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A method of designing a printed filtering dipole antenna using codesign of bandpass filter (BPF) and antenna is proposed in this article. The printed dipole antennas consist of two identical arms, which are placed on the opposite sides of the substrate. One arm of the dipole is used to construct the half-wavelength resonator of a typical BPF, and thus filtering and radiation performance can be obtained simultaneously. A third-order filtering dipole antenna is designed and analyzed in detail to demonstrate the codesign method. The measured S11 of the filtering dipole antenna is less than −11 dB in the range of 0.94–1.094 GHz and the peak gain is 7.8 dBi. To extend this design method, a third-order ±45° dual-polarized filtering dipole antenna is designed and measured. The measured S11 and S22 of the ±45° dual-polarized filtering dipole antenna are both less than −11 dB in the range of 0.94–1.08 GHz. Besides, the isolation between them is higher than 20 dB in the passband. The measured radiation patterns show that the dual-polarized filtering dipole antenna would be a potential candidate for base stations. [ABSTRACT FROM AUTHOR]

In this communication, an approach for designing multi-band microstrip slot antennas is proposed. Multiple resonators are loaded on a conventional microstrip slot antenna to introduce multiple resonances. The number of the operational bands of the antenna can be easily controlled by varying the number of the loading resonators. The locations of each resonance can be adjusted by varying the positions and lengths of the loading resonators together with the geometry of the slot if necessary. For validation, prototypes with dual-, tri-, and quad-band operations are designed, fabricated, and measured. Since no modified slot is used in this design method, all the operating bands show good bidirectional radiation patterns. The measured and simulated results agree well. The proposed antenna features low profile, small radiating slot, and easy fabrication, showing promising application prospect for modern communication system. [ABSTRACT FROM AUTHOR]

In this paper, two novel $4 \times 6$ filtering Butler matrices with uniform and nonuniform power distribution are proposed. The matrices, consisting of a network of coupled resonators and two phase shifters, provide power division and phase shift together with a bandpass transfer function. The analytical synthesis procedures for the $4 \times 6$ filtering Butler matrices are presented. To verify the concept experimentally, two $4 \times 6$ filtering Butler matrices, operating at 2.4 GHz, with uniform and nonuniform power distribution are designed, fabricated, and measured. Simulated and measured results are found to be in good agreement with each other. Multibeam antenna arrays are realized by using the Butler matrix, and the theoretical analysis has been confirmed by measurements of multibeam antenna arrays, which show reduced sidelobe level (SLL). [ABSTRACT FROM AUTHOR]

A wideband circularly polarized (CP) $4 \times 4$ millimeter-wave antenna array composed of novel microstrip antenna elements is presented for IEEE 802.11 aj (45 GHz) application. Through introducing the L-shaped branches and truncated corners to the microstrip antenna element, an impedance bandwidth of 24.9% and a 3 dB axial ratio (AR) bandwidth of 17.3% are achieved. To clarify the effects of the L-shaped branches and truncated corners, the phase difference and amplitude ratios of the 180° and 90° electric field components at the point of (0,0,r) are extracted and analyzed. A simple and compact microstrip feeding network is designed to excite the CP antenna array, and two-layer PCB boards are used to implement the proposed array. The electromagnetic energy is coupled to the radiators from the feeding network through the aperture etched on the middle ground. The measured 3 dB AR bandwidth of the antenna array is 16% from 41.9 to 49.1 GHz, and the measured gain is all greater than 17 dBic within the band from 41 to 49 GHz. [ABSTRACT FROM AUTHOR]

In this paper, a novel filtering 180° hybrid coupler is proposed and used to design a $2 \times 4$ filtering Butler matrix. The filtering 180° hybrid coupler can provide power division and phase shift together with a second-order bandpass transfer function, and is based only on coupled resonators. The $2 \times 4$ filtering Butler matrix is easily realized by utilizing several hybrid couplers. The analytical synthesis procedures for the hybrid coupler and Butler matrix are presented in this paper. Finally, broadside and end-fire arrays are realized by using the Butler matrix. To illustrate the concept experimentally, a filtering 180° microstrip hybrid coupler and a $2 \times 4$ filtering microstrip Butler matrix are designed, fabricated, and measured. Simulation and measured results are found to be in good agreement with each other. [ABSTRACT FROM AUTHOR]

This letter finds that bandwidth of a circularly polarized (CP) microstrip antenna can be enhanced by using two annular-sector-shaped parasitic patches. This is because the induced current on the parasitic patches involves both x- and y-components, hence it can control the theta and phi components of the electric field. For the purpose of demonstration, a bandwidth-enhanced CP microstrip antenna is proposed and analyzed. Except from low profile and compact size, its impedance matching can be adjusted while keeping the CP feature unchanged, which simplifies the design process. The axial-ratio bandwidth of the proposed antenna can be effectively increased from 1.3% to 3.3%, while its impedance bandwidth is increased from 4.3% to 6.0%. [ABSTRACT FROM AUTHOR]

A small annular slotted BeiDou antenna with symmetric slits is proposed for applications in Compass Navigation Satellite System of China. Two symmetric annular slots with tabs are embedded onto a circular microstrip patch for circularly polarized (CP) radiation. Good CP radiation and impedance matching can be achieved by reasonably adjusting the radii of the annular slots and the position of the tabs. Six pairs of symmetric slits are embedded along the radial direction of the circular patch to reduce antenna size. We achieve a total patch area reduction of 23.3% compared with the traditional tuning stub CP antenna. Owing to the symmetric structure, the deviation of the phase center is only about 1.76 mm at the central frequency. The measured results agree well with the simulated results. [ABSTRACT FROM AUTHOR]

This paper presents a novel tri-band (X/Ku/Ka-band) planar antenna array with dual polarizations and shared aperture. Compared with traditional dual-polarized arrays, the proposed array has advantages of low cost, low profile, and high integration. Three types of antennas resonating at different frequencies, including the perforated patch, stacked patch, and slim crosspatch, are innovatively interleaved in the same aperture. The crosspatch fed by proximity coupling is presented as Ku-band element for its advantages of compact size, high isolation, and pure polarization. The techniques such as series feed and reverse feed are utilized to implement the six feed networks in a compact size with reduced cross polarizations. Measured results agree well with the simulations, showing three operation bands at X-, Ku-, and Ka-bands with the bandwidths of 3.6%, 6.7%, and 5.3%, respectively. The antenna also exhibits excellent radiation performance with the cross-polarization discrimination over 25 dB at the three bands. To the best of the author’s knowledge, this is the first shared-aperture X/Ku/Ka-band dual-polarized antenna array reported, which is useful for potential synthetic aperture radar applications. [ABSTRACT FROM AUTHOR]

A novel wideband bandstop filter is proposed in this paper. Using one uniform impedance resonator and two stepped impedance resonators, five transmission zeros are introduced in the stopband. Appropriate positioning of these zeros ensures the high selectivity and flat rejection level of the stopband. The bandwidth of the filter can be conveniently controlled by the characteristic impedances of the connecting lines and resonators. A complete analytic analysis is proposed to fully control the positions of transmission zeros, and the design equations and design rules for the bandstop filter are given in detail by using the lossless transmission line model. To illustrate the concept, a wideband bandstop filter with center frequency at 2 GHz and rejection level below 20 dB is fabricated. Theoretical, simulated, and measured results are found in good agreement with each other, and the measured 20-dB rejection bandwidth is as wide as 150%. [ABSTRACT FROM PUBLISHER]

This paper proposes a quasi-elliptic filter with slot coupling and nonadjacent cross coupling based on the substrate integrated waveguide (SIW) cavity. The slots etched on the top metal plane of SIWcavity are used to produce electrical coupling, and the cross coupling is realized by the microstrip transmission line above the SIW cavity. The coupling strength is mainly controlled by the width and height of the slot. The length of the open-ended microstrip line controls the sign of the cross coupling. The cross coupling with different signs are used in the filter to produce a pair of transmission zeros (TZs) at both sides of the passband. In order to prove the validity, a fourth-order SIW quasi-elliptic filter with TZsat both sides of the passband is fabricated in a two-layer printed circuit board. The measured insertion loss at a center frequency of 3.7 GHz is 1.1 dB. The return loss within the passband is below −18 dB with a fractional bandwidth of 16%. The measured results are in good agreement with the simulated results. [ABSTRACT FROM PUBLISHER]

This paper proposes a simple and effective method to designing wide-stopband bandpass filters and diplexers using uniform impedance resonators. Microstrip terminated parallel coupled lines are utilized to generate the filtering functions. By adjustment of the electrical lengths of the parallel coupled lines and open-circuited stubs, multiple transmission zeros can be obtained. Appropriate positioning of these zeros enables the suppression of spurious frequencies. A complete analytic analysis is proposed to fully control the positions of transmission zeros, and the design equations and design rules for both homogeneous and inhomogeneous mediums are given in detail. Different combinations of the frequency position of the transmission zeros can provide various characteristics. To extend the stopband bandwidth, one or more transmission zeros can be distributed on different harmonic frequencies. To demonstrate the proposed method, two bandpass filters and a diplexer are designed and fabricated. The measured results are in good agreement with the simulated ones. The first filter provides a high attenuation of 40 dB up to 6.8 times the fundamental frequency $(f_{{{0}}})$ and the second filter provides a lower attenuation of 28 dB, but this time extending up to $14.9f_{{{0}}}$ . [ABSTRACT FROM AUTHOR]

Compact microstrip low-pass filters (LPFs) with ultrawide stopband based on a defected ground structure (DGS) and their design procedures are presented in this paper. A key merit of the filter configuration is that the selectivity of the LPFs can be conveniently controlled, whereas the bandwidth is fixed. The LPFs are realized using open-circuited uniform impedance stubs and stepped-impedance stubs (SISs). The position of the transmission zeros can be freely controlled by tuning the impedance ratio of the SISs. To expand the stopband, the dumbbell DGS is used to suppress the spurious passbands of the LPFs. Two demonstration filters with a cutoff frequency at 1 GHz have been designed, fabricated, and measured. The measured results indicate good performance: broad stopband ( >15 fc or 20~fc ), low passband insertion loss (<0.3 dB), compact size, and sharp skirt characteristic. [ABSTRACT FROM PUBLISHER]

A circularly polarized antenna with wide axial-ratio beamwidth is presented by placing two pairs of parallel dipoles in a square contour. Firstly, our study demonstrates that circular polarization can be achieved at the broadside by setting a 90^\circ phase difference between the vertical and horizontal paired-dipoles. Secondly, the principle of wide-beamwidth circularly-polarized radiation is described under the similarity in polar and azimuthal radiation pattern for a pair of parallel dipoles. After the spacing between two parallel dipoles is studied, the similar radiation patterns in these two orthogonal planes are derived. As such, a wide-beamwidth circular polarization can be achieved by placing the two pairs of parallel dipoles vertically and horizontally while setting a 90^\circ phase difference between them. In final, a circularly-polarized printed antenna is designed and fabricated on a single dielectric substrate. The two arms of its four dipoles are formed on the lower and upper interfaces of the substrate, and they are excited by a 1-to-4 probe-to-microstrip feeding network. Experimental results show good agreement with simulated ones in terms of radiation pattern/gain, axial ratio and returned loss. In particular, the 3-dB axial ratio beamwidth at the central frequency of 1.6 GHz has extended to 126^\circ in an angular range from -63^\circ to +63^\circ. The fabricated antenna exhibits a low-profile property with the height of 0.0043 free-space wavelength. [ABSTRACT FROM PUBLISHER]

ABSTRACT This article proposes a novel type of microstrip cascaded triplet filter with controllable electric and magnetic coupling. The electric coupling can be tuned by adjusting the gap between the resonators, while the magnetic coupling is dominated by the diameter of the via-hole. A transmission zero on the upper stopband is produced by the inductive cross-coupling. To further improve the selectivity of the filter, the source-load coupling is also proposed to introduce two tunable transmission zeros. To expand the stopband, proper feeding position is selected to suppress the third and fifth harmonics. Based on the proposed structure, a third-order filter are designed and fabricated. Good agreement between the measured and simulated data is obtained. Measured results indicate that a rejection level of 20 dB up to more than six times the passband frequency can be obtained. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2937-2940, 2014 [ABSTRACT FROM AUTHOR]

In this paper, an E-plane waveguide power divider and a waveguide-to-microstrip transition are used to form a waveguide magic-T with four arms in the same E-plane. The input port of the original E-plane waveguide power divider acts as the difference port of the magic-T, and a waveguide-to-microstrip transition is utilized to realize the sum port. The four arms are in the same plane, and traditional matching elements, such as cones, wedges, pins, and irises are not needed. The proposed magic-T features easy connection, fabrication, and assembly. The principle and design procedure are described in detail. A Ka-band E-plane waveguide magic-T is designed, fabricated, and measured. A fractional bandwidth of 21% is achieved. The measured and simulated results show good amplitude, phase, and isolation characteristics validating the proposed magic-T. [ABSTRACT FROM AUTHOR]

This letter reports a new kind of matching network for quad-channel diplexers. The matching network is comprised by some open- and short-circuited transmission lines, which can be chosen based on the design graph. The impact of loading resonators on the network is discussed. The diplexer can be easily realized by the combination of different bandpass filters without complicated tuning. To illustrate the concept, one quad-channel diplexer is designed, fabricated, and measured. Simulated and measured results are found to be in good agreement with each other. [ABSTRACT FROM PUBLISHER]

ABSTRACT Compact microstrip triband bandpass filters are proposed and designed based on asymmetrically loaded resonators in this letter. By attaching single open-circuited stub or short-circuited stub at the proper position of the microstrip line and adjusting their lengths, the first three resonant modes of the proposed resonators can be usefully allocated within the three passbands of the triband filter. Two alternative triband filters with compact size are designed and measured. The measured results provide successful verification for the theoretical analysis. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1862-1865, 2014 [ABSTRACT FROM AUTHOR]

A compact single-feed circularly-polarized (CP) wide beam microstrip antenna is proposed for CNSS application. The antenna is designed with a double-layer structure, comprising a circular patch with two rectangular stubs along the diameter direction and a parasitic ring right above it. The resonance frequency and the CP characteristics are mainly controlled by the circular patch and the rectangular stubs, respectively. The vertical HPBW (half power beam width) could be widened by the parasitic ring. Experimental results show that the measured vertical HPBW is approximately 140^\circ and the measured out-of-roundness for the horizontal radiation pattern is only 1.1 dB. Besides, it could maintain good low-profile characteristics. [ABSTRACT FROM PUBLISHER]

This paper presents, for the first time, the design and implementation of a planar tunable crossover. This crossover is derived from the conventional two-section branch-line crossover by substituting its three vertical transmission lines with the two fixed capacitors and one tunable capacitor to realize the tunable passband. By designing its horizontal transmission lines as coupled lines and replacing its vertical transmission lines by three capacitors, the circuit size is greatly reduced. Closed-form equations for design parameters are derived to simplify design procedure of the proposed crossover. For verification, a crossover with tunable frequency of 1.2–2.4 GHz is designed based on the given design closed-form equations. Finally, a microstrip tunable crossover with one varactor diode 1sv277 is fabricated and measured. The measured results are in good agreement with the simulated ones. The results show that the passband can be tuned in a frequency range from 1.29 to 2.06 GHz, yielding 46% tuning range with better than 20-dB return loss and isolation, while the insertion loss varies from 0.59 to 1.22 dB. The crossover occupies a small size of 0.25\ \lambda g \times 0.04\ \lambda g, which is only 8% of the area of conventional two-section branch-line crossover. [ABSTRACT FROM AUTHOR]

ABSTRACT Tri-band bandpass filter using centrally loaded resonators is presented in this article. The triple-passband characteristics are realized by properly controlling the lengths and impedances of the uniform impedance resonator and the stub. To illustrate the concept, two tri-band filters are designed, fabricated, and measured. Simulated and measured results are found to be in good agreement with each other. The prototype of the tri-band filters achieve insertion loss of 1.6, 1.9, and 1.9 dB at 2.4, 3.5, 5.8 GHz, 1.2, 1.3, and 1.3 dB at 1.57, 2.45, 5.2 GHz, respectively. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2695-2699, 2013 [ABSTRACT FROM AUTHOR]

A dual-band planar crossover with simple structure is proposed. This crossover is derived from the conventional single-band two-section branch-line crossover by doubly extending the length of its vertical transmission lines, which realizes the dual-band operation. Closed-form equations for design parameters are derived, which simplifies design procedure of the proposed crossover and shows that the available bandwidth of the passband increases with the increasing frequency ratio. By adding one short-circuited stub and one open-circuited stub to the originally proposed dual-band crossover, two types of modified dual-band crossovers and their closed-form design equations are proposed for smaller and larger frequency ratios applications. For verification, four different dual-band crossovers are designed and simulated, of which two microstrip crossovers operating at 1/1.8 and 1/2.3 GHz are fabricated and measured. The measured results are in good agreement with the simulated ones. [ABSTRACT FROM PUBLISHER]

A compact broadband Gysel power divider with arbitrary power-dividing ratio is proposed. This divider is derived from the conventional Gysel power divider by substituting an ideal phase inverter for the 180^\circ phase shifter, which significantly improves the bandwidth and reduces the circumference to 1 \lambdag evaluated at the center frequency. A wide range of power-dividing ratio (1–6.25) is supported by changing the impedance ratio of the transmission lines, while the dual-band impedance matching characteristic with frequency ratio (1–2.9) is obtained only by varying the impedances of the transmission lines (\20\--\135∼\Omega). Closed-form equations are derived for design parameters. The ideal phase inverter is realized by two transitions: microstrip-to-slotline and slotline-to-microstrip transitions. By utilizing this phase inverter, two microstrip Gysel dividers with power-dividing ratios of 1:1 and 2:1 and operating at 1.5/2.5 and 1/2 GHz, respectively, are designed, fabricated, and measured. The measured results are in good agreement with the simulated ones. The first measured results show a bandwidth of 80% with better than 15-dB return loss and 29-dB isolation from 1.19 to 2.76 GHz. The second measured results show a bandwidth of 95.8% with better than 12-dB return loss and 24-dB isolation from 0.8 to 2.27 GHz. To the authors' knowledge, the most wideband Gysel power divider using microstrip technology is proposed for the first time. [ABSTRACT FROM AUTHOR]

This article presents a novel approach for designing dual- and tri-band bandpass filters with independently controlled center frequencies and bandwidths. λ/4 and λ/2 resonators are used to obtain dual- and tri-band responses. λ/4 resonators are designed to operate at the lower passband(s) and λ/2 resonators are designed to operate at the higher passband. The bandwidth of each passband can be tuned independently by adjusting the coupling gap. To verify the presented concept, two experimental examples of filters have been designed and fabricated and good agreements are shown between the simulation and the measurement. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 638–641, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24111 [ABSTRACT FROM AUTHOR]

A novel branch-line coupler with three controllable operating frequencies is presented for tri-band operation. The tri-band operation is achieved by attaching a matching circuit to each port of the conventional branch-line coupler. Closed-form design equations are derived. For verification, a microstrip 3 dB branch-line coupler operating at 0.9/2/2.45 GHz is designed, fabricated and measured. The measured results are in good agreement with the simulated results. When the return loss and isolation are better than 15 dB and 20 dB simultaneously, the measured bandwidths of three operating bands are all almost 40 MHz, while the amplitude imbalance is below 0.8 dB and the phase difference is within -90^\circ\pm 3^\circ. [ABSTRACT FROM PUBLISHER]

A response from the authors of the article "Compact broadband Gysel power divider with arbitrary power-dividing ratio using microstrip/slotline phase inverter" in the May 2012 issue is presented.