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This paper presents a low-loss 4-6-GHz 3-bit tunable filter on a quartz substrate using a high-Q 3-bit orthogonal bias RF microelectromechanical systems capacitance network. Detailed design equations for the capacitively loaded coupled [lambda]/2 resonators and with capacitive external coupling and source-load impedance loading are discussed. Measurements show an unloaded Q of 85-170, an insertion loss of 1.5-2.8 dB, and a 1-dB bandwidth of 4.35 [+ or -] 0.35% at 4-6 GHz. The measured third-order intermodulation intercept point and 1-dB power compression point at 5.91 GHz are >40 and 27.5 dBm, respectively. The unloaded Q can be improved to 125-210 with the use of a thicker bottom electrode. To our knowledge, this is the highest Q tunable planar filter to date at this frequency range. Index Terms--Capacitance network, capacitive loading, coupled open-loop resonators, RF microelectromechanical systems (RF-MEMS), source--load impedance loading, tunable filter.

A four-element phased-array front-end receiver based on 4-bit RF phase shifters is demonstrated in a standard 0.18-[micro]m SiGe BiCMOS technology for Q-band (30-50 GHz) satellite communications and radar applications. The phased-array receiver uses a corporate-feed approach with on-chip Wilkinson power combiners, and shows a power gain of 10.4 dB with an [IIP.sub.3] of -13.8 dBm per element at 38.5 GHz and a 3-dB gain bandwidth of 32.8-44 GHz. The rms gain and phase errors are [less than or equal to] 1.2 dB and [less than or equal to] 8.7[degrees] for all 4-bit phase states at 30-50 GHz. The beamformer also results in [less than or equal to] 0.4 dB of rms gain mismatch and [less than or equal to] 2[degrees] of rms phase mismatch between the four channels. The channel-to-channel isolation is better than -35 dB at 30-50 GHz. The chip consumes 118 mA from a 5-V supply voltage and overall chip size is 1.4 x 1.7 [mm.sup.2] including all pads and CMOS control electronics. Index Terms--BiCMOS analog integrated circuit, millimeter wave, multiple input/multiple output (MIMO), phased array, phase shifter, radar, SiGe BiCMOS, smart antenna, Wilkinson coupler, wireless communication.

A design method is presented for contiguous-channel multiplexing filters with many channels covering a wide band-width. The circuit topology extends previous work on cochlea-like channelizers by introducing multiple resonator-channel filter sections. The new design provides increased stopband rejection, lower insertion loss, and improved passband shape compared with the earlier version while retaining a simple design method and a compact layout, and requires no post-fabrication tuning. Results of a three-pole ten-channel channelizer covering from 182 MHz to 1.13 GHz with 17.5% bandwidth channels and 1.1-dB insertion loss are presented, and agree well with theory. A discussion of the power handling of planar channelizers is also presented. Index Terms--Channelizer, cochlea, filter, manifold, multiplexer.

This paper presents a 1 : 8 differential power divider implemented in a commercial SiGe BiCMOS process using fully shielded broadside-coupled striplines integrated vertically in the silicon interconnect stackup. The 1:8 power divider is only 1.12 X 1.5 mm2 including pads, and shows 0.4-dB rms gain imbalance and < 3[degrees] rms phase imbalance from 40 to 50 GHz over all eight channels, a measured power gain of 14.9 [+ or -] 0.6 dB versus a passive divider at 45 GHz, and a 3-dB bandwidth from 37 to 52 GHz. A detailed characterization of the shielded broadside-coupled striplines is presented and agrees well with simulations. These compact lines can be used for a variety of applications in SiGe/CMOS millimeter-wave circuits, including differential signal distribution, miniature power dividers, matching networks, filters, couplers, and baluns. Index Terms--BiCMOS, differential power divider, RF integrated circuit (RFIC), shielded broadside-coupled striplines, SiGe.

This paper presents designs and measurements of Ka-band single-pole single-throw (SPST) and single-pole double-throw (SPDT) 0.13-[micro]m CMOS switches. Designs based on series and shunt switches on low and high substrate resistance networks are presented. It is found that the shunt switch and the series switch with a high substrate resistance network have a lower insertion loss than a standard designs. The shunt SPST switch shows an insertion loss of 1.0 dB and an isolation of 26 dB at 35 GHz. The series SPDT switch with a high substrate resistance network shows excellent performance with 2.2-dB insertion loss and > 32-dB isolation at 35 GHz, and this is achieved using two parallel resonant networks. The series-shunt SPDT switch using deep n-well nMOS transistors for a high substrate resistance network results in an insertion loss and isolation of 2.6 and 27 dB, respectively, at 35 GHz. For series switches, the input 1-dB compression point ([IP.sub.1] dB) can be significantly increased to ~ 23 dBm with the use of a high substrate resistance design. In contrast, [IP.sub.1 dB] of shunt switches is limited by the self-biasing effect to 12 dBm independent of the substrate resistance network. The paper shows that, with good design, several 0.13-/[micro]m CMOS designs can be used for state-of-the-art switches at 26-40 GHz. Index Terms--CMOS switch, Ka-band, millimeter wave, RF switch, single-pole double-throw (SPDT) switch, single-pole single-throw (SPST) switch, substrate networks, 0.13-[micro]m CMOS.

This paper presents a radical departure from the standard RF microelectromechanical systems (MEMS) devices and introduces novel miniature MEMS switched capacitors for RF to millimeter-wave applications, which are around 150 times smaller in lateral dimensions than standard MEMS designs. The measured capacitance of a single device (l, w, t of 20, 9.5, 0.37 [micro]m), suspended 0.25 [micro]m above the pull-down electrode, is 3.9 and 11.7-12.1 fF ([C.sub.r] : 3.0-3.1) in the up- and down-state positions, respectively. The measured capacitance ratio of a 4 x 4 array fabricated on quartz substrates and in a coplanar waveguide (CPW) configuration is 3.0 with an electrical Q > 90 at 20 GHz. The miniature MEMS spring constant is very high, and is much less sensitive to residual stress or temperature variations than standard MEMS devices. Dielectric charging simulations show that these devices can withstand a charge density 6.25 times higher than the standard MEMS devices. The mechanical resonant frequency for a gold device is 2.6 MHz and results in a switching time of 200 ns under a 32-V actuation voltage. Preliminary reliability tests at 13 GHz using bipolar actuation ([+ or -]30 V) and hot power switching have been performed on five 4 x 4 devices at 100 mW for 20 billion cycles, and at 500 mW for 5 billion cycles with no failures. A 4 x 4 array has also been used in the design of a tunable CPW resonator at 19.3 GHz with a 21% tuning range and 1.6-dB insertion loss. The authors believe that miniature MEMS devices will be very useful in the future for high-reliability MEMS and reconfigurable networks. Index Terms--Microelectromechanical systems (MEMS), RF MEMS, reliability, tunable resonator.

This paper presents a state-of-the-art discrete RF microelectromechanical systems (MEMS) tunable filter designed for 25-75-MHz operation. This paper also presents an enhanced model of the RF MEMS switch, which is used for accurate prediction of the tunable filter response. The two-pole lumped-element filter is based oil digital capacitor banks with on-chip metal-contact RF MEMS switches and lumped inductors, and results in a tuning range of 3 : 1 with fine frequency resolution, and a return loss better than 13 dB for the entire tuning range. The relative bandwidth of the filter is 4 [+ or -] 1% over the tuning range and the insertion loss is 3-5 dB, limited mostly by the inductor Q and the switch loss. The II[P.sub.3] measurements prove that tunable filters with metal-contact series RF MEMS switches show extremely linear behavior (II[P.sub.3] > 68 dBm). Index Terms--Microelectromechanical systems (MEMS), RF MEMS, tunable filters.

Low-loss 3.6-GHz fixed and 5.15-5.70-GHz RF microelectromechanical systems switchable filters were designed and fabricated on quartz substrates. Detailed design equations for the capacitively loaded coupled open-loop [lambda]/2 resonators are given and the realization of the tunable filter using these equations is discussed. The use of capacitively loaded coupled open-loop [lamda]/2 resonators made it possible to realize the fixed and switchable filters with unloaded Q of around 150 resulting in a -1.4-dB insertion loss. The measured -1-dB bandwidth for the 3.6-GHz fixed and 5.15-5.70-GHz switchable filters were 4% and 5%, respectively. To our knowledge, this represents the lowest loss planar tunable filter to-date in the 4-6-GHz frequency range. Index Terms--Capacitive loading, coupled open-loop resonators, RF microelectromechanical systems (MEMS), switchable filter, tunable filter.

This paper presents a state-of-the-art RF microelectromechanical systems (MEMS) wide-band tunable filter designed for the 12-18-GHz frequency range. The coplanar-waveguide filter, fabricated on a glass substrate using loaded resonators with RFMEMS capacitive switches, results in a tuning range of 40% with very fine resolution, and return loss better than 10 dB for the whole tuning range. The relative bandwidth of the filter is 5.7 [+ or -] 0.4% over the tuning range and the size of the filter is 8 mm x 4 mm. The insertion loss is 5.5 and 8.2 dB at 17.8 and 12.2 GHz, respectively, for a 2-k[ohms]/sq bias line. The loss improves to 4.5 and 6.8 dB at 17.8 and 12.2 GHz, respectively, if the bias line resistance is increased to 20 k[ohms]/sq. The measured [IIP.sub.3] level is >37 dBm for [delta]f > 200 kHz. To our knowledge, this is the widest band planar tunable filter to date. Index Terms--Coplanar-waveguide (CPW) filter, loaded resonators, microelectromechanical systems (MEMS), RF MEMS, wide-band tunable filter.

This paper presents the design and analysis of an SiGe high isolation single-pole double-throw (SPDT) differential absorptive switch at 24 GHz for pulsed ultra-wideband applications. Sub-100-ps envelope rise times are achieved through the use of differential current steering. The SPDT results in 1.9 dB of gain in the passband and an isolation of 35 dB while remaining matched at its ports (absorptive). The measured rise time of the RF envelope is 70 ps using a transistor with an [f.sub.T] of 80 GHz and agrees with both the simulated and analytically determined values. Index Terms--Current mode logic (CML), emitter coupled logic (ECL), RF switches, rise time, silicon-germanium (SiGe), switching speed, ultra-wideband (UWB).

This paper presents a state-of-the-art RF microelectromechanical systems wide-band miniature tunable filter designed for 6.5-10-GHz frequency range. The differential filter, fabricated on a glass substrate using digital capacitor banks and microstrip lines, results in a tuning range of 44% with very fine resolution, and return loss better than 16 dB for the whole tuning range. The relative bandwidth of the filter is 5.1 [+ or -] 0.4% over the tuning range and the size of the filter is 5 mm x 4 mm. The insertion loss is 4.1 and 5.6 dB at 9.8 and 6.5 GHz, respectively, for a 1-k[OMEGA]/sq fabricated bias line. The simulations show that, for a bias line with 10- k[OMEGA]/sq resistance or more, the insertion loss improves to 3 dB at 9.8 GHz and 4 dB at 6.5 GHz. The measured II[P.sub.3] level is > 45 dBm for [DELTA]f > 500 kHz, and the filter can handle 250 mW of RF power for hot and cold switching. Index Terms--Differential filter, digital capacitor bank, microelectromechanical systems (MEMS), RF MEMS, wide-band tunable filter.

This paper presents the design and measurement of a 12-GHz active phase shifter with an integrated low-noise amplifier in SiGe. The phase is controlled with a 1-bit (180[degrees]) digital phase shifter and a 180[degrees] continuous analog phase shifter. The 1-bit digital phase shifter is implemented by switching between a -90[degrees] low-pass network and a +90[degrees] high-pass network. The analog phase shifter is implemented using a lumped-element loaded line technique where both series and shunt elements are adjusted to continuously vary the phase while maintaining a constant port impedance. Design equations for this constant-impedance phase-shift network are derived and presented. The phase shifter achieves 3.7 [+ or -] 0.5 dB of gain, with a noise figure of 4.4 dB at a center frequency of 11.5 GHz. The total chip size including pads is 1920 [micro]m x 780 [micro]m, and the area of the active circuitry without pads is 1680 [micro]m x 660 [micro]m (1.1 [mm.sup.2]). Index Terms--All-pass networks, direct broadcast satellite (DBS), phased arrays, phase shifters, RF integrated circuit (RFIC), satellite communications, silicon germanium.

High-efficiency monolithic SiGe balanced frequency doublers have been developed for Ku- and Ka-band applications. A novel miniature second harmonic reflector is presented, and the impact of the parasitic inductor from emitter to ground is also explored to optimize the conversion efficiency of the doubler. The Ku-band design presents an output power of 5-6 dBm from 15.4-18 GHz for an input power of 1.5 dBm. DC power consumption is 28 mW and the corresponding power-added efficiency (PAE) is 9.2%. The Ka-band design demonstrates an output power of 10.5 dBm at 36 GHz for an input power of 6 dBm while consuming 114 mW of dc power, which results in a PAE of 6.4%. It also shows high spectral purity operation with the fundamental suppression of 35 dB. To our knowledge, these are the best results for active doublers using any technology. Index Terms--Balanced frequency doubler, high efficiency, high power, high spectral purity, monolithic microwave integrated circuit (MMIC), SiGe.

A switchable frequency-selective surface (FSS) was developed at 30 GHz using RF microelectromechanical systems (MEMS) switches on a 500-[micro]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 [degrees]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 [kappa][alpha]-band frequencies. Index Terms--Frequency selective surface (FSS), microelectromechanical devices, quasi-optical, RF microelectromechanical systems (MEMS), tunable filters.

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. Index Terms--Antenna-filter-antenna (AFA), bandpass filter, frequency-selective surface (FSS), high-order FSS.

This paper presents state-of-the-art RF microelectromechanical (MEMS) phase shifters at 75-110 GHz based on the distributed microelectromechanical transmission-line (DMTL) concept. A 3-bit DMTL phase shifter, fabricated on a glass substrate using MEMS switches and coplanar-waveguide lines, results in an average loss of 2.7 dB at 78 GHz (0.9 dB/bit). The measured figure-of-merit performance is 93[degrees]/dB-100[degrees]/dB (equivalent to 0.9 dB/bit) of loss at 75-110 GHz. The associated phase error is [+ or -] 3[degrees] (rms phase error is 1.56[degrees]) and the reflection loss is below -10 dB over all eight states. A 2-bit phase shifter is also demonstrated with comparable performance to the 3-bit design. It is seen that the phase shifter can be accurately modeled using a combination of full-wave electromagnetic and microwave circuit analysis, thereby making the design quite easy up to 110 GHz. These results represent the best phase-shifter performance to date using any technology at W-band frequencies. Careful analysis indicates that the 75-110-GHz figure-of-merit performance becomes 150[degrees]/dB-200[degrees]/dB, and the 3-bit average insertion loss improves to 1.8-2.1 dB if the phase shifter is fabricated on quartz substrates. Index Terms--Automotive radar, microelectromechanical systems (MEMS), millimeter wave, phase shifter, RF MEMS, switches, true-time delay, W-band.

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 ([[epsilon].sub.r] = 3.8, tan[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 ([[epsilon].sub.r] = 4.6, tan[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 [+ or -] 0.2% and a midband insertion loss of 3.85-4.15 dB. The II[P.sub.3] of the miniature-tunable filter is measured at 32 dBm for the difference frequency of 50 kHz. The II[P.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/[micro]s. Index Terms--Filters, microelectromechanical system (MEMS), MEMS varactors, MEMS devices, miniature filters, tunable filters.

This paper presents W-band coplanar waveguide RF microelectromechanical system (MEMS) capacitive shunt switches with very low insertion loss (-0.2 to -0.5 dB) and high-isolation ([less than or equal to] -30 dB) over the entire W-band frequency range. It is shown that full-wave electromagnetic modeling using Sonnet can predict the performance of RF MEMS switches up to 120 GHz. Also presented are W-band 0[degree]/90[degrees] and 0[degree]/180[degree] switched-line phase shifters with very good insertion loss (1.75 dB/bit at 90 GHz) and a wide bandwidth of operation (75-100 GHz). These circuits are the first demonstration of RF MEMS digital-type phase shifters at W-band frequencies and they outperform their solid-state counterparts by a large margin. Index Terms--Microelectromechanical system (MEMS), microwave, millimeter wave, phase shifters, switches.

This paper presents a theoretical and experimental study of the nonlinear effects generated RF-microelectromechanical system (MEMS) varactors and capacitive switches. The theoretical part includes an analytic derivation, as well as an electromechanical model suitable for computer-aided design (CAD) simulation. The simulations agree very well with measurements performed on a 24-GHz three-pole MEMS tunable filter. It is shown that MEMS capacitive components with a spring constant k > 10 N/m generate very low intermodulation, as compared to semiconductor devices, and lead to a two-tone third-order intermodulation intercept point (IIP3) greater than +40 dBm for [DELTA] 3-5 [f.sub.o], where [f.sub.o] is the mechanical resonant frequency. In fact, the IIP3 increases to +80 dBm for a difference signal ([DELTA] f) of 5 MHz. The CAD model also allows the evaluation of the power-handling capabilities of the tunable filter and, it is seen that, for the case presented here, distortions become significant for an input power greater than +20 dBm. Noise generation due to thermal effects on a movable membrane (Brownian noise) is also modeled and it is shown that the tunable filter results in a very low phase-noise level close to the carrier. Index Terms--Filters, intermodulation (IM), microelectromechanical system (MEMS), microwave, millimeter wave, phase noise, power handling, switches, varactors.

2-bit wide-band distributed coplanar-waveguide phase shifters have been developed on a 500-[micro]m quartz substrate for X- and Ka-band operation. The designs utilize microelectromechanical system (MEMS) switches in a distributed MEMS transmission line) periodically loaded by MEMS switches and high Q ([greater than or equal to]250 at 30 GHz) metal-air-metal capacitors. The MEMS switches are actuated by a [+ or -] 20-V voltage waveform using a high-resistance bias line. Estimated spring constant and switching time is 30 N/m and 9 [micro]s, respectively. The Ka-band 2-bit design results in a reflection coefficient better than -11.5 dB, an average insertion loss of -1.5 dB and phase shifts of 0[degrees], 89[degrees], 180[degrees], and 270[degrees] at 37.7 GHz. The X -band 2-bit design results in a reflection coefficient better than -12.5 dB, an average insertion loss of -1.2 dB and phase shifts of 0[degrees], 94[degrees], 176[degrees], and 270[degrees] at 13.6 GHz. These results are very competitive with switched transmission-line and reflection-based phase shifters. The distributed design can be easily scaled to V- and W-band frequencies for wide-band low-loss performance. Index Terms--Microelectromechanical system (MEMS), microwave, phase shifter, switches, true-time delay.

2- and 4-bit microelectromechanical system (MEMS) X- to [K.sub.u]-band true-time-delay phase shifters with a very low insertion loss are described. The phase shifters are fabricated on 200-[micro]m GaAs substrates and the low loss is achieved using MEMS SP4T switches, which reduce the number of switches in the signal path by half when compared to conventional designs with SP2T switches. Measurements indicate an insertion loss of -0.6 [+ or -] 0.3 and -1.24 [+ or -] 0.5 dB at 10 GHz for the 2- and 4-bit designs, respectively. The measured losses agreed very well with Momentum simulations and are the lowest reported to date. The 2-bit phase shifter performed well from dc-18 GHz, with -0.84 [+ or -] 0.3-dB insertion loss at 18 GHz and a return loss of < -10.5 dB over dc-18 GHz. Index Terms--Microelectromechanicai system (MEMS) devices, phase shifters, radar antennas, radar receivers.

A new approach to wide scan-angle antennas at millimeter-wave frequencies is introduced with special focus on ease of manufacturing and reliability. The system is composed of planar feed antennas (tapered-slot antennas), which are positioned around a homogeneous spherical Teflon lens. Beam scanning can be achieved by switching between the antenna elements. The spherical-lens system is analyzed through a combined ray-optics/diffraction method. It is found that a maximum efficiency of 50%-55% can be achieved using Teflon, Rexolite, or quartz lenses. The efficiency includes taper, spillover, and reflection loss. Calculations also indicate that the maximum lens diameter is 30-40 [[lambda].sub.0], which results in a maximum directivity of 39.5-42 dB. Measurements done on a single-element feed and a 5-cm Teflon lens agree very well with theory and result in a 3-dB beamwidth of 5.5[degrees] and better than -20-dB sidelobe levels at 77 GHz. Absolute gain measurements show a system efficiency of 46%-48% (including dielectric loss). A 23- and 33-element antenna array with a scan angle of [+ or -]90[degrees] and a -3.5- and -6-dB crossover, respectively, in the far-field patterns was also demonstrated. The 23-element array resulted in virtually no gain loss over the entire 90[degrees] scan angle. This represents, to our knowledge, the first wide scan-angle antenna at millimeter-wave frequencies. Index Terms--Automotive radars, imaging systems, millimeter waves, planar antennas, spherical lens, tapered slot antenna, wide scan angle.