Wideband Waveguide Research Articles

THEORY AND EXPERIMENT OF A COMPACT WAVEGUIDE DUAL CIRCULAR POLARIZER

A new compact and wide-band waveguide dual circular polarizer at Ka-band is presented and tested in this paper. This compact structure is composed of a three-port polarizing diplexer and a circular polarizer realized by a simple pair of large grooves. The polarizing diplexer includes two rectangular waveguides with a perpendicular H-plane junction, one circular waveguide coupled in E- plane. A cylindrical step and two pins are used to match this structure. For a LHCP or RHCP wave in the circular port, only one speciflc rectangular port outputs power and the other one is isolated. The accurate analysis and design of the circular polarizer are conducted by using full-wave electromagnetic simulation tools. The optimized dual circular polarizer has the advantage of compact size with a volume smaller than 1.5‚ 3 , broad bandwidth, uncomplicated structure, and is especially suitable for use at high frequencies such as Ka-band and above. The prototype of the polarizer has been manufactured and test, the experimental results are basically consistent with the theories.

Broadband waveguide slot array for SAR

A new kind of wideband waveguide slot array for synthetic aperture radar (SAR) is presented. Elliptical slots are first used for designing the waveguide slot antenna. An eight-element waveguide slot array operating at X-band is designed and measured. Predicted results are compared with measured data and good agreement is reported. The measured bandwidth for VSWR≤1.5 has reached 19.6%.

Wideband waveguide to microstrip probe transition with LTCC technology

A novel broadband waveguide to microstrip probe transition based on low-temperature co-fired ceramic (LTCC) technology is presented and experimentally verified for the first time. To improve the bandwidth and impedance matching, a multilayer step-shape matching structure beneath the probe is buried in the LTCC substrate, which is implemented by installing conducting ground strips on different substrate layers connected by the staggered via side walls. A waveguide to microstrip probe transition is fabricated to verify the design with compact size. Measured results show good agreement with simulated results.

Dimensional synthesis for wide-band pseudo-elliptic waveguide filters using cavity-backed inverters

This study presents a dimensional synthesis method for the design of wide-band pseudo-elliptic waveguide filters without resorting to global full-wave optimisation. In this approach, the authors introduce and employ two novel cavity-backed inverters, which produce transmission zeros (TZs) in the out-of-band response, however, the frequency response in the passband is similar to that of normal iris inverters. So, the design procedures for the passband and out-of-band filter responses are carried out independently. As design examples, pseudo-elliptic waveguide filters with TZs in the lower and upper frequency bands are designed, respectively. The results show good equal-ripple performance in the passband and improved rejection performance with preset TZs beyond the passband.

Broadband Propagative Microwave Imaging of Steel Fiber Reinforced Concrete Wall Structures

In this paper, a system for the broadband microwave nondestructive testing of steel fiber reinforced concrete (SFRC) is presented. The system is able to produce a pixeled image of the fiber dosage in the concrete. The SFRC material is seen as a dielectric mixture formed by thin-wire metallic inclusions and a host medium. An electromagnetic model based on the Maxwell-Garnett approach for dielectric mixtures is used to relate the electromagnetic properties of the SFRC to the fiber dosage. A criterion to determine the practical upper frequency limit for the measurements is formulated. A measurement system based on two wideband waveguide antennas is designed for the analysis of two SFRC multiblock test structures. The electric capacitive host medium calibration is proposed in the cases where the concrete structures have parts fabricated with different processes. The laboratory measurements on the individual SFRC elements and on the SFRC multiblock structures are conducted to obtain the images of the fiber dosage in the SFRC. Good agreement between the real, simulated, and measured values is achieved.

Dimensional Synthesis of Symmetric Wideband Waveguide Cross-Coupled Filters Without Global Full-Wave Optimization

This paper presents a dimensional synthesis method for the design of symmetric wideband waveguide cross-coupled filters without resorting to global full-wave optimization. In this method, we propose two circuit models suitable for the synthesis of wideband cross-coupled filters. Besides, we propose a novel physical realization of the cross-coupled K-inverter in the waveguide filter. As a design example, an X-band four-pole waveguide cross-coupled filter has been designed and fabricated. The results show good equal-ripple performance in the passband and improved rejection performance beyond the passband.

Design of Wide-Band Pseudo-Elliptic Waveguide Filters With Cavity-Backed Inverters

This letter presents a method for the design of wide-band pseudo-elliptic waveguide filters without resorting to global full-wave optimization. In this approach, we introduce and employ two novel cavity-backed inverters, which produce transmission zeros in the out-of-band response, however, whose frequency response in the passband is similar to that of normal iris inverters. As a design example, a pseudo-elliptic waveguide filter with transmission zeros in the lower and upper frequency bands are designed and fabricated. The results show good equal-ripple performance in the passband and improved rejection performance with preset transmission zeros beyond the passband.

Dimensional synthesis method for wide-band waveguide iris filters

This study presents a dimensional synthesis method for the design of wide-band waveguide iris filters without global optimisation. In the synthesis method, an alternative edge frequency mapping method is introduced and applied. In addition, an improved iris model with the exponent-weighted turns ratio is proposed in order to incorporate the frequency dependence of inverters. Based on the edge frequency mapping method and the improved iris model, a dimensional synthesis procedure is then presented. As design examples, two H-plane waveguide iris filters are designed for 17.6 and 20.2% fractional bandwidth, respectively. The measured and calculated results show good equal ripple performance within the whole frequency band.

60-GHz Wideband Substrate-Integrated-Waveguide Slot Array Using Closely Spaced Elements for Planar Multisector Antenna

A new wideband waveguide slot array is proposed for covering a wide elevation-angle range with a planar sector antenna of a multigigabit wireless LAN in the 60-GHz band. The requirement of millimeter-wave sector antennas is to realize both wide bandwidth of 11.2% and wide elevation-angle coverage with a required gain of over 10 dBi. To satisfy both the required gain and bandwidth, the important structural features of the proposed antenna are that multiple slot elements are successively arranged at an interval of the length less than one quarter guide wavelengths and that the slot length increases from the shorted waveguide end to the feed end. The operational principle of the slot array is based on multisection quarter-wavelength reflection cancellation, so the slot array can achieve the required bandwidth. Furthermore, this antenna produces a unidirectional radiation pattern by using the radiators and the reflectors, resulting in the required gain over a wide elevation-angle range. In the design, the structural parameters of the slot array are selected to meet the requirements for 60-GHz-band sector antenna. The developed substrate-integrated-waveguide (SIW) slot array achieves both the 10 dB return-loss bandwidth of 15% and the specified gain in 88-96% of the one-sector coverage range of 59-66 GHz. The effectiveness of the proposed slot array for a sector antenna is verified by the good agreement between the simulated and measured results.

Microplasma Array Serving as Photonic Crystals and Plasmon Chains

An array of microplasmas with sizes ranging from a millimeter to a micrometer, has potential for novel and promising electromagnetic-wave media, especially when the wave frequency is below the electron plasma frequency. Photonic crystals or band-gap materials composed of microplasmas have unique properties arising from their loss term, and they can become band-pass filters instead of the band-stop filters usually observed in photonic crystals of dielectrics. Such behavior is well understood using the dispersion relation in a three-dimensional space of frequency and complex wavenumber with real and imaginary parts. Another functional array is a simple one-dimensional (1D) array; it can conduct microwaves for a wide frequency range below the electron plasma frequency. The propagating modes are similar to the coupling of localized surface plasmon polaritons observed along a metallic nanoparticle chain in the photon range; however a 1D microplasma array features differ from those of a metallic sphere array, leading to a dynamic wide-band waveguide.

Wideband waveguide loading impedance matching on the basis of photonic crystals with nanometer metal layers

Theoretically shown and experimentally proven is the possibility of creating wideband matched loading on the basis of photonic crystals, composed of alternating nanometer metal and isolator layers with different electro-physical parameters.

Dimensional Synthesis for Wide-Band Waveguide Filters and Diplexers

Broad-band waveguide filter and diplexer designs are widely used for telecommunications, space, and terrestrial applications. Fairly accurate design procedures giving equivalent-circuit information are well known for bandpass filters, but this data needs to be converted into physical dimensions, i.e., waveguide cavity lengths and iris dimensions. A novel procedure giving dimensions of bandpass filters directly for wide- and narrow-band applications is described. Iris network models are generated with the aid of electromagnetic simulators and used to derive correct iris dimensions and accurate susceptance slope parameters of the cavities, avoiding global optimization of the entire structure. The results demonstrate very good equiripple performance up to bandwidths of approximately 20% in frequency or 40% in terms of guide wavelength. A similar dimensional synthesis to design waveguide noncontiguous bandpass diplexers is also given. The method uses a fast and efficient optimization with a reduced number of variables, which is fixed and independent of the order of the two filters. The simplicity of the method leads to good return-loss levels and the derivation of the diplexer dimensions takes less than 10 min, including optimization.

Numerical Matrix Analysis for Performances of Wideband 100GHz Branch-Line Couplers

The wideband waveguide 3-dB branch-line coupler suitable for use in SSB heterodyne receivers in radio astronomy is designed and its performances are reported. The coupler is designed by a numerical analytical method by using matrices based on the circuit theory and has good performances in the range of frequencies from 84GHz to 116GHz.

Microwave filters-applications and technology

This paper describes the development of microwave filter technology from an applications perspective. Military applications required wide-band and tunable devices for electronic support measures receivers, which led to the development of highly selective wide-band waveguide filters, coaxial resonator and suspended-substrate multiplexers, and electronically tunable filters. The satellite communications industry created demand for low-mass narrow-band low-loss filters with severe specifications on amplitude selectivity and phase linearity. These requirements resulted in the development of dual-mode waveguide and dielectric-resonator filters, and advances in the design of contiguous multiplexers. Cellular communications base-stations demanded low-loss high power-handling selective filters with small physical size, capable of being manufactured in tens of thousands at a reasonable cost. These demands led to advances in coaxial resonator, dielectric resonator, and superconducting filters, and also to methods of cost-reduction, including computer-aided alignment. Cellular radio handsets have required the manufacture of hundreds of millions of extremely small very low-cost filters, still with reasonably low loss and high selectivity. This has driven significant advances in integrated ceramic, surface, and bulk acoustic-wave active filters and filters using micromachined electromechanical systems.

A wideband waveguide transition design with modified dielectric transformer using edge-based tetrahedral finite-element analysis

A waveguide transition analysis approach has been established to deal with arbitrary shaped three-dimensional (3-D) waveguide discontinuity problems, by hybridizing the edge-based tetrahedral finite-element method for the junction region and the analytic modal expansion technique for the waveguide region. Several unique features have been imbedded in the analysis, including a variational formula for the scattering coefficients, a modified Delaunay triangulation for the mesh generation, and a frontal solution technique for the sparse matrix solution. As a result, the analysis is verified to be accurate, versatile, and efficient through extensive comparisons with the theoretical and measurement data in the available literature. The approach is then applied to design a rectangular to dielectric-filled circular waveguide transition with less than -20 dB return loss over a 40% bandwidth by using a suitable modified dielectric rod transformer.

Wide-band waveguide and ridge waveguide T-junctions for diplexer applications

Scattering parameters of E- and H-plane stepped waveguide and E-plane ridge waveguide stepped T-junctions are obtained using an extension of the three-plane mode matching method. An optimization process is applied to find the T-junctions and step dimensions that yield a low reflection coefficient in one of the T-junctions arms over a wide frequency band. An example of the design of a wideband T-junction diplexer is presented. The diplexer filters are inductive window waveguide filters, and are rigorously modeled using mode matching and a novel two-dimensional curve fitting method, which greatly reduces the CPU time for optimization. The diplexer optimization procedure, as well as the filter modeling method, are described. Experimental results on the optimized T-junction and the diplexer are presented; both show excellent agreement with their computed optimum results, without any adjustments or tuning. >

Millimetrewave groove guide with V-shaped grooves

The use of a V-groove guide has been investigated and compared with rectangular-groove guide. The V-groove guide is found to be superior. It has lower attenuation and rejects higher-order modes more effectively. Connection losses are small, and guide losses are around 0.4 dB/m at 96 GHz for an aluminium machined guide even with intermediate connections. For a 90° V-groove of depth equal to 0.4 of the plane separation, the guide wavelength is about 1% larger than the free-space wavelength. It is expected that the V-groove guide will provide a valuable single-mode low-loss and wideband waveguide for millimetrewave propagation.

Harmonic operation of GaAs millimetre wave transferred electron oscillators

Harmonic operation of GaAs millimetre wave transferred electron (TE) oscillators has been identified using a wideband waveguide system. The harmonic number was determined by precisely measuring the frequency as well as the frequency variations of the harmonic components when the oscillator was tuned mechanically or electrically. We find that GaAs TE oscillators at 94 GHz, matched to a waveguide circuit by means of a resonant disc, operate at the second or third harmonic frequency, depending on the length of the active GaAs region, which was between 1.8 and 2.6 ?m.

Theoretical design of wideband waveguide circulators

This letter describes the procedure used in designing, by purely theoretical means, wideband waveguide 3-port circulators. An extension of earlier field analysis, together with the usual Polder expressions for ferrite permeability, enables a computer programme to give optimum wideband circulators for any size waveguide with any low-loss ferrite material. Experimental results are given of circulators so designed.

Computation of wide-band waveguide directional couplers

Computation of wide-band waveguide directional couplers