IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 55, NO. 7, JULY 2007 2107 Fig. 9. The simulated radiation patterns for RHCP and LHCP at 1.21 and 1.467 GHz, respectively. REFERENCES [1] X. L. Bao and M. J. Ammann, “Compact annular-ring embedded cir- cular patch antenna with a cross-slot ground plane for circular polar- ization,” Electron. Lett., vol. 42, no. 4, pp. 192–193, 2006. [2] J. S. Row, “Dual-frequency circularly polarized annular-ring microstrip antenna,” Electron. Lett., vol. 40, no. 3, pp. 153–154, 2004. [3] D. M. Pozar and S. M. Duffy, “A dual-band circularly polarized aper- ture-coupled stacked microstrip antenna for global positioning satel- lite,” IEEE Trans. Antennas Propag., vol. 45, pp. 1618–1625, 1997. [4] F. Ferrero, C. Luxey, G. Jacquemod, and R. Staraj, “Dual-band circu- larly polarized microstrip antenna for satellite applications,” IEEE An- tennas Wireless Propag. Lett., vol. 4, pp. 13–15, 2005. [5] L. Boccia, G. Amendola, and G. D. Massa, “A dual frequency mi- crostrip patch antenna for high-precision GPS applications,” IEEE An- tennas Wireless Propag. Lett., vol. 3, pp. 157–160, 2004. [6] K. P. Yang and K. L. Wong, “Dual-band circularly-polarized square mi- crostrip antenna,” IEEE Trans. Antennas Propag., vol. 49, pp. 377–382, 2001. Surface-Micromachined Dual Ka-Band Cavity Backed Patch Antenna Milan V. Lukic and Dejan S. Filipovic Abstract—A dual Ka-band rectangular coaxial line fed cavity backed patch antenna fabricated by a sequential surface micromachining process with ten structural layers is presented in this letter. The antenna band- width is 4.1% around 36 GHz, with gain and radiation efficiency of 5.7 dBi and 95%, respectively. The lower band is characterized with 5.1% bandwidth around 28 GHz and a monopole-like radiation pattern with 5.1 dBi maximum gain. Analysis and design are conducted with a finite element code and good agreement with measurements is demonstrated Index Terms—Patch antenna, rectangular coaxial lines, surface micro- machining. I. INTRODUCTION Extensive research of micro-electromechanical systems over the past decade have contributed to the development of new fabrication technologies for high-performance millimeter wave systems, including surface and bulk micromachining [1]–[4]. Several micromachined patch antennas have already been reported, such as those in [5]–[7]. Q-band micro-patch antennas presented in [5] were implemented on a high resistivity silicon substrate using the surface micromachining composed of conventional thick photoresist lithography and copper plating process. In [6], a surface- micromachined air-filled elevated patch antenna resonating at 25 GHz is demonstrated. A 60 GHz 2 1 patch array antenna fabricated using micromachining process fully compatible with commercial CMOS foundries is presented in [7]. In this paper, we demonstrate an all copper, recta-coax fed, air-cavity backed dual-band patch antenna designed for multifunctional Ka-band communications. The patch is supported by two metallic posts, which along with the pulled-up cavity walls contribute to the 28 GHz band. The two slits in the patch are utilized to tune the higher frequency band at 36 GHz where the antenna exhibits efficient broadside radiation. The lower band pattern resembles that of a top-loaded monopole, and is uti- lized for terrestrial communications on the move. The antenna is built using a sequential micro-fabrication technique, the PolyStrata process [8], and can be easily integrated with other recta-coax based passive components within the same wafer. II. ANTENNA DESCRIPTION A scanning electron microscope (SEM) photograph of the fabricated antenna with the probing structure is shown in Fig. 1, while a sketch of the designed antenna with included characteristic dimensions is shown in Fig. 2. The length of the patch is , which is about 1/3 of the wavelength at the operating frequency of 36 GHz. The holes in the cavity walls and in the patch are used for the removal of the sacrificial photoresist. There are eight release holes in the patch, and a total of 34 holes in the cavity walls. Another important feature of the proposed patch antenna is the incorporation of the two slits in the Manuscript received October 29, 2006; revised March 6, 2007. This work was supported by the DARPA-MTO under the 3D Micro-Electromagnetics Radio Frequency Systems (3D MERFS) program. The authors are with the Department of Electrical and Computer Engi- neering, University of Colorado at Boulder, CO 80309-0425 USA (e-mail: milan.lukic@colorado.edu; dejan@colorado.edu). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TAP.2007.900273 0018-926X/$25.00 © 2007 IEEE