Microstrip Parallel-coupled Bandpass Filters Research Articles

Spurious-response suppression in microstrip Parallel-Coupled bandpass filters by using Defected Microstrip Structures

This paper presents a novel Parallel-Coupled Microstrip Line (PCML) bandpass filter by etching of some slot resonators on the strip for suppressing the first spurious response. These slots perform a serious LC resonance property in certain frequency and suppress the spurious signals. Slot on the strip that is called Defected Microstrip Structure (DMS). The DMS interconnection disturbs the current distribution only across the strip, thereby giving a modified microstrip line with certain stop band and slow-wave characteristics. The measured results show a satisfactory rejection level more than 30dB at first spurious passband without affecting the passband response.

Spurious-Response Suppression in Microstrip Parallel-Coupled Bandpass Filters by Grooved Substrates

Application of the grooved substrate is presented to suppress the first spurious response of microstrip parallel coupled-line filters. The grooves are oriented parallel to all coupled lines and just next to them. It is shown that the grooves equalize the even- and odd-mode phase velocities in microstrip coupled lines and, therefore, suppress the spurious response. Sets of design graphs are derived for various depths of the grooves and the curves of equal even/odd-mode phase velocities are shown. Design equations based on well-known arbitrary image impedances are reviewed and the image impedances are optimized according to the design graphs. This eventually makes it possible to select the even/odd-mode characteristic impedances for each section of the filter as close as possible to the phase velocity equalization curve. Finally, an equal ripple filter of order 3 is designed using the proposed method. The grooves were simply machined and the measurement shows a rejection of more than 35 dB in the first spurious response, as predicted in simulated results.

Optimized Design Method of Microstrip Parallel-coupled Bandpass Filters with Compensation for Center Frequency Deviation

An optimized design method is presented to compensate for the open-end effect in parallel-coupled microstrip bandpass filters. The analysis of the relationship between center frequency deviation and microstrip open-end effect is given. Based on the theoretical analysis, a design example of 10GHz bandpass filter is presented, which has proved the validity of this method.

Effect of tolerances on the performance of microstrip parallel-coupled bandpass filters

The response of microstrip parallel-coupled bandpass filters has been calculated, and the effect of the tolerances on a microstrip realisation on the response given. It is shown that the substrate thickness and the relative electrical lengths of each section are the most critical. A method of compensating for the reduction in bandwidth due to losses is also described.