Controllable microstrip phase shifter using actuating membrane ground plane

In this paper, a new reconfigurable microstrip structure is presented where line impedance can be actively controlled to induce phase shift on a transmission-line signal. Micromachining is used to fabricate thin-film copper membranes in the ground plane below the transmission line. Actuation of these membranes enables control of transmission-line to ground-plane spacing and, thus, the line capacitance. The performance of this reconfigurable microstrip transmission line as a phase shifter is investigated between 5-32 GHz for a variety of membrane geometries. A phase shift of up to -32.1/spl deg/ at 15.00 GHz is achieved by actuating an array of five 4.3-mm-diameter membranes beneath a 30-/spl Omega/ microstrip line. A single 10.0-mm-diameter membrane achieved a phase shift of -25.57/spl deg/ at 15.05 GHz on a 50-/spl Omega/ line, while a 10.4-mm membrane achieved a phase shift of -55.5/spl deg/ at 14.25 GHz on a 30-/spl Omega/ line. Both single and multiple series ground-plane membranes are possible, and they can be activated with discrete or continuous control signals, individually or together. Discrete and continuous phased array beam steering are, therefore, feasible.

A novel distributed digital MEMS (micro-electro-mechanical system) microwave phase shifter, fabricated with bulk Si micromachining techniques, is presented. Using a distributed nonlinear transmission line technique, with single crystal silicon based multilayer microbridge structures as loading varactors, this phase shifter delivers true time delay and wideband performance. A micromachining process flow, combining anodic bonding and single crystal silicon etching with heavy boron doping, was developed to fabricate the movable Si-based microbridges over a coplanar waveguide (CPW). An electrostatic voltage, applied between the Si layer of the microbridges (varactors) and CPW ground plane, pulls down the microbridges, effecting a phase shift varying linearly with. frequency. The principle, process and RF performance characterization are described. The actuated phase shifter has achieved 90.2/spl deg/ phase shift at 20.5 GHz, with good reflection loss (-12 dB) in the frequency range of 5-20.5 GHz. The insertion loss is a little high, 3.87 dB, however, due to the lossy substrate of Pyrex 7740 glass and the thin metalization of the CPW.

Distributed MEMS transmission line (DMTL) phase shifter has been developed using planar inductors. The design consists of a coplanar waveguide line capacitively and inductively loaded by the periodic set of electrostatic force actuated microelectromechanical system switches as capacitors and inductors. By applying a single bias voltage on the line, the characteristic impedance can be changed, which in turn changes the phase velocity of the line and creates a true time delay phase shift. The governing equations for the impedance and loss are derived. The ABCD matrix is defined for a unit and multi-cell DMTL phase shifter to extract scattering parameters equations. The device containing 15 cells calculated, simulated, and fabricated. Fabricated results show that the device can be considered as a new type of the DMTL phase shifter with small size, higher phase shift and acceptable scattering parameters.

In this paper, a computer simulation of a MIMO system comprising phased array antennas (PAA) in all receiving branches is presented. In order to examine the system performance under relatively realistic conditions, a ray-tracing simulator was applied to generate a baseband channel impulse response matrix <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> . The PAA consists of L antenna elements where a variable-gained low-noise amplifier and a 360deg continuously adjustable phase shifter are inserted in each antenna element and an adder for the array output is connected into the RF front-end of each receive branch. The phase shifters are adaptively controlled to increase the total channel capacity of MIMO systems.

We propose an S-band active phased array antenna (APAA) with analog phase shifters (PSs) that use double-balanced mixers (DBMs). The quadrature phase shift keying modulator integrated circuits (ICs) used as the phase shifters can control both the amplitude and phase of the input signal continuously and independently by using the control voltages. The phase and amplitude errors during phase rotation were 0.5/spl deg/ rms (max=1.7/spl deg/) and 0.3 dB rms (max=0.7 dB), respectively. The range in which the amplitude could be linearly changed was 7 dB. The proposed antenna exhibited sufficient performance for mobile vehicles to handle satellite communications: beam-pointing resolution of 0.04/spl deg/, beam-pointing accuracy in the null pointing of 0.4/spl deg/ rms, and sidelobe suppression with an amplitude taper achieved by setting the amplitude of the PS using two DBMs. Comparison between the analog PS and a reflection-type four-bit digital PS showed that although the analog one is unsuitable for use in a passive PAA, it is suitable for use in an APAA.

Today's phased-array antennas use hundreds of radiating elements that use relatively high-loss phase shifters that operate over a limited bandwidth. The number of elements and the phase shifter losses affect the overall cost of the antenna system. Ferroelectric RF phase shifters have the potential to meet the low-loss, low-cost requirements driving many phased-array applications. Some of the issues affecting the development of ferroelectric phase shifters include ferroelectric tunability, dielectric losses, conductor losses, and impedance mismatch. We used the measured tunability (250 kHz, room temperature), dielectric constant, and loss tangent (10 GHz, room temperature) of Ba1-xSrx/TiO3 (0.4x 0.6) with various amounts of MgO additive, 0 to 60 wt.%, to estimate the device performance of microstrip phase shifters. The electromagnetic model of the microstrip (which uses a standard 3-mil-wide 1-oz. copper line, 3-mil-thick BST/MgO composite and the bias criteria of 2 V/μm) has produced performance benchmarks for a number of composites providing 360° of phase shift. While the accuracy of the electromagnetic model used to evaluate these materials has limitations, the results do provide some insight as to which materials may be better suited for 10-GHz phase shift devices.

This paper presents a Tapered Tunable Transmission Line (Tapered TTL) phase shifter that achieves a higher area efficiency than conventional Tunable Transmission Line (TTL) phase shifters while maintaining the same phase shift range with similar insertion losses. A systematic methodology is provided for the optimum design of the proposed phase shifter to maximize its area efficiency while providing the desired phase shift range and satisfying the maximum allowed input/output return and insertion losses. To verify the efficacy of the proposed solution, an eleven-cell phase shifter is fabricated in a standard 65-nm Complementary Metal–Oxide–Semiconductor (CMOS) technology and the measurement results are reported. The fabricated circuit provides a 180-degree phase shift over the frequency range of 16.5 to 31 GHz with an average insertion loss of 7.2 dB. The proposed design presents a 25 percent reduction in the chip area per unit delay in comparison to the conventional design with the same average insertion loss.

Chapter 11 - Phase Shifters

This paper presents a 21 to 30-GHz merged passive vector sum phase shifter (PS) and programmable gain amplifier (PGA) with sub-degree phase resolution for 5-G phased array application. In PS, a transformer-based full-differential high-order resonant coupler functions as a quadrature generator (QG) with a novel layout strategy to achieve broad bandwidth, low loss, and accurate quadrature phase within only one inductor-footprint. Compared to the conventional transformer-based fourth order resonant coupler, the proposed resonant coupler with higher order features much wider quadrature bandwidth. Two phase invariant 6-bit binary-weighted arrays of vector modulators scale the quadrature signals to achieve the desired high resolution vector phase interpolation. In PGA, a phase invariant and dB-linear gain is achieved by adopting a fractional-bit-based PGA design. The chip prototype is fabricated in a 65-nm CMOS process, this implementation achieves 43% fractional BW -3dB (20 to 31-GHz). The phase control operates with 0.8° steps while maintaining a minimum RMS phase error of 0.42°, demonstrating the best phase accuracy when compared to state-of-the-art mm-wave PSs.

Broad-band analog and digital reflection-type phase shifters (RTPSs), showing constant phase shift over 1:3 bandwidth, have been developed using microelectromechanical systems (MEMS) technology. Two-unit RTPSs centered at two different frequencies have been cascaded to achieve flat phase responses over a wide frequency band. Each phase shifter uses air-gap overlay coplanar-waveguide couplers for low-loss 3-dB coupling and bridge-type MEMS capacitors for reflective terminations. The fabricated analog phase shifter shows the average insertion loss of 3.5 dB, and maximum phase error of /spl plusmn/4.9/spl deg/ from 15 to 45 GHz. The 2-bit digital RTPS shows reduced maximum phase error of /spl plusmn/2.8/spl deg/ together with a comparable insertion loss of 3.1 dB from 5 to 15 GHz. The details of the circuit design, analysis, and fabrication procedures are presented together with the measurement results. Compared with the similar constant phase shifters using semiconductor diodes and transistors, the micromachined RTPS of this study shows superior performance in terms of phase errors, insertion losses, and bandwidth.

In this paper, a wideband photonic phased array antenna is demonstrated. The array configuration consists of a 4x1 Vivaldi single-polarization antenna array and an independent photonic phasing system for each element. The phasing network of this array is implemented using two novel photonic phase shifters based on the vector summation approach. A vector sum phase shifter (VSPS), which can be continuously tuned from 0-100/spl deg/ frequency-linear from DC to 15 GHz, is presented along with a novel second harmonic VSPS (SH-VSPS), which can provide continuously tunable phase shifts in the range 0-430/spl deg/ which is linear over a bandwidth from 8-16 GHz. This paper presents the operation and characterization of each component of the array including the radiation elements and the various photonic phase shifters and finally, a demonstration of the combined system. A discussion on the practicality of this system for airborne applications is presented along with suggestions for simplification and improvement.

Beam-scanning capabilities for space-borne submillimeter-wave spectrometers are critical for instrument calibration and field-of-view mapping. However, the lack of low-loss waveguide-integrated phase shifters above 500 GHz has been a significant challenge for realizing Terahertz phased array antennas. Recently developed microelectromechanical system (MEMS)-actuated phase shifters have emerged as promising candidates, initially demonstrating a 145<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${}^\circ$</tex-math></inline-formula> phase shift. As a first demonstration of the efficacy of these phase shifters for electronic beam-steering, we present the design, fabrication, and characterization of a linear, near-Nyquist sampled, 4 × 1-element phased array operating from 500 to 600 GHz. The array element is a silicon micromachined leaky-wave feed based on a Fabry–Pérot cavity to enhance directivity and reduce grating lobes while achieving bandwidth requirements with minimal scan loss. It is shown, through measurements, that this antenna feed is suitable for use in larger 8 × 1-element arrays for applications that require moderate gain (20 dBi) and scanning (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm 20^\circ$</tex-math></inline-formula>) with a fan beam. Furthermore, we present measurement results of a second generation of MEMS phase shifters with an increased measured phase shift up to 350<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${}^\circ$</tex-math></inline-formula>. A full 360<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${}^\circ$</tex-math></inline-formula> phase-wrapping capability is desired as this will enable high-gain lens-scanning phased arrays that can be used for future submillimeter-wave spectrometers.

This paper presents a novel phased-array antenna system with multifrequency, full-duplex operation, and wide-beam scanning. The system consists of a wideband power divider, a low-loss and low-cost multiline phase shifter controlled by dual piezoelectric transducers (PETS), a four-channel multiplexer, microwave monolithic integrated circuit (MMIC) amplifiers, and a stripline-fed Vivaldi antenna array. The multiline PET phase shifter has a low perturbation loss of less than 2 dB and a total loss of less than 4 dB up to 40 GHz, with a maximum phase shift of 650/spl deg/. Using dual-aligned PETS for bidirectional phase shifting results in wide scan angles of 38.6/spl deg/, 37.6/spl deg/, 43/spl deg/, and 40/spl deg/ for the four channels at 10, 12, 19, and 21 GHz, respectively. The four-channel diplexer demonstrates low insertion loss with high isolation between channels. The new multifrequency phased-array system provides wide-beam scanning and full-duplex capability using a simple, low-cost architecture. The system can be used for applications in mobile satellite communications.

Monolithic Ka-band phase shifter circuit that employs voltage tunable BaSrTiO/sub 3/ (BST) parallel plate capacitors is presented here. The circuit is capable of continuous 0/spl deg/-157/spl deg/ phase shift at 30 GHz with an insertion loss of only 5.8 dB and return loss better than 12 dB. In addition to promising loss performance (27.1/spl deg//dB) at 30 GHz, the circuit reported here has several advantages over previously reported BST phase shifters such as moderate control voltages (20 V), room temperature operation, and compatibility with monolithic fabrication techniques.

A novel 3-state unit cell for distributed MEMS transmission line (DMTL) phase shifters is designed and simulated in this paper. The proposed structure consists of a coplanar waveguide transmission line, a MEMS and two-pair metal-air-metal bridges. The bridges are actuated respectively in three different modes which produce three different phase shifts. The structure is simulated using HFSS software. Based on the simulation results, the return loss in all 3 states is better than -10dB and the phase shift is in good agreement with ideal values. The designed unit cell is very suitable for 5-bit and 6-bit DMTL phase shifters.