C. Di Nallo

The theory of surface-wave and space-wave leaky-mode excitation on microstrip lines

This paper discusses the excitation and physical validity of both surface-wave and space-wave leaky modes on microstrip lines. This is done by analyzing the discrete modal spectrum excited by a realistic source on or near an infinite microstrip line. A semi-analytical three-dimensional (3-D) Greens function is used for this purpose, which provides the current excited on the conducting strip due to the source. The 3-D Greens function is in the form of a spectral integration (inverse Fourier transform) in the longitudinal wavenumber plane. The poles of the integrand directly determine the excitation amplitudes of the modes on the structure that are launched by the source. The integrand also has different types of branch points, and the location of the poles on the various Riemann sheets is used to determine the physical significance of the leaky modes. Although the theory presented here is illustrated for a microstrip line, the conclusions apply in general to open printed-circuit structures.

A full-wave numerical approach for modal analysis of 1-D periodic microstrip structures

In this paper, a full-wave numerical approach for the analysis and design of one-dimensional (1-D) printed periodic structures is presented. Electromagnetic-bandgap structures and leaky-wave antennas are important special cases of structures that can be analyzed. The proposed technique is based on a mixed-potential integral equation in a unit-cell environment solved by the method of moments in the spatial domain through a triangular Delaunay mesh. The 1-D periodic vector and scalar Greens functions are derived in the spectral domain and an efficient sum of spectral integrals is carried out to obtain the spatial-domain quantities. An appropriate choice of the spectral integration path is used in order to consider leakage effects. The method developed here can thus analyze both bound and leaky modes on printed structures that have an arbitrary metallization within the unit cell.

Multimode dielectric resonator antenna of very high permittivity

In this paper a design strategy to obtain low loss, small size dielectric antennas, by using very high dielectric constant materials is described. It is shown how by properly selecting the resonator shape and combining different resonant modes it is possible to design dielectric resonator antennas (DRA) with compact size and wide frequency coverage even at the cellular frequencies. Simple formulas are presented to illustrate the design procedure and allow a quick dimensioning of the antenna. Furthermore the paper describes techniques to enhance the response provided by the natural resonance frequencies of DRA, by adding parasitically coupled conducting strips, to enable multi-band operation. Results and examples are reported, showing the effectiveness of the proposed technique.

Attractive features of leaky-wave antennas based on ferrite-loaded open waveguides

A complete investigation is presented as regards the performances of a class of leaky-wave antennas which are electronically scannable by varying either frequency or magnetization. The basic topology is derivable from that one of a laterally-open rectangular guide, loaded with a transversely-magnetized ferrite rod. It is seen that the characterization of the radiation properties may suitably be achieved by considering a leaky-wave approach also for this kind of structure. A parametric analysis is then developed, based on an innovative transverse resonance technique, expressly extended to nonreciprocal structures. The phase and leakage constants are derived as functions of the involved physical quantities, thus identifying immediately those conditions that may really be useful in the applications. The relevant radiation patterns are then computed with both rigorous and approximate techniques. It is finally shown that, even with simple isotropic sources, such a topology can present various interesting distinctive features (structural simplicity, wide forward/backward angular beam scannings, etc.).

Properties of NRD-guide and H-guide higher-order modes: physical and nonphysical ranges

New interesting modal properties are presented for the waveguiding structure constituted by a rectangular-section dielectric rod sandwiched between parallel conducting plates, which can represent either a non-radiative dielectric (NRD) guide or an H guide. A rigorous quantitative analysis of the dispersion properties indicates that higher-order modes can show different anomalous behaviors, as geometrical and electromagnetic parameters vary. A discussion of the physical nature of the waves related to complex wavenumbers allows us to illuminate the performance differences between NRD and H guides, as regards certain previously unexplored leakage effects.<<ETX>>

Wideband antenna using non-foster loading elements

This paper proposes a different approach to non-Foster or active matching. An antenna structure with two ports is considered. One port is used to couple the signal, while the other one is connected to a non-Foster network. The advantage of this configuration is that the antenna can be designed to have real input impedance, as seen from the feeding port, fairly constant across a very broad band when the active load is applied. The input reactance compensation is essentially performed by the non-Foster network, typically behaving as a negative inductor.

The folded inverted conformal antenna (FICA) for multi-band cellular phones

A multi-band internal antenna for mobile phones is realized by means of an elongated flat conductor featuring a closed slot, a ground leg, and a feed leg. A benchmark on a Motorola T192 handset is employed to illustrate the operation of this structure - called folded inverted conformal antenna (FICA) - showing that it provides significantly more radiating bandwidth that a conventional dual band PIFA under the same operating conditions. Because of its favorable performance, FICA is employed in several Motorola handsets in the consumer market.

Small Wideband Antenna with non-Foster Loading Elements

The paper demonstrates a new way of overcoming the fundamental limit imposed on the fractional bandwidth of small antennas in relation to antenna volume by means of using a non-Foster (active) network. Unlike the techniques known in literature that use non-Foster matching circuits to broaden the operating bandwidth of electrically small antennas, the present approach utilizes the specific antenna structure with an additional port which is loaded by a non-Foster reactive element. The combination of properties of the specific two port antenna structures and the reactive loads produces an extremely wideband response not achievable with passive antennas of the same volume.

The enhanced bandwidth folded inverted conformal antenna (EB FICA) for mufti-band cellular handsets

An internal multi-band antenna for mobile phones featuring wide fractional bandwidth is presented. The antenna is realized by a flat conformal conductor above the ground plane, featuring a feed and ground connections to the PCB. A slot is cut in the flat conductor, which is open only in between the ground and feeding connections of the flat conductor, thus forming a slit. This structure is called enhanced bandwidth folded inverted conformal antenna (EB-FICA), with reference to its precursor FICA (Di Nallo and Faraone, 2005). The EB-FICA can be designed to be penta-band, covering the four GSM bands and the UMTS Rx band, and has been adopted in several Motorola products.

Effect of amplitude modulation of the CDMA IS-95 signal on SAR measurements

Miniature probes employed for specific absorption rate (SAR) measurements are typically calibrated using a sinusoidal waveform (SW), even though they may be employed to measure a wide variety of communication signals with complex waveforms. This paper shows that the compression produced by the nonlinear response of the probe versus SAR, due to its diode detector, may introduce a significant overestimation of the SAR produced by CDMA IS-95 waveforms when the diode detector operates well into the compression region. This finding is demonstrated theoretically, verified numerically and experimentally, and physically interpreted. The effect is typically small and may be neglected in many practical circumstances involving low-power RF energy emitters, such as mobile phones or two-way dispatch radios