Abbas Abbaspour-Tamijani

Miniature and tunable filters using MEMS capacitors

Microelectromechanical system (MEMS) bridge capacitors have been used to design miniature and tunable bandpass filters at 18-22 GHz. Using coplanar waveguide transmission lines on a quartz substrate (/spl epsiv//sub r/ = 3.8, tan/spl delta/ = 0.0002), a miniature three-pole filter was developed with 8.6% bandwidth based on high-Q MEMS bridge capacitors. The miniature filter is approximately 3.5 times smaller than the standard filter with a midband insertion loss of 2.9 dB at 21.1 GHz. The MEMS bridges in this design can also be used as varactors to tune the passband. Such a tunable filter was made on a glass substrate (/spl epsiv//sub r/ = 4.6, tan/spl delta/ = 0.006). Over a tuning range of 14% from 18.6 to 21.4 GHz, the miniature tunable filter has a fractional bandwidth of 7.5 /spl plusmn/ 0.2% and a midband insertion loss of 3.85-4.15 dB. The IIP/sub 3/ of the miniature-tunable filter is measured at 32 dBm for the difference frequency of 50 kHz. The IIP/sub 3/ increases to >50 dBm for difference frequencies greater than 150 kHz. Simple mechanical simulation with a maximum dc and ac (ramp) tuning voltages of 50 V indicates that the filter can tune at a conservative rate of 150-300 MHz//spl mu/s.

Antenna-filter-antenna arrays as a class of bandpass frequency-selective surfaces

A method is introduced for designing bandpass frequency-selective surfaces (FSSs) using arrays of antenna-filter-antenna (AFA) modules. An AFA module is a filter with radiation ports, which is obtained by integrating two antennas and a nonradiating resonant structure in between. AFA modules are designed based on circuit models and microwave filter design techniques. Three types of these AFA modules are designed using microstrip antennas and coplanar-waveguide resonators, and are used to form FSSs with three- and four-pole shaped bandpass response at 35 GHz. FSS structures are formed by arraying these modules in a periodic grid with an optimal cell size. The proposed concept and the design method are validated using numerical simulation (finite-element method), as well as experimental results.

A Programmable Lens-Array Antenna With Monolithically Integrated MEMS Switches

This paper describes a reconfigurable millimeter-wave lens-array antenna based on monolithically integrated microelectromechanical systems (MEMS) switches. This device is constructed as a planar array of 2-bit programmable MEMS antenna-filter-antenna (AFA) unit cells that are used to provide a 1-D programmable ldquoaperture transfer functionrdquo between the input and output wavefronts. The fully integrated device consists of 484 (22 times 22) AFA elements and 2420 switches. Switches, bias lines, antennas, and the rest of the RF structure are fabricated on two quartz wafers (epsivr = 3.8, tandelta = 0.002) that are subsequently stacked using adhesive bonding to form the tri-layer metal structure of the AFA array. The bonded structure also forms a package for the MEMS switches. This paper investigates the design and fabrication issues and presents the measured data related to yield and frequency response of this lens-array. It also characterizes the performance of this device as a steerable antenna. Measured results show that this lens-array can be used to steer the beam of a low gain horn antenna to plusmn40deg in either the E- or the H-plane. For the fabricated prototype, the yield is estimated to be 50% for the best region of the array, resulting in a relatively high insertion loss and sidelobe level.

An affordable millimeter-wave beam-steerable antenna using interleaved planar subarrays

Design and fabrication aspects of an affordable planar beam steerable antenna array with a simple architecture are considered in this paper. Grouping the elements of a phased array into a number of partially overlapped subarrays and using a single phase shifter for each subarray, generally results in a considerable reduction in array size and manufacturing costs. However, overlapped subarrays require complicated corporate feed networks and array architectures that cannot be easily implemented using planar technologies. In this paper a novel feed network and array architecture for implementing a planar phased array of microstrip antennas is presented that enables the fabrication of low-sidelobe, compact, beam-steerable millimeter-wave arrays and facilitates integration of the RF front-end electronics with the antenna structure. This design uses a combination of series and parallel feeding schemes to achieve the desired array coefficients. The proposed approach is used to design a three-state switched-beam phased array with a scanning width of /spl plusmn/10/spl deg/. This phased array which is composed of 80 microstrip elements, achieves a gain of >20 dB, a sidelobe level of 6.3% for all states of the beam. The antenna efficiency is measured at 33-36% in X band. It is shown that the proposed feeding scheme is insensitive to the mutual coupling among the elements.

Integration of filters and microstrip antennas

A new implementation of the integrated antenna-filter module has been proposed that is based on the single material technology and uses the same substrate for both the antenna and filter layers. An X band device has been designed on the low permittivity substrate and examined for X band operation. This example proves the feasibility of achieving a well-defined filtering response and proper radiation performance through simple and compact integrated modules.

Study of 2-bit Antenna–Filter–Antenna Elements for Reconfigurable Millimeter-Wave Lens Arrays

This paper presents a new reconfigurable antenna-filter-antenna (AFA) element based on slot antennas and switchable resonators. This reconfigurable AFA can operate in four modes of operation as a three- or four-pole filter, and yields a 2-bit variable phase delay. As a result, the multimode AFA can be used as the building block of 2-bit adaptive lens arrays. This paper details design, modeling, and miniaturization of the reconfigurable AFA, and demonstrates its performance through preconfigured prototypes. The proposed AFA has a loss of 1.4-1.6 dB measured at 32 GHz in both three- and four-pole filter modes, and exhibits a frequency response that is almost insensitive to the angle of incidence. Several proof-of-concept fixed lens arrays have been also fabricated for output beams scanned to 0deg, 15deg, 30deg, 45deg, and 60deg in the E- and H-plane. The measurement results show that the output beam can be scanned to plusmn60deg in both principle planes, with a worst case sidelobe level of less than -11 dB and a scan loss that hardly exceeds the theoretical limit

A Fully Passive Wireless Microsystem for Recording of Neuropotentials Using RF Backscattering Methods

The ability to safely monitor neuropotentials is essential in establishing methods to study the brain. Current research focuses on the wireless telemetry aspect of implantable sensors in order to make these devices ubiquitous and safe. Chronic implants necessitate superior reliability and durability of the integrated electronics. The power consumption of implanted electronics must also be limited to within several milliwatts to microwatts to minimize heat trauma in the human body. In order to address these severe requirements, we developed an entirely passive and wireless microsystem for recording neuropotentials. An external interrogator supplies a fundamental microwave carrier to the microsystem. The microsystem comprises varactors that perform nonlinear mixing of neuropotential and fundamental carrier signals. The varactors generate third-order mixing products that are wirelessly backscattered to the external interrogator where the original neuropotential signals are recovered. Performance of the neurorecording microsystem was demonstrated by wireless recording of emulated and in vivo neuropotentials. The obtained results were wireless recovery of neuropotentials as low as approximately 500 microvolts peak-to-peak (μVpp) with a bandwidth of 10 Hz to 3 kHz (for emulated signals) and with 128 epoch signal averaging of repetitive signals (for in vivo signals).

A high performance MEMS miniature tunable bandpass filter

A miniature tunable 3-pole filter is fabricated using coplanar waveguide (CPW) transmission-tines on glass substrate (C/sub r/ = 4.6, tan /spl delta/ = 0.006) and an array of RF-MEMS varactors. The filter is tuned using a bias voltage of 0-80 Volts. The filter is /spl sim/3.6 mm long and gives a near ideal frequency response. A tuning range of 14% from 18.6 to 21.4 GHz was achieved, with a constant fractional bandwidth of 7.4 /spl plusmn/ 0.1% and a mid-band insertion loss of 3.85-4.15 dB.

Tunable Filters With Nonuniform Microstrip Coupled Lines

A basic wideband tunable filter design based on combline topology is presented. At the presence of the parasitic effects, the structure of the filter must be modified by introducing additional degrees of freedom to the geometry of the coupled line segment. A design procedure involving iterative steps will be described. This procedure is used to design two bandpass filters with more than one octave tuning range in the UHF band. The experimental results are presented for the filter prototypes implemented using printed circuit boards and PIN diodes.

A planar filter-lens array for millimeter-wave applications

The novel concept of filter-lens array (FLA) is introduced in this paper. Measured results for a Ka-band design show that a typical FLA can meet system requirements for a wide range of applications. FLAs present a compact and simple means of focusing and filtering at millimeter-wave frequencies, and can replace the standard combinations of dielectric lenses and bandpass filters. They are expected to find application in power combining, medium-angle beam-steering, and millimeter-wave (mm-wave) imaging systems.