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Wideband conformal transmitarrays at E-band are developed for multibeam applications in this article. A triple-layer element with double split rings is presented for wideband transmissions, achieving a 360° continuous phase variation range at 74 GHz with less than 2.3 dB transmission loss. A comprehensive design methodology of multibeam conformal transmitarrays is demonstrated for various platforms with different curvatures. To validate the theoretical analysis, conformal transmitarrays with two different curvatures are designed, fabricated, and measured. Multiple radiation beams are realized between ± 30° and ± 45° for the two prototypes, respectively. Good agreement is obtained between simulation and measurement. The 3 dB gain bandwidths are 30% from 66.5 to 90 GHz, and 27.8% from 68 to 90 GHz for the two designs, respectively, covering the entire E-band. [ABSTRACT FROM AUTHOR]

A Ku-band electronic 2-dimensional (2-D) beam-scanning transmitarray employing a new reconfigurable dual-layer Huygens element is developed in this article. The Huygens element consists of two metallic crosses printed on two layers of a dielectric substrate, which enables a near nonreflection Huygens resonance. A 1 bit phase compensation with low transmission loss is realized by controlling two p-i-n diodes on the element. Compared with many other reconfigurable transmitarray elements using multilayer structures with metallic vias, the proposed reconfigurable Huygens element has a much simpler configuration with a simpler biasing network, and it is not affected by multilayer alignment errors. This particularly facilitates large aperture array development at higher frequencies. To validate the design concept, an electronically reconfigurable transmitarray with the proposed element is fabricated at 13 GHz. Good agreement between the measured and simulated results is found, showing 2-D scanning beams within ±50° in the E-plane and ±40° in the H-plane with a maximum realized gain of 18.4 dBi. [ABSTRACT FROM AUTHOR]

A multiport circular array of endfire Yagi–Uda monopoles with a full beam coverage of the azimuth plane is developed in this communication. The known issue that a vertical monopole antenna on a finite-sized horizontal ground plane radiates an elevated beam is investigated. It is demonstrated that this effect can be mitigated by inserting resonant structures, i.e., slots, into the ground plane to redirect the radiated beam back to the horizontal direction. An endfire monopole-based Yagi–Uda antenna is then developed that radiates a directed endfire beam. A multiport circular array of these antennas is optimized to provide beam coverage over the full 360° azimuthal plane. A sector of this circular array of monopole-based Yagi–Uda antennas was simulated, fabricated, and measured to verify the concepts. Good agreement between the simulated and measured results is confirmed. [ABSTRACT FROM AUTHOR]

A transmitarray antenna with an elliptical cylindrical shape is presented for a wide-angle multibeam radiation in this communication. The transmitarray has a cylindrical radiating aperture with an elliptical cross-section, namely, elliptical cylindrical shape. Multiple feeds can be placed on the middle horizontal plane to realize multiple beams. Inspired by a 2-D Ruze lens, the antenna shape and the phase compensation are jointly designed according to the desired maximal beam direction. Innovative methods including a feed refocusing analysis and a virtual focal length are utilized to achieve the phase compensation across the 3-D aperture for multiple beam radiations with a small scanning loss. In order to validate the proposed antenna, a prototype operating in the millimeter-wave (mm-wave) $E$ -band has been designed, fabricated, and measured. By changing the position of the feeding gain horn along the refocusing arc, the main beam of antenna can be scanned in 11 directions. The measured peak boresight realized gain is 27 dBi at 70.5 GHz and a beam coverage of ±43° with a less than 2.7 dB scanning loss is obtained. [ABSTRACT FROM AUTHOR]

In contrast to using multilayer frequency selective surface (FSS) elements or tightly coupled elements, a novel technique is introduced here to achieve ultrawideband planar and conformal transmitarrays, which are based on connected elements like those used in connected arrays. In particular, the elements consist of a horizontally connected slot-bowtie and vertical meander slot-lines. The elements are capable of achieving a 360° phase variation range at the highest frequency 17 GHz with the transmission loss less than 3 dB from 6 to 17 GHz. The transmitarrays have been designed, fabricated, and measured in both planar and conformal versions. Stable boresight radiation patterns from 6 to 17 GHz have been obtained for both antennas. Compared to conformal transmitarrays using multilayer FSS elements, the proposed solution has a much wider bandwidth of radiation patterns. Good agreement has been found between simulation and measurement. [ABSTRACT FROM AUTHOR]

A low radar cross section (RCS) transmitarray is presented in this communication using phase controllable absorptive frequency-selective transmission (AFST) elements. The element consists of asymmetrical resonators with resistors to obtain an absorption–transmission–absorption response. The transmission phase within the transmission band can be controlled by rotating the AFST elements, achieving a 1 bit phase change. A low-RCS transmitarray using the developed elements is designed, fabricated, and measured. Compared with a reference transmitarray, the radiation performance of the low-RCS one is almost unchanged with a realized gain of 24.4 dBi. Significant RCS reductions have been realized for dual polarizations of the impinging electromagnetic (EM) waves. The 10 dB RCS reduction bandwidths are 18% and 14% for the lower and upper absorption bands, respectively. [ABSTRACT FROM AUTHOR]

A high-efficiency conformal transmitarray with ultrathin dual-layer Huygens element is developed. The element consists of “I” shape patches for magnetic response and “T” shape stubs for electric response printed on two metal layers of a single substrate with only 0.5 mm thickness ($\lambda _{0}$ /60 at 10 GHz). By tuning the magnetic and electric responses, the transmitting phase of the element can be changed. Eight elements are designed to cover quantized 360° phase range with a maximal 1.67 dB loss. Then, the proposed elements are employed in a small conformal transmitarray design. To improve the antenna efficiency, the elements’ dimensions are calculated by considering the oblique incidence effects. Finally, a cylindrically conformal transmitarray with a larger aperture size is simulated, fabricated, and measured. It can achieve a measured gain of 20.6 dBi with a 47% aperture efficiency. [ABSTRACT FROM AUTHOR]

A simple single-layer reconfigurable leaky-wave antenna (LWA) is presented that has polarization agility and beam-scanning functionality. This LWA system realizes a scanned beam that can be switched between all of its linear polarization (LP) and circular polarization (CP) states using only one dc biasing source. A slot-loaded substrate-integrated waveguide (SIW)-based LWA is first explored to attain CP performance with continuous beam scanning through broadside. This CP LWA realizes a measured CP performance with a 3 dB gain variance within 2.75–3.35 GHz for scan angles ranging from −28.6° to +31.5°. A row of shorted stubs is then incorporated into the CP LWA to obtain similar LP performance. Finally, by introducing p-i-n diodes into this LP LWA configuration to facilitate reconfigurable connections between the main patch and the shorted stubs, the radiated fields can be switched between all of its CP and LP states. The measured results of all three antennas confirm their simulated performance. It is demonstrated that the main beam of the polarization-reconfigurable LWA can be scanned from −31.5° to +17.1° with gain variations between 9.5 and 12.8 dBic in its CP state and from −34.3° to +20° with them between 7.8 and 11.7 dBi in its LP state. [ABSTRACT FROM AUTHOR]

Fixed-frequency beam scanning leaky-wave antennas (LWAs) that can scan their main beam over a specific frequency band are highly desired for future wireless communication systems. A composite right-/left-handed (CRLH) LWA is developed in this article that facilitates fixed-frequency continuous beam scanning over a wide operational frequency band. A variation of a simple single-layer nonreconfigurable frequency-based continuous beam scanning CRLH LWA is considered first. Its dispersion properties are approximately investigated using an equivalent circuit model. It is reported how two groups of varactor diodes can be incorporated into its basic circuit model to electronically control its dispersion behavior. An optimized reconfigurable CRLH LWA with practical dc biasing lines is then realized from this nonreconfigurable design. Fixed-frequency continuous beam scanning, from backward to forward directions through broadside, is reported over a wide operational frequency band. Simulations predict that the antenna can operate from 4.75 to 5.25 GHz with the main beam being continuously scannable at each frequency point. A prototype was fabricated, assembled, and tested. The measured results confirm its simulated performance characteristics. [ABSTRACT FROM AUTHOR]

A novel conformal transmitarray with beam steering ability is presented. First, an ultra-thin transmitarray element consisting of three layers of identical square ring slots is developed. The element has a thickness of 0.508 mm (0.04 wavelength in the free space at 25 GHz), achieving a transmission phase range of 330° with a maximum 3.6 dB loss. The element is then applied to a curved transmitarray conformal to a cylindrical surface fed by a standard gain horn with about a 10-dBi gain. A prototype is fabricated radiating a boresight beam with a peak measured gain of 19.6 dBi and an aperture efficiency of 25.1%. Second, when the transmitting surface of the above array is divided into two parts from the middle with different main beam directions, the combined beam can be radiated to an oblique angle with respect to the boresight direction. Using this method, a mechanical beam scanning conformal transmitarray antenna is designed. Its size is about 2.5 times larger than the fixed-beam one and consists of six transmitting surfaces with main beams directed to different angles. By rotating the feed horn to different positions, the main beam of the array can be switched to ±15°, ±10°, ±5°, and 0°. A prototype is fabricated with a stable gain of about 18.7 dBi at all beam angles. [ABSTRACT FROM AUTHOR]

Circularly polarized (CP) antennas are in high demand for use in future wireless communications. To advance the development of CP substrate-integrated-waveguide (SIW) leaky-wave antennas (LWAs) with the intent to meet this demand, a novel benzene-ring-shaped slot-loaded LWA with partially reflecting wall (PRW) vias is investigated and verified to realize wide-angle continuous beam scanning with consistent gain. The dispersion features of slot-loaded SIW LWAs with PRW vias are theoretically explored using an equivalent circuit model. The CP radiation feature is investigated numerically utilizing the E- and H-field distributions of an initial design and its equivalent magnetic currents. The results of these studies are used to demonstrate that improved CP performance over a wide-angle scan range can be attained with a change from a standard slot shape to a benzene-ring-shaped slot. The resulting benzene-ring-shaped slot-loaded CP SIW LWA was optimized, fabricated, and measured. The measured results verify that a CP beam was continuously scanned through a wide angle from backward to forward directions with a consistent gain. The prototype exhibits a continuous 97.1° CP beam scan with a gain variation between 8 and 11.3 dBic when the source frequency is swept from 9.35 to 11.75 GHz. [ABSTRACT FROM AUTHOR]

A wideband, low-profile, tightly coupled antenna array with a simple feed network is presented. The dipole and feed networks in each unit cell are printed on both sides of a single RT/Duroid 6010 substrate with a relative dielectric constant of 10.2. The feed network, composed of meandered impedance transformer and balun sections, is designed based on Klopfenstein tapered microstrip lines. The wide-angle impedance matching is empowered by a novel wideband metasurface superstrate. For the optimum design, scanning to 70° along the E-plane is obtained together with a very high array figure of merit PA = 2.84. The H-plane scan extends to 55°. The broadside impedance bandwidth is 5.5:1 (0.80–4.38) GHz with an active voltage standing-wave ratio value ≤2. The overall height of the array above the ground plane is $0.088\lambda _{\mathrm {L}}$ , where $\lambda _{\mathrm {L}}$ is the wavelength at the lowest frequency of operation. A prototype was fabricated and tested to confirm the design concepts. [ABSTRACT FROM AUTHOR]

For many leaky-wave antennas (LWAs), it is challenging to realize beam scanning through broadside. A problem is the presence of an open stopband (OSB), which restricts radiation in the broadside direction. In this paper, a novel substrate integrated waveguide (SIW)-based LWA is described to overcome the OSB problem and provide beam scanning continuously from the backward to the forward direction from a conventional periodic LWA. It is demonstrated that the $n =-1$ spatial harmonic can be excited efficiently from an SIW LWA and enables broadside radiation. However, it was found in our initial design that when the beam scans through the broadside, the cross-polarization level increases significantly compared to the beam close to the backfire direction. A technique is developed to reduce the cross-polarization level. As a result, a new antenna configuration is created. The antenna design has been realized and measured to validate the concept. The measured beam scanning range of the prototype is from −74° to +45° (119° of beam scanning) when the frequency sweeps from 7.625 to 11 GHz, and the measured cross-polarization level is 20.8 dB low at the main beam direction for the broadside beam. [ABSTRACT FROM AUTHOR]

A major challenge for a combined reconfigurable antenna is to realize both polarization switching and beam steering independently in a compact antenna structure. A cavity-backed proximity-coupled reconfigurable microstrip antenna proposed in this communication provides an efficient solution. Beam lead p-i-n diodes DSM8100–000 are employed as switching elements to achieve reconfiguration. Three different linear polarizations (0°, 45°, and 90°) are realized by switching the diodes on a proximity-coupled feed network. For each polarization state, the main beam can be steered to three directions by using a reconfigurable parasitic-element network. The parasitic-element network is printed on the same plane of the radiating patch, thereby making the antenna compact. This antenna has nine different working modes, and for all the working modes, the reflection coefficients are below −10 dB with the measured realized gains ranging from 7.2 to 8.1 dBi. [ABSTRACT FROM PUBLISHER]

This communication introduces a wideband hybrid feeding method for full-wavelength dipole antennas with a reflector. A full-wavelength dipole is designed to cover the band from 698 to 960 MHz for cellular base station applications. Its matching circuit consists of a triple-tuned circuit and a quasi-quarter-wavelength impedance transformer. The proposed matching circuit can provide balanced feeding as a balun and has a compact size. The working mechanism and a complete design scheme of the proposed matching circuit are elaborated. The matching circuit is designed and optimized using a circuit theory model and then physically realized using microstrip lines based on full-wave simulation. The measured reflection coefficient |S11| is lesser than −14 dB across the entire band from 698 to 960 MHz, exhibiting a bandwidth of 32%. This is the first time that a wideband center-fed full-wavelength dipole is proposed. [ABSTRACT FROM AUTHOR]

A novel multi-linear polarization (multi-LP) reconfigurable unidirectional circular patch antenna is proposed, which can switch among four LPs at every 45° rotation. The patch antenna is fed in the center and shorting posts are used to excite TM11 mode with LP. By controlling the connections between the four shorting posts and the ground plane using p-i-n diodes, four reconfigurable polarization states at \phi =0 ^\circ , \phi =45 ^\circ , \phi =90 ^\circ , or \phi =135 ^\circ can be realized. The size of this antenna is about $0.57\lambda \times 0.57\lambda \times 0.07\lambda $ at 2.45 GHz. It can be easily fabricated and has a simple biasing network. The measured overlapping impedance bandwidth for different polarizations under the condition |\text{S}11| \leq -10 dB is from 2.33 to 2.50 GHz, which agrees well with the simulated one. Moreover, the antenna maintains stable radiation patterns and the measured realized gains range from 5.3 to 5.9 dBi. [ABSTRACT FROM PUBLISHER]

A novel partially reflective surface (PRS) antenna is proposed, which can electronically alter its polarization between linear polarization, left-hand circular polarization (CP), and right-hand CP. The antenna consists of a shorted annular patch antenna as the source, a PRS structure to enhance the gain, and a reconfigurable Wilkinson power divider as the feed network. Four p-i-n diodes are inserted into each branch of the power divider to change its electrical length. By switching the p-i-n diodes ON and OFF, a phase difference of 0°, 90°, or −90° can be realized at the two output ports of the feed network, hence enabling the antenna to radiate either a linearly polarized signal or left/right-handed circularly polarized signal. A prototype antenna with the biasing network is designed, fabricated, and measured. Good agreement between the simulated and measured results is achieved. Measurement results show that the proposed antenna has an overlapped 10-dB impedance bandwidth and 3-dB axial-ratio bandwidth of 4.7–5.36 GHz (13.1%). The average realized gains are $\sim 9$ dBi/dBic, which remain reasonably stable for different polarizations. The proposed antenna outperforms most of the reported polarization reconfigurable antennas for its wide bandwidth and relatively high gain. [ABSTRACT FROM PUBLISHER]

A linearly polarized broadband reflectarray is presented employing a novel single layer subwavelength phase shifting element. The size of the element is a fifth of a wavelength at the center frequency of 10 GHz and the element consists of double concentric square rings of meander lines. By changing the length of the meander line, a 420° phase variation range is achieved at the center frequency. This characteristic makes the proposed configuration unique, as most of the reported subwavelength reflectarray elements can only realize a phase range far less than 360°. In addition, the slope of the phase response remains almost constant from 9 to 11 GHz, demonstrating a broadband property. A $48 \times 48$-element reflectarray antenna is simulated, fabricated, and measured. Good agreement is obtained between simulated and measured results. A measured 1.5-dB gain bandwidth of 18% and 56.5% aperture efficiency is achieved. [ABSTRACT FROM AUTHOR]

The design of a novel partially reflective surface (PRS) antenna with the capability of beam steering is presented in this paper. The beam steering is realized by employing a reconfigurable PRS structure to achieve a changeable reflection phase as well as using a phased array as the source to excite the PRS antenna. A prototype antenna including the biasing network is fabricated and measured. It achieves a consistent beam steering from – 15° to 15° with respect to the broadside direction across an overlapped frequency range from 5.5 to 5.7 GHz with measured realized gains over 12 dBi. Good agreement between the simulated and measured results for the input reflection coefficients and radiation patterns is achieved, which validates the feasibility of the design principle. Compared with other beam steering PRS antennas, the proposed one enables a larger beam steering angle with comparable gains, requires a simpler biasing network, and is more compact. [ABSTRACT FROM PUBLISHER]

A novel microstrip circular disc monopole antenna with a reconfigurable 10-dB impedance bandwidth is proposed in this communication for cognitive radios (CRs). The antenna is fed by a microstrip line integrated with a bandpass filter based on a three-line coupled resonator (TLCR). The reconfiguration of the filter enables the monopole antenna to operate at either a wideband state or a narrowband state by using a PIN diode. For the narrowband state, two varactor diodes are employed to change the antenna operating frequency from 3.9 to 4.82 GHz continuously, which is different from previous work using PIN diodes to realize a discrete tuning. Similar radiation patterns with low cross-polarization levels are achieved for the two operating states. Measured results on tuning range, radiation patterns, and realized gains are provided, which show good agreement with numerical simulations. [ABSTRACT FROM PUBLISHER]

A compact phase shifter using reconfigurable defected microstrip structure (RDMS) is proposed for phased array antennas. A complete phase shifter design scheme that serves as an engineering guidance is described. Stepwise phase shifters that have phase-shifting ranges of 90° and 180° with a step size of 45° are designed, fabricated, and tested. The experimental results demonstrate that the size, maximum insertion loss of the phase shifters, and the quantity of the lumped elements are reduced by 80%–90%, 25%–30%, and 50%, respectively, compared to our previous work. Subsequently, a four-element phased array is built employing such RDMS-based phase shifters, realizing a size reduction of 55% in the array size. The measurement results show that the phased array antenna is able to switch its main beam between $-15^\circ$, 0°, and 15° in the H-plane, with the average realized gain around 10 dBi. [ABSTRACT FROM PUBLISHER]

In this paper, a beam-steering antenna array that employs a new type of reconfigurable phase shifter is presented. The phase shifter consists of a number of cascaded reconfigurable defected microstrip structure (DMS) units. Each DMS unit is made by etching a slot in a microstrip line and loading the slot with PIN diodes. The “on” and “off” states of the PIN diodes in the DMS unit provide the phase shifts by changing the current paths. Analyses on the performance of various phase shifters cascading different numbers of DMS units are conducted by both simulations and experiments. Using the proposed phase-shifter units and Wilkinson power dividers, a four-element beam-steering antenna array was designed, fabricated, and tested. Experimental results agree well with the simulated ones. The proposed antenna array employing DMS-based phase shifters offers a low-cost solution to beamforming in wireless communications. [ABSTRACT FROM PUBLISHER]

A new microstrip dual-band polarization reconfigurable antenna is presented for wireless local area network (WLAN) systems operating at 2.4 and 5.8 GHz. The antenna consists of a square microstrip patch that is aperture coupled to a microstrip line located along the diagonal line of the patch. The dual-band operation is realized by employing the TM10 and TM30 modes of the patch antenna. Four shorting posts are inserted into the patch to adjust the frequency ratio of the two modes. The center of each edge of the patch is connected to ground via a PIN diode for polarization switching. By switching between the different states of PIN diodes, the proposed antenna can radiate either horizontal, vertical, or 45^\circ linear polarization in the two frequency bands. Measured results on reflection coefficients and radiation patterns agree well with numerical simulations. [ABSTRACT FROM PUBLISHER]

A high gain beam switching pattern reconfigurable quasi-Yagi dipole antenna is presented for wireless local area network (WLAN) systems at 5.2 GHz. The antenna consists of a microstrip-to-coplanar stripline (CPS) balun, the length of which can be controlled by using PIN diodes. The change of the length of the balun allows the currents on the two arms of the dipole to have different phase differences, thereby making the antenna operate at three states with the E-plane maximum beam direction towards 20^\circ, -20^\circ, and 0^\circ, respectively. In order to validate the design method, a prototype of the proposed antenna with a practical biasing network was fabricated and measured. Measured results on the reflection coefficients, radiation patterns, and realized gains for three operating states are provided, which agree well with the numerical simulations. [ABSTRACT FROM AUTHOR]

A frequency switchable printed Yagi-Uda dipole sub-array is proposed as an array element for base station antennas. The sub-array consists of four Yagi-Uda dipole elements loaded with PIN diodes. The electrical lengths of the director and driven dipole elements can be changed by controlling the PIN diodes states so that the sub-array can operate in two different frequency bands. The impedance bandwidth (\vert S 11 \vert \leq -10~dB) is measured to be 4.9% and 12.9% in the lower (from 2.39 to 2.51 GHz) and higher band (from 3.18 to 3.62 GHz), respectively. The measured gain of the sub-array is 9.2 and 11.9 dBi at 2.44 and 3.4 GHz, respectively. The end-fire fan-beam pattern is obtained across the two operation bands, which makes the antenna element suitable for base station application with frequency reconfigurablity. [ABSTRACT FROM PUBLISHER]

A new compact pattern reconfigurable U-slot antenna is presented. The antenna consists of a U-slot patch and eight shorting posts. Each edge of the square patch is connected to two shorting posts via PIN diodes. By switching between the different states of the PIN diodes, the proposed antenna can operate in either monopolar patch or normal patch mode in similar frequency ranges. Therefore, its radiation pattern can be switched between conical and boresight patterns electrically. In addition, the plane with the maximum power level of the conical pattern can be changed between two orthogonal planes. Owing to a novel design of the switch geometry, the antenna does not need dc bias lines. The measured overlapping impedance bandwidth (\vertS11\vert<-10\ dB) of the two modes is 6.6% with a center frequency of 5.32 GHz. The measured radiation patterns agree well with simulated results. The antennas are incorporated in a 2 \times 2 multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system to demonstrate the improvement in system capacity. In the real-time MIMO-OFDM channel measurement, it is shown that compared to omnidirectional antennas, the pattern reconfigurable antennas can enhance the system capacity, with 17% improvement in a line-of-sight (LOS) scenario and 12% in a non-LOS (NLOS) scenario at a signal-to-noise ratio (SNR) of 10 dB. [ABSTRACT FROM PUBLISHER]

A compact U-slot microstrip patch antenna with reconfigurable polarization is proposed for wireless local area network (WLAN) applications. PIN diodes are appropriately positioned to change the length of the U-slot arms, which alters the antenna's polarization state. Two antenna prototypes with identical dimensions are designed, fabricated and measured. The first antenna prototype enables switching between linear and circular polarization by using a PIN diode and a capacitor located on the U-slot. The second antenna prototype uses two PIN diodes to switch between the two circular polarization senses. A good impedance match (S11 \leq {-}10 dB) for both linear and circular polarization is achieved from 5.725 to 5.85 GHz, a band typically used for WLAN applications, and the 3 dB axial ratio bandwidth is greater than 2.8%. Details of the simulated and measured reflection coefficient, axial ratio, gain and radiation patterns are presented. [ABSTRACT FROM PUBLISHER]