POTENTIAL CAPABILITIES OF THE FILTER ON HAIRPIN RESONATORS WITH METALLIZED HOLES

Abstract

In the design tasks of microstrip filters, a good choice of the initial approximation for the values of
the required geometric dimensions of the filter elements plays an important role. This is especially important
if the filter being designed has new design features and synthesis methods for this device are still
under development. The paper considers some results of the design of band-pass microstrip filters consisting
of counter-directional hairpin resonators with a metallized hole in the middle of each resonator. Such
a technical solution makes it possible to significantly expand the barrier band of the filter by suppressing
the parasitic bandwidth, which is inevitably formed in a traditional filter on half-wave resonators due to
the occurrence of resonance at twice the frequency of the main bandwidth. The introduction of metallized
holes into the resonator leads to the need to study the properties of these resonators and to determine the
potential capabilities of a bandpass filter consisting of such resonant elements. The most important characteristic
of a bandpass filter, specified in any design specification, is the width of the main bandwidth and
its position on the frequency axis. Estimates of the relative bandwidth of the filter are obtained depending
on the width of the microstrip conductor forming the hairpin and on the gap between the half of the hairpin.
As a result, the potential capabilities of the filters in question are determined by the relative bandwidth
they implement. The physical feasibility of the filter is understood as the ability to technologically
realize the values of all geometric dimensions of the filter elements, based on reasonable restrictions imposed
on them. These limits are determined by technological tolerances for minimum geometric dimensions
and dimensional and frequency limits for maximum dimensions. The paper defines a range of realizable
geometric dimensions. The method of solving the problem of filter synthesis is based on the transition
from a filter to a 2n pole, and in this work it is used as a tool to determine the potential capabilities of the
studied filters in the electrodynamic environment of HFSS modeling. The realized values of the relative
bandwidth of the filter range from 10% to 32%, which makes it possible to attribute this type of filter to
devices with moderate bandwidth. The results of designing filters on two hairpin resonators for cases of
extremely narrow and extremely wide bandwidth are presented.