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A dual-band antenna with large frequency ratio for microwave and millimeter-wave applications based on the dual-mode coplanar waveguide (CPW) transmission line is investigated in this letter. The dual-mode operation of the transmission line is obtained by introducing a rectangular stub to traditional CPW, which can provide different phase shift in different frequency bands. In the millimeter-wave band, the dual-mode transmission line can support odd mode while it supports even mode in the microwave band. Based on this, the dual-band antenna which operates as monopole antenna in the microwave band and Vivaldi antenna in the millimeter-wave band is realized using the same aperture. Moreover, the radiation structure for monopole in the microwave band is designed to enhance the radiation performance of the antenna in the millimeter-wave band. For verifying, the prototype of the antenna is fabricated on a Rogers 4003 substrate with an overall size of 45 × 20 × 0.508 mm3 and the measured results agree well with the simulated ones.

In this letter, a high selectivity filtering magnetoelectric (ME) dipole antenna with harmonic suppression is investigated. By etching a complementary split resonant ring (CSRR) on shorted wall of ME dipole, a radiation null at upper passband edge can be obtained. The intrinsic radiation null at lower passband edge of ME dipole is utilized, together with the radiation null generated by CSRR, to obtain high selectivity. In addition, to suppress the third harmonic of the antenna, a stepped impedance resonator is loaded on the Г-shaped feeding structure. For verifying, a prototype operating from 1.44–2.79 GHz is designed, fabricated, and measured. Compared with the traditional ME dipole antenna, the proposed filtering antenna shows upper and lower stopband rejection levels as high as 16.61 and 17.84 dB, respectively. Furthermore, a third harmonic suppression level of 12.78 dB is obtained. Good agreement can be observed between the simulation and measurement.

A reconfigurable antenna with radiation pattern and polarization reconfiguration capabilities is investigated in this communication. The antenna consists of a central dielectric resonator antenna (DRA) and two parasitic DRAs made of a liquid solution with low dielectric loss. Utilizing the flowing of liquid, the existing of parasitic DRA can be changed to produce different patterns. An omnidirectional pattern can be realized when only the central DRA radiates, while a unidirectional pattern can be obtained using the parasitic DRAs. Furthermore, the polarization of the antenna with unidirectional radiation can be changed by forming different parasitic DRAs, which can be realized via liquid flowing. Based on this principle, three different radiation states, namely, omnidirectional radiation and unidirectional radiation with $x$ - or $y$ -polarization, can be obtained. To verify the design, a prototype of the antenna operating at 2.4 GHz was simulated, fabricated, and measured. The measurement results indicate that the antenna provides effective impedance matching over the band of interest as well as radiation pattern and polarization reconfiguration capabilities.

A broadband printed dipole fed by a balun with third-order impedance matching is proposed in this paper. Firstly, a circuit model of the antenna is given based on the principle of marchand balun. The balun is composed of a stepped impedance microstrip line and marchand balun, which form a three-stage match and its good broadband characteristics are verified by ADS. Furthermore, a printed dipole antenna is integrated using the proposed balun, and the results show that the antenna is obtained a wide impedance bandwidth of 72.7% for VSWR < 2.

In this paper, a new design method of microstrip series-fed array antenna for vehicle radar technology is proposed. The energy transmission and radiation between antenna elements are expressed and deduced using S-parameters in this method. A constant-amplitude and in-phase microstrip series-fed array antenna is designed through the analysis of this method. The results show that the bandwidth of the antenna ranges from 23.78 GHz to 24.27 GHz for| S 11 | < −10 dB and the gain is 12.35 dBi at the center frequency.

This paper presents $\mathrm{a}\pm 45$ degree polarization reconfigurable antenna based on liquid medium. The antenna consists of a central dielectric resonator antenna (DRA) and three liquid DRAs (The liquid medium is ethyl acetate with low dielectric loss and low toxicity). The DRA on the y-axis keeps the liquid filled, and the other two parasitic DRAs on the x-axis work through the flow of liquid medium to realize the unidirectional radiation. The polarization of the antenna changes with the selection of different parasitic DRAs, which is generated by the flow of liquid medium. Based on this principle, two polarization modes (the polarization is ± 45 degree to the positive direction of Y axis) perpendicular to each other can be obtained, which realizes the reconfiguration of polarization states. In order to verify the design of the antenna, an antenna operating at 2.4GHz band is simulated. The simulation results indicate that the antenna achieves effective impedance matching and sufficient antenna gain in the target operating frequency band, and also verifies its capability of polarization reconfiguration.

A wideband horizontally polarized (HP) omnidirectional antenna is proposed in this communication, which consists of 12 printed arc dipole units, a wideband 1-to-12 feed network, 2 rows of parasitic arc strips, and a row of director elements. Based on the tightly coupled dipole array design, 12 printed arc dipoles (about $0.2 \lambda_{\rm L}$ , $\lambda_{\rm L}$ : effective wavelength at low frequency) are formed as a ring with their edge overlap for strong mutual coupling. Meanwhile, the two rows of parasitic arc strips are radially placed around these arc dipoles as an impedance matching layer. Owing to the strong mutual coupling and impedance matching layer, the proposed HP omnidirectional antenna has a wideband operating band. Additionally, a row of director elements is utilized to enhance the radiation in horizontal plane. The printed arc dipoles are fed by a wideband 1-to-12 power divider with identical magnitude and phase. Experimental results show that this antenna has a wide 10-dB return loss operating bandwidth of 70.2% (1.7–3.54 GHz) and good omnidirectionality performance with gain variation in horizontal plane being less than 1.2 dB among 1.7–3.2 GHz.

A tri-band multiple-input-multiple-output (MIMO) antenna that covers all frequency bands required for WLAN and WiMAX applications is presented. Three resonant bands are achieved by a folded monopole with a compact size of 11.5 × 15. 6m m 2 . The MIMO system consists of two symmetrically placed monopoles. A stepped slot ended with an ellipse on the ground plane is etched to reduce the mutual coupling between the two monopoles. The overall dimension of this MIMO system is 50 × 50 mm 2 . The prototype of the antenna is fabricated and measured. Measured results show that the antenna's impedance bandwidth is 450 (18%), 350 (10%), 1200 (21.8%) MHz at the three resonant frequency points (2.5 GHz, 3.5 GHz, 5.5 GHz) with mutual coupling between the antenna elements less than �18 dB in whole frequency band, making this antenna a good candidate for portable application.

A wideband planar printed quasi-Yagi antenna with band-notched characteristic is presented. The proposed antenna consists of a microstrip-to-slotline transition structure, a gradient driver dipole, and two parasitic strips as directors. Meanwhile, the arms of the driver and two directors are rotated in a certain angle to improve the gain. To avoid the frequency interference from WLAN operating in the frequency band from 5.15 GHz to 5.825 GHz, an L-shape slot etched on the driver dipole is adopted to achieve a notched band ranging from 4.8 GHz to 6.1 GHz. The ground plane is symmetrically added two stubs to implement the lateral size reduction. The measured bandwidth, determined by the reflection coefficient less than −10 dB, covers from 3 GHz to 10.8 GHz. Better than 8.1 dB F/B ratio and the measured antenna gain varying between 4.7 and 8.3 dBi are also achieved in the operating bandwidth excepting in the notched band.

A closely spaced dual-band notched UWB MIMO antenna is proposed in this paper. A traditional semi-circular monopole with ultra-wideband operation is chosen as an element of the proposed MIMO antenna. When two of the UWB monopoles are put together closely, the mutual coupling between them is apparently strong. To reduce the coupling between the antenna elements, a T-shaped branch is inserted between them, which reduces the mutual coupling obviously over the entire operating band. Also, the T-shaped branch can perform as a compensating radiator which can lower the operating frequencies of the proposed antenna. In order to achieve dual band-notched characteristics, meandering slots are cut in the patches, and symmetrical C-shape strips are nearly placed to the monopoles' feed-lines. The meandering slot is for lower band notch (WiMAX, 3.3{3.7GHz) while the C-shape strips are for upper band (WLAN, 5.15{5.825GHz). The measured radiation e-ciencies, peak gains and radiation patterns are illustrated and show good agreement as anticipated.

A novel compact UWB antenna with 3.5/5.5GHz dual notch-band characteristics is presented. The proposed antenna has a simple structure and compact size of 30 £ 35mm 2 . Firstly, a compact modifled rotated monopole antenna that covers UWB band is achieved. Then by inserting a ‚/4 stub and etching two symmetrical ‚/4 L-shape slots on the UWB antenna achieved before, a dual band-notched ultra-wideband antenna is obtained. The prototypes of UWB antenna with and without notched bands were fabricated and measured. Good performance of dual notched bands, stable gain and omnidirectional radiation patterns make the proposed antenna promising for UWB application.

A novel broadband planar rotated cross monopole antenna, which consists of a vertical patch (area A) and a rotated horizontal patch (area B), is proposed. By rotating the horizontal patch, the bandwidth of the proposed antenna can be signiflcantly enhanced. The efiect of the rotated angle of the horizontal patch on the bandwidth has been deeply studied. The measured results show that the proposed antenna with compact size of 50 £ 50mm 2 can achieve a wide impedance bandwidth (10-dB re∞ection coe-cient) as large as 8.76GHz (2.33{11.09GHz) or about 130%, which is nearly two times of what the corresponding conventional cross monopole antenna was.

A compact multiple-input-multiple-output (MIMO) antenna that covers the WLAN (2.4GHz) and UWB (3.1{10.6GHz) bands for wireless device applications is presented. The proposed antenna consists of two open L-shaped slot (LS) antenna elements and a narrow slot on the ground plane. The antenna elements are placed perpendicularly to each other to obtain a high isolation, and the narrow slot is added to reduce the mutual coupling between antenna elements at the WLAN band (2.4GHz). The presented MIMO antenna has a small size of 40£40mm 2 , and the prototypes of antenna is fabricated and measured. The measured results show that the antenna has an impedance bandwidth of larger than 2.4{10.6GHz with the mutual coupling less than 20dB in WLAN band and 18dB in 3.1{10.6GHz, making the antenna a good candidate for portable applications.

This study proposes a difierential-fed microstrip antenna, which is characterized with an ultra-wideband of 120% (3{12GHz), improved radiation patterns, stable gains, and compact size. Two symmetrical trapezoid shaped slots and four triangle-cut corners on the ground are used to improve the impedance matching over the UWB frequency band. To clarify the improved radiation characteristics, the simulated radiation patterns of the proposed antenna are compared with the conventional single- ended feed UWB antennas. The measured results show that, in the entire frequency band, the designed antenna exhibits a stable radiation patterns and the gain variation is less than 2dB. Furthermore, the polarization purity are increased compared with the conventional ones, especially in the high frequency band.

The design of a novel printed dipole antenna with bandwidth enhancement is proposed for wideband applications. The antenna consists of an integrated balun, two rectangular radiating arms and a modified inductive coplanar stripline (CPS) impedance tuner. By adjusting the parameters of the CPS-tuner and the balun properly, a good performance of bandwidth enhancement is achieved. The measured results indicate that the impedance bandwidth of the proposed antenna, defined by 10-dB return loss, is about 73.9% from 2.54 to 5.52GHz. In addition, good omnidirectional radiation characteristics are also obtained over the whole operating band. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1585–1590, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26883

A novel multiband rhombic slot antenna with a truncated corner is proposed for wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) applications simultaneously. By introducing a pair of straight strips and two etched ∩-shaped slots, the proposed antenna can operate in multibands. The prototype of the proposed antenna has been successfully constructed and tested. The 10 dB return loss bandwidths of them are 550 MHz (3.15–3.70 GHz) and 920 MHz (5.05–5.97 GHz), respectively, which can cover both the WLAN bands (5.15–5.35 GHz and 5.725–5.825 GHz) and the WiMAX bands (3.4–3.6 GHz and 5.25–5.85 GHz). In addition, good monopole-like radiation characteristics with sufficient antenna gains are obtained over the operating bands. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1466–1469, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26837

A novel microstrip-fed ultrawideband elliptical antenna with dual band-notched characteristics is proposed and fabricated. Dual band-notched characteristics are achieved by a defected ground structure and using a tuning stub embedded in the microstrip feed line. The operation bandwidth of the designed antenna is from 2.6 to 12 GHz for voltage standing wave ratio less than 2, except two frequency notched bands of 3.2–4.1 GHz for WiMAX and 4.9–6.0 GHz for wireless local area network. Moreover, the proposed antenna provides a good radiation pattern and a relatively flat gain over the entire frequency band excluding the rejected bands. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:780–783, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26625

A novel tri-band monopole antenna design employing Tshaped quasi-self-complimentary (QSC) resonators is presented. The proposed antenna is composed of a pair of symmetrical QSC resonators, an octagonal monopole radiator and two L-shaped slots. By utilizing these structures, the antenna can yield different resonances to cover the desired bands while maintaining small size and simple structure. Based on this concept, a prototype of tri-band antenna is designed, fabricated and tested. The experimental results show that the antenna has the impedance bandwidths of 190 MHz (2.36–2.55 GHz), 680 MHz (3.37–4.05 GHz) and 1760 MHz (5.12–6.88 GHz), which can cover both WLAN in the 2.4/5.2/5.8 GHz bands and WiMAX in the 3.5 GHz band.

In this paper, a novel triple-band monopole antenna with double coupled C-shaped strips for WLAN/WiMAX applications is presented. By adjusting the dimensions of the outer and inner C-shaped strips, three separated impedance bandwidths of 20% (2.28 ∼ 2.78 GHz), 14% (3.33 ∼ 3.83 GHz) and 19% (4.86 ∼ 5.86 GHz) can be obtained. Especially, the asymmetry inner C-shaped strip can be used to adjust the middle and high band characteristics. With these double coupled C-shaped strips, the proposed antenna shows a good triple-band property to satisfy the requirements of 2.4/5.2/5.8 GHz WLAN bands and 2.5/3.5/5.5 GHz WiMAX bands.

A low-profile and small circularly polarized (CP) antenna is proposed and developed in this letter. The proposed CP antenna consists of two modified linearly polarized (LP) inverted-L antenna (ILA) elements with double-folded arms. The double-folded structure plays a significant role in improving impedance matching and radiation characteristics. By properly adjusting the lengths of two arms, quadrature currents can be produced on two orthogonal elements so that circular polarization is achieved. Since the proposed LP elements are low-profile and small in size, the proposed CP antenna is minimized to be about λ0/4 in lateral size and λ0/7 in height. In addition, the feeding configuration is simplified by using only a short vertical probe instead of an external polarizer. Good agreement is obtained between the simulated and measured results, which validate our design concept. The measured results show that the fabricated CP antenna has a wide impedance bandwidth (VSWR

In this paper, a technique using a novel cross-shaped defected ground structure (DGS) to broaden the operating bandwidth and reduce the size of a conventional DC bias line is proposed. The conventional DC bias line is composed of a λ/4 high impedance transmission line and a proper fan-shaped capacitor. Due to the slowwave characteristics introduced by the DGS, the original length of the λ/4 high impedance transmission line can be shortened while maintain the same electrical length. The experimental result shows that the proposed DC bias line has a much wider operating bandwidth than that of the conventional one by 153% and 83.3% of the initial λ/4 length.

A novel rectangular ring patch antenna with tri-band operation is presented for WLAN and WiMAX applications. The proposed antenna consists of a rectangular ring patch and a pair of straight strips with different lengths. By placing the two strips asymmetrically with respect to the microstrip feed line, the proposed antenna can operate in triple bands. The 10 dB return loss bandwidths of them are 310 MHz (2.39–2.70 GHz), 490 MHz (3.38–3.87 GHz) and 2680 MHz (4.82–7.50 GHz) respectively, which can cover both the WLAN bands (2.4–2.484 GHz, 5.15–5.35 GHz, and 5.725–5.825 GHz) and the WiMAX bands (2.4–2.6 GHz, 3.4–3.6 GHz, 5.25–5.85 GHz). In addition, the overall dimensions of this proposed antenna are 36 mm (length) × 20 mm (width) × 1 mm (thickness), which is compact compared to conventional tri-band antennas.

A novel fractal triangular monopole antenna with truncated and notched ground for the ultra-wideband (UWB) application is presented and studied in this paper. The proposed antenna is designed based on the fractal theory. By inserting three small triangles and three thin slots central symmetrily in the radiation patch, smaller antenna size and more resonant frequencies in the required frequency range are obtained. The antenna has been simulated, fabricated and measured. It is shown that high performance of the designed-antenna is obtained and the Voltage Standing Wave Ratio (VSWR) requirement of less than 2.0 in the frequency band from 2.6 GHz to 14.26 GHz is well satisfied.

A multifunctional meander line polarizer is described. The polarizer is capable of effecting conversions between linear and circular polarization and between left-hand and right-hand circular polarization. It can also cause arbitrary rotation of linear polarization, including converting a wave from horizontal polarization to vertical. The polarizer is analyzed by the spectral domain approach.

A novel printed antenna with dual widebands is proposed and studied for simultaneously satisfying wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) applications. In this study, the configuration consists of a back-to-back F-shaped monopole antenna with a microstrip feedline for excitation and an elliptic conductor-backed plane for band broadening. This antenna has a satisfactory impedance bandwidth sufficiently cover the 2.4/5.2/5.8 GHz WLAN bands and 2.5/3.5/5.5 GHz WiMAX bands.

This article studied a novel Log-Periodic Dipole Antenna (LPDA) with distributed inductive load for size reduction. By adding a short circuit stub at top of the each element, the dimensions of the LPDA are reduced by nearly 50% compared to the conventional one. The impedance bandwidth of the presented antenna is nearly 122% (54∼223MHz) (S11

A compact antenna for dual-band operation is presented. The proposed antenna consists of a C-shaped ground plane and an L-shaped monopole radiator. The Γ-shaped stub extending from the ground can achieve a resonance covering the lower band, whereas the L-shaped monopole operates at the upper band. The antenna prototype is designed, fabricated and tested. The experimental results show the antenna covers 2.37–2.53 GHz and 5–6.37 GHz with 10-dB return loss, satisfying the desired standards of WLAN applications. Besides, good radiation patterns and antenna gains over the operating bands have been obtained.

This paper described the design of microstrip array antenna with operating frequency at 5.8 GHz. The antenna element is realized by the single-layer inset-fed patch antenna with the size of antenna element determined by the operating frequency. The proposed array antenna consists of 12 elements, with all elements arranged symmetrically on two concentric circles. The array factor is calculated by Matlab and compared with the simulated results obtained by the electromagnetic simulation software, which shows a good agreement. The simulated peak gain of the array is 17.56 dBi. The simulation and measured results in this paper can provide a design reference for the practical design of circular array antennas.

A novel method of radiation pattern shaped of dipole-disk antenna by adding a hemisphere conductor is proposed in this paper. The improved dipole-disk antenna has identical beamwidths in E- and H-plane, while its profile does not increase. A model of this antenna is built, stimulated and optimized by a commercial software Ansoft HFSS. Numerical analysis based on stimulation results is made and the design principles involved are described.

A novel antenna called self-structuring antenna (SSA) is proposed. The SSA has an advantage of altering its electrical shape in response to changing the states of switches, which makes it a multi-band antenna. The SSA comprised of rectangular ring antennas is designed by numerical electromagnetic code (NEC), and many numerical investigations are presented and shown that the proposed antenna can achieve multi-band operation.

A wideband printed dipole antenna array is proposed for WLAN and Bluetooth applications. The proposed antenna array, consisting of two printed-strip dipoles, the arms of which are printed on opposite side of an electrically thin dielectric substrate and connected through a parallel strip-line, is presented. The printed strip dipole antenna element is simulated by Ansoft HFSS 8.0. Several prototype antennas are designed and fabricated. Broadband antennas with bandwidth greater than 12% for VSWR /spl les/1.5 operating near 3.5GHz are obtained. This antenna is a good candidate for operation at 2.4GHz, 3.5GHz, or 5.8GHz. The important advantages of these antennas are simplicity in structure, low cost, and ease of manufacture and production largely as printed circuits.

A novel wideband patch dipole antenna is proposed and simulated by Ansoft HFSS. Calculated results show that the relative bandwidth can reach 66.7% with VSWR less than 2. A model antenna is fabricated with microstrip structure. Good agreement is achieved between experimental and simulated results. When mounted on an infinite conducting plane, antenna gain of 7.5 dB is obtained.

A nonradiative dielectric (NRD) waveguide structure (symmetric or asymmetric) Y-branch power combiner/divider is proposed and characterized by full wave mode-matching approach. The analysis is based on step approximation of the waveguide geometry and cascading procedure. A vertical conducting plate is inserted between branches of the Y-type structure to isolate the neighboring ports and then obtain low coupling loss. Bifurcated discontinuity due to insertion of the conducting metallic plate is studied and the generalized scattering matrix for the whole structure is presented mathematically and then simulated numerically.

A novel coplanar waveguide-fed tri-band monopole antenna with a compact radiator (10 × 23 mm2) for WLAN/WiMAX applications is presented. By etching properly an inverted-L slot on the straight strip loaded with a rectangular tuning patch and further adjusting the dimensions and positions of these structures, three distinct wide bands can be achieved. The measured and simulated results show that the proposed antenna has 10 dB impedance bandwidth of 470 MHz (2.38–2.85 GHz), 360 MHz (3.36–3.72 GHz) and 890 MHz (4.98–5.87 GHz) to cover all the 2.4/5.2/5.8 GHz WLAN bands and 2.5/3.5/5.5 GHz WiMAX bands. Also, the proposed antenna produces good dipole-like radiation pattern over the covering bands.

A novel compact printed double-folded inverted-L antenna is presented. The radiator is modified from a printed inverted-L antenna by extending and folding its radiated arm. A unidirectional radiation pattern is obtained as the radiator is mounted on a vertical printed rectangular ground. A slit etched on the ground of proper length and position is used to improve antenna directivity and suppress backward radiation. Measured results indicate that the proposed antenna has a good impedance characteristic (9% for return loss less than 10 dB), excellent front-to-back ratio and forward gain of 5.09 dBi. The antenna is applicable for long-range RFID handheld reader application.

A novel dual-band planar monopole antenna design based on the concept of edge resonator loading is presented. The proposed antenna consists of a pair of symmetry resonators and a bevelled planar radiator. The resonators embedded into the edges of the radiator can provide a new resonance and the resonant frequency can be independently tuned. As an example of this concept, a dual-band antenna prototype for WLAN/C-band applications is designed, fabricated and tested. Measurement results show that the fabricated antenna has good impedance matching, wide bandwidth, omnidirectional radiation patterns, and stable gains in the desired bands.