Traveling-wave Array Research Articles

A Double-Layer Shaped-Beam Traveling-Wave Slot Array Based on SIW

A double-layer shaped-beam traveling-wave slot array based on substrate integrated waveguide (SIW) at $X$ -band is presented. The double-layer SIW longitudinal slot-coupled cavity slot is proposed as the array element, which has an improved bandwidth performance due to the double-resonant feature. By using this kind of slots, a planar nonuniformly spaced shaped-beam traveling-wave array is constructed. To achieve the desired distribution for the shaped-beam pattern, an efficient optimization method, with the mutual coupling effect being considered, is proposed to optimize the array structure parameters. Experimental results show that the array achieves good shaped-beam pattern in a 4.8% frequency band and low-loss characteristic.

Ku-Band Traveling Wave Slot Array Scanned Via Positioning a Dielectric Plunger

This paper introduces a feeding concept aimed at eliminating the backend (phase shifters) of traditional phased arrays. A goal is to make phased arrays simpler and less costly for satellite communications. Accordingly, we employ a traveling wave array (TWA) using a single feedline whose propagation constant is controlled via a single, small, and mechanical movement of a dielectric plunger to enable scanning. The dielectric plunger is positioned within a parallel plate waveguide (PPW) transmission line (TL) that feeds the TWA. By adjusting the position of the dielectric plunger within the TL, the feedline achieves a propagation constant range of $\text{1}\leq k_{eff}/k_{\text{0}}\leq\text{2.1}$ , corresponding to scan angles of $-\text{32.6}^\circ\leq\theta\leq\text{34.2}^\circ$ with an element spacing of $d=\text{0.65}\lambda_{\text{0}}$ . That is, beam steering is achieved using a single feed and a simple linear mechanical movement (for any size array) without using phase shifters. A 20-element array was designed for stable realized gain across $-\text{25}^\circ\leq\theta\leq\text{25}^\circ$ beam steering. Additionally, a proof of concept array was fabricated and measured. The simulated copolarized realized gain closely matches the fabricated TWA patterns.

Design and Operation of an Edge-Wall Slotted Waveguide Array Antenna with Ultralow Side Lobes for Application of Off-Shore Radar

This paper presents the design, fabrication, and operation of an edge-wall slotted waveguide array antenna with metal flare for the generation of ultralow side lobes fan-beam radiation. The single traveling wave array antenna consists of 71 radiating elements. The radiation pattern at the operating band was designed utilizing the Taylor's aperture distribution to achieve an ultralow side lobe level (SLL) of -33 dB. The mathematical relationship between the slot characteristics and the conductance is evaluated by the least squared quadratic curve fitting procedure. Finite element method software is used to analyze the various antenna characteristics of the radiating slots, including return loss, insertion loss, and radiation patterns. The array antenna was fabricated and the performance characteristics of the antenna were measured in an antenna near-field measurement chamber. The well match of the measured and simulated results indicated the excellent design of the array antenna with ultralow side lobes. Finally, the unit was fitted onto a search radar system and an experimental test on the radar returns on Keelung Islet was carried out. The clear radar signals of the islet showed the well design of the unit.

Low-Sidelobe Design of Microstrip Comb-Line Antennas Using Stub-Integrated Radiating Elements in the Millimeter-Wave Band

A novel radiating element with a matching circuit was developed for comb-line antennas of traveling-wave operation. In the design of low-sidelobe traveling-wave array antennas, large coupling is required for array elements of the comb-line antenna around the input port. Furthermore, the traveling-wave arrays, whose number of elements is small, also require large coupling because the radiation power for each array element is assigned to be much larger. However, wide radiating elements for large coupling perform poor impedance matching characteristics and radiate large cross polarization. Thus, we proposed a novel radiating element with matching stub in parallel to the radiating element to realize strong radiating power, low reflection, and low cross-polarization, simultaneously. The simulated and measured performances of low-sidelobe 14-element and 6-element antennas were demonstrated in this paper.

Traveling‐wave RF shimming and parallel MRI

At sufficiently high Larmor frequencies, traveling electromagnetic waves along a magnet bore can be used for remote magnetic resonance excitation and detection, effectively using the bore as a waveguide. So far, this approach has relied only on the lowest waveguide modes and thus has not supported multiple-channel operation for radiofrequency shimming and parallel imaging. In this work, this limitation is addressed by establishing a larger number of propagating modes and tapping their spatial field diversity with multiple waveguide ports. The number of available modes is increased by loading with dielectric inserts; the ports are implemented by stub and loop couplers at the end of a waveguide extension. The resulting traveling-wave array, operated at 298 MHz in a 7T whole-body magnet, is shown to enable radiofrequency shimming as well as parallel imaging with commonly used acceleration factors. The last part of the study concerns the amount of dielectric loading that is required. For the given Larmor frequency and bore dimensions, it is found that rather few water-filled inserts, occupying ∼5% of the bore cross-section, are sufficient for effective parallel imaging.

A Substrate Integrated Waveguide Circular Polarized Slot Radiator and Its Linear Array

A top-wall substrate integrated waveguide (SIW) slot radiator for generating circular polarized (CP) field is proposed and characterized in this letter. The reflection of the slot radiator is extremely weak, which simplifies the linear traveling wave array design. Based on such a structure, a 16-element CP SIW traveling wave antenna array is designed, fabricated, and measured at 16 GHz. A -23 dB side lobe level (SLL) with an axial ratio (AR) of 1.95 dB is experimentally achieved. The size of the proposed SIW CP linear array antenna is 285 mm times 22 mm. The measured gain is 18.9 dB, and the usable bandwidth is 2.5%.

Analytical solutions of the dielectrophoretic and travelling wave forces generated by interdigitated electrode arrays

In AC electrokinetics, the application of an AC electric field to a suspension of particles results in the manipulation and separation of the particles also the movement of the fluid. One application is dielectrophoresis (DEP). The second effect is travelling wave dielectrophoresis (twDEP). This paper presents the analytical solutions of the dielectrophoretic and travelling wave forces for the interdigitated electrode arrays energised with either a two- or four-phase signal, respectively. The torque that rotates the particle in the four-phase travelling wave arrays is also analytically solved.

The effect of electrode height on the performance of travelling-wave electroosmotic micropumps

Arrays of microelectrodes for pumping electrolytes in microchannels are currently under research. In this letter we demonstrate theoretically an enhancement in the performance of arrays of microelectrodes subjected to travelling wave potentials. Net fluid velocity can increase up to 2.7 times when the electrodes are raised above the channel bottom, proving that the viscous friction on the walls between electrodes is a key factor to account for in the design of microelectrode arrays. Finally, we perform a comparison with previous results for the asymmetric step electrode array. It is found that the maximum velocity for the travelling wave array is roughly twice that for the asymmetric step array.

Design of Circularly Polarized Waveguide Slot Linear Arrays

A design procedure for circularly polarized waveguide slot linear arrays is presented. The array element, a circularly polarized radiator, consists of two closely spaced inclined radiating slots. Both the characterization of the isolated element and the evaluation of the mutual coupling between the array elements are performed by using a method of moments procedure. A number of traveling wave arrays with equiphase excitations are designed and then analyzed using a finite element method commercial software. A good circular polarization is achieved, the design goals on the far field pattern are fulfilled and high antenna efficiency can be obtained

Experiments on AC electrokinetic pumping of liquids using arrays of microelectrodes

Net fluid flow induced by ac potentials applied to arrays of co-planar interdigitated microelectrodes is reported. Two types of microelectrode structures have been employed: arrays of unequal width electrodes subjected to a single ac signal, and arrays of identical electrodes subjected to a travelling-wave potential. A square glass chamber was constructed around the electrode arrays and filled with a concentration of KCI in water of conductivity around 1 mS/m. A map of the fluid velocity as a function of voltage (0-8 Vpp) and frequency (0,1-100 kHz) is presented for the travelling-wave array. In both microstructures, two fluid flow regimes have been observed: at small voltage amplitudes the fluid moves in a certain direction, and at higher voltage amplitudes the fluid flow is reversed. The fluid flow seems to be driven at the level of the electrodes in the two flow regimes. The observations at low-voltages are in qualitative accordance with an ac electroosmotic model based upon the Debye-Huckel theory for the double layer.

Polyethylene Glycol Deposition Techniques for Antifouling Surfaces: Using Antistiction to Conserve Bioparticles for Recovery and Analysis

ABSTRACTFor bioparticle analysis within microfluidic devices, there is a risk of analytes adhering to surfaces, thereby compromising particle manipulation and recovery. To address this we have implemented polyethylene glycol (PEG)-type coatings by self-assembled monolayer (SAM) and plasma-polymerizing deposition techniques. Silane chemistry is used to deposit SAM films directly onto silicon dioxide surfaces, and in a special case for which a composite of metallic arrays and SiON within our MEMS device must be coated, an ultrathin layer of sputtered Si is added before the SAM protocol. We have also deposited PEG-like tetraglyme by plasma-polymerization onto substrates using an onsite-built reactor to provide antistiction treatment to all surfaces, including those that do not have chemical compatibility for the SAM technique. Three tests demonstrate the effectiveness of our surface treatments: static exposure to microbial suspensions, bioparticle transport across MEMS traveling-wave (TW) arrays, and bioparticle recovery from a circulating flow device. Our static microbial assays show significant reduction in B. thuringiensis adhesion to both the SAM and plasma-polymerized coatings and reduction in B. globigii adhesion to the plasma-polymerized coating. Our TW arrays, when coated with either the SAM or plasma-polymerized PEG film, are effective at reducing adhesion to polystyrene beads as well as both Bacillus species. Lastly, our bioparticle recovery, as gauged by spectrophotometry, improves by as much as one order of magnitude when we coat flow chambers with our plasma-polymerized film.

A Waveguide Broad-Wall Transverse Slot Linear Array with Reflection-Canceling Inductive Posts and Grating-Lobe Suppressing Parasitic Dipoles

A design of a linearly-polarized non-resonant waveguide broad-wall transverse slot linear array with suppressed grating lobes is presented. Each unit element in the array consists of a transverse slot, an inductive post and a parasitic dipole-pair at a height of half of the free space wavelength. It is designed as an isolated unit without considering mutual coupling by using the Method of Moments (MoM) for radiation suppression in grating beam direction and reflection cancellation at the input. The elements thus designed are used in a travelling wave array environment. It is predicted that the reflection is less than -20dB at 11.95 GHz while the grating lobes are suppressed by more than 15dB. The design and the characteristics of the array are confirmed by measurements.

Design of dual-polarized series-fed microstrip arrays with low losses and high polarization purity

The design of a dual-polarized microstrip series-fed linear traveling-wave array is described in this paper. The array is composed of two identical subarrays formed by cascading an equal number of four-port aperture-coupled cross-patch elements and terminated on a two-port radiating matched load. By properly exciting the array, dual linear or circular polarization can be accomplished and by virtue of the symmetric arrangement of the antenna cross-polarization is annihilated. A straightforward design strategy is proposed for the synthesis of a desired current distribution along the array antenna. Some proof-of-concept linear arrays are developed and the corresponding numerical results, obtained through a full-wave approach based on the method of moments (MoM), are provided. As an independent validation, supplementary analyses by the finite integration technique (FIT) are also reported. Very close agreement is found between prescribed and synthesized array performance, which qualifies the proposed design approach as an accurate and effective tool for the synthesis of series-fed aperture-coupled patch arrays.

Dual-polarized linear series-fed microstrip arrays with very low losses and cross polarization

The design of a microstrip series-fed linear traveling-wave array is described in this paper. The array is composed of two symmetric subarrays formed by cascading an equal number of four-port aperture-coupled cross-patch elements and terminated on a two-port radiating matched load. Dual-linear and circular polarization can be achieved by appropriately exciting the array and by virtue of the symmetric arrangement of the antenna high polarization purity is obtained. A proof-of-concept linear array is developed and the corresponding numerical results performed through a full-wave approach based on the method of moments are presented.

5.8-GHz circularly polarized dual-rhombic-loop traveling-wave rectifying antenna for low power-density wireless power transmission applications

This paper reports a right-hand circularly polarized (RHCP) high-efficiency traveling-wave rectifying antenna (rectenna) designed in a coplanar stripline (CPS) circuit that is etched on a Rogers Duroid 5870 substrate with /spl epsiv//sub r/=2.2 and 20-mil thickness. A 4 /spl times/ 1 traveling-wave array of RHCP high-gain dual-rhombic-loop antennas (DRLAs) and a reflecting plane are used to provide highly efficient RF-to-DC conversion in the presence of lower power densities regardless of the rectenna's broadside orientation. The DRLA array has a circularly polarized antenna gain of 14.6 dB with a 2:1 voltage standing-wave ratio bandwidth of 17% and a better than 3 dB axial ratio fractional bandwidth of 7% centered about 5.8 GHz. The rectenna achieves 82% RF-to-DC conversion efficiency at 5.8 GHz and uses a low-profile CPS band-reject filter to suppress the re-radiated second harmonic by over 14 dB. The rectenna operating at low power density should have many applications when the transmitting power is low and/or the transmission distance is long.

Numerical solution of the dielectrophoretic and travelling wave forces for interdigitated electrode arrays using the finite element method

AC electrokinetics is the study of the movement of polarisable particles under the influence of AC electric fields. The fields are applied to a suspension of particles by planar microelectrode structures and one particular design, the interdigitated bar electrode has been used in both dielectrophoretic (DEP) field flow fractionation and travelling wave dielectrophoresis. This paper presents, numerical solutions of the DEP and travelling wave forces for an interdigitated electrode array energised with either a 2- or 4-phase signal. The electrorotational torque experienced by the particle in the 4-phase travelling wave array is also calculated. The solutions are compared with previous results.

Coherent combining of RF signals in a traveling-wave photodetector array

Analog fiber-optic links are used in a variety of microwave applications. The RF insertion loss and RF output power available from these links is currently limited by photodetector optical power handling. Using traveling-wave concepts similar to those in distributed amplifiers, we have demonstrated traveling-wave detector arrays (TWDAs) in which photodetectors are embedded within an artificial transmission line. By feeding this network with suitably time-delayed optical signals, this arrangement coherently combines the RF photocurrents from two detectors, yielding a 6-dB improvement in insertion loss and RF output power, while retaining 12 GHz of operating bandwidth.

Principles and performance of traveling-wave photodetector arrays

Analog fiber-optic links are used in a variety of microwave applications, including cable-TV and cellular-telephone distribution, as well as antenna remoting. The RF insertion loss and output power obtainable from externally modulated links is primarily limited by photodetector optical-power handling capabilities. Using traveling-wave concepts similar to those in microwave distributed amplifiers, we demonstrate the principle of traveling-wave detector arrays (TWDAs) in which discrete photodiodes are embedded within an artificial transmission line. By feeding these detectors with suitably time-delayed optical signals, this arrangement coherently combines multiple RF photocurrents into a single output. This paper presents the theory, construction details, and results of two- and four-element TWDA's operating up into the Ku-band. We demonstrate a two-element TWDA yielding a 6-dB improvement in insertion loss and RF output power with 12 GHz of operating bandwidth, and a four-element TWDA yielding 12-dB improvement up to 18 GHz.

Analysis and design of aperture-coupled microstrip patch antennas and arrays fed by dielectric image line

This paper presents the analysis and design of aperture-coupled microstrip patch antennas and arrays fed by an dielectric image line. A theory based on the cavity model of the microstrip patch antenna and the change in the modal voltage of the image line at the aperture was developed to analyze the single element aperture-coupled microstrip patch antenna. The theory developed was combined with the array theory to design linear traveling wave arrays at X-band and Ka-band frequencies. The required taper in the excitations of the individual patches of the array was achieved by varying the aperture dimensions. Experiments show very good results for the antennas and the arrays.

Beam scanning microstrip arrays using diodes

The feasibility of using diodes in linear microstrip antenna arrays to facilitate electronic beam scanning is investigated. The first concept concerns a microstrip line loaded with varactor diodes serving the dual purpose of phase shifter and feeder for a linear travelling wave array. Theoretical and practical results provide antenna design data on the number and type of diodes, optimisation of the radiating elements and temperature effects. Likely noise figure degradation, transient beam scanning response, and the antenna construction are other design aspects discussed. An array at 7.5 GHz containing 24 varactor diodes demonstrates that some 20° of beam scan is achievable before the travelling wave action is disrupted, and confirms the usefulness of the concept for applications demanding modest beam scan range and a simple low cost construction. The second concept introduced is a novel microstrip patch element with embedded diode and polariser enabling mixer action to take place. The theoretical and practical design of this antenna mixer element, and its deployment in an eight element linear beam scanning array at 2.92 GHz, is presented. Other mixer configurations, using additional diodes offering superior suppression of spectral products, are noted and the possible influence of the polariser on interelement mutual coupling investigated. Computations and measurements show that coupling effects are not significantly increased and confirm the usefulness of the antenna mixer element concept in beam forming array applications where no premixer low noise amplification is demanded.