Meander line antennas placed on various objects suffer a shift in resonant frequency. Numerical modeling demonstrated that the frequency increases with wire diameter and object conductivity, and decreases with increasing permittivity. This contrasts with a linear dipole where an increase in wire diameter results in a decrease in resonant frequency. A 4% bandwidth is sufficient for conductivity (σ) values up to 0.01 S/m and small changes in permittivity. This has implications for RFID antennas designed for placement on a wide variety of materials.

A ring type frequency selective surface (FSS) can provide transmission stop-band characteristics in rooms. This allows adjacent rooms to be isolated for one LAN for frequency reuse while other frequencies pass through the walls with minimal attenuation. The FSS was screen printed on a thin flexible plastic substrate of permittivity 3.2 with a stop band at 12.3GHz and 10dB bandwidth of 3.5GHz. The variation in bandstop characteristics was investigated for various wall materials. The centre frequency varied by more than 3 GHz for common wall materials which means significant transparency for some building materials. The technique is a low cost method of confining LAN picocells in one room.

Planar antenna modeling requires a constrained solution space and open boundaries and so is highly computationally intensive. One of the methods used to overcome this is by using method of moments simulation. The method of moments is a highly efficient method of solving wire antenna structures and is commonly used in antenna optimization. A method of transforming a wire antenna structure to a planar antenna structure is presented using a 4-element Yagi-Uda antenna designed to resonate at 905 MHz. The wire to planar transformation is based on the circular cross section wire to planar strip, a spacing adjustment based on interelement capacitance, and a length scaling to compensate for the change in effective permittivity. The planar antenna shows slightly improved impedance performance at the resonance [voltage standing wave ratio (VSWR) 5 1.39]. This transformation decreased the antenna footprint by 15.11% after conversion for a wire antenna to a planar antenna in air with similar radiation characteristics and on FR4 (1.6 mm thickness), the footprint increased by 52%. The antenna simulation time was reduced from 15 min using finite element method to less than 10 s for one cycle by using the method of moments solver. All antenna properties are essentially unchanged.

Abstract-Dipole antennas on a substrate without a ground plane are common in wireless sensor networks and RFID applications. This paper reviews a number of theoretical approaches to solving for the effective permittivity when the substrate material is thin. The surface impedance and slab waveguide propagation techniques are compared to a capacitive solution and an insulated wire antenna. The insulated wire method gives most accurate results (< 3.5%) and was verified using numerical modeling and experimental work. Measurements on a planar straight dipole on FR4 (f c = 1.50 GHz) compare favorably with the antenna modeled without the substrate and scaled using the insulated wire technique at (f c = 1.49 GHz). The method can be readily incorporate the effect of an RFID antenna on a thin plastic film placed on a wide variety of lossy and lossless objects.

Fiber reinforced composites offer strength and light weight but are electrically anisotropic. The resonant frequency of dipole antennas is orientation dependent. While FEM modeling showed a cosine relationship between the effective permittivity and angle, experimental measurements at UHF on cardboard reinforced with fine copper wire did not fit this relationship. The electromagnetic anisotropy has implications for radio communications systems located on UAVs and other platforms. Carbon nanotubes in polymeric composites provide a renewable option for high strength materials.I.