Search

Dielectric rod waveguide antennas of rectangular cross section have a number of advantages over conventional waveguide and horn antennas as an antenna array element. Dielectric rod waveguide antennas have relatively low cost, low losses, a broadband input match and a high packing potential. Additionally the radiation pattern of such antennas is almost frequency independent. In this paper the suitability of Sapphire rod waveguides for an antenna array is studied with simulations and prototype measurements at W band. Strong mutual coupling is observed when the elements are close to each other. [ABSTRACT FROM AUTHOR]

A hologram based compact antenna test range (CATR) is designed, constructed, and used to test a 15-m antenna at 650 GHz The CATR is based on a 3 16 m diameter hologram as the collimating element. So far, this is the highest frequency at which any CATR has been used for antenna tests. The quiet zone is measured and optimized before the antenna tests. The measured antenna pattern results at 650 GHz are analyzed and compared to the simulated patterns. Feed scanning antenna pattern comparison technique is used to correct the antenna pattern. These tests show the hologram CATR to be promising for antenna measurements up to 650 GHz. [ABSTRACT FROM AUTHOR]

In this paper, propagation properties of a parallel-plate waveguide with tunable artificial impedance surfaces as sidewalls are studied both analytically and numerically. The impedance surfaces comprise an array of patches over a dielectric slab with embedded metallic vias. The tunability of surfaces is achieved with varactors. Simple design equations for tunable artificial impedance surfaces, as well as dispersion equations for the TE and TM modes are presented. The propagation properties are studied in three different regimes: multimode waveguide, single-mode waveguide, and below-cutoff waveguide. The analytical results are verified with numerical simulations. [ABSTRACT FROM AUTHOR]

Simple analytical formulas are introduced for the grid impedance of electrically dense arrays of square patches and for the surface impedance of high-impedance surfaces based on the dense arrays of metal strips or square patches over ground planes. Emphasis is on the oblique-incidence excitation. The approach is based on the known analytical models for strip grids combined with the approximate Babinet principle for planar grids located at a dielectric interface. Analytical expressions for the surface impedance and reflection coefficient resulting from our analysis are thoroughly verified by full-wave simulations and compared with available data in open literature for particular cases. The results can be used in the design of various antennas and microwave or millimeter wave devices which use artificial impedance surfaces and artificial magnetic conductors (reflect-array antennas, tunable phase shifters, etc.), as well as for the derivation of accurate higher-order impedance boundary conditions for artificial (high-) impedance surfaces. As an example, the propagation properties of surface waves along the high-impedance surfaces are studied. [ABSTRACT FROM AUTHOR]

Transmittance and monostatic reflectivity of different radar absorbing materials at 650 GHz are presented. The reflectivity was measured in plane-wave conditions in a radar cross-section (RCS) range with vertical polarization. The lowest reflectivity level (-70 dB) was achieved with commercial absorbers TK THz RAM and Firam-500 with oblique incidence angles. Floor carpets were also studied, and the reflectivity level of those was found to be sufficiently low (from -50 to -60 dB) for use in antenna test ranges. Results agree with earlier studies and indicate the applicability of the RCS method in reflectivity measurements also at 650 GHz. [ABSTRACT FROM AUTHOR]

We present the design, simulations, fabrication, and measurements of a W-band waveguide impedance tuner. The design consists of a WR-10 waveguide with two E-plane arms for tunable dielectric-based backshorts. The impedance tuner is fabricated using a simple split-block technique and is easily scalable to submillimeter wavelengths. Our design shows an excellent input impedance range, tuning accuracy, repeatability, and a high attainable maximum reflection coefficient over the frequency band of 75–110 GHz. Our tuner applies dielectric-based backshorts, which provide a tuning accuracy better than that of other waveguide backshorts. [ABSTRACT FROM AUTHOR]

An antenna pattern correction technique, is presented that is based on an adaptive array algorithm. In the method, the antenna pattern of the antenna under test (AUT) is measured several times at different positions in the quiet-zone. The corrected antenna pattern is obtained by taking a weighted average of the measured patterns. An array synthesis algorithm is employed for obtaining the averaging weights at each rotation angle of the AUT. The weights are adapted specifically for a given AUT. The adaptive array correction technique is demonstrated in a hologram based compact antenna test range (CATR) at 310 GHz with both a synthetic antenna and a physical test antenna. For verification, the accuracy provided by the adaptive array correction technique is compared to that provided by uniform weighting. [ABSTRACT FROM AUTHOR]

The measurement accuracy of a compact antenna test range (CATR) is limited by the level of spurious signals. At millimeter and submillimeter wavelengths the spurious signals are caused by range reflections and deformations of the range collimating element. Several antenna pattern and range evaluation techniques that can be used to mitigate the effects of these nonidealities have been published. At submillimeter wavelengths these techniques are typically time consuming or they are not able to correct the antenna pattern close to the main beam. The frequency shift technique does not have these limitations in a hologram based CATR. In this paper, the applicability of the frequency shift technique is analytically studied for a hologram based CATR. The technique is verified by measurements. The accuracy provided by the frequency shift technique is compared to that of the antenna pattern comparison (APC) technique. [ABSTRACT FROM AUTHOR]

This paper presents monostatic reflectivity measurements of radar absorbing materials at 310 GHz in a phase-hologram-based compact range. The radar cross-section method was used and the backscattered reflection was measured with horizontal and vertical polarizations in plane-wave conditions. Transmission was also studied. The reflectivity was measured over an incidence angle of 0°-.45°. The reflectivity of Thomas Keating Terahertz RAM at normal incidence was found to be -56 dB-the smallest of the studied materials. The reflectivity of carpet material measured was also below -40 dB and it was found to be suitable for use as an absorber. The results are in line with those available from previous studies of reflectivity and complement them with new materials, frequency, and angle information. [ABSTRACT FROM AUTHOR]

A compact radar cross section (RCS) test range based on a phase hologram has been developed for scale-model measurements. The phase hologram converts the feed-horn radiation to a plane wave needed for RCS determination. The measurements are performed at 310 GHz using continuous-wave operation. A monostatic configuration is realized using a dielectric slab as a directional coupler. The main advantage of a scale-model RCS range is that the dimensions of radar targets are scaled down in proportion to the wavelength. Therefore, RCS data of originally large objects can be measured indoors in a controlled environment. Test objects such as metal cylinders and simplified targets have been measured. The feasibility of the phase-hologram RCS range has been verified. The operation and measurement results of the monostatic measurement range are reported here. A comparison with simulated results is also included [ABSTRACT FROM PUBLISHER]

Manufacturing of large computer-generated submillimeter wave holograms with high pattern accuracy has been the main challenge in the development of hologram based compact antenna test ranges (CATRs). Illumination of the hologram with a shaped beam produced by a dual reflector feed system (DRFS) simplifies the hologram manufacturing by eliminating the narrow slots in the hologram pattern. In this paper, the design of a shaped dual reflector feed for a hologram CATR is described. The simulated and measured illumination field amplitude and phase at 310 GHz are presented and compared to the desired hologram illumination. The measured amplitude is within ±0.5 dB from the design objective in the most significant central region of the illuminating beam. Measurement results of the quiet-zone field of a demonstration CATR illuminated by the DRFS are presented and compared to the measured quiet-zone amplitude and phase of a hologram fed directly with a corrugated horn. The quiet-zone diameters of the both holograms are over 0.25 meters and the measured root mean squared (rms) amplitude and phase ripples are below ±0.4 dB and ±5°, respectively. Further improvements to the hologram CATR, such as greater tolerance to manufacturing errors, are also discussed. [ABSTRACT FROM AUTHOR]

Computer-generated holograms can be used as collimating elements in compact antenna test ranges (CATR5). Recently, a 1.5 m parabolic antenna, the ADMIRALS representative test object (RTO), was tested at 322 GHz using a hologram-based CATR that was built specifically for these tests. The construction of the compact range is discussed in this paper. A 3 m hologram was used to realize a 1.8 m diameter quiet zone. The measured quiet-zone field amplitude and phase and the measured H-plane radiation pattern cut of the representative test object are presented. The measured -3 dB beam width of the antenna was 0.0500 in the H plane. [ABSTRACT FROM AUTHOR]

A novel differential method based on the open resonator is developed for permittivity measurement of thin dielectric films on optically dense substrates at millimeter wavelengths. The method is based on measurement of resonant frequency shifts due to appearance of a thin film on upper and lower sides of the substrate. The advantages of the method are that there is no need to know the geometry of the open resonator nor the thicknesses of the film and substrate, though one has to measure separately dielectric properties of the substrate. [ABSTRACT FROM AUTHOR]

The measurement accuracy of a compact antenna test range (CATR) depends on the level of spurious signals. To improve the measurement accuracy, several error compensation methods have been developed, but most of them are not feasible at submillimeter wavelengths. This paper introduces an error compensation technique for compact antenna test ranges, which is especially suitable at submillimeter wavelengths. The method is based on antenna pattern comparison (APC). In the original APC technique the antenna pattern is recorded several times at different positions of the quiet-zone field, and the corrected pattern is obtained by averaging the measured patterns. In the proposed method, the lightweight transmitter is moved instead of moving the heavy combination of the antenna under test (AUT) and the rotation stage. The feasibility of the method is studied and the method is tested with measurements in a hologram based compact antenna test range at 310 GHz. The accuracy provided by the proposed method is compared to the accuracy provided by the conventional APC. The accuracies provided by both methods are practically equal. [ABSTRACT FROM AUTHOR]

A hologram-based compact antenna test range (CATR) is being developed to overcome challenges met in antenna testing at submillimeter wavelengths. For the first time, this type of CATR has been built for testing of a large reflector antenna at submillimeter wavelengths. The CATR is based on a 3-m computer-generated hologram as the focusing element. This paper discusses the design and the construction of the CATR, and the verification of the CATR operation with quiet-zone tests done for the CATR prior to the antenna testing. Assembly of the CATR, testing of the 1.5-m reflector antenna at 322 GHz, and the disassembly were all done within two months in 2003. The quiet-zone field measurement results are analyzed in this paper. The CATR was concluded to be qualified for antenna testing. The antenna testing is described in a separate paper. [ABSTRACT FROM AUTHOR]

Hologram-based compact antenna test range (CATR) is a potential method for testing large antennas at submillimeter wavelengths. This paper describes testing of a 1.5-m single offset parabolic reflector antenna with a 3-m-diameter hologram-based CATR. This is the first time such a measurement is carried out at submillimeter wavelengths. The antenna tests were done in a CATR that was specifically designed and constructed for these tests. The measured radiation pattern at the frequency of 322 GHz is presented. The measured pattern corresponds reasonably well to the simulated pattern of the antenna. The effect of the quiet-zone field nonidealities on the measurement results and the reasons for the discrepancies in the measured antenna beam are discussed. [ABSTRACT FROM AUTHOR]

This paper studies the feasibility of a hologram-based compact antenna test range (CATR) for submillimeter-wave frequencies. In the CATR, a hologram is used as a collimating element to form a plane wave for antenna testing. The hologram is a computer-generated interference pattern etched on a thin metal-plated dielectric film. Two demonstration holograms of approximately 1 m in diameter were designed for 650 GHz, and they were manufactured on two different Mylar films. The holograms were illuminated with a horn, and the plane-wave field was probed at 644 GHz. The measured amplitude and phase ripples were 2 dB and 15° peak-to-peak for one of the holograms. A higher quiet-zone field quality can be achieved by increasing the manufacturing accuracy by further manufacturing tests. After this, the hologram-based CATR should have a potential for high-quality antenna tests at frequencies up to 650 GHz. [ABSTRACT FROM AUTHOR]

Passive intermodulation (PIM) distortion is a challenging problem in the design and manufacturing of base station antennas. Small nonlinearities, typically in junctions, may cause a distortion signal that interferes with the receiver even with a level of -155 dBc in a GSM900 system. The PIM level specification of an outdoor base station antenna is difficult to achieve and the sources of PIM generation are laborious to track down. In this paper, a near-field measurement method is presented to localize and investigate passive intermodulation sources in antennas and open transmission lines. The principle of the PIM near-field measurement is otherwise the same as in a common reactive near-field measurement, but instead of measuring the signal at the input frequency, the signal amplitude and phase at the PIM frequency of interest are acquired. The constructed measurement system is capable of measuring PIM signal levels down to -110 dBm with 2 × 43 dBm transmit power in the GSM900 frequency band. As demonstration measurements, PIM sources in a two-element base station antenna and in a microstrip line are localized. [ABSTRACT FROM AUTHOR]

A new coplanar waveguide (CPW)-to-rectangular waveguide transition is proposed for wide-band millimeter-wave applications. The transition has an in-line structure, which provides easy fabrication of the CPW circuit and waveguide block. An X-band (8.2-12.4 GHz) model has been designed and tested. Measurements of a back-to-back double transition have yielded a return loss of over 17 dB and an insertion loss of less than 05 dB over the full X-band. These results agree well with the simulated results obtained with a commercial electromagnetic structure simulator. In addition, this type of a transition has been designed and used for a local oscillator feed with a full F-band (90-140 GHz) coverage of a submillimeter-wave general-purpose harmonic mixer. [ABSTRACT FROM AUTHOR]

A passive intermodulation (PIM) near-field XY scanner for the GSM900 frequency band has been constructed to localize distortion sources in antennas and in other open structures. The equipment should be able to measure distortion levels down to -115 dBm with an input power of 2 × 20 W, since the noise floor of a GSM900 base station is typically around -110 dBm. The sensitivity is limited either by thermal noise or by residual intermodulation distortion, depending on the probe coupling. Various causes of residual intermodulation distortion in the passive intermodulation near-field measurement are considered and evaluated. Sensitivity measurements of the scanner have been carried out on two test devices. Sensitivities of -112 dBm and -110 dBm have been achieved with an electric and a magnetic field probe, respectively. [ABSTRACT FROM AUTHOR]

Millimeter and submillimeter wave receivers in scanning planar near-field test systems are commonly based on harmonic mixing and thus require at least one flexible microwave cable to be connected to them. The phase errors originated in these cables get multiplied and added to the phase of the final detected signal. A complete submillimeter setup with on-the-fly measurement of phase errors is presented. The novel phase error correction system is based on the use of a pilot signal to measure the phase errors caused by cable flexing. The measured phase error surface in the quiet-zone region of a 310 GHz compact antenna test range (CATR) based on a hologram is shown as an application example. The maximum measured phase error due to the cable within a 80 × 90 cm² scan area was 38°. [ABSTRACT FROM AUTHOR]

Presents an overview of microwaves activities and infrastructures in Europe. History of microwaves in each region; Association of microwave activities with research centers, laboratories and institutions, industry, education and national conferences; Reformation of university education in Italy.

Focuses on the designing of a cryogenic millimeter-wave ring filter for a space application. Compensation of the detuning of the center frequency caused by thermal deformations; Reference to the common use of ring filters based on the resonance properties of ring circuits; Application of the temperature-compensation mechanism.

Presents a study that described a planar antenna in which box horns are used as radiating elements. Purpose of the feed network; Experimental results; Conclusions.

Examines the modification of Marcatili's method for the calculation of rectangular dielectric rod waveguides for uniaxial anisotropic dielectric materials. Use of the averaging method; Solution of propagation constant for uniaxial anisotropic waveguides; Measurement of the wavelength.

A correction to the article "Simple and Accurate Analytical Model of Planar Grids and High-Impedance Surfaces Comprising Metal Strips or Patches," by Olli Luukkonen and colleagues is presented.