Rayleigh-wave delay line using two grating-array transducers at 2.55 GHz

Grating-array transducers are used to launch acoustic surface waves at 2.55 GHz on a LiNbO3 substrate. The insertion loss of a 1.5 ?s delay line is equal to 39 dB with matching stubs at input and output. The 3 dB bandwidth is equal to 87 MHz. For this frequency range, array transducers are easier to fabricate than standard interdigital transducers. Performances of the two types of transducers are compared.     

Evaluation of LiNbO/sub 3/ intensity modulator using electrodes buried in buffer layer

For highly efficient operation, a new type LiNbO/sub 3/ Mach-Zehnder intensity modulator using electrodes buried in the buffer layer was designed and fabricated. The modulator was designed considering velocity matching between light and microwave, microwave propagation loss and characteristic impedance Z/sub 0/ of 50 Omega . This modulator for a 1.5 mu m wavelength operates with a V/sub pi / of 3.2 V, a 3 dB down bandwidth of 14 GHz and a temperature dependence of 17 mV/ degrees C.<>     

Distributed 2- and 3-bit W-band MEMS phase shifters on glass substrates

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/spl deg//dB-100/spl deg//dB (equivalent to 0.9 dB/bit) of loss at 75-110 GHz. The associated phase error is /spl plusmn/3/spl deg/ (rms phase error is 1.56/spl deg/) 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/spl deg//dB-200/spl deg//dB, and the 3-bit average insertion loss improves to 1.8-2.1 dB if the phase shifter is fabricated on quartz substrates.     

2.4 GHz continuously variable ferroelectric phase shifters using all-pass networks

Continuously variable ferroelectric (BST on sapphire) phase shifters based on all-pass networks are presented. An all-pass network phase shifter consists of only lumped LC elements, and thus the total size of the phase shifter is kept to less than 2.2 mm /spl times/ 2.6 mm at 2.4 GHz. The tunability (C/sub max//C/sub min/) of a BST interdigital capacitor is over 2.9 with a bias voltage of 140 V. The phase shifter provides more than 121/spl deg/ phase shift with the maximum insertion loss of 1.8 dB and the worst case return loss of 12.5 dB from 2.4 GHz to 2.5 GHz. By cascading two identical phase shifters, more than 255/spl deg/ phase shift is obtained with the maximum insertion loss of 3.75 dB. The loss figure-of-merit of both the single- and double-section phase shifters is over 65/spl deg//dB from 2.4 GHz to 2.5 GHz.     

A photonic bandgap microstrip filter based on YBCO superconducting film

Photonic bandgap (PBG) structures can stop propagation of electromagnetic waves of certain frequencies and hence can be applied to construction of microstrip filters. In this paper, a novel PBG microstrip filter based on YBa/sub 2/Cu/sub 3/O/sub 7/ high-temperature superconductor films is presented. The PBG patterns forming the filters were etched on a 0.3- and a 0.7-/spl mu/m-thick film. Experimental results showed that the transmission coefficient S/sub 21/ of the filter is dependent on the thickness of the YBa/sub 2/Cu/sub 3/O/sub 7-x/ film. The thinner PBG filter exhibits an effective stopband of a center frequency of 20 GHz, a bandwidth of 4.7 GHz (at -40 dB), an attenuation of -55 dB, and a rolloff rate of 38 dB/GHz, while the thicker structure exhibits narrow notches only in the S/sub 21/ characteristics.     

Microwave noise performance of AlGaN-GaN HEMTs with small DC power dissipation

We report low microwave noise performance of discrete AlGaN-GaN HEMTs at DC power dissipation comparable to that of GaAs-based low-noise FETs. At 1-V source-drain (SD) bias and DC power dissipation of 97 mW/mm, minimum noise figures (NF/sub min/) of 0.75 dB at 10 GHz and 1.5 dB at 20 GHz were achieved, respectively. A device breakdown voltage of 40 V was observed. Both the low microwave noise performance at small DC power level and high breakdown voltage was obtained with a shorter SD spacing of 1.5 /spl mu/m in 0.15-/spl mu/m gate length GaN HEMTs. By comparison, NF/sub min/ with 2 /spl mu/m SD spacing was 0.2 dB greater at 10 GHz.     

Microwave Characterization of Partially Magnetized Ferrites

In order to assist the microwave engineer in predicting the performance of partially magnetized devices, we have characterized the microwave permeability of partially magnetized materials. The real part of the tensor permeability elements, /spl mu/, /spl kappa/, and /spl mu//sub z/, depends primarily on the parameters /spl gamma/4/spl pi/M//spl omega/ and /spl gamma/4/spl pi/M/sub s/ / /spl omega/. Empirical formulas have been developed which show the dependence. At frequencies sufficiently below /spl omega/ = /spl pi/4/spl pi/M/sub s/, the loss can be characterized by the value of /spl mu/' at 4/spl pi/M = 0./spl mu/, /spl kappa/, and /spl mu//sub z/ depend weakly on composition, whereas /spl mu/' (4/spl pi/M = 0) does depend upon the chemical composition.     

Microwave Faraday Effect and Propagation in a Circular Solid-State Plasma Waveguide

The microwave Faraday effect in a solid-state plasma waveguide under a relatively high magnetic field (/spl mu//sub e/B/sub 0/>>1) is investigated. Field configurations in the solid-state plasma waveguide are first analyzed. It is shown that two types of nondegenerate circularly polarized quasi-TE waves exist in the waveguide. The propagation constants of the quasi-TE waves are obtained by means of a variational method. The microwave Faraday effect in the solid-state plasma waveguide is formulated. It is shown that geometrical factors and reflections from the waveguide discontinuities have significant influences on the Faraday effect. Experimental results of the Faraday effect at 36 GHz through a soIid-state plasma waveguide are reported. In the experiment n-type indium antimonide crystals are used. The comparison of the experimental data with the theory shows good agreement.     

SAW Bandpass Filter Design for 1.6-GHz PCM Timing Tank Applications

A 1.6-GHz surface acoustic wave (SAW) timing tank for a self-timed regenerative repeater for an ultrahigh-speed PCM optical fiber transmission system is described. A SAW narrow bandpass filter with 0.74-mu m linewidth interdigital transducers with double electrode geometry and 20-nm aluminum metallization on AT-quartz substrate is realized by conventional optical photolithography. Typical performance obtained is as follows: center frequency f/sub 0/ is 1.5993 GHz; insertion loss is 22 dB; stopband attenuation is above 23 dB with respect to the passbaand; stability is |2Q/sub L//spl dot/Delta f /f/sub 0/| < 0.1, where Q/sub L/ is loaded Q value and Delta f is mistuning due to temperature effects. It is demonstrated that SAW quartz transversal filters can be made into new practical filters which have both high Q value and high stability fn the GHz range and are satisfactory from the standpoints of precise design, fabrication technique, and performance.     

Voltage and frequency dependent dielectric properties of BST-0.5 thin films on alumina substrates

Dielectric properties of Ba/sub 0.5/Sr/sub 0.5/TiO/sub 3/ (BST-0.5) polycrystalline thin films, deposited on alumina substrates by means of reactive pulsed laser deposition (PLD), were measured at GHz frequencies using an interdigital capacitor (IDC). By applying a voltage up to 40 V between the two groups of fingers at room temperature, a high tunability of /spl sim/27% was achieved at 5 GHz. A relative dielectric constant of /spl sim/500 (consistent with the low-frequency IDC measurements) has been obtained using coplanar waveguides by means of the through-reflect-line (TRL) analysis combined with either a conformal mapping model or a full wave calculation. The BST loss tangent was estimated as /spl sim/0.05 in the range 3-16 GHz.     

High temperature dielectric stability of liquid crystal polymer at mm-wave frequencies

The temperature dependent dielectric stability and transmission line losses of liquid crystal polymer (LCP) are determined from 11-105 GHz. Across this frequency range, LCP's temperature coefficient of dielectric constant, /spl tau//sub /spl epsi/r/, has an average value of -42 ppm//spl deg/C. At 11GHz the /spl tau//sub /spl epsi/r/ is the best (-3 ppm//spl deg/C), but this value degrades slightly with increasing frequency. This /spl tau//sub /spl epsi/r/ average value compares well with the better commercially available microwave substrates. In addition, it includes information for mm-wave frequencies whereas standard values for /spl tau//sub /spl epsi/r/ are usually only given at 10 GHz or below. Transmission line losses on 3- and 5-mil LCP substrates increase by approximately 20% at 75/spl deg/C and 50% or more at 125/spl deg/C. These insertion loss increases can be used as a design guide for LCP circuits expected to be exposed to elevated operating temperatures.     

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.     

Polarization dependent loss in a Ti:LiNbO/sub 3/ polarization scrambler/controller

We have investigated the polarization dependent loss (PDL) of a waveguide-type polarization scrambler/controller consisting of a half-wave plate (HWP) and a quarter-wave plate (QWP) in series fabricated in x-cut/z-propagating Ti-diffused LiNbO/sub 3/ optical waveguides. Based on the polarization dependences of both the propagation loss coefficient and mode-mismatch loss with fiber at 1.55 /spl mu/m combined with a numerical analysis, the PDL of the fabricated device is estimated to be 0.063 dB. It is shown that the low PDL is a direct consequence of a special anisotropy relation between the propagation loss and waveguide-fiber mode-mismatch loss.     

A slotted post-wall waveguide array with interdigital structure for 45/spl deg/ linear and dual polarization

This work proposes a dual-polarized planar antenna; two post-wall slotted waveguide arrays with orthogonal 45/spl deg/ linearly-polarized waves interdigitally share the aperture on a single layer substrate. Uniform excitation of the two-dimensional slot array is confirmed by experiment in the 25 GHz band. The isolation between two slot arrays is also investigated in terms of the relative displacement along the radiation waveguide axis in the interdigital structure. The isolation is 33.0 dB when the relative shift of slot position between the two arrays is -0.5/spl lambda//sub g/, while it is only 12.8 dB when there is no shift. The cross-polarization level in the far field is -25.2 dB for a -0.5/spl lambda//sub g/ shift, which is almost equal to that of the isolated single polarization array. It is degraded down to -9.6 dB when there is no shift.     

10-GHz power performance of a type II InP/GaAsSb DHBT

Type-II InP/GaAsSb double heterojunction bipolar transistors (DHBTs) were fabricated and microwave power performance was measured. For an InP collector thickness of 150 nm, the DHBTs show a current gain of 24, low offset voltages, and a BV/sub CEO/>6V. The 1.2/spl times/16 /spl mu/m/sup 2/ devices show f/sub T/=205GHz and f/sub MAX/=106GHz at J/sub C/=304 kA/cm/sup 2/. These devices delivered 12.6 dBm to the load at P/sub AVS/=3.3 dBm operating at 10 GHz, yielding a power-added efficiency of 41% and G/sub T/=9.3 dB.     

Broadband microwave noise characteristics of high-linearity composite-channel Al/sub 0.3/Ga/sub 0.7/N/Al/sub 0.05/Ga/sub 0.95/N/GaN HEMTs

We report broadband microwave noise characteristics of a high-linearity composite-channel HEMT (CC-HEMT). Owing to the novel composite-channel design, the CC-HEMT exhibits high gain and high linearity such as an output third-order intercept point (OIP3) of 33.2 dBm at 2 GHz. The CC-HEMT also exhibits excellent microwave noise performance. For 1-/spl mu/m gate-length devices, a minimum noise figure (NF/sub min/) of 0.7 dB and an associated gain (G/sub a/) of 19 dB were observed at 1 GHz, and an (NF/sub mi/) of 3.3 dB and a G/sub a/ of 10.8 dB were observed at 10 GHz. The dependence of the noise characteristics on the physical design parameters, such as the gate-source and gate-drain spacing, is also presented.     

A wide-band and low-driving-power phase modulator employing a Ti:LiNbO/sub 3/ optical waveguide at 1.5 mu m

A wide-band and low-driving-power Ti:LiNbO/sub 3/ optical modulator at 1.5- mu m wavelength is described. A relatively thick SiO/sub 2/ buffer layer is effectively utilized to improve phase velocity mismatch between the microwaves and optical waves. A coplanar waveguide is used as an efficient traveling-wave electrode, and is designed utilizing the upper bound calculation in the spectral domain. Wide-band modulation of 12 GHz (3 dB optical and 6 dB electrical cutoff frequency) and small driving-power-to-modulation-bandwidth ratio of 20 mW/GHz are realized.<>     

A Catalog of Low Power Loss Parameters and High Power Thresholds for Partially Magnetized Ferrites

The low power loss and high power threshold properties have been measured on a number of candidate ferrite phase-shifting materials. The low power loss is characterized by /spl mu//sub 0/', the imaginary part of the diagonal component of the permeability tensor for the completely demagnetized state. /spl mu/sub 0/' was measured from 3.0 to 16.8 GHz. The high power properties are characterized by the parallel pump threshold at a bias field correspontig to H/sub i/ /spl equiv/ 0 and to 4/spl pi/M /spl equiv/ 4/spl pi/M/sub s/. The threshold was measured between 3.0 and 16.8 GHz. For the purposes of computer calculation /spl mu//sub 0/' and h/sub crit/ were fit to an equation of the form A (/spl gamma/4/spl pi/M/sub s/ / /spl omega/)/sup N/. Translating /spl mu//sub 0/' and h/sub crit/ to /spl Delta/H/sub eff/ and /spl Delta/H/sub k/ gives the YIG plus Al as the lowest loss and lowest threshold materials followed by the Gd garnets and MgMn spinels. The Ni spinels are very Iossy.     

Efficient PDFA module using high-NA PbF/sub 2//InF/sub 3/-based fluoride fiber

The highest reported single-pass gain coefficient of 0.36 dB/mW has been achieved using a newly developed Pr/sup 3+/-doped high-NA PbF/sub 2//InF/sub 3/-based fluoride fiber, with a /spl Delta/n of 6.6%, a core diameter of 1.2 /spl mu/m and a transmission loss of 250 dB/km at 1.2 /spl mu/m. This fiber was used to construct an efficient PDFA module with a MOPA-LD. A small-signal net gain of 22.5 dB was achieved at 1.30 /spl mu/m with a pump power of 23m mW.     

A 310/spl deg//3.6-dB K-band phaseshifter using paraelectric BST thin films

Ferro- and para-electric BaSrTiO/sub 3/ (/spl epsiv//sub r//spl sim/350 and tg/spl delta//spl sim/5/spl times/10/sup -2/ at 0V) thin films were deposited by low-cost sol-gel techniques. Subsequently, the films were used for fabricating coplanar waveguide phaseshifters using tunable finger-shaped capacitors. A 310/spl deg/ phaseshift was obtained at 30GHz and 35V of tuning voltage with 3.6dB of insertion loss yielding a figure of merit of 85/spl deg//dB.