Abstract-Assuming there is an infinite periodically sinusoidal signal x with known frequency, one can sample x at Nyquist zone or sampling-rate to recover the signal. In terms of digital predistortion (DPD) with modulated signal as input, this paper will show the same concept that theoretically one can sample the feedback signal at arbitrary sampling rate to obtain the same coefficient of DPD or behavioural models as the one calculated from the high sampling rate feedback signal. The performance of a generalised DPD technique using a traditional memory polynomial with low-rate analog-to-digital device(ADC) is experimentally validated. The NMSE and ACPR results indicate the same performance by using an ADC sampling from 100 MHz to 10 MHz.

This paper presents a study on different microwave structures used to integrate MEMS devices in printed circuit boards, and their effect on the linear phase response for switched delay lines applications. Three different prototypes were designed to realize the RF tracks required to integrate 0.5 mm pitch MEMS devices together with the meander delay lines. The structures includes: microstrip lines, conventional coplanar waveguides (CPW) and finite grounded coplanar waveguides (FGCPW). The three prototypes were designed to deliver a group delay of 600 ps. Simulations were carried out using CST Microwave Studio. The FGCPW proved to have the highest phase linearity with only ± 4 ps (±0.67%) delay deviations up to 2.7 GHz. The paper also presents the design of two wideband MEMS switched time delay line circuits; one used to provide a fine tuning for the group delay with a step of only 10 ps and another for coarse tuning with 50 ps delay step. Finite grounded coplanar waveguides were selected to obtain a high linearity of phase response. The simulation of the two circuits resulted in a constant delay with relatively small deviations, as well as low insertion and return losses of 0.75 dB and 20 dB, respectively for frequencies up to 5 GHz.

Abstract-This paper presents a newly developed modification to the structure of a linearly polarized reflectarray antenna cell, called Phoenix [1]. The idea of Phoenix is based on employing multi-resonators to improve the antenna bandwidth characteristics. Another interesting feature is the phase variation cycle which is characterized by a rebirth capability that was the reason behind the Phoenix name. The new developed modifications resulted in reducing the cell size by 0.16 λo. In addition to improving the linearity of the phase variation characteristics which in turn reduced the phase errors by 10 o compared to Phoenix. Two reflectarray antennas (200 x 200 mm 2 ) were designed at 9.4 GHz in order to test the new modifications applied. The simulations and measurements indicated an increased antenna directivity for the new modified phoenix reflectarray antenna. Moreover, the measured gain of Phoenix and modified Phoenix at 9.4 GHz is 17.8 dB and 20.9 dB, respectively.

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-This paper presents a study on the effect of impedance mismatch on phase linearity (group delay variations) in grounded coplanar waveguide (GCPW) structures. Two 400 ps GCPW delay lines were designed using a short circuited stub and a transmission line. The structures were simulated over a wide frequency range (0.1 GHz-5 GHz) using both ADS circuit model and CST electromagnetic simulation tool. Based on mathematical analysis and simulation results, impedance mismatch appears to have a large effect on group delay variations in stubs when compared to transmission lines. The simulated time delay of the short circuited stub shows a maximum delay deviation of ±0.75% and ±7.4% for 1.6% and 5.8% impedance mismatch values, respectively. On the other hand, the transmission delay line simulation results show only ±0.1% and ±1.5% for the same impedance mismatch. For the electromagnetic simulation, the presented results indicate even larger variation of time delay for GCPW short stub as it reaches ±3.75% and ±7.5% at 2 GHz and 4.5 GHz for 1.6% impedance mismatch, respectively.