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A monopole-like stacked microstrip antenna with dual-layer patches is proposed for ultra-wideband applications. The characteristic mode analysis (CMA) is utilized and contributes to the multi-mode behavior investigation, guiding the design process. The dual-layer patches both consist of two concentric-coupled rings. The patch configuration is optimized according to the desired mode behaviors at different frequencies. Correspondingly, the three merged resonant modes, containing the modes TM01 and TM02 of the middle layer and TM01 in the top layer, effectively broaden the operation band. The measurements demonstrate that the impedance bandwidth (IBW) of the antenna reaches 4.70–10.20 GHz (73.8%) with the return loss of 10 dB and a maximum gain of 8.7 dBi. The cross-polarization level is better than −28 dB. The proposed antenna possesses a small radius of 30 mm (0.47 λ L ${\lambda }_{L}$ ), and a low-profile of 5.78 mm (0.09 λ L ${\lambda }_{L}$ ). λ L ${\lambda }_{L}$ is the free-space wavelength at the lowest operation frequency.

This paper presents a planar wideband circularly polarized (CP) antenna with end-fire radiation for millimeter-wave (mmWave) applications. The antenna is realized by the combination of an open-ended substrate integrated waveguide (SIW) line and a pair of open-ended SIW cavities. The SIW line consisting of trapezoidal notch and inductive window is used for feeding network, symmetrical notches etched on the open-ended SIW cavities are designed for generating CP end-fire radiation. Its operating mechanism is explained for easy understanding. To verify the design, a prototype is fabricated and measured, which demonstrates the reflection coefficient bandwidth of 35.3%, 3dB axial ratio (AR) bandwidth of 37.3%, front-to-back ratio (FTBR) of larger than 6.8 dB, and a peak left handed circularly polarized (LHCP) gain of 4.87 dBic. The proposed CP end-fire antenna would be an attractive candidate for mmWave wireless applications.

A planar circularly polarized substrate integrated waveguide (SIW) stacked patch antenna array consisting of four sequential-rotation (SR) subarrays is presented for $Ka$ -band applications. Antenna element is realized based on a pair of stacked cavities by the combination of a driven patch layer and a parasitic patch layer, which are formed by a shorted square patch and multiple identical stacked square patches, respectively. Each subarray consisting of two pairs of elements, excited by a coplanar waveguide (CPW) network with four metallic vias, is well matched to a novel SIW SR feeding network. A narrow transverse coupling slot, a semiopening resonant cavity, two pairs of inductive vias, and an inductive window are introduced in the SIW-based feeding network to implement functions of phase shifter, impedance matching, and power divider in the two layers. By employing the proposed SR feeding network, the CPW network, and the four subarrays, the excellent performance of the array is realized. To verify the design, a prototype is fabricated and measured, which demonstrates a −10 dB impedance bandwidth of 29.6%, a 3 dB axial ratio bandwidth of 25.4%, and a peak gain of 20.32 dBic.

A low-profile circularly polarised (CP) antenna with conical-beam radiation pattern is presented. The proposed antenna consists of a monopolar patch antenna fed by a probe in the centre and a ring-shaped array formed by eight modified parasitic patch elements. Two resonant modes of the monopolar patch which connects to a ground plane by a set of conductive shorting vias are utilised to achieve wide impedance bandwidth. A CP conical-beam radiation pattern is formed by loading the designed array. Loop current and slot resonant mode are employed to discuss the operating principle. A parametric study is carried out for the detailed design concept illustration. To verify the design, a prototype has been fabricated and measured, which shows a low profile of 0.059 λ 0 , a maximum gain of 7.45 dBic, a 10-dB impedance bandwidth of 23.1%, a 3-dB axial ratio bandwidth of 9.6% and a good conical-beam radiation pattern.

A low-profile substrate-integrated waveguide (SIW) cavity-based antenna with conical-beam circularly polarized (CP) radiation is presented. Conical-beam CP radiation is obtained by the combination of a radial current source and a loop current source, which are produced by a shorted monopole patch and an annular array, respectively. The proposed annular array configuration is designed by combining multiple identical customized parasitic patch elements arranged around the monopole. Phase compensatory lines and shorted annular ring slots are introduced in the array to tune phase difference of two current sources and to generate in-phase currents on the elements, respectively. All antenna elements are simultaneously excited within a center-fed SIW cavity. In order to fully picture the operating mechanism, we analyze the wide impedance and axial-ratio (AR) bandwidths based on an equivalent circuit model and an electromagnetic theory. Then, parametric studies are carried out for a detailed design illustration. To verify the design, a prototype has been fabricated and measured, which shows a stable conical-beam radiation and good performance including: a low profile of $0.062\lambda _{0}$ , a 10 dB impedance bandwidth of 20.4%, a 3 dB AR bandwidth of 17%, a maximum gain of 8.25 dBic, and an advantage of large ground compatibility.

A low-profile broadband circularly polarised patch antenna with four parasitic patches (PPAs) is presented. The proposed antenna has the advantages of broadband reflection coefficient, broadband axial-ratio (AR) performance and low-profile structure. First, a broadband feed network is employed to realise wide reflection coefficient and AR bandwidths. To enhance the gain performance, two types of PPAs employing parasitic technique scheme are designed and compared. Then, resonance mode theories and simulated current distributions are utilised to explain the gain enhancement issue within the operating frequency. Furthermore, the designed antenna is optimised carefully by adopting parametric analysis before fabricating and measuring. Finally, the gain enhancement is verified by the measured results of designed antenna possessing the characteristic of both high-gain and low-profile structure. The results indicate that the adding PPAs scheme and the resonance mode analysis are helpful on research of this type of patch antenna.

Heterogeneous cellular networks (HCNs) have emerged as the primary solution for explosive data traffic. However, an increase in the number of base stations (BSs) inevitably leads to an increase in energy consumption. Energy efficiency (EE) has become a focal point in HCNs. In this paper, we apply tools from stochastic geometry to investigate and optimize the energy efficiency (EE) for a two-tier HCN. The average achievable transmission rate and the total power consumption of all the BSs in a two-tier HCN is derived, and then the EE is formulated. In order to maximize EE, a one-dimensional optimization algorithm is used to optimize picocell BS density and transmit power. Based on this, an alternating optimization method aimed at maximizing EE is proposed to jointly optimize transmit power and density of picocell BSs. Simulation results validate the accuracy of the theoretical analysis and demonstrate that the proposed joint optimization method can obviously improve EE.

In this paper, a wideband circularly-polarized patch antenna is presented. The patch is fed by four probes arranged by sequential rotation arrays, the four probes are connected to a feed network comprising of a pair of broadband 90° phase shifter and Wilkinson power divider. The proposed antenna shows a compact low profile, wide axial-ratio (AR) bandwidth, wide reflection coefficient bandwidth, as well as easiness of integration. To verify the simulation performance of the design, the antenna has been fabricated and measured. The measured results show that the impedance bandwidth S11< −10 dB of 70.2%, the 3-dB AR bandwidth of 63.1%, the gain is 6.65 dBi at 5.8 GHz, and the 3-dB gain bandwidth is 39.3% from 4.9 to 7.3 GHz. Good agreement is observed between simulation and measurement by comparison.

This paper proposes a structure of the joint frequency-phase carrier recovery loop for all-digital Quadrature Amplitude Modulation (QAM)receivers. The steady-state estimation variance is greatly reduced by introducing a non-zero-mean input to the Stop-and-Go controller. It has been verified by simulation tools that the circuit can acquire frequency offset up to 6% of the symbol rate and phase offset up to 30 degree in only 11000 symbol periods, while its steady-state phase jitter also significantly reduces to 0.11 degrees.

It is known to us, double-ridged horn antenna is one of common and important antenna types, it has been widely used in the EMC, measurement, radar and communication system. A 118GHz double-ridged horn antenna that possesses high performance is designed with the HFSS. VSWR, Gain and radiation pattern of the antenna can fulfill engineering demands based on the simulation of HFSS. Further, this paper shows a new comparatively method of post-cavity treatment in antenna.