1 Antenna pattern synthesis EM theory 2 EMLAB

Antenna radiation pattern 2 An antenna is a device that helps electrical signals to be radiated in the form of electromagnetic wave. It is well known that a time-varying current segment produces radiated emission which is axially symmetric along the direction of current, and the total radiated power is equal to the energy provided by the current source. If we want to transport substantial electromagnetic waves to the point farther away, we should confine the radiated energy to a region occupying narrow solid angle. There are many ways to squeeze the radiated waves into a narrow angular region. The most frequently used method is utilizing a number of identical antennas fed by current sources with different magnitudes and phase angles. Then, the total electromagnetic field can be obtained by adding up the contributions from each element antenna. Array factor EMLAB

3 Top view If the observation point is far from the antenna array, the total electric field can be approximated by the product of the field due to an element antenna and the ‘array factor’ which are the weighted sum of the element antenna current by the space factor. By adjusting element antenna current In and distance between element ‘d’, desired radiation patterns can be synthesized. The current In has complex value which has magnitude and phase. If the phases and distances between adjacent elements are kept constant, the array factor simplifies to EMLAB

Examples 4 (1) Two element array (2) Two element array EMLAB

5 (3) Five element array 3 d. B Beamwidth Beam direction (4) Five element array (5) Five element array EMLAB

Design procedures 6 (1) Adjust the number of element antennas (N+1), distances (d), phase differences (α), magnitudes of currents to change the radiation patterns. Design constraint for antenna synthesis: (1) Beam directions should be pointed to +45 ◦ and 120◦ (ignore the angle range 180 ◦ ~ 360 ◦) (2) 3 -d. B Beam width of each beam should be less than 10◦ 120◦ 45◦ EMLAB

Project report 7 must include the following items. (1) Radiation patterns. (2) Currents of elementary antennas. (3) Spacings between elementary antennas. (4) Explanations on the pattern synthesis procedure. EMLAB

Sample MATLAB codes 8 phi=0: 0. 01: 2*pi; %0<phi<2*pi k=2*pi; d=0. 5; % 0. 5 lambda spacing. shi=k*d*cos(phi); alpha = pi*0. 0; beta = exp(i*alpha); %Currents=[1, 2*beta, 3*beta^2, 2*beta^3, 1*beta^4]; %Current excitations Currents=[1, 1*beta^2, 1*beta^3, 1*beta^4]; %Current excitations E=freqz(Currents, 1, shi); %E for different shi values E = DB(E)+30; % 최대값에서 30 d. B 범위까지 그림. E = (E>0. ). *E; polar(phi, E); %Generating the radiation pattern EMLAB