Designer's Notebook Research Articles

A Circularly Polarized Conical Horn with an Inserted Metallic Cone-Sphere [Antenna Designer's Notebook

The paper presents simulation-based investigations of a circularly polarized (CP) X-band conical horn with an inserted metallic cone-sphere. The performance of this horn is compared with that of dielectric-loaded and unloaded circularly polarized short horns. It emerges that in general, inserting a metallic cone-sphere improves the overall radiation performance of the unloaded circularly polarized horn better than dielectric loading.

Ideas for Antenna Deigner's Notebook [Antenna Designer's Notebook

Ideas for Antenna Deigner's Notebook [Antenna Designer's Notebook

Triple-Tuning Small Antennas for Increased Bandwidth [Antenna Designer's Notebook

A method for designing a lossless network to triple tune an electrically small antenna is presented. This approach is based jointly upon Wheeler's definition of the reflection coefficients at the edges of the band, and upon Fano's criterion defining the maximum possible bandwidth. Examples are given for a small top-loaded antenna operated at two center frequencies, 175.5 MHz and 300 MHz, with values of Q equal to 100 and 19, respectively.

Ideas for Antenna Deigner's Notebook [Antenna Designer's Notebook

Ideas for Antenna Deigner's Notebook [Antenna Designer's Notebook

Empirical Equations for the Resonant Frequencies of a Dual-Band Microstrip Loop Antenna [Antenna Designer's Notebook

Empirical formulas are presented for predicting the resonant frequencies of a coplanar-waveguide-fed dual-band microstrip loop antenna. The resonant frequencies predicted by the formulas compared with experiments with an average error of about 1.85%.

Broadband Approximation of Radiation Patterns for Doubly Curved Reflector Antennas [Antenna Designer's Notebook

Avery simple broadband approximation of the radiation patterns for shaped-beam reflector antennas with a primary feed (rectangular horn), producing cosine amplitude and uniform phase aperture distributions, is presented. Typical values, beamwidth changes, sidelobe levels, and aperture efficiencies are given for frequency changes up to approximately three times the operating frequency. A comparison of the approximated and measured patterns of doubly curved reflector antennas shows that the given approximation can be reliably used for analyses of pattern changes due to very broad frequency changes. This is very valuable for electromagnetic compatibility analyses, both from the electromagnetic interference and susceptibility points of view.

A Performance Comparison of a Ku-Band Conical Horn with an Inserted Cone-Sphere with Horns with an Integrated Dielectric Lens and Metamaterial Loading [Antenna Designer's Notebook

This article presents a comparative study based on measurements and simulations of a Ku-band conical horn with an inserted metallic cone-sphere with horns having an integrated dielectric lens and meta material loading. The results revealed that the performance of the horn with the cone-sphere was better than that of the metamaterial-loaded horn. The performance of the horn with the cone-sphere was comparable to that of the horn with the dielectric lens. In addition, the horn with the cone-sphere offered advantages of lower weight and cost in comparison to the other horns under consideration.

Experimental Rotary Transformers For Antenna Power Supplies and Control [Antenna Designer's Notebook

Rotary transformers can be effectively used for low-noise amplifier (LNA) or down-converter power supply and control signal transmission in scanning-antenna applications. Three air-core designs, utilizing a square wave at audio frequencies, using HCMOS logic and giving a 5 V/0.6 A dc power feed, are discussed. The constructions allow further installation of RF rotary joints or other coaxial hardware up to a diameter of 100 mm. They add about 30 to 80 mm to the overall height of the antenna, depending on application and requirements. Bearing replacement with such a transformer is also possible, if adequate tolerances are met and suitable coil-support materials are selected.

Estimation of Gain Enhancement Replacing PTFE by Air Substrate in a Microstrip Patch Antenna [Antenna Designer's Notebook

An easy estimation of the gain enhancement of a microstrip patch that occurs when a standard PTFE substrate is replaced by air is presented. The theory is verified for a wide range of antenna dimensions, using some measured and simulated data, indicating very close agreement amongst the data. This approach should be very handy and useful to a designer dealing with air-substrate microstrip antennas.

Design of Short Backfire Antennas [Antenna Designer's Notebook

The design proposed in this article is dedicated to short backfire antennas fed by a dipole or a crossed dipole. The studies were carried out with different types of short backfire antennas. The directivity of the antennas designed ranged between 12 and 20.5 dB, The presented design procedure may be very useful for the creation of high-efficiency and compact microwave antennas with various applications.

Design and Optimization of ESPAR Antennas via Impedance Measurements and a Genetic Algorithm [Antenna Designer's Notebook

A method for the design of electronically steerable passive array radiator (ESPAR) antennas is proposed herein, based on impedance-matrix measurements and a genetic algorithm. The proposed technique is best suited for cases where commercial elements are used as building blocks for ESPAR development, since in such cases the conventional numerically based techniques used in the literature may not be applicable. An emulated ESPAR design and respective results are presented. They demonstrate the applicability and performance of the proposed technique, as well as its consistency with results derived from a commercially available electromagnetic simulator.

Antenna Designer's Notebook

In his classic 1948 paper, Lan J. Chu presented the equivalent circuit for an electrically small antenna. This circuit quantified the relationship between the lower bound for the radiation Q of an electrically small antenna and its physical size relative to the wavelength. A recent article has highlighted the fact that Chu defined a lower bound for a hypothetical antenna. A key issue is how close can the Chu limit be approached, in practice? Chu's lower bound assumes that there is no stored energy inside a sphere that circumscribes the largest antenna dimension. Another recent article has extended Chu's work to include the internal stored energy, and provides new lower bounds for electrically small antennas. This paper presents a summary of the recent findings regarding this issue.

Design, optimization, and validation of a planar nine-element quasi-Yagi antenna array for X-band applications [antenna designer's notebook

A planar antenna array, based on nine identical quasi-Yagi elements, is presented in this paper. Contrary to conventional designs, the feeding network is composed of three-way power dividers, which are carefully designed in order to provide synchronized output signals over a wide frequency range. The use of spline-shaped microstrip lines suppresses coupling effects by parallel lines. Thus, signal distortions within the feeding network are minimized. Compared to conventional designs with eight elements, the additional antenna element will enhance the gain of the array, which is between 10.5 dBi and 13 dBi in the X band. The input return loss of the antenna array is below -15 dB over most parts of the relevant spectrum, with a total bandwidth of 45%. The planar antenna array is well suited as a radiating element in linear phased arrays for multifunction radars, including SAR and MTI. Additionally, the suitability of this antenna for phased-array applications is studied by an experimental setup consisting of five antenna plates.

Quasi-Analytical Synthesis of Moderate and Large Arrays Radiating Arbitrary "Star-Shaped" Footprint Patterns [Antenna Designer's Notebook

The proposed quasi-analytical method undertakes the shaping of a desired footprint as a composition of several phi-symmetric circular Taylor patterns exhibiting flat-topped beams. The final pattern is obtained after sampling the circular aperture that is obtained for rectangular-grid planar arrays. A triangular-shaped footprint and a footprint of continental Europe, radiated by planar arrays with moderate and large numbers of elements, show the technique's performance.

Antenna designer's notebook - Wheeler and Fano Impedance Matching

A recent series of articles in this Magazine's Antenna Designer's Notebook column highlighted Fano's fundamental work on the limitations of the impedance matching of arbitrary impedances and its application to antenna design. Lopez, using Harold Wheeler's methodology, constructed a closed-form solution to the nonlinear simultaneous equations of Fano. This article presents the Wheeler methodology that was the basis for this work, and is still invaluable in the understanding of optimum impedance matching.

Design, optimization, and validation of a planar nine-element Quasi-Yagi antenna array for X-band applications [Antenna designer's Notebook

A planar antenna array, based on nine identical quasi-Yagi elements, is presented in this paper. Contrary to conventional designs, the feeding network is composed of three-way power dividers, which are carefully designed in order to provide synchronized output signals over a wide frequency range. The use of spline-shaped microstrip lines suppresses coupling effects by parallel lines. Thus, signal distortions within the feeding network are minimized. Compared to conventional designs with eight elements, the additional antenna element will enhance the gain of the array, which is between 10.5 dBi and 13 dBi in the X band. The input return loss of the antenna array is below -15 dB over most parts of the relevant spectrum, with a total bandwidth of 45%. The planar antenna array is well suited as a radiating element in linear phased arrays for multifunction radars, including SAR and MTI. Additionally, the suitability of this antenna for phased-array applications is studied by an experimental setup consisting of five antenna plates.

Millimeter-wave printed antenna arrays for covering various sector widths - [Antenna Designer's Notebook

We introduce new millimeter-wave corner antenna arrays (MWCA) with eight axially placed printed dipoles fed by an integrated symphase network. The antenna array is placed between two metal plates that make the corner reflector. The antennas were simulated and realized in the frequency range about 26 GHz, which is popular for microwave communication networks. Three antennas, with different H-plane beamwidths (intended for azimuth) of 55', 1100, and 1800, were investigated, simulated, and realized. The bandwidths of all of the antennas were wider than 12%. The losses in all of the antennas were less than 1 dB. The agreement between simulated and measured results was very good. Millimeter-wave corner antenna arrays are low in cost and very simple to realize, and are also suitable for integration.

Performance Analysis of Small Tuned Trans mitti ng Loop Antennas Evaluated by Experiment and Simulation [Antenna Designer's Notebook

Frequency-swept input-impedance measurements to determine Q factors and field strengths for an electrically small tuned transmitting loop antenna in its operating environment have recently been made. These observational results are compared with numerical modeling by the computational electromagnetic code NEC-4D, since the validity of this code to simulate the performance of electrically small loops - and, in fact, even the fundamental characteristics of small loop antennas - has been questioned.

Optimization of Helical antennas [Antenna Designer's Notebook

Helical antennas have been known for more than half a century, but it seems that reliable design data for helical antennas do not exist in the open literature. This paper points out some inaccurate data about helical antennas, and presents a new set of data related to the optimum design of helical antennas. The antenna's performance is optimized by varying the antenna's geometrical parameters for narrowband and broadband designs. Based on these results, a set of diagrams is provided to enable simple but accurate design of helical antennas above an infinite ground plane. Finally, the results are experimentally verified.

Antenna Designer's Notebook - Receiving mutual impedance between two normal-mode helical antennas (NMHAs)

A new mutual impedance - the receiving mutual impedance - between two normal-mode helical antennas is defined, measured, and theoretically calculated. The variations of the receiving mutual impedance with antenna separation, with frequency, and with excitation source direction are critically investigated. An application of the receiving mutual impedance in direction finding demonstrates its more accurate description of the mutual coupling effect than that using the conventional mutual impedance