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.     

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.     

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 <-19 dB and a 10-dB bandwidth 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.     

Switchable low-loss RF MEMS Ka-band frequency-selective surface

A switchable frequency-selective surface (FSS) was developed at 30 GHz using RF microelectromechanical systems (MEMS) switches on a 500-/spl mu/m-thick glass substrate. The 3-in-diameter FSS is composed of 909 unit cells and 3636 MEMS bridges with a yield of 99.5%. The single-pole FSS shows a transmission loss of 2.0 dB and a -3-dB bandwidth of 3.2 GHz at a resonant frequency of 30.2 GHz with the MEMS bridges in the up-state position. The -1-dB bandwidth is 1.6 GHz. When the MEMS bridges are actuated to the down-state position, an insertion loss of 27.5 dB is measured. Theory and experiment agree quite well. The power handling is limited to approximately 25 W with passive air cooling and >150 W with active air cooling due to the increased temperature of the overall circuit resulting from the transmission loss (for continuous-wave operation with the assumed maximum allowable temperature of 80/spl deg/C), or 370 W-3.5 kW due to self-actuation of the RF MEMS bridges (for pulsed incident power). Experimental results validate that 20 W of continuous-wave power can be transferred by the RF MEMS FSS with no change in the frequency response. This is the first demonstration of a switched low-loss FSS at Ka-band frequencies.     

Closed-Form Formulas for Predicting the Nonlinear Behavior of All-Pole Bandpass Filters

The nonlinear behavior of the all-pole passive bandpass filters close to their center frequency is studied using first-order approximations. The focus of this study is on approximate calculation of third-order intermodulations through an iterative process, and it is shown that it can be generalized to higher order effects. Nonlinearities in both resonators and inverters are considered. Simple formulas are given to calculate the effect of individual elements in the overall response in lossless and lossy filters. It is shown that the presence of loss will increase the third-order intermodulation intercept point of the filter, while it usually decreases the output third-order intercept point. In comparison to the nonlinear resonators, the relative effect of nonlinear inverters is larger; however, the losses of the inverters are found to have a smaller effect on the nonlinear response. Finally, simple formulas are given to predict the changes in the center frequency due to the reactive effects of the nonlinearities. In all cases, the analytical results are verified through comparison with harmonic balance simulations.