Spurious Self-Suppression Method: Application to TM Cavity Filters

Abstract

This article presents a new approach for improving spurious free bands in filters. The main idea is to control the coupling coefficients of the spurious resonances, in order to force them to cancel each other. This approach is completely different from the classical one where all couplings are minimized in order to excite spurious resonances as less as possible. In fact, in this approach, all spurious couplings are maximized except the central coupling that is instead minimized. This method is first explained in terms of equivalent circuits. Then, in order to show its applicability to real microwave filters, it is applied to the TM cavity filters and used to remove both spurious resonances due to higher order cavity modes and to TE 10 mode of coupling irises. Design examples of fourth-and sixth-order TM cavity filters are presented. With respect to the classical TM cavity filter, where the first spurious appears around 11.4 GHz, the TM filters designed by exploiting the self-suppression method present spurious free bands up to 20.2 GHz (20 GHz for sixth-order filter), improving the filter response up to 2.2 times the center frequency of 9.2 GHz. Another advantage is that, in contrast to the classical spurious suppression method that does not allow responses with TZs in TM filters, the self-suppression method allows for a number of TZs equal to N-2 (N being the filter order) and it also allows a certain control of their position.

Wideband Bandpass TM Cavity Filters with Wide Spurious Free Band

“…Keeping in mind the limitations of the different filter technologies discussed above, this paper extends the previous contribution presented in [23] about TM mode filters designed by exploiting the spurious self-suppression method. In particular, in this paper the limited capability in terms of the bandwidth related to the structures presented in [23] has been addressed by introducing new iris geometries that allow filters with wider passbands. The bandwidth increasing in TM filters related to the structures presented in [23], creates spurious frequencies due to the iris resonances close to the filter passband.…”

“…Recently, a new method called spurious self-suppression has been proposed in [22] and [23]. In [24], it has been applied to substrate-integrated waveguide (SIW) filters.…”

“…This method is different from the classical one [6], which consists in the minimization of all possible couplings to spurious resonances, with the aim of avoiding (or better saying limiting) the excitation of spurious modes. The limitations of [6] were also addressed in [23], by providing example of TM mode filters. Another possible limitation of TM mode filters could be their limited bandwidths, especially when wide stopbands are required and the spurious self-suppression method is applied, as can be seen in the examples provided in [23].…”

“…The limitations of [6] were also addressed in [23], by providing example of TM mode filters. Another possible limitation of TM mode filters could be their limited bandwidths, especially when wide stopbands are required and the spurious self-suppression method is applied, as can be seen in the examples provided in [23]. Although recent studies [25] and [26] show, it is possible to achieve wide passbands up to 9.33% in TM cavity filters, using resonant irises and direct coupled TE-TM waveguide cavities.…”

Q-Learning Empowered Cavity Filter Tuning with Epsilon Decay Strategy

“…I n the field of microwave engineering, cavity filters are broadly used in distinct application fields owing to their exceptional performance and distinctive characteristics [1]. The key application domains include communication systems, such as satellite communications [2,3], wireless communications [4], cellular networks, and base stations [5], where the filters are positioned at the front end connected to the antenna inside the transceiver [6]. Additionally, the domain of wireless technologies includes: Wi-Fi, Bluetooth, and RFID operating in the S-band.…”