Ozlem Aydin Civi

Frequency Tunable Microstrip Patch Antenna Using RF MEMS Technology

A novel reconfigurable microstrip patch antenna is presented that is monolithically integrated with RF microelectromechanical systems (MEMS) capacitors for tuning the resonant frequency. Reconfigurability of the operating frequency of the microstrip patch antenna is achieved by loading it with a coplanar waveguide (CPW) stub on which variable MEMS capacitors are placed periodically. MEMS capacitors are implemented with surface micromachining technology, where a 1-mum thick aluminum structural layer is placed on a glass substrate with a capacitive gap of 1.5 mum. MEMS capacitors are electrostatically actuated with a low tuning voltage in the range of 0-11.9 V. The antenna resonant frequency can continuously be shifted from 16.05 GHz down to 15.75 GHz as the actuation voltage is increased from 0 to 11.9 V. These measurement results are in good agreement with the simulation results obtained with Ansoft HFSS. The radiation pattern is not affected from the bias voltage. This is the first monolithic frequency tunable microstrip patch antenna where a CPW stub loaded with MEMS capacitors is used as a variable load operating at low dc voltages

A Monolithic Phased Array Using 3-bit Distributed RF MEMS Phase Shifters

This paper presents a novel electronically scanning phased-array antenna with 128 switches monolithically implemented using RF microelectromechanical systems (MEMS) technology. The structure, which is designed at 15 GHz, consists of four linearly placed microstrip patch antennas, 3-bit distributed RF MEMS low-loss phase shifters, and a corporate feed network. MEMS switches and high-Q metal-air-metal capacitors are employed as loading elements in the phase shifter. The system is fabricated monolithically using an in-house surface micromachining process on a glass substrate and occupies an area of 6 cm times 5 cm. The measurement results show that the phase shifter can provide nearly 20deg/50deg/95deg phase shifts and their combinations at the expense of 1.5-dB average insertion loss at 15 GHz for eight combinations. It is also shown by measurements that the main beam can be steered to required directions by suitable settings of the RF MEMS phase shifters.

Beam Switching Reflectarray Monolithically Integrated With RF MEMS Switches

A reflectarray antenna monolithically integrated with 90 RF MEMS switches has been designed and fabricated to achieve switching of the main beam. Aperture coupled microstrip patch antenna (ACMPA) elements are used to form a 10 × 10 element reconfigurable reflectarray antenna operating at 26.5 GHz. The change in the progressive phase shift between the elements is obtained by adjusting the length of the open ended transmission lines in the elements with the RF MEMS switches. The reconfigurable reflectarray is monolithically fabricated with the RF MEMS switches in an area of 42.46 cm2 using an in-house surface micromachining and wafer bonding process. The measurement results show that the main beam can be switched between broadside and 40° in the H-plane at 26.5 GHz.

On the Poisson sum formula for the analysis of wave radiation and scattering from large finite arrays

Poisson sum formulas have been previously presented and utilized in the literature for converting a finite element-by-element array field summation into an alternative representation that exhibits improved convergence properties with a view toward more efficiently analyzing wave radiation/scattering from electrically large finite periodic arrays. However, different authors appear to use two different versions of the Poisson sum formula; one of these explicitly shows the end-point discontinuity effects due to array truncation, whereas the other contains such effects only implicitly. It is shown, via the sifting property of the Dirac delta function, that first of all, these two versions of the Poisson sum formula are equivalent. Second, the version containing implicit end point contributions has often been applied in an incomplete fashion in the literature to solve finite-array problems; it is also demonstrated that the latter can lead to some errors in finite-array field computations.

Circumferential Traveling Wave Slot Array on Cylindrical Substrate Integrated Waveguide (CSIW)

Traveling wave slot array on cylindrical substrate integrated waveguide (CSIW) is designed, fabricated and measured at K-band. CSIW is formed by wrapping the substrate integrated waveguide (SIW) around the cylinder in the circumferential direction. 16 element longitudinal slot array on the broad wall of single CSIW is designed by the Elliots design procedure. The spacings between the slot elements are determined to reduce the half power beam width (HPBW) and to obtain good matching at 25 GHz. A 4 × 16 slot array is formed using 4 CSIW array each having 16 traveling wave longitudinal slots and the array is fed by 1 × 4 SIW power divider structure. About 10 ° beam steering is achieved when frequency is swept from 24 to 26 GHz. Gain of the antenna is 14 dB. Very good agreement between the simulated and measured results is obtained.

A monolithic phased array using 3-bit DMTL RF MEMS phase shifters

This paper presents a phased array system designed at 15 GHz employing 3-bit distributed MEMS transmission line (DMTL) type phase shifters which are monolithically integrated with the feed network of the system and the radiating elements on the same substrate. The phase shifter can give 0deg-360deg phase shift with 45deg steps at 15 GHz which is used to obtain various combinations of progressive phase shift in the excitation of radiating elements. The phased array is composed of four linearly placed microstrip patch antennas. In order to monolithically integrate the patch antennas and phase shifters, tapered lines with low return loss from microstrip to coplanar waveguide (CPW) have been designed. The design of the phased array system and its components is given. Since the DC biasing schema of a MEMS system is also an important issue in terms of the RF losses, the paper also addresses the effect of the bias lines on the loss characteristics of the phase shifters. Moreover, the process steps, which are used in the fabrication of the phased array, are also summarized

Array guided surface waves on a finite planar array of dipoles with or without a grounded substrate

The existence of array guided surface waves (AGSWs) on partially finite (finite times infinite) array of dipoles in air have been demonstrated earlier; the work in this paper extends this study to fully finite (finite times finite) planar arrays both in air and on a grounded material slab of infinite extent. Effects of AGSWs on scattering characteristics are examined and a ray interpretation is provided for the edge/corner excitation of AGSWs and conventional substrate surface waves

Reconfigurable Nested Ring-Split Ring Transmitarray Unit Cell Employing the Element Rotation Method by Microfluidics

A continuously tunable, circularly polarized X-band microfluidic transmitarray unit cell employing the element rotation method is designed and fabricated. The unit cell comprises a double layer nested ring-split ring structure realized as microfluidic channels embedded in Polydimethylsiloxane (PDMS) using soft lithography techniques. Conductive regions of the rings are formed by injecting a liquid metal (an alloy of Ga, In, and Sn), whereas the split region is air. Movement of the liquid metal together with the split around the ring provides 360 ° linear phase shift range in the transmitted field through the unit cell. A circularly polarized unit cell is designed to operate at 8.8 GHz, satisfying the necessary phase shifting conditions provided by the element rotation method. Unit cell prototypes are fabricated and the proposed concept is verified by the measurements using waveguide simulator method, within the frequency range of 8-10 GHz. The agreement between the simulation and measurement results is satisfactory, illustrating the viability of the approach to be used in reconfigurable antennas and antenna arrays.

A Reconfigurable RF MEMS Triple Stub Impedance Matching Network

This paper presents a reconfigurable triple stub impedance matching network using RF MEMS technology centered at 10GHz. The device is capable of covering impedances on the whole Smith Chart. The device structure consists of three variable length stubs which are designed as distributed MEMS transmission lines and two lambdag/8 length CPW transmission lines connecting the stubs. The variable length stubs are implemented with 12 MEMS switches over CPW lines and CPW lines connecting the switches. lambdag/8 spacing between the stubs is selected to obtain a uniform distribution of the impedance points on the Smith Chart. Initial measurement results of the fabricated structure show a good agreement with the simulation results

Dual-frequency reconfigurable slot dipole array with a CPW-based feed network using RF MEMS technology for X- and ka-band applications

In recent years there is a growing interest to combine various wireless applications in a single system for miniaturization purposes. A reconfigurable MEMS antenna that can operate in multi- frequencies is an appropriate way of reducing system volume. The monolithic integration of tunable MEMS components with antennas can also reduce parasitic effects, the losses, and packaging costs. Moreover an array of these types of antennas can offer solutions for the systems requiring high antenna gains. This paper presents a 4-element linear array of dual-frequency slot dipole antennas whose resonant frequencies are controlled via MEMS switches placed on the slots. The corporate feed network of the array is realized with coplanar wave transmission (CPW) lines. A CPW-based feed network has advantages over a microstrip feeding network, such as low radiation losses, less dispersion, easier in combining active devices for active array implementation, and the possibility of connecting shunt lumped without the need of via holes through the substrate. The CPW-based feed network in this paper includes properly designed T-junctions, chamfered corners, and dual-frequency impedance transformers in order to match the input impedance at the resonant frequency of the antennas. The proposed array structure, reconfigurable slot dipole antenna, and the details about the dual-frequency impedance transformer are presented in the following sections.