Microstrip Balun Research Articles

A Low-Profile Dual-Polarized Patch Antenna With Simple Feed and Multiple Decoupling Techniques

A low-profile dual-polarized patch antenna with simple feed and multiple decoupling techniques is proposed. The proposed antenna consists of two substrates separated by 5 mm. At the top and bottom of Sub 1 are a microstrip balun (Port 2), and a rectangle patch etched with two symmetrical small rectangular slots. A rectangular slot, etched on the metal reflector of Sub 2, is excited by a microstrip line (Port 1). Multiple decoupling techniques are synthesized to achieve high port-to-port isolation, including physical isolation, the shorting pins grounding, orthogonal polarization, and different radiation modes. In particular, the designed antenna has a low profile without any complex feed structure, and the simulated isolation achieves better than 52 dB. Furthermore, its profile is only 0.08 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength at 3.55 GHz, and the measured isolation achieves 45 dB in the working bandwidth of 3.3 <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">–</b> 3.8 GHz <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">.</b> The fabricated prototype is a promising candidate for the 5G New Radio band n78 communication systems.

Design of the Composite Fractal Embedded Slot Monopole Antenna

In this paper, the rectangular nested fractal and Cantor fractal slot are skillfully fused together, and the composite fractal embedded slot radiation structure is creatively designed. It combines the microstrip monopole antenna of high radiation intensity and excellent directional radiation capability with the microstrip Balun feed structure of wide frequency range and step-by-step impedance matching capability to design composite fractal embedded slot monopole antenna that can meet the performance requirements of BeiDou Navigation Satellite System. Actual test results show that the antenna has the advantages of both a high-performance redundant antenna and a directional radiation antenna and can completely cover the BeiDou Navigation Satellite System working for the frequency band. It is a high-performance satellite positioning antenna with strong application potential.

Dual-band Microstrip Balun with Different Complex Load Impedances in Frequency Bands

Dual-band Microstrip Balun with Different Complex Load Impedances in Frequency Bands

A new balun that can improve port isolation degree of a dual‐polarized antenna

AbstractBased on the traditional dielectric microstrip balun, a new‐type coupling balun is presented in this study. The front side of this balun is composed of an open stub and two rectangular patches. One end of the rectangular patches is open‐circuited, and the other end connects with the dipole. On the back side, there are two other rectangular patches with one end grounded and the other end open‐circuited. When using such balun for feeding, one can still get a wide bandwidth, and more importantly, obtain higher port isolation. Compared with the dipole fed by the traditional balun, the maximum/average port isolation of the dipole fed by the new‐type one is increased by 10.8 dB/7.9 dB. The new‐type balun has a good application prospect in dual‐polarized antenna.

Investigating the upper bound of high-frequency electromagnetic waves on unshielded twisted copper pairs

This paper explores the behaviour of the ubiquitous twisted pairs at high frequencies and wideband excitation of twisted pairs up to 12 GHz. Higher carrier frequencies on twisted pairs can enable the data rates required by the future communication networks; hence, the existing copper infrastructure can be utilised on the last mile complementing the fibre networks. In this paper, we show a fundamental limit on the operating frequency of twisted pairs beyond which twisted pairs start to radiate and behave like an antenna. To validate our theoretical derivations through measurements, we designed a microstrip balun to excite the differential mode on the twisted pairs. At the end, we demonstrate that the standard twisted pairs used in the UK can be used up to 5 GHz carrier frequency without any radiation effect and this upper-bound can be moved to higher frequencies by decreasing the twist lengths.

Packable and Readily Deployable Tightly Coupled Dipole Array (TCDA) With Integrated Planar Balun

To overcome the limited payload dedicated to onboard antennas for CubeSat/SmallSat applications, this paper presents a novel, foldable, dual-polarized Tightly Coupled Dipole Array (TCDA). In comparison to previous vertical feeds used for TCDAs, this array integrates a planar microstrip balun feed to enable foldability. The proposed array attains 5.4:1 (0.6-3.20 GHz) impedance bandwidth with VSWR < 3 at broadside and scans down to 45∘ at all azimuth planes. Notably, a substrate-integrated in-plane folding mechanism based on Lamina Emergent Torsion (LET) joints is employed to achieve foldability coupled with a simple fabrication process. The average simulated radiation efficiency was 95% across the band. A 5 × 8 prototype array was fabricated and tested to verify the finite array’s foldability, bandwidth, and gain performance. This prototype achieves 80% one-dimensional size reduction, yielding 60% overall volume reduction. Consequently, the array prototype can be folded and stowed in a compact volume of 1.4U ( 25 cm× 7.2 cm× 9 cm ).

A Miniaturized Cavity backed Archemedian Spiral Antenna for mm-Wave Applications

Design of a UWB circularly polarized, cavity-backed Archimedean spiral antenna is presented in this paper. The antenna is designed for 18- 40 GHz frequency range with a binomially tapered parallel-strip to microstrip balun and RF foam absorbent for controlling the backscattering. The peak-measured gain is 4.5 dBi and is greater than 2 dBi for the entire band. The antenna is characterized by greater than 50 degrees 3 dB gain and axial ratio beam-widths which makes it highly suitable for airborne applications. Axial ratio is below 2 dB for the band of interest. The height of the antenna cavity is 19 mm and the diameter is 23 mm giving the antenna a low profile meeting the space requirements of any RF system.

A Review of Passive and Active Ultra-Wideband Baluns for Use in Ground Penetrating Radar

Microwave ultra-wideband technology has been widely adopted in instrumentation and measurement systems, including ground-penetrating radar (GPR) sensors. Baluns are essential components in these systems to feed balanced antennas from unbalanced feed cables. Baluns are typically introduced to avoid issues with return signals, asymmetrical radiation patterns and radiation from cables. In GPR systems, these issues can cause poor sensitivity due to a reduction in radiated power, blind spots due to changes in the radiation pattern and additional clutter from common mode radiation. The different balun technologies currently available exhibit a wide variation in performance characteristics such as insertion loss, reflection coefficient and phase balance, as well as physical properties such as size and manufacturability. In this study, the performance of two magnetic transformer baluns, two tapered microstrip baluns and an active balun based on high-speed amplifiers were investigated, all up to frequencies of 6 GHz. A radio frequency current probe was used to measure the common mode currents on the feed cables that occur with poor performing baluns. It was found that commercially available magnetic transformer baluns have the best phase linearity, while also having the highest insertion losses. The active balun design has the best reflection coefficient at low frequencies, while, at high frequencies, its performance is similar to the other baluns tested. It was found that the active balun had the lowest common mode current on the feed cables.

Design and Verification of an Electrically Small, Extremely Thin Dual-Band Quasi-Isotropic Antenna

A novel design of an electrically small, dual-band quasi-isotropic antenna with a microstrip balun is presented in this letter. A quasi-isotropic radiation pattern is realized from the total current flow over the proposed structure at two different frequency bands. The electrical size ka of the antenna is 0.49 with an extremely thin profile of 0.0014λg. The antenna measurements reveal good uniformity of the radiation pattern with a maximum gain deviation of 5.83 dB at 942 MHz and 8.24 dB at 1.71 GHz with 57% and 95% radiation efficiency, respectively. The radiation performance of the antenna is also verified through wireless power receiving experiments in an office non-line-of-sight (NLOS) environment.

A Wideband Isolated Real-to-Complex Impedance Transforming Uniplanar Microstrip Line Balun for Push–Pull Power Amplifier

In this article, a three-port uniplanar microstrip line balun is proposed to transform the balanced complex load termination to 50- $\Omega $ unbalanced port impedance. The proposed device is designed based on a symmetric four-port network with an open-ended transmission line inserted between branch lines in the middle of structure. To improve the isolation and match the complex termination, a resistive network is proposed and inserted between the two balanced ports. In addition, the theoretical analysis is carried out for the even and odd mode circuits to expand the bandwidth of the proposed real–complex impedance transforming balun. With the proposed design theory, the impedance trajectory follower splitting and combining baluns are designed for wideband push–pull power amplifier (PPPA). To verify the design concept, first, a real–complex impedance transforming uniplanar microstrip line balun is designed and characterized at 1 GHz. Then, a prototype for the wideband PPPA with impedance trajectory follower microstrip baluns is designed, fabricated, and validated in experiment. For the proposed balun, the simulated and measured results agree well with each other to prove the design concept. From the experimental results, the PPPA with the proposed balun shows a gain of 10.2–12.2 dB, output power of 42.7–44.7 dBm, and a drain efficiency of 59.8%–74.6% within the frequency range of 1.8–2.7 GHz.

Ultra-Wideband Low-Cost High-Efficiency Cavity-Backed Compound Spiral Antenna

A low-cost high-efficiency ultra-wideband (UWB) cavity-backed spiral antenna is proposed. It employs an equiangular spiral enclosed by an Archimedean spiral and it is fed through a tapered microstrip balun. A center-raised cylindrical absorber-free cavity backs the spiral to minimize the backward radiation without decreasing the efficiency. The cavity is designed to ensure an impedance bandwidth exceeding 16:1 ratio (from 350 MHz to 5.5 GHz). Simulated and measured results are presented and compared, demonstrating competitive performance in terms of impedance bandwidth and efficiency. Time–domain measurements indicate fidelity of 0.62 at boresight.

A Dual-Band Balun BPF Using Codirectional Split Ring Resonators

In this letter, a novel dual-band microstrip balun bandpass filter (BPF) is designed by using interdigital capacitor-loaded codirectional split ring resonators (CDSRRs). The utilized resonator is analyzed by coupled line theory and exhibits independently controllable dual resonance behavior. The proposed balun BPF is constructed by coupling two identical CDSRRs to rotationally symmetrical balanced output ports. Two transmission zeros (TZs) between the passbands can be observed by means of the CDSRRs. The designed balun BPF centered at 1.59 and 1.92 GHz was also fabricated and measured. The measured results show a good agreement with the predicted results. Phase and magnitude imbalances between the balanced output ports have been measured as better than 180 ± 5° and 0.4 dB, respectively. The proposed dual-band balun BPF exhibits high filtering performances in terms of closely spaced passbands, selectivity, and clean upper stopband.

Design and Simulation Analysis of a 17 Element Spiral Antenna Array for Brain Imaging.

In this paper, a simple Archemedian spiral antenna fed by a 6-section exponential impedance transformer cum parallel-strip to microstrip balun is presented. Antenna and the balun are designed for ultra wide-band (UWB) (1.6-12 GHz) frequency range. Using this antenna, a 17 element array helmet is simulated in 3-5 GHz band, around CST voxel model of human brain with a 1 cm blood-clot introduced in it. A comparison of difference in reflection loss with and without tumor for various antenna positions is carried out.

A Compact Crossed Inverted-V Antenna with a Common Reflector for Polarization Diversity in the IoT

This article presented a compact and high gain antenna with reconfigurable polarization based on two inverted-V dipoles fabricated in a crossed configuration, and with a common planar reflector. The proposed antenna could generate four different types of polarizations, such as vertical polarization (VP), horizontal polarization (HP), right-hand circular polarization (RHCP), and left-hand circular polarization (LHCP). A pair of inverted-V dipoles drove the polarization diversity, where each dipole had an integrated matching circuit and a microstrip balun. Using a crossed inverted-V configuration with a ground plane as the common reflector, we could achieve compactness in size, high directivity, and a wider beamwidth than a normal dipole antenna. To verify the performance of the proposed antenna, we fabricated a sub-6GHz antenna with a Taconic TLX-9 substrate, which had a relative permittivity of 2.5. The proposed antenna showed a measured 10-dB impedance bandwidth of 752 MHz (5.376 GHz to 6.128 GHz). The peak gains for the VP, HP, RHCP and LHCP operations at 5.8 GHz were about 5.2 dBi, 4.61 dBi, 5.25 dBic, and 5.51 dBic, respectively. In addition, the half-power beamwidth (HPBW) for all the polarizations were greater than 78° in the operation band.

Design and Analysis of a Wideband Multiple-Microstrip Dipole Antenna with High Isolation

A wideband multiple-microstrip dipole antenna with dual polarization is proposed in this letter. The antenna consists of a radiator, a cross-shaped slot coupler, a pair of microstrip baluns, and a reflector. When baluns are excited, the cross-shaped slot coupler would work as a four-way equal-split power divider and generate four differential signals at four ends of the slotlines. Afterward, the signals would be coupled to four modified dipoles to radiate and synthesize slant ±45° linear polarizations. The proposed design is verified by the fabrication and testing of a prototype antenna. Measured results agree well with the simulated ones, giving a wide impedance bandwidth from 1.68 to 2.75 GHz, a high port-to-port isolation (better than 37 dB) within the operating frequency bandwidth, and a good radiation pattern. Besides, the proposed antenna maintains a compact structure measuring 0.78 λ 0 × 0.78 λ 0 × 0.18 λ 0.

Base Station Antenna with Enhanced Cross Polarization Discrimination Performance by Using Horizontal Meandered Dipole and Vertical Parasitic Elements

This study is related with the design of a ± 45° dual polarized base station antenna with improved cross-polarization discrimination (XPD) values. Parasitic elements are added to antenna design formed by orthogonal two compact meandered dipole above ground plane. The antenna designed with CST Microwave Studio program has VSWR ≤ 2 within 1.71-2.69 GHz frequency band, which covers GSM 1800/3G/LTE bands. The antenna has minimum of 0 dBi gain in the beamwidth of 120° ( 60°) at azimuth plane (ϕ = 0°) along the band, and XPD values being minimum of 2 dB at 1.71-2.4 GHz for 60° without parasitic elements are improved to 10 dB with parasitic elements. This design initially had two horizontal straight monopoles on the ground plane perpendicular to each other. Afterwards, antenna with microstrip balun feed applied but the XPD values were not appropriate to expected results. Because of that, by using image theory, vertical parasitic elements were added to get appropriate XPD values. Later, meandered structure used to make antenna smaller. Finally, according to base station applications, antenna frequencies optimized to 1.71 GHz and 2.69 GHz. The designed and optimized antenna produced and measured in laboratory environment. Return losses for port 1 and port 2 are measured above the 10 dB and isolation between the port 1 and port 2 are measured above the 20 dB. In addition, the maximum gain values are measured between 3 dB and 7 dB in 1.71 GHz and 2.69 GHz frequency band. Finally, XPD values are measured more than 10 dB in bandwidth.

Design of a multiband ground radiation antenna by utilizing balun excitation

AbstractThe design and performance of a triple‐band ground radiation antenna with a compact balun are shown in this paper. A microstrip balun is integrated with a modified rectangular ground plane has provided wideband frequency characteristics. With the help of the theory of the characteristic mode, the resonance phenomenon of the rectangular ground plane is analyzed. An eight‐like‐loop slit is embedded in the ground plane to excite multiple resonant modes. In, addition, by etching two rectangular slots at two terminals of the eight‐like‐loop slit, the capacitance of the ground‐plane resonator decreases such that the impedance‐matching condition in the upper‐frequency band can be improved. Finally, a triple‐band frequency performance is derived by embedding a simple matching circuit. The proposed antenna achieves the measured impedance bandwidths from 1.02 to 1.06, from 1.35 to 1.62, and from 1.96 to 2.55 GHz. The simulated current distributions of a ground‐plane prototype are also experimentally verified.

Design and validation of miniaturize Rat Race Coupler based microstrip Balun

This work presents a compact Balun with enhanced bandwidth and better isolation between output ports using Interdigital Capacitor (IDC). Firstly, a Rat Race Coupler (RRC) is designed, later Balun is proposed by replacing the isolation port with a 50 Ω isolation resistor. The proposed Transmission line (TL) is designed using an IDC in parallel with a high impedance TL. Based on a π-equivalent circuit the proposed TL has been investigated and optimized to achieve 70.7 Ω impedance. The Balun is designed and fabricated. The simulated and fabricated results are in accord. The fractional bandwidth (FBW) of RRC and Balun are 37.5% and 33% respectively at centre frequency 2.4 GHz. The size occupied by the proposed Balun is 0.51λg × 0.22λg. The structure is low cost, uniplanar and compact.

A Wide Stopband Balun Bandpass Filter with Its Application to Balanced Quasi‐Yagi Antenna

A new microstrip balun bandpass filter (BPF) with wide stopband is presented. It is realized by utilizing the out‐of‐phase feature of standing‐wave distribution on a half‐wavelength (λ/2) open‐ended microstrip line and the resonant characteristics of the triple‐mode resonators. For demonstration, a prototype balun BPF operating at central frequency (f0) of 2.34 GHz with fractional bandwidth (FBW) of about 16.7% is designed. The presented balun BPF not only exhibits nice balanced response with 0.47 dB magnitude imbalance and 4.3° phase difference but also achieves 30‐dB harmonic suppression up to 6.40 GHz (2.7f0). Afterward, this presented design is embedded into a balanced quasi‐Yagi antenna to obtain high‐selective radiation and wide stopband rejection. Experimental results of the implemented antenna indicate less than −10 dB reflection coefficient, 4.49–5.38 dBi gain, and 12.71–19.62 dB front‐to‐back ratio within the operating bandwidth.

A Broadband Dual Circularly Polarized Conical Four-Arm Sinuous Antenna

A novel wideband four-arm sinuous antenna with dual circular polarizations (CPs) and unidirectional radiation is proposed. Different from the conventional designs, this sinuous antenna is realized in a conical form and no ground plane or absorptive cavity is required to obtain unidirectional radiation. The beamforming network for dual circularly polarized operations consists of a wideband quadrature coupler and two wideband baluns, and an auxiliary feeding patch is introduced to facilitate the connection between baluns and sinuous arms. The design of baluns and coupler is inspired from the printed exponentially tapered microstrip balun and broadside-coupled microstrip coupler, respectively. The dynamic differential evolution algorithm is employed to optimize the geometry of coupler for optimal performance. For both polarizations, the presented antenna has wide impedance bandwidth, good axial ratio, moderate realized gain, and front-to-back ratio within 2–5 GHz. An antenna prototype is fabricated and tested. The agreement between simulation and measurement results validates the proposed antenna framework. The demonstrated antenna has advantages of wide bandwidth, dual CPs, unidirectional radiation, lightweight, and low cost, and is promising for applications in wireless systems.