A low-blockage dipole array reflector antenna feed for the lower microwave frequencies

An antenna is described which was devised as a feed for a small axisymmetrical paraboloid reflector at an operational frequency of just over 1 GHz. The antenna consists of a broadside array of two dipoles on a printed circuit board (PCB), joined by a common transmission line. Each dipole is backed by a small strip reflector. With this simple array, which has one central feed point, theH-plane radiation pattern can be varied independently of theE-plane pattern. In addition, the aperture blockage of the feed is small.     

A parasitic slot array

The analysis of an endfire array of tunable parasitic slots is described. Self and mutual admittances between thin half-wavelength slots are found by an application of Babinet's Principle. To solve the circuit equations of the array, the condition is imposed that the phase velocity remain constant along the array. Then, by matrix inversion, the excitation amplitude and self-reactance of the parasitic elements are determined. The phase of the reflector is chosen to maximize the coupling between the driven element and the directors. Finally, experimental patterns are compared with computed results.     

A waveguide transverse slot for array applications

The characteristics of a radiating rectangular transverse slot in a rectangular waveguide have been studied. A moment method solution is used with entire basis expansion and testing functions (Galerkin) including the effect of wall thickness. The results are presented in terms of normalized resistance and reactance versus slot length and frequency. Excellent agreement with a previous pulse basis solution is found, as well as with measured data. An array of resonantly spaced transverse slots radiates large grating lobes. A spatial filter using baffles to suppress the grating lobes is described, suppressed. The effect of the baffles on the transverse slot impedance is analyzed for the case of baffles with infinite height     

A dual-band slot array technique

A technique is discussed for simultaneously operating a waveguide slot array in two different frequency bands to generate two independent radiation patterns. The technique permits frequency separations which differ by a factor up to about 2:1. The technique utilizes the propagation of orthogonal, dominant modes in a rectangular waveguide, each mode operating in a different frequency band. Several linear arrays were investigated atXandK_{mu}band; satisfactory array performance demonstrated the feasibility of the technique.     

Classical axis-displaced dual-reflector antennas for omnidirectional coverage

The aim of this work is to discuss the synthesis and performance of classical dual-reflector antennas suited for an omnidirectional coverage. The reflector arrangements are axially symmetric with surfaces of revolution generated by axis-displaced conic sections, established from geometrical-optics (GO) standpoints to achieve omnidirectional radiation characteristics. Closed-form equations are derived for the design of all possible reflector configurations. The vector GO aperture field is also obtained, yielding an approximate analysis by the aperture method. Some pertinent geometrical characteristics and efficiency curves are then presented and discussed for several antenna configurations fed by transverse electromagnetic coaxial horns (for vertical polarization). A practical antenna design is conducted and analyzed by the method-of-moments technique, demonstrating the accuracy of the efficiency analysis yield by the aperture method for moderately large antenna apertures.     

Secondary-emission amplification at microwave frequencies

Two types of photomultipliers exhibiting flat base-band response to ∼4 Gc/s are described. One photomultiplier employs crossed electric and magnetic fields, the other is purely electrostatic. At present both devices consist of eight Cu-Be secondary emission stages and an internally situated, opaque-backed S-1 photocathode. Current gain exceeds 10⁵, and the transit time dispersion is less than7 times 10^{-11}s. Frequency response measurements have used heterodyning between the modes of the Zeeman-split Doppler profiles of a 6328 Å He-Ne laser, and also shot noise in the current from a steadily illuminated photocathode as sources of microwave modulated currents. Transient response measurements have been made using sub-nanosecond light pulses from phase-locked He-Ne and argon ion lasers, the results being consistent with the measured frequency response. A calculation of the frequency response to be expected fromnidentical stages of secondary emission when only the secondary electron emission velocities contribute to electron transit time differences, as is true of the geometries used in the experiments, gives results in agreement with experiment, assuming a value of 3 eV for the most probable secondary electron emission energy from BeO. This value is consistent with direct observations by others.     

一种水平全向平面偶极子阵列天线

基于偶极子组阵结构,设计了一种具有水平全向辐射方向图和水平极化特性的平面天线。该天线由3只偶极子天线组成,每只振子弯折30°并上下交错印刷在PCB板的表面上,构成正六边形环,环的直径为0.45λ0(λ0为中心频率处的自由空间波长)。3只偶极子天线均采用SMA接头直接顶馈,从而省略了偶极子天线的馈电巴伦。通过优化偶极子天线振子长度和间距等结构参数,以及控制馈电相位,实现水平全向辐射。设计和加工制作了一只工作频率为2.45 GHz的天线样品,测试与仿真结果吻合良好,其|S11|≤10 dB的相对阻抗带宽为12.94%(2.367~2.684 GHz),水平全向增益约为1.42 dBi,不圆度小于±0.7 dB。     

A conformal cylindrical microstrip array for producing omnidirectional radiation pattern

Radiation patterns of rectangular microstrip patches arranged circumferentially on a circular cylinder have been computed. Both the axial patches and circumferential patches have been used. It has been found that the number of circumferential patches required for a given ripple in gain pattern is considerably less, thus simplifying the feed network. Comparison with experimental measurements shows good agreement.     

The epHEMT gate at microwave frequencies

This paper examines the high-frequency behavior of the enhancement-mode pseudomorphic high electron-mobility transistor (epHEMT) gate. During this study, no bias was applied between the drain and source. Rather, the gate was forward biased with either the drain, source, or channel (drain and source connected together) grounded. While applying positive voltage V/sub g/ to the gate, one-port S-parameters were measured from 0.1 to 10 GHz and then converted to Z-parameters. Plotting the real part R of the impedance reveals two sharp peaks. The first peak occurs near the device threshold voltage for conduction in the InGaAs well. A second peak occurs at higher voltages where conduction begins to occur in the surface AlGaAs layer. An equivalent-circuit model is proposed to account for the epHEMT gate's high-frequency behavior and the proposed model is shown to be in good agreement with the experimental data.     

Cable shielding measurements at microwave frequencies

A matched triaxial device is developed and constructed to measure the transfer impedance of braided coaxial cables at microwave frequencies. Full-design principles of the device have been developed and given in detail in the paper. The device is particularly suited for shielding measurements at frequencies up to 3.5 GHz, for which no comparable technique exists. The performance of the device is fully evaluated both theoretically and by measurements. The accuracy of the device is studied by comparing the results against those obtained from the low-frequency International Electrotechnique Committee triple-coaxial apparatus, and using well-known theoretical models.     

The silicon cryosar at microwave frequencies

Microwave and low-frequency measurements are reported onn^{+}-v-n^{+}silicon cryosars fabricated with narrow intrinsic region widths. The low-frequency measurements includeV-Idata with and without incident microwave power. The electric field required to cause impact ionization of the donors was found to be greater than 10⁵V/m. The microwave measurements include a demonstration of mixing, harmonic mixing, and harmonic generation. Small-signal impedance measurements as a function of bias are reported at 1.33 and 3.05 GHz, and the diode noise temperature was measured to be 16 000 or 3000 K depending on bias polarity. Mobile electron lifetime is 10^-10s.     

`Source-pull? technique at microwave frequencies

A technique to produce a variable and controlled source impedance is described in order to evaluate the performance of microwave devices under source impedance variable conditions. The procedure for a systematic error correction is also presented.     

Active load technique for load-pull characterisation at microwave frequencies

The letter describes a load-pulling method that allows an extension of the two-signal approach to applications where the output frequency spectrum is different from the input one, as in the case of power devices operating with multicarrier input signals.     

Measurement of surface impedance at microwave frequencies

A technique for measuring the surface impedance of a plane stratified media at microwave frequencies is given, and preliminary tests are made for a variety of situations ranging from capacitive impedances to surfaces, which display a purely inductive reactance. The technique utilises a modulated scatterer to measure the elliptically polarised electric field of a TM wave propagation over the surface.     

An omnidirectional microwave antenna for use on spacecraft

The qualitative theory, design, and development of a parallel-plate waveguide-fed antenna, suitable for flush-mounted broad-band spacecraft applications, are presented. The antenna makes use of wedge-like metal posts placed uniformly about the periphery of the feed plates to provide both structural strength and practical interconnection routes for cables without disrupting the antenna impedance and patterns. Measurements taken on the antenna, which is mounted on spheroids up to 50 wavelengths in circumference, are presented; equatorial patterns are omnidirectional withinpm 0.25dB, and polar patterns have beam widths similar to a half-wave dipole.     

Measurement of ferrite parameters at microwave frequencies

A method for determining, at microwave or millimetre-wave frequencies, the relative permittivity and the saturation magnetisation of a ferrite is described. The method is based on the measurement of the guide wavelength in a rectangular guide completely filled with the ferrite and magnetised transversely. Tentative results are presented.     

Continuous-time integrated FIR filters at microwave frequencies

We discuss adaptive integrated finite-impulse response (FIR) filters operating in the continuous time domain. These filters become attractive to implement at microwave frequencies. An important topological property of the traveling wave FIR filter is presented, and its advantages when used as an adaptive equalizer are pointed out. Design considerations and modeling aspects of compact on-chip delay lines are given. Simulation results for an adaptive equalizer operating at a data rate of 10 Gb/s are presented.     

Inverse black body radiation at microwave frequencies

The inverse black body radiation, which is the problem of determining the area-temperature distribution of a black body from its measured radiated power spectrum, was recently solved by Bojarski. His solution employs the inverse Laplace transform to reconstruct the area-coldness distribution from an integral equation based on Planck's law. Our solution is similar but restricted to microwave frequencies and employs the Rayleigh-Jeans approximation to yield the corresponding portion of the area-coldness distribution using the inverse Laplace transform but avoiding the iterative procedure of Bojarski.