In this thesis two different research topics are undertaken, both in the area of compact
RF/microwave circuits design. The first topic involves the design of a compact circularly
polarized (CP) slot-ring antenna. A study of several compact CP microstrip and slotline
antennas reported in the past has been carried out. In this research, a method of reducing
the size of a printed slot-ring antenna is proposed. The reduction in size is achieved by
introducing meandered-slot sections in the ring. Circular polarization is achieved by
introducing an asymmetry, also a meandered-slot section, and feeding the antenna at an
angle of 45o from the asymmetry using a microstrip feed line. The minimum axial ratio
of 0.4 dB is obtained at 2.46 GHz, which is the operating frequency of the antenna. The
size of the proposed antenna is reduced by about 50% compared to a conventional CP
slot-ring antenna and it displays a CP bandwidth of about 2.5%. The simulated and
measured results are presented, and they are in good agreement. The small size of the
antenna makes it very suitable for use in modern RF/microwave wireless systems which
require compact, low cost, and high performance circuits. Moreover, its CP behavior
makes it more attractive for applications such as satellite communications. The second topic in the thesis involves the design of a compact microstrip bandpass
filter using triangular open-loop resonators. A new compact three-pole microstrip
bandpass filter using four triangular open-loop resonators is presented. A fourth
resonator is placed to provide cross-coupling in the structure which gives a better skirt
rejection. The measured pass-band center frequency is 2.85 GHz. The filter demonstrates
about 7% bandwidth with insertion loss of less than 1 dB in the passband, a return loss
of greater than 15 dB and out-of-band rejection of greater than 30 dB. The simulated
and measured results are in good agreement. The proposed filter is very attractive for use
in modern wireless systems which require bandpass filters having compact size, low
insertion loss, high selectivity, and good out-of-band rejection
