across every diode. Furthermore, it is expected that the higher the values of the surface-mount resistors, the smaller the microwave ohmic losses in the passband FSS region will be.Having incorporated the surface-mount resistors, the experiment for the single diode-C FSS was repeated. The results are shown in Figure 4(a). Also shown in Figure 4, are the tuning range results of the 2 diode B in series FSS and 2 diode C in series FSS. The results demonstrate that the use of resistors improves the band-stop filter performance. Wideband tunability, well in excess of 500 MHz, can be seen in Figure 4(c). It must be stressed that the tunability of varactor-diode-based FSS is achieved with negligible power consumption.When using diodes of high tunability and high resistance, such as diode B, FSS configurations with diodes in parallel [ Fig. 2(f)] can be employed. These configurations improve the filter attenuation by reducing the total resistance at the expense of reduced tunability. This is confirmed by comparing Figures 3(b) and 4(d). CONCLUSIONIn this paper, it has been demonstrated that the presence of biasing electrodes distorts the frequency response of tunable FSS and that this distortion is avoided through the novel use of high value (1 M⍀) surface-mount resistors. Furthermore, significant wideband tuning can be achieved using varactor diodes in series configurations at the expense of an increase in the overall FSS element resistance (which lowers the Q factor and increases the bandwidth). This resistance was found to decrease when the diodes were used in parallel configurations.Improvements in printing technology, which we are currently researching, will enable the proposed configurations to be employed in low-cost large-scale FSS deposition on a variety of substrates, such as wallpaper. Furthermore, although the proposed structures were required to block only one polarisation, as they were employed in a waveguide setup, current research work demonstrates that dipoleelement and loop-element tunable FSS can be fabricated to block linearly polarised incident waves of arbitrary electric-field orientation; this will be the subject of a forthcoming paper. ACKNOWLEDGMENTThis work was funded by Ofcom under the Spectrum Efficiency Scheme (contract no. AY4462), managed by Culham Electromagnetics and Lightning Ltd.

ishes. Again, the effect of the presence of a surface wave is apparent in the Figure. It has also been verified that the copolar component of the field coincides, in the limit p' -+ a/2, with the expressions obtained by the application of the standard Maliuzhinets method, valid at normal incidence. V. CONCLUSIONSA uniform high-frequency solution has been presented for three-dimensional diffraction at an edge in a planar anisotropic impedance surface. The solution applies to those cases where the anisotropic surface constitutes a face of either a half plane or a full plane, with the other face perfectly conducting. The particular kind of anisotropic impedance boundary condition adopted for the loaded face is characterized by a vanishing surface impedance in the direction perpendicular to the edge. It is suitable for modeling corrugated surfaces and strip-loaded grounded dielectric slabs, with the direction of either corrugations or strips normal to the edge. KEY TERMSFrequency-selectilje surface, bias fem'te substrate. tunable resonan/ frequency, Jerusalem cross, moment method ABSTRACT The response characteristic of a frequency-selectire surface (FSS) made up of a Jerusalem cross on a iri-plane biased fem'ie substrate is analyzed with the full-walre moment method. It is shown that the resonant frequent-v of a FSS cut1 be dynamically adjusted l>y changing the dc bias magnetic ,field. For nornial incidence of the plane electrotnagnetic wai'e, a resotlant-frequency s i l i~ of about 5 GHz can be obtained by tuning the bias dc magnetic field. It is furtherprorvd that it is easier tog~t the shifi of resonant frequency of a FSS fot the case of the Jerusalem cross than for the cross dipole for a girw range of bias magnetic field. For an oblique incidence of 45", about a 3-GHz resonant-frequency shift can be easily achieLmi. 0 I996 Johri Wiley & Sons, lnc. ABSTRACTWe describe the use of fiber-optic low coherence reflectometry to nonini'asiuely acquire three-dimensional images of Lysozyme protein cryftals in solution, with a 1-5-pm depth resolution. This &pe of noninc'asii'e protein ctystal growth monitoring might ultimately be used to impror>e the growth ptocesses in micrograr?ty environments. 0 I996 John Wley & Sons, Inc.

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