A bandwidth‐agile balanced filtering power divider

In this article, a balanced filtering power divider (FPD) that allows for operational agility of the bandwidth (BW) is presented. The differential‐mode power dividing and high common‐mode (CM) suppression can be realized by microstrip‐to‐slotline transition. Two slotline open stubs with different lengths are added in shunt to the main slotline for the transition, which can not only introduce transmission poles for extending and controlling transition BW, but also generate two extra transmission zeros (TZs) near to the passband edges, featuring good filtering response. The two transmission poles can be independently tunable by loading varactors to the open ends of slotline stubs and two TZs will be changed accordingly so that the filtering passband BW is electrically tunable. To verify the theoretical prediction, a prototype of tunable balanced FPD is fabricated and measured. The measured results show that the 3‐dB fractional bandwidth (FBW) of the passband varies from 5.6% to 12.6%, meaning more than a double tuning range for the FBW, and the CM suppression is better than 40 dB across the frequency band of interest.     

Dual‐passband bandpass‐filtering power divider using half‐mode substrate integrated waveguide resonator with high frequency selectivity

In this paper, a half‐mode substrate integrated waveguide (HMSIW) power divider with bandpass response and good frequency selectivity is proposed. The proposed power divider includes input/output microstrip lines, four HMSIW resonators, cross‐coupling circuits, and an isolation resistor. The dual‐band bandpass‐filtering response is obtained by using the dual‐mode slotted HMSIW. To get good frequency selectivity, the input/output cross‐coupling circuits have been used, and several transmission zeros can be observed. A dual‐band filtering‐response HMSIW power divider is designed, fabricated and measured. The total size of the fabricated power divider is 0.58λg × 0.45λg. The measured results show a reasonable agreement with the simulated ones. The measured central operating frequencies of the dual‐band HMSIW power divider are at 2.43 and 3.50 GHz, respectively. The measured 3‐dB fractional bandwidth is about 13.3% and 6.3% in the two passbands, and the measured output isolation is about 20 dB.     

Wideband and spurious‐suppressed differential bandpass filter based on strip‐loaded slot‐line structure

In this article, a wideband and spurious‐suppressed differential bandpass filter based on strip‐loaded slot‐line structure is presented. By means of the differential microstrip‐slot‐line‐microstrip transition, the proposed filter has a wideband bandpass filtering response. Simultaneously, the utilization of the strip‐loaded slot‐line extends its upper stop‐band. The proposed bandpass filter has wider upper‐stopband, wideband bandpass response, and intrinsic high common‐mode (CM) suppression. To verify the design concept, one filter example has been designed, fabricated, and measured. It has a differential‐mode (DM) 3‐dB fractional bandwidth of 157% with a low 0.82 dB minimum insertion loss. What's more, it shows a very wide 20 dB DM stop‐band bandwidth of 6.5 f_0d. The experienced results are in good agreement with the theoretical and simulated results.     

A 1‐to‐n way single‐ended‐to‐balanced substrate integrated waveguide filtering power splitter

An approach to 1‐to‐n (n = 3, 4…) way single‐ended‐to‐balanced filtering power splitter (SETBFPS) is proposed. The properly placed balanced ports with 0.5λ_g (λ_g is the substrate integrated waveguide [SIW] guided wavelength at f₀) space make the TE32nd 103 and TE32nd 105 modes of n 32nd‐mode SIW multimode resonators form differential‐mode (DM) passband of the SETBFPS. Compared with the state‐of‐art single‐ended‐to‐balanced power splitters, the proposed approach has all the functions of 1‐to‐n way, filtering, and common‐mode (CM) suppression. A 1‐to‐3 way prototype is exemplified at 3.5 GHz with the minimum insertion loss (IL) of 0.09 dB, a fractional bandwidth (FBW) for a 15‐dB return loss of 35%, and a FBW for 15‐dB CM suppression of 52%. Low IL and wide bandwidth can be observed.     

A novel balanced wideband power divider based on microstrip‐slot transitions

A novel design of a balanced wideband power divider (PD) with enhanced common‐mode (CM) suppression is proposed. The top and bottom layers of the structure contain tapered microstrip line. Those microstrip lines are coupled via slotline in the ground plane, which is located at the middle layer. With appropriate placement of the slotline, the coupling between the slotline mode and the differential‐mode (DM) signals can be maximized, while that between the slotline mode and the CM signals can be minimized. Simulated and measured results show that the proposed PD has equal power division, low insertion loss, and good return loss. In the measurement, the fractional bandwidth of the measured ?10 dB (DM) return loss is about 101% (1.82–5.35 GHz), the insertion loss for the DM signals is less than 5 dB, the suppression of the CM signals is higher than 45 dB, and the DM isolation is better than 10 dB over the fractional bandwidth. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:437–442, 2014.     

Novel planar balanced bandpass filter with wideband common‐mode suppression and in‐band common‐mode noise absorption

This paper presents a novel planar balanced bandpass filter (BPF) with wideband common mode (CM) noise suppression and in‐band CM noise absorption using coupled lines (CLs) with short‐circuited stubs to realize high selectivity and wideband differential mode (DM) filtering performance. Two one‐quarter wavelength stubs loaded with grounded resistors are introduced to realize wideband CM noise suppression. Thus, CM noise can be suppressed under a certain level at all frequencies. Four resistors are used to achieve CM noise absorption by dissipating the CM noise into heat, which can avoid the noise being reflected to the communication system and realize a wide absorption bandwidth with 90% absorption efficiency. For demonstration, an absorptive balanced BPF operating at 3.5 GHz with wide 3‐dB fractional bandwidth (FBW) of 79.43% is fabricated and experimentally validated. It is worth noted that the absorptive balanced BPF can realize broadband CM noise suppression from 0 to 8 GHz, and the CM noise is well absorbed more than 10 dB from 2.41 to 4.63 GHz. Besides, wideband CM noise absorption with 90% efficiency from 2.51 to 4.60 GHz is realized, which indicates potential applications in improving the performance of the balanced radio frequency (RF) circuits. Good agreements between the simulated and measured results are observed.     

A balanced dual‐band BPF with independently controllable frequencies and bandwidths

A balanced second‐order dual‐band bandpass filter (BPF) with independently controllable center frequencies and bandwidths based on coupled stepped‐impedance resonators (SIRs) is designed in this article. To obtain a dual‐band differential‐mode (DM) response, two pairs of SIRs with different resonant frequencies are employed in the design. The bandwidths of the two DM passbands can be independently tuned by adjusting the coupling gaps and coupling lengths of the corresponding resonators. In addition, three transmission zeros are realized to enhance the selectivity of the DM passbands. The microstrip‐slotline transition structure is utilized to achieve a wideband common‐mode (CM) suppression. Moreover, the DM responses are independent of the CM ones, which significantly simplify the design procedure. Finally, a balanced dual‐band BPF is designed to validate the design method and a good agreement between the simulated and measured results is observed.     

A new dual‐band single‐ended‐to‐balanced filtering power divider

This article proposes a new dual‐band single‐ended‐to‐balanced (SETB) filtering power divider (FPD), which shows the excellent characteristics of wideband common‐mode (CM) suppression and good selectivity. By employing the structure of double‐sided parallel‐strip line with a mid‐inserted conductor and a T‐shaped defected ground structure etched in the mid‐inserted conductor, out‐of‐phase behavior and high CM suppression can be achieved successfully. Besides, to realize dual‐wideband filtering performance and high selectivity, two pairs of step impedance stubs (SIS) loaded quarter‐wavelength central line‐terminal‐shorted three parallel‐coupled microstrip lines structure are adopted. Meanwhile, two pairs of resistors are introduced so as to realize excellent isolation. To verify effectiveness of the design method, a prototype of dual‐band SETB FPD which operates at 3.2 and 4.9 GHz is designed, fabricated, and tested. Final results exhibit that the new dual‐band SETB FPD possess high selective dual‐band differential mode response, wideband CM suppression, and excellent isolation between the balanced output ports.     

A tunable balanced dual‐band BPF with quasi‐independently controlled center frequency and bandwidth

In this paper, a balanced dual‐band bandpass filter (BPF) with high selectivity and low insertion loss performance is presented by employing stub loaded resonators (SLRs) and stepped impedance resonators (SIRs) into balanced microstrip‐slotline (MS) transition structures. The balanced MS transition structures can achieve a wideband common‐mode (CM) suppression which is independent of the differential‐mode (DM) response, significantly simplifying the design procedure. Six varactors are loaded into the resonators to achieve the electrical reconfiguration. The proposed balanced dual‐band BPF can realize quasi‐independently tunable center frequencies and bandwidths. A tuning center frequency from 2.48 to 2.85 GHz and a fractional bandwidth (20.16%‐7.02%) with more than 15 dB return loss and less than 2.36 dB insertion loss are achieved in the first passband. The second passband can realize a tuning center frequency from 3.6 to 3.95 GHz with more than 12 dB return loss and less than 2.38 dB insertion loss. A good agreement between the simulated and measured results is observed.     

A balanced UWB power divider based on parallel coupling slotlines with improved isolation

A balanced‐to‐balanced ultra‐wide band (UWB) equal power divider (PD) based on parallel coupling slotlines is presented in this article. An ultra‐wide differential‐mode (DM) impedance bandwidth covering from 2.8 to 9.4 GHz can be achieved. It is noted that the DM performance is independent of the common‐mode (CM) response, which reduces the design complexity greatly. Meanwhile, CM response with a larger bandwidth and a higher suppression is obtained intrinsically. More importantly, two methods are designed and adopted to improve the DM isolation between the two output ports. To validate the correctness of the design method, a prototype circuit is fabricated and measured. The contrast of the simulated and measured results shows a good agreement.     

An unbalanced‐to‐balanced diplexer based on substrate integrated waveguide cavity

A novel unbalanced‐to‐balanced diplexer based on a dual‐mode substrate integrated waveguide (SIW) cavity is proposed and implemented. The diplexer is realized using one dual‐mode cavity and two single‐mode cavities. By properly choosing, feeding and coupling the cavity operating at the TE₁₀₂ or TE₂₀₁ mode, so as to not only provide capabilities to realize the desired unbalanced‐to‐balanced transmission within both Rx and Tx channels but also realize good differential‐mode channel‐to‐channel isolation. To the author's knowledge, we present for the first time an unbalanced‐to‐balanced type diplexer based on the application of SIW. The proposed diplexer was successfully designed, simulated, and fabricated. Good agreement can be observed between simulated and measured performances in our letter. The measured in‐band common‐mode rejection is better than 33 dB for both channels. A minimum differential‐mode isolation of about 50 dB across the Rx band and about 40 dB across the Tx band is also observed in the measurement. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:173–177, 2015.     

A balanced dual‐band bandpass filter with independently tunable differential‐mode frequencies

A balanced dual‐band bandpass filter (BPF) with independently tunable differential‐mode (DM) frequencies is proposed in this letter. The proposed BPF is composed of complementary split‐ring resonators (CSRRs) etched on the ground and varactors loaded on the resonators. A balanced stepped‐impedance microstrip‐slotline transition structure is introduced to transfer the DM signals successfully and block the common‐mode (CM) signals transmission. Good DM transmission and CM suppression can be achieved. Moreover, by changing the reverse bias voltages of the varactors loaded on coupling CSRRs, two DM resonant frequencies of the proposed balanced BPF can be tuned independently. To verify the feasibility of the design method, a balanced BPF with DM frequency ranging from 0.80 GHz to 1.12 GHz and 1.55 GHz to 2.05 GHz is fabricated and measured. Good agreement between the simulation and measurement results demonstrate the validity of the design.     

Ultracompact two‐way and four‐way SIW/HMSIW power dividers loaded by complementary split‐ring resonators

In this paper, two ultracompact power dividers based on the substrate integrated waveguide (SIW) and half‐mode SIW (HMSIW) technologies loaded by complementary split‐ring resonators (CSRRs) are presented. The presented structures are designed based on the theory of evanescent mode propagation. To obtain a size reduction, the CSRR unit cells are etched on the metallic surface of the SIW and HMSIW structures. First, a two‐way HMSIW power divider is reported. In this circuit, the concept of HMSIW is utilized aiming at a further size reduction in addition to the size reduction by the CSRR unit cells. Then, a four‐way SIW power divider is designed so that the direct coaxial feed is used for the input port and microstrip transmission lines are used for the output ports. Both two‐way and four‐way SIW/HMSIW power dividers at 5.8 GHz covering WLAN are designed, fabricated, and measured. They respectively have 0.18 × 0.21 λg² and 0.38 × 0.21 λg² total size. A fair agreement between simulated and measured results is achieved. The measured insertion losses are 0.5 ± 0.5 and 0.6 ± 0.5 dB for the two‐way and four‐way SIW/HMSIW power dividers, respectively, in the operating band of interest.     

An SIW filtering antenna array with quasi‐elliptic gain response based on intercavity bypass coupling

In this article, a filtering antenna array based on substrate integrated waveguide (SIW) is proposed with quasi‐elliptic gain responses for the first time. Two radiation nulls in the gain responses at two sides of the frequency band edges are designed by applying a novel intercavity bypass coupling scheme. First, by carefully analyzing the bypass coupling between the in‐band and out‐of‐band modes in a single oversized TE₁₀₃ mode cavity resonator, quasi‐elliptic filtering responses are achieved for a two‐output filter. Afterward, those cavity resonators coupled with the two outputs are replaced by cavity‐backed slot antennas to achieve the proposed filtering cavity‐backed slot antenna array. Only one cavity is required in our design to achieve the two transmission zeros and the function of power divider. As a result, the complexity of the proposed filtering antenna array is reduced. A prototype operating at Ka band is designed, fabricated and measured with a center frequency of 28.5 GHz and fractional bandwidth of 1.25%. Similar characteristics can be observed between the gain response of the proposed filtering antenna and the transmission responses of the two‐output filter. The proposed SIW filtering antenna array has great potential to be integrated into millimeter‐wave transceiver modules. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:191–198, 2016.     

Double‐layer microstrip ultra‐wideband filtering power divider with high selectivity and large isolation

In this article, a compact double‐layer microstrip ultra‐wideband (UWB) filtering power divider with high selectivity and isolation is proposed. The filtering power divider consists of a multimode resonator at the top layer coupled with a pair of branch lines at the bottom through a slotline in the middle ground. The slotline provides strong coupling between the two layers and equally distributes the power to two branch lines. The resistor loaded about a quarter‐wavelength away from the slotline achieves high isolation within UWB range. The UWB filtering properties with controllable transmission poles and zeros as well as power splitting with enhanced isolation have been analyzed. The adjustable transmission zeros of the filter unit enables the bandwidth control of the filtering power divider. Finally, a UWB filtering power divider operating at 3.1 to 10.6 GHz has been designed, fabricated, and measured. It achieves a compact size of only 26 × 28 mm², high isolation about 20 dB, and good out‐of‐band suppression of 40 dB.     

Wideband leaky‐wave antenna with consistent gain and wide beam scanning angle based on multilayered substrate integrated waveguide composite right/left‐handed transmission line

In this article, a wideband leaky‐wave antenna is designed for consistent gain and wide beam scanning angle by using the proposed multilayered substrate integrated waveguide (SIW) composite right/left‐handed transmission line (CRLH TL). The proposed SIW CRLH structure consists of two parts: an interdigital fingers slot of rotating 45° etched on the upper ground of the SIW, and a rotated parasitic patch beneath the slot. Due to the continuous phase constants change from negative to positive values of the proposed SIW‐CRLH under the balanced condition, the designed LWA can achieves a continuous beam‐scanning property from backward to forward over the operating frequency band. The designed antenna is fabricated and measured, the measured and simulated results are in good agreements with each other, indicating that the designed antenna obtains a measured continuous main beam scanning from backward ?78° to forward +76° over the frequency range from 7.7 to 12.8 GHz with a consistent gain of more than 9.5 dB. Besides, the designed antenna also exhibits a measured 3‐dB gain bandwidth of 45.1% with maximum gain of 15 dB. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:731–738, 2016.     

Six‐port balanced network with high unequal power division ratio using shorted coupled lines

A novel 6‐port balanced network with high unequal power division ratio using shorted coupled lines is proposed in this letter. The design parameters of the proposed power divider are analyzed according to transmission line theory. Two double‐sided parallel‐strip line 180° phase inverters loaded with 4 isolation resistors are used to realize high isolation for the power dividing output ports. A planar balanced network with bandwidth of 40.5% (power division ratio: 1:10) for the differential mode and wideband 23% common mode suppression is designed and fabricated. The measured results show good agreement with the theoretical expectations.     

A balanced dual‐band bandpass filter with a wide stopband and controllable differential‐mode frequencies and fractional bandwidths

In this article, a balanced microstrip dual‐band bandpass filter (BPF) is designed. The proposed filter is achieved by employing a microstrip U‐shape half‐wavelength resonator, a folded stub‐loaded resonator and balanced microstrip/slotline transition structures. The center frequencies and the fractional bandwidths of the two differential‐mode (DM) passbands can be controlled independently by changing the physical lengths of the two resonators and the gaps between each resonator, respectively. The balanced microstrip/slotline transition structures can achieve a wideband common‐mode (CM) suppression. Meanwhile, the DM passbands are independent from the CM responses, which significantly simplify the design procedure. In addition, a wide DM stopband is also realized. In order to validate the design strategies, a balanced dual‐band BPF centered at 2.57 and 3.41 GHz was fabricated and a good agreement between the simulated and measured results is observed.     

A BTB UWB power divider with arbitrary power‐dividing ratio based on three‐slotline structure

In this article, a balanced‐to‐balanced (BTB) ultra‐wide band (UWB) power divider (PD) is proposed, which can realize arbitrary power‐dividing ratio (PDR) with improved transmission bandwidth flatness. The proposed PD is primarily based on microstrip/slotline (MS) transition structures and parallel‐coupled three‐slotline structure. U‐type microstrip feed lines integrated with stepped‐impedance slotline resonators are adopted at the input and output ports, which make the differential‐mode (DM) responses independent of the common‐mode (CM) ones. Meanwhile, superior DM transmission and CM suppression are achieved intrinsically, thereby simplifying the design procedure significantly. By changing the distances between the coupled three slotlines, the PDR between the output ports is controllable. In order to verify the feasibility of the proposed design method, several prototype circuits of the proposed PDs with different PDRs are simulated and a prototype circuit with the 2:1 PDR is fabricated and measured. A good agreement between the simulation and measurement results is observed.     

Leaky‐wave antenna with high gain and wide beam‐scanning angle range based on novel SIW‐CRLH transmission line

A leaky‐wave antenna (LWA) with high gain and wide beam‐scanning angle is proposed in this article using a novel substrate integrated waveguide (SIW) composite left/right‐handed transmission line (CRLH TL). The novel SIW‐CRLH TL is analyzed and the equivalent circuit model is also provided. Considering the continuous phase constant of the balanced SIW‐CRLH TL from negative to positive values, the proposed LWA can obtain a continuous beam steering property from backward to broadside to forward. For verification, a periodic LWA, which is comprised of 10 unit cells of the balanced SIW‐CRLH TL, is fabricated and measured. The measured and simulated results agree well, showing that the proposed periodic LWA operates from has continuous beam‐scanning capabilities of about 90° from backward to forward (including the broadside) with gains of better than 10 dB within the operating band. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:36–41, 2016.