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Dual-beam steering has the advantage of providing extensive and efficient scanning in multitarget environment. However, the existing methods of dual-beam steering antenna arrays are generally large or complex in structure. Therefore, this communication proposes a simplified beamforming network based on the theoretical analysis on a Hadamard matrix. The proposed beamforming network was constructed using a simplified topology, consisting of three 0°/180° couplers and four p-i-n diodes. For verification, a dual-beam steering antenna array at 2.4 GHz was designed, fabricated, and measured. Both simulated and measured results agree well with each other. The size of the fabricated network is $0.70\,\,\lambda \text{g}\,\,\times 0.93\,\,\lambda \text{g}$ , which is only 20.3% of the size occupied by a traditional Hadamard matrix. At the center frequency, the implemented antenna array realizes steering angles of 0°, ±19°, ±31°, and ±51°, demonstrating good dual-beam steering properties.

In this article, a novel mode superposition method is proposed to implement a millimeter-wave (MMW) shared-radiator co-polarized in-band full-duplex (IBFD) antenna at 29 GHz. The proposed method is realized based on a dielectric resonator antenna (DRA). By simultaneously exciting the TM $_{01\delta }$ and HEM $_{21\delta }$ modes of a DRA, a superposed mode with a field pattern analogous to the TE211 mode can be produced. Since both the transmitter (TX) and the receiver (RX) ports locate at the weak-field regions of the superposed mode, a decoupling performance is therefore obtained without the use of any additional decoupling structures or circuits. For validation, a DRA with artificial electromagnetic boundaries (AEMBs) is employed, so that the TM $_{01\delta }$ and HEM $_{21\delta }$ modes can be simultaneously excited using a simple microstrip proximity coupling. It only needs to properly adjust the geometric parameters of the DRA, and the mutual coupling is substantially suppressed. The experiment demonstrates that the antenna can achieve maximum isolation of 42 dB and peak gain of 8.65 dBi. Due to the simple and integrated architecture, the proposed method is promising for MMW IBFD applications.

In this article, a novel self-decoupling method for the multi-input multi-ouput (MIMO) dielectric resonator antenna (DRA) arrays is investigated. This method is based on the transmission characteristics of the conformal strip that feeds the DRA. It is found that when the strip-fed DRA operates in the higher order mode, e.g., TE113 mode, the $E$ -field coupled to the metal strip of the adjacent passive DRA presents a standing-wave distribution. By appropriately adjusting the dimensions of the feeding strip, the $E$ -field can form a node with zero amplitude at its bottom where a coaxial probe is connected, preventing the energy from getting into the receiving port and hence achieving a high isolation level without requiring any extra decoupling structure. This self-decoupling method is applicable not only to 1-D H- and E-plane coupled MIMO linear arrays but also to 2-D MIMO planar arrays. To verify its feasibility, a prototype of $2\times $ 2 MIMO planar DRA array is simulated, processed, and tested. The results show that a usable bandwidth ( $\vert \text{S}_{\mathrm {ii}}\vert < -10$ dB and $\vert \text{S}_{\mathrm {ij}}\vert < -20$ dB) of 10.8% is achieved, and the maximum isolation is over 40 dB within the passband.

The Luneburg-lens is a prospective candidate for implementing multibeam antennas. However, the size of the conventional configuration is bulky, and most reported works are linearly polarized (LP), leading to some inconvenience in the practical applications. To deal with these problems, a new approach to realize a compact LP Luneburg-lens antenna is proposed first, and then, a method for implementing circular polarization (CP) property is further proposed. An air-coated dielectric cylinder is rotated around the center axis to form different layers of an equivalent cylindrical Luneburg-lens. The corresponding theoretical model to calculate the equivalent permittivity is given. Based on this approach, a Luneburg-lens is constructed using one dielectric cylinder and nine dielectric rings with the same permittivity but different dimensions. The proposed lens can be easily fabricated through the 3-D printing technology with low manufacturing complexity. For validation, an LP and a CP Luneburg-lens antenna operating at the Ka-band were designed, fabricated, and measured. A good consistency between simulated results and measured ones can be found. The LP antenna achieves a wide-scanning range of 174° and a bandwidth of 28.6%. Also, the CP one exhibits a scanning range of 134° and an AR bandwidth of 17.4%.

In this brief, a symmetrical Doherty power amplifier (DPA) which exhibits enhanced efficiency, bandwidth and output power back-off range by phase compensation, is proposed. This proposed architecture compensates the phase deviation between main and auxiliary amplifiers mainly caused by the load modulation circuit and parasitic parameters of transistors. With phase compensation, both saturation efficiency and bandwidth are significantly improved while maintaining an extended output back-off range. For verification, a 2.05–2.8-GHz symmetrical DPA is designed, fabricated and measured. Under continuous wave excitation, measurement results show that the implemented DPA exhibits drain efficiency of 40%–49% at 9 dB output back-off level and 66%–76% at saturation with a maximum output power of 43.9–44.9-dBm over the entire band.