G. Junkin

Holographic testing of terahertz antennas

In the light of future applications involving terahertz antenna measurements, this paper revisits Gabor (1949) holography as a direct method for recovering phase, offering some interesting advantages for near-field measurements. In particular, we examine the theory and parameterization of planar near-field Gabor holography and comment on the requirements for scanner precision at terahertz frequencies.

Improving the Performance of the Multilevel Matrix Decomposition Algorithm for 2.5-D Structures. Application to metamaterials

This paper presents an optimization of the multilevel matrix decomposition algorithm (MLMDA) that allows the efficient analysis of 2.5-D structures. This tool could be useful in the analysis of planar multilayer metamaterials (MM). Comparing its performance against the multilevel fast multiple algorithm (MLFMA) it was shown that MLMDA 2.5-D requires less computation time and provides better precision. Future work on the algorithm will be directed to take advantage of the periodicity present in MM

A Split-Ring-Resonator Loaded Monopole for Triple Band Applications

A monopole loaded with a split-ring resonator (SRR) will be presented for applications requiring efficient triple-band performance. The design is based on the principle of non-resonant traps and takes advantage of the dual-band behavior of the SRR. The mid-band frequency is mainly controlled by the dimensions of the monopole whereas the frequencies of the lower and upper bands are determined by the resonances of the SRR. As proof of concept, an antenna covering the universal 802.11 standard (2.4–2.5 GHz and 4.9–5.875 GHz) and the low band of the 802.15 standard (3.244–4.742 GHz) has been designed, fabricated and measured.

Conformal FDTD Modeling of Imperfect Conductors at Millimeter Wave Bands

The Dey-Mittra conformal finite difference time domain (CFDTD) algorithm for perfect electrical conductors is modified for the analysis of finite conductivity conductors at millimeter wave frequencies. Formulas are derived for CFDTD coefficients using voltage state variables and a constant surface impedance boundary condition (SIBC). The approach permits a fast implementation suitable for CUDA type GPU hardware. Accuracy and stability are investigated with respect to the stability constraints on intersection areas introduced by Dey-Mittra and Benkler as well as the distance stability constraints of Zagorodnov that permits 100% Courant temporal sampling. A relaxation of the Zagorodnov distance constraints permits increased accuracy with respect to all alternative area constraints. Analytic solutions are used to judge the performance of the proposed CFDTD modifications for millimeter wave band applications.

Planar Near-Field Phase Retrieval Using GPUs for Accurate THz Far-Field Prediction

With a view to using Phase Retrieval to accurately predict Terahertz antenna far-field from near-field intensity measurements, this paper reports on three fundamental advances that achieve very low algorithmic error penalties. The first is a new Gaussian beam analysis that provides accurate initial complex aperture estimates including defocus and astigmatic phase errors, based only on first and second moment calculations. The second is a powerful noise tolerant near-field Phase Retrieval algorithm that combines Andersons Plane-to-Plane (PTP) with Fienups Hybrid-Input-Output (HIO) and Successive Over-Relaxation (SOR) to achieve increased accuracy at reduced scan separations. The third advance employs teraflop Graphical Processing Units (GPUs) to achieve practically real time near-field phase retrieval and to obtain the optimum aperture constraint without any a priori information.

Dual-Band Mixer Using Composite Right/Left-Handed Transmission Lines

The concept of composite right left-handed transmission lines provides for one additional degree of freedom in realizing arbitrary dual-band frequency response devices. In this letter, an arbitrary dual-band operation mixer, based on the classical balanced mixer topology is proposed. The prototype demonstrates the mixer performance for a ratio of 2.5 between the two operation bands (860 MHz and 2,150 MHz). The conversion losses are better than 8.5 dB in both bands.

Resonator-Loaded Dual-Band Monopole for Universal WLAN

This letter presents a novel monopole antenna design for efficient dual-band operation over the entire international wireless local area network (WLAN) frequency bands of 2.4-2.5 GHz (802.11b/g) and 4.9-5.875 GHz (802.11a/h/j). The design is based on the principle of out-of-band loading using a magnetic resonator whose natural frequency is chosen to lie between the lower and upper WLAN bands. The position of the resonator and the frequency of its natural resonance are chosen to produce more than 1 GHz wideband match in the 5 GHz band. The length of the monopole combined with the out-of-band resonator inductance determines the match in the 2.45 GHz band.

Artificial magnetic reflector based on spiral resonators

An artificial magnetic reflector is built based on squared spiral resonators. Numerical simulations using efficient MLMDA (multilevel matrix decomposition algorithm) techniques are used for designing the reflector and the antenna. Measurements of the reflection coefficient of the artificial screen are carried out in order to verify the viability of the proposal. The performance of the reflector in combination with a folded dipole as an active element is also evaluated.

A New System for Microwave Holographic Imaging of Buried Services

A new method for improving resolution without increasing operating frequency is proposed. This bistatic version of the holographic technique involves illuminating the buried services from a source antenna placed on, or implanted slightly below the interface. Resolution is improved by scanning in the surface wave region close to the interface. Computer simulations are used to predict the scattered field in sandy soils with 10 and 20% gravimetric moisture content at 300MHz. Some experimental simulations at 500MHz in tap water at 15°C illustrate the improvement in resolution gained by scanning in close proximity to the surface.

Smaller resonators for artificial magnetic surfaces

Artificial magnetic surfaces have interesting applications in antenna design where one wants to replace, over a limited frequency range, electric conducting surfaces with magnetic equivalents. One of the many challenges in constructing such a surface is that of miniaturizing the resonator elements making up the structure whilst at the same time maintaining a reasonable bandwidth and a tolerable level of dielectric and copper losses. In this paper we present some novel structures, fabricated using chemical etching techniques, which have only 6.5% of the area of a capacitive loaded loop (CLL) and less than 30% of the area of spiral resonators and have measured return losses of less than 1.5 dB.