Evaporation duct is an anomalous mechanism of transhorizon propagation in marine and coastal regions. In order to better understand the characteristics of signal fading, a C band signal transhorizon propagation experiment was carried out with a 107 km path length over the Bohai Sea of China. Using an iron tower with meteorological and oceanographic (METOC) sensors at multiple altitudes, a direct diagnostic method of evaporation duct is presented. The dependence of signal strength on evaporation duct height, antenna height, and METOC parameters is analysed. The experimental results indicate that the signal strength tends to be linearly dependent on the evaporation duct height when the transmitter and receiver antennas are submerged within the duct layer. Normally, the signal strength is stronger when the relative humidity is lower. Stronger signal strength tends to occur under near-neutral or stable atmospheric conditions or when the air–sea temperature difference is higher. The results indicate that the signal strength distribution of fast fading is close to Rayleigh distribution, and the probability density of fade slope is symmetric at 0 dB/s. These results have important implications for the design of ducting communications system.

In this study, a novel and compact design of frequency duplex antenna based on quarter-mode substrate integrated waveguide (QMSIW) is presented. The proposed antenna consists of two orthogonal QMSIWs excited by two separate feed lines. Independent frequency tunability is exhibited by adjusting the size of QMSIW. The electric wall formed by metal vias is used to suppress the coupling between QMSIW units. Thus, a high isolation (>26.6 dB) is achieved, which promotes the frequency duplexing characteristic. The proposed antenna resonates at 4.83 and 5.0 GHz with magnetic dipole radiation patterns and has corresponding gains of 2.08 and 2.21 dBi, respectively. Furthermore, a model is proposed to achieve the frequency multiplexing characteristic by taking advantage of the stable port isolation while changing the angle of two QMSIWs. A frequency triplex antenna working at 4.86, 4.95, and 5.05 GHz is also designed, it still exhibits good isolation (>20 dB) and excellent radiation performance although the frequency ratio remains extremely low (1.02).

A novel miniaturised antenna with a split elliptical patch and three left/right handed (LRH) cells is proposed. The antenna has a wideband circularly polarised (CP) characteristic and it is easy to perform the impedance matching. A simple microstrip line is used to excite the antenna and another microstrip line is matched by a proper chip resistor. By splitting the elliptical patch and adjusting the position of three LRH cells, an improved CP characteristic and a wide impedance bandwidth are achieved. Compared to the referenced antenna, the lower resonant frequency is decreased and the higher resonant frequency is increased. Also, the miniaturisation, wideband width and broadband CP are achieved. The measured results demonstrate that this structure achieves 69% (2.4–4.93 GHz) of the 3-dB axial ratio bandwidth and 107.9% (1.8–6.23 GHz) of the 10 dB return loss bandwidth. The antenna performs an average gain of over 2.7 dB across the CP region.

A dual-polarised broad-band array antenna with high gain is presented for base transceiver station applications. The structure of the proposed antenna consists of four radiating elements and L-shaped feed lines. Each radiating element includes two suspended copper plates. The electromagnetic waves have been coupled to radiating elements through feed lines. The ports’ isolation is obtained using a cubic isolator between two L-shaped feed lines. The high gain of the proposed antenna is obtained using the sum of four elements placed at a specified distance from each other. A prototype of the proposed antenna is fabricated on a flame retardant-4 substrate. Through experiments carried out within the frequency range of 1.6–2.3 GHz, the bandwidth, return loss, isolation between ports, and the gain of this prototype are obtained to be 66%, <−10 dB, better than −15 dB, and almost 11 dBi, respectively. In addition, within the frequency range of 3.4–3.7 GHz, the values of the same parameters are obtained to be 8.4%, <−10 dB, better than −15 dB, and almost 5.8 dBi, respectively.

In this work, a novel dual-band orthogonally polarised, the shared-aperture array is proposed for the L-band and S-band frequencies. An elliptical monopole antenna is used as a radiating element in the proposed array. In this design, the common inter-element spacing is used for both the bands. Owing to this, L- and S-band arrays have the same number of elements. The L-band radiators are closely placed and designed taking the mutual coupling into account. The S-band antenna follows the traditional array design process. The inter-band coupling is reduced by using a metallic ridge in the reflector of the array. This array can be used in the dual-band radar applications. The proposed methodology offers the modular, low-profile and low-cost solution for a large array. To verify the proposed concept, a prototype array of 4 × 4 elements for each band has been fabricated and tested.