A Ka‐band power divider/combiner using two side‐inserted magnetic coupling semicircular ring probes

A Ka‐band power divider/combiner with dual magnetic coupling semicircular ring probes is proposed in this paper. Firstly, a broadband microstrip‐to‐waveguide transition with semicircular ring probe is designed based on the side‐inserted structure of magnetic field excitation in a rectangular waveguide. The insertion loss of the proposed transition is less than 0.7 dB in Ka‐band assisted by the dual symmetrical broadband probes and rectangular waveguide. Then, the divider/combiner is proposed using the new transition with magnetic coupling from narrow wall into the rectangular waveguide. The bandwidth of the divider/combiner is more than 9 GHz (from 27 to 36.7 GHz), and the insertion loss of the single divider/combiner is less than 3.3 dB. Finally, the performance of the proposed divider/combiner is validated through simulations and measurements. The proposed design has potential applications in microstrip circuits.     

A Ka band microstrip to waveguide transition using a quasi‐triangle probe

In this article, a new Ka band microstrip to waveguide transition with combination of electric and magnetic coupling is introduced by using a quasi‐triangle structure. Consequently, the length of the proposed transition has been significantly diminished. A back‐to‐back prototype was fabricated based on the optimized dimensions to validate the design concept. The measured and simulated results are in a good alignment. The experimental results show that the return loss is better than 14.8 dB across the frequency range of 32‐40 GHz with an insertion loss of lower than 0.9 dB. The conversion efficiency for the single transition, therefore, is larger than 90.5%. Because of its broad operation bandwidth, low insertion loss, and compact size, the proposed embedded transition could find wide applications in most modern miniaturized MMIC devices and systems.     

An efficient method of designing dual‐ and wide‐band power dividers with arbitrary power division

Capability of microstrip nonuniform transmission lines (MNTLs) for construction of dual‐band and broadband unequal Wilkinson power dividers with arbitrary‐way, arbitrary frequency band operations, and arbitrary power divisions is evaluated. Also, the MNTL transformers are introduced for dual‐band/broadband matching of the unequal output impedances of the MNTL power divider with arbitrary output terminal impedances. The strip width of MNTLs is considered variable and is written as a truncated Fourier series expansion. To show the validity of the design procedure, three experimental MNTL Wilkinson power dividers, which are dual‐band two‐ and three‐way power dividers with different power divisions working at 1 and 3.4 GHz and one broadband equal power divider working from 0.4 to 1.8 GHz, have been designed and fabricated. In the first ones with power division of 1.5, outputs isolation and ports matching of less than ?30 dB are achieved. Next, an extended recombinant structure is presented for achieving three‐way MNTL power dividers with dual‐band operation. The measured isolation between outputs and ports matching are better than 30 dB and measured forward transmissions are between ?4.87 and ?5.45 in two passbands of the divider. Also, for the proposed broadband divider, the measured isolation between the outputs is better than 13 dB in 127% desired bandwidth. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

A broadband coplanar waveguide to rectangular waveguide power divider using a slot

In this article, a broadband coplanar waveguide (CPW) to rectangular waveguide power divider using the dipole slot is proposed. The power divider consists of an input CPW port and two output rectangular waveguide ports. The CPW to rectangular waveguide power divider using the dipole slot has a return loss larger than 15 dB and an insertion loss equal to 3.08–3.27 dB in the whole X‐band (8.2–12.4 GHz). Furthermore, to broaden the bandwidth, the dipole slot is replaced by the bow‐tie slot. The CPW to rectangular waveguide power divider using the bow‐tie slot yields a return loss larger than 16 dB and an insertion loss equal to 3.05–3.29 dB from 8 to 13 GHz, which exceeds the X‐band. To verify our design, power dividers that use the dipole slot or the bow‐tie slot are fabricated and measured. The measurement results of both power dividers are in good agreement with the simulation results. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

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.     

Simple,compact and broadband right‐angle transition between substrate integrated waveguide and rectangular waveguide at Ka‐band

In this article, a simple compact broadband right‐angle transition between substrate integrated waveguide (SIW) and rectangular waveguide (RWG) working at Ka‐band is proposed. Three coupling slots etched on the interface are developed to couple the electromagnetic field from SIW to RWG. A metallic via is introduced into the end slot to enhance the inductance and all the slots are developed in different dimensions for multi‐resonance. By proper optimizing, three resonances are obtained which broadens the impedance matching effectively. All details of the transition are designed on the SIW part for the purpose of simple and compact. Two back‐to‐back prototypes working at Ka‐band are designed, fabricated and measured. The measured results show that the mean value of insertion loss for a single transition is about 0.51 dB and the return loss is better than 15 dB over the full Ka‐band. The proposed right‐angle transition has advantages of simple assembly, compact size and broadband characteristics and it can be a good candidate for millimeter‐wave applications.     

Wideband orthomode transducer for the Square Kilometre Array band4 single pixel feed

The design of a compact wideband orthomode transducer (OMT) for band4 single pixel feed of the Square Kilometre Array (SKA) dish is presented. The geometry of the proposed OMT is based on circular quad‐ridged waveguide to obtain wideband characteristics, which consists of a coaxial to quad‐ridged waveguide transition and a circular to quad‐ridged waveguide tapered transition. By adopting circular quad‐ridged waveguide and high‐order cosine taper for the ridges, the length of OMT is compact and the levels of higher‐order modes generated at the circular waveguide aperture are lower. To verify the OMT performance, a prototype is manufactured and tested using a vector network analyzer. The measured results agree very well with the calculated ones across the frequency range 2.8‐5.18 GHz. The tested reflection coefficients are less than –19 dB, the insertion losses are less than 0.25 dB for both polarization channels, and the isolation between two output ports is better than 37.7 dB. It is confirmed that the designed OMT can be satisfied with the requirement of the SKA band4 feed system.     

A new broadband circularly polarized square‐slot antenna with low axial ratios

A new broadband circularly polarized (CP) square‐slot antenna with low axial ratios is proposed in this article. The antenna is comprised of an L‐shaped microstrip line with tapered section and a square‐slot ground plane with some stubs and slots, which are utilized as perturbations for the desirable antenna performance. By loading stubs and slots in the square‐slot ground plane, the 2‐dB axial ratio bandwidth (ARBW) and 10‐dB return loss bandwidth for the presented antenna can be markedly improved. The measured results show that its 2‐dB ARBW is 4.2 GHz (54.2% from 5.65 GHz to 9.85 GHz) and its 10‐dB return loss bandwidth is about 8.9 GHz (92.7% from 5.15 GHz to 14.05 GHz). The proposed antenna features compact structure and broad 2‐AR bandwidth which could completely cover the WLAN (5.725‐5.85 GHz) band. Therefore, the proposed antenna is suitable for circular polarization applications in C band.     

Four‐way waveguide power divider design for W‐band applications

In this article, a four‐way waveguide power divider is proposed for W‐band applications. The waveguide power divider employs an improved H‐plane T‐junction configuration. With the introduction of a metallic tetrahedral protrusion into the waveguide junction, good impedance matching can be achieved within a wide frequency range. First, a two‐way power divider is designed and analyzed, achieving almost identical amplitude and phase response at its two output ports. Then, other two same T‐junctions are cascaded, respectively, at the two output ports of the two‐way power divider to realize the proposed four‐way power divider. The four‐way power divider has been optimized, fabricated, and measured. The measurement results agree with the simulation ones reasonably, which demonstrates that the input return loss of the proposed four‐way power divider maintains above 14 dB across the entire W‐band with an insertion loss of less than 1.3 dB. Therefore, it could find wide applications in W‐band power splitting and combining modules.     

Design scheme for broadband Doherty power amplifier using broadband load combiner

This article proposes a design strategy for broadband Doherty power amplifier (PA) using broadband load combiner. The bandwidth of the Doherty PA based on the proposed combiner using packaged transistor is about 2.5 times the bandwidth of conventional Doherty PA using a quarter‐wave transformer. An easy to implement analytical design methodology has been presented for the proposed load‐combiner while describing the bandwidth enhancement strategy. The design methodology is validated with the design of a broadband Doherty PA based on CREE 10 W packaged GaN high electron mobility transistor devices using the proposed load combiner. Measurement results show more than 45% drain efficiency at 6 dB output power back‐off (OPBO) over 400 MHz frequency range, centred around 1.95 GHz. The peak drain efficiency at saturation is better than 60% over this band of operation. At 6 dB OPBO, the maximum improvement of 18.5% in drain efficiency is achieved as compared to the balanced mode PA. Measurement with single carrier wideband code division multiple access modulated signal shows the average drain efficiency of more than 44% at 36.6 dBm average output power at center frequency of operation. The adjacent channel power ratio is better than ?45 dBc after applying digital predistortion. The circuit is realized with microstrip technology, which can be easily fabricated using conventional printed circuit processes. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:655–674, 2015.     

Low loss and broadband transition between substrate integrated waveguide and rectangular waveguide

In this article, a novel transition between substrate integrated waveguide (SIW) and rectangular waveguide is proposed. A pair of antipodal tapered probes is developed to convert the E‐field of SIW to that of waveguide, acting as an antipodal dipole antenna to improve the performance of the SIW‐to‐waveguide transition. A back‐to‐back prototype of the proposed transition is fabricated and measured, the results show that the transition achieve a bandwidth of 51.1% from 23.7 to 40 GHz, and a size reduction of 75.3% compared to the SIW‐to‐waveguide transition using antipodal fin‐line. A tolerance analysis is performed via the simulation to verify the reliability of this transition design. For further validation, the antipodal tapered probes are employed for the design of partially filled SIW‐to‐waveguide transition. From its experimental results, it demonstrates that the loss of a single SIW‐to‐waveguide is less than 0.26 dB over the frequency range of 24.9–40 GHz. In addition, such proposed SIW‐to‐waveguide transition is suitable for hermetic packaging due to the inherent property in transition structure. These results show that the proposed transition can offer the advantages of broad bandwidth, low loss, compact size, and stable performance at millimeter‐wave frequencies. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:54–61, 2016.     

Compact dual‐band single‐ended‐to‐balanced power dividers with open/short‐ended stubs

In this article, two novel topologies of compact‐size dual‐band single‐ended‐to‐balanced power dividers that are loaded with open‐ and short‐ended stubs are presented. Quarter‐wavelength open‐ended stubs and half‐wavelength short‐ended stubs are respectively exploited in the proposed dual‐band power‐divider configurations to incorporate the dual‐band functionality into them for flexibly‐adjustable dual‐frequency‐ratio specifications. Each engineered five‐port power‐divider circuit features high in‐band input/output power‐matching levels, high in‐band power‐isolation levels between the two differential‐mode outputs, and high common‐mode‐rejection levels in a broad spectral range. Two microstrip prototypes designed at 0.9/1.8 GHz (GSM bands) and 1.57/2.45 GHz (GPS and WLAN bands) are constructed and characterized for experimental‐demonstration purposes.     

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 broadband circularly polarized slot antenna with a compact microstrip to CPW transition

A simple structure of broadband circularly polarized slot antenna based on coplanar waveguide (CPW) feeding is proposed in this article. To obtain circular polarization with a single feed, a transition from microstrip to CPW is designed to excite the even and odd modes of the CPW simultaneously. By adjusting the relative position and dimensions of the two circular patches introduced at the end of microstrip line and CPW, a 90° phase difference between two modes can be produced. When the two modes are coupled into the wide slot antenna, broadband circular polarization operation can be realized. The 10‐dB reflection coefficient bandwidth of the proposed antenna is 88.2% (2.49‐6.42 GHz) and 3‐dB AR bandwidth attains 50% (2.72‐4.49 GHz).     

A novel symmetrical Wilkinson power divider for dual‐band application

A symmetrical two‐way Wilkinson power divider with shifted output ports, much wide bandwidth and large frequency‐ratio is proposed for dual‐band application. The corresponding transcendental design equations are derived by using the even‐ and odd‐mode analysis. Moreover, the closed‐form scattering parameter expressions are derived. Transcendental design equations are solved and accurate numerical design parameters along with different frequency ratios are obtained. Finally, the proposed structure and design method are validated by simulated and experimental results of typical microstrip planar power dividers, the performance is clearly observed for the input and output matching, isolation and transmission characteristic very well at the two band frequencies. More specifically, the measured transmission characteristics of the divider are 3.11 dB/3.58 dB at the 1.0 GHz/3.5 GHz, respectively. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:102–108, 2014.     

Design and analysis of wideband eight‐way SIW power splitter for mm‐wave applications

High‐performance, wideband three‐stage power splitters based on substrate integrated waveguide (SIW) are presented. Broadband‐tapered microstrip transitions are used for feeding the SIW structures, which provide 7.5 GHz bandwidth from 21.5 to 29 GHz with return loss below ?20 dB. In addition, various T junctions are tuned, not only to provide broadband performance up to mm‐wave frequencies but also offer low‐phase and amplitude imbalance when cascaded in multistage 1 × 8 splitters. 1 × 4 and 1 × 2‐T junctions are adjusted through parametric analysis to provide wide bandwidth of 3.5 GHz at 24.5 GHz and ?15 dB reflection coefficient. The optimal microstrip transitions and T junctions are used to design a broadband, eight‐way power splitter with 15 dB return loss from 23.0 to 26.4 GHz and phase and amplitude imbalance of ±2.5° and ±0.8° dB, respectively. Furthermore, optimum positions of all inductive posts in terms of guided wavelength are also provided for assisting the direct design of mm‐wave, high‐performance power splitters.     

Dual‐band filtering power divider with unequal power division ratio and low‐loss characteristic

In this article, a dual‐band filtering power divider with unequal power‐division ability is proposed. Different from conventional equal power dividers constructed by filters or coupled resonators, noncoupled structures are employed in this design. As a result, low‐loss characteristic is realized for the proposed power divider. In this proposed structure, the dual‐band unequal power allocation is realized by replacing conventional single‐band λ/4 transformers with dual‐band ones (T‐junction structures). Three identical λ/4 stepped impedance resonators are properly attached to all the three ports of the proposed power divider to generate an extra transmission zero between two operational bands. Therefore, a filter‐like shaping in its S‐parameter results is obtained. A resistor is located between two outputs for output isolation. Mathematical derivations of the overall design procedure are also provided based on the circuit models and transmission line theory. Meanwhile, a resistor for output isolation is also included between two outputs, whose value can be calculated using given equations. For validation, a prototype operating at 0.9 and 2.1 GHz are designed, fabricated, and measured. The isolations between two outputs are 30 and 26 dB while the phase differences are only 2.5°and 4.9° at 0.9 and 2.1 GHz in the measurement, indicating good consistence of outputs. Measured |S21| and |S31| are ?(1.76 + 0.3) dB, ?(4.77 + 0.2) dB at 0.9 GHz and ?(1.76 + 0.6) dB, ?(4.77 + 0.5) dB at 2.1 GHz.     

Design of a compact orthogonal fed self‐diplexing bowtie‐ring slot antenna based on substrate integrated waveguide

In this article, a novel design of compact cavity‐backed slot antenna based on substrate integrated waveguide (SIW) technology is presented for dual‐frequency communication services. A single layer printed circuit board is applied to implement the proposed antenna. The bowtie‐ring slot engraved on the SIW square cavity is excited using two orthogonal microstrip feed lines to operate at two distinct frequencies (6.62 GHz and 11.18 GHz). The proposed antenna allows each of these frequencies to be designed independently. A prototype of the proposed cavity‐backed antenna that radiates at both 6.62 GHz and 11.18 GHz is fabricated and measured. The port isolation better than 29.3 dB is achieved by utilizing the transmission zeros (TZs), which are produced due to the orthogonal feed lines, TE₁₁₀ mode and coupling between the TE₁₂₀ and TE₂₁₀ modes. The measured peak gains of the proposed diplexing antenna are 5.77 dBi and 5.81 dBi at lower and upper resonating frequencies, respectively. The proposed dual‐frequency antenna exhibits the front‐to‐back‐ratio (FTBR) and cross‐polarization level greater than 26 dB and 21 dB, respectively, at both resonating frequencies.     

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.     

Array of waveguide‐fed microstrip antennas

A low‐cost Ku‐band array of microstrip antennas, which is fed by standard waveguide, is presented in this article. The 72 corner‐fed square patches of the array are arranged in a 6‐by‐12 configuration. A novel waveguide‐to‐microstrip transition with power divider is employed as the fed for the array to reduce the loss of the microstrip feed line. The resonant frequency of the array is 12.5 GHz and the gain was measured to be 24.3 dBi. The measurement results show good agreements with full‐wave simulation. This array of waveguide‐fed microstrip antennas can be used in many modern communication systems, such as a mobile radar sensor, in which the transition can be fixed as a connection between the module with a front‐end waveguide and the antennas. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.