Fei-Ran Yang

A uniplanar compact photonic-bandgap (UC-PBG) structure and its applications for microwave circuit

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 PEG 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/spl lambda//sub 0/ at the cutoff frequency, resulting in the most compact PEG lattice ever achieved. In the passband, the measured slow-wave factor (/spl beta//k/sub 0/) is 1.2-2.4 times higher and insertion loss is at the same level compared to a conventional 50-/spl Omega/ 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.

Aperture-coupled patch antenna on UC-PBG substrate

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.

A novel TEM waveguide using uniplanar compact photonic-bandgap (UC-PBG) structure

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 a 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.

A novel low-loss slow-wave microstrip structure

A low-loss slow-wave microstrip line using a periodic structure in the ground plane is presented. The periodic structure is realized with metal pads etched in the ground plane connected by thin lines to form a distributed LC network. The slow-wave factor is demonstrated to be 1.2-2.4 times larger than that of conventional microstrip lines over a wide frequency range. Due to the unique design of the structure, low insertion loss comparable to conventional microstrips has been achieved. The proposed structure is easier to fabricate than other slow-wave devices which require multilayer substrates or very fine features.

A novel uniplanar compact PBG structure for filter and mixer applications

A novel lowpass filter with a uniplanar, compact photonic band-gap structure etched in the ground plane has been proposed and demonstrated. This new filter has a deep attenuation and spurious-free response. A drain mixer using this novel filter suppresses the LO leakage by over 10 dB compared to a reference mixer with a conventional filter.

Leakage suppression in stripline circuits using a 2-D photonic bandgap lattice

A novel method for suppressing leakage due to parallel-plate mode in stripline circuits using a uni-planar compact 2-D PBG lattice is proposed and demonstrated. The leakage is suppressed by the stopband of the PBG lattice, which is easily etched in the ground planes with standard planar process. Good agreements between simulation and measurement results verify the effectiveness of this novel concept which suppresses leakage coupling by over 30 dB in the PBG stopband.

Analysis and application of coupled microstrips on periodically patterned ground plane

Coupled microstrips on periodically patterned ground plane have been analyzed using the FDTD method to compute the effect of strip width and gap spacing on the characteristic impedance and effective dielectric constant of even and odd modes. Results have been employed to design a bandpass filter with a spurious-free response as well as good passband performance. Design criteria have been successfully established for filter applications and they are also valuable for implementing other components such as phase shifters and couplers.

Analysis and Application of Photonic Band-Gap (PBG) Structures for Microwave Circuits

Abstract The analysis and application of photonic band-gap (PBG) structures for microstrip circuits are presented. Microstrip PBG structures can be realized by either drilling holes in the dielectric substrates or etching periodic shapes in the ground planes. A simple analysis method, based on an equivalent microstrip line model, is proposed and verified by means of comparison with measured data. The equivalent microstrip line model can be used with commercial software to efficiently analyze the effect of a defect in the microstrip PBG structure. Optimization of the defect geometry allows realizing a planar resonator.

A novel high-Q image guide resonator using band-gap structures

This paper presents a novel high-Q resonator using photonic band-gap structures in an image guide. Our initial measurement with an X-band prototype demonstrates a Q-factor of 697, which is limited by the dielectric material (Duroid) used for experiment. A new planar integration technique for image guides using Yagi-Uda slot array is also developed. This resonator structure is potentially useful for millimeter-wave integrated circuits.

Recent Advances in UC-PBG Structures

This paper summaries recent progress of uniplanar compact photonic band-gap (UC-PGB) structure at the authors group, including: (1) coupled lines on UC-PBG ground plane, (2) cavity-backed slot antenna using UC-PBG as a reflector, and (3) TEM waveguide.