Peak and Average Power Handling Capability of Microstrip Filters

Abstract

In this work, the power handling capability of microstrip filters is studied in detail. This study is addressed from two perspectives, depending on the physical phenomenon limiting the maximum power that the microstrip filter can handle. One of these phenomena is air breakdown or corona effect, which is linked to the peak power handling capability (PPHC) of the device, and the other is the self-heating, which limits the device average power handling capability (APHC). The analysis is focused on three kinds of filtering topologies widely used both in academia and industry, such as the coupled-line, stepped impedance resonator and the dual-behaviour resonator based filters. Closed-form expressions are computed to predict both the PPHC and the APHC as a function of the geometrical parameters of the resonators integrating the filter. Guidelines are also given to extrapolate the provided computations to other filtering topologies based on other kinds of resonators. To validate this research study, three bandpass filters centered at 5 GHz have been implemented and fully characterized by means of two measurements campaigns which have been carried out, one for the PPHC and another one for the APHC. The measured results have validated the performed study and corroborated the conclusions obtained throughout the paper. Index Terms-Average power handling capability (APHC), coupled-line filter, electro-thermal analysis, microstrip filter, peak power handling capability (PPHC), power applications, stepped impedance resonator (SIR).

Enhancement of corona discharge thresholds in microstrip bandpass filters by using cover-ended resonators

“…From the measured data of Fig. 14, one can see that, as expected, the obtained power thresholds are higher than simulations in SPARK3D ® (see [13]), mainly for the increase of the insertion losses with regard to the simulated frequency response. As we can see in Fig.…”

“…9(d), there are not covers in the fifth resonator. For the five-pole filter, simulations with SPARK3D ® have shown that first, second, third, and fourth resonators have the possibilities to generate corona breakdown at center and/or critical frequencies, due to their higher voltage magnification (see [13]). This does not occur in the fifth resonator, where the stored energy is the lowest one (see [6]), thus, the use of covers can be avoided in this resonator.…”

“…Its resonant frequency is centered at f 0 = 1.6 GHz (L-band), where W = 2 mm and the low-loss standard substrate material Rogers RO4003C ® is used ( h = 1.524 mm, t = 0.017 mm, tanδ = 0.0027, and ε r = 3.60, the latter value extracted from measurements). Previous studies in the literature demonstrate that the maximum electric field occurs in the cavity center of waveguide filters (see [6]), meanwhile in microstrip filters it occurs at the open-circuit terminations [13]. For the latter reason, as a way to reduce the electric field intensity in air for improving the peak power thresholds, two dielectric covers with the same substrate material are placed at zones where the voltage magnification is maximum, as shown in Fig.…”

“…Moreover, a study of corona breakdown thresholds has been carried out for arbitrarily-shaped waveguide-based filters in [9]. On the other hand, in planar technology, corona RF breakdown has been focused on the connector of a microstrip transmission line [10][11][12] and, more recently, the PPHC and maximum voltage peak at the open-circuit terminations in microstrip filters have been analyzed in [13,14].…”

Increasing Peak Power Handling in Microstrip Bandpass Filters by Using Rounded-End Resonators

“…On the other hand, in microstrip circuits, the study of corona discharge has been mainly focused on the connectors feeding microstrip transmission lines [10]- [12]. Recently, some investigations have analyzed the maximum peak voltage and PPHC of microstrip coupled-line filters [13]. In this context, therefore, the main aim of this paper is to contribute to the state-of-the-art by proposing a modified microstrip filter structure with improved power handling capability.…”