filter response is thus obtained as shown in Fig. 76. The effective circuit volume for this design is now reduced to 3.524 mm 3.712 mm 0.1905 mm× × in x-, y- and z- direction accordingly. It is noted that the volume of this design is much smaller compared to other LTCC bandpass filters designs, which normally consist 6 to 10 metal layers [108]-[109].
Fig. 75 Dimensions of the proposed two-layered filter design
Fig. 76 Simulated (IE3D) results for the proposed two-layered design
4.4
The two proposed CPW bandpass filters were fabricated using an in-house six-layered Ferro A6 LTCC technology. The relative permittivity of the substrate is 5.9 and the thickness of each layer is 0.1905 mm. The photographs of the two proposed designs are given in Fig. 77.
The responses of these filters were measured using HP-8510C vector network analyzer.
The simulated and measured results for the single-layered structure are compared in Fig. 78. This bandpass filter was designed to have a centre frequency of 2.46 GHz with a minimum insertion loss of 1.8 dB, a return loss of 27.2 dB at centre frequency
.2.5 Experimental Results and Discussions
the center frequency is slightly shifted to 2.39 GHz and the insertion loss at centre equency is 4.12 dB and the return loss is around 26 dB.
80. This filter is designed to have a centre frequency at 2.45 GHz, which has a
center frequency is shifted to 2.2 GHz. The measured insertion loss is 1.2 dB and the 25 dB. It is also noted that the 3-dB bandwidth for the two-layered filter is increased to 30.6% as compared to single-layered filter, which is fr
The simulated and measured results for the two-layered structure are compared in Fig.
minimum insertion loss of 0.375 dB, a return loss of 25dB at centre frequency and a fractional 3-dB bandwidth of 30.6%. From the measured results shown in Fig. 78, the
measured return loss is around
given as 5.4%.
The possible reasons of discrepancy between simulated and measures results have been discussed in detail in the previous chapter. For single-layered structure, the effect of variation of the permittivity is shown in Fig. 79. A frequency shift of 70 MHz is observed at two extreme cases, i.e. εr =5.7 andεr =6.1. F r two-layered structureo , e effect of variation of the perm frequency shift of 60
th ittivity is shown in Fig. 81. A
MHz is observed at two extreme cases, i.e. εr =5.7 andεr =6.1.
Instead of using lumped elements for LTCC filter implementation, two novel and miniaturized LTCC CPW filters were realized by using a sequence of capacitance le-layered filter, an insertion loss of 4.12 dB and a return loss of loading. For the sing
26 dB were achieved. Similarly, for the two-layered filter, an insertion loss of 1.2 dB and a return loss of 25 dB were obtained.
(i)
Fig. 77 Photographs for the proposed designs: (i) Single-layered CPW bandpass filter as shown in Fig. 73, (ii) Two-layered CPW bandpass filter with via as shown in
Fig. 78 Simulated (IE3D) and measured results for Design (i) in Fig. 77 (ii)
(a) Comparison of S11
(b) Comparison of S21
parison of S-parameters with
Fig. 79 Com εr =5.7, 5.9εr = and εr =6.1
Fig. 80 Simulated (IE3D) and measured results for Design (ii) in Fig. 77
(a) Comparison of S
(b) Comparison Fig. 81 Comparison of S-parameters wit
of S21
hεr =5.7, 5.9εr = and εr =6.1