2472 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 51, NO. 9, SEPTEMBER 2003 Shorted Microstrip Antenna on a Photonic Bandgap Substrate D. Pavlickovski and Rod B. Waterhouse Abstract—A microstrip shorted patch antenna with a photonic bandgap (PBG) ground plane is presented. A shorted patch with identical dimen- sions on a conventional ground plane is also included, so that a direct per- formance comparison can be made. Measured data shows a gain improve- ment of over 3 dB and a significant reduction in cross polarization for the new PBG antenna. Index Terms—Microstrip antennas, photonic bandgap. I. INTRODUCTION Recently, much emphasis has been placed on reducing the size of microstrip antennas such that they can be used in wireless terminal ap- plications. Several methods have been proposed to reduce the size of a microstrip patch radiator and the two main techniques include utilizing shorting pins or walls and using high-dielectric constant materials. It has been shown that significantly better impedance bandwidth and ra- diation performance for shorted patch antennas can be achieved when the antenna is mounted on foam substrates, rather than on microwave laminates [1]. However, using such a material (foam) jeopardizes the ease of manufacturing and the robustness of the antenna, contrary to the often-touted advantages of printed circuit technology. Like most patch antennas, the performance of a shorted patch is com- promised as the dielectric constant of the material is increased. One reason can be attributed to the excitation of surface waves. These elec- tromagnetic waves propagate along/near the surface of the substrate and are radiated to free space at the truncation of the dielectric sub- strate. The radiated surface waves can significantly distort the radiation pattern of the antenna. Several schemes can be found in the literature to suppress these surface waves, including the use of photonic bandgap (PBG) structures (i.e., [2], [3]). Probably the most effective and com- pact approach thus far in the microwave domain makes use of periodic structures composed of metallic pads connected to the ground plane with vias [2]. Several types of antennas with these PBG structures as ground planes have been investigated, including vertical monopoles, horizontal wire antennas, and the conventional microstrip antenna [2], [3]. Prior to this paper and to the best of the author’s knowledge, a shorted patch an- tenna has not been investigated. In this paper, we present two shorted patch antennas fabricated on the same microwave substrate, Duriod 5880 . This material was specifically chosen, as it is a common substrate used in microstrip antennas operating in the S-band. One shorted patch has been manufactured with a high impedance elec- tromagnetic surface surrounding the patch conductor while the other is without, in order to ascertain the usefulness of the proposed antenna. It will be shown that the radiation performance of the new antenna has been dramatically changed, yielding a printed antenna with radiation characteristics similar to a conventional patch antenna, but a fraction of the size. The two shorted microstrip patch configurations have been Manuscript received April 16, 2002; revised September 25, 2002. D. Pavlickovski is with the School of Electrical and Computer Systems En- gineering, RMIT University, Melbourne, VIC 3001, Australia. R. Waterhouse was with the School of Electrical and Computer Systems Engineering, RMIT University, Melbourne, VIC 3001, Australia. He is now with R&D Transmission Technology, Corvis Corporation, Columbia MD 21046-9400 USA (e-mail: r.waterhouse@ieee.org). Digital Object Identifier 10.1109/TAP.2003.816315 (a) (b) Fig. 1. Schematic diagram of (a) conventional microstrip shorted patch antenna and (b) proposed PBG shorted patch. (Configuration 1 parameters: 2.2, 9.51 mm, 12 mm, 6 mm, 0.6 mm, 0.6 mm, 3 mm, 0 mm, 5 mm, 1.5 mm, 5 mm, 1.5 mm, 69 mm, 69 mm.) (Configuration 2 parameters: 2.2, 9.51 mm, 12 mm, 6 mm, 0.6 mm, 0.6 mm, 3 mm, 0 mm, 5 mm, 1.5 mm, 5 mm, 1.5 mm, 69 mm, 69 mm, 9 mm, 9 mm, 10 mm, 0.5 mm, 2.5 mm, 3.5 mm.) investigated theoretically; however, for the sake of brevity, only mea- sured results that include input impedance, radiation patterns, and gain are presented. II. ANTENNA AND PBG CONFIGURATION Fig. 1 shows a schematic diagram for the two shorted patch antennas. The antenna consists of a coaxial probe of radius located at ( , ) and two shorting posts of radius located at ( , ) and ( , ) from the center of the patch conductor. The shorted patch antenna has been constructed with two shorting posts, as it reduces the fabrica- tion tolerance between the probe and shorting pins [1]. The patch con- ductor has a length and width shown in Fig. 1(a). In order to in- vestigate the effectiveness of PBG structures on shorted patch antennas, 0018-926X/03$17.00 © 2003 IEEE