Xiaoyong Shan

Wide-band measurement of complex permittivity using an overmoded circular cavity

A large terminating circular cavity structure is proposed in this paper for measuring the complex permittivity of low-loss dielectric materials over a very wide frequency range of 20–100 GHz. Compared to many other widely used configurations employing off-resonant circular cavity, this new overmoded circular cavity provides higher precision of relative permittivity results and a wider frequency range. Extensive measurements are carried out and measured results for two sample materials are presented. An inverse algorithm using the mode-matching method is introduced to calculate the complex permittivity of the dielectric sample. An error analysis is also presented to estimate the errors incurred due to the uncertainty in the S-parameter measurement, sample size, location of the coupling probe.

Mode-Matching Analysis of Waveguide T-Junction Loaded With an H-Plane Dielectric Slab - Abstract

This paper presents a full-wave mode-matching analysis of a rectangular waveguide T-junction partially loaded with an H-plane dielectric slab. First, the longitudinal section electric (LSE) and longitudinal section magnetic (LSM) modes in an H-plane dielectric-filled rectangular waveguide are obtained. Second, the dielectric-loaded T-junction is then divided into four regions and their electromagnetic fields are expanded into the summation of their modal functions using the resonator method. Finally, a mode-matching process for the tangential field components across regional interfaces is carried out to derive the generalized scattering matrix of the waveguide T-junction. Using the cascading connection technique of generalized scattering matrix, various waveguide couplers and power dividers/combiners with H-plane dielectric slabs can be easily analyzed and designed. Numerical results are presented and compared with those obtained by measurement or Ansofts HFSS. Good agreement is observed.

A Suspended-Substrate Ku-Band Symmetric Radial Power Combiner

This letter presents a novel eight-way radial power combiner that exhibits wide bandwidth and very low insertion loss. The peripheral ports of this power combiner use low loss suspended substrate stripline. A cylindrical cavity is introduced as the power combining structure to obtain high combining efficiency and high power handling capability. The proposed power combining structure successfully integrates planar transmission lines with a 3-D cavity structure to realize a wide band, low loss, and compact eight-way power combiner. Measured results show a bandwidth of 3.6 GHz from 12.1 to 15.7 GHz with return loss better than 19 dB and insertion loss less than 0.17 dB, which agree very well with simulated results.

A new microstrip-fed cavity-backed annular slot antenna

However, a unidirectional radiation pattem is preferred for many applications. This can be readily achieved by adding a metallic cavity at the tack of slot. Gale and Thompson [3] analyzed the admittance of a cavity-backed annular slot antenna in 1962. Morishita, Hilasawa and Fujimto [4] investigated the characteristics of a cavity-backed annular slot and pointed out that by selecting a slot shorting position a wider impedance bandwidth, circular polarization and other usell antenna characteristics can be obtained. Theoretical study of a cavity-backed annular-slot antenna was also conducted recently by Nikolic, Kot and Bird [SI, b a d on a map&-field integral equation and verified the assertion through experimental measurements that the bandwidth of an annular slot is MITOW when it is backed by a cavity.

Mode-Matching Analysis of Waveguide T-Junction Loaded with an H-Plane Dielectric Slab

This paper presents a full-wave mode-matching analysis of a rectangular waveguide T-junction partially loaded with an H-plane dielectric slab. First, the longitudinal section electric (LSE) and lon- gitudinal section magnetic (LSM) modes in an H-plane dielectric-filled rectangular waveguide are obtained. Second, the dielectric-loaded T- junction is then divided into four regions and their electromagnetic fields are expanded into the summation of their modal functions using the resonator method. Finally, a mode-matching process for the tan- gential field components across regional interfaces is carried out to derive the generalized scattering matrix of the waveguide T-junction. Using the cascading connection technique of generalized scattering matrix, various waveguide couplers and power dividers/combiners with H-plane dielectric slabs can be easily analyzed and designed. Numerical results are presented and compared with those obtained by measurement or Ansofts HFSS. Good agreement is observed.

A Novel 8-way radial power combiner

A novel 8-way radial power combiner is developed with wide bandwidth and low insertion loss. The combiner consists of eight microstrip line peripheral ports and one coaxial output port. A cylindrical cavity is introduced in the combining structure to obtain high combining efficiency and high power handling capability. The simulated 20dB return loss bandwidth is around 1.9GHz from 13.5GHz to 15.4GHz. Mechanical tolerance and graceful degradation are also analyzed.

A novel waveguide transverse slot antenna array

Josefesson [2] used parallel-plate baffles of infinite length to prevent the grating lobes and analyzed the effect of the baffles on the transverse slot impedance. The selfimpedance of a transverse slot radiating between baffles of finite length was calculated by Dich and, Rengarajan 131. Another technique used to suppress the grating lobes is to reduce the guided wavelength by filling the waveguide with dielectric slab. The radiating slots in a partially dielectric slab loaded waveguide were characterized by Joubert and McNamara [4]. Later, Joubert [SI suggested the structure of a transverse slot in a rectangular waveguide with the dielectric slab situated against one of the waveguide sidewalls for array applications.

A rectangular waveguide to multiple microstrip lines transition for power combining application

A transition from a rectangular waveguide to multiple microstrip lines is proposed in this paper for power combining applications. First, the electromagnetic fields of shielded microstrip lines are obtained by solving a set of homogeneous simultaneous equations. The mode-matching technique is then implemented to solve the junction between a rectangular waveguide and microstrip lines. A C-band six-way power combiner is finally designed based on the transition. The 20dB return loss bandwidth of the power combiner covers the whole operating bandwidth of the WR137 rectangular waveguide from 5.8GHz to 8.2GHz.

An accurate circuit model for probe-fed CBS antenna

An accurate lumped-element model for probe-fed CBS antenna has been presented in this paper. In this model, the probe-fed CBS antenna is separated into three parts: a coaxial line to rectangular waveguide transition, two rectangular waveguide transmission lines and a rectangular slot cut at the end of a rectangular waveguide. A C-band probe-fed CBS is designed using this model. The results agree well with the HFSS simulation results. Utilizing this model, the design procedure for probe-fed CBS can be fast and efficient.