A compact triple-band coplanar waveguide (CPW)-fed antenna for WLAN/WiMAX applications is proposed. The radiation patch is fed by capacitive coupling of the top transmission line. By only using one metallic strip etched on the bottom of the substrate, tri-band resonances of the antenna are generated. The proposed antenna has a compact size of 30 × 27 mm 2 , which can provide stable omnidirectional radiation patterns in three bands. The measured − 10 dB impedance bandwidths are 150 MHz (2.39-2.54 GHz), 360 MHz (3.37-3.73 GHz) and 1170 MHz (5.02-6.19 GHz), which is suitable for WLAN/WiMAX applications.Introduction: The prodigious rate of development of wireless communication technology as a viable and cost-effective high-speed data connectivity solution demands high-performance multi-band antennas with good radiation characteristics. In view of the practical needs, many promising antennas have been proposed to cover the WLAN (2.4-2.484, 5.1-5.35 and 5.725-5.85 GHz) operation and WiMAX (3.4-3.69 and 5.25-5.85 GHz) standards. These include monopole antennas with several branches to generate low band and two upper bands [1, 2], a slot monopole antenna for dual-band [3], a monopole antenna with a split-ring [4] and a slot-monopole antenna with embedded rectangular parasitic elements [5]. However, these antennas either need large size or the shapes are too complex. In [6], dual-band was achieved by adding L-and E-elements together with a total area of only 8 × 11.3 mm 2 . However, it just covers the WLAN bands.In this Letter, a compact coplanar waveguide (CPW)-fed antenna for WLAN/WiMAX application is proposed. The patch on the bottom of the substrate could generate three resonant modes with an inverted L-shaped strip to further improve the impedance matching performance at 5.5 GHz. The measured impedance bandwidths can cover the 2.4/5.2/ 5.8 GHz WLAN bands and 3.5/5.5 GHz WiMAX bands. In addition, the proposed antenna has the advantages of small size, low profile, a simple structure and cheap production. Details of the antenna design and simulated and measured results are presented and discussed.

A novel multilayer substrate integrated waveguide (SIW) filter with an improved stopband using mixed coupled modified trisections (MCMTs) is presented. The proposed filter is composed of two cascade MCMTs embedded in LTCC substrate. Four transmission zeros (TZs) can be generated with only three resonators, where two TZs near the passband are utilised to achieve sharper skirt selectivity, and another two TZs for the upper wide stopand. A 10 GHz experimental filter has been designed, fabricated and measured to validate the proposed method.Introduction: Substrate integrated waveguide (SIW) filters, which are synthesised in a planar substrate with arrays of metallic vias, could provide a low-profile, easy-integration and low-cost solution while maintaining high performance as conventional metal waveguide filters [1]. To meet the increasing requirements of modern communication systems in terms of compact size and high selectivity, SIW filters, with multiple transmission zeros (TZs) using the printed circuit board (PCB) or low temperature co-fired ceramic (LTCC) processes have been extensively studied in recent years. Cross-coupled SIW filters can obtain additional signal paths to generate TZs at certain frequencies. An X-band narrowband trisection elliptic SIW filter in [2] and a K-band quadruplet SIW filter with source-load coupling in [3] have been reported. Three TZs are obtained to improve frequency selectivity, whereas they are still large due to their single-layer and planar structures. The application of multilayer LTCC technology makes the realisation of cross-coupled SIW filters with compact size possible. In [4,5], X-band LTCC trisection SIW filters with one TZ are introduced. In [6], an LTCC narrowband SIW filter with two TZs for V-band application is presented. Although the structures in [4][5][6] are comparatively compact, their selectivity and upper stopband need to be improved.In this Letter, a miniaturised SIW filter with an improved stopband using cascade MCMTs is presented. By implementing mixed coupling into two cascade modified trisections (MT), the proposed three-order SIW filter not only has four TZs to improve frequency selectivity and upper stopband, but also has a small size by profiting from its LTCC multilayer structure. To verify the validity of the proposed method, an experimental filter has been designed, fabricated and measured.

A broadband gain enhancement endfire antenna is presented. The gain enhancement is achieved by loading with an I-shaped resonator (ISR) structure in the endfire direction. Broad bandwidth is realised by using a microstrip-to-coplanar balun and bowtie dipole elements, while gain enhancement is achieved by loading the ISR structure in the endfire direction. The measurements show that the ISR-loaded antenna presents a gain of about 4-8 dB in the whole working band (4.5-9.5 GHz), which is about 2 dB more than the unloaded one. The advantages of broad bandwidth and high gain make this antenna valuable in wireless communication systems.Introduction: In recent years, many metamaterials that exhibit unique properties have been widely applied in microwave component and antenna applications [1]. These artifical materials can be formed by periodic arrangements of many small inclusions; for example, electric resonators, such as complementary split-ring resonators [2] and electric LC resonators [3], or composite right-/left-handed transmission lines (CRLH TLs) [4] or magnetic resonators, such as split-ring resonators (SRRs) [5]. Great interest has been focused on meta-based antennas. Among them, low-/zero-index materials have features of controlling the direction of a microstrip patch antenna, and 1-2 dB gain improvement was obtained. However, this kind of structure makes the antenna heavy in weight and thick in profile. The SRR structure was introduced to achieve high gain along the endfire direction [6]. However, the bandwidth of this antenna was quite narrow. The dipoles are widely used for their simple structure and broad bandwidth [7]. However, the feature of low gain restrict their applications. In [7], a wideband endfire antenna with an impedance bandwidth of 70% and directional patterns was proposed based on the idea of a quasi-Yagi antenna. Nevertheless, its gain with an average of 4 dB was still low.In this Letter, we combine the advantages of the metamaterial structures and the wide bandwidth endfire antenna together to develop a broadband high-gain antenna as given in [8]. Instead, I-shaped resonators (ISRs) with a simpler structure are introduced in this design. Gain enhancement is achieved by loading with two rows of ISRs symmetrically in the endfire direction while maintaining the wideband performance of the periodic endfire antenna. The ISR-loaded antenna has a gain of about 4-8 dB in the whole working band (4.5-9.5 GHz), which is about 2 dB more than the unloaded one. HFSS software is used to optimise this antenna, and good agreement between the measured and simulated results is achieved.

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