Their measured frequency responses agree reasonably with the ideal responses. Three dual-band bandpass filters have been designed and implemented using non-uniform pitch helical resonators. Resonator examples have been presented to show the applicability and validity of the analysis and simulation. It is also employed in the general design process of the non-uniform pitch helical resonators. The theoretical models of the non- uniform pitch helical resonators have been developed for accurate prediction of its dual-band characteristics. Two non-uniform pitch helical resonator structures have been analytically modelled. Non-uniform pitch helical resonators are also proposed for the implementation of dual-band bandpass filters. The estimated breakdown power shows that the filter is capable of high power applications. The measured frequency response agree well with the simulated response. A second order dual-band bandpass filter formed by coaxial stepped impedance resonators has been designed, fabricated and tested. Stepped impedance resonators in stripline and coaxial configurations have been presented and analysed for the realisation of dual-band bandpass filters. The dual-band resonator methods employ multiple resonant modes of the resonator operating at different frequencies to implement the multiple passbands, respectively. The investigation based on simulation studies and measured results revealed that unloaded quality factor of the resonator is required to be ten times greater than the quality factor of each passband in order to realise the narrow passbands. Two filters have been designed and fabricated using microstrip square open-loop and TE01δ mode quarter cylindrical dielectric resonators. The transformed dual-passband response is characterised by the synthesised coupling matrix that consists of the coupling coefficients between coupled resonators. The dual-passband response synthesis method synthesises a response with dual passbands that is generated by a frequency transformation that places a finite frequency zero within the single- passband of a filter to split it into dual passbands. The second approach employs dual-band resonators that have tuneable the first and the second resonant frequencies to form the dual-passbands filter response.
The first approach is based on synthesising a dual-passband filter response utilising only one resonant frequency of the resonators. This thesis demonstrates two design approaches for the development of compact microwave dual-band bandpass filters. The lower the value of the Q factor the wider is the bandwidth of the filter and consequently the higher the Q factor the narrower and more “selective” is the filter.The modern wireless communication systems require dual-band bandpass filters to support the standards that work at multiple frequency bands. This Q Factor is a measure of how “Selective” or “Un-selective” the band pass filter is towards a given spread of frequencies. In a Band Pass Filter circuit, the overall width of the actual pass band between the upper and lower -3dB corner points of the filter determines the Quality Factor or Q-point of the circuit. Ƒ H is the upper -3db cut-off frequency point The “Q” or Quality Factor Ƒ L is the lower -3dB cut-off frequency point The center frequency is generally calculated as being the geometric mean of the two -3dB frequencies between the upper and the lower cut-off points and the resonant frequency is given as: Īn active band pass filter is a 2nd Order type filter since it has “two” reactive components (two capacitors) within its circuit design.ĭue to these two reactive components, the filter will have a peak response or Resonant Frequency ( ƒr ) at its “center frequency”, ƒc. The frequency response and phase shift for an active band pass filter will be shown below. Frequency Response of Active Band Pass Filter The amplifier also provides isolation between the two stages and defines the overall voltage gain of the circuit. In this filter circuit, a reasonable separation is required between the two cut-off points to prevent any interaction between the low pass and high pass stages.