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This paper presents a novel photonic bandgap (PBG) structure for microwave integrated circuits. This new PBG structure is a two-dimensional square lattice with each element consisting of a metal pad and four connecting branches. Experimental results of a microstrip on a substrate with the PBG ground plane displays a broad stopband, as predicted by finite-difference time-domain simulations. Due to the slow-wave effect generated by this unique structure, the period of the PBG lattice is only 0.1[[Lambda].sub.0] at the cutoff frequency, resulting in the most compact PBG lattice ever achieved. In the passband, the measured slow-wave factor ([Beta]/[k.sub.0]) is 1.2-2.4 times higher and insertion loss is at the same level compared to a conventional 50-[Ohms] line. This uniplanar compact PBG (UC-PBG) structure can be built using standard planar fabrication techniques without any modification. Several application examples have also been demonstrated, including a nonleaky conductor-backed coplanar waveguide and a compact spurious-free bandpass filter. This UC-PBG structure should find wide applications for high-performance and compact circuit components in microwave and millimeter-wave integrated circuits. Index Terms - Bandpass filter, conductor-backed coplanar waveguide, photonic bandgap, slow-wave factor.

The global time-domain analysis of microwave circuits involving highly nonlinear phenomena such as injection locking and intermodulation, along with parasitic effects and electromagnetic compatibility (EMC) issues is presented in this paper. Employing the concept of equivalent sources, the device-wave interaction is characterized and incorporated into the finite-difference time-domain method. The investigation of nonlinear phenomena is accomplished by utilizing a large-signal device circuit model. Measured results are also provided for comparisons with simulated results. The applicability of this equivalent-source algorithm for investigating EMC effects is also demonstrated. A correspondence between simulated and measured EMC phenomenon indicates the usefulness of this algorithm in providing an effective tool for real world radio-frequency front-end circuit designs. Index Terms - Crosstalk, electromagnetic compatibility, equivalent-source algorithm, finite-difference time-domain method, housing effect, ring oscillator, self-oscillating mixer.

A novel broad-band coplanar waveguide (CPW) to slotline transition and several new CPW passive circuits based on this transition are proposed and analyzed in this paper. This transition utilizes CPW-slotline mode-conversion to convert CPW-mode field to slotline-mode field, and the transition bandwidth is broadened by the use of air-bridges. The transition consists of three parts, including a uniform CPW, phase shifter, and slotline. The phase shifter converts the CPW mode to slotline mode and the bandwidth of the transition is broadened due to the modes 'bounce back-and-forth' in between the air-bridge and slotline. This new transition is used to realize three CPW passive circuits, including a CPW-fed Vivaldi antenna, CPW power divider, and side-coupled CPW-slotline coupler. The finite-difference time-domain method is employed to analyze those circuits, and good agreements are obtained with measured results. Index Terms - CPW-fed Vivaldi antenna, CPW power divider, CPW-slotline coupler, CPW-slotline mode-conversion, CPW-slotline transition, FDTD method.

Simple design maxims to restrict slot dimensions in enclosure designs below a half-wave length are not always adequate for minimizing electromagnetic interference (EMI). Complex interactions between cavity modes, sources, and slots can result in appreciable radiation through non-resonant length slots. The finite-difference time-domain (FDTD) method can be employed to pursue these issues with adequate modeling of thin slots. Subcellular FDTD algorithms for modeling thin slots in conductors have previously been developed. One algorithm based on a quasistatic approximation has been shown to agree well with experimental results for thin slots in planes. This FDTD thin-slot algorithm is compared herein with two-dimensional (2-D) moment method results for thin slots near corners and plane-wave excitation. FDTD simulations are also compared with measurements for slots near an edge of a cavity with an internal source. Index Terms - EMI, FDTD, shielding enclosures, slots.

Subcellular modeling of thin slots in the finite-difference time-domain (FDTD) method is investigated. Two sub-cellular algorithms for modeling thin slots with the FDTD method are compared for application to shielding enclosures in electromagnetic compatibility (EMC). The stability of the algorithms is investigated, and comparisons between the two methods for slots in planes, and slots in loaded cavities are made. Results for scattering from a finite-length slot in an infinite plane employing one of the algorithms are shown to agree well with published experimental results, and power delivered to an enclosure with a slot agree well with results measured for this study. Index Terms - FDTD, slot.

The recently developed uniplanar compact photonic bandgap (UC-PBG) substrate is successfully used to reduce surface-wave losses for an aperture-coupled fed patch antenna on a thick high dielectric-constant substrate. The surface-wave dispersion diagram of the UC-PBG substrate has been numerically computed for two different substrate thickness (25 and 50 mil) and found to have a complete stopband in the frequency range of 10.9-13.5 and 11.4-12.8 GHz, respectively. The thicker substrate is then used to enhance broadside gain of a patch antenna working in the stopband at 12 GHz. Computed results and measured data show that, due to effective surface-wave suppression, the antenna mounted on the UC-PBG substrate has over 3-dB higher gain in the broadside direction than the same antenna etched on a grounded dielectric slab with same thickness and dielectric constant. Cross-polarization level remains 13 dB down the co-polar component level for both E- and H -planes. Index Terms--Aperture-coupled patch antenna, electromagnetic crystals, finite-difference time domain, photonic bandgap, surface waves.

A novel waveguide using a photonic bandgap (PBG) structure is presented. The PBG structure is a two-dimensional square lattice with each cell consisting of metal pads and four connecting lines, which are etched on a conductor-backed Duroid substrate. This uniplanar compact PBG structure realizes magnetic surface in the stopband and is used in the waveguide walls to provide magnetic boundary conditions. A relatively uniform field distribution along the cross section has been measured at frequencies from 9.4 to 10.4 GHz. Phase velocities close to the speed of light have also been observed in the stopband, indicating that TEM mode has been established. A recently developed quasi-Yagi antenna has been employed as a broad-band and efficient waveguide transition. Meanwhile, full-wave simulations using the finite-difference time-domain method provide accurate predictions for the characteristics of both the perfect magnetic conductor impedance surface and the waveguide structure. This novel waveguide structure should find a wide range of applications in different areas, including quasi-optical power combining and the electromagnetic compatibility testing. Index Terms--Perfect magnetic conductor, phase velocity, photonic bandgap, quasi-Yagi antenna, TEM waveguide.