This paper presents the design and implementation of a broadband down-converter system using the AWR (Advancing the Wireless Revolution) modeling and Microwave Office tool. The radio frequency (RF) signal coming to the antenna interface requires a frequency down-converter to be lowered to the intermediate frequency (IF) band. It includes mixing blocks, oscillators, amplifiers, step attenuators, isolators, and filters. The input frequency band (RF) is 8250 ± 250 MHz, while the output frequency (IF) band is 720 ± 200 MHz. The gain dynamic range of the circuit is expanded through the use of digital attenuators. It is a superheterodyne down-conversion circuit, combining the IF band to produce the desired RF spectrum in one pass. Two phase-locked oscillators are used at the local oscillator port of the mixer, one providing a single frequency, while the other has a programmable frequency synthesizer with 1 MHz steps in the frequency range from 7280 to 7780 MHz.

This contribution presents miniaturization techniques for folded circular substrate integrated waveguide (FCSIW) cavity filters. The cavities support dual-mode operation. Two of these cavities are combined to form a fourth-order filter. Two filter designs are implemented. The first one serves as a reference and exhibits good manufacturability. For the second one, the cavity is modified, which leads to $50\%$ more compactness. The designs are experimentally verified with 10 GHz bandpass filters. Even though the achieved level of compactness requires higher technological effort, the measurements validate the miniaturization concept. The out-of-band rejection exceeds 40 dB between 11.2 and 30 GHz for the reference filter and between 11.3 and 33 GHz for the miniaturized one. The implemented components are compared with state-of-the-art filters.

This study presents a new design of a four-element multiple-input multiple-output (MIMO) antenna, which is suitable for X-band applications. The circular polarization (CP) operation in this work is attained by using Tai Chi-shaped patches and L-shaped feeds. The proposed four-element MIMO antenna achieves two resonant frequencies, the first one at around 7.75 GHz and the second one with CP radiation is at approximately 10.15 GHz frequency. The measured isolations between ports with 46.7 × 46.7 mm2 total dimensions are <−20 dB. Due to the experiments, the envelop correlation coefficient for the orthogonal and parallel ports of the proposed MIMO antenna is <0.003 and 0.005, respectively. Additionally, the presented antenna has a circularly polarized performance in the frequency band of 9.75–10.41 GHz and the average realized peak gain almost 2 dBic. The investigated antenna in this work is fabricated and tested in which the results are in a good agreement.

To prevent far-field radiation characteristics degradation while increasing bandwidth, an attempt has been made to design and fabricate a microstrip antenna. An electromagnetic band gap (EBG) structure, including a layer of a metallic ring on a layer of Rogers 4003C substrate, is used. For a better design, a patch antenna with and without the EBG substrate has been simulated. The results show that the bandwidth can be improved up to 1.6 GHz in X-band by adding the EBG substrate. Furthermore, using this structure, a dual-band antenna was obtained as well. Finally, to validate the simulation results, a comparison has been done between simulation data and experimental results which demonstrate good agreement.

Laterally diffused metal oxide semiconductor (LDMOS) transistors with 10 V breakdown voltage have been implemented in a 65 nm Complementary metal oxide semiconductor (CMOS) process without extra masks or process steps. Radio frequency (RF) performance for Wireless local area network (WLAN) frequencies and in X-band at 8 GHz is investigated by load-pull measurements in class AB operation for both 3.3 and 5 V supply voltage. Results at 2.45 GHz showed 290 mW/mm output power density with 17 dB linear gain and over 45% power added efficiency (PAE) at 4 dB compression at a supply voltage of 5 V. Furthermore, results in X-band at 8 GHz show 8 dB linear gain, 320 mW/mm output power density and over 22% PAE at 4 dB compression. Third-order intermodulation measurements at 8 GHz revealed OIP3 of 18.9 and 21.9 dBm at 3.3 and 5 V, respectively. The transistors were also tested for reliability which showed no drift in quiescent current after 26 h of DC stress while high-power RF stress showed only small extrapolated drift at 10 years in output power density. This is to the authors' knowledge the first time high output power density in X-band is demonstrated for integrated LDMOS transistors manufactured in a 65 nm CMOS process without extra process steps.

In this article, a new construction of a small planar dual-band fed printed monopole antenna based on coplanar waveguide is suggested. Impedance matching for dual-band operations is obtained by embedding three vertical strips with different sizes in the U-shaped conductor-backed plane. The main problem of the designed antenna is the measuring of the specifications with the Agilent 8722ES Vector Network Analyzer, when the coaxial cable is connected to the antenna. Hence, in this paper a new method for decoupling the cable from the antenna is presented. This method is based on using the ferrite bead. The ferrite bead reduces the cable radiation, so that its position plays the important part in the antenna radiation characteristics. The fabricated antenna includes the benefits of the miniaturized size and dual-band operating specifications, so that the mentioned properties have been achieved without modifying the coplanar-waveguide-ground surface or radiator patch. The antenna has the small size of 15 × 15 × 0.8 mm3and bandwidths with S11 < −10 dB about 2.2 GHz (5.05–7.25 GHz) for WLAN-band or IEEE 802.11a-band and 5.2GHz (7.6–12.8 GHz) for X-band, which correspond to 36 and 51% practical bandwidths, respectively. The antenna measured peak gains are about 1.8 dBi at WLAN-band and 4.3 dBi at X-band.

Amplifiers for the next generation of T/R modules in future active array antennas are realized as monolithically integrated circuits (MMIC) on the basis of novel AlGaN/GaN (is a chemical material description) high electron mobility transistor (HEMT) structures. Both low-noise and power amplifiers are designed for X-band frequencies. The MMICs are designed, simulated, and fabricated using a novel via-hole microstrip technology. Output power levels of 6.8 W (38 dBm) for the driver amplifier (DA) and 20 W (43 dBm) for the high-power amplifier (HPA) are measured. The measured noise figure of the low-noise amplifier (LNA) is in the range of 1.5 dB. A T/R-module front-end with mounted GaN MMICs is designed based on a multi-layer low-temperature cofired ceramic technology (LTCC).