A Planar Dual-Band Filter based on the Reduced Length Parallel Coupled Lines
Seungku Lee and Yongshik Lee, Member, IEEE
Review paper summary: A Dual-Band Filter is obtained by cascading the reactively loaded parallel coupled lines of reduced length (< 〖90〗^0).The proposed filter have same electrical performance at both the passbands at frequencies f1 and mf1, where m is the frequency of separation between the two passbands. A complete set of design equations are derived for arbitrary number of Filter stages using standard filter synthesis technique. This provides simple, low cost and high performance filter with multiple bands.
Introduction: Multiple channels are used by ...view middle of the document...
8421〗^0 and the frequency of separation m is 2.167.The bandwidth is found to be 192MHz for both the frequency which is 8% of 2.4GHz and 3.69% of 5.2GHz.
Conventional Design: A conventional bandpass filter is implemented when the coupled line of electrical length equal to 〖90〗^0 is cascaded at ports 1 and 4. The ports 2 and 3 can be made open or short. This design operates only at one frequency (f1).The equation for designing this filter is derived by even and odd mode analysis. The bandwidth of the filter with dual band is less compared to the conventional filter with single frequency of operation. This reduction in bandwidth is due to the Shunt stubs which are used to load the parallel coupled lines.
Novel Design: The electrical length of the coupled line is reduced to 〖34.84〗^0 . This decrease in length can be obtained only by increasing the frequency of separation m to 4.167.Hence the passband frequencies thus obtained are 2.4GHz and 10GHz.The even and mode impedances of the coupled line and the impedance of the shunt stub are calculated using the filter design equations. The shunt impedance value is found to be decreased when compared to filter with length 〖56.8421〗^0.The bandwidth at both the frequencies are increased to 216MHz for a filter with 9% fractional bandwidth at 2.4GHz and 2.16% fractional bandwidth at 10GHz.Thus a reduced length filter would have increased bandwidth and decreased stub impedance. A graph is plotted for frequency Vs insertion loss. The insertion loss is found to be 0.66dB at 2.4GHz and 19.8dB at 10GHz.A better insertion loss of 2.9dB is obtained with a little shift in the frequency at 12.1GHz.
Table 1: 2.4/10GHz Dual band filter
Z_(e,n) (Ω) Z_(o,n) (Ω) Z_(s,n) (Ω)
115.91 54.276 25.963
102.23 72.65 14.39
102.23 72.65 16.126
115.91 54.276 14.39
Table 2: Comparison of three designs
Parameters Design 1
(Proposed design) Design 2
(Conventional implementation) Design 3
Frequency of operation 2.4 GHz/ 5.2GHz 2.4GHz...