In this paper, a new design for two-port transmit/ receive full-duplex microstrip patch antenna for 4G and 4G advanced communication systems is introduced. The proposed duplex antenna consists of a single gear-shaped radiating patch for bidirectional radiation. The isolation between transmit and receive ports is achieved by using frequency space filtering technique where two omega-shaped defected ground structure (DGS) based-band pass filters (BPF) are created at transmit and receive ports of the antenna. The antenna achieves a compact size of (70 × 70) $mm^2$ , high isolation larger than −36 dB at the transmit frequency $f_t = 3.3\ GHz$ and larger than −45 dB at the receive frequency $f_r = 3.215\ GHz$ , and small Tx-Rx frequency space ratio $r = 0.0245$ . Also, the proposed structure can cover the entire S-band from $2\ GHz$ to $4\ GHz$ by scaling the sizes of the omega-shaped DGSs to control the resonance frequencies of the embedded BPFs before fabrication. Furthermore, the embedded BPFs have sharp cutoff characteristics, high selectivity, and channel bandwidth of about $BW \le 790\ MHz$ at $|s_{11}| = |s_{22}| = -10dB$ . The simulation and measurement results are highly coincided.

In this paper, new virtual antenna array (VAA) based synthesis techniques are introduced for side lobe level (SLL) reduction, beam thinning, and number of elements minimization for elliptical cylindrical antenna arrays (ECAA) of radar systems. Thereby, significant improvements in the array gain and directivity are achieved, which enhance the detection range and angular resolution of the radar. Furthermore, the overall implementation cost of the system is highly reduced by saving the number of elements and the corresponding RF chains and simplifying the feeding network. Firstly, the proposed technique decomposes the single transmit/receive ECAA into a separate transmit linear antenna array (LAA) and receive elliptical antenna array (EAA). Secondly, the number of antenna elements, element spacing, and excitations of the created LAA and EAA are optimized using particle swarm optimization (PSO) to produce efficient beamformed patterns. Finally, the Kronker product of the optimized LAA and EAA patterns is performed to form the optimized virtual ECAA (V-ECAA) pattern. We also introduced both the uniform feeding based V-ECAA technique and the non-uniform feeding based V-ECAA synthesis technique for more flexibility and better productivity in antenna arrays design. The simulation results revealed that the uniform feeding based V-ECAA provides an identical pattern to that of the traditional uniform feeding ECAA while saves the number of elements by 66.6%. While in the case of non-uniform feeding based V-ECAA, it provides much lower SLL and narrower HPBW than those of the ECAA while saving the number of elements by 63.8%. Furthermore, the HB is applied to provide additional beam thinning and SLL reduction of the proposed non-uniform V-ECAA that is denoted as (HBV-ECAA). The possibility of practical validations of the synthesized V-ECAAs is verified using the computer simulation technology (CST) microwave studio package, which gives users an integrated design environment and achieves realizable and robust designs.

The synthesis of pencil beam and arbitrarily shaped beam patterns of linear antenna arrays (LAA) using reduced number of antenna elements attracts the attention of researchers in recent years. In this paper, a hybrid beamforming technique based on the combination of the genetic algorithm (GA) optimization technique and the $l_{1}$ minimization method denoted as (GA/ $l_{1}$ ) is introduced for LAAs synthesis. The proposed GA/ $l_{1}$ beamforming technique optimizes both the elements excitations and interelement spacing to synthesize the desired LAA pattern with a minimum number of antenna elements. The GA/ $l_{1}$ technique provides an excellent approximation to the desired radiation pattern with high accuracy and low complexity (less number of iterations and computational time) compared to the other synthesis approaches introduced in the literature. In addition, as an application of this work, the proposed GA/ $l_{1}$ technique is used to build up a proposed hybrid precoding and beamforming (HP-BF) structure for Massive Multi-input Multi-output (M-MIMO) systems. In this structure, the transmit antenna array is synthesized for maximum gain realization using the existing number of antenna elements. In the HP-BF structure, the proposed GA/ $l_{1}$ technique is used to make full use of the existing transmit array elements to synthesize the radiation pattern of much larger size and higher gain arrays without the need for additional elements. Thereby, significant savings in the number of antenna elements and their corresponding radio frequency (RF) chains are achieved, which reduces the system complexity. In addition, the array gain maximization will maximize the received signal to noise ratio (SNR) giving rise to higher system performance in terms of spectral efficiency (SE) and power utilization.

The number of elements reduction in different antenna array configurations such as linear, circular, rectangular, planar, and non-planar is of main concern for several research groups. This minimizes the complexity of the feeding network in static antenna arrays, whereas, in adaptive antenna arrays, it reduces the number of active components. The main issue in the array synthesis is to preserve the radiation pattern with minimum distortion compared to the original pattern. These issues are addressed by many researchers in linear, planar, and concentric circular arrays, but no attempt is made in the synthesis of uniform circular antenna arrays (UCAAs) that have elements distributed on a single circle. This is because the synthesis is almost performed in one plane where the radiation patterns in other planes are not predicted. In this paper, most of the aforementioned challenges are treated; the number of elements is reduced, the radiation pattern has minimum distortion, and the radiation pattern is symmetric in all array orthogonal planes. This is performed by dividing the original UCAA’s 3D radiation pattern into a suitable number of 2D plane patterns, each of which is separately synthesized using the specified number of elements. The 2D pattern synthesis process for a particular plane is confined to estimating a new set of non-uniform excitation coefficients while keeping the original UCAA’s array radius. To construct the final set of synthesized excitation coefficients for the 3D array pattern synthesis, we aggregate all of the estimated sets of excitation coefficients and take the average. To verify the efficacy of the proposed technique, the original and synthesized arrays are realized using the CST Microwave Studio using $\lambda \mathord {\left /{ {\vphantom {\lambda 2}} }\right. } 2$ dipole elements. The results indicated that substantially matched patterns were obtained. Furthermore, the coupling between the synthesized array elements is decreased, which enhances the radiation efficiency and realized array gain.

Cognitive radio (CR) is one of the most important emerging technologies that have been introduced to meet the heavy data traffic of future wireless networks. Effective implementation of CR networks strongly requires devolution of efficient spectrum sensing (SS) techniques. Recently many SS techniques based on the utilization of multiple antenna elements (MAE) and matched filtering (MF) at the CR receiver are emerged due to their high detection performance. In this paper, a multi-dimensional small-scale cooperative SS approach based on the use of MAE, MF, and DOA estimation is proposed. The multi-dimensional detection is performed by identifying both the primary user (PU) signal and its DOA, which corresponds to the temporal domain and spatial domain, respectively. The use of MAE provides many versions of the received PU signal, which considered as the backbone of many signal processing operations such as DOA estimation of PU signals. DOA estimation is based on calculating time difference of arrival (TDOA) between the output correlation signals coming from fast convolution blocks. The received PU signal versions are also used as inputs for separate MF detectors to obtain various decisions taking the advantage of the spatial diversity at the CR receiver antennas. Moreover, the estimated DOA of the PU signal is used to make a combination of the signal versions emanating from each antenna branch, using the delay and sum combiner to produce a strong signal with high signal to noise ratio (SNR). This strong signal is also used as input to a separate MF to produce an accurate decision. Finally, the principle of cooperation is achieved by combining these various decisions to obtain a reliable decision. Several simulation scenarios are carried out to verify the superiority of the proposed SS approach compared to the traditional MAE based SS technique under extremely low SNR regimes and high interference. Moreover, the simulations and theoretical closed-form expressions are highly matched together.