A dielectric resonator body for a multi-mode cavity filter, the resonator including a piece of dielectric material, with at least one substantially flat face for mounting on a substrate layer, the piece of dielectric material having a shape such that it can support at least a first resonant mode and at least one substantially degenerate resonant mode; wherein the shape of the piece of dielectric material is such that the first resonant mode and the at least one substantially degenerate resonant mode are capable of being simultaneously independently excited, and wherein the piece of dielectric material is at least partially covered with a layer of conductive material. The piece of first dielectric material may include at least one region having a different dielectric constant to the first dielectric material, whereby the presence of the region of different dielectric constant alters the frequency separation of the resonant mode and the spurious response.

Multi-mode filter

On the basis of doublet and its properties, a class of multiple-mode narrow band bandpasss filter is designed and fabricated by simultaneously exploiting the three resonant modes in a single rectangular cavity: TE101, TE011, and TM110 modes. The input/output ports of the proposed filter are fed by coupling a microstrip line to a slot on the side wall of a rectangular cavity. Different modes are excited by changing the position and shape of the two slots at input and output of the rectangular cavity without any intra-cavity coupling. Besides three poles within the passband, a pair of transmission zeros (TZs) is achieved, which can be controlled independently by setting the positions of the two TZs at the lower and/or upper stopband. High stopband attenuation and high filtering selectivity are achieved by considerably allocating three transmission poles and two zeros. In order to verify the proposed theory, two filter prototypes are fabricated and measured.

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Triple-Mode Cavity Bandpass Filter on Doublet With Controllable Transmission Zeros

A delay filter uses the dielectric mono-block triple-mode resonator and unique inter-resonator coupling structure, having smaller volume and higher power handling capacity. The triple-mode mono-block resonator has three resonators in one block. An input/output probe is connected to each metal plated dielectric block to transmit microwave signals. Corner cuts couple a mode oriented in one direction to a mode oriented in a second, mutually orthogonal direction. An aperture between two blocks couples all six resonant modes, and generates two inductive couplings by magnetic fields between two modes, and one capacitive coupling by electric fields. The input/output probes, coupling corner cuts and aperture are aligned such that all six resonators are coupled in the desired value and sign, so constant delay on the transmitted signal within certain bandwidth can be achieved. By connecting the input and output probes to the base printed circuit board, the delay filter is surface mountable.

Dielectric mono-block triple-mode microwave delay filter

This study presents the analysis and design of a new triple-mode filter that employs the recently proposed triple mode conductor-loaded cavity resonator. The resonator consists of a cubic-shaped metallic structure suspended in a metallic enclosure. The resonator is mounted in the cavity through a low-loss low-dielectric-constant support structure. The triple-mode conductor-loaded cavity resonator is considerably cheaper, easier to design and manufacture, and offers a significantly wider spurious-free response in comparison with the triple-mode dielectric resonator. A six-pole filter is designed using Ansoft HFSS employing the proposed triple mode conductor-loaded cavity resonator. The analysis shows that introducing asymmetry into the structure of the resonator in the form of chamfers or corner cuts creates the necessary perturbation to achieve the required coupling between the degenerate modes inside each block to realise the desired filter response. The six-pole triple-mode conductor-loaded cavity filter is fabricated and tested. Finally, two applications of the proposed concept are identified. The triple mode conductor-loaded cavity resonator is combined with higher Q-factor triple-mode ceramic resonators to realise a small size, high Q-factor filter with wide spurious-free response. Also, a direct-coupled band-stop filter is proposed employing the triple-mode conductor-loaded cavity filter.

Analysis, design and applications of the triple-mode conductor-loaded cavity filter

On the basis of triplet and its properties, a class of triple-mode and triple-band narrow-band bandpass filters is presented and designed by simultaneously exploiting the three resonant modes in a single rectangular cavity: TE101, TE011, and TM110 modes. The input/output ports of the proposed filter are formed by coupling a waveguide feed to a slot on the side wall of a rectangular cavity. These resonant modes are excited by making use of the position and shape of the slots at input/output of the rectangular cavity without any intra-cavity coupling structure. Besides three poles within the desired passband, a pair of transmission zeros (TZs) can be produced and controlled to appear at the inner or outer sides of this passband. Due to emergence of the three resonant modes and realization of a pair of TZs, a highly attenuated and sharpened filtering selectivity is achieved. In order to verify the proposed approach, two filter prototypes are in final fabricated and measured.

Triple-Mode and Triple-Band Cavity Bandpass Filter on Triplet Topology With Controllable Transmission Zeros

A practical triple-mode dielectric monoblock band pass filter integrated with a wide bandwidth pre-select mask bandpass filter and a microstrip low pass filter for WCDMA base station application is presented. The dielectric monoblock triple-mode filter was designed and optimized using 3D EM simulation software incorporating the equivalent circuit model. The pre-select filter and low pass filter were used to clean up the spurious response of the triple-mode filter up to 12 GHz. Both triple mode and mask filters are directly mounted on the PCB to minimize the cost and loss.

B. Engst

Papers

A practical triple-mode monoblock bandpass filter for base station applications