Search

Either passive calibration targets are expensive and complex to manufacture or their bistatic radar cross section (RCS) levels are significantly lower than the monostatic RCS levels of targets such as spheres, dihedral, and trihedral corner reflectors. In this paper the performance of an active calibration target with relative high bistatic RCS values is illustrated as a reference target for bistatic RCS measurements. The reference target is simple to manufacture, operates over a wide frequency range, and can be configured to calibrate all four polarizations (VV, HH, HV, and VH). Bistatic RCS measurements of canonical targets, performed in a controlled environment, are calibrated with the reference target and the results are compared to simulated results using FEKO.

The radar cross section (RCS) of passive calibration targets is relatively low, which leads to a commensurate increase in the uncertainty of the radar's calibration. To address this deficiency, an active radar calibration (ARC) target was developed, which was mounted on a small remote controlled tri-copter and used for radar calibration. Results are presented for this relatively small, light weight and cost effective airborne ARC, which is suitable for the calibration of a ground to air RCS measurement system. The static RCS characteristics of the airborne ARC target were measured in a compact range and compared to outdoor measurements with the ARC target mounted on the tri-copter. The airborne capability of the calibration target was used to reduce the effects of multi-path and clutter. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1041–1044, 2016

Conventional rectangular waveguides are commonly used for high power and other microwave and millimeter-wave applications. Their use at lower frequencies has been limited by their bulky nature. A new type of compact waveguide called a partial $H$ -plane waveguide has previously been proposed that has only one quarter of the cross-sectional area of a conventional waveguide. However, only limited information relating to the feeding of such waveguides is available. This paper presents two types of transitions to partial $H$ -plane waveguides from the coaxial and microstrip transmission mediums. Additionally, in the coaxial case, the transition is end-launched to offer collinear properties. The development of both transitions is discussed and optimized designs presented with simulated and measured results over $H$ -band (3.95–5.85 GHz).

An approach where polar curves are used to miniaturize hybrid couplers is presented. The design of such couplers can be done with the optimization of a few parameters using full-wave analysis software. The results show similar or better electrical performance for a rat-race and branch-line coupler with, respectively, a 75 and 50% size reduction. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2637–2640, 2015

Ultra-wideband (UWB) communications technology increasingly plays an important role in modern communications systems. The complex antenna transfer function (CATF) of a UWB antenna provides valuable information that can be used for better UWB channel and communication system designs. Currently, only the two-antenna and three-antenna measurement techniques are used to measure the transfer functions and impulse responses of UWB antennas. In this paper, a modified version of the gain-transfer method is presented to enable the characterization of UWB antennas using a compact antenna test range facility (CATR). A double-ridged guide horn (DRGH) antenna was used as a UWB transfer-standard, and the complex antenna transfer function of the transfer-standard was determined a priori using full-wave simulations. The gain-transfer method to measure the complex antenna transfer function of UWB antennas in a compact antenna test range was illustrated with two test cases. In the first test case, the measured complex antenna transfer function of an ETS-Lindgren double-ridged guide horn antenna was verified with numerical data from a FEKO model of the antenna. The second case compared the complex antenna transfer function of a UWB circular disc monopole antenna measured in a compact antenna test range to measured data using two identical antennas in a two-antenna measurement setup.

The analysis and design of an omnidirectional antenna that functions over a very broad frequency band is presented. Design guidelines for this antenna have been derived using electromagnetic analysis software. Measured results of a prototype developed according to these guidelines are presented. These results are compared to simulation results to illustrate the validity of the model used to derive the empirical design guidelines. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1352–1356, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25990

A double-dipole antenna design is proposed for wireless local area network (WLAN) applications. Two parallel dipoles are used to facilitate operation in both the standard WLAN frequency bands (IEEE 802.11b and IEEE 802.11a) simultaneously. The lower band dipole is rhombus shaped and radiates above a planar ground plane, whereas radiation from the rectangular higher band dipole is directed through the use of a passive director. The antenna is characterized in terms of impedance bandwidth, gain and radiation patterns through simulations and measurements. The design addresses the need for dual-band operation, whereas delivering directional radiation patterns with adequate gain, low cross-polarization, and good front-to-back ratio. The 2.4/5 GHz WLAN bands are covered with an impedance bandwidth of 17.8 and 26.4%, respectively, for a VSWR better than 2:1. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2034–2038, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24540

An extended reciprocity-based formulation for finding mutual admittance between coplanar waveguide fed slots on conductor-backed two-layer substrates was presented. The formulation updates the field distribution in both slots iteratively to account for coupling interaction between slots. This is especially relevant for cases of high mutual coupling. The results agree well with moment method-based calculations. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 91–94, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24012

In this study, it is shown how dual-band performance can be achieved from a single coplanar-waveguide-fed slot by using an impedance matching design approach. The coplanar-waveguide-fed slot is connected to a high-impedance coplanar-waveguide transmission line stub terminated with a capacitor. The two elements (slot and terminated stub) forming the antenna can be designed such that the series slot impedance added to the input impedance of the terminated stub result in two distinct resonances at the desired center frequencies for a dual-band application. A dual-band 2.4/5.2 GHz antenna is designed, and simulations are validated by the measured reflection coefficient and radiation pattern results. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2031–2034, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23565

The self-impedance and radiation properties of a first-resonance CPW-fed slot are characterized for possible use as an array element. It is shown that an interdigital capacitor in the center feed line of the CPW allows excellent control over the resonant resistance of the slot, and allows one to realize a wide range of impedances. Simulations are validated by measured results. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1523–1527, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23411

Improvements proposed over the years in the edge-diffraction model for a pyramidal-horn antenna have been extended to include the three-dimensional nature of the pyramidal horn in evaluating the edge-diffraction fields. The theoretical model was compared with measured results, measured over a number of years at an international standards laboratory for frequencies ranging from 2.45 GHz to 18 GHz, with measurement uncertainties between /spl plusmn/0.04 dB and /spl plusmn/0.1 dB.

Radiation efficiency and impedance bandwidth of optimally matched conductor-backed coplanar waveguide-fed slot dipoles on two-layer substrates are investigated as a function of bottom substrate layer height. It is demonstrated that low radiation efficiency due to parasitic parallel-plate modes may be notably improved through increased height of the bottom layer at the cost of decreasing bandwidth. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 138–141, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10396

A synthesis method is modified to synthesize patterns with multiple nulls in an otherwise omnidirectional pattern for cylindrical microstrip patch arrays. The directive radiation pattern of a cylindrical microstrip patch is incorporated into the synthesis procedure. The effect of the number of array elements and interelement spacing is investigated. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 32: 442–446, 2002.

A number of papers have been published on the prediction of backscatter from engine-inlet-type structures. Measured data used to verify these predictions mostly consists of backscattered data from canonical structures, e.g., cylindrical waveguide cavities. In this paper, measured backscattered data for an unmanned aerial vehicle-type engine-inlet system is presented. The effects of the application of radar-absorbing materials to the engine-inlet system on the contribution to the RCS is discussed, and data measured in a compact-range facility are presented.

Compact-range radar backscatter measurements are taken of aircraft scale models. In addition, computer software is used to predict the RCS of the aircraft. Synthetic down-range profiles formed from the two sources of backscatter data are compared and visualized in an innovative manner. Similar discrimination rates between the two aircraft are obtained on data from both sources. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 17: 207–213, 1998.

The effect of back-plane distance on the mutual admittance between twin coplanar waveguide (CPW)-fed slots on conductor-backed two-layer substrates with an air bottom layer was investigated. Distances of λo/6 and λo/4 yielded significantly increased mutual coupling over the case of no back plane. Measurements supporting the numerical results are presented. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 407–409, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21184

The design and radiation characteristics of a wideband quarter-wave patch with a single-layer capacitive feed are presented. The E-plane radiation pattern of the antenna is shown to be very dependent on the size of the ground plane, and the results for two extreme cases are obtained in order to illustrate this effect. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 225–227, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20777

A technique to estimate the frequency dependence of electromagnetic scattering centers is proposed. The technique employs a superresolution algorithm to estimate poles corresponding to the various scattering centers contributing to the total backscattered field. A relationship between the amplitudes of the estimated poles and the frequency dependence of the scatterers is derived. The technique is applied to estimate the frequency dependence of simulated and measured backscattered field data. © 1995 John Wiley & Sons, Inc.

In this article TLS-ESPRIT [1] will be used to generate two-dimensional high-resolution microwave images. To enable the utilization of the 1D algorithm, a two-dimensional data matrix is decoupled into two one-dimensional sequences by forming an enhanced data matrix [2]. Pairing of the two 1D estimates is also addressed. To demonstrate the performance of the 2D algorithm, a microwave image was generated for a target measured in a compact range. © 1995 John Wiley & Sons. Inc.

The high computational load associated with multidimensional high-resolution algorithms is overcome by using only 1D LP techniques. The 3D backscattered field is approximated by three 1D AR models that are solved in succession for the down-range, horizontal cross-range, and vertical cross-range positions of the scattering centers of a target.

Simulated and measured results of a diplexing feed network for a wideband dual-frequency stacked microstrip patch antenna are presented. The microstrip feed network is easy to design and consists of a T-junction and a single decoupling resonator for each frequency band. The return loss in each of the frequency bands is better than 10 dB, over a better than 10% bandwidth. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 100–102, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10686