High isolation,proximity‐fed monostatic patch antennas with integrated self‐interference cancellation‐taps for ISM band full duplex applications

This work presents two dual polarized proximity‐fed monostatic patch antennas with improved interport isolation for 2.4 GHz industrial, scientific and medical band same frequency full duplex wireless applications. The presented antennas achieves the high interport decoupling through intrinsic isolation of the polarization diversity in conjunction with a simple single‐tap and two‐taps self‐interference cancellation (SIC) topologies. The polarization diversity isolation is achieved through two perpendicular microstrip feeds for proximity feeding to excite orthogonal polarization mode for transmit (T_x) and receive (R_x) modes. The prototype for proposed antenna with integrated single‐tap and two‐taps SIC circuit is tested to record its interport isolation, impedance bandwidths and gains for both T_x and R_x ports. The implemented antenna with single‐tap SIC circuit demonstrates 10 dB return‐loss bandwidth of ≥100 MHz for both T_x and R_x ports. The measured isolation exceeds 40 dB over the 40 MHz bandwidth. Moreover, the recorded peak isolation is better than 74 dB for implemented antenna prototype. Furthermore, the 40 MHz bandwidth with 40 dB isolation can be tuned with the help of SIC‐tap as demonstrated through the experimental results. The measured gain levels are around 4.6 dBi for both T_x and R_x port. The same antenna structure with integrated two‐taps SIC topology features better than 55 dB isolation within 10 dB return loss bandwidth of 100 MHz. The peak isolation exceeds 97 dB and isolation levels are better than 60 and 80 dB over 50 and 20 MHz bandwidths, respectively, for presented antenna with two‐taps SIC configuration. The compact antenna offers comparatively wider impedance and isolation bandwidth with improved SIC levels compared to previous designs.     

A dual‐band and wideband omnidirectional circularly polarized antenna based on VO2

In this article, a dual‐band and wideband omnidirectional circularly polarized (CP) antenna based on the vanadium dioxide (VO₂) is investigated. The operating bandwidth of such an antenna can be regulated by altering the outside temperature (T), which is attained by the insulator‐metal transition of VO₂. The omnidirectional CP antenna is based on a loop antenna‐dipole model, which is composed of four tilted metal and VO₂ resonant units that are loaded around a cuboid and a feeding network for broadening bandwidth. The simulated results show that when T = 50°C (State I), the 10‐dB impedance bandwidth is 45.7% (1.67‐2.66 GHz), and the 3‐dB axial ratio (AR) bandwidth is 40% (1.9‐2.85 GHz). When T = 80°C (State II), the 10‐dB impedance bandwidth is 13.8% (1.62‐1.86 GHz), and the 3‐dB AR bandwidth is 21.8% (1.68‐2.09 GHz). In order to further characterize the concept of the proposed antenna, the related parameters of such an antenna are studied using simulation software HFSS.     

A compact proximity‐fed 2.4 GHz monostatic antenna with wide‐band SIC characteristics for in‐band full duplex applications

This article presents a dual polarized, proximity‐fed monostatic patch antenna (single radiator for both transmit and receive modes) with improved interport isolation for 2.4 GHz in‐band full duplex (IBFD) applications. The proximity‐fed radiating patch offers comparatively wider impedance bandwidth for presented design. Very nice self‐interference cancelation (SIC) levels for intended impedance bandwidth have been achieved through differential receive (R_x) mode configuration. The differential R_x mode based on 180° ring hybrid coupler acts as a signal inversion mechanism for effective suppression or cancelation of in‐band self‐interference (SI) that is, the leakage from transmit port. The implemented prototype of proposed antenna achieves ≥87 dB peak isolation for dual polarized IBFD operation. Moreover, the recorded interport isolation for validation model ≥60 dB within 10 dB‐return loss bandwidth of 90 MHz (2.36‐2.45 GHz). The measured radiation characteristics of implemented antenna demonstrate nice gain and low cross‐polarization levels for both transmit (T_x) and receive (R_x) modes. The dimensions of implemented antenna are 70 × 75 × 4.8 mm³. The novelty of this work is wide‐band SIC performance for monostatic antenna configuration with compact structure of presented design.     

Design of a tunable omnidirectional circularly polarized antenna based on VO2

In this article, a VO₂‐based tunable omnidirectional circularly polarized (CP) antenna is designed. The proposed antenna combines copper and metamaterial VO₂. By utilizing the characteristics of insulator‐metal phase transition of VO₂, we can change the length of the resonant branches to achieve tunable working bandwidth. The proposed antenna is composed of a modified floor loaded with VO₂ and copper resonant branches, a top patch with slits, and 14 shorting vias connecting the top path and bottom floor. Different from the traditional electric controlled antennas, antennas based on metamaterial VO₂ do not need to design complicated circuit structures and can be easily tailored by the external temperature (T). The simulated results illustrate that when T ≥ 68°C (state I), the proposed antenna has a 10‐dB impedance bandwidth of 15.9% (2.09‐2.45 GHz), and a 3‐dB axial ratio (AR) bandwidth of 23.4% (2.04‐2.58 GHz). When T < 68°C (state II), it has a bandwidth of 6.5% (2.38‐2.54 GHz) with S₁₁ below ?10 dB, and a bandwidth of 19.9% (2.39‐2.92 GHz) with AR below 3 dB.     

A compact dual‐band zeroth‐order resonator antenna loaded with meander line inductor

A novel zeroth‐order resonator (ZOR) meta‐material (MTM) antenna with dual‐band is suggested using compound right/left handed transmission line as MTM. In this article, suggested antenna consists of patch through series gap, two meander line inductors, and two circular stubs. The MTM antenna is compact in size which shows dual‐band properties with first band centered at 2.47 GHz (2.05‐2.89 GHz) and second band is centered at 5.9 GHz (3.70‐8.10 GHz) with impedance bandwidth of (S₁₁ < ? 10 dB) 34.69% and 72.45%, respectively. At ZOR mode (2.35 GHz), the suggested antenna has overall dimension of 0.197λ_o × 0.07λ_o × 0.011λ_o with gain of 1.65 dB for ZOR band and 3.35 dB for first positive order resonator band which covers the applications like Bluetooth (2.4 GHZ), TV/Radio/Data (3.700‐6.425 GHz), WLAN (5‐5.16 GHz), C band frequencies (5.15‐5.35, 5.47‐5.725, or 5.725‐5.875 GHz) and satellite communication (7.25‐7.9 GHz). The radiation patterns of suggested structure are steady during the operating band for which sample antenna has been fabricated and confirmed experimentally. It exhibits novel omnidirectional radiation characteristics in phi = 0° plane with lower cross‐polarization values.     

Compact broadband circularly polarized slot‐patch antenna array

A simple design of circularly polarized slot‐patch antenna array with broadband operation and compact size is presented in this article. The antenna element consists of a circular slot and a semicircular patch, which are etched on both sides of a substrate. For the gain and axial ratio (AR) bandwidth enhancement, its array antennas are implemented in a 2 × 2 arrangement and fed by a sequential‐phase feeding network. The final 2 × 2 antenna array prototype with compact lateral dimension of 0.8λ_L × 0.8λ_L (λ_L is the lowest frequency within AR bandwidth) yielded a measured impedance bandwidth of 103.83% (2.76‐8.72 GHz) and a measured AR bandwidth of 94.62% (2.45‐6.85 GHz). The peak gain values within the AR bandwidth are from 2.85 to 8.71 dBi. A good agreement between the simulated and measured results is achieved. This antenna array is suitable for multiservice wireless systems covering WiMAX, WLAN and C‐band applications such as satellite communications.     

A novel wideband circularly polarized modified square‐slot antenna with loaded strips

In this article, a novel inverted L‐shaped microstrip‐fed wideband circularly polarized (CP) modified square‐slot antenna is designed. By cutting a pair of triangle chamfers and introducing a pair of triangle patches at the square‐slot, the antenna achieves a wideband CP radiation. Moreover, CP performance of the antenna can also be remarkably enhanced by protruding an L‐shaped strip and embedding a tuning rectangle slot into the slot ground. The measured results demonstrate that the axial‐ratio bandwidth for AR < 3 is 75.1% (from 4.45 to 9.8 GHz) and the impedance bandwidth (|S₁₁| < ?10 dB) reaches 65.8% (from 4.95 to 9.8 GHz). In addition, surface current studies are performed to illustrate the operating mechanism of CP operation, and the antenna has bidirectional radiation characteristics with an average gain of ~4 dBic within the CP band.     

Wideband circularly polarized hybrid dielectric resonator antenna with bi‐directional radiation characteristics for various wireless applications

In this article, a wideband circularly polarized (CP) dielectric resonator (DR) over an asymmetric‐slot radiator based hybrid‐DR antenna is proposed with bi‐directional radiation characteristics. Bi‐directional CP radiation of the dual sense is obtained using a rectangular‐DR over asymmetric‐rectangular‐slot radiator with L‐shaped feed line. The asymmetric‐slot radiator feed by L‐shaped stub with the coplanar waveguide is used for generating two orthogonal modes, namely TE ^x _δ11 and TE^y_1δ1 in the combined (rectangular‐DR and asymmetric‐slot radiator) hybrid‐DR antenna, which is verified by the distribution of electric field inside the rectangular DRA. The measured reflection coefficient bandwidth (S₁₁ < ?10 dB) and axial ratio (AR) bandwidth (AR < 3 dB) of the hybrid‐DR antenna are 80.5% (1.87‐4.39 GHz) and 43.8% (1.75‐2.73 GHz), respectively. The antenna radiation is in the broadside (θ = 0°, ? = 0°) direction as well as in the backside (θ = 180°, φ = 0°) direction with equal magnitudes in both the directions. Right‐handed and left‐handed CP waves are achieved respectively, in the boresight (+Z) and the backside (?Z) directions. The proposed CP hybrid‐DR antenna gives an average gain of 3.55 dBic and radiation efficiency of 95.0% in both directions. The proposed antenna covers various wireless useful bands such as ISM 2400 band, Wi‐Fi, Bluetooth, and Wi‐MAX (2.5‐2.7 GHz).     

A‐shaped wideband dielectric resonator antenna for wireless communication systems and its MIMO implementation

In this article, a new A‐shaped dielectric resonator antenna (DRA) excited by a conformal strip is proposed for wideband applications. The wide bandwidth is achieved by combining two adjacent modes that is, TM₁₀₁ and TM₁₀₃. The experimental results demonstrate that the proposed DRA offers an impedance bandwidth (for S11?10 dB) of 59.7% (3.24‐6.0 GHz), covering IEEE 802.11 and U‐NII bands. The antenna provides a fairly stable radiation pattern with the gain ranging from 5.29 to 7 dBi across the operating bandwidth. A dual‐element multiple‐input multiple‐output (MIMO) system is also realized using the proposed wideband DRA. The impedance bandwidth of the dual‐element MIMO antenna is 59.2% and 60.9% for Port1 and Port2, respectively and the isolation between the ports is better than 20 dB across the bandwidth. For Port1, the gain of the MIMO antenna ranging from 6.03 to 7.45 dBi is obtained across the bandwidth. Furthermore, the diversity performance of the MIMO antenna is found to be good with envelope correlation coefficient below 0.003 over the operating band. The proposed antenna could be the potential candidate for worldwide interoperability for microwave access (WiMAX), wireless local area network (WLAN) and lower European UWB frequency band (3.4‐5.0 GHz) applications.     

A wideband circularly polarized slot antenna with antipodal strips for WLAN and C‐band applications

A single‐fed circularly polarized square shaped wide slot antenna with modified ground plane and microstrip feed has been presented. The field in the slot is perturbed by introducing an antipodal strips section attached with a microstrip line to produce circular polarization in a wide band of frequencies. The antipodal strip section consists of a group of four strips of unequal length and separation. The presence of asymmetric perturbations in the slot is mainly responsible for exciting two orthogonal modes in the slot having equal magnitude and 90° phase difference which results in circular polarization. A wide bandwidth of 3.3 GHz (4.4 GHz‐7.7 GHz) has been achieved for an axial ratio value AR < 3 dB with the minimum axial ratio value being 0.3 dB. The impedance bandwidth for |S₁₁| < ?10 dB ranges from 4.3 GHz to 8 GHz, and therefore covers most of the C‐band communication systems. The antenna exhibits stable radiation patterns throughout the circular polarization bandwidth with a gain around 6 dBi in entire operational bandwidth. A prototype of antenna was fabricated and measured. The antenna has a planar size 0.40λ₀ × 0.40λ₀ and thickness of 0.02λ₀ where λ₀ is the wavelength in free space at the lowest frequency. With its compact size and low profile, the antenna is a favorable choice for WLAN (5.15‐5.85 GHz) and a wide variety of C‐band wireless applications.     

A new modified CPW‐fed wideband circularly polarized half‐split cylindrical dielectric resonator antenna with different permittivity of two layers in radial direction

In this article, a wideband circularly polarized half‐split cylindrical dielectric resonator antenna (HS‐CDRA) having two layers with different permittivity in radial direction is investigated. Designed antenna is excited by a new modified CPW fed which consists of signal line, helps to realization of circular polarization, half‐split cylindrical dielectric resonator (HS‐CDR), to confirm that circular polarization in proposed antenna. HS‐CDR is made of two different materials which can supports to enhance the input impedance bandwidth and 3‐dB axial ratio bandwidth. From the distributions of E‐fields in HS‐CDRA, it is observed that TM_11δ mode has been excited. To confirmed the circular polarization in proposed antenna, E‐field distribution on different phases (φ = 0º, 90º, 180º, and 270º) have been plotted. This antenna provides measured ?10 dB input impedance bandwidth of 25.94% (centered on 4.70 GHz) and 3‐dB axial ratio bandwidth in broadside direction of 17.34% (centered on 4.90 GHz). The average gain and radiation efficiency in working band are 1.56 dBi and 93.43% in broadside direction, respectively. CP radiation pattern shows that the proposed antenna has left hand circular polarization and this developed antenna could be useful for wireless applications like WLAN/Wi‐MAX bands.     

A compact six port antenna for better spectrum utilization efficiency in cognitive radio applications

In this article, a novel six port antenna for better spectrum utilization efficiency in cognitive radio (CR) applications is presented. In this six port antenna system, an ultra‐wideband (UWB) sensing antenna and five wideband/narrowband (NB) antennas are integrated on the same substrate in a compact area of 1134 mm² . Antenna associated with port 1, which is meant for sensing, has ?10 dB reflection coefficient bandwidth of 3 to 11 GHz and the antennas associated with ports 2, 3, 4, 5, and 6 have ?10 dB reflection coefficient bandwidths of 3.6 to 5.8 GHz (single band), 2.9 to 3.6 GHz and 5.4 to 7.98 GHz (dual band), 7.95 to 8.38 GHz and 9 to 9.85 GHz (dual band), 8.38 to 9 GHz (single band) and 9.7 to 10.7 GHz (single band), respectively. Minimum isolation of 20 dB is attained between UWB sensing antenna and any narrowband/wideband antenna except between the antennas associated with ports 1 and 2 where minimum isolation of 12 dB is achieved over the operating bandwidth of UWB sensing antenna. Moreover, among all wideband/narrowband antennas, isolation of less than 15 dB is achieved. More importantly, the narrowband and wideband antennas meant for communication cover all frequency bands in UWB and a good match between the simulated and measured results is noticed.     

Circularly polarized rectangular DRA coupled through orthogonal slot excited with microstrip circular ring feeding structure for Wi‐MAX applications

In this article, a wideband circularly polarized rectangular dielectric resonator antenna (RDRA) coupled through orthogonal slots and excited with a new microstrip circular ring has been investigated. Circular polarization has been achieved by using plus shaped (+) slot on the ground plane and excited through a new microstrip circular ring feed. TE_11δ mode has been excited in the RDRA which has been confirmed through the distribution of E ‐field and dielectric waveguide model (DWM) method of RDRA. Circularly polarized (CP) RDRA offering measured ?10 dB input impedance bandwidth of 20.79% (centered at 3.27 GHz) and 3 dB axial ratio bandwidth in broadside direction of 12.09% (centered at 3.39 GHz), respectively. From the CP radiation pattern, proposed design confirms that right ‐ handed CP (RHCP) in broadside direction. The difference between RHCP field and left ‐ handed CP (LHCP) field are above ?26 dB in operational band. In addition, the proposed CP antenna offers stable gain and radiation efficiency in working bands and it is suitable for IEEE 802.16e/d Wi‐MAX (3.3‐3.7 GHz) band.     

A tunable wideband omnidirectional circularly polarized antenna regulated by the gravity field

In this article, a tunable wideband omnidirectional circularly polarized (CP) antenna regulated by the gravity field based on the liquid metal Hg is investigated. Under the action of the gravity field, Hg flows in the upper and lower parts by rotating such an antenna, which can constitute dissimilar resonant units to achieve the dynamic regulation of the operating bandwidths. The proposed antenna consists of four tilted glass containers that are filled with Hg in the upper or lower parts, and a feeding structure for power distribution and impedance matching. To verify concept of the design, equivalent prototypes have been fabricated and measured. The measured results are roughly consistent with simulated results within a reasonable error range. The antenna has a 10‐dB impedance bandwidth of 44.3% (2.37‐3.72 GHz), and a 3‐dB axial ratio (AR) bandwidth of 18.9% (2.83‐3.42 GHz) when the proposed antenna is not rotated (state I). When such an antenna is rotated (state II), it has a bandwidth of 40.7% (2.35‐3.55 GHz) with S₁₁ below ?10 dB, and a bandwidth of 22.9% (2.40‐3.02 GHz) with AR below 3 dB. Therefore, the operating band of the antenna can be altered between two wide bands. The proposed antenna has the advantages of tunable bandwidth, novel efficient regulation mechanism, and simple structure.     

Millimeter‐wave antenna with wide‐scan angle radiation characteristics for MIMO applications

A three‐element quasi Yagi‐Uda antenna array with printed metamaterial surface generated from the array of uniplanar capacitively loaded loop (CLL) unit‐cells printed on the substrate operating in the band 25‐30 GHz is proposed. The metamaterial surface is configured to provide a high‐refractive index to tilt the electromagnetic (EM) beam from the two dipole antennas placed opposite to each other. The metamaterial region focuses the rays from the dipole antenna and hence increases the gain of the individual antennas by about 5 dBi. The antenna elements are printed on a 10 mil substrate with a center to center separation of about 0.5 λ ₀ at 28 GHz. The three‐element antenna covers 25‐30 GHz band with measured return loss of 10 dB and isolation greater than 15 dB between all the three ports. The measured gain of about 11 dBi is achieved for all the antenna elements. The three antenna elements radiate in three different directions and cover a radiation scan angle of 64°.     

A wideband compact antenna with quad‐circular polarized bands in its operating regions

This article presents the design of an offset CPW‐fed slot antenna which exhibits a narrow impedance bandwidth (IBW; |S₁₁| ≤ ?10 dB) extending from 1.20 GHz to 1.45 GHz and another wide impedance bandwidth from 1.86 GHz to 8.4 GHz thus covering almost all the conventional operating frequencies. The antenna is loaded with semicircular and rectangular stubs and meandered microstrip lines to realize circular polarization at 1.35 GHz, 3.3 GHz, 4.9 GHz, and 7.5 GHz with axial ratio bandwidth (axial ratio ≤ 3 dB) of 19.25% (1.2‐1.46 GHz), 4.24% (3.24‐3.38 GHz), 4.1%(4.8‐5 GHz), and 5.2% (7.3‐7.69 GHz) respectively thus covering the GPS, WiMAX, WLAN, and X‐band downlink satellite communication application bands. The mechanism of generation of CP is discussed using vector analysis of surface current density distribution. The gain is fairly constant in the wide IBW region with maximum fluctuation of 1.2 dB. The structure is compact with an overall layout area of 0.27λ × 0.27λ, where λ is the free‐space wavelength corresponding to the lowest circular polarized (CP) frequency. A comparison of the proposed antenna with previously reported structures is performed with respect to impedance bandwidth, compactness, number of CP bands, LHCP to RHCP isolation and gain to comprehend the novelty of the proposed design. A prototype of the proposed antenna is fabricated and the measured results are in accord with the simulated results.     

Low‐profile omnidirectional circularly polarized antenna based on substrate integrated waveguide technology

A substrate integrated waveguide (SIW) circularly polarized (CP) antenna with omnidirectional radiation in the azimuthal plane is proposed. The antenna consists of five identical end‐fire CP antenna elements in a pentagonal array configuration, which is loaded on a circular substrate. Each element contains an H‐plane horn antenna in SIW structure and a printed dipole antenna. Five parasitic curve elements are introduced to improve the omnidirectional property of the antenna. Combined with complementary dipoles theory and SIW technology, prototype antenna is designed, fabricated and measured. With a low profile of 0.024λ₀, the antenna has a 10‐dB return‐loss impedance bandwidth of 4.08% (2.4～2.5 GHz) and a 3‐dB axial‐ratio (AR) bandwidth of 5.76% (2.36～2.50 GHz). The antenna works well in the 2.45 GHz ISM band, with good cross‐polarization and excellent omnidirectional property.     

Wideband bandpass filtering branch‐line balun with high‐isolation

The wideband bandpass filtering branch‐line balun with high isolation is presented in this paper. The proposed balun can be designed for wideband performances by choosing a proper characteristics impedance of input vertical transmission line and odd‐mode impedance of parallel‐coupled lines. The proposed balun was designed at a center frequency (f₀) of 3.5 GHz for validation. The measured results are in good agreement with the simulations. The measured power divisions are ?3.31 dB and ?3.24 dB at f₀ and ?3 ± 0.17 dB within the bandwidth of 0.95 GHz (3 GHz to 3.95 GHz). The input return loss of 24.09 is measured at f₀ and higher than 20 dB over the same bandwidth. Moreover, the measured output losses are better than 11 dB within a wide bandwidth. The isolation between output ports is 20.32 dB at f₀ and higher than 13.2 dB for a broad bandwidth from 1 GHz to 10 GHz. The phase difference and magnitude imbalance between two output ports are 180° ± 4.5° and ± 0.95 dB, respectively, for the bandwidth of 0.95 GHz.     

Design and packaging of ultra‐wideband multiple‐input‐multiple‐output/diversity antenna for wireless applications

In this article, a new compact eight‐element three‐dimensional (3D) design of ultra‐wideband (UWB) multiple‐input‐multiple‐output (MIMO) antenna is proposed. For realizing polarization diversity, four elements of the MIMO antenna are oriented horizontally and four elements are arranged vertically. In the horizontal arrangement, the antenna resonating elements are placed orthogonally to each other, which reduces interelement coupling and offers a consistent link with the wireless systems/devices. The proposed antenna shows a bandwidth (S₁₁ ≤ ?10 dB) of 17.99 GHz (2.83‐20.82 GHz) and isolation larger than 15 dB in the resonating band. The proposed MIMO/diversity antenna performance parameters such as envelope correlation coefficient, diversity gain, and total active reflection coefficient are evaluated and presented. Furthermore, the unit cell of the MIMO system is simulated for the packaged environment and it is observed that the antenna housing does not affect the antenna performance.     

Dual‐functional QM SIW cavity integrating two‐element MIMO antenna and second‐order bandpass filter

A quarter‐mode (QM) substrate‐integrated‐waveguide (SIW) cavity is designed as a dual‐functional component. By etching three slots, four sub‐cavities are formed and then two of them with the same size are individually fed by a coaxial port. Three resonating frequencies are excited in the single QM SIW cavity. One of them can radiate cavity energy input by these ports into free space, implying a two‐element multiple‐input‐multiple‐output (MIMO) antenna, whereas the other two can transmit energy from one port to the other port, indicating a second‐order bandpass filter. Moreover, antenna isolation and filter bandwidth can be adjusted to a certain degree. A prototype with the overall size of 0.40λ₀ × 0.40λ₀ × 0.02λ₀ has been fabricated. The integrated bandpass filter demonstrates the measured center frequency of 3.8 GHz and operating bandwidth of 32 MHz while the integrated MIMO antenna exhibits the frequency of 3.4 GHz, bandwidth of 67 MHz, port isolation of 18.0 dB, radiation gain of 4.0 dBi, and envelope correlation coefficient of 0.25.