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In this paper, an X-band CMOS single chip integrating 16 building blocks is developed for frequency modulation continuous wave radar application. The quadrature and monopulse transceiver consists of a voltage-controlled oscillator, amplifiers, Wilkinson power dividers, 90[degrees] hybrid low-noise amplifiers, rat-race hybrid, a single-pole double-throw switch, an active bandpass filter (BPF), and mixers. The transceiver is fabricated in a standard mixed-signal/RF bulk 0.18-[micro]m CMOS technology with a chip area of 2.6 mm x 3.3 mm, including contact pads. The transceiver is implemented by meandered complementary-conducting-strip transmission lines demonstrating their capability of miniaturizing circuits such as 90[degrees] hybrid and rat-race hybrid with 95% and 98% size reduction compared to the prototype designs, respectively. The active BPF consumes 4.5 mW achieving 0-dB insertion loss at the passband. The total power consumption of the transceiver is 0.35 W. Output power of the transmitter is 1 dBm with a 35-dB second harmonic suppression. Moreover, the on-chip isolations between T/R in this compacted transceiver are more than 60 dB. The measured receiver gain and NF are -4.5 and 11.5 dB, respectively. Finally, the obtained in-phase and quadrature signals demonstrate 0.6-dB amplitude and 7[degrees] phase imbalance. Index Terms--CMOS, FM radar, hybrid, monolithic microwave integrated circuits (MMICs), transmission line (TL).

This paper presents the design guidelines of the synthetic quasi-TEM transmission line (TL) based on standard 0.18-[micro]m one-poly six-metal complementary metal--oxide--semi-conductor (CMOS) technology. The synthetic quasi-TEM TL also called the complementary-conducting-strip transmission line (CCS TL), is composed of five structural parameters to synthesize its guiding characteristics. Twenty-four designs of CCS TL are reported, with the following unique attributes. First, a characteristic impedance range of 8.62-104.0 [2 is yielded. Second, the maximum value of the slow-wave factor is 4.79, representing an increase of 139.5% over the theoretical limit of the quasi-TEM TL. Third, the ratio of the area of the CCS TL to its corresponding quality factor (Q factor) can help to estimate the cost of the loss for the circuit miniaturizations. Additionally, the important CMOS manufacturing of metal density is for the first time involved in the reported TL designs. By following the proposed design methodologies, a practical design example of a Ka-band CMOS rat-race hybrid is reported and experimentally examined in detail to reveal the feasibility of the proposed design guidelines to synthesize the CMOS CCS TL. The chip size without contact pads is 420.0 [micro]m x 540.0 [micro]m. The measured loss and isolation of the hybrid at 36.3 GHz are 3.84 and 58.0 dB, respectively. Index Terms--Complementary metal-oxide-semiconductor (CMOS), hybrid, quasi-TEM, thin-film microstrip (TFMS), transmission line (TL).

This paper presents a fully monolithic transmission-line-based active bandpass filter (BPF) fabricated in a 0.18-[micro]m standard complementary metal--oxide--semiconductor (CMOS) technology. The half-wavelength resonators are realized by synthetic quasi-TEM complementary conducting-strip transmission lines (CCS TLs). To lower the insertion loss of the BPF, the differential nMOS cross-coupled pairs are combined with the parallel resonators. Besides, the active devices and CCS TLs are vertically integrated on the standard CMOS substrate. The Q-enhanced resonator, which is comprised of a CCS TL and an nMOS cross-coupled pair, is theoretically investigated. Simulation results indicate that the Q factor of the resonator can be increased from 3.4 to 84.0 at 6.53 GHz. Additionally, the prototype of the second-order BPF occupies an area of 1230 [micro]mx 880 [micro]m, and the measured results demonstrate that the center frequency is 6.02 GHz with a bandwidth of 1.14 GHz. The [P.sub.1dB] and insertion loss are--15.2 dBm and 2.2 dB, respectively, when the BPF consumes 3.0 mA from a 1.8-V supply. A two-port noisy network is also reported to examine the noise figure (NF) of the proposed BPF. Theoretical results reveal that the NF is 11.38 dB at 6.0 GHz, with a difference of less than 7.2% among the measured data. Index Terms--Active bandpass filter (BPF), C-band, CMOS, transmission line (TL).

A synthetic rectangular waveguide (SRW), which consists of two electrical sidewalls and two parallel periodical structures placed at the top and bottom surfaces of the waveguide, is presented. The SRW is made by multilayered integrated circuit processes, which typically have large ratios of SRW lateral dimensions to substrate thickness. Two theoretical methods, finite-element method and deembedding of composite structure consisting of SRW and mode converters, are applied to investigate the propagation characteristics of the SRW. Application of the dispersion characteristics of the two-dimensional periodical structures coupled with appropriate mode converter designs leads to results in SRW designs supporting T[E.sub.10], T[M.sub.00], and T[M.sub.10] modes. Measurements and the two theoretical approaches indicate that the slow-wave factor is 4.9 and Q-factor is 260 at 6.85 GHz for the T[E.sub.10] mode propagation with a cutoff frequency of 4.10 GHz (0.348 factor of cutoff frequency of conventional rectangular waveguide using the same material and dimensions). The theoretical data show the T[M.sub.00] mode to have a slow-wave factor of 1.8, Q-factor of 187.6 at 11.4 GHz, and cutoff frequency of 10.2 GHz. The T[M.sub.10] mode has a slow-wave factor of 1.98, Q-factor of 187.6 at 12.5 GHz, and cutoff frequency of 10.4 GHz. Index Terms--Microwave integrated circuit (MIC), periodical structure, rectangular waveguide, slow-wave device, T[E.sub.10], T[M.sub.00], T[M.sub.10].

This paper presents the modal characteristics of one-dimensional periodical transmission lines, including the microstrip with even-symmetric periodical perturbations, the microstrip on an electromagnetic bandgap (EBG) surface without via holes, and the electric-magnetic-electric (EME) microstrip, in the bound, stopband, and radiation regions. The Brillouin diagram, or the so-called k - [beta] diagram, is employed to represent the dispersion characteristics of the periodical transmission lines. The matrix-pencil method is applied to analysis the surface currents [J.sub.s] obtained by invoking the method of moment simulation, and the results are verified by the finite-element method analyzes. The complex modes in the form of +j[alpha] [+ or -] [beta] and -j[alpha] [+ or -] [beta] could be observed in the microstrip with even-symmetric periodical structure and form the stopband of the periodical microstrip. In the case study of the microstrip on the EBG surface, the complexity of the modal behaviors could be illustrated in the stopband. The complex mode pair in the form of +j[alpha] [+ or -] [beta] exists in the stopband. In the stopband of the EME microstrip, the complex mode in the form of +j[alpha] [+ or -] [beta] appears. Energy vanishes due to the space-wave leakages near the corner frequencies of the stopband of the microstrip on the EBG ground plane and the EME microstrip. The dispersion characteristics of three case studies exhibit the different modal behaviors although the scattering analyzes show the similar results in the passband, stopband, and radiation regions. Index Terms--Electromagnetic bandgap (EBG), matrix-pencil method, periodical structure, photonic bandgap (PBG).

The analysis and design of a microstrip antenna array with a conical beam are presented. The antenna array employs a periodic structure derived from the microstrip on a perforated ground plane. The microstrip antenna array consists of eight leaky lines evenly distributed around a circle. Each line radiates mainly a pair of forward and backward beams, forming a conical beam. The new leaky line design employs the concept of space-harmonic modulation on the E[H.sub.0] mode launched at the common joint of the antenna array. The scattering and dispersion characteristics of the leaky line are thoroughly investigated. The fact that the perturbation of the antisymmetric holes made by photolithographic etching excites the leaky [EH.sub.1] mode is theoretically and experimentally validated. Scattering analyses of the surface currents on the microstrip, however, reveal in detail the physical operation of the leaky line. The dispersion characteristics are, thus, established and shown in a Brillouin diagram, indicating the role of each space harmonic, denoted by its complex propagation constant [[gamma].sup.[+ or -].sub.m,n] * [[gamma].sup.[+ or -].sub.m,n] represents a traveling-wave component of the nth higher-order spatial component in association with the [EH.sub.m] mode: the superscript, + (-), signifies a forward (backward) traveling wave. For the particular leaky line design, [[gamma].sup.+.sub.0,-1] and [[gamma].sup.+.sub.1,0] space harmonics, both showing odd-symmetric field polarization, and both outside the triangular Brillouin region, form the backward and forward leaky waves, respectively. When the leaky lines are evenly and collinearly tied, an 11.5-GHz radial antenna array prototype is formed, and emits a conical beam, showing a 3-dB beamwidth of 24[degrees] at the flare angle of 31[degrees]. Index Terms--Conical beam, leaky waves, periodic structures, radial antenna array.

The aim of this paper is to provide: 1) a detailed description of the higher order leaky modes of the much-used broadside-coupled microstrips and 2) demonstrate the practical application of such leaky modes as an antenna. A representative broadside-coupled transmission-line structure is examined to elucidate the detail of leakage effects at higher order of multilayered three-dimensional microwave and millimeter-wave circuits. Two-layer cases are analyzed from a physical perspective and the total number of first higher order leaky modes is found to be equal to that of microstrips. One of the two first higher order leaky modes obtained in the two-layer case is weakly attenuated, while the other is strongly attenuated. A high-gain narrow-beam leaky-mode antenna using only the weakly attenuated leaky mode is designed and measured as an application of this broadside-coupled structure, exhibiting a marked beamwidth reduction of 60%. This antenna is the first Yagi-Uda-like array antenna that utilizes the higher order leaky modes of the microstrip, for which the three basic elements--driver, reflector, and director--are stacked in the broadside direction. The attenuation rate can be further reduced by adjusting the strip width of the director. The half-power beamwidth of the leaky-mode antenna applying two-layer broadside-coupled microstrips with a wider top microstrip is measured to be 2.10[degrees] at 25.20[degrees] from the broadside at 34 GHz. Index Terms--Antenna arrays, high gain, muitilayered, narrow beam.

This paper presents a dual-frequency electric-magnetic-electric (EME) microstrip exhibiting two leaky-wave regions of similar radiation characteristics like the microstrip E[H.sub.1] mode. The EME microstrip incorporates a photonic bandgap (PBG) structure, which is a two-dimensional array consisting of unit cell made of coupled coils connected by a via. The PBG structure employed in the EME prototype conducts at dc and shows the first stopband between 8.8-12.4 GHz, thus rendering the so-called magnetic surface. The EME microstrip is essentially made by substituting the PBG cells for the metal strip of a conventional microstrip. The finite-element method (FEM) analyses of the PBG structure show that the first and second modes are TM-like and TEM-iike, respectively. Thelatter is leaky between 12.4-12.9 GHz and is found to be responsible for the second leaky region of the EME microstrip. The dispersion characteristics of the EME microstrip are obtained by two theoretical methods, namely, the matrix-pencil method and the FEM. Both show excellent agreement in the two leaky regions. Furthermore, the measured far-field radiation patterns of the two leaky regions also validate the dispersion curves. The first leaky region is of E[H.sub.1] type and between 5.05-5.45 GHz. The second leaky region radiates a frequency-scanning fan beam between 11.95-13.0 GHz, similar to those of the E[H.sub.1] mode. Detailed modal current analyses show even and odd symmetry along longitudinal and transverse plane of EME microstrip, respectively, further confirming the two leaky regions behave like the well-known E[H.sub.1] leaky mode. The proposed EME microstrip enriches the modal characteristics of the conventional, uniform microstrip and is thus a manifestation of application of PBG structure for new guiding device. Index Terms--Dual frequency, leaky-mode antenna, photonic bandgap (PBG).

This paper experimentally and theoretically confirms the validity of the definition proposed by Das for computing the complex characteristic impedance of the first higher order (E[H.sub.1]) microstrip mode. The normalized complex propagation constant and complex characteristic impedance of the microstrip obtained by the rigorous full-wave integral-equation method is also presented. To better understand the circuit behavior of the leaky mode at the respective frequencies, the results are analyzed in both frequency and transformed steepest descent plane. A differential time-domain reflectometry (TDR) experiment shows that the experimental results are in excellent agreement with the time-domain plots obtained theoretically by the inverse discrete Fourier transform of the transmission line modeled by the dispersive characteristic. The propagation characteristics of the echoed signals in the time domain, which are reflected from the open end of the leaky line, are analyzed in detail using the corresponding group velocity of the E[H.sub.1] mode. The wide spread of the echoed signals in the time domain is the direct result of the highly dispersive group velocity. The slowest group velocity is in the leaky region. The time-to-frequency conversion of the measured TDR data reveals that the reflection, leaky, and propagation zones coexist simultaneously for the E[H.sub.1] mode propagation. The conversion also accurately assesses the attenuation constant of the E[H.sub.1] mode if the attenuation is not too high. The Fourier transform of the TDR responses also simultaneously yields the input reflection coefficient ([S.sub.11]) and the complex characteristic impedance. The complex characteristic impedance extracted from the TDR responses also agrees closely with the theoretical data. Index Terms--Group velocity leaky waves, impedance measurement, microstrip, time-domain reflectrometry.

By closely examining the resonant phenomena of a suspended, fiat wire resonator, this paper speculates the existence of the fast-wave mode causing the anomalous resonance that cannot possibly be explained by the well-known bound mode. Followed by proposing a guiding structure model that allows the assessment of the effects of ground plane and sidewalls (external objects) on the guiding properties, the numerical accuracy of the full-wave spectral-domain approach method for the electrically large model is validated by performing the rigorous convergence study. A series of measurements on the resonator are conducted for the same guiding structure of various lengths, confirming that the anomalous resonance is indeed caused by a fast-wave in the form of a space-wave type leaky mode which also exhibits almost identical modal currents to those of the bound mode. Index Terms - Fast-wave, leaky mode, resonance, space-wave.

This paper presents a novel full-wave segmentation method for analyzing a complex and large microwave planar circuit which is divided into several smaller segments with corresponding multiport network parameters. They are obtained by a full-wave space-domain integral-equation technique in connection to a proposed excitation model based on the equivalence principle. The integral equation is solved numerically by Galerkin's procedure resulting in the generalized scattering-matrix (GSM) descriptions of all the subcircuit segments. The combination of these GSM's yields an overall network characterization of the composite circuit. Rigorous convergence studies and extensive validity checks confirm the reliability and accuracy of the proposed method. The novel technique immediately demonstrates its obvious application for quantitative characterization of higher order modes associated with a microwave-circuit discontinuity problem. Finally, very good agreement is obtained in a comparative study of an arbitrary planar structure analyzed by our full-wave method with and without segmentation, respectively. Index Terms - Equivalence principle, equivalent source excitation, full-wave segmentation method, generalized scattering matrix (GSM), higher order modes, multimode, near discontinuity de-embedding, space-domain integral equation.

This paper describes basic research carried out to design a microwave source module employing the concept of an active-integrated leaky-mode antenna. The novel active-antenna source module utilizes a microstrip as the radiating element while adopting uniplanar technology for the active circuit design. The microstrip is operated in the first higher order odd mode, which is a leaky mode, and excited by a proximity-coupled center-fed slotline on the same surface of the uniplanar microwave-integrated circuit. The measured performance of an X-band transmission-type injection-locked active-integrated antenna source module demonstrated that such a design approach was suitable for linear array integration for quasi-optical power combining. The harmonic-balance (HB) analysis of the proposed active-integrated antenna agrees with the measurements in both free-running frequency and power level. The measured radiation patterns of the active-integrated antenna also agree well with the theoretical predictions.

Three arrangements of the feeding structure for the excitation of a microstrip leaky wave antenna are proposed and investigated in this paper. A full-wave spectral domain integral equation method combined with the fundamental mode sampling technique is applied to determine the reflection coefficient of the excitation source. Tabulation technique is used to reduce the computational effort. Dependence on structural parameters such as line width, line spacing and overlap length is fully analyzed to obtain the design criteria for a microstrip leaky wave antenna. Additionally, an experimental setup is used to check the validity of our numerical results and verify the radiation nature of the microstrip line first higher-order mode.

A new quasi-planar leaky-wave antenna is presented. It consists of microstrip line on one side of the substrate and uniplanar circuit on the other side placed in a partially opened waveguide. The leakage is produced by the excitation of the first higher order (odd) microstrip mode coupled electromagnetically through slotline on the opposite side of the substrate. Theoretic results based on rigorous Green's impedance integral equation method show that the new microstrip-slotline-coupled leaky-wave antenna has broadband tuning range via structure parameters and is insensitive to microstrip line width variation. Measured relative power absorbed (RPA) results indicate that the useful frequency bandwidth agrees with what rigorous field theory predicts. The measured antenna radiation patterns also agree very well with approximate theoretic computations. Theory and experiments show that the proposed leaky-wave antenna can interface to feeding structure easily and directly, the new antenna may become good candidate for microwave and millimeter-wave integrated antenna design.

The evolution of complex leaky waves in partially open gyromagnetic slotlines into complex modes in a shielded slotline is presented. Given a particular stratified gyromagnetic slotline with two sidewalls present, four types (Types I-IV) of guided structures are defined and investigated, depending upon the four possible combinations of top and bottom covers. The behavior of the complex solutions is discussed for the partially open gyromagnetic slotlines. Initially, the slotline of Type I, which lacks both top and bottom covers, shows that no coupling exists among various pairs of leaky waves. By adding only a top cover into Type I, the resultant slotline of Type II exhibits certain coupling between different sets of leaky waves. Similarly, by adding only a bottom cover into Type I, the resultant slotline of Type III shows that certain strong leaky waves of Types I and II now become weak leaky waves. From these numerical experiments, we deduce that the complex modes supported by Type IV, which is completely shielded, can be the result of the mode coupling of the two previously found leaky waves in Types II and III waveguides, respectively. Therefore, the formation of complex modes in shielded slotline is related to the effects of covering on mode coupling of the various leaky waves of the partially open slotlines.

A newly proposed generalized full-wave space-domain integral equation technique incorporation dyadic Green's impedance function and a new set of basis functions are presented for the analysis of striplines and slotlines arbitrarily integrated on multiple nonlayered sustrates. The generalized full-wave integral equation technique is validated by conducting convergence study and several case studies. The theoretical dispersion characteristic of the transmission lines obtained here are in very good agreement with the published and measured data for the modified Microslab and the microstrip proximity effect near substrate edge. For the slotline type problem, where a new set of current basis function must be derived to be incorporated into Green's impedance function approach the new approach presented here shows that the corresponding propagation characteristics thus obtained are also in excellent agreement with those reported in the available literature, which normally used the slot electric fields as the unknowns. To explain how general the present formulation is, it can be reduced to the well-known spectral domain formulation for any guided-wave structure containing only layered substrates.

A realistic termination scheme is proposed for closely coupled N-conductor microstrips. The design aims to achieve satisfactorily low signal reflection and good fabrication feasibility for the planar MMIC (Monolithic Microwave Integrated Circuit) process. The matched termination network (MTN) for a lossless three-line coupled microstrip structure is presented. High-speed pulse transmission along terminated tightly coupled microstrip lines is analyzed using modal analysis in the frequency domain. Theoretical results for the propagating and reflected waveforms are obtained by applying the inverse discrete Fourier transform (IDFT) to the system responses. These responses are obtained by applying the theory of multiconductor transmission lines to a dispersive database which has been computed using the spectral-domain approach (SDA). The response of a six-line closely coupled microstrip circuit terminated by the proposed termination scheme is measured using the HP8510B network analyzer. The measured results show that the reflected signal is below -30 dB and the results are in good agreement with the theoretical waveforms.

This paper presents theoretical and experimental results for a finite-width conductor-backed coplanar waveguide (FW-CBCPW). The guiding characteristics of FW-CBCPW are investigated first by the rigorous method of mode matching. An FW-CBCPW through line is then placed within a test fixture commonly used in laboratories, and the scattering parameters of the through line are obtained theoretically by approximating the FW-CBCPW as a simple system of coupled transmission lines. Experimental results are shown to agree very well with the theoretical ones. In particular, the anomalous behavior observed in the transmission characteristic of the through line is related to the resonant phenomenon of the terminated side planes which are short-circuited at both input and output ends due to the test fixture. Finally, a technique of mode suppression in the side-plane regions is suggested for the improvement of signal transmission over a broad band of frequency spectrum. The effects of extra higher order modes on the transmission characteristics at high frequencies are also discussed.

This paper studies and models the mechanism for forming the complex modes commonly found in boxed quasi-planar or planar guided-wave structures. To illustrate the fact that the mode-coupling among the various forms of modes is closely related to the formation of complex modes, the dispersion characteristics of the complex propagation constants (or the so-called mode spectrum) of a nonreciprocal unilateral finline are obtained by the rigorous full-wave SDA (spectral-domain approach). It is found that in the mode spectrum of the nonreciprocal finline, a forward wave and a backward wave interact to produce a pair of complex modes. The interactions between two forward (backward) traveling waves, between a forward wave and a backward wave, and between two complex waves (modes) are modeled by applying the model-coupling theory. The concept of hypothetical modes is introduced in the model. These hypothetical modes are obtained by applying mode-coupling theory to the mode spectrum previously obtained. The approximate values obtained for the propagation constants of the three types of wave interactions using the model presented in the paper are in close agreement with those given by the full-wave SDA.

The quasi-planar realizations of combine bandpass filter and diplexer using multiple coupled suspended substrate striplines (MCSSS's) have demonstrated good performance at K-band without any tuning. The N MCSSS's excite N zero-cutoff-frequency quasi-TEM modes. A new computer-aided filter design approach employing rigorous SDA (spectral-domain-approach) and 2N-port microwave circuit theory accounts for the effects of the N quasi-TEM modes, the couplings through non-adjacent MCSSS's, and cover height. Two 19.5-to-20.5 GHz MCSSS's combline filters with different cover heights are built and tested to compare their filter characteristics. The reduction in cover height decreases the amount of non-adjacent couplings through MCSSS's and results in better filter stopband performance. Another 18.5-to-19 GHz and 20-to-20.5 GHz MCSSS's diplexer is also presented. All the measured results for the combline filters and diplexer agree well with the theoretic calculations.

This paper presents the coupled-mode approach to the analysis and design of a large leaky-mode array, in which an N-element microstrip array above a common ground plane supports N coupled leaky modes (leaky [EH.sub.1] modes) at the first higher order. Following a brief description of a conventional full-wave nonstandard eigenvalue problem for solving the complex propagation constants, we present the detailed formulation of the coupled-mode approach, clearly showing the transformation of the nonstandard eigenvalue problem into a standard one. Thus, all the eigenvalues (complex propagation constants) and eigenvectors (modal current distributions) are solved simultaneously, regardless of the size of the array (N). Two key issues pertinent to the successful implementation of the proposed coupled-mode approach are addressed: the determination of the coupling coefficients and the uniqueness of the isolated uncoupled leaky mode, which represents the leaky modal solution of a single microstrip, but is derived from a system of coupled leaky-mode solutions provided the coupled microstrips have equal width and spacing. Closed-form expressions for obtaining the coupling coefficients of orders two, three, and four are presented. Theoretical studies of closely coupled microstrip arrays of two, three, and four elements show that the magnitude of the coupling coefficient [C.sub.i,i+j] between elements i and i + j decreases at the order of [10.sup.-j]. These theoretical case studies also lead to the same isolated uncoupled leaky-mode solution as predicted. Furthermore, the dispersion characteristics of the microstrip array at the first higher order obtained by the coupled-mode approach and the full-wave approach agree excellently for all the case studies. Error analyses indicated that at least two coupling coefficients ([C.sub.i,i+1] and [C.sub.i,i+2]) are required for obtaining accurate complex propagation constants with rms errors less than 1% for most of the leaky region of the particular array under investigation. An example of applying the proposed coupled-mode approach for analyzing a corporate-fed leaky-mode array of eight elements is reported, revealing that only four out of the eight leaky modes are excited. The coupled-mode theory predicts the far-field radiation pattern in the main beam region in excellent agreement with the measured results. Index Terms--Coupled microstrip lines, coupled-mode approach, coupling coefficients, leaky-mode antenna, leaky modes.

The first-pass design of a linear eight-element microstrip leaky-mode antenna array is proposed, built, and tested, showing a gain of 18.5 dB, directivity of 23.5 dB, and pencil beam with 3-dB beamwidth (Az/EI) of 10.2 [degrees]/14.3 [degrees]. Excellent agreement between the theoretical prediction and measured result for the array antenna performance is obtained. Index Terms - Microstrip arrays.