Abstract:
An apparatus and methods for operating a frequency selective surface are disclosed. The apparatus can be tuned to an on/off state or transmit/reflect electromagnetic energy in any frequency. The methods disclosed teach how to tune the frequency selective surface to an on/off state or transmit/reflect electromagnetic energy in any frequency.

Description:
FIELD OF THE INVENTION  
       [0001]     This technology relates to a frequency selective surface that can be tuned to an on-state, off-state and/or can transmit/reflect electromagnetic energy in any frequency band.  
       BACKGROUND AND PRIOR ART  
       [0002]     Antennas  100  may be hidden behind a radome  110 , see  FIG. 1 , particularly if they are being used in an application where they could be exposed to the environment. The radome protects the antenna from both the natural environment such as rain and snow, and the man-made environment such as jamming signals. Often, the radome is made so that it transmits electromagnetic energy within a narrow band centered around the operating frequency of the antenna, so as to deflect or reflect jamming signals at other frequencies. This is done using a frequency selective surface (FSS), having a grid or lattice of metal patterns or holes in a metal sheet. The design and construction of FSSs is well known to those skilled in the art of radome design and electromagnetic material design.  
         [0003]     Two surfaces are commonly used in FSS design, the “Jerusalem cross” structure  200 , shown in  FIG. 2   a,  and its “Inverse structure”  300 , shown in  FIG. 3   a.  A unit cell equivalent circuit  201  of the Jerusalem cross  200 , FSS can be viewed as a lattice of capacitors  210  and inductors  220  in series, shown in  FIG. 2   b.  The capacitors  210  and inductors  220  are oriented in two orthogonal directions so that the surface can affect both polarizations. Near the LC resonance frequency, the series LC circuit has low impedance, and shorts out the incoming electromagnetic wave, thereby deflecting it off the surface. At other frequencies, the LC circuit is primarily transmitting, although it does provide a phase shift for frequencies near the stop band, shown in  FIG. 2   c.    
         [0004]     The Inverse structure  300 , shown in  FIG. 3   a,  has opposite characteristics. A unit cell equivalent circuit  301  of the Inverse structure  300 , FSS can be viewed as a lattice of capacitors  310  and inductors  320  in parallel, shown in  FIG. 3   b.  It is transmissive near LC resonance frequency and reflective at other frequencies, shown in  FIG. 3   c.    
         [0005]     The radome typically transmits RF energy through the radome only at the operating frequency of the antenna, and reflects or deflects at other frequencies. In some applications, it may be desirable to tune the radome, particularly when a tunable antenna is used inside the radome. It may also be desirable to set the radome to an entirely opaque (off) state, so that it is deflective or reflective over a broad range of frequencies. It may also be desirable to program the radome so that different regions have different properties, either transmitting within a frequency band, or opaque as desired. To achieve these requirements the FSS needs to be tunable.  
         [0006]     Throughout the years, different techniques have been implemented to achieve the tuning of the FSS. The tuning has been achieved by: varying the resistance, see Chambers, B., Ford, K. L., “Tunable radar absorbers using frequency selective surfaces”, Antennas and Propagation, 2001. Eleventh International Conference on (IEEE Conf. Publ. No. 480), vol. 2, pp. 593-597, 2001; pumping liquids that act as dielectric loading, see Lima, A. C. deC., Parker, E. A., Langley, R. J., “Tunable frequency selective surface using liquid substrates”, Electronics Letters, vol. 30, issue 4, pp. 281-282, 1994; rotating metal elements, see Gianvittorio, J. P., Zendejas, J., Rahmat-Sami, Y., Judy, J., “Reconfigurable MEMS-enabled frequency selective surfaces”, Electronics Letters, vol. 38, issue 25, pp. 1627-1628, 2002; using a ferrite substrate, see Chang, T. K., Langley, R. J., Parker, E. A., “Frequency selective surfaces on biased ferrite substrates”, Electronics Letters, vol. 30, issue 15, pp. 1193-1194, 1994; pressurizing a fluid, see Bushbeck, M. D., Chan, C. H., “A tunable, switchable dielectric grating”, IEEE Microwave and Guided Wave Letters, vol. 3, issue 9, pp. 296-298, 1993; using a varactor tuned grid array that is a kind of quasi-optic oscillator, see Oak, A. C., Weikle, R. M. Jr., “A varactor tuned 16-element MESFET grid oscilator”, Antennas and Propagation Society International Symposium, 1995; using an electro-optic layer, see Rhoads&#39; patent (U.S. Pat. No. 6,028,692); using transistors, see Rhoads&#39; patent (U.S. Pat. No. 5,619,366); using ferroelectrics between an absorptive state and a transmissive state, see Whelan&#39;s patent (U.S. Pat. No. 5,600,325).  
         [0007]     Although the above-mentioned methods are used to tune the FSS, these methods are not ideal for use with a tunable antenna. Many of the above methods are not practical for rapid tuning because they use moving metal parts, or pumping dielectric liquids. Some of them include switching between discrete states using transistors, which is less useful than a continuous tunable surface. Others include only on and off states, and cannot be tuned in frequency. Others require bulk ferrite, ferroelectric, or electrooptic materials, which can be lossy and expensive. None of the prior art achieves the capabilities of the present technology, even though a need exists for those capabilities.  
         [0008]     The present technology  420  is able to transmit electromagnetic energy  450  in a particular frequency band through the radome, and deflect or reflect electromagnetic energy in other frequency bands, shown in  FIG. 4 . It can also be tuned to an off state where it is deflective or reflective, or an on state where it is absorptive over a broad range of frequencies. Also some regions  440  of the surface can be tuned to different frequencies while other regions  430  of the surface can be set to an opaque state, shown in  FIG. 4 . Further, it uses rapidly tunable varactor diodes and low cost printed circuit board construction. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES AND THE DRAWINGS  
       [0009]      FIG. 1  depicts an arrangement of the antenna and radome;  
         [0010]      FIG. 2   a  depicts a top view of the Jerusalem cross FSS;  
         [0011]      FIG. 2   b  depicts a unit cell equivalent circuit of the Jerusalem cross FSS;  
         [0012]      FIG. 2   c  depicts a transmission spectrum of the Jerusalem cross FSS;  
         [0013]      FIG. 3   a  depicts a top view of the Inverse structure of the Jerusalem cross FSS;  
         [0014]      FIG. 3   b  depicts a unit cell equivalent circuit of the Inverse structure of the Jerusalem cross FSS;  
         [0015]      FIG. 3   c  depicts a transmission spectrum of the Inverse structure of the Jerusalem cross FSS;  
         [0016]      FIG. 4  depicts an arrangement of the steerable antenna and tunable radome where the radome has an opaque region and a transparent region, and the antenna sending a microwave beam through the transparent region;  
         [0017]      FIG. 5   a  depicts an inappropriate series LC unit cell equivalent circuit;  
         [0018]      FIG. 5   b  depicts an appropriate parallel LC unit cell equivalent circuit;  
         [0019]      FIG. 5   c  depicts an example of an appropriate TFSS unit cells;  
         [0020]      FIG. 5   d  depicts an example of an appropriate TFSS unit cells;  
         [0021]      FIG. 6   a  depicts a surface view of a circuit board containing conductors and varactor on both sides;  
         [0022]      FIGS. 6   b - c  depict the front view of each surface of the circuit board in  FIG. 6   a;    
         [0023]      FIG. 6   d  depicts a transparent view of the first surface of the circuit board in  FIG. 6   a  over the second surface of the circuit board in  FIG. 6   a;    
         [0024]      FIG. 6   e  depicts the results of modeling the circuit board in  FIG. 6   a  on the Ansoft HFSS software;  
         [0025]      FIG. 6   f  depicts tuning both sides of the circuit board in  FIG. 6   a  to a resonance frequency;  
         [0026]      FIG. 6   g  depicts tuning the first surface of the circuit board in  FIG. 6   a  to three different resonance frequencies;  
         [0027]      FIG. 6   h  depicts tuning the second surface of the circuit board in  FIG. 6   a  to three different frequencies;  
         [0028]      FIG. 6   i  depicts a transparent view of the first surface over the second surface and the propagation of different resonance frequencies through the circuit board in  FIG. 6   a;    
         [0029]      FIG. 6   j  depicts setting the circuit board in  FIG. 6   a  to an opaque state;  
         [0030]      FIG. 6   k  depicts tuning a region of the first surface to one frequency and setting the remaining region of the first surface in opaque mode;  
         [0031]      FIG. 6   l  depicts tuning a region of the second surface to one frequency and setting the remaining region of the second surface in opaque mode;  
         [0032]      FIG. 6   m  depicts a transparent view of the first surface over the second surface and the propagation of frequency and opaque mode through the circuit board in  FIG. 6   a;    
         [0033]      FIG. 7   a  depicts a surface view of a circuit board containing conductors and varactor on both sides;  
         [0034]      FIGS. 7   b - c  depict the front view of each surface of the circuit board in  FIG. 7   a;    
         [0035]      FIG. 7   d  depicts a transparent view of the first surface of the circuit board in  FIG. 7   a  over the second surface of the circuit board in  FIG. 7   a;    
         [0036]      FIG. 7   e  depicts the results of modeling the circuit board in  FIG. 7   a  on the Ansoft HFSS software;  
         [0037]      FIG. 7   f  depicts tuning both sides of the circuit board in  FIG. 7   a  to a resonance frequency;  
         [0038]      FIG. 7   g  depicts setting the circuit board in  FIG. 7   a  to an opaque state;  
         [0039]      FIG. 8   a  depicts a surface view of a circuit board containing conductors and varactor on the first surface, conductors on the second surface and vias connecting first and second surface;  
         [0040]      FIGS. 8   b - c  depict the front view of each surface of the circuit board in  FIG. 8   a;    
         [0041]      FIG. 8   d  depicts a transparent view of the first surface of the circuit board in  FIG. 8   a  over the second surface of the circuit board in  FIG. 8   a;    
         [0042]      FIG. 8   e  depicts the results of modeling the circuit board in  FIG. 8   a  on the Ansoft HFSS software;  
         [0043]      FIG. 8   f  depicts tuning both sides of the circuit board in  FIG. 8   a  to a resonance frequency;  
         [0044]      FIG. 8   g  depicts setting the circuit board in  FIG. 8   a  to an opaque state;  
         [0045]      FIG. 9   a  depicts a surface view of a circuit board containing conductors on the first surface, conductors and varactor on the second surface and vias connecting the first and the second surface;  
         [0046]      FIGS. 9   b - c  depict the front view of each surface of the circuit board in  FIG. 9   a;    
         [0047]      FIG. 9   d  depicts a transparent view of the first surface of the circuit board in  FIG. 9   a  over the second surface of the circuit board in  FIG. 9   a;    
         [0048]      FIG. 10   a  depicts a surface view of a circuit board containing varactors on the first layer, conductors on the second and third layers and vias connecting all the layers;  
         [0049]      FIGS. 10   b - d  depict the front view of each layer of the circuit board in  FIG. 10   a;    
         [0050]      FIG. 10   e  depicts a transparent view of the first layer of the circuit board in  FIG. 10   a  over the second layer of the circuit board in  FIG. 10   a  over the third layer of the circuit board in  FIG. 10   a;    
         [0051]      FIG. 11   a  depicts a surface view of a circuit board containing conductors and varactors on the first surface, conductors on the second surface and vias connecting first surface and second surface;  
         [0052]      FIGS. 11   b - c  depict the front view of each surface of the circuit board in  FIG. 11   a;    
         [0053]      FIG. 11   d  depicts a transparent view of the first surface of the circuit board in  FIG. 11   a  over the second surface of the circuit board in  FIG. 11   a;    
         [0054]      FIG. 11   e  depicts the results of modeling circuit board in  FIG. 11   a  on the Ansoft HFSS software;  
         [0055]      FIG. 11   f  depicts tuning the circuit board in  FIG. 11   a  to a resonance frequency;  
         [0056]      FIG. 11   g  depicts setting the circuit board in  FIG. 11   a  to an opaque state;  
         [0057]      FIG. 11   h  depicts tuning the circuit board in  FIG. 6   a  to three different frequencies and an opaque state;  
         [0058]      FIG. 12   a  depicts a surface view of a circuit board containing conductors on the first surface, conductors and varactors on the second surface and vias connecting the first surface and second surface.  
         [0059]      FIGS. 12   b - c  depict the front view of each surface of the circuit board in  FIG. 11   a;    
         [0060]      FIG. 12   d  depicts a transparent view of the first surface of the circuit board in  FIG. 12   a  over the second surface of the circuit board in  FIG. 12   a;    
         [0061]      FIG. 13   a  depicts a surface view of a circuit board containing varactors on the first layer, conductors on the second and third layers and vias connecting all the layers.  
         [0062]      FIGS. 13   b - d  depict the front view of each layer of the circuit board in  FIG. 13   a;    
         [0063]      FIG. 13   e  depicts a transparent view of the first layer of the circuit board in  FIG. 13   a  over the second layer of the circuit board in  FIG. 13   a  over the third layer of the circuit board in  FIG. 13   a;   
     
    
     DETAILED DESCRIPTION  
       [0064]     Of the two surfaces that are commonly used in FSS design, the Inverse structure  300  is the most appropriate in designing a TFSS. The series LC circuit  510 , shown in  FIG. 5   a,  used by the Jerusalem cross  200  is difficult to use because it lacks a continuous metal path throughout the surface, so it is difficult to provide DC bias to the internal cells. Whereas, the parallel LC circuit  511 , shown in  FIG. 5   b,  used by Inverse structure  300 , does not have this limitation.  
         [0065]     The parallel circuit  512 , which is an equivalent circuit for LC circuit  511 , can be constructed as a varactor diode  530  in parallel with a narrow metal wire  540 , which acts as an inductor, and in parallel with a DC blocking capacitor  550 , as shown in  FIG. 5   c.    
         [0066]     The parallel circuit  513 , which is another equivalent circuit for LC circuit  511 , can also be constructed as two varactor diodes  560  and  561  in parallel with a narrow metal wire  570 , which acts as an inductor, as shown in  FIG. 5   d.    
         [0067]     Using varactor diodes has the advantage in that the opaque state is easy to achieve by simply forward-biasing the varactors, so that they are conductive. Although other kinds of varactors or equivalent devices could be presently used, such as MEMS varactors or ferroelectric varactors, for clarity&#39;s sake, this discussion will concentrate on implementing this technology using varactor diodes.  
         [0068]     In one embodiment, the TFSS includes a circuit board  600 , with an array of conductors  640   a - c,    650   a - c  and varactors  630  on a major surface  610  and an array of conductors  670   a - c,    680   a - c  and varactors  660  on a major surface  620 , as shown in  FIG. 6   a.    FIG. 6   a  shows the side view of the substrate  600 .  
         [0069]      FIG. 6   b  shows a schematic of a circuit on the major surface  610 . The major surface  610  has varactors  630  organized in rows where the orientation of the varactors in one row is a mirror image of the varactors in the neighboring row, as shown in  FIG. 6   b.  Conductors  640   a - c  and  650   a - c  run across the major surface  610  between the rows of varactors  630 .  
         [0070]      FIG. 6   c  shows a schematic of a circuit on the major surface  620 . The surface  620  has varactors  660  organized in columns where the orientation of the varactors in one column is a mirror image of the varactors in the neighboring column, as shown in  FIG. 6   c.  Conductors  670   a - c  and  680   a - c  run across the major surface  620  between the columns of varactors  660 .  
         [0071]     Although the conductors in  FIGS. 6   b  and  6   c  are represented as straight lines, it shall be understood that the conductors can have different shapes, including but not limited to straight lines, crenulated lines and/or wavy lines, for this technology to work.  
         [0072]     Although the conductors in  FIGS. 6   b  and  6   c  are represented as parallel lines, it is to be understood that the conductors do not have to be perfectly parallel for this technology to work. The distance between the conductors may vary throughout the length of the conductors.  
         [0073]     Structure  690  in  FIG. 6   d  shows an overlay of the circuit on the major surface  610  and the circuit on the major surface  620 . Varactors and conductors on major surface  610  are oriented at an angle to the varactors and conductors on the major surface  620 . Although the varactors and conductors on the major surface  610  are depicted at a 90° angle to the varactors and conductors on the major surface  620  as shown in structure  690  in  FIG. 6   d,  it needs to be appreciated that the angle can be varied.  
         [0074]     The lattice period of structure  690  is represented by distance  1 B and  1 C as shown in  FIGS. 6   b - d.  For this technology to work the distances  1 B and  1 C can range from 1/15 of the wavelength to ½ of the wavelength. It needs to be appreciated that the distances  1 B and  1 C do not have to be equal for this technology to work.  
         [0075]     The thickness  1 A of the circuit board  600 , shown in  FIG. 6   a,  is sufficiently small to produce capacitive coupling between the conductors on major surface  610  and the conductors on major surface  620 . Since capacitive coupling between conductors depends on the distance between the conductors and the width of the conductors, in this embodiment the width of all the conductors and thickness  1 A are matched so as to produce capacitive coupling between the conductors on major surface  610  and the conductors on major surface  620 .  
         [0076]     Structure  690  was modeled using Ansoft HFSS software. See  FIG. 6   e.  In the first simulation the lattice period was modeled at  1 B= 1 C=1 cm, the conductors were modeled at 1 mm width, and substrate was modeled at  1 A=1 mm thickness. The varactors were modeled as a cube of dielectric material whose dielectric constant was tuned from 1 to 64 by factors of 2. Increasing the dielectric constant from 1 to 64 tuned the resonance frequency of the surface from 8 Ghz down to about 2 Ghz. In the second simulation, the lattice period was modeled at  1 B= 1 C=1 cm, the conductors were modeled at 1 mm width, and the substrate was modeled at  1 A=7 mm thickness. The varactors were modeled as a cube of dielectric material whose dielectric constant was  8 . Due to reduced capacitive coupling between conductors on the major surface  610  and the conductors on the major surface  620 , the transmission level in the pass-band was reduced by about 50%, and the pass-band shifted in frequency.  
         [0077]     Applying voltages to conductors on each major surface of the substrate controls the propagation of different frequencies through the TFSS. Depending on the voltages applied, the capacitance of the varactors is tuned and the resonance frequency of the TFSS is adjusted. Setting bias wires  640   a - c  and  670   a - c  to 0 volts and setting bias wires  650   a - c  and  680   a - c  to +10 volts, as shown in  FIG. 6   f,  will cause all of the varactors to be reverse biased and this will allow a certain resonance frequency to pass through the entire TFSS. The voltage numbers are just provided as an example; a person familiar with this technology would know that the voltage numbers could be varied to achieve desired resonance frequency.  
         [0078]     In this embodiment different regions of the TFSS can be tuned to propagate different resonance frequencies along the length of the conductors on each major surface of the circuit board  600 . The propagation of the resonance frequency with horizontal polarization through the TFSS can be controlled by applying appropriate voltages to the conductors on major surface  610  as shown in  FIG. 6   h.  Setting conductors  640   a - c  to 0 volts and setting conductor  650   a  to +10 volts will cause varactors in region R 1  to be reverse biased and this will allow only a resonance frequency with horizontal polarization HF 1  to propagate through the R 1  region of TFSS between the conductors  640   a  and  640   b,  as shown in  FIG. 6   g.  Setting conductor  650   b  to +15 volts will cause varactors in region R 2  to be reverse biased and this will allow only a resonance frequency with horizontal polarization HF 2  to propagate through the R 2  region of TFSS between the conductors  640   b  and  640   c,  as shown in  FIG. 6   g.  Setting conductor  650   c  to +20 volts will cause varactors in region R 3  to be reverse biased and this will allow only a resonance frequency with horizontal polarization HF 3  to propagate through the R 3  region of TFSS between the conductors  640   c  and  650   c,  as shown in  FIG. 6   g.  The voltage numbers are just provided as an example; the voltage numbers could be varied to achieve desired resonance frequency.  
         [0079]     The propagation of the resonance frequency with vertical polarization through the TFSS can be controlled by applying appropriate voltages to the conductors on major surface  620  as shown in  FIG. 6   h.  Setting conductors  670   a - c  to 0 volts and setting conductor  680   a  to +10 volts will cause varactors in region R 4  to be reverse biased and this will allow only a resonance frequency with vertical polarization VF 1  to propagate through the R 4  region of TFSS between the conductors  670   a  and  670   b,  as shown in  FIG. 6   h.  Setting conductor  680   b  to +15 volts will cause varactors in region R 5  to be reverse biased and this will allow only a resonance frequency with vertical polarization VF 2  to propagate through the R 5  region of TFSS between the conductors  670   b  and  670   c,  as shown in  FIG. 6   h.  Setting conductor  680   c  to +20 volts will cause varactors in region R 6  to be reverse biased and this will allow only a resonance frequency with vertical polarization VF 3  to propagate through the R 6  region of TFSS between the conductors  670   c  and  670   c,  as shown in  FIG. 6   h.  The voltage numbers are just provided as an example; the voltage numbers could be varied to achieve desired resonance frequency.  
         [0080]     The propagation of the resonance frequency with horizontal and vertical polarization is achieved through structure  690  in  FIG. 6   i.  When structure  690  is set up as shown in.  FIG. 6   i  there will be overlapping regions that will allow both a vertical and horizontal polarization of a single resonance frequency to propagate through the TFSS. Region R 7 , as shown in  FIG. 6   i,  allows the propagation of both HF 1  and VF 1  through the TFSS. Region R 8 , as shown in  FIG. 6   i,  allows the propagation of both HF 2  and VF 2  through the TFSS. Region R 9 , as shown in  FIG. 6   i,  allows the propagation of both HF 3  and VF 3  through the TFSS. The size and shape of the regions that allow both vertical and horizontal polarization resonance frequencies to propagate through TFSS shown here are just provided as an example. The size and shape of these regions can be adjusted by applying appropriate voltages to the appropriate conductors.  
         [0081]     When structure  690  is set up as shown in  FIGS. 6   i,  there will also be overlapping regions that will allow both a vertical and horizontal polarization of different resonance frequencies to propagate through the TFSS. Region R 10 , as shown in  FIG. 6   i,  allows the propagation of HF 1  and VF 2  through the TFSS. Region R 11 , as shown in  FIG. 6   i,  allows the propagation of HF 1  and VF 3  through the TFSS. Region R 12 , as shown in  FIG. 6   i,  allows the propagation of HF 2  and VF 1  through the TFSS. Region R 13 , as shown in  FIG. 6   i,  allows the propagation of HF 3  and VF 1  through the TFSS. Region R 14 , as shown in  FIG. 6   i,  allows the propagation of HF 3  and VF 2  through the TFSS. Region R 15 , as shown in  FIG. 6   i,  allows the propagation of HF 2  and VF 3  through the TFSS.  
         [0082]     In this embodiment, the TFSS can also be set to an opaque (off) state. The opaque state is achieved by forward biasing the varactors, as shown in  FIG. 6   j,  which shorts across the continuously conductive loop. Setting conductors  640   a - c  and  670   a - c  to 0 volts and setting conductors  650   a - c  and  680   a - c  to −1 volts, as shown in  FIG. 6   j,  will cause all of the varactors to be forward biased thereby blocking all the resonance frequencies from propagating though the TFSS. The voltage numbers are just provided as an example; the voltage numbers could be varied and still cause all of the varactors to be forward biased.  
         [0083]     In this embodiment, the region of the TFSS can be set to an opaque state while the remaining region is set to propagate a certain resonance frequency. The propagation of a particular resonance frequency with horizontal polarization through a region of the TFSS and blocking the remaining resonance frequencies with horizontal polarization through the rest of the TFSS can be controlled by applying appropriate voltages to the conductors on major surface  610  as shown in  FIG. 6   k.  Setting conductors  640   a - c  to 0 volts and setting conductors  650   a  and  650   c  to −1 volts will cause varactors in regions R 16  and R 18  to be forward biased and this will block any resonance frequency with horizontal polarization from propagating through the R 16  and R 18  regions of TFSS, as shown in  FIG. 6   k.  Setting conductors  650   b  to +15 volts will cause varactors in region R 17  to be reverse biased and this will allow a resonance frequency with horizontal polarization HF 2  to propagate through the R 17  region of TFSS, as shown in  FIG. 6   k.  The voltage numbers are just provided as an example. The voltage numbers could be varied to achieve desired resonance frequency or an opaque state.  
         [0084]     The propagation of a particular resonance frequency with vertical polarization through a region of the TFSS and blocking the remaining resonance frequencies with vertical polarization through the rest of the TFSS can be controlled by applying appropriate voltages to the conductors on major surface  620  as shown in  FIG. 6   l.  Setting conductors  670   a - c  to 0 volts and setting conductors  680   a  and  680   c  to −1 volts will cause varactors in the regions R 19  and R 21  to be forward biased and this will block any resonance frequency with vertical polarization from propagating through the R 19  and R 21  regions of TFSS, as shown in  FIG. 6   l.  Setting conductor  680   b  to +15 volts will cause varactors in the region R 20  to be reverse biased and this will allow a resonance frequency with vertical polarization VF 2  to pass through the R 20  region of TFSS, as shown in  FIG. 6   l.  The voltage numbers are just provided as an example, the voltage numbers could be varied to achieve desired resonance frequency or an opaque state.  
         [0085]     The propagation of a particular resonance frequency with horizontal and vertical polarization through a region of the TFSS and blocking of the remaining resonance frequencies through the rest of the TFSS is achieved through the structure  690  in  FIG. 6   m.  When structure  690  is set up as shown in  FIG. 6   m  there will be a region propagating a particular resonance frequency, regions with horizontal and vertical polarization, regions blocking all the frequencies, regions propagating only horizontal polarization of the particular frequency and regions propagating only vertical polarization of the particular resonance frequency. Region R 30 , as shown in  FIG. 6   m,  allows the propagation of HF 2  and VH 2  through the TFSS. Regions R 22 , R 29 , R 27  and R 25  as shown in  FIG. 6   m,  block all the vertical and horizontal polarizations of all the resonance frequencies from propagating through the TFSS. Regions R 26  and R 23  allow propagation of only VF 2  through the TFSS. Regions R 28  and R 24  allow propagation of only HF 2  through the TFSS. The size and shape of the region that allows both vertical and horizontal polarization resonance frequencies to pass through TFSS shown here are just provided as an example. The size and shape of these regions can be adjusted by applying an appropriate voltage to the appropriate conductors. The size and shape of the opaque regions shown here are also just provided as an example. The size and shape of these opaque regions can be adjusted by applying an appropriate voltage to the appropriate conductors.  
         [0086]     In another embodiment, the TFSS includes a circuit board  700 , with an array of conductors  740   a - d,    730   a - d  and varactors  750  on the major surface  710 , an array of conductors  760   a - c,    770   a - c  and varactors  780  on the major surface  720  and vias  795  and  796  connecting major surfaces  710  and  720  as shown in  FIG. 7   a - c.    FIG. 7   a  shows the side view of the substrate  700 .  
         [0087]      FIG. 7   b  shows a schematic of a circuit on the major surface  710 . The major surface  710  has a plurality of oppositely oriented varactors  750  connected in series and organized in rows where the orientation of the varactors in one row is a mirror image of the varactors in the neighboring row, as shown in  FIG. 7   b.  Conductors  740   a - d  run along the length of the major surface  710  between the rows of varactors  750 . Conductors  730   a - d  run along the width of the major surface  710  between the varactors  750  connecting the conductors  740   a - d,  as shown in  FIG. 7   b.    
         [0088]      FIG. 7   c  shows a schematic of a circuit on the major surface  720 . The major surface  720  has a plurality of oppositely oriented varactors  780  connected in series and organized in columns where the orientation of the varactors in one column is a mirror image of the varactors in the neighboring column, as shown in  FIG. 7   c.  Conductors  760   a - c  run along the width of the major surface  720  between the columns of varactors  780 . Conductors  770   a - c  run along the length of the major surface  720  between the varactors  780  connecting the conductors  760   a - c,  as shown in  FIG. 7   c.    
         [0089]     Although the conductors in  FIGS. 7   b  and  7   c  are represented as straight lines, it is to be understood that the conductors can have different shapes, including but not limited to straight lines, crenulated lines and/or wavy lines, for this technology to work.  
         [0090]     Although the conductors in  FIGS. 7   b  and  7   c  are represented as parallel lines, it is to be understood that the conductors do not have to be perfectly parallel for this technology to work. The distance between the conductors may vary throughout the length of the conductors.  
         [0091]     Although conductors  730   a - d  appear to be perpendicular to conductors  740   a - d  in  FIG. 7   b,  it is to be understood that these conductors do not have to be perfectly perpendicular for this technology to work. The angle between the intersecting conductors may vary.  
         [0092]     Although conductors  760   a - c  appear to be perpendicular to conductors  770   a - c  in  FIG. 7   c  it is to be understood that these conductors do not have to be perfectly perpendicular for this technology to work. The angle between the intersecting conductors may vary.  
         [0093]     Structure  790  in  FIG. 7   d  shows an overlay of the circuit on the major surface  710  and the circuit on the major surface  720 . Varactors and conductors on major surface  710  are oriented at an angle to the varactors and conductors on the major surface  720 . Although the varactors and conductors on the major surface  710  are depicted at a 90° angle to the varactors and conductors on the major surface  720  as shown in structure  790  in  FIG. 7   d,  it needs to be appreciated that the angle can be varied.  
         [0094]     Vias  796  connect the varactors  780  on the major surface  720  to conductors  730   a - d  on the major surface  710 , shown in  FIG. 7   d.  Vias  795  connect the varactors  750  on the major surface  710  to conductors  770   a - c  on the major surface  720 , shown in  FIG. 7   d.    
         [0095]     The lattice period of structure  790  is represented by distance  2 B and  2 C as shown in  FIG. 7   d.  For this technology to work, the distances  2 B and  2 C can range from 1/15 of the wavelength to ½ of the wavelength. The distances  2 B and  2 C do not have to be equal for this technology to work.  
         [0096]     The thickness  2 A of the circuit board  700 , shown in  FIG. 7   a,  is less important than the thickness  1 A of the circuit board  600  described above. Vias  796  and  795  make the circuit board  700  less susceptible to the variations in the thickness  2 A.  
         [0097]     Structure  790  was modeled using Ansoft HFSS software. See  FIG. 7   e.  In the first simulation the lattice period was modeled at  2 B= 2 C=1 cm, the conductors were modeled at 1 mm width, and the substrate was modeled at  2 A=1 mm thickness. The varactors were modeled as a cube of dielectric material whose dielectric constant was tuned from 1 to 64 by factors of 2. Increasing the dielectric constant from 1 to 64 tuned the resonance frequency of the surface from 8 Ghz down to about 2 Ghz. In the second simulation the lattice period was modeled at  2 B= 2 C=1 cm, the conductors were modeled at 1 mm width, and the substrate was modeled at  2 A=7 mm thickness. The varactors were modeled as a cube of dielectric material whose dielectric constant was 8. As can be seen by the results, shown in  FIG. 7   e,  this design is more resistant to variations in the substrate thickness. The transmission level in the pass-band was reduced by about 20%. This design is less concerned with maintaining capacitive coupling and is more resistant to variations in the thickness  2 A.  
         [0098]     Applying voltages to conductors on each major surface of the substrate controls the propagation of different frequencies through the TFSS. Depending on the voltages applied, the capacitance of the varactors is tuned and the resonance frequency of the TFSS is adjusted. Setting conductors on the major surface  710  to 0 volts and setting conductors on the major surface  720  to +10 volts, as shown in  FIG. 7   f,  will cause all of the varactors to be reverse biased and this will allow a certain resonance frequency to pass through the entire TFSS. The voltage numbers are just provided as an example; the voltage numbers could be varied to achieve desired resonance frequency.  
         [0099]     In this embodiment, the TFSS can also be set into an opaque (off) state. The opaque state is achieved by forward biasing the varactors, as shown in  FIG. 7   g,  which shorts across the continuously conductive loop. Setting conductors on major surface  710  to 0 volts and setting conductors on major surface  720  to −1 volts, as shown in  FIG. 7   g,  will cause all of the varactors to be forward biased, thereby blocking all the resonance frequencies from propagating through the TFSS. The voltage numbers are just provided as an example; the voltage numbers could be varied and still cause all of the varactors to be forward biased.  
         [0100]     In another embodiment, the TFSS includes a circuit board  800 , with an array of conductors  840   a - d,    830   a - d  and varactors  880  on the major surface  810 , an array of conductors  860   a - c,    870   a - c  on the major surface  820  and vias  895  connecting major surfaces  810  and  820  as shown in  FIG. 8   a - c.    FIG. 8   a  shows the side view of the substrate  800 .  
         [0101]      FIG. 8   b  shows a schematic of a circuit on the major surface  810 . The major surface  810  has a plurality of oppositely oriented, interconnected varactors  880  organized in rows where the orientation of the varactors in one row is a mirror image of the varactors in the neighboring row, as shown in  FIG. 8   b.  Conductors  840   a - d  run along the length of the major surface  810  between the rows of varactors  880 . Conductors  830   a - d  run along the width of the major surface  810  between the varactors  880  connecting the conductors  840   a - d,  as shown in  FIG. 8   b.    
         [0102]      FIG. 8   c  shows a schematic of a circuit on the major surface  820 . The major surface  820  has conductors  860   a - c  running along the width of the major surface  820  and conductors  870   a - c  running along the length of the major surface  820  connecting the conductors  860   a - c,  as shown in  FIG. 8   c.    
         [0103]     Although the conductors in  FIGS. 8   b  and  8   c  are represented as straight lines, it is to be understood that the conductors can have different shapes, including but not limited to straight lines, crenulated lines and/or wavy lines, for this technology to work.  
         [0104]     Although the conductors in  FIGS. 8   b  and  8   c  are represented as parallel lines, it is to be understood that the conductors do not have to be perfectly parallel for this technology to work. The distance between the conductors may vary throughout the length of the conductors.  
         [0105]     Although conductors  830   a - d  appear to be perpendicular to conductors  840   a - d  in  FIG. 8   b,  it is to be understood that these conductors do not have to be perfectly perpendicular for this technology to work. The angle between the intersecting conductors may vary.  
         [0106]     Although conductors  860   a - c  appear to be perpendicular to conductors  870   a - c  in  FIG. 8   c,  it is to be understood that these conductors do not have to be perfectly perpendicular for this technology to work. The angle between the intersecting conductors may vary.  
         [0107]     Structure  890  in  FIG. 8   d  shows an overlay of the circuit on the major surface  810  and the circuit on the major surface  820 . Conductors on major surface  810  are oriented at an angle to the conductors on the major surface  820 . Although the conductors on the major surface  810  are depicted at a 90° angle to the conductors on the major surface  820  as shown in structure  890  in  FIG. 8   d,  it needs to be appreciated that the angle can be varied.  
         [0108]     Vias  895  connect the varactors  880  on the major surface  810  to the point of intersection of conductors  870   a - c  and  860   a - c  on the major surface  820 , shown in  FIG. 8   d.    
         [0109]     The lattice period of structure  890  is represented by distance  3 B and  3 C as shown in  FIG. 8   d.  For this technology to work, the distances  3 B and  3 C can range from 1/15 of the wavelength to ½ of the wavelength. The distances  3 B and  3 C do not have to be equal for this technology to work.  
         [0110]     The thickness  3 A of the circuit board  800 , shown in  FIG. 8   a,  is less important than the thickness  1 A of the circuit board  600  described above. Vias  895  make the circuit board  800  less susceptible to the variations in the thickness  3 A.  
         [0111]     Structure  890  was modeled using Ansoft HFSS software. See  FIG. 8   e.  In the first simulation, the lattice period was modeled at  3 B= 3 C=1 cm, the conductors were modeled at 1 mm width, and the substrate was modeled at  3 A=1 mm thickness. The varactors were modeled as a cube of dielectric material whose dielectric constant was tuned from 1 to 64 by factors of 2. Increasing the dielectric constant from 1 to 64 tuned the resonance frequency of the surface from 8 Ghz down to about 2 Ghz. In the second simulation, the lattice period was modeled at  3 B= 3 C=1 cm thickness, the conductors were modeled at 1 mm width, and the substrate was modeled at  3 A=7 mm thickness. The varactors were modeled as a cube of dielectric material whose dielectric constant was tuned from 1 to 64 by factors of 2. As can be seen by the results, shown in  FIG. 8   e,  this design is more resistant to variations in the substrate thickness and requires less varactors which offers simpler construction.  
         [0112]     Applying voltages to conductors on each major surface of the substrate controls the propagation of different frequencies through the TFSS. Depending on the voltages applied, the capacitance of the varactors is tuned and the resonance frequency of the TFSS is adjusted. Setting conductors on the major surface  810  to 0 volts and setting conductors on the major surface  820  to +10 volts, as shown in  FIG. 8   f,  will cause all of the varactors to be reverse biased and this will allow a certain resonance frequency to pass through the entire TFSS. The voltage numbers are just provided as an example; the voltage numbers could be varied to achieve desired resonance frequency.  
         [0113]     In this embodiment, the TFSS can be set into an opaque (off) state. The opaque state is achieved by forward biasing the varactors, as shown in  FIG. 8   g,  which shorts across the continuously conductive loop. Setting conductors on major surface  810  to 0 volts and setting conductors on major surface  820  to −1 volts, as shown in  FIG. 8   g,  will cause all of the varactors to be forward biased thereby blocking all the resonance frequencies from propagating though the TFSS. The voltage numbers are just provided as an example; the voltage numbers could be varied and still cause all of the varactors to be forward biased.  
         [0114]     It should be apparent that this embodiment could be implemented in other ways.  
         [0115]     For example, the TFSS includes a circuit board  900 , with an array of conductors  940   a - d,    930   a - d  on the major surface  910 , an array of conductors  960   a - c,    970   a - c,  varactors  980  on the major surface  920  and vias  995  connecting major sides  910  and  920  as shown in  FIG. 9   a - c.    FIG. 9   a  shows the side view of the substrate  900 .  
         [0116]      FIG. 9   b  shows a schematic of a circuit on the major surface  910 . The major surface  910  has conductors  930   a - d  running along the width of the major surface  910  and conductors  940   a - d  running along the length of the major surface  910  connecting the conductors  930   a - d,  as shown in  FIG. 9   b.    
         [0117]      FIG. 9   c  shows a schematic of a circuit on the major surface  920 . The major surface  920  has a plurality of oppositely oriented, interconnected varactors  980  organized in rows where the orientation of the varactors in one row is a mirror image of the varactors in the neighboring row, as shown in  FIG. 9   c.  Conductors  970   a - c  run along the length of the major surface  920  between the rows of varactors  980 . Conductors  960   a - c  run along the width of the major surface  920  between the varactors  980  connecting the conductors  970   a - c,  as shown in  FIG. 9   c.    
         [0118]     Although the conductors in  FIGS. 9   b  and  9   c  are represented as straight lines, it is to be understood that the conductors can have different shapes, including but not limited to straight lines, crenulated lines and/or wavy lines, for this technology to work.  
         [0119]     Although the conductors in  FIGS. 9   b  and  9   c  are represented as parallel lines, it is to be understood that the conductors do not have to be perfectly parallel for this technology to work. The distance between the conductors may vary throughout the length of the conductors.  
         [0120]     Although conductors  930   a - d  appear to be perpendicular to conductors  940   a - d  in  FIG. 9   b  it is to be understood that these conductors do not have to be perfectly perpendicular for this technology to work The angle between the intersecting conductors may vary.  
         [0121]     Although conductors  960   a - c  appear to be perpendicular to conductors  970   a - c  in  FIG. 9   c  it is to be understood that these conductors do not have to be perfectly perpendicular for this technology to work. The angle between the intersecting conductors may vary.  
         [0122]     Structure  990  in  FIG. 9   d  shows an overlay of the circuit on the major surface  910  and the circuit on the major surface  920 . Conductors on major surface  910  are oriented at an angle to the conductors on the major surface  920 . Although the conductors on the major surface  910  are depicted at a 90° angle to the conductors on the major surface  920  as shown in structure  990  in  FIG. 9   d,  it needs to be appreciated that the angle can be varied.  
         [0123]     Vias  995  connect the varactors  980  on the major surface  920  to the point of intersection of conductors  930   a - d  and  940   a - d  on the major surface  910 , shown in  FIG. 9   d.    
         [0124]     In another example, the TFSS includes a circuit board  1000 , with an array of conductors  1040   a - d,    1030   a - d  on the major surface  1010 , an array of conductors  1060   a - c,    1070   a - c  on the major surface  1020 , varactors  1080  on the major surface  1025  and vias  1095  and  1096  connecting major sides  1010 ,  1025  and  1020  as shown in  FIG. 10   a - d.    FIG. 10   a  shows the side view of the substrate  1000 .  
         [0125]      FIG. 10   b  shows a schematic of a circuit on the major surface  1010 . The major surface  1010  has conductors  1030   a - d  running along the width of the major surface  1010  and conductors  1040   a - d  running along the length of the major surface  1010  connecting the conductors  1030   a - d,  as shown in  FIG. 10   b.    
         [0126]      FIG. 10   c  shows a schematic of a circuit on the major surface  1020 . The major surface  1020  has conductors  1070   a - c  running along the length of the major surface  1020  and conductors  1060   a - c  running along the width of the major surface  1020  connecting the conductors  1070   a - c,  as shown in  FIG. 10   c.    
         [0127]      FIG. 10   d  shows a schematic of a circuit on the major surface  1025 . The major surface  1025  has a plurality of oppositely oriented, interconnected varactors  1080 , as shown in  FIG. 10   d.    
         [0128]     Vias  1095  connect the varactors  1080  on the major surface  1025  to the point of intersection of conductors  1030   a - d  and  1040   a - d  on the major surface  1010 , shown in  FIG. 10   e.    
         [0129]     Vias  1096  connect the varactors  1080  on the major surface  1025  to the point of intersection of conductors  1070   a - c  and  1060   a - c  on the major surface  1020 , shown in  FIG. 10   e.    
         [0130]     Although the conductors in  FIGS. 10   b  and  10   c  are represented as straight lines, it is to be understood that the conductors can have different shapes, including but not limited to straight lines, crenulated lines and/or wavy lines, for this technology to work.  
         [0131]     Although the conductors in  FIGS. 10   b  and  10   c  are represented as parallel lines, it is to be understood that the conductors do not have to be perfectly parallel for this technology to work. The distance between the conductors may vary throughout the length of the conductors.  
         [0132]     Although conductors  1030   a - d  appear to be perpendicular to conductors  1040   a - d  in  FIG. 10   b  it is to be understood that these conductors do not have to be perfectly perpendicular for this technology to work. The angle between the intersecting conductors may vary.  
         [0133]     Although conductors  1060   a - c  appear to be perpendicular to conductors  1070   a - c  in  FIG. 10   c  it is to be understood that these conductors do not have to be perfectly perpendicular for this technology to work. The angle between the intersecting conductors may vary.  
         [0134]     Structure  1090  in  FIG. 10   e  shows an overlay of the circuit on the major surface  1010 , the circuit on the major surface  1025  and the circuit on the major surface  1020 . Conductors on major surface  1010  are oriented at an angle to the conductors on the major surface  1020 . Although the conductors on the major surface  1010  are depicted at a 90° angle to the conductors on the major surface  1020  as shown in structure  1090  in  FIG. 10   e,  it needs to be appreciated that the angle can be varied.  
         [0135]     These are just some of the examples of implementing this embodiment; there are other implementations available although not specifically listed here.  
         [0136]     In another embodiment, the TFSS includes a circuit board  1100 , with an array of conductors  1130   a - h  and varactors  1150  on the major surface  1110 , an array of conductors  1140   a - h  on the major surface  1120  and vias  1160  connecting major sides  1110  and  1120  as shown as shown in  FIG. 11   a - c.    FIG. 11   a  shows the side view of the substrate  1100 .  
         [0137]      FIG. 11   b  shows a schematic of a circuit on the major surface  1110 . The major surface  1110  has a plurality of oppositely oriented, interconnected varactors  1150  organized in columns where the orientation of the varactors in one column is a mirror image of the varactors in the neighboring column, as shown in  FIG. 11   b.  Conductors  1130   a - h  run along the width of the major surface  1110  between the columns of varactors  1150 , as shown in  FIG. 11   b.    
         [0138]      FIG. 11   c  shows a schematic of a circuit on the major surface  1120 . The surface  1120  has conductors  1140   a - h  running across the length surface  1120 , as shown in  FIG. 11   c.    
         [0139]     Although the conductors in  FIGS. 11   b  and  11   c  are represented as straight lines, it is to be understood that the conductors can have different shapes, including but not limited to straight lines, crenulated lines and/or wavy lines, for this technology to work.  
         [0140]     Although the conductors in  FIGS. 11   b  and  11   c  are represented as parallel lines, it is to be understood that the conductors do not have to be perfectly parallel for this technology to work. The distance between the conductors may vary throughout the length of the conductors.  
         [0141]     Structure  1170  in  FIG. 11   d  shows an overlay of the circuit on the major surface  1110  and the circuit on the major surface  1120 . Conductors on major surface  1110  are oriented at an angle to the conductors on the major surface  1120 . Although the conductors on the major surface  1110  are depicted at a 90° angle to the conductors on the major surface  1120  as shown in structure  1170  in  FIG. 11   d,  it needs to be appreciated that the angle can be varied.  
         [0142]     Vias  1160  connect the varactors  1150  on the major surface  1110  to conductors on the major surface  1120 , shown in  FIG. 11   d.    
         [0143]     The lattice period of structure  1170  is represented by distance  6 B and  6 C as shown in  FIG. 11   d.  For this technology to work, the distances  6 B and  6 C can range from 1/15 of the wavelength to ½ of the wavelength. It needs to be appreciated that the distances  6 B and  6 C do not have to be equal for this technology to work.  
         [0144]     The thickness  6 A of the circuit board  1100 , shown in  FIG. 11   a,  is sufficiently small to produce capacitive coupling between the conductors on major surface  1110  and the conductors on major surface  1120 . The capacitive coupling between conductors depends on the distance between the conductors and the width of the conductors. In this embodiment, the width of all the conductors and thickness  6 A are matched so as to produce capacitive coupling between the conductors on major surface  1110  and the conductors on major surface  1120 .  
         [0145]     Structure  1170  was modeled using Ansoft HFSS software. See  FIG. 11   e.  In the first simulation, the lattice period was set at  6 B= 6 C=1 cm, the conductors were modeled at 1 mm width, and the substrate was modeled at  6 A=1 mm thickness. The varactors were modeled as a cube of dielectric material whose dielectric constant was tuned from 1 to 64 by factors of 2. Increasing the dielectric constant from 1 to 64 tuned the resonance frequency of the surface from 8 Ghz down to about 2 Ghz. In the second simulation, the lattice period was modeled at  6 B= 6 C=1 cm, the conductors were modeled at 1 mm width, and the substrate was modeled at  6 A=7 mm thickness. The varactors were modeled as a cube of dielectric material whose dielectric constant was  8 . As can be seen by the results, shown in  FIG. 11   e,  this design is more resistant to variations in the substrate thickness. There was only minor degradation of transmission magnitude as the substrate thickness was increased.  
         [0146]     Applying voltages to conductors on each major surface of the substrate controls the propagation of different frequencies through the TFSS. Depending on the voltages applied, the capacitance of the varactors is tuned and the resonance frequency of the TFSS is adjusted. Setting bias wires  1130   a - h  to 0 volts and setting bias wires  1140   a - h  to +10 volts, as shown in  FIG. 11   f,  will cause all of the varactors to be reverse biased and this will allow a certain resonance frequency to pass through the entire TFSS. The voltage numbers are just provided as an example; the voltage numbers could be varied to achieve desired resonance frequency.  
         [0147]     In this embodiment the TFSS can be set into an opaque (off) state. The opaque state is achieved by forward biasing the varactors, as shown in  FIG. 11   g,  which shorts across the continuously conductive loop. Setting conductors  1130   a - h  to 0 volts and setting conductors  650   a - c  and  680   a - c  to −1 volts, as shown in  FIG. 11   g,  will cause all of the varactors to be forward biased, thereby blocking all the resonance frequencies from propagating though the TFSS. The voltage numbers are just provided as an example; the voltage numbers could be varied and still cause all of the varactors to be forward biased.  
         [0148]     In this embodiment, different regions of the TFSS can also be tuned to propagate different resonance frequencies and be set to an opaque state. Setting conductors  1130   d - e  to 0 volts and setting conductors  1140   d - e  to +10 volts will cause varactors in region R 39  to be reverse biased and this will allow a resonance frequency with horizontal and vertical polarization HVF 4  to propagate through the R 39  region of TFSS, as shown in  FIG. 11   g.  Setting conductosr  1130   a - c  and  1130   f - h  to +5.5 volts and conductors  1140   a - c  and  1140   f - h  to 4.5 volts will cause varactors in region R 31 , R 33 , R 35  and R 37  to be forward biased, thereby blocking the propagation of all horizontal and vertical resonance frequencies through the R 31 , R 33 , R 35  and R 37  regions of TFSS, as shown in  FIG. 6   g.  As a by-product, varactors in the regions R 32  and R 36  are also reverse biased and this will allow a resonance frequency with horizontal and vertical polarization HVF 5  to propagate through the R 32  and R 36  region of TFSS, as shown in  FIG. 11   g.  Varactors in the regions R 38  and R 34  are also reverse biased and this will allow a resonance frequency with horizontal and vertical polarization HVF 6  to propagate through the R 38  and R 34  region of TFSS, as shown in  FIG. 11   g.  The voltage numbers are just provided as an example. A person familiar with this technology would know that the voltage numbers could be varied to achieve any desired resonance frequency. The size and shape of the regions that allow the resonance frequencies to propagate or not propagate through TFSS shown here are just provided as an example. The size and shape of these regions can be adjusted by applying appropriate voltages to the appropriate conductors.  
         [0149]     It should be apparent that this embodiment could be implemented in other ways.  
         [0150]     For example, the TFSS includes a circuit board  1200 , with an array of conductors  1230   a - h  on the major surface  1210 , an array of conductors  1240   a - h  and varactors  980  on the major surface  1220 , and vias  1260  connecting major sides  1210  and  1220  as shown in  FIG. 12   a - c.    FIG. 12   a  shows the side view of the substrate  1200 .  
         [0151]      FIG. 12   b  shows a schematic of a circuit on the major surface  1210 . The major surface  1210  has conductors  1230   a - h  running along the width of the major surface  1210 , as shown in  FIG. 9   b.    
         [0152]      FIG. 12   c  shows a schematic of a circuit on the major surface  1220 . The major surface  1220  has a plurality of oppositely oriented, interconnected varactors  1250  organized in rows where the orientation of the varactors in one row is a mirror image of the varactors in the neighboring row, as shown in  FIG. 12   c.  Conductors  1240   a - h  run along the length of the major surface  1220  between the rows of varactors  1250 , as shown in  FIG. 12   c.    
         [0153]     Although the conductors in  FIGS. 12   b  and  12   c  are represented as straight lines, it is to be understood that the conductors can have different shapes, including but not limited to straight lines, crenulated lines and/or wavy lines, for this technology to work.  
         [0154]     Although the conductors in  FIGS. 12   b  and  12   c  are represented as parallel lines, it is to be understood that the conductors do not have to be perfectly parallel for this technology to work. The distance between the conductors may vary throughout the length of the conductors.  
         [0155]     Structure  1270  in  FIG. 12   d  shows an overlay of the circuit on the major surface  1210  and the circuit on the major surface  1220 . Conductors on major surface  1210  are oriented at an angle to the conductors on the major surface  1220 . Although the conductors on the major surface  1210  are depicted at a 90° angle to the conductors on the major surface  1220 , as shown in structure  1270  in  FIG. 12   d,  it needs to be appreciated that the angle can be varied.  
         [0156]     Vias  1260  connect the varactors  1250  on the major surface  1220  to conductors on the major surface  1210 , shown in  FIG. 12   d.    
         [0157]     In another example, the TFSS includes a circuit board  1300 , with an array of conductors  1330   a - h  on the major surface  1310 , an array of conductors  1340   a - h  on the major surface  1320 , varactors  1350  on the major surface  1325 , and vias  1360  and  1365  connecting major sides  1310 ,  1325  and  1320  as shown in  FIG. 13   a - d.    FIG. 13   a  shows the side view of the substrate  1000 .  
         [0158]      FIG. 13   b  shows a schematic of a circuit on the major surface  1310 . The major surface  1310  has conductors  1330   a - h  running along the width of the major surface  1310 , as shown in  FIG. 13   b.    
         [0159]      FIG. 13   c  shows a schematic of a circuit on the major surface  1320 . The major surface  1320  has conductors  1340   a - h  running along the length of the major surface  1320 , as shown in  FIG. 13   c.    
         [0160]      FIG. 13   d  shows a schematic of a circuit on the major surface  1325 . The major surface  1325  has a plurality of oppositely oriented, interconnected varactors  1350 , as shown in  FIG. 13   d.    
         [0161]     Vias  1360  connect the varactors  1350  on the major surface  1025  to the conductors  1330   a - h  on the major surface  1310 , shown in  FIG. 13   e.    
         [0162]     Vias  1365  connect the varactors  1500  on the major surface  1025  to the conductors  1340   a - h  on the major surface  1320 , shown in  FIG. 13   e.    
         [0163]     Although the conductors in  FIGS. 13   b  and  13   c  are represented as straight lines, it is to be understood that the conductors can have different shapes, including but not limited to straight lines, crenulated lines and/or wavy lines, for this technology to work.  
         [0164]     Although the conductors in  FIGS. 13   b  and  13   c  are represented as parallel lines, it is to be understood that the conductors do not have to be perfectly parallel for this technology to work. The distance between the -conductors may vary throughout the length of the conductors.  
         [0165]     Structure  1370  in  FIG. 13   d  shows an overlay of the circuit on the major surface  1310 , the circuit on the major surface  1325 , and the circuit on the major surface  1320 . Conductors on major surface  1310  are oriented at an angle to the conductors on the major surface  1320 . Although the conductors on the major surface  1310  are depicted at a 90° angle to the conductors on the major surface  1320 , as shown in structure  1370 , in  FIG. 13   d,  it needs to be appreciated that the angle can be varied.  
         [0166]     These are just some of the examples of implementing this embodiment; there are other implementations available although not specifically listed here.  
         [0167]     While several illustrative embodiments of the invention have been shown and described, numerous variations and alternative embodiments will occur to those skilled in the art. Such variations and alternative embodiments are contemplated, and can be made without departing from the scope of the invention as defined in the appended claims.