ment C-1, (ii) orthogonal PIFA arrangement O-1, (iii) parallel PIFA arrangement P-1, (iv) array PM of PIFA and monopole, and (v) two-monopole array MM. While the graphs in Figures 3– 6 are limited only to the coupling dependency on spacing, at the design frequency of 2.45 GHz, the pictures in Figure 7 contain abundant information about the array coupling and match performance in the 0.1– 0.9 spacing domain and 2–3-GHz frequency domain. Several observations follow from this figure: 1. as expected, S 11 is equal to S 22 for the symmetrical arrays C-1, P-1, and MM, while for the nonsymmetrical arrays O-1 and PM, S 11 differs from S 22 ; 2. all antenna-array elements have practically preserved their design resonant frequency, bandwidth, and match perfor- mance for spacing greater than 0.4– 0.5; 3. for smaller spacing (say, less than 0.4), the resonant (match) frequency of both PIFAs becomes somewhat shifted from the design frequency; 4. the two-monopole array has better frequency bandwidth but worse match performance than the two-two-PIFA array—a behavior similar to that described in the comparison be- tween the single monopole and PIFA (section 2). 5. CONCLUSION A numerical and experimental study of mutual coupling and match performance in several two-PIFA arrays as functions of spacing and joint orientation has resulted in a large amount of numerical and experimental data. In the spacing domain, it was observed that the coupling depends mainly on the distance between the PIFA open-ended sides. For a constant spacing between the feed points, the coupling experiences considerable changes with the relative angular orientation of the PIFA elements. Also, the studied mixed-antenna array (PM) and two- monopole array (MM) have stronger coupling, about 3– 4 dB greater than the majority of two-PIFA arrangements. These differences are especially pronounced for larger array spacing. In the frequency domain, it has been found that for spacing greater than 0.4– 0.5, all PIFA array elements have practically preserved their single-element design resonant frequency, band- width, and match performance. The two-monopole array has better frequency bandwidth but worse input match than the two-PIFA array. The findings for mutual coupling in two-PIFA arrays will be of practical value for multi-PIFA array design and optimization. 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Ansoft HFSS 9.0 and Optimetrics, Ansoft Corporation, 2002. 16. Rohde & Schwarz catalog, Test and measurement products, 2001/ 2002. © 2004 Wiley Periodicals, Inc. ENCRYPTION-SELECTABLE HOLOGRAPHIC STORAGE IN LiNbO 3 WITH ANGLE MULTIPLEXING Wei-Chia Su, 1 Ching-Cherng Sun, 2 and Wei-Chen Su 2 1 Graduate Program in Electro-Optical Engineering Tatung University Taipei 104, Taiwan 2 Institute of Optical Sciences National Central University Chung-Li 320, Taiwan Received 9 January 2004 ABSTRACT: An encryption-selectable holographic storage algorithm in LiNbO 3 using angular multiplexing is proposed and demonstrated. It offers more flexibility to encrypt or not encrypt the data (optionally) during the recording processes. The functions encryption and nonen- cryption storage are alternately handled by a random-phase pattern and a uniform-phase pattern. The random phase pattern is also used to de- crypt the encrypted information. The experimental results obtained using a ground glass to realize the proposed method are presented. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 227–230, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20260 Key words: volume holography; optical storage; optical security; ran- dom-phase encoding MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 42, No. 3, August 5 2004 227