The effect of mutual coupling between array elements on the performance of adaptive arrays is examined. The study includes both steady state and transient performance. An expression for the steady state output signal-to-interference-plus-noise ratio (SINR) of adaptive arrays, taking into account the mutual coupling between the array elements, is derived. The expression is used to assess the steady state performance of adaptive arrays. The transient response is studied by computing the eigenvalues associated with the signal covariance matrix. The steering vector required to maximize the output SINR of Applebaum-type adaptive arrays in the presence of mutual coupling is also given.

Effects of mutual coupling on the performance of adaptive arrays

In this communication, a metasurface-based decoupling method (MDM) is proposed to reduce the mutual couplings at two independent bands of two coupled multiple-input-multiple-output (MIMO) antennas. The metasurface superstrate is composed of pairs of non-uniform cut wires with two different lengths. It is compact in size and effective in decoupling two nearby dual-band patch antennas that are strongly coupled in the H-plane with the edge-to-edge spacing of only 0.008 wavelength at low-frequency band (LB). The antenna is fabricated and measured and the results show that the isolation between two dual-band antennas can be improved to more than 25 dB at both 2.5–2.7 GHz and 3.4–3.6 GHz bands, while their reflection coefficients remain to be below −10 dB after the metasurface superstrate is introduced. Moreover, the total efficiency is improved by about 15% in the low band and the envelope correlation coefficient (ECC) between the two antennas is reduced from 0.46 to 0.08 at 2.6 GHz and 0.08 to 0.01 at 3.5 GHz. The proposed method can find plenty of applications in dual-band MIMO and 5G communication systems.

Dual-Band Metasurface-Based Decoupling Method for Two Closely Packed Dual-Band Antennas

Two 4-bit active phase shifters integrated with all digital control circuitry in 0.13-mu m RF CMOS technology are developed for X- and Ku-band (8-18 GHz) and K-band (18-26 GHz) phased arrays, respectively. The active digital phase shifters synthesize the required phase using a phase interpolation process by adding quadrature-phased input signals. The designs are based on a resonance-based quadrature all-pass filter for quadrature signaling with minimum loss and wide operation bandwidth. Both phase shifters can change phases with less than about 2 dB of RMS amplitude imbalance for all phase states through an associated DAC control. For the X- and Ku-band phase shifter, the RMS phase error is less than 10 degrees over the entire 5-18 GHz range. The average insertion loss ranges from -3 dB; to -0.2 dB at 5-20 GHz. The input P-1dB for all 4-bit phase states is typically - 5.4 +/- 1.3 dBm at 12 GHz in the X- and.Ku-band phase shifter. The K-band phase shifter exhibits 6.5-13 degrees of RMS phase error at 15-26 GHz. The average insertion loss is from -4.6 to -3 dB at 15-26 GHz. The input P-1dB of the K-band phase shifter is -0.8 +/- 1.1 dBm at 24 GHz. For both phase shifters, the core size excluding all the pads and the output 50 Omega matching circuits, inserted for measurement purpose only, is very small, 0.33 x 0.43 mm(2). The total current consumption is 5.8 mA in the X- and Ku-band phase shifter and 7.8 mA in the K-band phase shifter, from a 1.5 V supply voltage.

/pdf/0-13-mu-m-cmos-phase-shifters-for-x-ku-and-k-band-phased-224uhr9k0o.pdf

0.13-mu m CMOS phase shifters for X-, Ku-, and K-band phased arrays - eScholarship

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

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

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

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.

Design Considerations for Octave-Band Phase Shifters Using Discrete Components

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

The design of digital phase shifters with bandwidths from 2:1 up to 20:1 using common mode all-pass networks (APNs) is presented. Because of the inherently large return loss value of the APNs, the phase shift response is not affected by the return loss and therefore the phase shift can be treated separately. The common mode APNs enable the use of standard switches and low cost fabrication. By properly designing the common mode APN phase shifter, an equal ripple phase shift response over a very large bandwidth can be realized. As an example, a 3 b 360° phase shifter covering a bandwidth of one decade (10:1) is designed using discrete components on PCB. An RMS phase error less than 10°, a return loss larger than 10 dB, and an amplitude imbalance less than 1.5 dB are measured from 100 MHz to 940 MHz.

Design of Large Bandwidth Phase Shifters Using Common Mode All-Pass Networks

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