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RF SYSTEMS COMPONENTS FILTERS ANTENNAS NANO-CERAMICS SUPERCONDUCTIVE SPECTRUM REGULATIONS HTS BAND PASS FILTER
Chebyshev
filter of order 12 will meet the rejection requirements, see Fig. 1. Figure is
showing absolute values of S-parameters (in dB) against frequency axis
(frequency, Hz): Solid blue line is depicting Insertion Loss, red line – Return
Loss. Dashed lines of corresponding
colours show specifications for Return Loss (red dashed line), Rejection
outside pass-band and Insertion Loss inside pass-band (dashed blue line).
Fig.
1. Rejection and Return Loss for Chebyshev order 12 filter
Fig.
3. Insertion Loss performance of conventional inductive iris filter In practice BPF will be realized as a waveguide structure. This will lead to significant dispersion effects that are known to compromise rejection levels at the high frequency end of the filter response. Based on the previous experience of designing dispersive structures as well as on preliminary full-wave analysis of such structure it was recommended to increase the filter order up to 13. This will introduce necessary margins on the high frequency side of the filter response. Additional manufacturing margins have been assumed at the band edges to ensure design is not overly sensitive to mechanical tolerances. Based on the previous experience with thick-film HTS components, achievable Q-factor for practical HTS filter is in the order of 20000 or better. Dependence of the Insertion Loss value on the value of Q was studied using circuit theory model and shown in Fig. 3 Black curve – Q=3600
(conventional inductive iris filter design at 22 GHz) Blue curve
– Q=6000 (conventional dual-mode filter design at 22GHz) Magenta
curve – Q=10000, IL = 0.08 dB at the band edge Green
curve – Q=15000 Cyan curve
– Q=25000 Red curve
– Return Loss Dashed
curves – specified values
Fig.
3. Insertion Loss as function of Q-factor This analysis shows Insertion Loss is more strongly dependent on Q-factor for lower values of Q. For example, doubling the Q-values from 3000 to 6000 reclaimed about 0.15 dB (at the band edge) while changing Q from 10000 to 25000 brings about 0.05 dB improvement. This indicates importance of maintaining the Q-factor at least at the level of 15000 or better. This value was chosen as conservative assumption (green curve in Fig. 3) for specifying Insertion Loss for HTS filter only. As a result dashed blue curve indicates this specification at 0.07 dB for in-band Insertion Loss of the HTS BPF. |
