Ferroelectric phase shifters and their performance in microwave phased array antennas

In this paper we developed a ferroelectric CPW phase shifters which will be integrated with wideband CTS antenna array. For fabrication of the ferroelectric CPW, the vacuum sputter has been used with a optimized sputtering parameters. The experimental RF performances of the developed phase shifters were compared with those from simulations using WIPL-D software. The results showed that while the approach of using thin Ferroelectric films may be successful in designing low cost tunable coplanar waveguide phase shifters, the amount of achievable phase shifts are small (less that 10°) unless Ferroelectric compatable substrates such as STO are used (phase shifts are 27°). Good agreement was also observed between simulations and measured results and this provides high confidence in the developed fabrication process‥ While our group has been successful in fabricating thin film ferroelectric phase shifter, work is still underway to help develop multilayer ferroelectric phase shifters as well as on the development of an integrated CTS and ferroelectric phased antenna array. As a next step, our group is now pursuing fabrication of a ferroelectric multilayer CPW integrated with the CTS antenna array.

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.

In this paper, a method is introduced to improve the performance of ferroelectric phase shifter. The influences of periodically inserting spiral inductor into ground of coplanar waveguide (CPW) are investigated. Three dimensional electro-magnetic simulation shows that at frequency of 25 GHz, the maximal phase differential will be 449°, which is 97° more than the conventional one with no spiral inductor loaded. The novel ferroelectric phase shifter is also fabricated. Comparing with the conventional phase shifter, additional 49° phase shift is obtained at 18 GHz.

A phased array antenna using ferroelectric coplanar waveguide (CPW) phase shifter active modules is presented based on a Ba0.6Sr0.4TiO3 (BST) thin film. The ferroelectric BST thin film was deposited on an MgO substrate by using pulsed laser deposition. The active module amplifies an RF signal with low noise and changes the phase of a received RF signal to control the main beam of the array antenna. It is composed of low noise amplifier (LNA), dc block, and ferroelectric CPW phase shifter. The prototype of 6×12 phased array patch antenna with the active modules using a ferroelectric phase shifter is proposed. The proposed array antenna continuously scanned its main beam in elevation plane to 32° from its broadside direction at 11.85 GHz by applying the continuous dc voltage to the ferroelectric phase shifter.

A tunable capacitor based on a ferroelectric thin film grown on a dielectric substrate is a promising component for reconfigurable and tunable devices for numerous RF and microwave applications such as phase shifters, tunable filters, and tunable matching networks. The goal of this paper is characterization of the insertion loss in a reflection-type microwave phase shifter based on the ferroelectric tunable capacitor. The reflection-type phase shifter based on ferroelectric planar tunable capacitor was designed, manufactured, and tested. Its simulated and measured insertion loss and phase shift are compared. Two loss mechanisms in the phase shifter were distinguished: the loss in the tunable capacitor and the loss in the associated circuitry (metallization and substrate). The properly organized investigations of the dissipation of energy in metallization and dielectric substrate can result in a sufficient improvement of the quality of the devices. As a final result, one may anticipate that the figure-of-merit of a ferroelectric tunable or switchable phase shifter can reach 200 deg/dB

The analysis, construction, and performance of compact surface wave ferroelectric phase shifters suitable for operation in the100-to1000-MC frequency range are described. Although this ferroelectric loaded parallel-plane structure is a very low impedance structure, a satisfactory terminal impedance matching technique has been devised. Kilovolt level voltages are needed; but since the current required to maintain or rapidly shift phase is low, the over-all control power requirements are at least an order of magnitude less than those for comparable ferrite phase shifters. One of these room temperature operable phase shifters provided 348/spl deg/ of phase shift at 207 Mc. It had an insertion loss which varied from 3.7 to 2.2 db over a zero- to 4000-volt range of applied dc control voltage.

Recent advances in ferroelectric and high temperature superconductive technology have enabled new phase shifters incorporating ferrite, ferroelectric, and high temperature superconductor materials to be developed. Each material offers important and unique properties which may be combined with one of the other materials to obtain useful phase shifters. Ferrite materials with tunable magnetic permeabilities have classically been used for phase shifters. Ferrites offer large phase shifts with small changes in insertion loss. Ferroelectric materials employing variable dielectric constants can also be used as phase shifters. One advantage of ferroelectric phase shifters over ferrite phase shifters, ultra-wideband performance, enables coverage of the entire band from 2 to 18 GHz. Superconductors offer low losses and unique properties including the kinetic inductance effect and SQUIDs. The physics of the three materials will be reviewed briefly, and the difference between ferroelectricity and ferromagnetism will be discussed. Combination of magnetic and superconducting materials is possible, despite the fact that magnetic fields suppress superconductivity. A comparison of variable time delay and phase shift devices will show interesting contrasts between these devices and MMIC components. Superconducting phase shifters using only superconducting properties, and phase shifters combining superconductivity with ferrites or ferroelectrics will be described.

A reflection type phase shifter based on a tunable ferroelectric capacitor is under consideration. A design and characteristics of the one-bit ferroelectric phase shifter is proposed and discussed. The minimal insertion loss of the phase shifter is limited by the commutation quality factor of the capacitor and can be achieved in the case when the losses of the phase shifter in both states have the same value. The layout of the phase shifter based on a coplanar waveguide structure is shown. Measured characteristics of the phase shifter are compared with the predicted ones.

Chapter 11 - Phase Shifters

A design of 18 - 20 GHz GaAs Monolithic Microwave Integrated Circuit (MMIC) 4-bit phase shifter is presented. The phase shifter adopts high-pass/low-pass type and switched filter networks. The passive HEMTs are used as key components for controlling the phase shift. All the drain and source terminals are DC grounded while the gates are applied with 0 V or −3 V. The power consumption is almost zero. The phase shifter obtains 9 ± 1 dB insertion loss and the input and output return losses are higher than 9.8 dB over the 18 - 20 GHz bandwidth of interest. The phase resolution is 22.5° with the root mean square (RMS) phase error is less than 5° within the bandwidth. The phase shifter is designed by using GaAs 0.15 µm process. The chip area is very compact, just about 2 mm ×1 mm, including all the pads.

A Ka-band GaAs Monolithic Microwave Integrated Circuit (MMIC) 4-bit digital phase shifter for a soil moisture radiometer phased array antenna is presented. The phase shifter is comprised of GaAs pHEMT passive devices and high-pass/low-pass (HP/LP) and switched filter networks. The passive HEMT's gate is biased with 0 or -3 V to control the desired phase shifts. The simulation results demonstrate 11 ± 1 dB insertion loss (IL) and the input and output return loss (RL) is higher than 8.8 dB over the band of 36 - 38 GHz. The root mean square (RMS) phase error is smaller than 4° within the band. The phase shifter is designed using 0.15 μm GaAs pHEMT process. The phase shifter power consumption is almost zero. The chip size is about 2 mm × 1 mm, including the pads and scribe lines.

This paper presents a submillimeter-wave 500–550-GHz MEMS-reconfigurable phase shifter, which is based on loading a micromachined rectangular waveguide with 9 E-plane stubs. The phase shifter uses MEMS-reconfigurable surfaces to individually block/unblock the E-plane stubs from the micromachined waveguide. Each MEMS-reconfigurable surface is designed so that in the nonblocking state, it allows the electromagnetic wave to pass freely through it into the stub, while in the blocking state, it serves as the roof of the main waveguide and blocks the wave propagation into the stub. The phase-shifter design comprises three micromachined chips that are mounted in the H-plane cuts of the rectangular waveguide. Experimental results of the first device prototypes show that the microelectromechanical system (MEMS)-reconfigurable phase shifter has a linear phase shift of 20 $\mathbf {^{\circ }}$ in ten discrete steps (3.3 bits). The measured insertion loss is better than 3 dB, of which only 0.5–1.5 dB is attributed to the MEMS surfaces and switched stubs, and the measured return loss is better than 15 dB in the design frequency band of 500–550 GHz. It is also shown that the major part of the insertion loss is attributed to misalignment and assembly uncertainties of the micromachined chips and the waveguide flanges, shown by simulations and reproducibility measurements. The MEMS-reconfigurable phase shifter is also operated in an analog tuning mode for high phase resolution. Furthermore, a detailed study has been carried out identifying the reason for the discrepancy between the simulated (90 $\mathbf {^{\circ }}$ ) and the measured (20 $\mathbf {^{\circ }}$ ) phase shift. Comb-drive actuators with spring constant variations between 2.13 and 8.71 N/m are used in the phase shifter design. An actuation voltage of 21.94 V with a reproducibility better than $\mathbf {\sigma }=$ 0.0503 V is measured for the actuator design with a spring constant of 2.13 N/m. Reliability measurement on this actuator was performed in an uncontrolled laboratory environment and showed no deterioration in the functioning of the actuator observed over one hundred million cycles.

An analysis has been made of the factors affecting the performance of 4-port circulators based on non-reciprocal phase-shifter and directional-coupler networks. The effects on the adjacent-arm isolation of phase-shift error, coupling error, dissimilarities between the couplers, and non-reciprocal loss in the phase shifters are examined. The effects on the alternate-arm isolations and input matches of the isolations and matches of the couplers, and the matches of the phase shifters are then discussed. The power-handling capacity is not considered.The results of the analysis lead to the choice of a network using similar E-plane multi-branched waveguide couplers, two similar non-reciprocal phase shifters of ½π differential phase shift, and one reciprocal phase shifter of ½π phase lag relative to the unloaded line.Components meeting the limits derived by the analysis were developed, and used in the construction of two circulators in waveguide 14 working in the band 5.925–6.425 Gc/s. One of these maintained over an 8% bandwidth isolations greater than 30 dB, voltage standing-wave ratios greater than or equal to 0.95 and insertion losses less than or equal to 0.3 dB. The second maintained over a 4% bandwidth isolations greater than 33 dB, and similar v.s.w.r.s and insertion losses.The development work on the phase shifters and couplers is described, and the results obtained are given. The performance of a circulator is predicted by the theory from measurements on the components, and compared with measurements on the circulator.Finally, the factors limiting the performance of the present circulators are discussed, and suggestions are made for further improvement.

This paper proposes a new wideband phase shifter, aligning phase slope between the reference line and main line to reduce the slope deviation using 3 types of LC resonance circuits (series, parallel and composite type). Compared to the conventional ones, the proposed phase shifters have several advantages such as a simple structure with single layer, accurate LC values from the derived formulas that are not optimization values. In addition, any phase shift value is applicable to the proposed theory, since the phase shift range of the proposed phase shifter can be implemented from 0 to 360 degree. The design theory of the proposed phase shifter is derived by taking a differential of difference between reference line and LC resonant circuit with respect to angular frequency, then calculate the value of each element of L and C at the center frequency. Although the proposed phase shifter is designed with only one or three resonant circuits in this paper, the number of resonant circuits constituting the main line can be three or more. By the design theory, the total sum of the phase values allocated to each resonant circuit may be a phase shift value to indicate a desired phase difference between the reference line and the main line. To validate the design theory, 180○ wideband phase shifters with singles (series and parallel) and composite resonant circuits are designed, fabricated, and measured. The fractional bandwidth of the proposed circuits for a parallel and a composite resonant circuit are both greater than 64%. Therefore, the measurement results agree well with the design theory within 0.5 dB insertion loss ±10° and phase deviation, except fabrication error.

Error vector measurements (EVM) are used to investigate whether the nonlinear properties of a ferroelectric coupled microstrip phase shifter (CMPS) impact the quality of a radio frequency (RF) signal that is modulated, transmitted through the ferroelectric CMPS, and demodulated. Measurements were performed using a variety of phase shift key (PSK) and quadrature amplitude modulation (QAM) formats. At RF power levels up to +6 dBm and symbol rates up to 7 megasamples per second (Msps), we observed no degradation in EVM that could be associated with the ferroelectric phase shifter. These preliminary results are encouraging for the suitability of these devices to perform in high power, high bandwidth space communication applications.