Multiband antenna Research Papers - Academia.edu (original) (raw)

A low-profile antenna-triplexer is realized using a substrate integrated waveguide (SIW) technology for radio altimeter/ WLAN/ISM band applications. The antenna is composed of two SIW cavity resonators where a smaller cavity is nested inside the larger one. The larger cavity is excited by using two distinct microstrip feedlines, while the smaller one by a coax probe. The antenna produces three distinct resonances around 4.18, 5.2, and 5.8 GHz simultaneously employing one annular slot and two transverse slots. By exciting cavity modes (TE110/TE120) and the patch mode (TM10) simultaneously, an average isolation of better than 23 dB is accomplished among three input ports. As compared to the conventional counterparts, the proposed geometry is simple to realize in a compact space. To validate the proposed idea, the design is experimentally tested, and the measured responses show a good agreement with the simulations. Moreover, the antenna shows a front-to-back ratio better than 19 dB and measured gain values of 6.56, 4.2, and 5.85 dBi at three resonances. The proposed design is compact, easy to fabricate, and capable to integrate with planar circuits. Index Terms: Antenna-triplexer, isolation, multiband antenna, substrate integrated waveguide (SIW). I. INTRODUCTION IN RECENT years, with the excessive growth of modern wireless communication systems, the planar low-cost multiband antennas are in high demand. The compact mobile handheld devices are equipped with multiple transceivers to operate for different applications [1]. Therefore, to avoid interference between transmitting and receiving channels, a high intrinsic isolation among the input ports is extremely important. To achieve a high isolation, decoupling networks are used at the input ports of resonating circuits, which leads to an increase in the circuitry size and makes it complicated to use in compact portable devices [2]. Recently antenna diplexer/triplexer has drawn special attention of researchers, as it avoids the requirement of decoupling network and makes an RF front-end system more compact and simple [3]. In previous literature, different antenna-diplexers are designed by using several techniques such as using a defectiveground plane [4], multilayered patch [5], and spiral defected microstrip resonators [6]. The above-mentioned techniques are complex and multilayered structures that are difficult to integrate with planar circuits. However, in the present scenario, there is a demand for triple-frequency band circuits. An antennatriplexer is presented in [7], integrated into a small space using a double-layered structure, but the radiation characteristics are not satisfactory due to the multimode excitation. Recently, a substrate integrated waveguide (SIW) has been developed as a mature technology in realizing cavity-backing antennas in a planar circuit [8]. It offers the combined features of slot antennas such as low profile and cavity features of the unidirectional radiation pattern with high gain. Most recently, similar works based on the SIW self-diplexing/triplexing antennas have been introduced in [9]-[11]. In [10], the reported work shows a good in-band band performance, but it covers a relatively larger space than the proposed antenna. In [11], the antenna radiates through a T-shaped slot that produces three resonances in a compact structure, but it shows higher cross-polar level and relatively lower gain than the proposed geometry. This letter presents a simple SIW cavity-backed slot antennatriplexer for radio altimeter (4.2 GHz), WLAN (5.2 GHz), and ISM band (5.8 GHz) applications. An integrated antennatriplexer is designed by nesting a smaller SIW cavity inside the larger one. Three radiating slots produce three distinct resonant frequencies when they are excited by three separate feedlines. The intrinsic isolation is achieved below −23 dB at each operating frequency, which helps to realize triplexing functionality. The proposed antenna shows unidirectional radiation pattern at three operating frequencies due to a cavity-backed structure. The proposed design is a single-layered geometry containing a simple feeding network.