Low Band Antenna Research Articles

Combined scheme for mitigating coupling interference in dual‐band shared‐aperture base station antenna

AbstractA dual‐band shared‐aperture antenna array is presented, involving a combined scheme to suppress mutual coupling interference. The proposed array is comprised of a low‐band (LB) antenna, a frequency selective surface (FSS), sixteen high‐band (HB) antennas, and a reflector. The LB antenna utilises electromagnetic transparent (ET) characteristics to minimise scattering interference, while the FSS isolates resonance interference and port signal interference. The combined scheme integrates the benefits of both the ET antenna and FSS to suppress mutual coupling interference effectively. A prototype of the proposed antenna was fabricated and measured, operating at 1.7–2.7 GHz and 3.3–3.9 GHz. The simulated and measured results demonstrate stable patterns for both the LB antenna and the HB antennas. The cross‐band isolation is higher than 28 dB in the low‐band. With these advantages, the antenna array is suitable for base station applications.

Abell 0399–Abell 0401 radio bridge spectral index: First multi-frequency detection

Aims. Recent low-frequency radio observations at 140 MHz discovered a bridge of diffuse emission with a length of 3 Mpc that connects the galaxy clusters Abell 0399 and Abell 0401. We present follow-up observations at 60 MHz to constrain the spectral index of the bridge, which has only been detected at 140 and 144 MHz so far. Methods. We analysed deep (∼18 h) LOw Frequency ARray (LOFAR) Low Band Antenna (LBA) data at 60 MHz to detect the bridge at very low frequencies. We then conducted a multi-frequency study with LOFAR HBA data at 144 MHz and uGMRT data at 400 MHz. Assuming second-order Fermi mechanisms for the re-acceleration of relativistic electrons driven by turbulence in the radio bridge regions, we compared the observed radio spectrum with theoretical synchrotron models. Results. The bridge is detected in the 75″ resolution LOFAR image at 60 MHz, and its emission fully connects the region between the two galaxy clusters. Between 60 MHz and 144 MHz, we found an integrated spectral index value of α60144 = −1.44 ± 0.16 for the bridge emission. For the first time, we produced spectral index and related uncertainties maps for a radio bridge. We produce a radio spectrum that shows a significant steepening between 144 and 400 MHz. Conclusions. This detection at low frequencies provides important information for models of particle acceleration and magnetic field structure on very extended scales. The spectral index gives important clues about the origin of inter-cluster diffuse emission. The steepening of the spectrum above 144 MHz can be explained in a turbulent re-acceleration framework, assuming that the acceleration timescales are longer than ∼200 Myr.

Mesh-based antenna with broadband transparency for dual-band shared-aperture array

Mesh-based antenna with broadband transparency for a dual-band shared-aperture array is proposed in this design. The low-radar cross section (RCS) frequency selective surface (FSS) cell is obtained firstly by combining the capacitive and inductive strips. It can be found that the electromagnetic (EM) transparent bandwidth across the high band (HB: n77) of the FSS can be enhanced by increasing in the number of strips. Then the low band (LB) antenna composed of low-RCS mesh-based elements is constructed. Remarkably, the EM transparent characteristic and the LB working performance can be individually controlled, avoiding time-consuming optimization. Subsequently, the LB transparent antenna is introduced into the array to eliminate the blockage effect on the HB antenna. The radiation patterns of the HB antenna are recovered well across the entire HB. Finally, the array prototype is fabricated and measured results show that the array covers a dual band of 1.7–2.7 GHz (45%) and 3.3–4.2 GHz (24%), showing stable radiation patterns in both LB and HB antennas. The average gains of the LB and HB antennas are 8.64 dBi and 8.58 dBi, respectively. The results verify that the proposed broadband transparent mesh-based antenna is attractive in the shared-aperture array.

Broadband Dual-frequency High Isolation Base Station Antenna with Low RCS Structure Loaded

A novel dual-band dual-polarization shared aperture antenna is proposed, which covers frequencies 1.7–2.6 GHz and 3.3–3.8 GHz. The structure, with low radar cross section (RCS), is designed to reduce the radiation interference on the high band (HB) antenna. Additionally, by introducing U-shaped slots on the arms of the low band (LB) antenna, polarization isolation between the HB elements is significantly enhanced, which can reach up to 25 dB across the whole band. Moreover, to restore the radiation pattern of the LB antenna, the dielectric substrate is employed beneath the HB antenna as a substitute for the ground plane. The antenna proposed in this paper possesses attributes of broadband, compact size, and simplified structure.

Study of Sky Radio Frequency Interference Background Level Behavior During the Partial Solar Eclips on 25 Oct. 2022 at The Baghdad University Location

Radiofrequency interference (RFI) describes the weakening of radio astronomy transmissions caused by man-made radio signal noise in radio telescope observation indicates the level of radio frequency noise in the sky at all times, regardless of any astronomical sources. This noise is affected by various sources, including Earth's atmosphere or solar activity and all communications equipment operating near the radio telescope. In this study, the background noise which includes RFI was measured using HSA2000 series receiver spectrum analyzer, which connected with two dipole antennas in different frequency bands (15-80 MHz) low band antenna, and (110-240 MHz) high band antenna during the partial solar eclipse in Baghdad on October 25, 2022, at (12:00-15:00), as a simple radio telescope to observe the radio astronomical background level in the sky. It is clear that the average amount of RFI level during a partial solar eclipse (-83.249 dBm for LBA decreased by about (0.93) from the value on a normal day (-77.495 dBm). And For HBA -84.711 dBm decreased by about (0.85) from the value on a normal day (-72.784 dBm). Also, it was noticed that these amounts are approximately equal to the RFI level at night (-82.352 dBm for LBA and -82.739 dBm for HBA). It is (0.98) for LBA and (0.97) for HBA, respectively. This research confirms that despite the short duration of the partial eclipse, the average value during the partial eclipse period is close to the average values during the night period due to the decrease in the electronic density of the ionosphere, especially at low frequencies, and the FRI of ground disturbances as a result of the activities of human from the surrounding the monitoring area. also, found that at the monitoring point, there is a good relationship between the time of the maximum partial eclipse and the peaks of signal gain strength.

Simultaneous Suppression of Cross-Band Scattering and Coupling Between Closely Spaced Dual-Band Dual-Polarized Antennas

When two antennas working in different frequency bands are placed in proximity, they suffer from strong cross-band interactions that degrade their radiation performance and reduce the isolation between them. This paper presents holistic methods to simultaneously suppress cross-band scattering and coupling. Specifically, we develop a systematic solution to suppress the scattering of low-band (LB) antennas to high-band (HB) radiation as well as the scattering of HB antennas to LB radiation using three new techniques. This leads to much reduced cross-band coupling between the LB and HB antennas. The proposed methods are applied to a “1 LB + 1 HB” dual-band array configuration with only one LB cross-dipole and one HB cross-dipole placed side-by-side to exclude the effects of the array topology. The robustness of the proposed methods is comprehensively verified for different scenarios by simulations and experiments. Furthermore, the methods are evaluated in a “1 LB + 4 HB” array configuration. In addition to effectively suppressing cross-band scattering and coupling, the proposed methods also demonstrated a significant reduction in in-band coupling between adjacent HB antennas.

Dual‐band coaperture 4G/5G base station antenna array with low scattering elements

AbstractA kite‐shaped low‐band (LB) element loaded with mushroom‐shaped structure is proposed. The element has a bandpass characteristic for the electromagnetic wave within the frequency range of 3.4–3.8 GHz and can reduce the influence on the high‐band (HB) antenna in the dual‐band coaperture antenna. The LB elements operating in the 0.698–0.96 GHz frequency band are embedded in the massive multiple input, multiple output (MIMO) antenna. One prototype of the coaperture antenna is fabricated for demonstration. The measured results show that the pattern distortion of most of the antenna ports of the HB antenna is very small after adding the LB antenna. The maximum gain deviation of the traffic beam scanning within the range of ±60° is less than 0.57 dB, indicating that the LB element can effectively suppress scattering and is suitable for multiband coaperture base‐station antenna.

Compact Dual-Band and Dual-Polarized Base Station Antenna With Shared-Dipole Elements

In this letter, a compact dual-band and dual-polarized base station antenna with the LB and HB shared-dipole elements is presented. The proposed antenna consists of a low band (LB) element and a high band (HB) element with an embedded structure. By sharing the arms of the LB antenna dipoles, the antenna planar size is miniaturized greatly. To reduce the mutual effect between the LB and HB antenna elements, the slots on the LB arms are introduced, resulting in baffles on the four sides. And then, the baffles can also be optimized to stabilize the radiation patterns of the HB antenna. The antenna prototype is fabricated and measured for verification. Results show that the antenna can achieve fractional bandwidths of 40.2 % for the LB element and 45.5 % for the HB element while the in-band return losses are better than 15 dB, covering the frequency range 0.69-1.02 GHz and 1.70-2.71 GHz for 2G/3G/4G applications. Meanwhile, the measured port isolations are larger than 33 dB and 38 dB for the LB and HB elements, respectively.

Dual-Band Base Station Antenna Array With Cross-Band Scattering and In-Band Coupling Suppression

Dual-band base station antenna array mainly suffers from the drawbacks of cross-band scattering and in-band coupling, which will disturb the radiation performances of the antennas, especially for the high-band (HB) antennas. In this paper, a dual-band base station antenna array with cross-band scattering and in-band coupling suppression is proposed. It contains a low scattering low-band (LB) crisscross-shaped dipole antenna codesigned with four square rings and four patches and a 2×2 HB antenna array. The crisscross-shaped dipole antenna is fed by four L-shaped strips, and a photonic bandgap (PBG) cell is loaded in the middle of each arm of the LB antenna to achieve HB-induced current scattering suppression without affecting the LB antenna, so the radiation patterns distortion from the cross-band scattering can be avoided. As the LB antenna employs crisscross structure, the four rings and patches can be integrated together with the LB antenna on the same substrate, which not only help to broaden the bandwidth, but also act as the array-antenna decoupling surface (ADS). With the codesign of LB antenna and ADS, no extra substrates are required for in-band decoupling. A dual-band base station antenna array prototype is fabricated and measured, showing good performances in LB and HB.

The LOFAR LBA Sky Survey

Context. The Low Frequency Array (LOFAR) is the only existing radio interferometer able to observe at ultra-low frequencies (<100 MHz) with high resolution (<15") and high sensitivity (<1 mJy beam−1). To exploit these capabilities, the LOFAR Surveys Key Science Project is using the LOFAR Low Band Antenna (LBA) to carry out a sensitive wide-area survey at 41–66 MHz named the LOFAR LBA Sky Survey (LoLSS). Aims. LoLSS is covering the whole northern sky above declination 24° with a resolution of 15" and a sensitivity of 1–2 mJy beam−1 (1σ) depending on declination, field properties, and observing conditions. Here we present the first data release, including a discussion of the calibration strategy and the properties of the released images and catalogues. Methods. A fully automated pipeline was used to reduce the 95 fields included in this data release. The data reduction procedures developed for this project have a general application and are currently being used to process almost all LOFAR LBA interferometric observations. Compared to the preliminary release, direction-dependent errors have been derived and corrected for during the calibration process. This results in a typical sensitivity of 1.55 mJy beam−1, which is four times better than for the preliminary release, at the target resolution of 15". Results. The first data release of the LOFAR LBA Sky Survey covers 650 deg2 in the HETDEX spring field. The resultant data products released to the community include mosaic images (I and V Stokes) of the region, and a catalogue of 42 463 detected sources and related Gaussian components used to describe the sources' morphologies. Separate catalogues for the six in-band frequencies of 44, 48, 52, 56, 60, and 64 MHz are also released. Conclusions. The first data release of LoLSS shows that, despite the influences of the ionosphere and radio frequency interference, LOFAR can conduct large-scale surveys in the frequency window 42-66 MHz with unprecedentedly high sensitivity and resolution. The data can be used to derive unique information on the low-frequency spectral properties of many thousands of sources with a wide range of applications in extragalactic and galactic astronomy.

Reconfigurable Structure Reutilization Low-SAR MIMO Antenna for 4G/5G Full-Screen Metal-Frame Smartphone Operation

A multi-input multi-output (MIMO) antenna system for a 4G/5G full-screen metal frame smartphone with a narrow ground clearance of 2 mm is presented in this paper. The long-term evolution antenna structures (LTEAS) for the 4G communication system are devised on both short-side edges with two ports and different matching circuits. It is fully functional over 698-960 MHz (LTE low-band) and 1710-2690 MHz (LTE high-band). An RF switch is loaded on the LTEAS to form a reconfigurable LTE low-band antenna structure covering the band of LTE700. Four loop antennas on the long side edge are devised close to the LTEAS. By fully re-utilizing the structure of the LTEAS, new loop modes are generated in the 5G band. The 5G antenna structure can cover the spectrum of 3300-4500 MHz. The theory of low SAR (Specific absorption rate) is applied to antenna design. The proposed antennas can simultaneously cover a wideband of 4G and 5G with low SAR characteristics for the first time. The proposed MIMO antenna is fabricated and measured. The performances show great potential in the future 4G/5G smartphone application.

Astrophysical constraints from the SARAS 3 non-detection of the cosmic dawn sky-averaged 21-cm signal

Observations of the redshifted 21-cm line of atomic hydrogen have resulted in several upper limits on the 21-cm power spectrum and a tentative detection of the sky-averaged signal at $z\sim17$. Made with the EDGES Low-Band antenna, this claim was recently disputed by the SARAS3 experiment, which reported a non-detection and is the only available upper limit strong enough to constrain cosmic dawn astrophysics. We use these data to constrain a population of radio-luminous galaxies $\sim 200$ million years after the Big Bang ($z\approx 20$). We find, using Bayesian data analysis, that the data disfavours (at 68% confidence) radio-luminous galaxies in dark matter halos with masses of $4.4\times10^{5}$ M$_\odot \lesssim M \lesssim 1.1\times10^{7}$M$_\odot$ (where $M_\odot$ is the mass of the Sun) at $z = 20$ and galaxies in which $>5$% of the gas is converted into stars. The data disfavour galaxies with radio luminosity per star formation rate of $L_\mathrm{r}/\mathrm{SFR} \gtrsim 1.549 \times 10^{25}$ W Hz$^{-1}$M$_\odot^{-1}$ yr at 150 MHz, a thousand times brighter than today, and, separately, a synchrotron radio background in excess of the CMB by $\gtrsim 6%$ at 1.42 GHz.

A wearable low profile asymmetrical slotted ultra-wide band antenna for WBAN applications

In this article a low profile asymmetrical slotted Ultra-Wide Band (UWB) antenna is proposed for Wireless Body Area Networks (WBANs) applications. The antenna was fabricated using Printed Circuit Boards (PCBs). An improved radiation pattern was obtained with an optimized patch shape of the antenna that broadens the bandwidth and lowers the antenna’s profile. The proposed antenna is simulated in HFSS and CST Simulator, and the proposed antenna is fabricated on FR4 substrate with the reduced ground plane. In frequency ranges from 2.50 to 10.97 GHz simulation as well as measured results show that the reflection coefficient (S11) of the antenna is below − 10 dB and increased impedance bandwidth of 126%. The proposed antenna has desired radiation pattern and gain for wearable application. The wearable performance of proposed antenna on chest, leg, and the arms of the human body is analyzed with Specific Absorption Rate (SAR). The maximum value of the SAR is 0.785 W/Kg which is less than threshold value of 1.6 W/kg. The time-domain behavior of proposed antenna is investigated with the time domain parameters such as Group delay, Fidelity factor and Mean realized gain. The time domain results are evident for the proposed antenna is capable of pulse signal transmission and reception.

A Bayesian calibration framework for EDGES

ABSTRACT We develop a Bayesian model that jointly constrains receiver calibration, foregrounds, and cosmic 21 cm signal for the EDGES global 21 cm experiment. This model simultaneously describes calibration data taken in the lab along with sky-data taken with the EDGES low-band antenna. We apply our model to the same data (both sky and calibration) used to report evidence for the first star formation in 2018. We find that receiver calibration does not contribute a significant uncertainty to the inferred cosmic signal ($\lt 1{{\ \rm per\ cent}}$), though our joint model is able to more robustly estimate the cosmic signal for foreground models that are otherwise too inflexible to describe the sky data. We identify the presence of a significant systematic in the calibration data, which is largely avoided in our analysis, but must be examined more closely in future work. Our likelihood provides a foundation for future analyses in which other instrumental systematics, such as beam corrections and reflection parameters, may be added in a modular manner.

Electromagnetic Transparent Antenna With Slot-Loaded Patch Dipoles in Dual-Band Array

A novel electromagnetic transparent low-band (LB) antenna is given in this article, with a good impedance matching in the band of 0.69–0.96 GHz (VSWR < 1.5). The key feature lies in its great patch dipoles with low-scattering properties. The transparent performance is achieved by loading slots on the dipoles, instead of inserting chokes. Dagger-like slot plays an important role in both impedance matching improvement and scattering suppression. An extra resonance point can be introduced to the reflection coefficient curve in the operating band, so the impedance matching problems can be alleviated. Besides, a dual-band shared-aperture array was designed and fabricated for validation. Both simulated and measured results have proved that the LB antenna has satisfactory impedance characteristics within the operating band and achieves an electromagnetic transparency in the band of 1.7–2.4 GHz.

A New Multi-Band Multi-Array Antenna Configuration With Scattering Suppression for Radiation Pattern Distortion Mitigation of Base Station

This communication presents a new multiband multiarray (MBMA) scattering suppression antenna configuration for a dual-band and dual-polarized antenna array with reduced radiation distortion. The proposed antenna array configuration consists of a low-band (LB) antenna element working in the 690–960 MHz band and four high-band (HB) antenna elements working in the 1.7–2.7 GHz band. The LB antenna introduces U-shape structures to the radiation element to neutralize HB scattering currents. On the other hand, the HB antenna involves an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonant structure between its radiation arm and feeding balun to suppress LB scattering currents. An antenna array using the proposed LB and HB elements is designed to achieve MBMA functions. Experimental results show that the radiation distortions in both LB and HB bands are improved significantly. The VSWR of less than 1.5, the isolation of more than 25 dB, and the symmetrical radiation pattern are obtained in both bands.

Dual-Band Aperture Shared Antenna Array With Decreased Radiation Pattern Distortion

In this communication, a dual-band aperture-shared antenna array (ASAA) is developed for base station. This ASAA contains a 4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 4 high-band (HB) antenna array, which operates from 3.4 to 3.8 GHz, and low-band (LB) antenna, which operates from 0.69 to 0.96 GHz. For decreasing pattern distortion of HB array due to the induced current in the LB element, a method following two side chokes (TSC) is proposed. By loading the TSC, the LB element exhibits a cross-band scattering suppression performance in HB. Furthermore, ASAA is fabricated and measured. Measured results show that the proposed ASAA exhibits stable radiation performance in both LB and HB. Also, the LB antenna can cover 0.69–0.96 GHz (VSWR < 1.5). Hence, the antenna array can be a good candidate for future 5G and 2G/3G/4G aperture-shared base station antenna array.

Dual-Band Base Station Antenna Array Using the Low-Band Antenna as Parasitic Decoupler

In this letter, a dual-band interleaved base station antenna array with self-decoupling characteristic is studied. The low-band antenna radiator along with its feeding baluns can be considered as compensation and partition structures for the high-band (HB) antennas. The measured co- and cross-polarized in-band isolations between the HB subarrays are enhanced to > 24.6 dB and > 29.3 dB, respectively, without introducing extra decoupling layer. The HB radiation performances are recovered, exhibiting good capability of crossband scattering suppression. The decoupling principles are analyzed and explained.

Self-Decoupled Dual-Band Shared-Aperture Base Station Antenna Array

A new decoupling concept for dual-band shared-aperture base station antenna arrays is proposed. By loading arrow-shaped decoupling structures in the hollowed regions of the low-band (LB) loop dipole arms, the LB antenna can yield partial reflection to the high-band (HB) antennas, canceling the HB-coupled wave. A dual-band base station antenna array is designed, fabricated, and measured based on this decoupling concept. With decoupling, the HB radiation patterns are restored. The copolarized in-band couplings between the HB antennas are reduced by about 9 dB, reaching >26.9 dB. The proposed antenna array possesses both cross-band and in-band decoupling abilities, without extra decoupling layer.

Particle re-acceleration and diffuse radio sources in the galaxy cluster Abell 1550

Context. Radio observations of galaxy clusters reveal a plethora of diffuse, steep-spectrum sources related to the re-acceleration of cosmic-ray electrons, such as halos, relics, and phoenices. In this context, the LOw Frequency ARray Low-Band Antenna (LOFAR-LBA) Sky Survey (LoLSS) provides the most sensitive images of the sky at 54 MHz to date, allowing us to investigate re-acceleration processes in a poorly explored frequency regime. Aims. We study diffuse radio emission in the galaxy cluster Abell 1550, with the aim of constraining particle re-acceleration in the intra-cluster medium. Methods. We exploited observations at four different radio frequencies: 54, 144, 400, and 1400 MHz. To complement our analysis, we made use of archival Chandra X-ray data. Results. At all frequencies we detect an ultra-steep spectrum radio halo (Sν ∝ ν−1.6) with an extent of ∼1.2 Mpc at 54 MHz. Its morphology follows the distribution of the thermal intra-cluster medium inferred from the Chandra observation. West of the centrally located head-tail radio galaxy, we detect a radio relic with a projected extent of ∼500 kpc. From the relic, a ∼600 kpc long bridge departs and connects with the halo. Between the relic and the radio galaxy, we observe what is most likely a radio phoenix, given its curved spectrum. The phoenix is connected to the tail of the radio galaxy through two arms, which show a nearly constant spectral index for ∼300 kpc. Conclusions. The halo could be produced by turbulence induced by a major merger, with the merger axis lying in the NE-SW direction. This is supported by the position of the relic, whose origin could be attributed to a shock propagating along the merger axis. It is possible that the same shock has also produced the phoenix through adiabatic compression, while we propose that the bridge could be generated by electrons which were pre-accelerated by the shock, and then re-accelerated by turbulence. Finally, we detect hints of gentle re-energisation in the two arms that depart from the tail of the radio galaxy.