Waveguide Bandwidth Research Articles

Designing a symmetrical five-port waveguide junction

Studies have shown that for a symmetrical five-port junction to be used in a six-port reflectometer set-up, it should ideally be matched over the operating bandwidth. Using the results obtained from an electromagnetic model, a suitable symmetrical five-port E-plane waveguide junction (with five attached H-plane tapers) was designed. The junction-with-tapers prototype when tested yielded a residual mismatch of less than 0.18 over the entire waveguide bandwidth.

Six-port reflectometer

A six-port reflectometer consisting of a symmetrical five-port waveguide junction and a directional coupler was analysed, constructed and tested. Theoretical and experimental results showed that the circuit yielded optimum q-point distributions over the waveguide bandwidth. Actual measurements taken using the prototype reflectometer indicated that accuracies of ±005 in magnitude and ±0.5° in phase were obtainable.

A Broad-Band Directional Coupler for Both Dielectric and Image Guides (Short Papers)

A four-port directional coupler is presented for use in dielectric and image guides. Simple design equations are derived and the subsequent results are in good agreement with theory. Broad-band performance has been achieved over the entire conventiortal waveguide bandwidth (26-40 GHz).

A survey of planar integrated mm-wave components

Different approaches for the integration of mm-wave components have been presented recently, suggesting image line or shielded microstrip line for example. A very promising attempt employs quasi-planar structures, like fin-line, and related line configurations for this purpose. The paper gives a survey of various components being developed in the frequency range from 18 to 170 GHz using this approach. Broadband p-i-n-attenuators achieve an insertion loss below 1 dB and an isolation better than 25 dB covering either one or two entire waveguide bands. Narrowband resonator-type attenuators need only one diode to achieve similar results. At 94 GHz the attenuation of such a device can be adjusted between 1.5 and 35 dB. Fin-line detectors have been built between 18 and 170 GHz, with minimum sensitivity ranges from 400 to 100 mV/mW, depending on frequency. The conversion loss of a planar balanced mixer developed for Ka-band (26.5?40 GHz) amounts to 5 dB in a narrowband version and to 6?8 dB in a broadband, octave-wide version (18?40 GHz). For 60 GHz, a conversion loss down to 6.5 dB has been achieved. The unique advantage of the fin-line technique is demonstrated by a completely integrated Ka-band receiver front end, containing p-i-n-s.t.c, mixer and local oscillator. Fin-line couplers necessary for other integrated circuits have shown coupling factors up to crossover operation with full waveguide bandwidth.

A Compact Waveguide "Resolver" for the Accurate Measurement of Complex Reflection and Transmission Coefficients Using the 6-Port Measurement Concept

The theory of an optimum 5-port network for measuring complex reflection and transmission coefficients is developed. A compact realization in waveguide is described which allows these quantities to be determined over waveguide bandwidths from the measurements of two referenced power levels.

A travelling wave tube microwave spectrometer

The sensitivity of a Stark-modulated waveguide microwave spectrometer can be significantly improved by using a travelling wave tube or solid state microwave amplifier prior to the crystal detection. In this paper the authors discuss the travelling wave tube. The increase in the sensitivity results from the improved noise figure of the travelling wave tube relative to crystal video type detectors. Wide bandwidth travelling wave tube or solid state amplifiers are available so full waveguide bandwidths may be utilised. Rotational transitions for J=1 from 0 lines of cyanogen bromide, BrCN, were measured with the travelling wave tube system and a standard video detector and the spectra are given here.

A New Waveguide Flow Calorimeter for Levels of 1-20 W

A new dual waveguide flow calorimeter power meter used as a master reference standard in a top-echelon calibration laboratory is described. It operates at 1-20-W level and has been produced in 9 standard waveguide sizes from WG10 (WR284, R32) to WG22 (WR28, R320). These all have a VSWR 1.05 and a flat and stable RF/dc substitution efficiency over the full waveguide bandwidth. Referring only to dc standards, the Effective Efficiency Factor can be measured with built-in facilities. Comparison measurements with U. K. national standards have shown agreement within ±0.2 percent over 3 years.

A Higher Order Approximation for Waveguide Circulators (Short Papers)

Earlier work on the analysis and experimental performance of 3-port and 4-port waveguide circulators over the waveguide bandwidth has shown some discrepancies. The computed performance tended to be too optimistic. It is shown that an extension of Davies' analysis to include higher order cylindrical modes and evanescent modes in the waveguide arms yields excellent correlation between theory and practice.

Computer-Aided Design of Three-Port Waveguide Junction Circulators

The complete performance of a lossless three-port H-plane waveguide junction loaded coaxially with various inhomogeneous ferrite cylanders has been evaluated over the waveguide bandwidth and compared with experiment. Qualitative agreement between the predicted and measured performance was generally good using only the first three modes, n=0/spl plusmn/1. It has been shown theoretically and verified experimentally that if the 4/spl pi/M/sub s/ of a homogeneous rod or the internal field is increased, the circulation frequency f/sub 0/ increases; conversely, if the pemittivity is increased, f/sub 0/ decreases. These conflicting effects are modified when the magnetization 4/spl pi/M/sub s/ and permittivity /spl epsiv/ are inhomogeneous. For example, if the 4/spl pi/M/sub s/(/spl gamma/) is small at the outer surface of the rod (with permittivity held constant), the effect on f/sub 0/ is very small; but if 4/spl pi/M/sub s/(spl gamma) approaches zero for /spl gamma/ small, then f/sub 0/ may decrease significantly. On the other hand, if /spl epsiv//sub/spl gamma//(/spl gamma/) approaches unity near the outer surface of the rod, f/sub 0/ may increase significantly; but if /spl epsiv//sub/spl gamma//(/spl gamma/) approaches unity near the center of the rod, f/sub 0/ is affected relatively little. The inhomogeneous structure has also shown that decreasing the ferrite volume may improve the performance, and high-power applications are suggested. With a conducting pin down the center of the ferrite, relative bandwidths of 40-50 percent are predicted.

A new voltage-controlled millimeter thyratron waveguide switch with large switching ratio over full waveguide bandwidth

A new voltage-controlled millimeter thyratron waveguide switch with large switching ratio over full waveguide bandwidth

Waveguide-fed log periodic antennas

Abstract : Almost all log periodic antenna designs incorporate a parallel or tapered-vee transmission line, as the feeding mechanism for the radiating elements. These lines propagate the TEM mode. Techniques whereby log periodic antennas may be fed with waveguides are introduced in this report. In this case the dominant TE sub 10 mode of the waveguide is used in the feeder transmission line application. Methods of coupling energy to the radiating elements of the log periodic structure by probes inserted in the waveguide are presented. It is shown that an array may be fed either on the broad wall or narrow wall of the waveguide. The useful operating frequency range of these antennas is limited to the normal waveguide bandwidth. The waveguide-fed method is primarily useful for monopole arrays although dipole arrays can also be fed in this manner. Results of measurements performed on various antenna models are discussed. It is shown that VSWR responses below 2:1 and absolute radiation pattern gains above 10 db can be achieved. The effects of different design parameters on antenna characteristics are discussed. In addition, a requirement is presented in which either the element lengths or element spacings must be compensated to achieve constant H-plane radiation patterns. (Author)

A Study of Dielectric Covered Shunt Slots in a Waveguide

The purpose of this study was to experimentally determine the effects of placing dielectric covers of various thicknesses over a shunt slot in a waveguide. Slot lengths L and displacements x were chosen so that the data cover the waveguide bandwidth for dielectric constants ϵ' from ϵ' = 1 to ϵ' = 4. Utilizing the measured data, formulas are developed for the mean values of slot conductance and resonant frequency for cover thicknesses greater than λϵ'/4. In addition, it is shown that plane wave theory gives a bound on the conductance variation for covers thicker than λϵ'/4. Finally, pattern and VSWR measurements of linear arrays of dielectric covered slots designed with single slot data give predictable results.

Hexagonal Ferrite Isolators

Waveguide bandwidth isolators requiring virtually no externally applied magnetic field have been developed for the millimeter wave frequency range. These ferrimagnetic resonance-type devices utilize highly anisotropic uniaxial hexagonal ferrites. The specific ferrite compounds used are from the two families BaO·2NiO·ΔAl2O3 · (8-Δ) Fe2O3 and SrO·δAl2O3· (6-δ) Fe2O3 denoted Ni2W (ΔAl) and SrM (δAl), respectively. The substitution variables Δ and δ were adjusted to yield different materials whose effective magnetic anisotropy fields were appropriately spaced over the range 16 to 30 kOe. This spacing permitted their use in isolator designs throughout the frequency range 50 to 90 Gc/sec. Five materials from the Ni2W(ΔAl) family were used to cover the frequency range 50 to 60 Gc/sec and 12 materials from the SrM(δAl) family covered the range 60 to 90 Gc/sec. Pertinent electrical properties of these materials are reported as well as techniques essential to their successful application in the isolator structure. Waveguide bandwidth isolators using these materials were developed for the bands 50 to 75 and 60 to 90 Gc/sec.

Millimeter Resonance Isolators Utilizing Hexagonal Ferrites

Ferrimagnetic resonance isolators operating over waveguide bandwidths have been developed in K, V and Q bands using hexagonal ferrites. Preliminary results on similar isolators operating in M and W bands have also been obtained. The materials employed in these isolators are highly anisotropic uniaxial hexagonal compounds. The compounds of interest for the first three frequency bands are from the Ni/sub 2/W family. The anisotropy field of Ni/sub 2/W is 12.6 kilo-oersteds (Koe). This uniaxial anisotropy field can be controlled over the range of 4 to 12.6 Koe by producing solid solutions of the above compound with that of Zn/sub 2/W and/or Co/sub 2/W, and controlled over the range of 12.6-19.0 Koe by aluminum substitutions. The following operating characteristics have been obtained over the full waveguide bands: K band (18-26.5 Gc), isolation (minimum)---25 db, insertion loss (maximum)---0.7 db, VSWR (maximum)--- 1.15, applied field---1000 oersteds, length---4 1/2 inches weight---6 1/2 ounces; v band (26.5-40 Gc), isolation (minimum)---25 db, insertion loss (maximum)---1.25 db, VSWR (maximum)---1.15, applied field---1000 oersteds, length---4 inches, weight---6 ounces; Q band (33-50 Gc), isolation (minimum)---25 db, insertion loss (maximum) ---1.5 db, VSWR (maximum)---1.15, applied field---1000 oersteds, length---3 1/2 inches, weight---5 1/2 ounces. Improved attenuation ratios and size are obtained when the band-width is reduced. Examples of this are K band where a ratio of 40 to 1 is maintained over a 4-Gc bandwidth in a 3-inch unit, and V band where a ratio of 40 to 1 is maintained over a 5-Gc bandwidth in a 2-inch unit. At the present time the M (50-75 Gc) and W (75-110 Gc) band units provide attenuation ratios exceeding 10 to 1 over 5-Gc bandwidths.

Unloaded Q of Single Crystal Yttrium-Iron-Garnet Resonator as a Function of Frequency (Correspondence)

The practical feasibility of constructing magnetically tunable broad-tuning range microwave filters using single crystal yttriumiron-garnet resonators was demonstrated in a recent paper. Experimental results were presented on one- and two- resonator filters which can be tuned by varying a dc magnetic field bias over a full waveguide bandwidth and greater, at the same time maintaining an insertion loss performance which is comparable to mechanically-tuned cavity filters. The crucial parameter of the resonant elements in a band-pass filter is the unloaded Q, Q/sub u/. With a spherical single crystal of yttrium-iron-garnet the Q/sub u/ decreases with frequency below X-band frequencies reaching very low values at frequencies around 2000 Mc.

Broad-Band Quarter-Wave Plates

Analytical expressions are given for the propagation constant for the two orthogonal dominant modes in a square waveguide loaded with a centered slab of dielectric. These are combined to find the differential phase shift in a loaded section. Solutions of these equations are given for polystyrene which enables one to design broad-band quarter wave plates. The problem of transforming from unloaded to loaded guide is discussed and two solutions are given and another suggested. Experimental results are given and it is found that the work in square guide carries over to circular guide almost intact. It is shown that quarter-wave plates may easily be designed to cover a normal waveguide bandwidth.