A microstrip filtering power divider (FPD) with good isolation performance and harmonic suppression is presented. By replacing a simple resistor with a novel distributed stepped-impedance resonator network, better isolation and wider stopband are simultaneously attained. A transmission-matrix-based analysis method is then extensively described to determine the circuit geometrical parameters at the synthesis level by facilitating the incorporation of design indexes and structure dimension. A prototype FPD is designed, fabricated and measured. The proposed FPD exhibits a center frequency of 2.2 GHz ( $\text {f}_{0}$ ) with the isolation better than 17dB within the entire passband and a stopband extended to 12 GHz (5.45f0).

Filtering Power Divider With Good Isolation Performance and Harmonic Suppression

High-performance single-ended wideband and balanced bandpass filters loaded with stepped-impedance stubs are proposed in this paper. For the proposed wideband filter and the differential mode of the proposed balanced filter, two transmission zeros near the passband are realized by using simple stepped-impedance stubs, which enhances the passband selectivity of these new filters. The analytical and accurate design equations for transmission poles and zeros of these single-ended and balanced filters are provided based on the scattering-parameters theory. The single-ended bandpass filter, employing a T-shaped structure to produce a wide passband, is achieved with 3-dB fractional bandwidth of 79.33%, 19-dB passband return loss, and 35-dB harmonic suppression ( $1.56f_{\mathrm { {0}}}$ – $2.51f_{\mathrm { {0}}}$ , $f_{\mathrm { {0}}}$ is the center frequency of the wide passband). The 3-dB differential-mode fractional bandwidth of 33% with 22-dB passband return loss and the 30-dB harmonic suppression ( $1.29f_{\mathrm { {0}}}$ – $2.67f_{\mathrm { {0}}})$ are obtained in the proposed balanced bandpass filter. In addition, by inserting open-circuit stubs into the proposed balanced bandpass filter, over 25-dB common-mode suppression is obtained from 0 to $2.67f_{\mathrm { {0}}}$ . Good agreement is observed between the simulation and measurement results.

High Performance Single-Ended Wideband and Balanced Bandpass Filters Loaded With Stepped-Impedance Stubs

In this paper, two wideband balanced-to-unbalanced (balun) bandpass filters (BPFs) are synthetically designed with three- and four-pole filtering responses, respectively. Based on the simplified even- and odd-mode equivalent circuits of the proposed three-pole balun BPF, the exact impedance value of the cascaded microstrip sections connected with two balanced ports is first determined in order to attain a perfectly matched S-matrix. By the virtue of the modified two-port transmission-line network with asymmetrical port impedances, a quasi-Chebyshev filtering response for this three-pole balun filter is theoretically presented. Next, to improve the in-band performance, especially at the high frequency, a four-pole balun BPF designed with a folded slotline resonator is proposed. Via the virtually short-ended microstrip stubs of the modified two-port equivalent network, the four-pole frequency response can be directly analyzed with the Chebyshev polynomial function. For these two proposed wideband balun filters, their theoretical and simulated results are well confirmed by the circuit model responses with the same impedance values of the simulated microstrip and slotline resonators and the extracted turns ratios of the employed transformers. Finally, two prototype wideband balun BPFs are fabricated and measured to verify our design predictions.

Wideband Balanced-to-Unbalanced Bandpass Filters Synthetically Designed With Chebyshev Filtering Response

A narrowband dual-band bandpass filter (BPF) with independently tunable passbands is presented through a systematic design approach A size-efficient coupling system is proposed with the capability of being integrated with additional resonators without increasing the size of the circuit Two flag-shaped resonators along with two stepped-impedance resonators are integrated with the coupling system to firstly enhance the quality response of the filter, and secondly to add an independent adjustability feature to the filter The dual passband of the filter is centered at 442 GHz and 72 GHz, respectively, with narrow passbands of 212% and 115% The lower and upper passbands can be swept independently over 600 MHz and 1000 MHz by changing only one parameter of the filter without any destructive effects on the frequency response According to United States frequency allocations, the first passband is convenient for mobile communications and the second passband can be used for satellite communications The filter has very good in- and out-of-band performance with very small passband insertion losses of 05 dB and 086 dB as well as a relatively strong stopband attenuation of 30 dB and 25 dB, respectively, for the case of lower and upper bands To verify the proposed approach, a prototype of the filter is fabricated and measured showing a good agreement between numerically calculated and measured results

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A Compact C-Band Bandpass Filter with an Adjustable Dual-Band Suitable for Satellite Communication Systems

A new microstrip unbalanced-to-balanced (balun) diplexer based on stub-loaded dual-mode resonators is presented. The proposed balun diplexer primarily consists of two balun filter channels, and both channels are entirely independently designable, thus bringing great flexibility in the balun diplexer design. Besides, owing to the direct connection of two dual-mode balun filters, no additional matching networks are demanded at the common input port, leading to a significant size reduction. For demonstration, a prototype balun diplexer operating at 2.30 and 2.72 GHz is implemented. Both simulated and experimental results are provided in good agreement.

Compact microstrip balun diplexer using stub-loaded dual-mode resonators

A comprehensive study of a new planar-type balun prototype is presented in this paper for application in the design of balun bandpass filters (BPFs) with widely used open-type resonators. The proposed balun is in general composed of two identical back-to-back quarter-wavelength ( $\lambda $ /4) coupled line sections. The design concept originates from the analysis of the standing wave pattern on a half-wavelength ( $\lambda $ /2) open-circuited transmission line. After an intuitive illustration is given, its working principle is presented to validate the feasibility of the proposed balun. Afterward, two types of the coupled line prototypes are analyzed to implement the proposed balun with filtering response, whereas a basic rule is given to realize the transmission zeros. To further demonstrate the validity of the proposed balun prototype, two practical balun BPFs with common dual-mode resonators are designed and fabricated. As expected, transmission zeros are generated near the desired passband of our presented balun filters, thereby improving their frequency selectivity. Both simulated and measured results exhibit good filtering and balun performance.

Study of a New Planar-Type Balun Topology for Application in the Design of Balun Bandpass Filters

A new approach to design a microstrip dual-mode balun bandpass filter (BPF) is proposed in this letter. Its working principle is extensively explained by analysis of standing wave pattern on a half-wavelength $(\lambda/2)$ open-circuited transmission line. By selecting proper coupling topologies between the $\lambda/2$ open-circuited transmission line and dual-mode open-stub loaded resonators, a novel planar type dual-mode balun BPF is presented in this letter. To validate the feasibility of the new approach, a dual-mode balun BPF operating at 2.0 GHz with 0.35 dB magnitude imbalance and 5 $^{\circ}$ phase imbalance is designed and fabricated. Both simulated and experimental results are provided with good agreement.

A New Approach to Design a Microstrip Dual-Mode Balun Bandpass Filter

In this letter, a new dual-mode balun bandpass filter (BPF) with high selectivity is proposed. The balun BPF is mainly composed of two different types of microstrip-to-slotline transition structures, two identical dual-mode stub-loaded resonators, and a pair of balanced outputs. First, to convert unbalanced signals from port 1 into balanced signals between port 2 and port 3, two different types of microstrip-to-slotline transition structures are utilized. Afterward, two identical stub-loaded resonators are embedded in the circuit for realizing the dual-mode bandpass response. Furthermore, four transmission zeros generated outside the passband are wisely introduced and well elucidated, thus ensuring high selectivity performance. For demonstration, a sample of balun BPF centered at 2.78 GHz ( $f_{0})$ with 0.5-dB magnitude imbalance and 5° phase imbalance is designed, fabricated, and measured. Both simulation and measurement are in good agreements.

Design of a Dual-Mode Balun Bandpass Filter With High Selectivity

A new microstrip wideband bandpass filter with compact size and high selectivity is presented. Originated from conventional two-stage parallel coupled-line prototype, modified parallel coupled-line structure is proposed to obtain high selectivity with inherent transmission zeros nearby the passband. Centring at 2.5 GHz, the realised wideband filter exhibits a 3 dB fractional bandwidth of 54.4% with finite transmission zeros. Furthermore, the filter features with nice in-band performance, and sharp out-of-band rejection. Experimental results are in good agreement with the simulated results.

Feng Huang

Papers

Study of a New Planar-Type Balun Topology for Application in the Design of Balun Bandpass Filters

A New Approach to Design a Microstrip Dual-Mode Balun Bandpass Filter

Compact microstrip balun diplexer using stub-loaded dual-mode resonators

Design of a Dual-Mode Balun Bandpass Filter With High Selectivity

Compact microstrip wideband bandpass filter with high selectivity