A novel generalized coupled-line circuit structure for a dual-band Wilkinson power divider is proposed. The proposed power divider is composed of two coupled lines with different even- and odd-mode characteristic impedances and two lumped resistors. Using rigorous even- and odd-mode analysis, the analytical design equations for this proposed power divider are obtained and the ideal closed-form scattering parameters are constructed. Since the traditional transmission line is a special case of coupled line (coupled coefficient is zero), it is found that traditional noncoupled-line dual-band (including single band) Wilkinson power dividers and previous dual-band coupled-line power dividers are special cases of this generalized power divider. As a typical example, which could only be designed by using this given design equations, a compact microstrip 3-dB power divider operating at both 1.1 and 2.2 GHz is designed, fabricated, and measured. There is good agreement between calculated and measured results.

An Analytical Approach for a Novel Coupled-Line Dual-Band Wilkinson Power Divider

This paper presents a novel device integrating a power divider with two bandpass filters. It is capable of splitting power and selecting frequency at the same time. The phase shift of the filter is found to be ±90° at the center frequency. Therefore, when it is matched to 70.7 Ω, it can replace the conventional quarter-wave length transmission line in the power divider. The isolation elements are loaded at the filters' open ends to get a good isolation between the output ports. As a result, both the transmission and isolation property are satisfied. The equivalent even- and odd-mode circuits of the proposed structure are analyzed and design equations are derived. They are used to guide the design of the devices. For demonstration, filter-integrated power dividers with single- and dual-band operation are implemented, respectively. Comparisons of the measured and simulated results are presented to verify the theoretical predications.

Single- and Dual-Band Power Dividers Integrated With Bandpass Filters

A design methodology for a concurrent dual-band Doherty power amplifier (PA) with frequency-dependent backoff power ranges is presented in this paper. Based on a dual-band T-shaped network and a coupled line network, different dual-band components needed in Doherty PA topology, including a 3-dB branch-line coupler, an offset line, and a quarter-wavelength transformer, are developed. Two prototypes with balanced and imbalanced backoff power range modes are implemented to verify the feasibility. Continuous wave signal test results show that the proposed dual-band PA successfully achieves a power-added efficiency of 33% and 30% at the 6-dB backoff point from the saturated output power at 880 and 1960 MHz, respectively. To meet linearity requirements, the PA nonlinear behavior is characterized by using digital multitone signals, which categorize the distortions of a concurrent dual-band PA into intermodulation and cross-modulation. Finally, a 2-D digital predistortion technique is used to compensate for the nonlinearity of PA in dual bands. Two two-tone signals are applied to the dual bands for linearization, and the experimental results show that this technique achieves improvements of better than 19.1 and 24.6 dB for the intermodulation and cross-modulation in the dual bands, respectively.

Design and Linearization of Concurrent Dual-Band Doherty Power Amplifier With Frequency-Dependent Power Ranges

This letter presents a novel loaded transmission line, which has a constant phase shift over a wide bandwidth, referenced to a uniform transmission line. Compared with the conventional coupled line phase shifter, the configuration shows good performance with simplicity in both design and fabrication. The optimal design parameters for different phase shift values up to 120° are also presented to allow for a quick design process. To verify the configuration, a 90° phase shifter using a T shaped open stub loaded transmission line is designed, fabricated and measured. Excellent performance is achieved with small insertion loss and phase deviation over a bandwidth of 82%.

Broadband Phase Shifter Using Loaded Transmission Line

The single- and dual-layer metasurfaces are proposed to miniaturize a low-profile wideband antenna. The single- and dual-layer metasurfaces consist of one and two square patch arrays, respectively, both supported by grounded dielectric substrate to form the waveguided metamaterials. After retrieving the effective refractive index along the propagation direction in the waveguided metamaterial, the effective propagation constant is subsequently derived to initially estimate the resonant frequencies of the dual-mode antenna. With the increased effective refractive index, both the proposed antennas realize the gain greater than 6.5 dBi over the bandwidth of ~30% with a reduced radiating aperture of $0.46\lambda _{0} \times 0.46\lambda _{0}$ and a thickness of $0.06\lambda _{0}$ ( $\lambda _{0}$ is the free-space wavelength at 5.5 GHz). Moreover, the dual-layer metasurface provides more freedom to increase the effective refractive index with achievable gap widths compared with the single-layer metasurface.

Miniaturized Wideband Metasurface Antennas

This paper presents the theory and a design method for distributed digital phase shifters, where both the phase-error bandwidth and the return-loss bandwidth are considered simultaneously. The proposed topology of each phase bit consists of a transmission-line (TL) branch and a bandpass filter (BPF) branch. The BPF branch uses grounded shunt λ/4 stubs to achieve phase alignment with the insertion phase of the TL branch. By increasing the number of transmission poles of the BPF branch, the return-loss bandwidth can be increased. Analysis of the BPF topology with one, two, and three transmission poles is provided. The design parameters for 22.5° , 45° , 90° , and 180° are provided for bandwidths of 30%, 50%, 67%, and 100%. The relations between phase error, return loss, and maximum achievable phase shift are shown for the three topologies for design purposes. The methodology is also applicable to bandwidths larger than 100%. To validate the method, four separate L-band phase bits (1-2 GHz) are designed and measured. A complete 4-bit phase shifter with single-pole double-throw switches is then designed and measured. The measured rms phase error of the phase shifter is less than 3.6 °, while the return loss is larger than 15 dB from 1.06 to 1.95 GHz for all 16 phase states.

Phase-Shifter Design Using Phase-Slope Alignment With Grounded Shunt $\lambda/4$ Stubs

A tunable decoupling and matching network (DMN) for a two-element closely spaced antenna array is presented. The DMN achieves perfect matching for the eigenmodes of the array and thus simultaneously isolates and matches the system ports while keeping the circuit small. Arrays of closely spaced wire and microstrip monopole pairs are used to demonstrate the proposed DMN. It is found that monopoles with different lengths can be used for the design frequency by using this DMN, which increases the design flexibility. This property also enables frequency tuning using the DMN only without having to change the length of the antennas. The proposed DMN uses only one varactor to achieve a tuning range of 18.8% with both return loss and isolation better than 10 dB when the spacing between the antennas is 0.05 λ. When the spacing increases to 0.1 λ, and the antennas are properly matched, the simulated tuning range is more than 60%.

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Tunable Decoupling and Matching Network for Diversity Enhancement of Closely Spaced Antennas

This paper analyzes the two-way Wilkinson power dividers using coupled lines as λ/4 impedance transformer to have more compact layout. The analysis shows that the input port matching is only influenced by the even mode impedance of the coupled lines. Once the even mode impedance is fixed, all other specifications of the power divider are determined by the odd mode impedance of the coupled lines. Design tradeoffs among the output matching, isolation and the odd mode impedance are shown. By using smaller odd mode impedance, layout constraint can be relaxed. To validate the analysis, Wilkinson power dividers using coupled lines with areas of 1.5 cm2 and 1.25 cm2 are designed together with a conventional divider with an area of 3.8 cm2. The experimental results of the three designs are comparable. When coupled lines are used, the layout is more compact with a reduction in size of more than 50% compared to the conventional design.

Analysis and design of compact two-way Wilkinson power dividers using coupled lines

This paper proposes a novel Doherty power amplifier (PA) that realizes concurrent dual-band operation. A T-network is used to implement a dual-band impedance transformer and a phase shifter simultaneously. To prove the concept a PA is designed operating at 900 MHz and 2000 MHz simultaneously. In the experimental results, the concurrent dual-band PA achieves a drain efficiency of 39.8% with an output power of 36.9 dBm at the 5 dB back-off point from saturated output power at 900 MHz, and a drain efficiency of 41.4% with an output power of 36.2 dBm at the 5 dB back-off point at 2000 MHz. Compared to the balanced PA, the drain efficiency of the proposed PA has been approximately doubled in the entire back-off power region.

A concurrent dual-band doherty power amplifier

A new method for octave-band phase-shifter design based on high-pass, low-pass, bandpass, and all-pass networks (APNs) using discrete components is presented. First, the general synthesis method is provided to find the optimum return loss and phase error of a high-pass/low-pass phase shifter. It is also shown that the conventional design method is a special case of the method presented here. The proposed method facilitates tradeoffs between the bandwidth, phase error, and return loss, which is not possible in the conventional method. Phase bits of 22.5°, 45 °, and 90 ° are designed using this method. For the phase bit of 180° , a new topology using a third-order bandpass network and an APN is proposed. The phase error is reduced from 25 ° to 7.4 ° and the return loss is improved from 5 to 22 dB over the whole octave band compared to the conventional method. For the cascaded 4-bit phase shifter, the return loss is improved from 5 to 19 dB and the rms phase error is reduced from 13.5 ° to 4.3 ° in theory. The experimental results of the 4-bit phase shifter show an rms phase error of 5.9° and a return loss of 13 dB from 530 to 1090 MHz. The maximum amplitude imbalance is 0.6 dB for all 16 phase states.

Xinyi Tang

Papers

Phase-Shifter Design Using Phase-Slope Alignment With Grounded Shunt $\lambda/4$ Stubs

Tunable Decoupling and Matching Network for Diversity Enhancement of Closely Spaced Antennas

Analysis and design of compact two-way Wilkinson power dividers using coupled lines

A concurrent dual-band doherty power amplifier

Design Considerations for Octave-Band Phase Shifters Using Discrete Components