Filtering baluns are proposed based on the hybrid cavity-microstrip structures in this article. The cavity acts as the resonator to obtain the filtering response. In the meanwhile, the microstrip feeding networks are used to excite multiple modes and achieve the balun characteristics simultaneously. The coupling mechanism between the slots and the cavities is utilized to analyze the single- and dual-band filtering baluns. Therefore, by combining the benefits of the cavities and the microstrip lines, multifunctional filtering baluns are realized. Besides, to reduce the volume and insertion loss further, a filtering balun based on the dielectric cavity-microstrip structure is presented and designed. It possesses high selectivity passband response, magnitude imbalance of 0.075 dB, and phase difference of 180° ± 0.2°. It is much smaller than that fed by the waveguide. On the other hand, it is easy to integrate with other components and robust in structure compared to that fed by the probe. Thus, the proposed hybrid structure not only maintains the high performance of the cavity but also has the flexibility of the planar circuit.

Dual-Mode Filtering Baluns Based on Hybrid Cavity-Microstrip Structures

The design of dual-band filtering power divider based on dual-mode dielectric resonator (DR) is investigated. The external quality factors ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q_{e}$ </tex-math></inline-formula> ) of two modes can be controlled independently, which makes the design procedure for arbitrary power split ratio simple and efficient. Meanwhile, the phase difference between the output ports can be adjusted to be in-phase or out-of-phase by altering the quadrants where the feeding probes are located. To improve the band-to-band isolation, the generation mechanism of the transmission zero between the two bands has been analyzed. Based on the analysis, the dual-band filtering power dividers with in-phase/out-of-phase outputs and equal/unequal power split ratio are proposed. All of them can be easily built by properly changing the location or the length of the feeding probes without increasing the circuit size. To verify the design concept, the above-mentioned prototypes are simulated. Some of them are implemented and measured. The measured results match well with the simulated responses, showing good performance, such as low loss and good band selectivity. 

Dual-Band Dual-Mode Dielectric Resonator Filtering Power Divider With Flexible Output Phase Difference and Power Split Ratio

Dual-mode filtering switches using hybrid microstrip-cavity structures are proposed in this article. TE101 and TE011 modes of the cavity act as the resonant modes to obtain a dual-mode filtering response. The microstrip line integrating the control circuit is employed as the feeding network. In the ON-state, the diode of the control circuit is reverse biased. Based on the electromagnetic (EM) coupling theory, the two modes are excited to attain filtering performance, and the loss of the diode is significantly alleviated. When the diode is forward biased, the two modes are suppressed and isolation in the OFF-state is realized. Benefiting from the hybrid microstrip-cavity configuration, the coupling between source/load and resonator is flexible to control. Single-band and dual-band filtering switches are constructed. The dual-band filtering switch processes high selectivity passband response in the ON-state, the insertion losses are 0.4 dB, and three transmission zeros are distributed in the two bands. In the OFF-state, the isolations of the two bands are below 37 and 30.7 dB, respectively. Thus, the dual-mode filtering switches maintain high- $Q$ features as the cavities. Moreover, they have multifunctionality and flexibility compared to the conventional cavity structures fed by probes and waveguides.

Dual-Mode Filtering Switches Based on Hybrid Microstrip-Cavity Structures

This letter presents a novel dual-band balun filter based on dielectric resonators (DRs) fed by a suspended stripline (SSL) structure. By using the SSL feeding structure and the coupling slots, both the external couplings and the internal couplings of the two modes could be independently controlled at the same time. Thus, the bandwidths of two passbands are flexibly controlled. The principle of differential outputs is also analyzed. For demonstration, the dual-band balun filter centered at 3.93 and 4.14 GHz is fabricated and measured. From the measured results, low insertion loss, good amplitude, and phase imbalances are realized by the proposed balun filter.

Dual-Mode Dual-Band DR Balun Filter Using Suspended Stripline Feeding Structure

This letter presents a novel dual-band balun filter based on dielectric resonators (DRs) fed by a suspended stripline (SSL) structure. By using the SSL feeding structure and the coupling slots, both the external couplings and the internal couplings of the two modes could be independently controlled at the same time. Thus, the bandwidths of two passbands are flexibly controlled. The principle of differential outputs is also analyzed. For demonstration, the dual-band balun filter centered at 3.93 and 4.14 GHz is fabricated and measured. From the measured results, low insertion loss, good amplitude, and phase imbalances are realized by the proposed balun filter. 

A filtering balun based on multi-mode rectangular cavity is proposed in this paper for the first time. The printed circuit board (PCB) microstrip lines cooperated with coupling slots are utilized as feeding structures. The $TE_{101}$ mode is employed to construct the passband while the $TE_{011}$ and $TM_{110}$ modes are used to generate two out-of-band zeros. Besides, by analyzing the electromagnetic field distributions, the balun characteristic at the two outputs are achieved due to the antisymmetrical arrangement of the output feeding lines. For demonstration, a second order cavity filtering balun is designed and measured. Both good filtering response and balun characteristic are observed in the measurement, which validate the proposed method.

Xin Fang

Papers

Dual-Mode Filtering Baluns Based on Hybrid Cavity-Microstrip Structures

Dual-Mode Filtering Switches Based on Hybrid Microstrip-Cavity Structures

Filtering Balun Based on Multi-Mode Rectangular Cavity Integrated With PCB Feeding Structure