Bryan D. Raines

Design of Frequency Reconfigurable Antennas Using the Theory of Network Characteristic Modes

This paper demonstrates a design procedure for frequency tunable reconfigurable antennas based on the application of reactive loads. Unlike other design procedures, antennas of arbitrary geometry can be tuned utilizing the proposed design framework. The design technique utilizes the theory of network characteristic modes to systematically compute reactive load values required to resonate any antenna at many frequency points in a wide frequency range. For simplicity, a 1.2 m dipole antenna is used to demonstrate the design procedure by tuning it at four loading ports along the antenna body. Both simulations and measurements demonstrate wide frequency tunability characteristics of the dipole input impedance (tunability range wider than 1:4) while preserving the radiation pattern and polarization at seven different frequency states. Lastly, a loaded PIFA is briefly examined as a more complex application of the procedure.

Wideband Characteristic Mode Tracking

A method is proposed by which a large number of characteristic modes of an arbitrary structure are tracked over a very wide frequency range; it is necessary for any serious wideband modal analysis of complex structures. The method can track a large number of modes using the modal eigenvectors from a generalized eigenvalue problem parameterized by frequency and has been successfully applied to over one hundred antenna geometries. The method is detailed and applied to two distinct geometries and the results discussed.

Application of Characteristic Modes and Non-Foster Multiport Loading to the Design of Broadband Antennas

A conceptual framework is proposed to systematically design antennas with broadband impedance and pattern characteristics using multiple reactive loads. Antennas of arbitrary geometry can have their bandwidths expanded using this technique. The technique is applied to a narrow band thin wire dipole antenna to demonstrate its main features. It is shown that the loaded antenna resonates a desired current over a wide frequency band. The loads are shown to require non-Foster elements when realized. Simulations demonstrate the broadband characteristics of both the dipole input impedance and radiation pattern.

Multiport Reactive Loading Matching Technique for Wide Band Antenna Applications Using the Theory of Characteristic Modes

A systematic framework is presented for designing an antenna with arbitrary shape and expanding its input impedance and pattern bandwidths using reactive loading. This method, unlike other design procedures, allows us to control the current distribution over the antenna structure with potentially fine granularity. This technique is applied to wire and microstrip antennas and it is shown to achieve a very good impedance and radiation pattern performance over the desired band. The loads are combination of Foster and non-Foster elements, which are generally required to obtain such dramatically improved performance.

Design and analysis of a helical spherical antenna using the theory of characteristic modes

Electrically small dipole antennas with ka less than 0.5 exhibit low radiation resistance, high capacitive reactance and high Q factor which is inversely proportional to antenna bandwidth. Here, the k is the free space wave number and a is the radius of an imaginary sphere which circumscribes the whole antenna. Spherical dipole antennas potently have higher effective volume if compared to other small antennas with maximum dimension equal to a. The higher the effective volume the lower the Q if proper feeding is used. Characteristic mode theory, as formulated in (Harrington and Mautz, 1971), will be used to analyze the input impedance and currents of a one-turn four-arm spherical antenna to improve the antennapsilas broadband behavior.

Antenna design and analysis using characteristic modes

Characteristic mode theory as formulated in the works of Garbacz and Turpin (1971) and Harrington and Mautz (1971), has been used in a variety of applications, including radiation and scattering analysis and pattern synthesis. In this work, the theory of characteristic modes was used to analyze the input impedance and currents of a two-arm spherical antenna. Suggestions were given on improving broadband behavior of an antenna based on the analysis.

Characteristic mode-based design and analysis of an electrically small planar spiral antenna with omnidirectional pattern

The antenna under consideration is a five-turn Archimedean rectangular two-arm wire spiral antenna, which is 46 x 15.7cm in size is presented in this paper. It is placed in the x-y plane. There are two ports (one per arm) located at the center. Normally, a two-arm spiral antenna cannot practically radiate spiral mode 2, as it requires the two-ports at the center to be excited in phase (i.e. an unbalanced feed), but it can be simulated using a method of moments code (MoM) without any problems. All simulation results are obtained using an MoM code. The goal is to produce the best possible horizontally polarized omnidirectional pattern. The reader should note that all gain values cited in this section do not include mismatch losses. Absolute gain, which includes matching networks, will be presented at the conference.